Enstar Group Limited (ESGR) 10-K 28 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 26, 2018	Jun. 30, 2017
Document Information [Line Items]
Entity Registrant Name	Enstar Group LTD
Entity Central Index Key	1,363,829
Trading Symbol	ESGR
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Voluntary Filers	Yes
Entity Public Float			$ 2,150
Voting ordinary shares
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		16,429,569
Non-voting ordinary shares
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,004,443

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Trading, at fair value	$ 5,876,284	$ 4,611,160
Equities, trading, at fair value	106,603	95,047
Other investments, at fair value	913,392	937,047
Other investments, at cost	125,621	131,651
Total investments	7,232,185	6,042,672
Cash and cash equivalents	955,150	954,871
Restricted cash and cash equivalents	257,686	363,774
Funds held - directly managed	1,179,940	994,665
Premiums receivable	425,702	406,676
Deferred tax assets	13,001	11,374
Prepaid reinsurance premiums	245,101	219,115
Reinsurance balances recoverable	1,478,806	1,460,743
Reinsurance balances recoverable, fair value	542,224	0
Funds held by reinsured companies	175,383	82,073
Deferred acquisition costs	64,984	58,114
Goodwill and intangible assets	180,589	184,855
Other assets	831,320	842,356
Assets held for sale	24,351	1,244,456
TOTAL ASSETS	13,606,422	12,865,744
LIABILITIES
Losses and loss adjustment expenses	5,603,419	5,987,867
Losses and loss adjustment expenses, fair value	1,794,669	0
Policy benefits for life and annuity contracts	117,207	112,095
Unearned premiums	583,197	548,343
Insurance and reinsurance balances payable	236,697	394,021
Deferred tax liabilities	15,262	28,356
Debt obligations	646,689	673,603
Other liabilities	972,457	705,318
Liabilities held for sale	11,271	1,150,787
TOTAL LIABILITIES	9,980,868	9,600,390
COMMITMENTS AND CONTINGENCIES
REDEEMABLE NONCONTROLLING INTEREST	479,606	454,522
SHAREHOLDERS’ EQUITY
Treasury shares at cost (Preferred shares 2017 and 2016: 388,571)	(421,559)	(421,559)
Additional paid-in capital	1,395,067	1,380,109
Accumulated other comprehensive income (loss)	10,468	(23,549)
Retained earnings	2,132,912	1,847,550
Total Enstar Group Limited Shareholders’ Equity	3,136,684	2,802,312
Noncontrolling interest	9,264	8,520
TOTAL SHAREHOLDERS’ EQUITY	3,145,948	2,810,832
TOTAL LIABILITIES, REDEEMABLE NONCONTROLLING INTEREST AND SHAREHOLDERS’ EQUITY	13,606,422	12,865,744
Voting ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	16,402	16,175
Series C non-voting convertible ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	2,600	2,792
Series E non-voting convertible ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	405	405
Series C non-voting preferred shares
SHAREHOLDERS’ EQUITY
Series C Preferred Shares (issued and outstanding 2017 and 2016: 388,571)	389	389
Short-term investments
ASSETS
Trading, at fair value	180,211	222,918
Available-for-sale, at fair value	0	268
Fixed maturities
ASSETS
Trading, at fair value	5,696,073	4,388,242
Available-for-sale, at fair value	$ 210,285	$ 267,499

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Short-term investments, available-for-sale, at fair value, amortized cost	$ 208,097	$ 269,864
Ordinary shares, par value (dollars per share)	$ 1	$ 1
Preferred shares, par value (dollars per share)	$ 1	$ 1
Share capital, authorized (shares)	156,000,000	156,000,000
Voting ordinary shares
Ordinary shares, par value (dollars per share)	$ 1	$ 1
Ordinary shares, issued (shares)	16,402,279	16,175,250
Ordinary shares, outstanding (shares)	16,402,279	16,175,250
Series C non-voting convertible ordinary shares
Ordinary shares, issued (shares)	2,599,672	2,792,157
Ordinary shares, outstanding (shares)	2,599,672	2,792,157
Series E non-voting convertible ordinary shares
Ordinary shares, issued (shares)	404,771	404,771
Ordinary shares, outstanding (shares)	404,771	404,771
Series C non-voting preferred shares
Preferred shares, issued (shares)	388,571	388,571
Preferred shares, outstanding (shares)	388,571	388,571
Treasury shares (shares)	388,571	388,571
Short-term investments
Short-term investments, available-for-sale, at fair value, amortized cost	$ 0	$ 287
Fixed maturities
Short-term investments, available-for-sale, at fair value, amortized cost	$ 208,097	$ 269,577

Consolidated Statements of Earn

Consolidated Statements of Earnings - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INCOME
Net premiums earned	$ 160,627	$ 148,025	$ 155,571	$ 148,898	$ 216,188	$ 205,730	$ 208,709	$ 192,887	$ 613,121	$ 823,514	$ 753,744
Fees and commission income	19,627	15,895	18,667	11,914	13,266	9,187	10,487	6,424	66,103	39,364	39,347
Net investment income	58,605	52,028	49,417	48,739	42,229	48,022	44,932	50,280	208,789	185,463	122,564
Net realized and unrealized gains (losses)	50,637	29,301	51,877	58,519	(61,570)	66,608	34,503	38,277	190,334	77,818	(41,523)
Other income	9,303	(3,848)	10,856	12,198	(1,277)	414	3,289	2,410	28,509	4,836	30,328
Total income	298,799	241,401	286,388	280,268	208,836	329,961	301,920	290,278	1,106,856	1,130,995	904,460
EXPENSES
Net incurred losses and loss adjustment expenses	30,327	75,712	9,620	77,892	1,321	(6,902)	96,462	83,218	193,551	174,099	104,333
Life and annuity policy benefits	(1,033)	1,060	4,289	(301)	(2,265)	1,682	(1,613)	158	4,015	(2,038)	(546)
Acquisition costs	21,449	24,281	30,355	20,821	47,619	50,074	43,847	45,029	96,906	186,569	163,716
General and administrative expenses	126,702	100,325	106,490	102,468	123,497	103,097	104,206	92,934	435,985	423,734	389,159
Interest expense	7,251	6,410	7,573	6,868	4,796	5,027	5,421	5,398	28,102	20,642	19,403
Net foreign exchange losses	1,925	4,775	7,122	3,715	(1,527)	2,276	(1,856)	1,772	17,537	665	3,373
Loss on sale of subsidiary	0	6,740	9,609	0	0	0	0	0	16,349	0	0
Total expenses	186,621	219,303	175,058	211,463	173,441	155,254	246,467	228,509	792,445	803,671	679,438
EARNINGS BEFORE INCOME TAXES	112,178	22,098	111,330	68,805	35,395	174,707	55,453	61,769	314,411	327,324	225,022
INCOME TAXES	9,629	(1,432)	(4,731)	2,929	(11,228)	(8,227)	(8,050)	(7,369)	6,395	(34,874)	(12,650)
NET EARNINGS FROM CONTINUING OPERATIONS	121,807	20,666	106,599	71,734	24,167	166,480	47,403	54,400	320,806	292,450	212,372
NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE	11,998	3,495	(4,871)	371	5,483	3,897	2,378	205	10,993	11,963	(2,031)
NET EARNINGS	133,805	24,161	101,728	72,105	29,650	170,377	49,781	54,605	331,799	304,413	210,341
Net loss (earnings) attributable to noncontrolling interest	(6,206)	14,832	(11,542)	(17,425)	(7,005)	(14,329)	(9,187)	(9,085)	(20,341)	(39,606)	9,950
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED	$ 127,599	$ 38,993	$ 90,186	$ 54,680	$ 22,645	$ 156,048	$ 40,594	$ 45,520	$ 311,458	$ 264,807	$ 220,291
Basic:
Net earnings from continuing operations (dollars per share)	$ 5.96	$ 1.83	$ 4.90	$ 2.80	$ 0.91	$ 7.89	$ 1.98	$ 2.34	$ 15.50	$ 13.10	$ 11.55
Net earnings (loss) from discontinuing operations (dollars per share)	0.62	0.18	(0.25)	0.02	0.26	0.20	0.12	0.02	0.56	0.62	(0.11)
Net earnings per ordinary share (dollars per share)	6.58	2.01	4.65	2.82	1.17	8.09	2.10	2.36	16.06	13.72	11.44
Diluted:
Net earnings from continuing operations (dollars per share)	5.90	1.81	4.87	2.78	0.90	7.82	1.97	2.33	15.39	13	11.46
Net earnings (loss) from discontinuing operations (dollars per share)	0.61	0.18	(0.25)	0.02	0.26	0.20	0.12	0.02	0.56	0.62	(0.11)
Net earnings per ordinary share (dollars per share)	$ 6.51	$ 1.99	$ 4.62	$ 2.80	$ 1.16	$ 8.02	$ 2.09	$ 2.35	$ 15.95	$ 13.62	$ 11.35
Weighted average ordinary shares outstanding:
Basic (shares)									19,388,621	19,299,426	19,252,072
Diluted (shares)									19,527,591	19,447,241	19,407,756

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
NET EARNINGS	$ 331,799	$ 304,413	$ 210,341
Other comprehensive income, net of tax:
Unrealized holding gains (losses) on fixed income investments arising during the year	4,776	4,776	(3,219)
Reclassification adjustment for net realized gains included in net earnings	(491)	(384)	(266)
Unrealized gains (losses) arising during the year, net of reclassification adjustment	4,285	4,392	(3,485)
Decrease in defined benefit pension liability	1,501	3,079	3
Change in currency translation adjustment	9,423	4,793	(24,694)
Reclassification to earnings on disposal of subsidiary	20,751	0	0
Total currency translation adjustment	30,174	4,793	(24,694)
Total other comprehensive gain (loss)	35,960	12,264	(28,176)
Comprehensive income	367,759	316,677	182,165
Comprehensive (income) loss attributable to noncontrolling interest	(22,285)	(40,257)	15,650
COMPREHENSIVE INCOME ATTRIBUTABLE TO ENSTAR GROUP LIMITED	$ 345,474	$ 276,420	$ 197,815

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Treasury Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Currency translation adjustment	Defined benefit pension liability	Unrealized gains (losses) on investments	Retained Earnings	Noncontrolling Interest (excludes redeemable noncontrolling interests)	Foreign currency translation adjustments	Net movement in unrealized holding losses on investments	Voting ordinary sharesOrdinary Shares	Class C converted to ordinary sharesOrdinary Shares	Class E converted to ordinary sharesOrdinary Shares	Series A non-voting convertible ordinary sharesOrdinary Shares	Series C non-voting convertible ordinary sharesOrdinary Shares	Series E non-voting convertible ordinary sharesOrdinary Shares	Series C non-voting preferred sharesPreferred Stock
Balance, beginning of year at Dec. 31, 2014			$ 1,321,715	$ (12,686)	$ (2,779)	$ (7,726)	$ (2,181)	$ 1,395,206	$ 217,970			$ 15,761			$ 2,973	$ 2,726	$ 714	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issue of shares												63
Issue of shares and warrants			1,765
Conversion of convertible securities			0										$ 0	$ 309	0	0	(309)	0
Warrants exercised																0
Amortization of share-based compensation			7,867
Purchase of noncontrolling shareholders' interest in subsidiaries			41,697		2,937		312		(195,347)
Reclassification to earnings on disposal of subsidiary					0
Change in defined benefit pension liability	$ 3					3
Net earnings (loss)								220,291	(1,153)
Change in redemption of redeemable noncontrolling interests								(37,185)
Dividends paid									(733)
Contribution of capital									680
Reallocation to redeemable noncontrolling interest									(15,801)
Other comprehensive income (loss)	(28,176)				(23,948)		(1,780)			$ (1,558)	$ (147)
Balance, end of year at Dec. 31, 2015		$ (421,559)	1,373,044	(35,162)	(23,790)	(7,723)	(3,649)	1,578,312	3,911			16,133			2,973	2,726	405	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle								0
Issue of shares												42
Issue of shares and warrants			529
Conversion of convertible securities			2,584										0	0	(2,973)	0	0	389
Warrants exercised																66
Amortization of share-based compensation			3,952
Purchase of noncontrolling shareholders' interest in subsidiaries			0		0		0		0
Reclassification to earnings on disposal of subsidiary					0
Change in defined benefit pension liability	3,079					3,079
Net earnings (loss)								264,807	(1,034)
Change in redemption of redeemable noncontrolling interests								4,431
Dividends paid									0
Contribution of capital									5,643
Reallocation to redeemable noncontrolling interest									0
Other comprehensive income (loss)	12,264				4,797		3,737			0	0
Balance, end of year at Dec. 31, 2016	2,810,832	(421,559)	1,380,109	(23,549)	(18,993)	(4,644)	88	1,847,550	8,520			16,175			0	2,792	405	389
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle								0
Issue of shares												35
Issue of shares and warrants			450
Conversion of convertible securities			0										$ 192	$ 0	0	(192)	0	0
Warrants exercised																0
Amortization of share-based compensation			14,508
Purchase of noncontrolling shareholders' interest in subsidiaries			0		0		0		0
Reclassification to earnings on disposal of subsidiary					20,751
Change in defined benefit pension liability	1,501					1,501
Net earnings (loss)								311,458	722
Change in redemption of redeemable noncontrolling interests								(30,978)
Dividends paid									0
Contribution of capital									22
Reallocation to redeemable noncontrolling interest									0
Other comprehensive income (loss)	35,960				9,413		2,352			$ 0	$ 0
Balance, end of year at Dec. 31, 2017	$ 3,145,948	$ (421,559)	$ 1,395,067	$ 10,468	$ 11,171	$ (3,143)	$ 2,440	2,132,912	$ 9,264			$ 16,402			$ 0	$ 2,600	$ 405	$ 389
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle								$ 4,882

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES:
Net earnings	$ 331,799	$ 304,413	$ 210,341
Net (earnings) loss from discontinued operations	(10,993)	(11,963)	2,031
Adjustments to reconcile net earnings to cash flows provided by (used in) operating activities:
Realized losses (gains) on sale of investments	(5,887)	7,036	(15,859)
Unrealized losses (gains) on investments	(154,763)	(84,854)	57,380
Other non-cash items	15,490	8,566	3,984
Depreciation and other amortization	32,461	34,938	40,922
Net change in trading securities held on behalf of policyholders	25,597	(1,284)	(7,241)
Sales and maturities of trading securities	5,742,845	3,406,788	3,651,680
Purchases of trading securities	(7,024,062)	(3,100,515)	(4,052,430)
Net loss on sale of subsidiary	16,349	0	0
Changes in:
Reinsurance balances recoverable	(530,857)	(21,866)	391,182
Funds held by reinsured companies	(278,585)	(967,379)	32,435
Losses and loss adjustment expenses	1,363,032	259,339	(276,711)
Policy benefits for life and annuity contracts	(3,314)	(11,037)	9,110
Insurance and reinsurance balances payable	(157,741)	120,515	(20,635)
Unearned premiums	34,854	5,682	(19,355)
Other operating assets and liabilities	260,668	(151,068)	(271,986)
Net cash flows used in operating activities	(343,107)	(202,689)	(265,152)
INVESTING ACTIVITIES:
Acquisitions, net of cash acquired	(4,185)	(18,454)	130,667
Sale of subsidiary, net of cash sold	126,611	0	0
Sales and maturities of available-for-sale securities	86,359	81,596	142,824
Purchase of available-for-sale securities	(14,848)	(52,568)	(102,214)
Purchase of other investments	(109,885)	(91,093)	(315,583)
Redemption of other investments	232,827	245,069	165,711
Other investing activities	(23,617)	(7,841)	(1,520)
Net cash flows provided by investing activities	293,262	156,709	19,885
FINANCING ACTIVITIES:
Contribution by redeemable noncontrolling interest	22	5,643	680
Contribution by redeemable noncontrolling interest	0	0	15,728
Dividends paid to noncontrolling interest	(27,458)	0	(16,861)
Purchase of noncontrolling interest	0	0	(150,400)
Receipt of loans	874,100	571,048	657,700
Repayment of loans	(912,140)	(493,250)	(377,500)
Net cash flows provided by (used in) financing activities	(65,476)	83,441	129,347
EFFECT OF EXCHANGE RATE CHANGES ON FOREIGN CURRENCY CASH, CASH EQUIVALENTS AND RESTRICTED CASH	9,512	(13,985)	(18,533)
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(105,809)	23,476	(134,453)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF YEAR	1,318,645	1,295,169	1,429,622
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, END OF YEAR	1,212,836	1,318,645	1,295,169
Supplemental Cash Flow Information:
Income taxes paid, net of refunds	13,192	22,216	33,305
Interest paid	21,487	19,451	19,395
Reconciliation to Consolidated Balance Sheets:
Cash, cash equivalents and restricted cash	$ 1,318,645	$ 1,295,169	$ 1,429,622

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	1. DESCRIPTION OF BUSINESS Enstar Group Limited ("Enstar") is a Bermuda-based holding company, formed in 2001. Enstar is a multi-faceted insurance group that offers innovative capital release solutions and specialty underwriting capabilities through its network of group companies in Bermuda, the United States, the United Kingdom, Continental Europe, Australia, and other international locations. Our ordinary shares are listed on the NASDAQ Global Select Market under the ticker symbol "ESGR". Unless the context indicates otherwise, the terms "Enstar," "we," "us" or "our" mean Enstar Group Limited and its consolidated subsidiaries and the term "Parent Company" means Enstar Group Limited and not any of its consolidated subsidiaries. Our business is organized into three segments: (i) Non-life Run-off - This segment is comprised of the operations of our subsidiaries that are running off their property and casualty and other non-life business. It also includes our management business, which manages the run-off portfolios of third parties through our service companies. (ii) Atrium - Atrium Underwriters Ltd. is a managing general agent at Lloyd’s of London ("Lloyd's"), which manages Syndicate 609. Through a corporate capital vehicle, Atrium 5 Ltd., we provide 25% of the syndicate’s underwriting capacity and capital (with the balance provided by traditional Lloyd’s Names). Atrium underwrites specialist marine, energy, aerospace, non-marine and liability classes. (iii) StarStone - StarStone is a global specialty insurer that underwrites a diverse range of property, casualty and specialty insurance through its operations in Bermuda, the United States, the United Kingdom, and Continental Europe. Certain run-off business of StarStone is recorded in our Non-life Run-off segment. In addition to our three reportable segments, our other activities, which do not qualify as a reportable segment, include our corporate expenses, debt servicing costs, holding company income and expenses, foreign exchange, our remaining life business and other miscellaneous items.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	2. SIGNIFICANT ACCOUNTING POLICIES Basis of Preparation The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America ("U.S. GAAP"). The consolidated financial statements include our assets, liabilities and results of operations as of December 31, 2017 and 2016 and for the years ended December 31, 2017 , 2016 and 2015 . Results of operations for acquired subsidiaries are included from the date of acquisition. All significant intercompany transactions and balances have been eliminated. Use of Estimates The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amount of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Our actual results could differ materially from our estimates. Accounting policies that we believe are most dependent on assumptions and estimates are considered to be our critical accounting policies and are related to the determination of: • liability for losses and loss adjustment expenses ("LAE"); • liability for policy benefits for life and annuity contracts; • reinsurance balances recoverable; • gross and net premiums written and net premiums earned; • impairment charges, including other-than-temporary impairments on investment securities classified as available-for-sale, and impairments on goodwill, intangible assets and deferred charges; • fair value measurements of investments; • fair value estimates associated with accounting for acquisitions; • fair value estimates associated with loss portfolio transfer reinsurance agreements for which we have elected the fair value option; and • redeemable noncontrolling interests. Significant Accounting Policies (a) Premiums Non-Life Non-life premiums written are earned on a pro-rata basis over the period the coverage is provided. Reinsurance premiums are recorded at the inception of the policy, are based upon contractual terms and, for certain business, are estimated based on underlying contracts or from information provided by insureds and/or brokers. Changes in reinsurance premium estimates are expected and may result in adjustments in future periods. Any subsequent differences arising on such estimates are recorded as premiums written in the period in which they are determined. Certain non-life contracts are retrospectively rated and provide for a final adjustment to the premium based on the final settlement of all losses. Premiums on such contracts are adjusted based upon contractual terms, and management judgme nt is involved with respect to the estimate of the amount of losses that we expect to incur. Additional premiums are recognized at the time loss thresholds specified in the contract are exceeded and are earned over the coverage period, or are earned immediately if the period of risk coverage has passed. Life and Annuities Prior to going into run-off, our life and annuities subsidiaries wrote life insurance, including credit life and disability insurance, term life insurance, assumed life reinsurance and annuities. We will continue to recognize premiums on term life insurance, assumed life reinsurance and credit life and disability insurance. These premiums are generally recognized as revenue when due from policyholders. The policies include contracts with fixed and guaranteed premiums and benefits. Benefits and expenses are matched with such revenue to result in the recognition of profit over the life of the contracts. Premiums receivable Premiums receivable represent amounts currently due and amounts not yet due on insurance and reinsurance policies. Premiums for insurance policies are generally due at inception. Premiums for reinsurance policies generally become due over the period of coverage based on the policy terms. We monitor the credit risk associated with premiums receivable, taking into consideration the impact of our contractual right to offset loss obligations or unearned premiums against premiums receivable. Amounts deemed uncollectible are charged to net earnings in the period they are determined. Changes in the estimates of premiums written will result in an adjustment to premiums receivable in the period they are determined. Unearned premiums and prepaid reinsurance premiums Unearned premiums represent the portion of premiums written that relate to the unexpired terms of policies in force. Premiums ceded are similarly pro-rated over the period the coverage is provided with the unearned portion being deferred as prepaid reinsurance premiums. (b) Acquisition Costs Acquisition costs, consisting principally of commissions and brokerage expenses and certain premium taxes and fees incurred at the time a contract or policy is issued and that vary with and are directly related to the successful efforts of acquiring new insurance contracts or renewing existing insurance contracts, are deferred and amortized over the period in which the related premiums are earned. Deferred acquisition costs are limited to their estimated realizable value by line of business based on the related unearned premiums, anticipated claims and claim expenses and anticipated investment income. (c) Losses and LAE Non-life Run-off The liability for losses and LAE in the Non-life Run-off segment includes an amount determined from reported claims and an amount, based on historical loss experience and industry statistics, for losses incurred but not reported ("IBNR") determined using a variety of actuarial methods. These estimates are continually reviewed and are necessarily subject to the impact of future changes in factors such as claim severity and frequency, changes in economic conditions including the impact of inflation, legal and judicial developments, and medical cost trends. While we believe that the amount is adequate, the ultimate liability may be in excess of, or less than, the amounts provided. Adjustments will be reflected as part of net increase or reduction in losses and LAE liabilities in the periods in which they become known. Premium and commission adjustments may be triggered by incurred losses, and any amounts are recorded in the same period that the related incurred loss is recognized. Commutations of acquired companies’ exposures have the effect of accelerating the payout of claims compared to the probability-weighted ranges of actuarially projected cash flows that we apply when estimating the fair values of assets and liabilities at the time of acquisition. Any material acceleration of payout together with the impact of any material loss reserve savings in any period will also accelerate the amortization of fair value adjustments in that period. Gains or losses on settlement of losses and LAE liabilities by way of commutation or policy buy-back are recognized upon execution of a commutation or policy buyback with the insured or reinsured. Our insurance and reinsurance subsidiaries also establish provisions for LAE relating to run-off costs for the estimated duration of the run-off, which are included in losses and LAE. These provisions are assessed at each reporting date, and provisions relating to future periods are adjusted to reflect any changes in estimates of the periodic run-off costs or the duration of the run-off, including the impact of any acceleration of the run-off period that may be caused by commutations. Provisions relating to the current period together with any adjustment to future run-off provisions are included in net incurred losses and LAE in the consolidated statements of earnings. Atrium and StarStone The reserves for losses and LAE in the Atrium and StarStone segments include reserves for unpaid reported losses and for IBNR loss reserves. The reserves for unpaid reported losses and loss expenses are established by management based on reports from brokers, ceding companies and insureds and represent the estimated ultimate cost of events or conditions that have been reported to or specifically identified by us. The reserve for IBNR losses is established by us based on actuarially determined estimates of ultimate losses and loss expenses. Inherent in the estimate of ultimate losses and loss expenses are expected trends in claim severity and frequency and other factors which may vary significantly as claims are settled. Accordingly, ultimate losses and loss expenses may differ from the amounts recorded in the consolidated financial statements. These estimates are reviewed regularly and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments, if any, will be recorded in earnings in the period in which they become known. Prior period development arises from changes to loss estimates recognized in the current year that relate to loss reserves established in prev ious calendar years. (d) Policy Benefits for Life and Annuity Contracts Policy benefits for life and annuity contracts (“policy benefits”) are calculated using the net level premium method and are derived using locked-in assumptions. Policy benefits are established and maintained at a level that we estimate will, when taken together with future premium payments and investment income expected to be earn ed on associated premiums, be sufficient to support all future cash flow benefit obligations and third-party servicing obligations as they become payable. We review policy benefits regularly and perform loss recognition testing based upon cash flow projections. Since the development of the policy benefits is based upon projections of future cash flows, we are required to make assumptions for mortality, longevity and morbidity rates, lapse rates, expenses and investment income. The assumptions used to determine policy benefits are determined at the inception of the contracts, reviewed and adjusted at the point of acquisition, as required, and are locked-in throughout the life of the contract unless a premium deficiency develops. These locked-in assumptions are based on a best estimate view of experience at the time they are established and may include a provision for adverse deviation. Assumptions are established based upon a combination of historical and industry experience, when available, and management judgment. Actual results could differ from these estimates. Policy benefit liabilities are reviewed periodically to determine whether a premium deficiency exists. Management reviews emerging experience and updates best estimate assumptions where appropriate. If existing policy benefit reserves, reduced by unamortized acquisition costs, together with the present value of future gross premiums using current best estimate assumptions, are insufficient in covering the present value of future benefits, settlement, and maintenance costs using current best estimate assumptions, a premium deficiency is deemed to exist. To remediate, unamortized acquisition costs are reduced until the premium deficiency has been eliminated. If unamortized acquisition costs have been entirely written off and a premium deficiency still exists, locked-in assumptions are revised and a charge for policy benefits is recognized. Because of the many assumptions and estimates used in establishing policy benefits and the long-term nature of the contracts, the reserving process, while based on actua rial techniques, is inherently uncertain. (e) Reinsurance Balances Recoverable Amounts billed to, and due from, reinsurers resulting from paid movements in the underlying business are calculated in accordance with the terms of the individual reinsurance contracts. Similarly, reinsurance balances recoverable related to our case reserves are calculated by applying the terms of any applicable reinsurance coverage to movements in the underlying case reserves. Our estimate of reinsurance balances recoverable related to IBNR reserves is recognized on a basis consistent with the underlying IBNR reserves. Our reinsurance balances recoverable are presented net of a provision for uncollectible amounts, reflecting the amount deemed not collectible due to credit quality, collection problems due to the location of the reinsurer, contractual disputes with reinsurers over individual contentious claims, contract language or coverage issues. (f) Investments, Cash and Cash Equivalents Short-term investments and fixed maturity investments Short-term investments comprise investments with a maturity greater than three months up to one year from the date of purchase. Fixed maturities comprise investments with a maturity of greater than one year from the date of purchase. Short-term and fixed maturity investments classified as trading are carried at fair value, with realized and unrealized holding gains and losses included in net earnings and reported as net realized and unrealized gains and losses. Short-term and fixed maturity investments classified as available-for-sale are carried at fair value, with unrealized gains and losses excluded from net earnings and reported as a separate component of accumulated other comprehensive income. Realized gains and losses on sales of investments classified as available-for-sale are recognized in the consolidated statements of earnings. The costs of short-term and fixed maturity investments are adjusted for amortization of premiums and accretion of discounts, recognized using the effective yield method and included in net investment income. For mortgage-backed and asset-backed investments, and any other holdings for which there is a prepayment risk, prepayment assumptions are evaluated and reviewed on a regular basis. Investment purchases and sales are recorded on a trade-date basis. Realized gains and losses on the sale of investments are based upon specific identification of the cost of investments. Other-Than-Temporary Impairments Fixed maturity investments classified as available-for-sale are reviewed quarterly to determine if they have sustained an impairment of value that is, based on our judgment, considered to be other than temporary. The process includes reviewing each fixed maturity investment that is below cost and: (1) determining if we have the intent to sell the fixed maturity investment; (2) determining if it is more likely than not that we will be required to sell the fixed maturity investment before its anticipated recovery; and (3) assessing whether a credit loss exists, that is, whether we expect that the present value of the cash flows expected to be collected from the fixed maturity investment is less than the amortized cost basis of the investment. In assessing whether it is more likely than not that we will be required to sell a fixed maturity investment before its anticipated recovery, we consider various factors including our future cash flow requirements, legal and regulatory requirements, the level of our cash, cash equivalents, short-term investments and fixed maturity investments available-for-sale in an unrealized gain position, and other relevant factors. In evaluating credit losses, we consider a variety of factors in the assessment of a fixed maturity investment including: (1) the time period during which there has been a significant decline below cost; (2) the extent of the decline below cost and par; (3) the potential for the investment to recover in value; (4) an analysis of the financial condition of the issuer; (5) the rating of the issuer; and (6) failure of the issuer of the investment to make scheduled interest or principal payments. If we conclude that an investment is other-than-temporarily impaired ("OTTI"), then the difference between the fair value and the amortized cost of the investment is presented as an OTTI charge in the consolidated statements of earnings, with an offset for any non-credit related loss component of the OTTI charge to be recognized in other comprehensive income. Accordingly, only the credit loss component of the OTTI amount would have an impact on our earnings. Equities Equities are classified as trading and are carried at fair value with realized and unrealized holding gains and losses included in net earnings and reported as net realized and unrealized gains and losses. Other investments, at fair value Other investments include investments in limited partnerships and limited liability companies (collectively "private equities") and fixed income funds, hedge funds, equity funds, private credit funds and collateralized loan obligation ("CLO") equity funds that carry their investments at fair value, as well as direct investments in CLO equities. These other investments are stated at fair value, which ordinarily will be the most recently reported net asset value as advised by the fund manager or administrator. Many of our fund investments publish net asset values on a daily basis and provide daily liquidity; others report on a monthly basis. Private equities typically report quarterly. The change in fair value is included in net realized and unrealized gains and losses on investments and recognized in net earnings. Other investments, at cost Investments in life settlements are recorded as other investments, at cost, and are accounted for under the investment method whereby we recognize our initial investment in the life settlement contracts at the transaction price plus all initial direct external costs. Continuing costs to keep the policy in force, primarily life insurance premiums, increase the carrying amount of the investment. We recognize income on individual investments in life settlements when the insured dies, at an amount equal to the excess of the investment proceeds over the carrying amount of the investment at that time. The investments are subject to quarterly impairment review on a contract-by-contract basis. An investment in life settlements is considered impaired if the undiscounted cash flows resulting from the expected proceeds from the investment in life settlements are not sufficient to recover the current carrying amount for the investment in life settlements plus anticipated undiscounted future premiums and other capitalizable future costs, if any. Impaired contracts are written down to their estimated fair value, which is determined on a discounted cash flow basis using current market longevity assumptions and market yields, with any impairment charges included within net realized and unrealized gains (losses). Cash and cash equivalents Cash equivalents includes all highly liquid debt instruments purchased with an original maturity of three months or less. (g) Funds Held Under funds held arrangements, the reinsured company has retained funds that would otherwise have been remitted to our reinsurance subsidiaries. The funds balance is credited with investment income and losses payable are deducted. Funds held are shown under two categories on the consolidated balance sheets, where funds held upon which we receive the underlying portfolio economics are shown as "Funds held - directly managed", and funds held where we receive a fixed crediting rate are shown as "Funds held by reinsured companies". Funds held by reinsured companies are carried at cost. Funds held - directly managed, carried at fair value, represents the aggregate of funds held at cost and the value of an embedded derivative. The embedded derivative relates to our contractual right to receive the return on the underlying investment portfolio economics. The investment returns on both categories of funds held are recognized in net investment income and net realized and unrealized gains (losses). The revaluation of the embedded derivative is included in net unrealized gains (losses). (h) Fees and Commission Income Fees and commission income primarily includes profit commissions earned from managed Lloyd's syndicates as well as fees earned under fronting and consulting arrangements with third- party clients, which are recorded on an accrual basis. (i) Foreign Exchange Our reporting currency is the U.S. dollar. Assets and liabilities of entities whose functional currency is not the U.S. dollar are translated at period end exchange rates. Revenues and expenses of such foreign entities are translated at average exchange rates during the year. The effect of the currency translation adjustments for these foreign entities is included in accumulated other comprehensive income (loss). Other foreign currency assets and liabilities that are considered monetary items are translated at exchange rates in effect at the balance sheet date. Foreign currency revenues and expenses are translated at transaction date exchange rates. These exchange gains and losses are recognized in net earnings. (j) Share-based Compensation We have primarily used three types of share-based compensation: (i) restricted shares, restricted share units and performance share units, (ii) cash-settled stock appreciation rights ("SARs") and (iii) shares issued under our employee share purchase plans. With the exception of SARs and the incentive plan awards issued to certain employees of Atrium, our share-based compensation awards qualify for equity classification. The fair value of the compensation cost is measured at the grant date and is expensed over the service period of the award. The SARs and the Atrium incentive plan awards are classified as liability awards. Liability classified awards are recorded at fair value within other liabilities in the consolidated balance sheet with changes in fair value relating to the vested portion of the award recorded within general and administrative expenses in the consolidated statements of earnings. (k) Derivative Instruments We utilize derivative instruments in our foreign currency risk management strategy and recognize all derivatives as either assets or liabilities in the consolidated balance sheets and carry them at the fair value of the specific instrument utilized. Changes in the fair value as well as realized gains or losses on derivative instruments are recognized in net earnings if they are not designated as qualifying hedging instruments or if the criteria for establishing a perfectly effective designated hedging relationship for our net investment hedges has not been met. However, if a designated net investment hedge is deemed to be perfectly effective, then we recognize the changes in the fair value of the underlying hedging instrument in accumulated other comprehensive income (loss) until the application of hedge accounting is discontinued. Any cumulative gains or losses arising on designated net investment hedges are deferred in accumulated other comprehensive income (loss) until the CTA from the underlying hedged net investment is recognized in net earnings due to a disposal, deconsolidation or substantial liquidation. Certain of our funds held arrangements also contain embedded derivatives as described above and which are carried at fair value. (l) Income Taxes Certain of our subsidiaries and branches operate in jurisdictions where they are subject to taxation. Current and deferred income taxes are charged or credited to net income, or, in certain cases, to accumulated other comprehensive income, based upon enacted tax laws and rates applicable in the relevant jurisdiction in the period in which the tax becomes accruable or realizable. Deferred income taxes are provided for all temporary differences between the bases of assets and liabilities used in the financial statements and those used in the various jurisdictional tax returns. When our assessment indicates that it is more likely than not that all or some portion of deferred income tax assets will not be realized, a valuation allowance is recorded against the deferred tax assets. We recognize a tax benefit relating to uncertain tax positions only where the position is more likely than not to be sustained assuming examination by tax authorities. A liability is recognized for any tax benefit (along with any interest and penalty, if applicable) claimed in a tax return in excess of the amount allowed to be recognized in the financial statements under U.S. GAAP. Any changes in amounts recognized are recorded in the period in which they are determined. (m) Earnings Per Share Basic earnings per share is based on the weighted average number of ordinary shares outstanding and excludes potentially dilutive securities such as restricted shares, restricted share units, warrants, options and convertible securities. Diluted earnings per share is based on the weighted average number of ordinary and ordinary share equivalents outstanding calculated using the treasury stock method for all potentially dilutive securities. When the effect of dilutive securities would be anti-dilutive, these securities are excluded from the calculation of diluted earnings per share. (n) Acquisitions, Goodwill and Intangible Assets The acquisition method is used to account for all business acquisitions. This method requires that we record the acquired assets and liabilities at their estimated fair value. The fair values of each of the acquired reinsurance assets and liabilities are derived from probability-weighted ranges of the associated projected cash flows, based on actuarially prepared information and management’s run-off strategy. Our run-off strategy, as well as that of other run-off market participants, is expected to be different from the seller's as generally sellers are not specialized in running off insurance and reinsurance liabilities whereas we and other market participants do specialize in such run-offs. The key assumptions used by us and, we believe, by other run-off market participants in the fair valuation of acquired companies are (i) the projected payout, timing and amount of claims liabilities; (ii) the related projected timing and amount of reinsurance collections; (iii) an appropriate discount rate, which is applied to determine the present value of the future cash flows; (iv) the estimated unallocated LAE to be incurred over the life of the run-off; (v) the impact of any accelerated run-off strategy; and (vi) an appropriate risk margin. The difference between the original carrying value of reinsurance liabilities and reinsurance assets acquired at the date of acquisition and their fair value is recorded as an intangible asset or other liability, which we refer to as the fair value adjustment ("FVA"). The FVA is amortized over the estimated payout period of outstanding losses and loss expenses acquired. To the extent the actual payout experience after the acquisition is materially faster or slower than anticipated at the time of the acquisition, there is an adjustment to the estimated ultimate loss reserves, or there are changes in bad debt provisions or in estimates of future run-off costs following accelerated payouts, then the amortization of the FVA is adjusted to reflect such changes. The difference between the fair value of net assets acquired and the purchase price is recorded as a goodwill asset or as a gain from bargain purchase in the consolidated statements of earnings. Goodwill is established initially upon acquisition and assessed at least annually for impairment. If the goodwill asset is determined to be impaired it is written down in the period in which the determination is made. Intangible assets represent the fair value adjustments related to unpaid losses and LAE, reinsurance balances recoverable and policy benefits for life and annuity contracts along with the intangible assets arising from the acquisitions of Atrium and StarStone. Definite-lived intangible assets are amortized over their useful lives. Amortization of intangible assets is recognized in the consolidated statement of earnings. Indefinite-lived intangible assets are not subject to amortization. The carrying values of intangible assets are reviewed for indicators of impairment at least annually. Impairment is recognized if the carrying values of the definite-lived intangible assets are not recoverable from their undiscounted cash flows and are measured as the difference between the carrying value and the fair value. (o) Retroactive Reinsurance and Deferred Charges Retroactive reinsurance policies provide indemnification of losses and LAE with respect to past loss events. In our Non-life Run-off segment we use the balance sheet accounting approach for assumed loss portfolio transfers, whereby at the inception of the contract there are no premiums or losses recorded in earnings. At the inception of a contract, a deferred charge asset is recorded for the excess, if any, of the estimated ultimate losses payable over the premiums received. Deferred charges, recorded in other assets, are amortized over the estimated claim payment period of the related contract with the periodic amortization reflected in earnings as a component of losses and LAE. Deferred charges amortization is adjusted at each reporting period to reflect new estimates of the amount and timing of remaining loss payments. Changes in the estimated amount and the timing of payments of unpaid losses may have an effect on the unamortized deferred charges and the amount of periodic amortization. Deferred charges are assessed at each reporting period for impairment. If the asset is determined to be impaired, it is written down in the period in which the determination is made. In our Non-life Run-off and StarStone segments we have ceded business to KaylaRe Ltd., an affiliated reinsurer, as described in Note 21 - "Related Party Transactions" . The reinsurance ceded by StarStone to KaylaRe Ltd. during the year ended December 31, 2016 was mostly recognized as retroactive reinsurance, except for the unearned ceded premium as at December 31, 2016 which was recognized as prospective reinsurance. The reinsurance ceded by StarStone to KaylaRe Ltd. from January 1, 2017 was recognized as prospective reinsurance. (p) Retroactive Reinsurance - Fair Value Option In our Non-life Run-off segment we have elected to apply the fair value option for certain loss portfolio transfer reinsurance transactions. This is an irrevocable election that applies to all balances under the insurance contract, including funds held assets, reinsurance balances recoverable, and the liability for losses and loss adjustment expenses. We use an internal model to calculate the fair value of the liability for losses and loss adjustment expenses and the reinsurance balances recoverable asset. Note 8 - "Fair Value Measurements" describes the internal model, including the observable and unobservable inputs used in the model. (q) Redeemable Noncontrolling Interest In connection with the acquisitions of Arden, Atrium and StarStone, certain subsidiaries issued shares to noncontrolling interests. These shares provide certain redemption rights to the holders, which may be settled in our own shares or cash or a combination of cash and shares, at our option. Redeemable noncontrolling interest with redemption features that are not solely within our control are classified within temporary equity in the consolidated balance sheets and carried at the redemption value, which is fair value. Change in the fair value is recognized through retained earnings as if the balance sheet date were also the redemption date. (r) Internal-use Software Direct internal and external costs to acquire or develop internal-use software have been capitalized. We only capitalize costs incurred after the preliminary project stage has been completed, and when management has authorized and committed to funding the project and it is probable that the project will be completed and the software will be used to perform the functions intended. Capitalized costs related to internal-use software are amortized on a straight-line basis over the estimated useful lives of the assets. These capitalized costs are also assessed for impairment when impairment indicators exist. (s) Held-for-sale Business and Discontinued Operations We report a business as held-for-sale when certain criteria are met which include, (1) management either approving the sale or receiving approval to sell the business and is committed to a formal plan to sell the business, (2) the business is available for immediate sale in its present condition, (3) the business is being actively marketed for sale at a price that is reasonable in relation to its current fair value, (4) the sale is anticipated to occur during the next 12 months, among other specified criteria. A business classified as held for sale is recorded at the lower of its carrying amount or estimated fair value less costs to sell. If the carrying amount of the b

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisitions	3. ACQUISITIONS 2016 Dana Companies On December 30, 2016, we completed the acquisition of Dana Companies, LLC ("Dana Companies") from Dana Incorporated ("Dana"). Dana Companies holds liabilities associated with personal injury asbestos claims and environmental claims arising from its legacy manufacturing operations. Dana Companies’ assets include, amongst others, insurance rights related to coverage against these liabilities and marketable securities. The total consideration for the transaction was $88.5 million . Purchase price $ 88,500 Net assets acquired at fair value $ 88,500 Excess of purchase price over fair value of net assets acquired $ — The following table summarizes the fair values of the assets acquired and liabilities assumed at the acquisition date, recorded in our Non-life Run-off segment. Total ASSETS Short-term investments, trading, at fair value $ 22,747 Fixed maturities, trading, at fair value 61,389 Other investments, at fair value 46,589 Total investments 130,725 Cash and cash equivalents 58,430 Restricted cash and cash equivalents 1,692 Other assets - Insurance balances recoverable 133,032 Other assets 5,383 TOTAL ASSETS 329,262 LIABILITIES Other liabilities - Asbestos related 220,496 Other liabilities 20,266 TOTAL LIABILITIES 240,762 NET ASSETS ACQUIRED AT FAIR VALUE $ 88,500 From the date of acquisition to December 31, 2016, we did no t record any earnings from Dana Companies. 2015 Nationale Suisse Assurance S.A. On November 13, 2015, we completed the acquisition of Nationale Suisse Assurance S.A. ("NSA"). We changed the name of NSA to Alpha Insurance SA ("Alpha") at closing and placed the company into run-off. Alpha is a Belgium-based composite insurance company that wrote both non-life and life insurance that we are now operating as part of our non-life run-off segment and other activities, respectively. The total consideration for the transaction was €32.8 million (or $35.2 million ). Purchase price $ 35,225 Net assets acquired at fair value $ 35,225 Excess of purchase price over fair value of net assets acquired $ — The following table summarizes the fair values of the assets acquired and liabilities assumed in the Alpha transaction at the acquisition date, allocated between our Non-life Run-off segment and our other activities. Non-life Other Total ASSETS Short-term investments, trading, at fair value $ 8,644 $ — $ 8,644 Short-term investments, available-for-sale, at fair value — 6,687 6,687 Fixed maturities, trading, at fair value 31,350 — 31,350 Fixed maturities, available-for-sale, at fair value — 96,656 96,656 Other investments, at fair value 1,339 — 1,339 Total investments 41,333 103,343 144,676 Cash and cash equivalents 39,451 25,258 64,709 Reinsurance balances recoverable — reserves 4,041 302 4,343 Reinsurance balances recoverable — paid 10,831 1,320 12,151 Prepaid reinsurance premiums 3,213 — 3,213 Other assets 3,097 2,298 5,395 TOTAL ASSETS 101,966 132,521 234,487 LIABILITIES Losses and LAE 56,021 117,188 173,209 Funds withheld 473 — 473 Insurance and reinsurance balances payable 6,212 779 6,991 Unearned premium 5,969 — 5,969 Other liabilities 9,745 2,875 12,620 TOTAL LIABILITIES 78,420 120,842 199,262 NET ASSETS ACQUIRED AT FAIR VALUE $ 23,546 $ 11,679 $ 35,225 From the date of acquisition to December 31, 2015, we earned premiums of $ nil , recorded net incurred losses and LAE of $ nil on those earned premiums, and recorded $0.1 million in net losses attributable to Enstar Group Limited related to Alpha’s business. Wilton Re On May 5, 2015, we completed the acquisition of certain subsidiaries from Wilton Re Limited ("Wilton Re"), which hold in terests in life insurance policies. These interests were acquired by Wilton Re in the secondary and tertiary markets and through collateralized lending transactions. The total consideration for the transaction was $173.1 million , paid in two installments. The first installment of $89.1 million was paid on closing. The second installment of $83.9 million was paid on the first anniversary of closing. The companies are operating as part of our other activities. Purchase price $ 173,058 Net assets acquired at fair value $ 173,058 Excess of purchase price over fair value of net assets acquired $ — The purchase price was allocated to the acquired assets and liabilities of the two companies acquired based on estimated fair values at the acquisition date. The following table summarizes the fair values of the assets acquired and liabilities assumed at the acquisition date. ASSETS Other investments $ 142,182 Cash and cash equivalents 5,043 Other assets 26,376 TOTAL ASSETS $ 173,601 TOTAL LIABILITIES 543 NET ASSETS ACQUIRED AT FAIR VALUE $ 173,058 From the date of acquisition to December 31, 2015, we recorded $16.5 million in net earnings attributable to Enstar Group Limited related to the life settlement contract business. Canada Pension Plan Investment Board ("CPPIB"), together with management of Wilton Re, owns 100% of the common stock of Wilton Re. Subsequent to the closing of our transaction with Wilton Re, CPPIB separately acquired certain of our voting and non-voting ordinary shares in several third party transactions during 2015 and 2016, as described in Note 21 - "Related Party Transactions" . Sussex Insurance Company (formerly known as Companion) On January 27, 2015, we completed the acquisition of Companion Property and Casualty Insurance Company ("Companion") from Blue Cross and Blue Shield of South Carolina, an independent licensee of the Blue Cross Blue Shield Association. Companion is a South Carolina based insurance group with property, casualty, specialty and workers ' compensation business, and has also provided fronting and third-party administrative services. We changed the name of Companion to Sussex Insurance Company ("Sussex") following the acquisition, and the company is operating as part of the Non-life Run-off segment. In addition, StarStone is renewing certain business from Sussex. The total consideration for the transaction was $218.0 million , which was financed 50% through borrowings under a Term Facility Agr eement with two financial institutions (the "Sussex Facility") and 50% from cash on hand. Purchase price $ 218,000 Net assets acquired at fair value $ 218,000 Excess of purchase price over fair value of net assets acquired $ — The purchase price was allocated to the acquired assets and liabilities of Sussex based on estimated fair values at the acquisition date. The following table summarizes the fair values of the assets acquired and liabilities assumed at the acquisition date. ASSETS Short-term investments, trading, at fair value $ 85,309 Fixed maturities, trading, at fair value 523,227 Equities, trading, at fair value 31,439 Total investments 639,975 Cash and cash equivalents 358,458 Restricted cash and cash equivalents 15,279 Accrued interest receivable 3,984 Premiums receivable 37,190 Reinsurance balances recoverable 483,816 Prepaid reinsurance premiums 28,751 Other assets 43,939 TOTAL ASSETS 1,611,392 LIABILITIES Losses and LAE 1,257,205 Insurance and reinsurance balances payable 3,030 Unearned premium 79,293 Funds withheld 42,090 Other liabilities 11,774 TOTAL LIABILITIES 1,393,392 NET ASSETS ACQUIRED AT FAIR VALUE $ 218,000 The net unearned premiums acquired included a decrease of $34.6 million to adjust net unearned premiums to fair value. This fair value adjustment is included within unearned premiums on the consolidated balance sheet. As at December 31, 2017 , $16.1 million has been amortized to acquisition costs and $16.0 million has been amortized to net premiums earned in the consolidated statements of earnings and comprehensive income. As at December 31, 2017 , the remaining balance of the fair value adjustment was $2.5 million , which will be amortized to net premiums earned over the remaining terms of the underlying policies. From the date of acquisition to December 31, 2015, we earned premiums of $43.2 million , recorded net incurred losses and LAE of $44.4 million on those earned premiums, and recorded $42.4 million in net losses attributable to Enstar Group Limited related to Sussex’s non-life run-off business. Supplemental Pro Forma Financial Information (Unaudited) The following unaudited pro forma condensed combined statement of earnings for the year ended December 31, 2015 combines our historical consolidated statements of earnings with those of Sussex, Alpha and Wilton Re, giving effect to the business combinations and related transactions as if they had occurred on January 1, 2015. For the year ended December 31, 2015, the operating results of Sussex, Alpha and Wilton Re have been included in the consolidated financial statements from each of their respective dates of acquisition. The unaudited pro forma financial information presented below is for informational purposes only and is not necessarily indicative of the results of operations that would have been achieved if the acquisitions of Sussex, Alpha and Wilton Re and related transactions had taken place at the beginning of each period presented, nor is it indicative of future results. Enstar Group Unaudited 2015 Sussex Alpha Wilton Re Pro forma Enstar Total income $ 904,460 $ 29,990 $ 31,884 $ 5,793 $ 9,494 $ 981,621 Total expenses (694,119 ) (39,860 ) (47,026 ) (3,628 ) 5,894 (778,739 ) Total noncontrolling interest 9,950 — — — — 9,950 Net earnings (loss) $ 220,291 $ (9,870 ) $ (15,142 ) $ 2,165 $ 15,388 $ 212,832 Summary of the Pro Forma Adjustments to the Pro Forma Condensed Consolidated Statement of Earnings for the Twelve Months Ended December 31, 2015 (Unaudited): Income: (a) Reversal of amortization of fair value adjustments related to unearned premium included in Enstar Group results but reflected in 2014 pro formas 13,344 (b) Adjustment to recognize amortization of fair value adjustments related to unearned premium (3,850 ) 9,494 Expenses: (a) Adjustment to interest expense to reflect financing costs of the acquisition for the period (1,098 ) (b) Adjustment to recognize amortization of fair value adjustments related to acquired losses and LAE liabilities and reinsurance balances recoverable (451 ) (c) Reversal of amortization of fair value adjustments related to acquisition costs included in Enstar Group results but reflected in 2014 pro formas 16,173 (d) Adjustment to income taxes for pro forma adjustments (8,730 ) 5,894 Changes in Ownership Interests relating to Holding Companies for our Active Underwriting Businesses Corporate Holding Company Reorganization during 2015 On December 23, 2015, we completed a corporate reorganization of certain of our subsidiary holding companies. Following the reorganization, StarStone Holdings and Northshore are owned by a common parent, North Bay Holdings Limited ("North Bay"), as described in Note 16 - "Noncontrolling Interest" .

Significant New Business

Significant New Business	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Significant New Business	4. SIGNIFICANT NEW BUSINESS 2018 Zurich Australia On February 22, 2018, we entered into an agreement with an Australia subsidiary of Zurich Insurance Group ("Zurich") to reinsure its New South Wales Vehicle Compulsory Third Party ("CTP") insurance business. Under the agreement, which is effective as of January 1, 2018, we will assume gross reinsurance reserves of approximately AUD$350 million (approximately $275.0 million ). Following the initial reinsurance transaction, which transferred the economics of the CTP insurance business, we and Zurich are pursuing a portfolio transfer of the CTP insurance business under Division 3A Part III of Australia's Insurance Act 1973 (Cth), which will provide legal finality for Zurich's obligations. The transfer is subject to court, regulatory and other approvals. Neon RITC Transaction On February 16, 2018 , we closed the previously announced reinsurance-to-close transaction with Neon Underwriting Limited ("Neon"), under which we will reinsure to close the 2015 and prior underwriting years of account (comprising underwriting years 2008 to 2015) of Neon's Syndicate 2468. We have assumed gross reserves of £402.2 million (approximately $543.4 million ) or net reinsurance reserves of £337.8 million (approximately $456.4 million ) relating to the portfolio for cash consideration equal to the net amount of reserves assumed. Following the closing of the transaction, Enstar has taken responsibility for claims handling and will provide complete finality to Neon's obligations. Novae RITC Transaction On January 29, 2018, we entered into an RITC transaction with AXIS Managing Agency Limited, under which we will reinsure to close the 2015 and prior underwriting years of account of Novae Syndicate 2007. We will assume gross reserves of approximately £840.0 million (approximately $1.1 billion) relating to the portfolio or net reinsurance reserves of approximately £600.0 million (approximately $811.0 million) for cash consideration equal to the net amount assumed. 2017 Allianz On December 28, 2017 , we entered into a reinsurance agreement with Allianz SE (“Allianz”) to reinsure a portfolio of Allianz’s run-off business, effective December 31, 2017 . Pursuant to the reinsurance agreement, we reinsured 50% of certain U.S. workers' compensation, asbestos, and toxic tort business originally held by San Francisco Reinsurance Company, an affiliate of Allianz, and in the process assumed net reinsurance reserves of $81.4 million . Affiliates of Allianz retained $81.4 million of reinsurance premium as funds withheld collateral for the obligations under the reinsurance agreement and we transferred $8.1 million to a reinsurance trust to further support our obligations. We will also provide ongoing consulting services with respect to the entire $162.8 million portfolio, including the 50% share retained by affiliates of Allianz. RSA On February 7, 2017, we entered into an agreement to reinsure the U.K. employers' liability legacy business of RSA Insurance Group PLC ("RSA"). Pursuant to the transaction, our subsidiary assumed gross insurance reserves of £1,046.4 million ( $1,301.8 million ), relating to 2005 and prior year business. Net insurance reserves assumed were £927.5 million ( $1,153.9 million ) a nd the reinsurance premium received was £801.6 million ( $997.2 million ). We elected the fair value option for this reinsurance contract. The initial fair value adjustment on the gross reserves was $174.1 million , and on the net reserves was $156.7 million . Refer to Note 8 - "Fair Value Measurements" for a description of the fair value process and assumptions. Following the initial reinsurance transaction, which transferred the economics of the portfolio up to the policy's limits, we and RSA are pursuing a portfolio transfer of the business under Part VII of the Financial Services and Markets Act 2000, which would provide legal finality for RSA's obligations. The transfer is subject to court, regulatory and other approvals. QBE On January 11, 2017, we closed a transaction to reinsure multi-line property and casualty business of QBE Insurance Group Limited ("QBE"). We assumed gross reinsurance reserves of approximately $1,019.0 million (net reserves of $447.0 million ) relating to the portfolio, which primarily includes workers' compensation, construction defect, and general liability discontinued lines of business. The reinsurance premium received was $403.8 million , comprised of $227.6 million in restricted cash and $176.2 million in funds held. We elected the fair value option for this reinsurance contract. The initial fair value adjustment was $180.0 million on the gross reserves and $43.2 million on the net reserves. Refer to Note 8 - "Fair Value Measurements" for a description of the fair value process and assumptions. In addition, we pledged a portion of the premium as collateral to a subsidiary of QBE, and we have provided additional collateral and a limited parental guarantee. 2016 Coca-Cola On August 5, 2016, we entered into a reinsurance transaction with The Coca-Cola Company and its subsidiaries (“Coca-Cola”) pursuant to which we reinsured certain of Coca-Cola’s retention and deductible risks under its subsidiaries’ U.S. workers’ compensation, auto liability, general liability, and product liability insurance coverage. We assumed total gross reserves of $108.8 million , received total assets of $101.3 million and recorded a deferred charge of $7.5 million , included in other assets. We have transferred $108.8 million into a trust to support our obligations under the reinsurance agreements. We provided a limited parental guarantee, subject to an overall maximum of $27.0 million . Allianz On February 17, 2016, we entered into a reinsurance agreement with Allianz to reinsure portfolios of Allianz's run-off business. Pursuant to the reinsurance agreement, our subsidiary reinsured 50% of certain portfolios of workers' compensation, construction defect, and asbestos, pollution, and toxic tort business originally held by Fireman's Fund Insurance Company, and in the process assumed net reinsurance reserves of $1.1 billion . Affiliates of Allianz retained $1.1 billion of reinsurance premium as funds withheld collateral for the obligations of our subsidiary under the reinsurance agreement and we transferred $110.0 million to a reinsurance trust to further support our subsidiary's obligations. We have also provided a limited parental guarantee, which is subject to a maximum cap. The combined monetary total of the support offered by us through the trust and parental guarantee was initially be capped at $270.0 million . In addition to the reinsurance transaction described above, we have entered into a consulting agreement with San Francisco Reinsurance Company, an affiliate of Allianz, with respect to the entire $2.2 billion portfolio, including the 50% share retained by affiliates of Allianz. Shelbourne RITC Transaction On November 15, 2016, we entered into a RITC transaction of the 2007 and prior underwriting years of account of a Lloyd’s syndicate managed by Neon (formerly Marketform), under which we assumed total net insurance reserves of £121.5 million ( $158.0 million ) for cash consideration of an equal amount. 2015 Doctors On November 30, 2015, we completed the assignment and assumption of a portfolio of primarily workers' compensation business from The Doctors Company and its affiliates. Total assets and liabilities assumed were $29.5 million . Sun Life On September 30, 2015, we entered into two 100% reinsurance agreements and a related administration services agreement with Sun Life pursuant to which we reinsured all of the run-off workers' compensation carve-out and occupational accident business of Sun Life. We assumed reinsurance reserves of $128.3 million , received total assets of $122.5 million and recorded a deferred charge of $5.8 million , included in other assets. We transferred $30.6 million of additional funds into trust to further support our obligations under the reinsurance agreements. We provided limited parental guarantees, subject to an overall maximum of $36.8 million . Voya Financial On May 27, 2015, we entered into two 100% reinsurance agreements and related administration services agreements with a subsidiary of Voya, pursuant to which we reinsured all of the run-off workers' compensation and occupational accident assumed reinsurance business of the Voya subsidiary and that of its Canadian branch. Pursuant to the transaction, the Voya subsidiary transferred assets into two reinsurance collateral trusts securing our obligations under the reinsurance agreements. We assumed reinsurance reserves of $572.4 million , received total assets of $307.0 million and recorded a deferred charge of $265.4 million , included in other assets. We transferred $67.2 million of additional funds to the trusts to further support our obligations under the reinsurance agreements. We provided a limited parental guarantee, subject to a maximum cap with respect to the reinsurance liabilities. As of December 31, 2017 , the amount of the parental guarantee was $129.1 million . Reciprocal of America On January 15, 2015 , we completed a loss portfolio transfer reinsurance transaction with Reciprocal of America (in Receivership) and its Deputy Receiver relating to a portfolio of workers' compensation business that has been in run-off since 2003. The total insurance reserves assumed were $162.1 million with an equivalent amount of cash and investments received as consideration.

Divestitures, Held-For-Sale Bus

Divestitures, Held-For-Sale Businesses and Discontinuing Operations	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Divestitures, Held-For-Sale Business and Discontinuing Operations	5. DIVESTITURES, HELD-FOR-SALE BUSINESSES AND DISCONTINUING OPERATIONS Pavonia On December 29, 2017, the Company completed the previously announced sale of its subsidiary, Pavonia Holdings (US), Inc. (“Pavonia”), to Southland National Holdings, Inc. (“Southland”), a Delaware corporation and a subsidiary of Global Bankers Insurance Group, LLC. The aggregate purchase price was $120.0 million . The Company used the proceeds to make repayments under its revolving credit facility. Pavonia owns Pavonia Life Insurance Company of Michigan (“PLIC MI”) and Enstar Life (US), Inc. Pursuant to the amended stock purchase agreement between the Company and Southland, which partially restructured the transaction, Southland will acquire Pavonia Life Insurance Company of New York ("PLIC NY") for $13.1 million in a second closing that is expected to occur in the first or second quarter of 2018, subject to regulatory approval. The additional purchase price represents the cash consideration we paid to PLIC MI when we acquired PLIC NY from PLIC MI as a result of the restructuring of the first closing of the transaction. Pavonia was a substantial portion of our previously reported Life and Annuities segment. We have classified the assets and liabilities of the remaining businesses to be sold in the second closing as held-for-sale as at December 31, 2017. The following table summarizes the components of assets and liabilities held-for-sale on our consolidated balance sheet as at December 31, 2017 and 2016 in relation to Pavonia: December 31, December 31, Assets: Fixed maturities, trading, at fair value $ 20,770 $ 326,382 Fixed maturities, held-to-maturity, at amortized cost — 765,554 Equities, trading, at fair value 765 4,428 Other investments, at fair value — 15,114 Cash and cash equivalents 6,314 18,018 Restricted cash and cash equivalents 13 5,202 Deferred tax assets — 31,500 Reinsurance balances recoverable 1,728 18,029 Other assets 269 60,229 Assets of businesses held for sale 29,859 1,244,456 Less: Accrual of loss on sale (5,508 ) — Total assets held for sale $ 24,351 $ 1,244,456 Liabilities: Policy benefits for life and annuity contracts $ 10,666 $ 1,144,850 Other liabilities 605 5,937 Total liabilities held for sale $ 11,271 $ 1,150,787 As of December 31, 2017 and 2016 , included in the table above were restricted investments of $1.4 million and $786.0 million , respectively. The Pavonia business qualified as a discontinued operation. The following table summarizes the components of net earnings (losses) from discontinued operations on the consolidated statements of earnings for the years ended December 31, 2017 , 2016 and 2015 : December 31, December 31, December 31, Operations: INCOME Net premiums earned $ 55,906 $ 69,089 $ 85,327 Net investment income 41,117 38,140 35,404 Net realized and unrealized gains 577 4,263 271 Other income 1,564 1,912 7,690 $ 99,164 $ 113,404 $ 128,692 EXPENSES Life and annuity policy benefits 84,029 76,594 97,472 Acquisition costs 9,025 9,836 13,712 General and administrative expenses 12,813 14,416 13,886 Other expenses (26 ) 199 486 $ 105,841 $ 101,045 $ 125,556 EARNINGS (LOSS) BEFORE INCOME TAXES (6,677 ) 12,359 3,136 INCOME TAXES (3,190 ) $ (396 ) (5,167 ) NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS BEFORE GAIN ON SALE $ (9,867 ) $ 11,963 $ (2,031 ) Disposal: Consideration received $ 120,000 — — Less: Carrying value of subsidiary 86,961 — — Less: Cumulative currency translation adjustment previously recorded in accumulated other comprehensive income 12,179 — — Gain on sale of subsidiary $ 20,860 $ — $ — NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS $ 10,993 $ 11,963 $ (2,031 ) The following table presents the cash flows of Pavonia whilst under our ownership for the years ended December 31, 2017 , 2016 and 2015 : December 31, December 31, December 31, Operating activities $ 75,714 $ (71,521 ) $ (5,893 ) Investing activities 42,542 56,646 (24,766 ) Change in cash of businesses held for sale $ 118,256 $ (14,875 ) $ (30,659 ) The cash, cash equivalents and restricted cash carried on the balance sheet of Pavonia on December 29, 2017 were $135.1 million , as at the date of disposal. Laguna On August 29, 2017, we closed the previously-announced sale of our wholly-owned subsidiary Laguna Life DAC (“Laguna”) to a subsidiary of Monument Insurance Group Limited ("Monument"), for a total consideration of €25.6 million (approximately $30.8 million ). We have an investment in Monument, as described further in Note 21 - "Related Party Transactions" . Laguna was classified as held-for-sale during 2017 prior to its sale. Following the closing of the sale of Laguna, we recorded a loss on sale of $16.3 million for the year ended December 31, 2017 , which has been included in earnings from continuing operations before income taxes in our consolidated statement of earnings. This loss includes a cumulative currency translation adjustment balance of $(6.3) million , which has been reclassified from accumulated other comprehensive income and included in earnings as a component of the loss on sale of Laguna during the year ended December 31, 2017 , following the closing of the sale. Excluding the loss on sale, the net earnings (losses) relating to Laguna for the years ended December 31, 2017 , 2016 and 2015 were $(1.2) million , $1.0 million and $1.8 million , respectively. These amounts were not significant to our consolidated operations and therefore Laguna was not classified as a discontinued operation in current or prior periods.

Investments

Investments	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
INVESTMENTS	6. INVESTMENTS We hold: (i) trading portfolios of fixed maturity investments, short-term investments and equities, carried at fair value; (ii) available-for-sale portfolios of fixed maturity and short-term investments carried at fair value; and (iii) other investments carried at either fair value or cost. Trading The fair values of our fixed maturity investments, short-term investments and equities classified as trading were as follows: December 31, December 31, U.S. government and agency $ 554,036 $ 840,274 Non-U.S. government 607,132 267,363 Corporate 3,363,060 2,387,322 Municipal 100,221 47,181 Residential mortgage-backed 288,713 373,528 Commercial mortgage-backed 421,548 217,212 Asset-backed 541,574 478,280 Total fixed maturity and short-term investments 5,876,284 4,611,160 Equities — U.S. 106,363 95,047 Equities — International 240 — $ 5,982,887 $ 4,706,207 Included within residential and commercial mortgage-backed securities as at December 31, 2017 were securities issued by U.S. governmental agencies with a fair value of $152.4 million (as at December 31, 2016 : $362.9 million ). Included within corporate securities as at December 31, 2017 were senior secured loans of $68.9 million (as at December 31, 2016 : $90.7 million ). The contractual maturities of our fixed maturity and short-term investments classified as trading are shown below. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call o r prepayment penalties. As at December 31, 2017 Amortized Cost Fair Value % of Total Fair Value One year or less $ 398,054 $ 398,083 6.8 % More than one year through two years 340,531 341,753 5.8 % More than two years through five years 1,283,898 1,286,527 21.9 % More than five years through ten years 1,235,079 1,249,887 21.3 % More than ten years 1,278,126 1,348,199 22.9 % Residential mortgage-backed 285,312 288,713 4.9 % Commercial mortgage-backed 427,469 421,548 7.2 % Asset-backed 534,893 541,574 9.2 % $ 5,783,362 $ 5,876,284 100.0 % Available-for-sale The amortized cost and fair values of our fixed maturity and short-term investments classified as available-for-sale were as follows: As at December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Non-OTTI Fair Value U.S. government and agency $ 4,210 $ — $ (23 ) $ 4,187 Non-U.S. government 84,776 1,249 (588 ) 85,437 Corporate 113,561 2,436 (876 ) 115,121 Municipal 5,146 8 (18 ) 5,136 Residential mortgage-backed 31 — — 31 Asset-backed 373 — — 373 $ 208,097 $ 3,693 $ (1,505 ) $ 210,285 As at December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Non-OTTI Fair Value U.S. government and agency $ 12,784 $ 32 $ (106 ) $ 12,710 Non-U.S. government 86,897 1,303 (2,777 ) 85,423 Corporate 159,243 2,040 (2,628 ) 158,655 Municipal 6,585 12 (21 ) 6,576 Residential mortgage-backed 488 39 — 527 Asset-backed 3,867 9 — 3,876 $ 269,864 $ 3,435 $ (5,532 ) $ 267,767 The contractual maturities of our fixed maturity and short-term investments classified as available-for-sale are shown below. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. As at December 31, 2017 Amortized Cost Fair Value % of Total Fair Value One year or less $ 50,135 $ 49,828 23.7 % More than one year through two years 17,549 17,427 8.3 % More than two years through five years 53,690 54,355 25.8 % More than five years through ten years 46,743 47,735 22.7 % More than ten years 39,576 40,536 19.3 % Residential mortgage-backed 31 31 — % Asset-backed 373 373 0.2 % $ 208,097 $ 210,285 100.0 % Gross Unrealized Losses The following tables summarize our fixed maturity and short-term investments classified as available-for-sale in a gross unrealized loss position: 12 Months or Greater Less Than 12 Months Total As at December 31, 2017 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fixed maturity investments, at fair value U.S. government and agency $ 2,344 $ (16 ) $ 1,842 $ (7 ) $ 4,186 $ (23 ) Non-U.S. government 11,101 (373 ) 20,965 (215 ) 32,066 (588 ) Corporate 9,177 (807 ) 24,200 (69 ) 33,377 (876 ) Municipal 369 (5 ) 3,605 (13 ) 3,974 (18 ) Total fixed maturity investments $ 22,991 $ (1,201 ) $ 50,612 $ (304 ) $ 73,603 $ (1,505 ) 12 Months or Greater Less Than 12 Months Total As at December 31, 2016 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fixed maturity and short-term investments, at fair value U.S. government and agency $ — $ — $ 10,743 $ (106 ) $ 10,743 $ (106 ) Non-U.S. government 8,316 (1,794 ) 30,086 (983 ) 38,402 (2,777 ) Corporate 8,003 (1,800 ) 42,304 (828 ) 50,307 (2,628 ) Municipal — — 3,132 (21 ) 3,132 (21 ) Total fixed maturity and short-term investments $ 16,319 $ (3,594 ) $ 86,265 $ (1,938 ) $ 102,584 $ (5,532 ) As at December 31, 2017 and December 31, 2016 , the number of securities classified as available-for-sale in an unrealized loss position was 96 and 156 , respectively. Of these securities, the number of securities that had been in an unrealized loss position for twelve months or longer was 37 and 41 , respectively. Other-Than-Temporary Impairment For the years ended December 31, 2017 , 2016 and 2015 , we did no t recognize any other-than-temporary impairment losses on our available-for-sale securities. We determined that no credit losses existed as at December 31, 2017 and 2016 . A description of our other-than-temporary impairment process is included in Note 2 - "Significant Accounting Policies" . There were no changes to our process in the years ended December 31, 2017 and 2016 . Credit Ratings The following table sets forth the credit ratings of our fixed maturity and short-term investments as of December 31, 2017 : Amortized Cost Fair Value % of Total Investments AAA Rated AA Rated A Rated BBB Rated Non- Investment Grade Not Rated U.S. government and agency $ 561,483 $ 558,223 9.2 % $ 556,859 $ 1,364 $ — $ — $ — $ — Non-U.S. government 665,056 692,569 11.4 % 134,619 409,315 79,030 62,964 6,641 — Corporate 3,413,543 3,478,181 57.2 % 123,059 375,252 1,854,503 932,238 188,237 4,892 Municipal 103,299 105,357 1.7 % 26,313 62,605 12,864 3,575 — — Residential mortgage-backed 285,343 288,744 4.7 % 166,386 7,425 14,204 678 98,997 1,054 Commercial mortgage-backed 427,469 421,548 6.9 % 222,656 38,176 77,811 59,358 9,555 13,992 Asset-backed 535,266 541,947 8.9 % 272,784 43,539 68,489 69,116 88,019 — Total $ 5,991,459 6,086,569 100.0 % 1,502,676 937,676 2,106,901 1,127,929 391,449 19,938 % of total fair value 24.7 % 15.4 % 34.6 % 18.6 % 6.4 % 0.3 % Other Investments, at fair value The following table summarizes our other investments carried at fair value: December 31, December 31, Private equities and private equity funds $ 289,556 $ 300,529 Fixed income funds 229,999 249,023 Fixed income hedge funds 63,773 85,976 Equity funds 249,475 223,571 CLO equities 56,765 61,565 CLO equity funds 12,840 15,440 Private credit funds 10,156 — Other 828 943 $ 913,392 $ 937,047 The valuation of our other investments is described in Note 8 - "Fair Value Measurements" . Due to a lag in the valuations of certain funds reported by the managers, we may record changes in valuation with up to a three -month lag. We regularly review and discuss fund performance with the fund managers to corroborate the reasonableness of the reported net asset values and to assess whether any events have occurred within the lag period that would affect the valuation of the investments. The following is a description of the nature of each of these investment categories: • Private equities and private equity funds invest primarily in the financial services industry. All of our investments in private equities and private equity funds are subject to restrictions on redemptions and sales that are determined by the governing documents and limit our ability to liquidate those investments. These restrictions have been in place since the dates of our initial investments. • Fixed income funds comprise a number of positions in diversified fixed income funds that are managed by third-party managers. Underlying investments vary from high-grade corporate bonds to non-investment grade senior secured loans and bonds, but are generally invested in liquid fixed income markets. These funds have regularly published prices. The funds have liquidity terms that vary from daily up to 45 days' notice. • Fixed income hedge funds invest in a diversified portfolio of debt securities. The hedge funds have imposed lock-up periods of up to three years from the time of initial investment. Once eligible, redemptions will be permitted quarterly with 90 days’ notice. Approximately half of our portfolio of fixed income hedge funds are eligible for redemption. • Equity funds invest in a diversified portfolio of U.S. and international publicly-traded equity securities. The funds have liquidity terms that vary from daily up to 6 days' notice. • CLO equities comprise investments in the equity tranches of term-financed securitizations of diversified pools of corporate bank loans. CLO equities denote direct investments by us in these securities. • CLO equity funds comprise two funds that invest primarily in the equity tranches of term-financed securitizations of diversified pools of corporate bank loans. One of the funds has a fair value of $1.1 million , part of a self-liquidating structure which is expected to pay out over one to five years. The other fund has a fair value of $11.7 million and is eligible for redemption in 2018. • Private credit funds invest in direct senior or collateralized loans. The investments are subject to restrictions on redemption and sales that are determined by the governing documents and limit our ability to liquidate our positions in the funds. • Other primarily comprises a fund that provides loans to educational institutions throughout the United States and its territories. Investments of $0.5 million in fixed income hedge funds were subject to gates or side-pockets, where redemptions are subject to the sale of underlying investments. A gate is the ability to deny or delay a redemption request, whereas a side-pocket is a designated account for which the investor loses its redemption rights. As at December 31, 2017 , we had unfunded commitments to private equity funds of $164.7 million . Other Investments, at cost Our other investments carried at cost of $125.6 million as of December 31, 2017 consist of life settlement contracts. During the years ended December 31, 2017 and 2016 , net investment income included $13.8 million and $18.0 million , respectively, related to investments in life settlements. During the years ended December 31, 2017 and 2016 , there were impairment charges of $7.2 million and $5.3 million , respectively, recognized in net realized and unrealized gains/losses. The following table presents further information regarding our investments in life settlements as of December 31, 2017 and 2016 . December 31, 2017 December 31, 2016 Number of Contracts Carrying Face Value (Death Benefits) Number of Contracts Carrying Face Value (Death Benefits) Remaining Life Expectancy of Insureds: 0 – 1 year — $ — $ — 2 $ 461 $ 700 1 – 2 years 11 17,655 29,471 7 11,396 18,337 2 – 3 years 10 7,524 19,906 11 15,338 29,715 3 – 4 years 20 16,119 32,411 17 17,013 32,189 4 – 5 years 13 13,960 32,730 16 10,377 23,302 Thereafter 162 70,363 390,843 181 77,066 431,034 Total 216 $ 125,621 $ 505,361 234 $ 131,651 $ 535,277 Remaining life expectancy for year 0-1 in the table above references policies whose current life expectancy is less than 12 months as of the reporting date. Remaining life expectancy is not an indication of expected maturity. Actual maturity in any category above may vary significantly (either earlier or later) from the remaining life expectancies reported. At December 31, 2017 , our best estimate of the life insurance premiums required to keep the policies in force, payable in the 12 months ending December 31, 2018 and the four succeeding years ending December 31, 2022 is $17.8 million , $17.7 million , $16.6 million , $15.7 million , and $15.2 million , respectively. Net Investment Income Major categories of net investment income for the years ended December 31, 2017 , 2016 and 2015 are summarized as follows: 2017 2016 2015 Fixed maturity investments $ 144,367 $ 114,885 $ 87,512 Short-term investments and cash and cash equivalents 9,314 4,491 5,993 Funds held 601 22,583 234 Funds held – directly managed 32,479 5,769 — Investment income from fixed maturities and cash and cash equivalents 186,761 147,728 93,739 Equity securities 4,355 4,874 5,580 Other investments 14,337 22,515 11,712 Life settlements and other 14,370 18,191 20,871 Investment income from equities and other investments 33,062 45,580 38,163 Gross investment income 219,823 193,308 131,902 Investment expenses (11,034 ) (7,845 ) (9,338 ) Net investment income $ 208,789 $ 185,463 $ 122,564 Net Realized and Unrealized Gains (Losses) Components of net realized and unrealized gains (losses) for the years ended December 31, 2017 , 2016 and 2015 were as follows: 2017 2016 2015 Net realized gains (losses) on sale: Gross realized gains on fixed maturity securities, available-for-sale $ 616 $ 405 $ 396 Gross realized (losses) on fixed maturity securities, available-for-sale securities (125 ) (21 ) (130 ) Net realized investment gains (losses) on fixed maturity securities, trading 4,695 1,848 (4,291 ) Net realized investment gains on equity securities, trading 701 5,348 19,884 Net realized investment losses on funds held - directly managed (4,219 ) (14,616 ) — Total net realized gains (losses) on sale 1,668 (7,036 ) 15,859 Net unrealized gains (losses): Fixed maturity securities, trading 35,878 36,314 (52,918 ) Equity securities, trading 16,498 6,561 (21,875 ) Other investments 102,388 70,296 17,411 Change in fair value of embedded derivative on funds held – directly managed 32,928 (28,317 ) — Change in value of fair value option on funds held - directly managed 974 — — Total net unrealized gains (losses) 188,666 84,854 (57,382 ) Net realized and unrealized gains (losses) $ 190,334 $ 77,818 $ (41,523 ) The gross realized gains and losses on available-for-sale securities included in the table above resulted from sales of $40.8 million , $41.3 million and $95.1 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Restricted Assets We are required to maintain investments and cash and cash equivalents on deposit to support our insurance and reinsurance operations. The investments and cash and cash equivalents on deposit are available to settle insurance and reinsurance liabilities. We also utilize trust accounts to collateralize business with our insurance and reinsurance counterparties. These trust accounts generally take the place of letter of credit requirements. The assets in trusts as collateral are primarily highly rated fixed maturity securities. The carrying value of our restricted assets, including restricted cash of $257.7 million and $363.8 million , as of December 31, 2017 and 2016 , respectively, was as follows: December 31, December 31, Collateral in trust for third party agreements $ 3,118,892 $ 1,975,022 Assets on deposit with regulatory authorities 599,829 882,400 Collateral for secured letter of credit facilities 151,467 177,263 Funds at Lloyd's (1) 234,833 220,328 $ 4,105,021 $ 3,255,013 (1) Our underwriting businesses include three Lloyd's syndicates. Lloyd's determines the required capital principally through the annual business plan of each syndicate. This capital is referred to as "Funds at Lloyd's" and will be drawn upon in the event that a syndicate has a loss that cannot be funded from other sources. As at December 31, 2017 , our combined Funds at Lloyd's were comprised of cash and investments of $234.8 million and unsecured letters of credit of $165.0 million . At December 31, 2017 , we had an unsecured letter of credit agreement for Funds at Lloyd’s purposes ("FAL Facility") to issue up to $165.0 million of letters of credit, with a provision to increase the facility up to $200.0 million . On February 8, 2018, we amended and restated the FAL Facility to issue up to $325.0 million of letters of credit, with a provision to increase the facility up to $400.0 million . The FAL Facility is available to satisfy our Funds at Lloyd’s requirements and expires in 2022. The increase in the collateral in trust for third-party agreements was primarily due to the loss portfolio transfer reinsurance transactions with RSA and QBE described in Note 4 - "Significant New Business" .

Funds Held - Directly Managed

Funds Held - Directly Managed	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
FUNDS HELD - DIRECTLY MANAGED	7. FUNDS HELD - DIRECTLY MANAGED Funds held - directly managed consists of the following: • The funds held balance in relation to the Allianz transaction, described in Note 4 - "Significant New Business" , moved from a fixed crediting rate to a variable rate of return on the underlying investments on October 1, 2016. This variable return reflects the economics of the investment portfolio underlying the funds held asset and qualifies as an embedded derivative. We have recorded the aggregate of the funds held, typically held at cost, and the embedded derivative as a single amount in our consolidated balance sheet. As at December 31, 2017 and 2016 , the funds held at cost had a carrying value of $994.8 million and $1,023.0 million , respectively, and the embedded derivative had a fair value of $4.7 million and ($28.3) million , respectively, the aggregate of which was $999.5 million and $994.7 million , respectively, as included in the table below. • The funds held balance in relation to the QBE reinsurance transaction described in Note 4 - "Significant New Business" , for which we elected the fair value option. The following table presents the fair values of assets and liabilities underlying the funds held - directly managed account as at December 31, 2017 and 2016 : December 31, December 31, Fixed maturity investments: U.S. government and agency $ 69,850 $ 47,885 Non-U.S. government 2,926 5,961 Corporate 695,490 663,556 Municipal 58,930 38,927 Residential mortgage-backed 29,439 — Commercial mortgage-backed 211,186 151,395 Asset-backed 97,565 79,806 Total fixed maturity investments $ 1,165,386 $ 987,530 Other assets 14,554 7,135 $ 1,179,940 $ 994,665 The contractual maturities of our fixed maturity investments underlying the funds held - directly managed account are shown below. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. As at December 31, 2017 Amortized Cost Fair Value % of Total Fair Value One year or less $ 49,093 $ 49,007 4.2 % More than one year through two years 54,447 54,204 4.7 % More than two years through five years 230,872 230,256 19.8 % More than five years through ten years 248,525 248,675 21.3 % More than ten years 234,556 245,054 21.0 % Residential mortgage-backed 29,544 29,439 2.5 % Commercial mortgage-backed 215,603 211,186 18.1 % Asset-backed 97,160 97,565 8.4 % $ 1,159,800 $ 1,165,386 100.0 % Credit Ratings The following table sets forth the credit ratings of our fixed maturity investments underlying the funds held - directly managed account as of December 31, 2017 : Amortized Cost Fair Value % of Total Investments AAA Rated AA Rated A Rated BBB Rated U.S. government and agency $ 69,754 $ 69,850 6.0 % $ 69,850 $ — $ — $ — Non-U.S. government 2,977 2,926 0.3 % — — 2,926 — Corporate 688,239 695,490 59.6 % 7,754 25,418 315,385 346,933 Municipal 56,523 58,930 5.1 % — 20,921 30,449 7,560 Residential mortgage-backed 29,544 29,439 2.5 % 29,439 — — — Commercial mortgage-backed 215,603 211,186 18.1 % 202,608 6,576 2,002 — Asset-backed 97,160 97,565 8.4 % 93,849 3,716 — — Total $ 1,159,800 $ 1,165,386 100.0 % $ 403,500 $ 56,631 $ 350,762 $ 354,493 % of total fair value 34.6 % 4.9 % 30.1 % 30.4 % Net Investment Income Major categories of net investment income underlying the funds held - directly managed account for the year ended December 31, 2017 and 2016 are summarized as follows: 2017 2016 Fixed maturity investments $ 33,558 $ 5,705 Short-term investments and cash and cash equivalents 292 64 Gross investment income 33,850 5,769 Investment expenses (1,371 ) — Investment income on funds held - directly managed $ 32,479 $ 5,769 Net Realized Gains (Losses) and Change in Fair Value due to Embedded Derivative and Fair Value Option Net realized gains (losses) and change in fair value for the year ended December 31, 2017 and 2016 are summarized as follows: 2017 2016 Net realized losses on fixed maturity securities $ (4,219 ) $ (14,616 ) Change in fair value of embedded derivative 32,928 (28,317 ) Change in value of fair value option on funds held- directly managed 974 — Net realized gains (losses) and change in fair value of funds held- directly managed $ 29,683 $ (42,933 )

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	8. FAIR VALUE MEASUREMENTS Fair Value Hierarchy Fair value is defined as the price at which to sell an asset or transfer a liability (i.e. the "exit price") in an orderly transaction between market participants. We use a fair value hierarchy that gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data. The hierarchy is broken down into three levels as follows: • Level 1 - Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that we have the ability to access. Valuation adjustments and block discounts are not applied to Level 1 instruments. • Level 2 - Valuations based on quoted prices in active markets for similar assets or liabilities, quoted prices for identical assets or liabilities in inactive markets, or for which significant inputs are observable (e.g. interest rates, yield curves, prepayment speeds, default rates, loss severities, etc.) or can be corroborated by observable market data. • Level 3 - Valuations based on unobservable inputs where there is little or no market activity. Unadjusted third party pricin g sources or management's assumptions and internal valuation models may be used to determine the fair values. In addition, certain of our other investments are measured at fair value using net asset value ("NAV") per share (or its equivalent) as a practical expedient and have not been classified within the fair value hierarchy above. We have categorized our investments that are recorded at fair value on a recurring basis among levels based on the observability of inputs, or at fair value using NAV per share (or its equivalent) as follows: December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value Based on NAV as Practical Expedient Total Fair Value Investments: Fixed maturity investments: U.S. government and agency $ — $ 558,223 $ — $ — $ 558,223 Non-U.S. government — 692,569 — — 692,569 Corporate — 3,411,003 67,178 — 3,478,181 Municipal — 105,357 — — 105,357 Residential mortgage-backed — 285,664 3,080 — 288,744 Commercial mortgage-backed — 400,054 21,494 — 421,548 Asset-backed — 514,055 27,892 — 541,947 $ — $ 5,966,925 $ 119,644 $ — $ 6,086,569 Equities: Equities — U.S. $ 103,652 $ 2,711 $ — $ — $ 106,363 Equities — International — 240 — — 240 $ 103,652 $ 2,951 $ — $ — $ 106,603 Other investments: Private equities and private equity funds $ — $ — $ — $ 289,556 $ 289,556 Fixed income funds — 202,570 — 27,429 229,999 Fixed income hedge funds — — — 63,773 63,773 Equity funds — 121,046 — 128,429 249,475 CLO equities — — 56,765 — 56,765 CLO equity funds — — — 12,840 12,840 Private credit funds — — — 10,156 10,156 Other — — 314 514 828 $ — $ 323,616 $ 57,079 $ 532,697 $ 913,392 Total Investments $ 103,652 $ 6,293,492 $ 176,723 $ 532,697 $ 7,106,564 Funds Held - Directly Managed: U.S. government and agency $ — $ 69,850 $ — $ — $ 69,850 Non-U.S. government — 2,926 — — 2,926 Corporate — 695,490 — — 695,490 Municipal — 58,930 — — 58,930 Residential mortgage-backed — 29,439 — — 29,439 Commercial mortgage-backed — 211,186 — — 211,186 Asset-backed — 97,565 — — 97,565 Other assets — 14,554 — — 14,554 $ — $ 1,179,940 $ — $ — $ 1,179,940 Reinsurance balances recoverable: $ — $ — $ 542,224 $ — $ 542,224 Other Assets: Derivative Instruments $ — $ 319 $ — $ — $ 319 $ — $ 319 $ — $ — $ 319 Losses and LAE: $ — $ — $ 1,794,669 $ — $ 1,794,669 Other Liabilities: Derivative Instruments $ — $ 7,246 $ — $ — $ 7,246 $ — $ 7,246 $ — $ — $ 7,246 December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value Based on NAV as Practical Expedient Total Fair Value Investments: Fixed maturity investments: U.S. government and agency $ — $ 852,984 $ — $ — $ 852,984 Non-U.S. government — 352,786 — — 352,786 Corporate — 2,471,444 74,534 — 2,545,978 Municipal — 53,757 — — 53,757 Residential mortgage-backed — 374,055 — — 374,055 Commercial mortgage-backed — 204,999 12,213 — 217,212 Asset-backed — 467,463 14,692 — 482,155 $ — $ 4,777,488 $ 101,439 $ — $ 4,878,927 Equities: Equities — U.S. $ 91,287 $ 3,760 $ — $ — $ 95,047 $ 91,287 $ 3,760 $ — $ — $ 95,047 Other investments: Private equities and private equity funds $ — $ — $ 15,000 $ 285,529 $ 300,529 Fixed income funds — 223,636 — 25,387 249,023 Fixed income hedge funds — — — 85,976 85,976 Equity funds — 133,802 — 89,769 223,571 CLO equities — — 61,565 — 61,565 CLO equity funds — — — 15,440 15,440 Other — — 313 630 943 $ — $ 357,438 $ 76,878 $ 502,731 $ 937,047 Total Investments $ 91,287 $ 5,138,686 $ 178,317 $ 502,731 $ 5,911,021 Funds Held - Directly Managed: U.S. government and agency $ — $ 47,885 $ — $ — $ 47,885 Non-U.S. government — 5,961 — — 5,961 Corporate — 663,556 — — 663,556 Municipal — 38,927 — — 38,927 Commercial mortgage-backed — 151,395 — — 151,395 Asset-backed — 79,806 — — 79,806 Other assets — 7,135 — — 7,135 $ — $ 994,665 $ — $ — $ 994,665 Other Assets: Derivative Instruments $ — $ 2,930 $ — $ — $ 2,930 $ — $ 2,930 $ — $ — $ 2,930 Other Liabilities: Derivative Instruments $ — $ 74 $ — $ — $ 74 $ — $ 74 $ — $ — $ 74 Valuation Methodologies of Financial Instruments Measured at Fair Value Fixed Maturity Investments The fair values for all securities in the fixed maturity investments and funds held - directly managed portfolios are independently provided by the investment accounting service providers, investment managers and investment custodians, each of which utilize internationally recognized independent pricing services. We record the unadjusted price provided by the investment accounting service providers, investment managers or investment custodians and validate this price through a process that includes, but is not limited to: (i) comparison of prices against alternative pricing sources; (ii) quantitative analysis (e.g. comparing the quarterly return for each managed portfolio to its target benchmark); (iii) evaluation of methodologies used by external parties to estimate fair value, including a review of the inputs used for pricing; and (iv) comparing the price to our knowledge of the current investment market. Our internal price validation procedures and review of fair value methodology documentation provided by independent pricing services have not historically resulted in adjustment in the prices obtained from the pricing service. The independent pricing services used by the investment accounting service providers, investment managers and investment custodians obtain actual transaction prices for securities that have quoted prices in active markets. Where we utilize single unadjusted broker-dealer quotes, they are generally provided by market makers or broker-dealers who are recognized as market participants in the markets in which they are providing the quotes. For determining the fair value of securities that are not actively traded, in general, pricing services use "matrix pricing" in which the independent pricing service uses observable market inputs including, but not limited to, reported trades, benchmark yields, broker-dealer quotes, interest rates, prepayment speeds, default rates and other such inputs as are available from market sources to determine a reasonable fair value. In addition, pricing services use valuation models, using observable data, such as an Option Adjusted Spread model, to develop prepayment and interest rate scenarios. The Option Adjusted Spread model is commonly used to estimate fair value for securities such as mortgage-backed and asset-backed securities. The following describes the techniques generally used to determine the fair value of our fixed maturity investments by asset class, including the investments underlying the funds held - directly managed. • U.S. government and agency securities consist of securities issued by the U.S. Treasury and mortgage pass-through agencies such as the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation and other agencies. Non-U.S. government securities consist of bonds issued by non-U.S. governments and agencies along with supranational organizations. The significant inputs used to determine the fair value of these securities include the spread above the risk-free yield curve, reported trades and broker-dealer quotes. These are considered to be observable market inputs and, therefore, the fair values of these securities are classified as Level 2. • Corporate securities consist primarily of investment-grade debt of a wide variety of corporate issuers and industries. The fair values of these securities are determined using the spread above the risk-free yield curve, reported trades, broker-dealer quotes, benchmark yields, and industry and market indicators. These are considered observable market inputs and, therefore, the fair values of these securities are classified as Level 2. Where pricing is unavailable from pricing services, such as in periods of low trading activity or when transactions are not orderly, we obtain non-binding quotes from broker-dealers. Where significant inputs are unable to be corroborated with market observable information, we classify the securities as Level 3. • Municipal securities consist primarily of bonds issued by U.S.-domiciled state and municipal entities. The fair values of these securities are determined using the spread above the risk-free yield curve, reported trades, broker-dealer quotes and benchmark yields. These are considered observable market inputs and, therefore, the fair values of these securities are classified as Level 2. • Asset-backed securities consist primarily of investment-grade bonds backed by pools of loans with a variety of underlying collateral. Residential and commercial mortgage-backed securities include both agency and non-agency originated securities. Where pricing is unavailable from pricing services, we obtain non-binding quotes from broker-dealers. This is generally the case when there is a low volume of trading activity and current transactions are not orderly. The significant inputs used to determine the fair value of these securities include the spread above the risk-free yield curve, reported trades, benchmark yields, prepayment speeds and default rates. The fair values of these securities are classified as Level 2 if the significant inputs are market observable. Where significant inputs are unable to be corroborated with market observable information, we classify the securities as Level 3. Equities Our investments in equities are predominantly traded on the major exchanges and are primarily managed by our external advisors. We use an internationally recognized pricing service to estimate the fair value of our equities. Our equities are widely diversified and there is no significant concentration in any specific industry. We have categorized all of our investments in equities other than preferred stock as Level 1 investments because the fair values of these investments are based on unadjusted quoted prices in active markets for identical assets. The fair value estimates of our investments in preferred stock are based on observable market data and, as a result, have been categorized as Level 2. Other investments, at fair value We have ongoing due diligence processes with respect to the other investments carried at fair value in which we invest and their managers. These processes are designed to assist us in assessing the quality of information provided by, or on behalf of, each fund and in determining whether such information continues to be reliable or whether further review is warranted. Certain funds do not provide full transparency of their underlying holdings; however, we obtain the audited financial statements for funds annually, and regularly review and discuss the fund performance with the fund managers to corroborate the reasonableness of the reported net asset values ("NAV"). The use of NAV as an estimate of the fair value for investments in certain entities that calculate NAV is a permitted practical expedient. Due to the time lag in the NAV reported by certain fund managers we adjust the valuation for capital calls and distributions. Other investments measured at fair value using NAV as a practical expedient have not been classified in the fair value hierarchy. Other investments for which we do not use NAV as a practical expedient have been valued using prices from independent pricing services, investment managers and broker-dealers. The following describes the techniques generally used to determine the fair value of our other investments. • For our investments in private equities and private equity funds, we measure fair value by obtaining the most recently available NAV from the external fund manager or third-party administrator. The fair values of these investments are measured using the NAV as a practical expedient and therefore have not been categorized within the fair value hierarchy. • Our investments in fixed income funds and equity funds are valued based on a combination of prices from independent pricing services, external fund managers or third-party administrators. For the publicly available prices we have classified the investments as Level 2. For the non-publicly available prices we are using NAV as a practical expedient and therefore these have not been categorized within the fair value hierarchy. • For our investments in fixed income hedge funds, we measure fair value by obtaining the most recently available NAV as advised by the external fund manager or third-party administrator. The fair values of these investments are measured using the NAV as a practical expedient and therefore have not been categorized within the fair value hierarchy. • We measure the fair value of our direct investment in CLO equities based on valuations provided by our external CLO equity manager. If the investment does not involve an external CLO equity manager, the fair value of the investment is based on valuations provided by the broker or lead underwriter of the investment (the "broker"). Our CLO equity investments have been classified as Level 3 due to the use of unobservable inputs in the valuation and the limited number of relevant trades in secondary markets. In providing valuations, the CLO equity manager and brokers use observable and unobservable inputs. Of the significant unobservable market inputs used, the default and loss severity rates involve the most judgment and create the most sensitivity. A significant increase or decrease in either of these significant inputs in isolation would result in lower or higher fair value estimates for direct investments in CLO equities and, in general, a change in default rate assumptions will be accompanied by a directionally similar change in loss severity rate assumptions. Collateral spreads and estimated maturity dates are less subjective inputs because they are based on the historical average of actual spreads and the weighted-average life of the current underlying portfolios, respectively. A significant increase or decrease in either of these significant inputs in isolation would result in higher or lower fair value estimates for direct investments in CLO equities. In general, these inputs have no significant interrelationship with each other or with default and loss severity rates. On a quarterly basis, we receive the valuation from the external CLO manager and brokers and then review the underlying cash flows and key assumptions used by them. We review and update the significant unobservable inputs based on information obtained from secondary markets. These inputs are our responsibility and we assess the reasonableness of the inputs (and if necessary, update the inputs) through communicating with industry participants, monitoring of the transactions in which we participate (for example, to evaluate default and loss severity rate trends), and reviewing market conditions, historical results, and emerging trends that may impact future cash flows. If valuations from the external CLO equity manager or brokers are not available, we use an income approach based on certain observable and unobservable inputs to value these investments. An income approach is also used to corroborate the reasonableness of the valuations provided by the external manager and brokers. Where an income approach is followed, the valuation is based on available trade information, such as expected cash flows and market assumptions on default and loss severity rates. Other inputs used in the valuation process include asset spreads, loan prepayment speeds, collateral spreads and estimated maturity dates. • For our investments in CLO equity funds, we measure fair value by obtaining the most recently available NAV as advised by the external fund manager or third party administrator. The fair values of these investments were measured using the NAV as a practical expedient and therefore have not been categorized within the fair value hierarchy. • For our investments in private credit funds, we measure fair value by obtaining the most recently available NAV from the external fund manager or third-party administrator. The fair values of these investments are measured using the NAV as a practical expedient and therefore have not been categorized within the fair value hierarchy. Insurance Contracts - Fair Value Option The Company uses an internal model to calculate the fair value of the liability for losses and loss adjustment expenses and reinsurance balances recoverable assets for certain retroactive reinsurance contracts where we have elected the fair value option in our Non-life Run-off segment. The fair value was calculated as the aggregate of discounted cash flows plus a risk margin. The discounted cash flow approach uses (i) estimated nominal cash flows based upon an appropriate payment pattern developed in accordance with standard actuarial techniques and (ii) a discount rate based upon a high quality rated corporate bond plus a credit spread for non-performance risk. The model uses corporate bond rates across the yield curve depending on the estimated timing of the future cash flows and specific to the currency of the risk. The risk margin was calculated using the present value of the cost of capital. The cost of capital approach uses (i) projected capital requirements, (ii) multiplied by the risk cost of capital representing the return required for non-hedgeable risk based upon the weighted average cost of capital less investment income and (iii) discounted using the weighted average cost of capital. Derivative Instruments The fair values of our foreign currency exchange contracts, as described in Note 9 - "Derivative Instruments" are classified as Level 2. The fair values are based upon prices in active markets for identical contracts. Level 3 Measurements and Changes in Leveling Transfers into or out of levels are recorded at their fair values as of the end of the reporting period, consistent with the date of determination of fair value. Investments The following table presents a reconciliation of the beginning and ending balances for all investments measured at fair value on a recurring basis using Level 3 inputs during the years ended December 31, 2017 and 2016 : 2017 Corporate Residential mortgage-backed Commercial mortgage-backed Asset-backed Other Investments Total Beginning fair value $ 74,534 $ — $ 12,213 $ 14,692 $ 76,878 — $ 178,317 Purchases 28,872 711 21,306 9,749 435 — 61,073 Sales (37,941 ) (37 ) (424 ) (20,795 ) (12,350 ) — (71,547 ) Total realized and unrealized gains (losses) 249 (16 ) (434 ) 205 (7,884 ) — (7,880 ) Transfer into Level 3 from Level 2 24,431 3,085 18,974 56,074 — — 102,564 Transfer out of Level 3 into Level 2 (22,967 ) (663 ) (30,141 ) (32,033 ) — — (85,804 ) Ending fair value $ 67,178 $ 3,080 $ 21,494 $ 27,892 $ 57,079 — $ 176,723 2016 Corporate Residential mortgage-backed Commercial mortgage-backed Asset-backed Other Investments Total Beginning fair value $ — $ — $ 26,704 $ 120,440 $ 77,016 $ 224,160 Purchases 24,586 — 14,216 19,750 6,885 65,437 Sales (11,011 ) (2,178 ) (14,071 ) (25,581 ) (12,933 ) (65,774 ) Total realized and unrealized gains (losses) (841 ) (24 ) (460 ) (1,897 ) 5,910 2,688 Transfer into Level 3 from Level 2 64,134 2,781 23,628 31,778 — 122,321 Transfer out of Level 3 into Level 2 (2,334 ) (579 ) (37,804 ) (129,798 ) — (170,515 ) Ending fair value $ 74,534 $ — $ 12,213 $ 14,692 $ 76,878 $ 178,317 Net realized and unrealized gains related to Level 3 assets in the table above are included in net realized and unrealized (losses) gains in our consolidated statements of earnings. The securities transferred from Level 2 to Level 3 were transferred due to insufficient market observable inputs for the valuation of the specific assets. The transfers from Level 3 to Level 2 were based upon us obtaining market observable information regarding the valuations of the specific assets. Insurance Contracts - Fair Value Option The following table presents a reconciliation of the beginning and ending balances for all insurance contracts measured at fair value on a recurring basis using Level 3 inputs during the year ended December 31, 2017 : Year Ended December 31, 2017 Liability for losses and LAE Reinsurance balances recoverable Beginning fair value $ — $ — Assumed business 1,966,843 565,824 Changes in nominal amounts: Net incurred losses and LAE (122,797 ) (1,848 ) Paid losses (197,102 ) (56,256 ) Changes in fair value: Discounted cash flows 78,046 29,785 Risk margin (24,039 ) (6,034 ) Effect of exchange rate movements 93,718 10,753 Ending fair value $ 1,794,669 $ 542,224 Changes in fair value related to Level 3 assets and liabilities in the table above are included in net incurred losses and LAE in our consolidated statements of earnings. Below is a summary of the quantitative information regarding the significant observable and unobservable inputs used in the internal model to determine fair value on a recurring basis as at December 31, 2017 : December 31, 2017 Valuation Technique Unobservable (U) and Observable (O) Inputs Weighted Average Internal model Corporate bond yield (O) A rated Internal model Credit spread for non-performance risk (U) 0.2% Internal model Risk cost of capital 5.0% Internal model Weighted average cost of capital (U) 8.5% Internal model Duration - liability (U) 11.41 years Internal model Duration - reinsurance balances recoverable (U) 11.66 years The fair value of the liability for losses and LAE and reinsurance balances recoverable may increase or decrease due to changes in the corporate bond rate, the credit spread for non-performance risk, the risk cost of capital, the weighted average cost of capital and the estimated payment pattern as described below: • An increase in the corporate bond rate or credit spread for non-performance risk would result in a decrease in the fair value of the liability for losses and LAE and reinsurance balances recoverable. Conversely, a decrease in the corporate bond rate or credit spread for non-performance risk would result in an increase in the fair value of the liability for losses and LAE and reinsurance balances recoverable. • An increase in the weighted average cost of capital would result in an increase in the fair value of the liability for losses and LAE and reinsurance balances recoverable. Conversely, a decrease in the weighted average cost of capital would result in a decrease in the fair value of the liability for losses and LAE and reinsurance balances recoverable. • An increase in the risk cost of capital would result in an increase in the fair value of the liability for losses and LAE and reinsurance balances recoverable. Conversely, a decrease in the risk cost of capital would result in a decrease in the fair value of the liability for losses and LAE and reinsurance balances recoverable. • An acceleration of the estimated payment pattern would result in an increase in the fair value of the liability for losses and LAE and reinsurance balances recoverable. Conversely, a deceleration of the estimated payment pattern would result in a decrease in the fair value of the liability for losses and LAE and reinsurance balances recoverable. In addition, the estimate of the capital required to support the liabilities is based upon current industry standards for capital adequacy. If the required capital per unit of risk increases, then the fair value of the liability for losses and LAE and reinsurance balances recoverable would increase. Conversely, a decrease in required capital would result in a decrease in the fair value of the liability for losses and LAE and reinsurance balances recoverable. Disclosure of Fair Values for Financial Instruments Carried at Cost As of December 31, 2017 and 2016 , investments in life settlement contracts were carried at cost of $125.6 million and $131.7 million , respectively, and their fair values were $131.9 million and $129.5 million , respectively. The fair value of investments in life settlement contracts is determined using a discounted cash flow methodology that utilizes unobservable inputs. Due to the individual nature of each investment in life settlement contracts and the illiquidity of the existing market, significant inputs to the fair value include our estimates of premiums necessary to keep the policies in-force, and our assumptions for mortality and discount rates. Our mortality assumptions are based on a combination of medical underwriting information obtained from a third-party underwriter for each referenced life and internal proprietary mortality studies of older aged U.S. insured lives. These assumptions are used to develop an estimate of future net cash flows that, after discounting, are intended to be reflective of the asset's value in the life settlement market. As of December 31, 2017 , our 4.5% Senior Notes due 2022 had a carrying value of $347.5 million while the fair value based on observable market pricing from a third party service was $357.4 million . The fair value is classified as Level 2. Disclosure of fair value of amounts relating to insurance contracts is not required, except those for which we elected the fair value option, as described above. Our remaining assets and liabilities were generally carried at cost or amortized cost, which due to their short-term nature approximates fair value as of December 31, 2017 and 2016 .

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	9. DERIVATIVE INSTRUMENTS Foreign Currency Hedging of Net Investments We use foreign currency forward exchange rate contracts in qualifying hedging relationships to hedge the foreign currency exchange rate risk associated with certain of our net investments in foreign operations. At December 31, 2017 and 2016 , we had forward currency contracts in place which we had designated as hedges of our net investments in foreign operations. The following table presents the gross notional amounts and the estimated fair values recorded within other assets and liabilities related to our qualifying foreign currency forward exchange rate contracts as at December 31, 2017 and 2016 : December 31, 2017 December 31, 2016 Fair Value Fair Value Gross Notional Amount Assets Liabilities Gross Notional Amount Assets Liabilities Foreign exchange forward - AUD $ 32,810 $ — $ 965 $ 45,467 $ 2,753 $ 74 Foreign exchange forward - CAD 27,141 11 512 37,175 177 — Total qualifying hedges $ 59,951 $ 11 $ 1,477 $ 82,642 $ 2,930 $ 74 The following table presents the amounts of the net gains and losses deferred in the currency translation adjustment ("CTA") account, which is a component of AOCI, in shareholders' equity, related to our qualifying foreign currency forward exchange rate contracts for the years ended December 31, 2017 and 2016 : Amount of Gains (Losses) Deferred in AOCI 2017 2016 Foreign exchange forward - AUD $ (1,247 ) $ 2,568 Foreign exchange forward - CAD — 1,186 Total qualifying hedges $ (1,247 ) $ 3,754 Following the completion of the sale of Pavonia which closed on December 29, 2017, we reclassified into earnings, the cumulative losses of $1.1 million related to the CAD foreign currency forward contract that we had set up to hedge our CAD dominated net investment in Pavonia, and which had previously been deferred in the CTA. We also borrowed €75.0 million (approximately $88.5 million ) during 2016 that was designated as a non-derivative hedge of our net investment in certain subsidiaries whose functional currency is denominated in Euros, as described in Note 15 - "Debt Obligations" . We repaid €25.0 million (approximately $29.5 million ) of this outstanding loan balance during the year ended December 31, 2017 and reclassified the related foreign exchange losses of $1.1 million previously deferred in AOCI, into earnings. Derivatives Not Designated or Not Qualifying as Hedging Instruments From time to time, we may also utilize foreign currency forward contracts as part of our overall foreign currency risk management strategy or to obtain exposure to a particular financial market, as well as for yield enhancement in non-qualifying hedging relationships. We may also utilize equity call option instruments either to obtain exposure to a particular equity instrument or for yield enhancement in non-qualifying hedging relationships. Foreign Currency Forward Contracts The following table presents the gross notional amounts, estimated fair values recorded within other assets and liabilities and the amounts included in net earnings related to our non-qualifying foreign currency forward exchange rate hedging relationships as at December 31, 2017 . December 31, 2017 Fair Value 2017 Gross Notional Amount Assets Liabilities Losses on non-qualifying Foreign exchange forward - AUD $ 57,028 $ — $ 1,002 $ (1,002 ) Foreign exchange forward - GBP 207,323 262 4,312 (6,367 ) Foreign exchange forward - EUR 19,235 46 455 (971 ) Total non-qualifying hedges $ 283,586 $ 308 $ 5,769 $ (8,340 ) There were no such non-qualifying foreign currency forward contracts utilized as at December 31, 2016 or during the years ended December 31, 2016 and 2015 . Investments in Call Options on Equities During the year ended December 31, 2016 we purchased call options on equities at a cost of $5.5 million and sold these for a realized gain of $5.4 million . We did not have any equity derivative instruments as at or during the year ended December 31, 2017 .

Reinsurance Balances Recoverabl

Reinsurance Balances Recoverable	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
Reinsurance Balances Recoverable	$1 million 322,722 16,631 144,336 — 483,689 24.0 % 301,856 4,827 152,341 — 459,024 31.4 % Other reinsurers < $1 million 16,959 1,027 2,603 16 20,605 1.0 % 9,183 856 4,119 959 15,117 1.0 % Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 100.0 % $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743 100.0 % Six of the top ten external reinsurers, as at December 31, 2017 and 2016 , were all rated A- or better. The remaining four non-rated reinsurers, from which $687.6 million was recoverable as at December 31, 2017 ( December 31, 2016 : $512.2 million recoverable from four non-rated reinsurers), including KayleRe Ltd., have provided security in the form of pledged assets in trust, letters of credit issued to us, or funds withheld in the full amount of the recoverable. As at December 31, 2017 , reinsurance balances recoverable of $357.4 million related to KaylaRe Ltd. ( December 31, 2016 : $242.1 million ) and $320.0 million related to Hannover Ruck SE ( December 31, 2016 : $67.3 million ), both of which represent 10% or more of total reinsurance balances recoverable. KaylaRe Ltd. is not rated but is an affiliated company partly owned by Enstar, as described in Note 21 - "Related Party Transactions" , and security is provided in the form of funds withheld. Hannover Ruck SE is rated AA- by Standard & Poor's and A+ by A.M. Best. Provisions for Uncollectible Reinsurance Recoverables We evaluate and monitor concentration of credit risk among our reinsurers. Provisions are made for amounts considered potentially uncollectible. The following table shows our reinsurance balances recoverable by rating of reinsurer and our provisions for uncollectible reinsurance balances recoverable ("provisions for bad debt") as at December 31, 2017 and 2016 . The provisions for bad debt all relate to the Non-life Run-off segment. 2017 2016 Gross Provisions for Bad Debt Net Provisions as a Gross Provisions for Bad Debt Net Provisions as a Reinsurers rated A- or above $ 1,252,887 $ 51,115 $ 1,201,772 4.1 % $ 892,776 $ 35,184 $ 857,592 3.9 % Reinsurers rated below A-, secured 771,097 — 771,097 — % 544,894 — 544,894 — % Reinsurers rated below A-, unsecured 162,259 114,098 48,161 70.3 % 197,589 139,332 58,257 70.5 % Total $ 2,186,243 $ 165,213 $ 2,021,030 7.6 % $ 1,635,259 $ 174,516 $ 1,460,743 10.7 % 13. PREMIUMS WRITTEN AND EARNED The following tables provide a summary of net premiums written and earned for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Premiums Written Premiums Earned Premiums Written Premiums Earned Premiums Written Premiums Earned Non-life Run-off Gross $ 14,102 $ 23,950 $ 17,316 $ 25,989 $ 38,704 $ 116,494 Ceded (7,620 ) (9,788 ) (8,114 ) (9,234 ) (16,110 ) (72,125 ) Net $ 6,482 $ 14,162 $ 9,202 $ 16,755 $ 22,594 $ 44,369 Atrium Gross $ 153,472 $ 152,278 $ 143,170 $ 140,438 $ 149,082 $ 149,310 Ceded (19,258 ) (17,531 ) (2,733 ) (16,022 ) (14,502 ) (14,635 ) Net $ 134,214 $ 134,747 $ 140,437 $ 124,416 $ 134,580 $ 134,675 StarStone Gross $ 895,160 $ 865,159 $ 854,699 $ 830,186 $ 824,714 $ 769,875 Ceded (430,259 ) (405,756 ) (206,663 ) (153,578 ) (196,287 ) (196,729 ) Net $ 464,901 $ 459,403 $ 648,036 $ 676,608 $ 628,427 $ 573,146 Other Gross $ 5,719 $ 5,900 $ 7,157 $ 7,220 $ 2,883 $ 2,884 Ceded (926 ) (1,091 ) (896 ) (1,485 ) (1,330 ) (1,330 ) Net $ 4,793 $ 4,809 $ 6,261 $ 5,735 $ 1,553 $ 1,554 Total Gross $ 1,068,453 $ 1,047,287 $ 1,022,342 $ 1,003,833 $ 1,015,383 $ 1,038,563 Ceded (458,063 ) (434,166 ) (218,406 ) (180,319 ) (228,229 ) (284,819 ) Net $ 610,390 $ 613,121 $ 803,936 $ 823,514 $ 787,154 $ 753,744" id="sjs-B4">10. REINSURANCE BALANCES RECOVERABLE The following table provides the total reinsurance balances recoverable as at December 31, 2017 and 2016 : 2017 Non-life Run-off Atrium StarStone Other Total Recoverable from reinsurers on unpaid: Outstanding losses $ 932,284 $ 7,472 $ 211,650 $ 16 $ 1,151,422 IBNR 590,154 31,476 242,620 — 864,250 Fair value adjustments (12,970 ) 1,583 (2,253 ) — (13,640 ) Fair value adjustments - fair value option (131,983 ) — — — (131,983 ) Total reinsurance reserves recoverable 1,377,485 40,531 452,017 16 1,870,049 Paid losses recoverable 128,253 (451 ) 23,179 — 150,981 $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 Reconciliation to Consolidated Balance Sheet: Reinsurance balances recoverable $ 963,514 $ 40,080 $ 475,196 $ 16 $ 1,478,806 Reinsurance balances recoverable - fair value option 542,224 — — — 542,224 Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 2016 Non-life Run-off Atrium StarStone Other Total Recoverable from reinsurers on unpaid: Outstanding losses $ 621,288 $ 6,438 $ 182,478 $ 190 $ 810,394 IBNR 393,550 21,753 178,259 — 593,562 Fair value adjustments (13,885 ) 1,818 (3,506 ) — (15,573 ) Total reinsurance reserves recoverable 1,000,953 30,009 357,231 190 1,388,383 Paid losses recoverable 47,160 (1,081 ) 25,512 769 72,360 $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743 Our insurance and reinsurance run-off subsidiaries and assumed portfolios, prior to acquisition, used retrocessional agreements to reduce their exposure to the risk of insurance and reinsurance assumed. On an annual basis, both Atrium and StarStone purchase a tailored outwards reinsurance program designed to manage their risk profiles. The majority of Atrium’s and StarStone's third-party reinsurance cover is with highly rated reinsurers or is collateralized by pledged assets or letters of credit. The fair value adjustments, determined on acquisition of insurance and reinsurance subsidiaries, are based on the estimated timing of loss and LAE recoveries and an assumed interest rate equivalent to a risk free rate for securities with similar duration to the acquired reinsurance balances recoverable plus a spread to reflect credit risk, and are amortized over the estimated recovery period, as adjusted for accelerations in timing of payments as a result of commutation settlements. The determination of the fair value adjustments on the retroactive reinsurance contracts for which we have elected the fair value option is described in Note 8 - "Fair Value Measurements" . As of December 31, 2017 and 2016 , we had reinsurance balances recoverable of approximately $2.0 billion and $1.5 billion , respectively. The increase of $560.3 million in reinsurance balances recoverable was primarily a result of the QBE and RSA reinsurance transactions, which closed in the first quarter of 2017, and the impact of the recent hurricane losses on Atrium and StarStone, partially offset by reserve reductions, commutations and cash collections made during the year ended December 31, 2017 in our Non-life Run-off segment. Top Ten Reinsurers December 31, 2017 December 31, 2016 Non-life Atrium StarStone Other Total % of Non-life Atrium StarStone Other Total % of Top ten reinsurers $ 1,166,057 $ 22,422 $ 328,257 $ — $ 1,516,736 75.0 % $ 737,074 $ 23,245 $ 226,283 $ — $ 986,602 67.6 % Other reinsurers > $1 million 322,722 16,631 144,336 — 483,689 24.0 % 301,856 4,827 152,341 — 459,024 31.4 % Other reinsurers < $1 million 16,959 1,027 2,603 16 20,605 1.0 % 9,183 856 4,119 959 15,117 1.0 % Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 100.0 % $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743 100.0 % Six of the top ten external reinsurers, as at December 31, 2017 and 2016 , were all rated A- or better. The remaining four non-rated reinsurers, from which $687.6 million was recoverable as at December 31, 2017 ( December 31, 2016 : $512.2 million recoverable from four non-rated reinsurers), including KayleRe Ltd., have provided security in the form of pledged assets in trust, letters of credit issued to us, or funds withheld in the full amount of the recoverable. As at December 31, 2017 , reinsurance balances recoverable of $357.4 million related to KaylaRe Ltd. ( December 31, 2016 : $242.1 million ) and $320.0 million related to Hannover Ruck SE ( December 31, 2016 : $67.3 million ), both of which represent 10% or more of total reinsurance balances recoverable. KaylaRe Ltd. is not rated but is an affiliated company partly owned by Enstar, as described in Note 21 - "Related Party Transactions" , and security is provided in the form of funds withheld. Hannover Ruck SE is rated AA- by Standard & Poor's and A+ by A.M. Best. Provisions for Uncollectible Reinsurance Recoverables We evaluate and monitor concentration of credit risk among our reinsurers. Provisions are made for amounts considered potentially uncollectible. The following table shows our reinsurance balances recoverable by rating of reinsurer and our provisions for uncollectible reinsurance balances recoverable ("provisions for bad debt") as at December 31, 2017 and 2016 . The provisions for bad debt all relate to the Non-life Run-off segment. 2017 2016 Gross Provisions for Bad Debt Net Provisions as a Gross Provisions for Bad Debt Net Provisions as a Reinsurers rated A- or above $ 1,252,887 $ 51,115 $ 1,201,772 4.1 % $ 892,776 $ 35,184 $ 857,592 3.9 % Reinsurers rated below A-, secured 771,097 — 771,097 — % 544,894 — 544,894 — % Reinsurers rated below A-, unsecured 162,259 114,098 48,161 70.3 % 197,589 139,332 58,257 70.5 % Total $ 2,186,243 $ 165,213 $ 2,021,030 7.6 % $ 1,635,259 $ 174,516 $ 1,460,743 10.7 % 13. PREMIUMS WRITTEN AND EARNED The following tables provide a summary of net premiums written and earned for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Premiums Written Premiums Earned Premiums Written Premiums Earned Premiums Written Premiums Earned Non-life Run-off Gross $ 14,102 $ 23,950 $ 17,316 $ 25,989 $ 38,704 $ 116,494 Ceded (7,620 ) (9,788 ) (8,114 ) (9,234 ) (16,110 ) (72,125 ) Net $ 6,482 $ 14,162 $ 9,202 $ 16,755 $ 22,594 $ 44,369 Atrium Gross $ 153,472 $ 152,278 $ 143,170 $ 140,438 $ 149,082 $ 149,310 Ceded (19,258 ) (17,531 ) (2,733 ) (16,022 ) (14,502 ) (14,635 ) Net $ 134,214 $ 134,747 $ 140,437 $ 124,416 $ 134,580 $ 134,675 StarStone Gross $ 895,160 $ 865,159 $ 854,699 $ 830,186 $ 824,714 $ 769,875 Ceded (430,259 ) (405,756 ) (206,663 ) (153,578 ) (196,287 ) (196,729 ) Net $ 464,901 $ 459,403 $ 648,036 $ 676,608 $ 628,427 $ 573,146 Other Gross $ 5,719 $ 5,900 $ 7,157 $ 7,220 $ 2,883 $ 2,884 Ceded (926 ) (1,091 ) (896 ) (1,485 ) (1,330 ) (1,330 ) Net $ 4,793 $ 4,809 $ 6,261 $ 5,735 $ 1,553 $ 1,554 Total Gross $ 1,068,453 $ 1,047,287 $ 1,022,342 $ 1,003,833 $ 1,015,383 $ 1,038,563 Ceded (458,063 ) (434,166 ) (218,406 ) (180,319 ) (228,229 ) (284,819 ) Net $ 610,390 $ 613,121 $ 803,936 $ 823,514 $ 787,154 $ 753,744

Losses and Loss Adjustment Expe

Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
Losses and Loss Adjustment Expenses	11. LOSSES AND LOSS ADJUSTMENT EXPENSES The liability for losses and LAE, also referred to as loss reserves, represents our gross estimates before reinsurance for unpaid reported losses and losses that have been incurred but not reported ("IBNR") for our Non-life Run-off, Atrium and StarStone segments. We recognize an asset for the portion of the liability that we expect to recover from reinsurers. LAE reserves include allocated loss adjustment expenses ("ALAE"), and unallocated loss adjustment expenses ("ULAE"). ALAE are linked to the settlement of an individual claim or loss, whereas ULAE are based on our estimates of future costs to administer the claims. IBNR represents reserves for loss and LAE that have been incurred but not yet reported to us. This includes amounts for unreported claims, development on known claims and reopened claims. The following table summarizes the liability for losses and LAE by segment as at December 31, 2017 and 2016 : 2017 2016 Non-life Run-off Atrium StarStone Total Non-life Atrium StarStone Total Outstanding losses $ 3,185,703 $ 78,363 $ 590,977 $ 3,855,043 $ 2,697,736 $ 67,379 $ 502,115 $ 3,267,230 IBNR 2,903,927 150,508 599,221 3,653,656 1,935,659 130,118 541,305 2,607,082 Fair value adjustments (125,998 ) 9,547 (555 ) (117,006 ) (135,368 ) 12,503 (863 ) (123,728 ) Fair value adjustments - fair value option (314,748 ) — — (314,748 ) — — — — ULAE 300,588 2,455 18,100 321,143 218,336 2,122 16,825 237,283 Total $ 5,949,472 $ 240,873 $ 1,207,743 $ 7,398,088 $ 4,716,363 $ 212,122 $ 1,059,382 $ 5,987,867 Reconciliation to Consolidated Balance Sheet: Losses and loss adjustment expenses $ 5,603,419 $ 5,987,867 Losses and loss adjustment expenses, at fair value 1,794,669 — Total $ 7,398,088 $ 5,987,867 The overall increase in the liability for losses and LAE between December 31, 2016 and December 31, 2017 was primarily attributable to the assumed reinsurance agreements with RSA and QBE in our Non-life Run-off segment, for which we have elected the fair value option, as described in Note 4 - "Significant New Business" . The table below provides a consolidated reconciliation of the beginning and ending liability for losses and LAE for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Balance as at January 1 $ 5,987,867 $ 5,720,149 $ 4,509,421 Less: reinsurance reserves recoverable 1,388,193 1,360,382 1,154,196 Less: deferred charges on retroactive reinsurance 94,551 255,911 — Net balance as at January 1 4,505,123 4,103,856 3,355,225 Net incurred losses and LAE: Current period 437,853 493,016 476,364 Prior periods (244,302 ) (318,917 ) (372,031 ) Total net incurred losses and LAE 193,551 174,099 104,333 Net paid losses: Current period (82,273 ) (79,579 ) (99,933 ) Prior periods (862,921 ) (753,478 ) (681,956 ) Total net paid losses (945,194 ) (833,057 ) (781,889 ) Effect of exchange rate movement 158,429 (46,903 ) (65,069 ) Acquired on purchase of subsidiaries 10,251 10,019 878,815 Assumed business 1,525,703 1,340,444 612,441 Ceded business — (243,335 ) — Net balance as at December 31 5,447,863 4,505,123 4,103,856 Plus: reinsurance reserves recoverable 1,870,033 1,388,193 1,360,382 Plus: deferred charges on retroactive reinsurance 80,192 94,551 255,911 Balance as at December 31 $ 7,398,088 $ 5,987,867 $ 5,720,149 The tables below provide the components of net incurred losses and LAE by segment for the years ended December 31, 2017 , 2016 and 2015 : Year Ended December 31, 2017 Non-life Atrium StarStone Total Net losses paid $ 581,723 $ 55,678 $ 307,793 $ 945,194 Net change in case and LAE reserves (381,053 ) 8,338 31,685 (341,030 ) Net change in IBNR reserves (390,727 ) 7,679 (23,540 ) (406,588 ) Amortization of deferred charges 14,359 — — 14,359 Increase (reduction) in estimates of net ultimate losses (175,698 ) 71,695 315,938 211,935 Reduction in provisions for bad debt (1,536 ) 159 — (1,377 ) Increase (reduction) in provisions for unallocated LAE (53,810 ) 285 (187 ) (53,712 ) Amortization of fair value adjustments 10,114 (2,720 ) (945 ) 6,449 Changes in fair value - fair value option 30,256 — — 30,256 Net incurred losses and LAE $ (190,674 ) $ 69,419 $ 314,806 $ 193,551 Year Ended December 31, 2016 Non-life Run-off Atrium StarStone Total Net losses paid $ 533,806 $ 47,998 $ 251,253 $ 833,057 Net change in case and LAE reserves (608,785 ) (148 ) 73,049 (535,884 ) Net change in IBNR reserves (347,384 ) 13,700 75,643 (258,041 ) Amortization of deferred charges 168,827 — — 168,827 Increase (reduction) in estimates of net ultimate losses (253,536 ) 61,550 399,945 207,959 Reduction in provisions for bad debt (13,822 ) — — (13,822 ) Increase (reduction) in provisions for unallocated LAE (43,955 ) 145 3,543 (40,267 ) Amortization of fair value adjustments 25,432 (3,308 ) (1,895 ) 20,229 Net incurred losses and LAE $ (285,881 ) $ 58,387 $ 401,593 $ 174,099 Year Ended December 31, 2015 Non-life Atrium StarStone Total Net losses paid $ 517,295 $ 52,035 $ 212,559 $ 781,889 Net change in case and LAE reserves (355,335 ) (709 ) 77,219 (278,825 ) Net change in IBNR reserves (364,774 ) 2,844 37,904 (324,026 ) Amortization of deferred charges 15,265 — — 15,265 Increase (reduction) in estimates of net ultimate losses (187,549 ) 54,170 327,682 194,303 Increase in provisions for bad debt (25,271 ) — — (25,271 ) Reduction in provisions for unallocated LAE (62,653 ) (83 ) 3,537 (59,199 ) Amortization of fair value adjustments 4,643 (6,608 ) (3,535 ) (5,500 ) Net incurred losses and LAE $ (270,830 ) $ 47,479 $ 327,684 $ 104,333 Loss Development Information Methodology for Establishing Reserves The liability for losses and LAE includes an amount determined from reported claims and an amount based on historical loss experience and industry statistics for IBNR using a variety of actuarial methods. Our loss reserves cover multiple lines of business, which include workers' compensation, general casualty, asbestos and environmental, marine, aviation and transit, construction defects and other non-life lines of business. Our management, through our loss reserving committees, considers the reasonableness of loss reserves recommended by our actuaries, including actual loss development during the year. Case reserves are recognized for known claims (including the cost of related litigation) when sufficient information has been reported to us to indicate the involvement of a specific insurance policy. We use considerable judgment in estimating losses for reported claims on an individual claim basis based upon our knowledge of the circumstances surrounding the claim, the severity of the injury or damage, the jurisdiction of the occurrence, the potential for ultimate exposure, the type of loss, and our experience with the line of business and policy provisions relating to the particular type of claim. The reserves for unpaid reported losses and LAE are established by management based on reports from brokers, ceding companies and insureds and represent the estimated ultimate cost of events or conditions that have been reported to, or specifically identified, by us. We also consider facts currently known and the current state of the law and coverage litigation. IBNR reserves are established by management based on actuarially determined estimates of ultimate losses and loss expenses. We use generally accepted actuarial methodologies to estimate ultimate losses and LAE and those estimates are reviewed by our management. In addition, the routine settlement of claims, at either below or above the carried advised loss reserve, updates historical loss development information to which actuarial methodologies are applied often, resulting in revised estimates of ultimate liabilities. On an annual basis, independent actuarial firms are retained by management to provide their estimates of ultimate losses and to review the estimates developed by our actuaries. Within the annual loss reserve studies produced by either our actuaries or independent actuaries, exposures for each subsidiary are separated into homogeneous reserving categories for the purpose of estimating IBNR. Each reserving category contains either direct insurance or assumed reinsurance reserves and groups relatively similar types of risks and exposures (for example, asbestos, environmental, casualty, property) and lines of business written (for example, marine, aviation, non-marine). Based on the exposure characteristics and the nature of available data for each individual reserving category, a number of methodologies are applied. Recorded reserves for each category are selected from the actuarial indications produced by the various methodologies after consideration of exposure characteristics, data limitations and strengths and weaknesses of each method applied. This approach to estimating IBNR has been consistently adopted in the annual loss reserve studies for each period presented. The estimation of unpaid claim liabilities at any given point in time is subject to a high degree of uncertainty for a number of reasons. A significant amount of time can lapse between the assumption of risk, the occurrence of a loss event, the reporting of the event to an insurance or reinsurance company and the ultimate payment of the claim on the loss event. Our actuarial methodologies include industry benchmarking which, under certain methodologies, compares the trend of our loss development to that of the industry. To the extent that the trend of our loss development compared to the industry changes in any period, it is likely to have an impact on the estimate of ultimate liabilities. Unpaid claim liabilities for property and casualty exposures in general are impacted by changes in the legal environment, jury awards, medical cost trends and general inflation. Certain estimates for unpaid claim liabilities involve considerable uncertainty due to significant coverage litigation, and it can be unclear whether past claim experience will be representative of future claim experience. Ultimate values for such claims cannot be estimated using reserving techniques that extrapolate losses to an ultimate basis using loss development factors, and the uncertainties surrounding the estimation of unpaid claim liabilities are not likely to be resolved in the near future. In addition, reserves are established to cover loss development related to both known and unasserted claims. Consequently, our subsequent estimates of ultimate losses and LAE, and our liability for losses and LAE, may differ materially from the amounts recorded in the consolidated financial statements. These estimates are reviewed regularly and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments, if any, will be recorded in earnings in the period in which they become known. Prior period development arises from changes to loss estimates recognized in the current year that relate to loss reserves established in previous calendar years. Disclosures of Incurred and Paid Loss Development, IBNR, Claims Counts and Payout Percentages The loss development tables disclosed below, sets forth our historic incurred and paid loss development by accident year through December 31, 2017 , net of reinsurance, as well as the cumulative number of reported claims, IBNR balances, and other supplementary information. With the exception of our Atrium segment, the loss development tables disclosed below are presented by line of business for our Non-life Run-off and StarStone segments as follows: • Non-Life Run-off - The lines of business included within the loss development disclosures below include General Casualty, Workers’ Compensation and Professional Indemnity/Directors & Officers; and • StarStone - All the lines of business related to the StarStone segment have been included within the loss development disclosures below, namely, Casualty, Marine, Property, Aerospace and Workers’ Compensation. The loss development disclosures for our Atrium segment have not been disaggregated further by line of business as the segment comprised only 3% of our total consolidated liability for losses and LAE as at December 31, 2017 and was, therefore, not considered material for further disaggregation. Certain lines of business within our Non-Life Run-off segment were not included within the loss development disclosures presented below due to the following reasons: • The asbestos and environmental lines of business contain exposures which impact accident years older than those presented within the loss development tables disclosed below and have, therefore, not been included within those disclosures. These lines of business cumulatively comprised approximately 41% of our total net liabilities for losses and LAE, before reconciling items, within our Non-life Run-off segment, as at December 31, 2017 ; • The marine, aviation and transit and construction defect lines of business, which each comprised approximately 3% of our total net liabilities for losses and LAE, before reconciling items, within our Non-Life Run-off segment, as at December 31, 2017 were each not considered material for separate disclosure; and • The exposures included within the other category includes losses with several different development patterns that are not individually significant for separate disclosure. For each line of business for which loss development tables have been provided below, the disclosure approach and format adopted reflects the following: • The incurred loss triangle includes both reported case reserves and IBNR liabilities, as well as cumulative paid losses; • Both the incurred and cumulative paid loss triangles include allocated loss adjustment expense (i.e. claims handling costs allocated to specific individual claims) but exclude unallocated loss adjustment expenses (i.e. the costs associated with internal claims staff and third party administrators as well as consultants that cannot be allocated to specific individual claims); • Fair value adjustments arising from the business acquisitions that we have completed as well as the retroactive reinsurance agreements for which we have elected the fair value option are excluded from the incurred loss triangles; • The amounts included within the loss triangles for the years ended December 31, 2008 through to December 31, 2016 , (April 1, 2014 through to December 31, 2016 in the case of StarStone since its date of acquisition), as well as the historical average annual percentage payout ratios as of December 31, 2017 are presented as supplementary information and are therefore unaudited; • All data presented within the loss triangles is net of reinsurance recoveries, excluding provisions for uncollectible reinsurance recoverables; and • The IBNR reserves included within each incurred loss development table by accident year, reflect the net IBNR recorded as of December 31, 2017 , including expected development on reported losses. The historical dollar amounts disclosed within the loss development tables for all lines of business presented below are on a constant-currency basis, which is achieved by using constant foreign exchange rates between periods in the loss triangles, and translating prior period amounts denominated in currencies other than the U.S. dollar, which is our reporting currency, using the closing exchange rates as at December 31, 2017 . The impact of this exchange rate conversion is to show the change between periods exclusive of the effect of exchange rate fluctuations, which would otherwise distort the change in incurred losses and the cash flow patterns associated with those incurred losses shown within the loss development tables disclosed below. The change in incurred losses shown within the loss development tables below will, however, differ from other U.S. GAAP disclosures of incurred current and prior period reserve development amounts, which include the effect of exchange rate fluctuations. The loss development tables disclosed below are presented retrospectively with respect to the acquisitions and retroactive reinsurance agreements that we have completed, where it is practicable to do so. However, where it is not practicable, a prospective approach has been adopted in the presentation of the loss development tables disclosed below as follows: • Acquisitions - The information included within the incurred and paid loss development tables for all the lines of business related to the StarStone segment below have been presented on a prospective basis from the date of our acquisition of StarStone, which was effective on April 1, 2014. Providing pre-acquisition incurred and paid losses by accident year for years prior to 2014 was determined to be impracticable due to significant data limitations. This prospective treatment was also adopted for the disclosures included within our Non-Life Run-off segment with respect to StarStone’s run-off business whose exposures are included within the general casualty and professional indemnity/Directors & Officers lines of business disclosed within our Non-Life Run-off loss development tables below; and • Retroactive reinsurance agreements - For those loss portfolio transfers that we assume through retroactive reinsurance agreements for which we don’t have access to historical loss development information from the ceding entities or where the data is not sufficiently reliable, these have been presented prospectively within the loss development tables disclosed below, from the date that the reinsurance agreements became effective. This prospective treatment, therefore, results in loss development trends within the calendar year that either the business acquisition or retroactive reinsurance agreement is completed, that is not entirely reflective of the actual performance of the acquired business or the retroactive reinsurance agreement. Establishing an estimate for loss reserves requires the incorporation of various assumptions and judgment, therefore, the information contained within the loss development disclosures below only allows readers or users of our consolidated financial statements to understand, at the summary level presented in the development tables, the change over time in our reported incurred loss estimates as well as the nature and patterns of the cash flows associated with those estimates. We, therefore, believe that the information provided within the loss development tables disclosed below is of limited use for independent analysis or application of standard actuarial estimations, and any results obtained from doing so should be interpreted with caution. For a more detailed discussion on how our loss reserve estimates are established, refer to the discussion on “Losses and Loss Adjustment Expenses” within our Critical Accounting Policies. Cumulative Number of Reported Claims Reported claim counts, on a cumulative basis, are provided as supplemental information to each incurred loss development table by accident year. We measure claim frequency information on an individual claim count basis within each of our segments as follows: • Non-Life Run-off - The claim frequency information for the exposures included within our general casualty, workers’ compensation and professional indemnity lines of business includes direct and assumed open and closed claims by accident year at the claimant level. Reported claims that are closed without a payment are included within our cumulative number of reported claims because we typically incur claim adjustment expenses on them prior to their closure. The claim count numbers exclude counts related to claims within policy deductibles where the insured is responsible for the payment of losses within the deductible layer. Individual claim counts related to certain assumed reinsurance contracts such as excess-of-loss and quota share treaties are not available to us, and the losses arising from these treaties have been treated as single claims for the purposes of determining claim counts. Therefore, each treaty year within the reinsurance contract is deemed a single claim because the detailed underlying individual claim information is generally not reported to us by our cedents; and • StarStone and Atrium - The claim frequency information is determined at the claimant level for the exposures within the lines of business related to these segments. Our claims system assigns a unique claim identifier to each reported claim we receive. Each unique claim identifier is deemed to be a single claim, irrespective of whether the claim remains open or has been closed with or without payment. For certain insurance facilities and business produced or managed by managing general agents, coverholders and third party administrators where the underlying claims data is reported to us in an aggregated format, the information necessary to provide cumulative claims frequency is not available. In such cases, we typically record a “block” claim in our system. This also applies to a small amount of assumed reinsurance business that we write where, similarly, the underlying claims data is reported to us in an aggregated format. In such instances, each assumed reinsurance contract is deemed a single claim. The cumulative number of reported claims for our Atrium segment includes all claim counts for Syndicate 609. Our Atrium segment represents our 25% share of Syndicate 609's underwriting capacity and capital, however, the claims count is the same whether viewed at the 100% Syndicate level or for our 25% share. Our reported claim frequency information is subject to the following inherent limitations when analyzing our loss experience and severity: • Claim counts are presented only on a reported and not on an ultimate basis. Therefore, reported claim counts include open claims which have outstanding reserves but exclude IBNR claims. As such the reported claims are consistent with reported losses, which can be calculated by subtracting IBNR losses from incurred losses. However, the reported claim counts are inconsistent with the losses in the incurred losses triangles, which include IBNR losses, and to losses in the paid loss triangles, which exclude outstanding reserves; • Reported claim counts have not been adjusted for ceded reinsurance, which may distort any measures of frequency or severity; • For lines of business that have a mix of primary and excess layer exposures, such as our general casualty and workers’ compensation lines of business, the reported claim counts may fluctuate from period to period between exposure layers, thereby distorting any measure of frequency and severity; and • The use of our reported claim frequency information to project ultimate loss payouts by disaggregated disclosure category or line of business may not be as meaningful as claim count information related to individual contracts at a more granular level. Non-Life Run-off Segment The table below provides a reconciliation of the beginning and ending reserves for losses and LAE for the years ended December 31, 2017 , 2016 and 2015 for the Non-life Run-off segment: 2017 2016 2015 Balance as at January 1 $ 4,716,363 $ 4,585,454 $ 3,435,010 Less: reinsurance reserves recoverable 1,000,953 1,034,747 800,709 Less: deferred charges on retroactive reinsurance 94,551 255,911 — Net balance as at January 1 3,620,859 3,294,796 2,634,301 Net incurred losses and LAE: Current period 5,866 5,829 39,924 Prior periods (196,540 ) (291,710 ) (310,754 ) Total net incurred losses and LAE (190,674 ) (285,881 ) (270,830 ) Net paid losses: Current period (2,835 ) (3,869 ) (16,049 ) Prior periods (578,888 ) (529,937 ) (501,246 ) Total net paid losses (581,723 ) (533,806 ) (517,295 ) Effect of exchange rate movement 138,772 (27,478 ) (42,636 ) Acquired on purchase of subsidiaries 10,251 10,019 878,815 Assumed business 1,494,310 1,340,444 612,441 Ceded business — (177,235 ) — Net balance as at December 31 4,491,795 3,620,859 3,294,796 Plus: reinsurance reserves recoverable 1,377,485 1,000,953 1,034,747 Plus: deferred charges on retroactive reinsurance 80,192 94,551 255,911 Balance as at December 31 $ 5,949,472 $ 4,716,363 $ 4,585,454 Net incurred losses and LAE in the Non-life Run-off segment for the years ended December 31, 2017 , 2016 and 2015 were as follows: 2017 2016 2015 Prior Period Current Period Total Prior Period Current Period Total Prior Period Current Period Total Net losses paid $ 578,888 $ 2,835 $ 581,723 $ 529,937 $ 3,869 $ 533,806 $ 501,246 $ 16,049 $ 517,295 Net change in case and LAE reserves (381,450 ) 397 (381,053 ) (608,168 ) (617 ) (608,785 ) (366,262 ) 10,927 (355,335 ) Net change in IBNR reserves (393,100 ) 2,373 (390,727 ) (349,726 ) 2,342 (347,384 ) (377,722 ) 12,948 (364,774 ) Amortization of deferred charges 14,359 — 14,359 168,827 — 168,827 15,265 — 15,265 Increase (reduction) in estimates of net ultimate losses (181,303 ) 5,605 (175,698 ) (259,130 ) 5,594 (253,536 ) (227,473 ) 39,924 (187,549 ) Reduction in provisions for bad debt (1,536 ) — (1,536 ) (13,822 ) — (13,822 ) (25,271 ) — (25,271 ) Increase (reduction) in provisions for unallocated LAE (54,071 ) 261 (53,810 ) (44,190 ) 235 (43,955 ) (62,653 ) — (62,653 ) Amortization of fair value adjustments 10,114 — 10,114 25,432 — 25,432 4,643 — 4,643 Changes in fair value - fair value option 30,256 — 30,256 — — — — — — Net incurred losses and LAE $ (196,540 ) $ 5,866 $ (190,674 ) $ (291,710 ) $ 5,829 $ (285,881 ) $ (310,754 ) $ 39,924 $ (270,830 ) Net change in case and LAE reserves comprises the movement during the year in specific case reserve liabilities as a result of claims settlements or changes advised to us by our policyholders and attorneys, less changes in case reserves recoverable advised by us to our reinsurers as a result of the settlement or movement of assumed claims. Net change in IBNR represents the gross change in our actuarial estimates of IBNR, less amounts recoverable. Year Ended December 31, 2017 The net reduction in incurred losses and LAE for the year ended December 31, 2017 of $190.7 million included net incurred losses a nd LAE of $5.9 million related to current period net earned premium, primarily for the portion of the run-off business acquired with Sussex. Excluding current period net incurred losses and LAE of $5.9 million , net incurred losses and LAE liabilities relating to prior periods were reduced by $196.5 million , which was attributable to a reduction in estimates of net ultimate losses of $181.3 million , a reduction in provisions for bad debt of $1.5 million and a reduction in provisions for unallocated LAE of $54.1 million , relating to 2017 run-off activity, partially offset by amortization of fair value adjustments over the estimated payout period relating to companies acquired amounting to $10.1 million and a change in fair value of $30.3 million related to our assumed retroactive reinsurance agreements with RSA and QBE completed during the period and for which we have elected the fair value option. The reduction of estimates in net ultimate losses for the year ended December 31, 2017 was reduced by amortization of the deferred charge of $14.4 million . The reduction in estimates of net ultimate losses relating to prior periods of $181.3 million comprised reductions in IBNR reserves of $393.1 million , partially offset by net incurred loss development of $211.8 million , which includes amortization of deferred charges of $14.4 million . The decrease in the estimate of net IBNR reserves of $393.1 million (compared to $349.7 million during the year ended December 31, 2016 ), was comprised of a decrease of $70.0 million relating to asbestos liabilities (compared to an increase of $39.4 million in 2016 ), a decrease of $7.5 million relating to environmental liabilities (compared to an increase $35.5 million in 2016 ), a decrease of $7.2 million relating to general casualty liabilities (compared to $0.8 million in 2016 ), a decrease of $156.2 million relating to workers' compensation liabilities (compared to $333.2 million in 2016 ) and a decrease of $152.2 million relating to all other remaining liabilities (compared to $90.6 million in 2016 ). The reduction in net IBNR reserves of $393.1 million relating to prior periods was a result of the application, on a basis consistent with the assumptions applied in the prior period, of our actuarial methodologies to revised historical loss development data, following 59 commutations and policy buy-backs, to estimate loss reserves required to cover liabilities for unpaid losses and LAE relating to non-commuted exposures. The prior period estimate of net IBNR reserves was reduced as a result of the combined impact on all classes of business of loss development activity during 2017 , including commutations and the favorable trend of loss development related to non-commuted policies compared to prior forecasts. The net incurred loss development resulting from settlement of net advised case and LAE reserves of $381.5 million for net paid losses of $578.9 million related to the settlement of non-commuted losses in the year and 59 commutations and policy buy-backs of assumed and ceded exposures. Net advised case and LAE reserves settled by way of commutation and policy buyback during the year ended December 31, 2017 amounted to $7.4 million (comprising $23.2 million of assumed case reserves and LAE reserves, partially offset by $15.8 million of ceded incurred reinsurance recoverable case reserves). The reduction in provisions for bad debt of $1.5 million was a result of the favorable resolution of contractual disputes with reinsurers, the reduction in bad debt provisions for insolvent reinsurers as a result of distributions received and the reduction of specific provisions held for potential disputes with reinsurers. Year Ended December 31, 2016 The net reduction in incurred losses and LAE for the year ended December 31, 2016 of $285.9 million included current period net incurred losses and LAE of $5.8 million related to current period net earned premium of $7.1 million (primarily for the portion of the run-off business acquired with Sussex). Excluding current period net losses and LAE of $5.8 million , net incurred losses and LAE liabilities relating to prior periods were reduced by $291.7 million , which was attributable to a reduction in estimates of net ultimate losses of $259.1 million , reduction in provisions for bad debt of $13.8 million and a reduction in provision for unallocated LAE of $44.2 million , relating to 2016 run-off activity, partially offset by amortization of fair value adjustments over the estimated payout period relating to companies acquired amounting to $25.4 million . The reduction in estimates of net ultimate losses relating to prior periods of $259.1 million comprised reductions in IBNR reserves of $349.7 million partially offset by net incurred loss development of $90.6 million , which includes amortization of deferred charges of $168.8 million . The decrease in the estimate of net IBNR reserves of $349.7 million (compared to $377.7 million during the year ended December 31, 2015 ), was comprised of an increase of $39.4 million relating to asbestos liabilities (compared to a decrease of $32.0 million in 2015 ), an increase of $35.5 million relating to environmental liabilities (compared to a decrease of $1.6 million in 2015 ), a decrease of $0.8 million relating to general casualty liabilities (compared to $3.0 million in 2015 ), a decrease of $333.2 million relating to workers' compensation liabilities (compared to $243.4 million in 2015 ) and a decrease of $90.6 million relating to all other remaining liabilities (compared to $97.7 million in 2015 ). The reduction in net IBNR reserves of $349.7 million relating to prior periods was a result of the application, on a basis consistent with the assumptions applied in the prior period, o f our actuarial methodologies to revised historical loss development data, following 56 commutations and policy buy-backs, to estimate loss reserves required to cover liabilities for unpaid losses and LAE relating to non-commuted exposures. The prior period estimate of net IBNR reserves was reduced as a result of the combined impact on all classes of business of loss development activity during 2016 , including commutations and the favorable trend of loss development related to non-commuted policies compared to prior forecasts. The net incurred loss development resulting from settlement of net advised case and LAE reserves of $608.2 million for net paid losses of $529.9 million related to the settlement of non-commuted losses in the year and 56 commutations and policy buy-backs of assumed and ceded exposures. Net advised case a

Policy Benefits for Life Contra

Policy Benefits for Life Contracts	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
Policy Benefits for Life Contracts	11. LOSSES AND LOSS ADJUSTMENT EXPENSES The liability for losses and LAE, also referred to as loss reserves, represents our gross estimates before reinsurance for unpaid reported losses and losses that have been incurred but not reported ("IBNR") for our Non-life Run-off, Atrium and StarStone segments. We recognize an asset for the portion of the liability that we expect to recover from reinsurers. LAE reserves include allocated loss adjustment expenses ("ALAE"), and unallocated loss adjustment expenses ("ULAE"). ALAE are linked to the settlement of an individual claim or loss, whereas ULAE are based on our estimates of future costs to administer the claims. IBNR represents reserves for loss and LAE that have been incurred but not yet reported to us. This includes amounts for unreported claims, development on known claims and reopened claims. The following table summarizes the liability for losses and LAE by segment as at December 31, 2017 and 2016 : 2017 2016 Non-life Run-off Atrium StarStone Total Non-life Atrium StarStone Total Outstanding losses $ 3,185,703 $ 78,363 $ 590,977 $ 3,855,043 $ 2,697,736 $ 67,379 $ 502,115 $ 3,267,230 IBNR 2,903,927 150,508 599,221 3,653,656 1,935,659 130,118 541,305 2,607,082 Fair value adjustments (125,998 ) 9,547 (555 ) (117,006 ) (135,368 ) 12,503 (863 ) (123,728 ) Fair value adjustments - fair value option (314,748 ) — — (314,748 ) — — — — ULAE 300,588 2,455 18,100 321,143 218,336 2,122 16,825 237,283 Total $ 5,949,472 $ 240,873 $ 1,207,743 $ 7,398,088 $ 4,716,363 $ 212,122 $ 1,059,382 $ 5,987,867 Reconciliation to Consolidated Balance Sheet: Losses and loss adjustment expenses $ 5,603,419 $ 5,987,867 Losses and loss adjustment expenses, at fair value 1,794,669 — Total $ 7,398,088 $ 5,987,867 The overall increase in the liability for losses and LAE between December 31, 2016 and December 31, 2017 was primarily attributable to the assumed reinsurance agreements with RSA and QBE in our Non-life Run-off segment, for which we have elected the fair value option, as described in Note 4 - "Significant New Business" . The table below provides a consolidated reconciliation of the beginning and ending liability for losses and LAE for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Balance as at January 1 $ 5,987,867 $ 5,720,149 $ 4,509,421 Less: reinsurance reserves recoverable 1,388,193 1,360,382 1,154,196 Less: deferred charges on retroactive reinsurance 94,551 255,911 — Net balance as at January 1 4,505,123 4,103,856 3,355,225 Net incurred losses and LAE: Current period 437,853 493,016 476,364 Prior periods (244,302 ) (318,917 ) (372,031 ) Total net incurred losses and LAE 193,551 174,099 104,333 Net paid losses: Current period (82,273 ) (79,579 ) (99,933 ) Prior periods (862,921 ) (753,478 ) (681,956 ) Total net paid losses (945,194 ) (833,057 ) (781,889 ) Effect of exchange rate movement 158,429 (46,903 ) (65,069 ) Acquired on purchase of subsidiaries 10,251 10,019 878,815 Assumed business 1,525,703 1,340,444 612,441 Ceded business — (243,335 ) — Net balance as at December 31 5,447,863 4,505,123 4,103,856 Plus: reinsurance reserves recoverable 1,870,033 1,388,193 1,360,382 Plus: deferred charges on retroactive reinsurance 80,192 94,551 255,911 Balance as at December 31 $ 7,398,088 $ 5,987,867 $ 5,720,149 The tables below provide the components of net incurred losses and LAE by segment for the years ended December 31, 2017 , 2016 and 2015 : Year Ended December 31, 2017 Non-life Atrium StarStone Total Net losses paid $ 581,723 $ 55,678 $ 307,793 $ 945,194 Net change in case and LAE reserves (381,053 ) 8,338 31,685 (341,030 ) Net change in IBNR reserves (390,727 ) 7,679 (23,540 ) (406,588 ) Amortization of deferred charges 14,359 — — 14,359 Increase (reduction) in estimates of net ultimate losses (175,698 ) 71,695 315,938 211,935 Reduction in provisions for bad debt (1,536 ) 159 — (1,377 ) Increase (reduction) in provisions for unallocated LAE (53,810 ) 285 (187 ) (53,712 ) Amortization of fair value adjustments 10,114 (2,720 ) (945 ) 6,449 Changes in fair value - fair value option 30,256 — — 30,256 Net incurred losses and LAE $ (190,674 ) $ 69,419 $ 314,806 $ 193,551 Year Ended December 31, 2016 Non-life Run-off Atrium StarStone Total Net losses paid $ 533,806 $ 47,998 $ 251,253 $ 833,057 Net change in case and LAE reserves (608,785 ) (148 ) 73,049 (535,884 ) Net change in IBNR reserves (347,384 ) 13,700 75,643 (258,041 ) Amortization of deferred charges 168,827 — — 168,827 Increase (reduction) in estimates of net ultimate losses (253,536 ) 61,550 399,945 207,959 Reduction in provisions for bad debt (13,822 ) — — (13,822 ) Increase (reduction) in provisions for unallocated LAE (43,955 ) 145 3,543 (40,267 ) Amortization of fair value adjustments 25,432 (3,308 ) (1,895 ) 20,229 Net incurred losses and LAE $ (285,881 ) $ 58,387 $ 401,593 $ 174,099 Year Ended December 31, 2015 Non-life Atrium StarStone Total Net losses paid $ 517,295 $ 52,035 $ 212,559 $ 781,889 Net change in case and LAE reserves (355,335 ) (709 ) 77,219 (278,825 ) Net change in IBNR reserves (364,774 ) 2,844 37,904 (324,026 ) Amortization of deferred charges 15,265 — — 15,265 Increase (reduction) in estimates of net ultimate losses (187,549 ) 54,170 327,682 194,303 Increase in provisions for bad debt (25,271 ) — — (25,271 ) Reduction in provisions for unallocated LAE (62,653 ) (83 ) 3,537 (59,199 ) Amortization of fair value adjustments 4,643 (6,608 ) (3,535 ) (5,500 ) Net incurred losses and LAE $ (270,830 ) $ 47,479 $ 327,684 $ 104,333 Loss Development Information Methodology for Establishing Reserves The liability for losses and LAE includes an amount determined from reported claims and an amount based on historical loss experience and industry statistics for IBNR using a variety of actuarial methods. Our loss reserves cover multiple lines of business, which include workers' compensation, general casualty, asbestos and environmental, marine, aviation and transit, construction defects and other non-life lines of business. Our management, through our loss reserving committees, considers the reasonableness of loss reserves recommended by our actuaries, including actual loss development during the year. Case reserves are recognized for known claims (including the cost of related litigation) when sufficient information has been reported to us to indicate the involvement of a specific insurance policy. We use considerable judgment in estimating losses for reported claims on an individual claim basis based upon our knowledge of the circumstances surrounding the claim, the severity of the injury or damage, the jurisdiction of the occurrence, the potential for ultimate exposure, the type of loss, and our experience with the line of business and policy provisions relating to the particular type of claim. The reserves for unpaid reported losses and LAE are established by management based on reports from brokers, ceding companies and insureds and represent the estimated ultimate cost of events or conditions that have been reported to, or specifically identified, by us. We also consider facts currently known and the current state of the law and coverage litigation. IBNR reserves are established by management based on actuarially determined estimates of ultimate losses and loss expenses. We use generally accepted actuarial methodologies to estimate ultimate losses and LAE and those estimates are reviewed by our management. In addition, the routine settlement of claims, at either below or above the carried advised loss reserve, updates historical loss development information to which actuarial methodologies are applied often, resulting in revised estimates of ultimate liabilities. On an annual basis, independent actuarial firms are retained by management to provide their estimates of ultimate losses and to review the estimates developed by our actuaries. Within the annual loss reserve studies produced by either our actuaries or independent actuaries, exposures for each subsidiary are separated into homogeneous reserving categories for the purpose of estimating IBNR. Each reserving category contains either direct insurance or assumed reinsurance reserves and groups relatively similar types of risks and exposures (for example, asbestos, environmental, casualty, property) and lines of business written (for example, marine, aviation, non-marine). Based on the exposure characteristics and the nature of available data for each individual reserving category, a number of methodologies are applied. Recorded reserves for each category are selected from the actuarial indications produced by the various methodologies after consideration of exposure characteristics, data limitations and strengths and weaknesses of each method applied. This approach to estimating IBNR has been consistently adopted in the annual loss reserve studies for each period presented. The estimation of unpaid claim liabilities at any given point in time is subject to a high degree of uncertainty for a number of reasons. A significant amount of time can lapse between the assumption of risk, the occurrence of a loss event, the reporting of the event to an insurance or reinsurance company and the ultimate payment of the claim on the loss event. Our actuarial methodologies include industry benchmarking which, under certain methodologies, compares the trend of our loss development to that of the industry. To the extent that the trend of our loss development compared to the industry changes in any period, it is likely to have an impact on the estimate of ultimate liabilities. Unpaid claim liabilities for property and casualty exposures in general are impacted by changes in the legal environment, jury awards, medical cost trends and general inflation. Certain estimates for unpaid claim liabilities involve considerable uncertainty due to significant coverage litigation, and it can be unclear whether past claim experience will be representative of future claim experience. Ultimate values for such claims cannot be estimated using reserving techniques that extrapolate losses to an ultimate basis using loss development factors, and the uncertainties surrounding the estimation of unpaid claim liabilities are not likely to be resolved in the near future. In addition, reserves are established to cover loss development related to both known and unasserted claims. Consequently, our subsequent estimates of ultimate losses and LAE, and our liability for losses and LAE, may differ materially from the amounts recorded in the consolidated financial statements. These estimates are reviewed regularly and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments, if any, will be recorded in earnings in the period in which they become known. Prior period development arises from changes to loss estimates recognized in the current year that relate to loss reserves established in previous calendar years. Disclosures of Incurred and Paid Loss Development, IBNR, Claims Counts and Payout Percentages The loss development tables disclosed below, sets forth our historic incurred and paid loss development by accident year through December 31, 2017 , net of reinsurance, as well as the cumulative number of reported claims, IBNR balances, and other supplementary information. With the exception of our Atrium segment, the loss development tables disclosed below are presented by line of business for our Non-life Run-off and StarStone segments as follows: • Non-Life Run-off - The lines of business included within the loss development disclosures below include General Casualty, Workers’ Compensation and Professional Indemnity/Directors & Officers; and • StarStone - All the lines of business related to the StarStone segment have been included within the loss development disclosures below, namely, Casualty, Marine, Property, Aerospace and Workers’ Compensation. The loss development disclosures for our Atrium segment have not been disaggregated further by line of business as the segment comprised only 3% of our total consolidated liability for losses and LAE as at December 31, 2017 and was, therefore, not considered material for further disaggregation. Certain lines of business within our Non-Life Run-off segment were not included within the loss development disclosures presented below due to the following reasons: • The asbestos and environmental lines of business contain exposures which impact accident years older than those presented within the loss development tables disclosed below and have, therefore, not been included within those disclosures. These lines of business cumulatively comprised approximately 41% of our total net liabilities for losses and LAE, before reconciling items, within our Non-life Run-off segment, as at December 31, 2017 ; • The marine, aviation and transit and construction defect lines of business, which each comprised approximately 3% of our total net liabilities for losses and LAE, before reconciling items, within our Non-Life Run-off segment, as at December 31, 2017 were each not considered material for separate disclosure; and • The exposures included within the other category includes losses with several different development patterns that are not individually significant for separate disclosure. For each line of business for which loss development tables have been provided below, the disclosure approach and format adopted reflects the following: • The incurred loss triangle includes both reported case reserves and IBNR liabilities, as well as cumulative paid losses; • Both the incurred and cumulative paid loss triangles include allocated loss adjustment expense (i.e. claims handling costs allocated to specific individual claims) but exclude unallocated loss adjustment expenses (i.e. the costs associated with internal claims staff and third party administrators as well as consultants that cannot be allocated to specific individual claims); • Fair value adjustments arising from the business acquisitions that we have completed as well as the retroactive reinsurance agreements for which we have elected the fair value option are excluded from the incurred loss triangles; • The amounts included within the loss triangles for the years ended December 31, 2008 through to December 31, 2016 , (April 1, 2014 through to December 31, 2016 in the case of StarStone since its date of acquisition), as well as the historical average annual percentage payout ratios as of December 31, 2017 are presented as supplementary information and are therefore unaudited; • All data presented within the loss triangles is net of reinsurance recoveries, excluding provisions for uncollectible reinsurance recoverables; and • The IBNR reserves included within each incurred loss development table by accident year, reflect the net IBNR recorded as of December 31, 2017 , including expected development on reported losses. The historical dollar amounts disclosed within the loss development tables for all lines of business presented below are on a constant-currency basis, which is achieved by using constant foreign exchange rates between periods in the loss triangles, and translating prior period amounts denominated in currencies other than the U.S. dollar, which is our reporting currency, using the closing exchange rates as at December 31, 2017 . The impact of this exchange rate conversion is to show the change between periods exclusive of the effect of exchange rate fluctuations, which would otherwise distort the change in incurred losses and the cash flow patterns associated with those incurred losses shown within the loss development tables disclosed below. The change in incurred losses shown within the loss development tables below will, however, differ from other U.S. GAAP disclosures of incurred current and prior period reserve development amounts, which include the effect of exchange rate fluctuations. The loss development tables disclosed below are presented retrospectively with respect to the acquisitions and retroactive reinsurance agreements that we have completed, where it is practicable to do so. However, where it is not practicable, a prospective approach has been adopted in the presentation of the loss development tables disclosed below as follows: • Acquisitions - The information included within the incurred and paid loss development tables for all the lines of business related to the StarStone segment below have been presented on a prospective basis from the date of our acquisition of StarStone, which was effective on April 1, 2014. Providing pre-acquisition incurred and paid losses by accident year for years prior to 2014 was determined to be impracticable due to significant data limitations. This prospective treatment was also adopted for the disclosures included within our Non-Life Run-off segment with respect to StarStone’s run-off business whose exposures are included within the general casualty and professional indemnity/Directors & Officers lines of business disclosed within our Non-Life Run-off loss development tables below; and • Retroactive reinsurance agreements - For those loss portfolio transfers that we assume through retroactive reinsurance agreements for which we don’t have access to historical loss development information from the ceding entities or where the data is not sufficiently reliable, these have been presented prospectively within the loss development tables disclosed below, from the date that the reinsurance agreements became effective. This prospective treatment, therefore, results in loss development trends within the calendar year that either the business acquisition or retroactive reinsurance agreement is completed, that is not entirely reflective of the actual performance of the acquired business or the retroactive reinsurance agreement. Establishing an estimate for loss reserves requires the incorporation of various assumptions and judgment, therefore, the information contained within the loss development disclosures below only allows readers or users of our consolidated financial statements to understand, at the summary level presented in the development tables, the change over time in our reported incurred loss estimates as well as the nature and patterns of the cash flows associated with those estimates. We, therefore, believe that the information provided within the loss development tables disclosed below is of limited use for independent analysis or application of standard actuarial estimations, and any results obtained from doing so should be interpreted with caution. For a more detailed discussion on how our loss reserve estimates are established, refer to the discussion on “Losses and Loss Adjustment Expenses” within our Critical Accounting Policies. Cumulative Number of Reported Claims Reported claim counts, on a cumulative basis, are provided as supplemental information to each incurred loss development table by accident year. We measure claim frequency information on an individual claim count basis within each of our segments as follows: • Non-Life Run-off - The claim frequency information for the exposures included within our general casualty, workers’ compensation and professional indemnity lines of business includes direct and assumed open and closed claims by accident year at the claimant level. Reported claims that are closed without a payment are included within our cumulative number of reported claims because we typically incur claim adjustment expenses on them prior to their closure. The claim count numbers exclude counts related to claims within policy deductibles where the insured is responsible for the payment of losses within the deductible layer. Individual claim counts related to certain assumed reinsurance contracts such as excess-of-loss and quota share treaties are not available to us, and the losses arising from these treaties have been treated as single claims for the purposes of determining claim counts. Therefore, each treaty year within the reinsurance contract is deemed a single claim because the detailed underlying individual claim information is generally not reported to us by our cedents; and • StarStone and Atrium - The claim frequency information is determined at the claimant level for the exposures within the lines of business related to these segments. Our claims system assigns a unique claim identifier to each reported claim we receive. Each unique claim identifier is deemed to be a single claim, irrespective of whether the claim remains open or has been closed with or without payment. For certain insurance facilities and business produced or managed by managing general agents, coverholders and third party administrators where the underlying claims data is reported to us in an aggregated format, the information necessary to provide cumulative claims frequency is not available. In such cases, we typically record a “block” claim in our system. This also applies to a small amount of assumed reinsurance business that we write where, similarly, the underlying claims data is reported to us in an aggregated format. In such instances, each assumed reinsurance contract is deemed a single claim. The cumulative number of reported claims for our Atrium segment includes all claim counts for Syndicate 609. Our Atrium segment represents our 25% share of Syndicate 609's underwriting capacity and capital, however, the claims count is the same whether viewed at the 100% Syndicate level or for our 25% share. Our reported claim frequency information is subject to the following inherent limitations when analyzing our loss experience and severity: • Claim counts are presented only on a reported and not on an ultimate basis. Therefore, reported claim counts include open claims which have outstanding reserves but exclude IBNR claims. As such the reported claims are consistent with reported losses, which can be calculated by subtracting IBNR losses from incurred losses. However, the reported claim counts are inconsistent with the losses in the incurred losses triangles, which include IBNR losses, and to losses in the paid loss triangles, which exclude outstanding reserves; • Reported claim counts have not been adjusted for ceded reinsurance, which may distort any measures of frequency or severity; • For lines of business that have a mix of primary and excess layer exposures, such as our general casualty and workers’ compensation lines of business, the reported claim counts may fluctuate from period to period between exposure layers, thereby distorting any measure of frequency and severity; and • The use of our reported claim frequency information to project ultimate loss payouts by disaggregated disclosure category or line of business may not be as meaningful as claim count information related to individual contracts at a more granular level. Non-Life Run-off Segment The table below provides a reconciliation of the beginning and ending reserves for losses and LAE for the years ended December 31, 2017 , 2016 and 2015 for the Non-life Run-off segment: 2017 2016 2015 Balance as at January 1 $ 4,716,363 $ 4,585,454 $ 3,435,010 Less: reinsurance reserves recoverable 1,000,953 1,034,747 800,709 Less: deferred charges on retroactive reinsurance 94,551 255,911 — Net balance as at January 1 3,620,859 3,294,796 2,634,301 Net incurred losses and LAE: Current period 5,866 5,829 39,924 Prior periods (196,540 ) (291,710 ) (310,754 ) Total net incurred losses and LAE (190,674 ) (285,881 ) (270,830 ) Net paid losses: Current period (2,835 ) (3,869 ) (16,049 ) Prior periods (578,888 ) (529,937 ) (501,246 ) Total net paid losses (581,723 ) (533,806 ) (517,295 ) Effect of exchange rate movement 138,772 (27,478 ) (42,636 ) Acquired on purchase of subsidiaries 10,251 10,019 878,815 Assumed business 1,494,310 1,340,444 612,441 Ceded business — (177,235 ) — Net balance as at December 31 4,491,795 3,620,859 3,294,796 Plus: reinsurance reserves recoverable 1,377,485 1,000,953 1,034,747 Plus: deferred charges on retroactive reinsurance 80,192 94,551 255,911 Balance as at December 31 $ 5,949,472 $ 4,716,363 $ 4,585,454 Net incurred losses and LAE in the Non-life Run-off segment for the years ended December 31, 2017 , 2016 and 2015 were as follows: 2017 2016 2015 Prior Period Current Period Total Prior Period Current Period Total Prior Period Current Period Total Net losses paid $ 578,888 $ 2,835 $ 581,723 $ 529,937 $ 3,869 $ 533,806 $ 501,246 $ 16,049 $ 517,295 Net change in case and LAE reserves (381,450 ) 397 (381,053 ) (608,168 ) (617 ) (608,785 ) (366,262 ) 10,927 (355,335 ) Net change in IBNR reserves (393,100 ) 2,373 (390,727 ) (349,726 ) 2,342 (347,384 ) (377,722 ) 12,948 (364,774 ) Amortization of deferred charges 14,359 — 14,359 168,827 — 168,827 15,265 — 15,265 Increase (reduction) in estimates of net ultimate losses (181,303 ) 5,605 (175,698 ) (259,130 ) 5,594 (253,536 ) (227,473 ) 39,924 (187,549 ) Reduction in provisions for bad debt (1,536 ) — (1,536 ) (13,822 ) — (13,822 ) (25,271 ) — (25,271 ) Increase (reduction) in provisions for unallocated LAE (54,071 ) 261 (53,810 ) (44,190 ) 235 (43,955 ) (62,653 ) — (62,653 ) Amortization of fair value adjustments 10,114 — 10,114 25,432 — 25,432 4,643 — 4,643 Changes in fair value - fair value option 30,256 — 30,256 — — — — — — Net incurred losses and LAE $ (196,540 ) $ 5,866 $ (190,674 ) $ (291,710 ) $ 5,829 $ (285,881 ) $ (310,754 ) $ 39,924 $ (270,830 ) Net change in case and LAE reserves comprises the movement during the year in specific case reserve liabilities as a result of claims settlements or changes advised to us by our policyholders and attorneys, less changes in case reserves recoverable advised by us to our reinsurers as a result of the settlement or movement of assumed claims. Net change in IBNR represents the gross change in our actuarial estimates of IBNR, less amounts recoverable. Year Ended December 31, 2017 The net reduction in incurred losses and LAE for the year ended December 31, 2017 of $190.7 million included net incurred losses a nd LAE of $5.9 million related to current period net earned premium, primarily for the portion of the run-off business acquired with Sussex. Excluding current period net incurred losses and LAE of $5.9 million , net incurred losses and LAE liabilities relating to prior periods were reduced by $196.5 million , which was attributable to a reduction in estimates of net ultimate losses of $181.3 million , a reduction in provisions for bad debt of $1.5 million and a reduction in provisions for unallocated LAE of $54.1 million , relating to 2017 run-off activity, partially offset by amortization of fair value adjustments over the estimated payout period relating to companies acquired amounting to $10.1 million and a change in fair value of $30.3 million related to our assumed retroactive reinsurance agreements with RSA and QBE completed during the period and for which we have elected the fair value option. The reduction of estimates in net ultimate losses for the year ended December 31, 2017 was reduced by amortization of the deferred charge of $14.4 million . The reduction in estimates of net ultimate losses relating to prior periods of $181.3 million comprised reductions in IBNR reserves of $393.1 million , partially offset by net incurred loss development of $211.8 million , which includes amortization of deferred charges of $14.4 million . The decrease in the estimate of net IBNR reserves of $393.1 million (compared to $349.7 million during the year ended December 31, 2016 ), was comprised of a decrease of $70.0 million relating to asbestos liabilities (compared to an increase of $39.4 million in 2016 ), a decrease of $7.5 million relating to environmental liabilities (compared to an increase $35.5 million in 2016 ), a decrease of $7.2 million relating to general casualty liabilities (compared to $0.8 million in 2016 ), a decrease of $156.2 million relating to workers' compensation liabilities (compared to $333.2 million in 2016 ) and a decrease of $152.2 million relating to all other remaining liabilities (compared to $90.6 million in 2016 ). The reduction in net IBNR reserves of $393.1 million relating to prior periods was a result of the application, on a basis consistent with the assumptions applied in the prior period, of our actuarial methodologies to revised historical loss development data, following 59 commutations and policy buy-backs, to estimate loss reserves required to cover liabilities for unpaid losses and LAE relating to non-commuted exposures. The prior period estimate of net IBNR reserves was reduced as a result of the combined impact on all classes of business of loss development activity during 2017 , including commutations and the favorable trend of loss development related to non-commuted policies compared to prior forecasts. The net incurred loss development resulting from settlement of net advised case and LAE reserves of $381.5 million for net paid losses of $578.9 million related to the settlement of non-commuted losses in the year and 59 commutations and policy buy-backs of assumed and ceded exposures. Net advised case and LAE reserves settled by way of commutation and policy buyback during the year ended December 31, 2017 amounted to $7.4 million (comprising $23.2 million of assumed case reserves and LAE reserves, partially offset by $15.8 million of ceded incurred reinsurance recoverable case reserves). The reduction in provisions for bad debt of $1.5 million was a result of the favorable resolution of contractual disputes with reinsurers, the reduction in bad debt provisions for insolvent reinsurers as a result of distributions received and the reduction of specific provisions held for potential disputes with reinsurers. Year Ended December 31, 2016 The net reduction in incurred losses and LAE for the year ended December 31, 2016 of $285.9 million included current period net incurred losses and LAE of $5.8 million related to current period net earned premium of $7.1 million (primarily for the portion of the run-off business acquired with Sussex). Excluding current period net losses and LAE of $5.8 million , net incurred losses and LAE liabilities relating to prior periods were reduced by $291.7 million , which was attributable to a reduction in estimates of net ultimate losses of $259.1 million , reduction in provisions for bad debt of $13.8 million and a reduction in provision for unallocated LAE of $44.2 million , relating to 2016 run-off activity, partially offset by amortization of fair value adjustments over the estimated payout period relating to companies acquired amounting to $25.4 million . The reduction in estimates of net ultimate losses relating to prior periods of $259.1 million comprised reductions in IBNR reserves of $349.7 million partially offset by net incurred loss development of $90.6 million , which includes amortization of deferred charges of $168.8 million . The decrease in the estimate of net IBNR reserves of $349.7 million (compared to $377.7 million during the year ended December 31, 2015 ), was comprised of an increase of $39.4 million relating to asbestos liabilities (compared to a decrease of $32.0 million in 2015 ), an increase of $35.5 million relating to environmental liabilities (compared to a decrease of $1.6 million in 2015 ), a decrease of $0.8 million relating to general casualty liabilities (compared to $3.0 million in 2015 ), a decrease of $333.2 million relating to workers' compensation liabilities (compared to $243.4 million in 2015 ) and a decrease of $90.6 million relating to all other remaining liabilities (compared to $97.7 million in 2015 ). The reduction in net IBNR reserves of $349.7 million relating to prior periods was a result of the application, on a basis consistent with the assumptions applied in the prior period, o f our actuarial methodologies to revised historical loss development data, following 56 commutations and policy buy-backs, to estimate loss reserves required to cover liabilities for unpaid losses and LAE relating to non-commuted exposures. The prior period estimate of net IBNR reserves was reduced as a result of the combined impact on all classes of business of loss development activity during 2016 , including commutations and the favorable trend of loss development related to non-commuted policies compared to prior forecasts. The net incurred loss development resulting from settlement of net advised case and LAE reserves of $608.2 million for net paid losses of $529.9 million related to the settlement of non-commuted losses in the year and 56 commutations and policy buy-backs of assumed and ceded exposures. Net advised case a

Premiums Written and Earned

Premiums Written and Earned	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
PREMIUMS WRITTEN AND EARNED	$1 million 322,722 16,631 144,336 — 483,689 24.0 % 301,856 4,827 152,341 — 459,024 31.4 % Other reinsurers < $1 million 16,959 1,027 2,603 16 20,605 1.0 % 9,183 856 4,119 959 15,117 1.0 % Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 100.0 % $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743 100.0 % Six of the top ten external reinsurers, as at December 31, 2017 and 2016 , were all rated A- or better. The remaining four non-rated reinsurers, from which $687.6 million was recoverable as at December 31, 2017 ( December 31, 2016 : $512.2 million recoverable from four non-rated reinsurers), including KayleRe Ltd., have provided security in the form of pledged assets in trust, letters of credit issued to us, or funds withheld in the full amount of the recoverable. As at December 31, 2017 , reinsurance balances recoverable of $357.4 million related to KaylaRe Ltd. ( December 31, 2016 : $242.1 million ) and $320.0 million related to Hannover Ruck SE ( December 31, 2016 : $67.3 million ), both of which represent 10% or more of total reinsurance balances recoverable. KaylaRe Ltd. is not rated but is an affiliated company partly owned by Enstar, as described in Note 21 - "Related Party Transactions" , and security is provided in the form of funds withheld. Hannover Ruck SE is rated AA- by Standard & Poor's and A+ by A.M. Best. Provisions for Uncollectible Reinsurance Recoverables We evaluate and monitor concentration of credit risk among our reinsurers. Provisions are made for amounts considered potentially uncollectible. The following table shows our reinsurance balances recoverable by rating of reinsurer and our provisions for uncollectible reinsurance balances recoverable ("provisions for bad debt") as at December 31, 2017 and 2016 . The provisions for bad debt all relate to the Non-life Run-off segment. 2017 2016 Gross Provisions for Bad Debt Net Provisions as a Gross Provisions for Bad Debt Net Provisions as a Reinsurers rated A- or above $ 1,252,887 $ 51,115 $ 1,201,772 4.1 % $ 892,776 $ 35,184 $ 857,592 3.9 % Reinsurers rated below A-, secured 771,097 — 771,097 — % 544,894 — 544,894 — % Reinsurers rated below A-, unsecured 162,259 114,098 48,161 70.3 % 197,589 139,332 58,257 70.5 % Total $ 2,186,243 $ 165,213 $ 2,021,030 7.6 % $ 1,635,259 $ 174,516 $ 1,460,743 10.7 % 13. PREMIUMS WRITTEN AND EARNED The following tables provide a summary of net premiums written and earned for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Premiums Written Premiums Earned Premiums Written Premiums Earned Premiums Written Premiums Earned Non-life Run-off Gross $ 14,102 $ 23,950 $ 17,316 $ 25,989 $ 38,704 $ 116,494 Ceded (7,620 ) (9,788 ) (8,114 ) (9,234 ) (16,110 ) (72,125 ) Net $ 6,482 $ 14,162 $ 9,202 $ 16,755 $ 22,594 $ 44,369 Atrium Gross $ 153,472 $ 152,278 $ 143,170 $ 140,438 $ 149,082 $ 149,310 Ceded (19,258 ) (17,531 ) (2,733 ) (16,022 ) (14,502 ) (14,635 ) Net $ 134,214 $ 134,747 $ 140,437 $ 124,416 $ 134,580 $ 134,675 StarStone Gross $ 895,160 $ 865,159 $ 854,699 $ 830,186 $ 824,714 $ 769,875 Ceded (430,259 ) (405,756 ) (206,663 ) (153,578 ) (196,287 ) (196,729 ) Net $ 464,901 $ 459,403 $ 648,036 $ 676,608 $ 628,427 $ 573,146 Other Gross $ 5,719 $ 5,900 $ 7,157 $ 7,220 $ 2,883 $ 2,884 Ceded (926 ) (1,091 ) (896 ) (1,485 ) (1,330 ) (1,330 ) Net $ 4,793 $ 4,809 $ 6,261 $ 5,735 $ 1,553 $ 1,554 Total Gross $ 1,068,453 $ 1,047,287 $ 1,022,342 $ 1,003,833 $ 1,015,383 $ 1,038,563 Ceded (458,063 ) (434,166 ) (218,406 ) (180,319 ) (228,229 ) (284,819 ) Net $ 610,390 $ 613,121 $ 803,936 $ 823,514 $ 787,154 $ 753,744" id="sjs-B4">10. REINSURANCE BALANCES RECOVERABLE The following table provides the total reinsurance balances recoverable as at December 31, 2017 and 2016 : 2017 Non-life Run-off Atrium StarStone Other Total Recoverable from reinsurers on unpaid: Outstanding losses $ 932,284 $ 7,472 $ 211,650 $ 16 $ 1,151,422 IBNR 590,154 31,476 242,620 — 864,250 Fair value adjustments (12,970 ) 1,583 (2,253 ) — (13,640 ) Fair value adjustments - fair value option (131,983 ) — — — (131,983 ) Total reinsurance reserves recoverable 1,377,485 40,531 452,017 16 1,870,049 Paid losses recoverable 128,253 (451 ) 23,179 — 150,981 $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 Reconciliation to Consolidated Balance Sheet: Reinsurance balances recoverable $ 963,514 $ 40,080 $ 475,196 $ 16 $ 1,478,806 Reinsurance balances recoverable - fair value option 542,224 — — — 542,224 Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 2016 Non-life Run-off Atrium StarStone Other Total Recoverable from reinsurers on unpaid: Outstanding losses $ 621,288 $ 6,438 $ 182,478 $ 190 $ 810,394 IBNR 393,550 21,753 178,259 — 593,562 Fair value adjustments (13,885 ) 1,818 (3,506 ) — (15,573 ) Total reinsurance reserves recoverable 1,000,953 30,009 357,231 190 1,388,383 Paid losses recoverable 47,160 (1,081 ) 25,512 769 72,360 $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743 Our insurance and reinsurance run-off subsidiaries and assumed portfolios, prior to acquisition, used retrocessional agreements to reduce their exposure to the risk of insurance and reinsurance assumed. On an annual basis, both Atrium and StarStone purchase a tailored outwards reinsurance program designed to manage their risk profiles. The majority of Atrium’s and StarStone's third-party reinsurance cover is with highly rated reinsurers or is collateralized by pledged assets or letters of credit. The fair value adjustments, determined on acquisition of insurance and reinsurance subsidiaries, are based on the estimated timing of loss and LAE recoveries and an assumed interest rate equivalent to a risk free rate for securities with similar duration to the acquired reinsurance balances recoverable plus a spread to reflect credit risk, and are amortized over the estimated recovery period, as adjusted for accelerations in timing of payments as a result of commutation settlements. The determination of the fair value adjustments on the retroactive reinsurance contracts for which we have elected the fair value option is described in Note 8 - "Fair Value Measurements" . As of December 31, 2017 and 2016 , we had reinsurance balances recoverable of approximately $2.0 billion and $1.5 billion , respectively. The increase of $560.3 million in reinsurance balances recoverable was primarily a result of the QBE and RSA reinsurance transactions, which closed in the first quarter of 2017, and the impact of the recent hurricane losses on Atrium and StarStone, partially offset by reserve reductions, commutations and cash collections made during the year ended December 31, 2017 in our Non-life Run-off segment. Top Ten Reinsurers December 31, 2017 December 31, 2016 Non-life Atrium StarStone Other Total % of Non-life Atrium StarStone Other Total % of Top ten reinsurers $ 1,166,057 $ 22,422 $ 328,257 $ — $ 1,516,736 75.0 % $ 737,074 $ 23,245 $ 226,283 $ — $ 986,602 67.6 % Other reinsurers > $1 million 322,722 16,631 144,336 — 483,689 24.0 % 301,856 4,827 152,341 — 459,024 31.4 % Other reinsurers < $1 million 16,959 1,027 2,603 16 20,605 1.0 % 9,183 856 4,119 959 15,117 1.0 % Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 100.0 % $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743 100.0 % Six of the top ten external reinsurers, as at December 31, 2017 and 2016 , were all rated A- or better. The remaining four non-rated reinsurers, from which $687.6 million was recoverable as at December 31, 2017 ( December 31, 2016 : $512.2 million recoverable from four non-rated reinsurers), including KayleRe Ltd., have provided security in the form of pledged assets in trust, letters of credit issued to us, or funds withheld in the full amount of the recoverable. As at December 31, 2017 , reinsurance balances recoverable of $357.4 million related to KaylaRe Ltd. ( December 31, 2016 : $242.1 million ) and $320.0 million related to Hannover Ruck SE ( December 31, 2016 : $67.3 million ), both of which represent 10% or more of total reinsurance balances recoverable. KaylaRe Ltd. is not rated but is an affiliated company partly owned by Enstar, as described in Note 21 - "Related Party Transactions" , and security is provided in the form of funds withheld. Hannover Ruck SE is rated AA- by Standard & Poor's and A+ by A.M. Best. Provisions for Uncollectible Reinsurance Recoverables We evaluate and monitor concentration of credit risk among our reinsurers. Provisions are made for amounts considered potentially uncollectible. The following table shows our reinsurance balances recoverable by rating of reinsurer and our provisions for uncollectible reinsurance balances recoverable ("provisions for bad debt") as at December 31, 2017 and 2016 . The provisions for bad debt all relate to the Non-life Run-off segment. 2017 2016 Gross Provisions for Bad Debt Net Provisions as a Gross Provisions for Bad Debt Net Provisions as a Reinsurers rated A- or above $ 1,252,887 $ 51,115 $ 1,201,772 4.1 % $ 892,776 $ 35,184 $ 857,592 3.9 % Reinsurers rated below A-, secured 771,097 — 771,097 — % 544,894 — 544,894 — % Reinsurers rated below A-, unsecured 162,259 114,098 48,161 70.3 % 197,589 139,332 58,257 70.5 % Total $ 2,186,243 $ 165,213 $ 2,021,030 7.6 % $ 1,635,259 $ 174,516 $ 1,460,743 10.7 % 13. PREMIUMS WRITTEN AND EARNED The following tables provide a summary of net premiums written and earned for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Premiums Written Premiums Earned Premiums Written Premiums Earned Premiums Written Premiums Earned Non-life Run-off Gross $ 14,102 $ 23,950 $ 17,316 $ 25,989 $ 38,704 $ 116,494 Ceded (7,620 ) (9,788 ) (8,114 ) (9,234 ) (16,110 ) (72,125 ) Net $ 6,482 $ 14,162 $ 9,202 $ 16,755 $ 22,594 $ 44,369 Atrium Gross $ 153,472 $ 152,278 $ 143,170 $ 140,438 $ 149,082 $ 149,310 Ceded (19,258 ) (17,531 ) (2,733 ) (16,022 ) (14,502 ) (14,635 ) Net $ 134,214 $ 134,747 $ 140,437 $ 124,416 $ 134,580 $ 134,675 StarStone Gross $ 895,160 $ 865,159 $ 854,699 $ 830,186 $ 824,714 $ 769,875 Ceded (430,259 ) (405,756 ) (206,663 ) (153,578 ) (196,287 ) (196,729 ) Net $ 464,901 $ 459,403 $ 648,036 $ 676,608 $ 628,427 $ 573,146 Other Gross $ 5,719 $ 5,900 $ 7,157 $ 7,220 $ 2,883 $ 2,884 Ceded (926 ) (1,091 ) (896 ) (1,485 ) (1,330 ) (1,330 ) Net $ 4,793 $ 4,809 $ 6,261 $ 5,735 $ 1,553 $ 1,554 Total Gross $ 1,068,453 $ 1,047,287 $ 1,022,342 $ 1,003,833 $ 1,015,383 $ 1,038,563 Ceded (458,063 ) (434,166 ) (218,406 ) (180,319 ) (228,229 ) (284,819 ) Net $ 610,390 $ 613,121 $ 803,936 $ 823,514 $ 787,154 $ 753,744

Goodwill, Intangible Assets and

Goodwill, Intangible Assets and Deferred Charges	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill, Intangible Assets and Deferred Charges	14. GOODWILL, INTANGIBLE ASSETS AND DEFERRED CHARGES The following tables present a reconciliation of the beginning and ending goodwill, intangible assets and deferred charges for the years ended December 31, 2017 and 2016 : 2017 Goodwill Intangible assets with a definite life - Other Intangible assets with an indefinite life Total Intangible assets with a definite life - FVA Other assets - Deferred Charges Balance as at January 1, 2017 $ 73,071 $ 24,753 $ 87,031 $ 184,855 $ 145,158 $ 94,551 Acquired during the year — — — — 958 — Amortization — (4,266 ) — (4,266 ) (5,723 ) (14,359 ) Balance as at December 31, 2017 $ 73,071 $ 20,487 $ 87,031 $ 180,589 $ 140,393 $ 80,192 2016 Goodwill Intangible assets with a definite life - Other Intangible assets with an indefinite life Total Intangible assets with a definite life - FVA Other assets - Deferred Charges Balance as at January 1, 2016 $ 73,071 $ 31,202 $ 87,031 $ 191,304 $ 127,170 $ 255,911 Acquired during the year — — — — 37,005 7,467 Amortization — (6,449 ) — (6,449 ) (19,017 ) (168,827 ) Balance as at December 31, 2016 $ 73,071 $ 24,753 $ 87,031 $ 184,855 $ 145,158 $ 94,551 Goodwill as at December 31, 2017 and 2016 , related to Non-life Run-off, Atrium and StarStone, was $21.2 million , $38.9 million and $13.0 million , respectively. For the year ended December 31, 2017 , we completed our assessment for impairment of goodwill and concluded that there had been no impairment of our carried goodwill amount. Intangible assets with a definite life - Other includes the distribution channel, Lloyd’s capacity, technology and brand related to our acquisitions of Atrium and StarStone. These assets are amortized on a straight-line basis over a period ranging from four to fifteen years. Intangible asset amortization for the years ended December 31, 2017 , 2016 and 2015 was $4.3 million , $6.4 million and $9.8 million , respectively. Amortization for the year ended December 31, 2015 included an impairment charge of $4.0 million for the Torus brand in relation to the StarStone rebranding exercise. Intangible assets with an indefinite life includes assets associated with the Lloyd’s syndicate capacity for StarStone and Atrium, StarStone's U.S. insurance licenses, and Atrium’s management contract with Syndicate 609 in relation to underwriting, actuarial and support services it provides. Intangible assets with a definite life - fair value adjustments ("FVA") relates to outstanding losses and LAE, unearned premiums, other liabilities, reinsurance recoverables and other assets from acquisitions of companies. These are included as a component of each balance sheet item. FVA are amortized in proportion to the recovery period for outstanding losses and LAE and reinsurance recoverables and as the unearned premiums expire for business in-force as of the acquisition date. Intangible asset amortization (accretion) of fair value adjustments for the years ended December 31, 2017 , 2016 and 2015 was $5.7 million , $19.0 million and $(5.6) million , respectively. The FVA acquired during the year ended December 31, 2017 related to the acquisition of some small U.S. companies. Other assets - deferred charges relate to retroactive reinsurance policies providing indemnification of losses and LAE with respect to past loss events. For insurance and reinsurance contracts for which we do not elect the fair value option, a deferred charge asset is recorded for the excess, if any, of the estimated ultimate losses payable over the premiums received at the inception of the contract. These amounts relate to the transactions with Voya Financial, Sun Life and Coca-Cola, described in Note 4 - "Significant New Business" . Amortization of the deferred charges included $14.4 million and $130.2 million related to a reduction in the liability for losses and LAE for the years ended December 31, 2017 and December 31, 2016, respectively, and $ nil and $38.6 million primarily related to a change in the expected return on the underlying assets for the years ended December 31, 2017 and 2016, respectively. The gross carrying value, accumulated amortization and net carrying value of intangible assets by type and deferred charge at December 31, 2017 and 2016 were as follows: 2017 2016 Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Intangible assets with a definite life: Fair value adjustments: Losses and LAE liabilities $ 462,455 $ (345,449 ) $ 117,006 $ 458,202 $ (334,475 ) $ 123,727 Reinsurance balances recoverable (179,219 ) 165,579 (13,640 ) (175,924 ) 160,350 (15,574 ) Other Assets (48,840 ) 440 (48,400 ) (48,840 ) — (48,840 ) Other Liabilities 85,845 (418 ) 85,427 85,845 — 85,845 Total $ 320,241 $ (179,848 ) $ 140,393 $ 319,283 $ (174,125 ) $ 145,158 Other: Distribution channel $ 20,000 $ (5,444 ) $ 14,556 $ 20,000 $ (4,111 ) $ 15,889 Technology 15,000 (13,210 ) 1,790 15,000 (10,978 ) 4,022 Brand 7,000 (2,859 ) 4,141 7,000 (2,158 ) 4,842 Total $ 42,000 $ (21,513 ) $ 20,487 $ 42,000 $ (17,247 ) $ 24,753 Intangible assets with an indefinite life: Lloyd’s syndicate capacity $ 37,031 $ — $ 37,031 $ 37,031 $ — $ 37,031 Licenses 19,900 — 19,900 19,900 — 19,900 Management contract 30,100 — 30,100 30,100 — 30,100 Total $ 87,031 $ — $ 87,031 $ 87,031 $ — $ 87,031 Deferred charges on retroactive reinsurance $ 278,643 $ (198,451 ) $ 80,192 $ 278,643 $ (184,092 ) $ 94,551 The table above excludes fair value adjustments of $ 2.7 million and $46.5 million as at December 31, 2017 and 2016 , respectively, relating to policy benefits for life and annuity contracts relating to our Pavonia operations which are classified as held-for-sale. Amortization of fair value adjustments relating to Pavonia were $6.1 million and $ 7.0 million during the years ended December 31, 2017 and 2016 , respectively. The estimated amortization expense for each of the five succeeding fiscal years related to our intangible assets with a definite life is as follows: Year Non-life Run-off Atrium StarStone Total 2018 $ 8,082 $ (463 ) $ 255 $ 7,874 2019 $ 7,927 $ (69 ) $ (401 ) $ 7,457 2020 $ 7,634 $ 760 $ (246 ) $ 8,148 2021 $ 7,169 $ 1,254 $ (166 ) $ 8,257 2022 $ 6,559 $ 1,506 $ (108 ) $ 7,957

Debt Obligations

Debt Obligations	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt Obligations	15. DEBT OBLIGATIONS We utilize debt facilities primarily for acquisitions and, from time to time, for general corporate purposes. Under these facilities, debt obligations as of December 31, 2017 and 2016 were as follows: Facility Origination Date Term 2017 2016 Senior Notes March 10, 2017 5 years $ 350,000 $ — Unamortized debt issuance costs (2,484 ) — Total Senior Notes 347,516 — EGL Revolving Credit Facility September 16, 2014 5 years 225,110 535,103 Sussex Facility December 24, 2014 4 years — 63,500 EGL Term Loan Facility November 18, 2016 3 years 74,063 75,000 Total debt obligations $ 646,689 $ 673,603 During the year ended December 31, 2017 , we utilized $874.1 million and repaid $912.1 million under our facilities. The facilities were primarily utilized for funding significant new business as described in Note 4 - "Significant New Business" . For the years ended December 31, 2017 , 2016 and 2015 , interest expense was $26.0 million , $20.3 million and $19.3 million , respectively, on our loan facilities. Senior Notes On March 10, 2017, we issued Senior Notes (the "Notes") for an aggregate principal amount of $350.0 million . The Notes pay 4.5% interest semi-annually and mature on March 10, 2022. The Notes are unsecured and unsubordinated obligations that rank equal to any of our other unsecured and unsubordinated obligations, senior to any future obligations that are expressly subordinated to the Notes, effectively subordinate to any of our secured indebtedness to the extent of the value of the assets securing such indebtedness, and structurally subordinate to all liabilities of our subsidiaries. The Notes are rated BBB- and are redeemable at our option on a make whole basis at any time prior to the date that is one month prior to the maturity of the Notes. On or after the date that is one month prior to the maturity of the Notes, the Notes are redeemable at a redemption price equal to 100% of the principal amount of the Notes to be redeemed. We incurred costs of $2.9 million in issuing the Notes. These costs included underwriters’ fees, legal and accounting fees, and other fees, and are capitalized and presented as a direct deduction from the principal amount of debt obligations in the consolidated balance sheets. These costs are amortized over the term of the Notes and are included in interest expense in our consolidated statements of earnings. EGL Revolving Credit Facility This 5 -year revolving credit facility, originated on September 16, 2014, and most recently amended on March 20, 2017 is among the Parent Company and certain of its subsidiaries, as borrowers and as guarantors, and various financial institutions. We are permitted to borrow up to an aggregate of $831.3 million . The individual outstanding loans under this facility are short-term loans, and the fair values of these loans approximate their book values. As of December 31, 2017 , there was $607.2 million of available unutilized capacity under this facility. Subsequent to December 31, 2017 , we utilized $307.4 million and repaid $132.0 million bringing the available unutilized capacity under this facility to $431.8 million . Interest is payable at least every six months at a LIBOR rate plus a margin and utilization fee as set forth in the credit facility agreement. The margin could vary based upon any change in our long term senior unsecured debt rating assigned by Standard & Poor’s Ratings Services or Fitch Ratings Ltd. We also pay a commitment fee for any unutilized portion of the facility. In the event of default, the interest rate may increase and the agent may cancel lender commitments and may demand early repayment. Financial and business covenants imposed on us include certain limitations on mergers and consolidations, acquisitions, indebtedness and guarantees, restrictions as to dispositions of stock and assets, and limitations on liens. Generally, the financial covenants require us to maintain a gearing ratio of consolidated indebtedness to total capitalization of not greater than 0.35 to 1.0 and to maintain a consolidated tangible net worth of not less than the aggregate of (i) $1.5 billion , (ii) 50% of positive net income since June 30, 2014, and (iii) 75% of the proceeds of any common stock issuance. In addition, the weighted-average credit rating of our cash and fixed maturity investments must be "BBB" or greater at all times. We are in compl iance with the covenants of the EGL Revolving Credit Facility. As at December 31, 2017 and December 31, 2016 , there were borrowings of €50.0 million (approximately $60.1 million ) and €75.0 million (approximately $88.5 million ), respectively, under the facility that were designated as non-derivative hedges of our net investment in certain subsidiaries whose functional currency is denominated in Euros. The foreign exchange effect of revaluing these Euro borrowings resulted in a loss of $9.4 million and a gain of $6.0 million recognized in the currency translation adjustment within accumulated other comprehensive income (loss) for the years ended December 31, 2017 and 2016 , respectively. These amounts were offset against equivalent amounts recognized upon the translation of those subsidiaries' financial statements from their Euro-denominated functional currency into U.S. dollars. There were no ineffective portions of the net investment hedge during the year ended December 31, 2017 and 2016 . During the year ended December 31, 2017 , we repaid €25.0 million (approximately $29.5 million ) of the non-derivative hedge and reclassified the related foreign exchange losses of $1.1 million previously deferred in CTA within accumulated other comprehensive income (loss) into earnings. Sussex Facility On December 24, 2014, we entered into a four -year term loan (the "Sussex Facility", formerly called the Companion Facility) with two financial institutions. This facility was fully utilized to borrow $109.0 million to fund 50% of the consideration payable for the acquisition of Sussex, which was completed on January 27, 2015 . We repaid the outstanding principal in June 2017 and terminated the facility. EGL Term Loan Facility On November 18, 2016, we entered into and fully utilized a three -year $75.0 million unsecured term loan (the "EGL Term Loan Facility"). During the year ended December 31, 2017 , we repaid $0.9 million of the outstanding principal under this facility. Interest is payable at least every three months at either (i) a base rate plus a margin or (ii) a LIBOR rate plus a margin as set forth in the loan agreement. In the event of default, an interest rate increase and early repayment may be demanded. Financial and business covenants imposed on us include certain limitations on mergers, consolidations, acquisitions, indebtedness and guarantees, restrictions on dividends, and limitations on liens. We are also required to maintain an average credit quality in our fixed income investment portfolio of BBB or its equivalent, and certain of our subsidiaries are restricted from engaging in certain derivative transactions without lender consent. The covenants require our regulated insurance subsidiaries to maintain capital resources of at least 1.1 times the amount required to meet solvency requirements.

Noncontrolling Interest

Noncontrolling Interest	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Noncontrolling Interest	16. NONCONTROLLING INTEREST Redeemable Noncontrolling Interest Redeemable noncontrolling interest ("RNCI") as of December 31, 2017 comprises the ownership interest held by Trident ( 39.3% ) and Dowling ( 1.7% ) in North Bay Holdings Limited ("North Bay"). On December 23, 2015, we completed a corporate reorganization of certain of our subsidiary holding companies. Following the reorganization, StarStone Holdings, Northshore and all of the interests in a segregated cell of one of our non-life run-off subsidiaries that reinsured all of StarStone’s non-life run-off reserves with effect from January 1, 2014 are owned by a common parent, North Bay. Northshore owns 100% of Atrium and Arden. StarStone Holdings owns 100% of StarStone. The following is a reconciliation of the beginning and ending carrying amount of the equity attributable to the RNCI for the years ended December 31, 2017 and 2016 : 2017 2016 Balance at beginning of year $ 454,522 $ 417,663 Dividends paid (27,458 ) — Net earnings attributable to RNCI 19,619 40,639 Accumulated other comprehensive income attributable to RNCI 1,945 651 Change in redemption value of RNCI 30,978 (4,431 ) Balance at end of year $ 479,606 $ 454,522 We carried the RNCI at its estimated redemption value, which is fair value, as of December 31, 2017 . The increase was primarily attributable to an increase in comparable company market valuations, an increase in the net assets due to net earnings, partially offset by a reduction in net assets due to the distribution of dividends during the year ended December 31, 2017 . Refer to Note 2 - "Significant Accounting Policies" , Note 21 - "Related Party Transactions" and Note 23 - "Commitments and Contingencies" for additional information regarding RNCI. Noncontrolling Interest As of December 31, 2017 , we had $9.3 million of noncontrolling interest ("NCI") primarily related to an external interest in one of our non-life run-off subsidiaries. A reconciliation of the beginning and ending carrying amount of the equity attributable to NCI is included in the Consolidated Statement of Changes in Shareholders Equity.

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Share Capital	17. SHARE CAPITAL As at December 31, 2017 and 2016 , the authorized share capital was 111,000,000 ordinary shares ("Voting Ordinary Shares") and non-voting convertible ordinary shares ("Non-Voting Ordinary Shares"), each of par value $1.00 per share, and 45,000,000 preference shares of par value $1.00 per share. The Voting Ordinary Shares are listed and trade on the NASDAQ Global Select Market. Each Voting Ordinary Share entitles the holder thereof to one vote. In accordance with the bye-laws, any U.S. shareholder or direct foreign shareholder group whose shares constitute 9.5% or more of the voting power of the Voting Ordinary Shares is entitled to less than one vote for each Voting Ordinary Share held by it. The Non-Votin g Ordinary Shares are comprised of several different series as of December 31, 2017 : • the Series A shares were issued and held in treasury, but were not outstanding. These shares were canceled in June 2016 in an internal reorganization as described below. • the Series C shares were originally issued in connection with investment transactions in April and December of 2011. In addition, there were 66,520 Series C Non-Voting Ordinary Shares issued in March 2017 in connection with the exercise of warrants as described below. The Series C shares: (i) have all of the economic rights (including dividend rights) attaching to Voting Ordinary Shares but are non-voting except in certain limited circumstances; (ii) will automatically convert at a one -for-one exchange ratio (subject to adjustment for share splits, dividends, recapitalizations, consolidations or similar transactions) into Voting Ordinary Shares if the registered holder transfers them in a widely dispersed offering; (iii) may only vote on certain limited matters that would constitute a variation of class rights and as required under Bermuda law, provided that the aggregate voting power of the Series C shares with respect to any merger, consolidation or amalgamation will not exceed 0.01% of the aggregate voting power of our issued share capital; and (iv) require the registered holders’ written consent in order to vary the rights of the shares in a significant and adverse manner. During the three months ended March 31, 2017, 192,485 Series C Non-Voting Ordinary Shares were converted into Voting Ordinary Shares in a widely dispersed offering by their registered holders. • the Series B and Series D shares were created in connection with the 2011 investment transactions, but no shares in these series are issued and outstanding. Holders of the Series C shares have the right to convert such shares, on a share-for-share basis, subject to certain adjustments, into Series D shares at their option. There is no economic difference in Series B, C or D shares, but there are slight differences in the conversion rights and the limited voting rights of each series. • there were 404,771 Series E shares issued and outstanding as of December 31, 2017 . There were 714,015 Series E shares originally issued and outstanding in connection with the acquisition of StarStone. During 2015, 309,244 of the previously issued and outstanding Series E shares were converted into Voting Ordinary Shares upon market sales constituting a widely dispersed offering. The Series E shares have substantially the same rights as the Series C shares, except that (i) they are convertible only into Voting Ordinary Shares and (ii) they may only vote as required under Bermuda law. The Series E shares include all other Non-Voting Ordinary Shares authorized under our bye-laws but not classified as Series A, B, C or D Non-Voting Ordinary Shares. As of December 31, 2017 , there were warrants outstanding to acquire 175,901 Series C Non-Voting Ordinary Shares for an exercise price of $115.00 per share, subject to certain adjustments (the "Warrants"). The Warrants were issued in April 2011 and expire in April 2021. The Warrant holder may, at its election, satisfy the exercise price of the Warrants on a cashless basis by surrender of shares otherwise issuable upon exercise of the Warrants in accordance with a formula set forth in the Warrants. During December 2016, 164,919 Warrants were exercised on a cashless basis, resulting in the issuance of 66,520 Series C Non-Voting Ordinary Shares. As of December 31, 2017 , there were 388,571 Series C Participating Non-Voting Perpetual Preferred Stock ("Series C Preferred Shares") issued and held by one of our wholly-owned subsidiaries. The Series C Preferred Shares were issued in June 2016 in an internal reorganization transaction that resulted in the cancellation of all of the Series A Shares, which had an equivalent value and were also previously held by our wholly-owned subsidiary. The Series C Preferred Shares (i) upon liquidation, dissolution or winding up of the Company, entitle their holders to a preference over holders of our ordinary voting and non-voting shares of an amount equal to $0.001 per share with respect to surplus assets and (ii) are non-voting except in certain limited circumstances. The Series C Preferred shares have dividend rights equal to those of the ordinary voting shares, subject to certain limitations and in an amount determined by a "participation rate" that is generally reflective of the reduction in the number of Series C Preferred Shares issued in exchange for the previously outstanding Series A Shares. The Series C Preferred Shares otherwise rank on parity with the ordinary voting and non-voting shares, and they rank senior to each other class or series of share capital, unless the terms of any such class or series shall expressly provide otherwise.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share	18. EARNINGS PER SHARE The following table sets forth the computation of basic and diluted earnings per share for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Numerator: Net earnings from continuing operations $ 300,465 $ 252,844 $ 222,322 Net earnings (losses) from discontinuing operations 10,993 11,963 (2,031 ) Net earnings attributable to Enstar Group Limited $ 311,458 $ 264,807 $ 220,291 Denominator: Weighted-average ordinary shares outstanding — basic 19,388,621 19,299,426 19,252,072 Effect of dilutive securities: Share-based compensation plans 62,732 48,428 76,801 Warrants 76,238 99,387 78,883 Weighted-average ordinary shares outstanding — diluted 19,527,591 19,447,241 19,407,756 Earnings per share attributable to Enstar Group Limited: Basic: Net earnings from continuing operations $ 15.50 $ 13.10 $ 11.55 Net earnings (loss) from discontinuing operations 0.56 0.62 (0.11 ) Net earnings per ordinary share $ 16.06 $ 13.72 $ 11.44 Diluted: Net earnings from continuing operations $ 15.39 $ 13.00 $ 11.46 Net earnings (loss) from discontinuing operations 0.56 0.62 (0.11 ) Net earnings per ordinary share $ 15.95 $ 13.62 $ 11.35

Share-Based Compensation and Pe

Share-Based Compensation and Pensions	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Share-Based Compensation and Pensions	19. SHARE-BASED COMPENSATION AND PENSIONS Share-based compensation Employee share awards have been granted under the 2016 and 2006 Equity Incentive Plans. Restricted Shares and Restricted Share Units Restricted shares and restricted share units are service awards that typically vest over three to four years. These awards are share-settled and are recorded in additional paid-in capital on the consolidated balance sheets. The fair value of these awards is measured at the grant date and expensed over the service period. The following ta ble summarizes the activity related to restricted shares and restricted share awards during 2017 : Number of Shares Weighted- Average Share Price of Award Nonvested — January 1 78,992 $ 165.94 Granted 56,333 202.82 Vested (31,199 ) 163.75 Forfeited (4,821 ) 159.93 Nonvested — December 31 99,305 187.84 Compensation costs of $7.3 million , $3.0 million and $6.1 million relating to these share awards were recognized in our statement of earnings for the years ended December 31, 2017 , 2016 and 2015 , respectively. The unrecognized compensation cost related to our non-vested share awards as at December 31, 2017 was $11.7 million . This cost is expected to be recognized over the next 1.75 years, which is the weighted average contractual life of the awards. Performance Share Units ("PSUs") PSUs are share-settled and vest on the third anniversary of the grant date. The number of shares to vest will be determined by a performance adjustment based on the change in fully diluted book value per share ("FDBVPS") over three years , based upon the following award terms: Grant Year PSU's Granted at Target Nonvested Units Change in FDBVPS (3 - year) at December 31, 2017 Threshold Target Maximum 2017 36,321 34,878 20.00 % 30.00 % 40.00 % 2017 91,875 91,875 30.30 % 35.70 % 41.00 % 128,196 126,753 An increase of Target to Maximum or more in FDBVPS results in a settlement of 100% to a maximum of 150% of the units granted, respectively. An increase of Threshold to Target in FDBVPS results in a settlement of 50% to 100% of the units granted, respectively. Straight-line interpolation applies within these ranges and no settlement occurs if the increase in FDBVPS is less than the Threshold. The following table summarizes the activity related to PSUs during 2017 : Number of Shares Weighted- Average Share Price of Award Nonvested — January 1 — $ — Granted 128,196 188.15 Forfeited (1,443 ) 196.11 Nonvested — December 31 126,753 188.06 Compensation costs of $5.8 million , $nil and $nil relating to these share awards were recognized in our statement of earnings for the years ended December 31, 2017 , 2016 and 2015 , respectively. The unrecognized compensation cost related to our non-vested share awards as at December 31, 2017 was $18.0 million . This cost is expected to be recognized over the next 2.3 years, which is the weighted average contractual life of the awards. Cash-Settled Stock Appreciation Rights Cash-settled stock appreciation right awards ("SARs") give the holder the right, upon exercise, to receive in cash the difference between the market price per share of our ordinary shares at the time of exercise and the exercise price of the SARs. The exercise price of each SAR is equal to the market price of our ordinary shares on the date of the grant. Vested SARs are exercisable for periods not to exceed either 4 years or 10 years from the date of grant. The following t able summarizes the activity related to SARs during 2017: Number of SARs Weighted- Average Exercise Price of SARs Weighted Average Expected Term (in years) Aggregate Intrinsic Value (1) Balance, beginning of year 941,168 $ 140.70 Exercised (630,301 ) 140.39 Balance, end of year 310,867 141.30 1.58 $ 18,471 (1) The aggregate intrinsic value is calculated as the pre-tax difference between the exercise price of the underlying share awards and the closing price per share of our ordinary shares of $200.75 on December 31, 2017 . Compensation expense for SARs is based on the estimated fair value on the date of grant using the Black-Scholes valuation model, which requires the use of subjective assumptions related to the expected stock price volatility, expected term, expected dividend yield and risk-free interest rate. SARs are liability-classified awards for which compensation expense and the liability are re-measured using the then-current Black Scholes assumptions at each interim reporting date based upon the portion of the requisite service period rendered. Compensation costs of $8.9 million , $35.6 million and $8.9 million relating to these share awards were recognized in our statement of earnings for the years ended December 31, 2017 , 2016 and 2015 , respectively. The unrecognized compensation cost related to our SARs as at December 31, 2017 was $0.2 million . This cost is expected to be recognized over the next 0.61 years, which is the weighted-average remaining vesting term of the awards. The following table sets forth the assumptions used to estimate the fair value of the SARs using the Black-Scholes option valuation model as at December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Weighted-average fair value per SAR $ 75.38 $ 62.39 $ 29.02 Weighted-average volatility 19.44 % 19.82 % 22.08 % Weighted-average risk-free interest rate 1.65 % 1.12 % 1.29 % Dividend yield 0.00 % 0.00 % 0.00 % Other share-based compensation plans Northshore Incentive Plan Our subsidiary, Northshore, has long-term incentive plans that award time-based restricted shares of Northshore to certain Atrium employees. Shares generally vest over two to three years. These share awards have been classified as liability awards. For the years ended December 31, 2017 , 2016 and 2015 , compensation costs of $3.2 million , $2.8 million and $3.9 million , respectively, relating to the long-term incentive plans were recorded in our consolidated statement of earnings. The unrecognized compensation cost related to the Northshore incentive plan at December 31, 2017 was $5.4 million . This cost is expected to be recognized over the next 1.87 years, which is the weighted average contractual life of the awards. Deferred Compensation and Ordinary Share Plan for Non-Employee Directors For the years ended December 31, 2017 , 2016 and 2015 , 3,852 , 4,298 and 5,174 restricted share units, respectively, were credited to the accounts of non-employee directors under the Enstar Group Limited Deferred Compensation and Ordinary Share Plan for Non-Employee Directors (the "Deferred Compensation Plan"). Expense related to the restricted share units for the years ended December 31, 2017 , 2016 and 2015 , was $0.8 million , $0.7 million and $1.0 million , respectively. During the year ended December 31, 2015 , 2,393 restricted share units previously credited to the accounts of two directors under the Deferred Compensation Plan were converted into ordinary shares following their resignations. Employee Share Purchase Plan For the years ended December 31, 2017 , 2016 and 2015 , compensation costs relating to the shares issued under the Amended and Restated Enstar Group Limited Employee Share Purchase Plan ("Share Plan") of $0.4 million , $0.3 million and $0.3 million , respectively, were recorded in our consolidated statement of earnings. For the years ended December 31, 2017 , 2016 and 2015 , 12,401 , 12,234 and 11,998 shares, respectively, were issued to employees under the Share Plan. Pension Plans We provide retirement benefits to eligible employees through various plans that we sponsor. Defined Contribution Plans Pension expense relating to defined contribution plans for the years ended December 31, 2017 , 2016 and 2015 was $12.2 million , $10.8 million and $10.3 million , respectively. Pension expense can be affected by changes in our employee headcount as a result of our acquisitions described in Note 3 - "Acquisitions" . Defined Benefit Plan We have a noncontributory defined benefit pension plan that was acquired in the Providence Washington transaction in 2010. Pension expense relating to this defined benefit plan was $1.9 million , $2.3 million and $0.6 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. The increase in pension expense during 2016 was due to the completion of a lump sum buyout offering during 2016 and was offset by a reduction in accumulated other comprehensive loss in shareholders' equity. During 2017 , an actuarial review was performed, which determined that the plan’s unfunded liability, as at December 31, 2017 , was $9.4 million as compared to $10.3 million as at December 31, 2016 . As at December 31, 2017 and 2016 , we had an accrued liability of $9.4 million and $10.3 million , respectively, for this p lan.

Taxation

Taxation	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Taxation	20. TAXATION Enstar Group Limited is incorporated under the laws of Bermuda and under Bermuda law is not required to pay taxes in Bermuda based upon income or capital gains. The Company, under the Exempted Undertakings Tax Protection Act of 1966, is protected against any legislation that may be enacted in Bermuda which would impose any tax on profits, income, or gain until March 31, 2035. We have foreign operating subsidiaries and branch operations principally located in the United States, United Kingdom, Continental Europe and Australia that are subject to federal, foreign, state and local taxes in those jurisdictions. Deferred income tax liabilities have not been accrued with respect to the undistributed earnings of our foreign subsidiaries. If the earnings were to be distributed, as dividends or other distributions, withholding taxes may be imposed by the jurisdiction of the paying subsidiary. For our U.S. subsidiaries, we have not currently accrued any withholding taxes with respect to unremitted earnings as management has no current intention of remitting these earnings. For our United Kingdom subsidiaries, there are no withholding taxes imposed. For our other foreign subsidiaries, it would not be practicable to compute such amounts due to a variety of factors, including the amount, timing, and manner of any repatriation. Because we operate in many jurisdictions, our net earnings are subject to risk due to changing tax laws and tax rates around the world. The current, rapidly changing economic environment may increase the likelihood of substantial changes to tax laws in the jurisdictions in which we operate. The following table presents earnings before income taxes by jurisdiction from continuing operations : 2017 2016 2015 Domestic (Bermuda) $ 167,263 $ 191,647 $ 61,695 Foreign 147,148 135,677 163,327 Total earnings before income tax on continuing operations $ 314,411 $ 327,324 $ 225,022 The following table presents our current and deferred income tax expense (benefit) from continuing operations by jurisdiction: 2017 2016 2015 Current: Domestic (Bermuda) $ — $ — $ — Foreign 10,299 21,485 30,028 10,299 21,485 30,028 Deferred: Domestic (Bermuda) — — — Foreign (16,694 ) 13,389 (17,378 ) (16,694 ) 13,389 (17,378 ) Total tax expense (benefit) on continuing operations $ (6,395 ) $ 34,874 $ 12,650 The actual income tax rate differs from the amount computed by applying the effective rate of 0% under Bermuda law to earnings from continuing operations before income taxes as shown in the following reconciliation: 2017 2016 2015 Earnings before income tax $ 314,411 $ 327,324 $ 225,022 Bermuda income taxes at statutory rate 0.0 % 0.0 % 0.0 % Foreign income tax rate differential 13.1 % 8.8 % 17.6 % Change in valuation allowance (34.9 )% (0.1 )% (10.5 )% Effect of change in foreign (U.S.) tax rate 20.3 % — % — % Other (0.5 )% 2.0 % (1.5 )% Effective tax rate (2.0 )% 10.7 % 5.6 % Our effective tax rate is generally driven by the geographical distribution of our pre-tax net earnings between our taxable and non-taxable jurisdictions. We have recorded the effects of U.S. Tax Reform in 2017, primarily related to our deferred tax asset and valuation allowance thereon, as described below. Deferred Tax Assets and Liabilities Deferred tax assets and liabilities reflect the tax effect of the differences between the financial reporting and income tax bases of assets and liabilities. Significant components of the deferred tax assets and deferred tax liabilities related to our continuing operations were as follows: December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 177,695 $ 262,271 Tax credits and other carryforwards — 7,487 Insurance reserves 9,082 19,265 Unearned premiums 1,690 8,760 Lloyd's underwriting losses taxable in future periods 9,131 6,581 Provisions for bad debt 6,371 16,018 Other deferred tax assets 1,944 7,946 Gross deferred tax assets 205,913 328,328 Valuation allowance (188,300 ) (290,861 ) Deferred tax assets 17,613 37,467 Deferred tax liabilities: Unrealized gains on investments (3,798 ) (12,804 ) Intangible assets — (20,615 ) Other deferred tax liabilities (16,076 ) (21,030 ) Deferred tax liabilities (19,874 ) (54,449 ) Net deferred tax liability $ (2,261 ) $ (16,982 ) The change in the deferred tax liability during the year ended December 31, 2017 differs from deferred tax expense for 2017 primarily due to reclassification of our deferred tax asset to other assets in relation to Alternative Minimum Tax ("AMT") recoverable as described below in relation to U.S. Tax Reform, partially offset by the adoption of ASU 2016-09 which resulted in a reduction of our deferred tax liability and an increase in retaining earnings on the consolidated statement of changes in shareholders' equity. Net Deferred Tax Liability balance for continuing operations by major jurisdiction: December 31, 2017 2016 Net Deferred Tax Asset / (Liability) Net Deferred Tax Asset / (Liability) United States $ 4,947 $ (513 ) United Kingdom (5,150 ) (12,297 ) Other (2,058 ) (4,172 ) Total $ (2,261 ) $ (16,982 ) As of December 31, 2017 , we had net operating loss carryforwards that could be available to offset future taxable income, as follows: Tax Jurisdiction Loss Carryforwards Tax effect Expiration Operating and Capital Loss Carryforwards: United States - Net operating loss $ 528,226 $ 110,927 2030-2036 United States - Capital loss 14,339 3,011 2021-2022 United Kingdom 324,784 62,521 None Other 19,105 1,236 None Impact of US Tax Reform On December 22, 2017, the U.S. Government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the “Tax Act”). The Tax Act resulted in a reduction of the U.S. Federal Tax rate to 21% from 35% , effective for tax years beginning after December 31, 2017. Consequently, we have recorded a $63.8 million write down of our U.S. deferred tax asset in 2017. The Tax Act also repealed the corporate AMT. Taxpayers with AMT credit carryovers in excess of their tax liability may have the credits refunded over multiple years between 2018 and 2022. As a result, we have recorded a reduction to our valuation allowance of $7.4 million and reclassified our AMT credit carryforward to other assets on our consolidated balance sheet. Assessment of Valuation Allowance on Deferred Tax Assets As of December 31, 2017 and 2016 , we had deferred tax asset valuation allowances of $188.3 million and $290.9 million , respectively, related to foreign subsidiaries. We recorded a reduction of $102.6 million in our deferred tax valuation allowance for continuing operations during 2017 . The valuation allowance was decreased in relation to (i) the decrease of the deferred tax asset due to the reduction in the U.S. income tax rate from 35% to 21% , (ii) the current year utilization of deferred tax assets, partially offset by an increase relating to deferred tax assets for which we have deemed are not likely to be realized. The realization of deferred tax assets is dependent on generating sufficient taxable income in future periods in which the tax benefits are deductible or creditable. Taxes are determined and assessed jurisdictionally by legal entity or by filing group. Certain jurisdictions require or allow combined or consolidated tax filings. We have estimated future taxable income of our foreign subsidiaries and provided a valuation allowance in respect of those assets where we do not expect to realize a benefit. We have considered all available evidence using a “more likely than not” standard in determining the amount of the valuation allowance. Our assessment weighs both positive and negative evidence and considers the extent to which the evidence can be objectively verified. When negative evidence outweighs positive evidence then it can be difficult to support a conclusion that a valuation allowance is not needed. We consider the following evidence: (i) net earnings or losses in recent years; (ii) the future sustainability and likelihood of positive net earnings of our subsidiaries; (iii) the carryforward periods of tax losses including the effect of reversing temporary differences; and (iv) tax planning strategies. Uncertainty in Income Taxes During the years ended December 31, 2017 , 2016 and 2015 , there were no unrecognized tax benefits. There were no accruals for the payment of interest and penalties related to unrecognized tax benefits as at December 31, 2017 , 2016 and 2015 . Our operating subsidiaries may be subject to audit by various tax authorities and may have different statutes of limitations expiration dates. Tax authorities may propose adjustments to our income taxes. Listed below are the tax years that remain subject to examination by a major tax jurisdiction as of December 31, 2017 : Major Tax Jurisdiction Open Tax Years United States 2014-2016 United Kingdom 2014-2016 Australia 2012-2016

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	21. RELATED PARTY TRANSACTIONS Stone Point Capital LLC Through several private transactions occurring from May 2012 to July 2012, Trident acquired 1,350,000 of our Voting Ordinary Shares (which now constitutes approximately 8.2% of our outstanding Voting Ordinary Shares). On November 6, 2013, we appointed James D. Carey to our Board of Directors. Mr. Carey is the sole member of an entity that is one of four general partners of the entities serving as general partners for Trident, is a member of the investment committees of such general partners, and is a member and senior principal of Stone Point Capital LLC ("Stone Point"), the manager of the Trident funds. In addition, we have entered into certain agreements with Trident with respect to Trident’s co-investments in the Atrium, Arden, and StarStone acquisitions. These include investors’ agreements and shareholders’ agreements, which provide for, among other things: (i) our right to redeem Trident’s equity interest in the Atrium/Arden and StarStone transactions in cash at fair market value within the 90 days following September 9, 2018 and April 1, 2019, respectively, and at any time following September 9, 2020 and April 1, 2021, respectively; and (ii) Trident’s right to have its equity co-investment interests in the Atrium/Arden and StarStone transactions redeemed by us at fair market value (which we may satisfy in either cash or our ordinary shares) following September 9, 2020 and April 1, 2021. As of December 31, 2017 , we have included $459.6 million ( December 31, 2016 : $435.6 million ) as RNCI on our balance sheet relating to these Trident co-investment transactions. Pursuant to the terms of the shareholders’ agreements, Mr. Carey serves as a Trident representative on the boards of the holding companies established in connection with the Atrium/Arden and StarStone co-investment transactions. Trident also has a second representative on these boards who is a Stone Point employee. As at December 31, 2017 , we had investments in funds (carried within other investments) and a registered investment company affiliated with entities owned by Trident or otherwise affiliated with Stone Point. The fair value of the investments in the funds was $255.9 million and $232.1 million as of December 31, 2017 and December 31, 2016 , respectively. The fair value of our investment in the registered investment company was $22.1 million and $20.9 million as at December 31, 2017 and December 31, 2016 , respectively. For the years ended December 31, 2017 and 2016 , we recognized net unrealized gains of $22.3 million and $17.2 million , respectively, in respect of the fund investments, and net unrealized gains of $2.9 million and net realized and unrealized losses of $0.4 million , respectively, in respect of the registered investment company investment. For the years ended December 31, 2017 and 2016 , we recognized interest income of $2.5 million and $3.1 million , respectively, in respect of the registered investment company. We also have separate accounts, with a balance of $183.4 million and $215.0 million as at December 31, 2017 and 2016, respectively, managed by Eagle Point Credit Management and PRIMA Capital Advisors, which are affiliates of entities owned by Trident, with respect to which we incurred approximately $0.5 million in management fees for each of the years ended December 31, 2017 and 2016 . In addition, we are invested in two funds (carried within other investments) managed by Sound Point Capital, an entity in which Mr. Carey has an indirect minority ownership interest and serves as director. The fair value of our investments in Sound Point Capital funds was $27.4 million and $25.4 million as of December 31, 2017 and December 31, 2016 , respectively. For the years ended December 31, 2017 and 2016 , we have recognized net unrealized gains of $2.0 million and $1.9 million , respectively, in respect of investments managed by Sound Point Capital. Sound Point Capital has acted as collateral manager for certain of our direct investments in CLO equity securities. The fair value of these investments was $17.8 million and $20.3 million as at December 31, 2017 and December 31, 2016 , respectively. For the years ended December 31, 2017 and 2016 , we recognized net unrealized losses of $2.5 million and net unrealized gains of $2.1 million , respectively. For the years ended December 31, 2017 and 2016, we recognized interest income of $4.3 million and $6.7 million , respectively, in respect of these investments. We have a separate account managed by Sound Point Capital, with a balance of $63.6 million and $61.2 million as at December 31, 2017 and 2016 , respectively, with respect to which we incurred approximately $0.3 million in management fees for each of the years ended December 31, 2017 and 2016 . CPPIB CPPIB, together with management of Wilton Re, owns 100% of the common stock of Wilton Re. Subsequent to the closing of our transaction with Wilton Re, as described in Note 3 - "Acquisitions" , CPPIB purchased voting and non-voting shares in Enstar from FR XI Offshore AIV, L.P., First Reserve Fund XII, L.P., FR XII-A Parallel Vehicle L.P. and FR Torus Co-Investment, L.P. On September 29, 2015, CPPIB exercised its acquired right to appoint a representative, Poul Winslow, to our Board of Directors. During November 2016, CPPIB acquired additional non-voting shares in Enstar from Goldman Sachs affiliates in a private transaction. Following this transaction, CPPIB's shares constitute an approximate 9.1% voting interest and an approximate 16% aggregate economic interest in Enstar. In addition, approximately 4.5% of our voting shares (constituting an aggregate economic interest of approximately 3.8%) are held indirectly by CPPIB through CPPIB Epsilon Ontario Limited Partnership ("CPPIB LP"). CPPIB is the sole limited partner of CPPIB LP, and CPPIB Epsilon Ontario Trust ("CPPIB Trust") is the general partner. CPPIB's director representative is a trustee of CPPIB Trust. We also have a pre-existing reinsurance recoverable from a company later acquired by Wilton Re, which was carried on our balance sheet at $7.0 million and $9.4 million as of December 31, 2017 and December 31, 2016 , respectively. KaylaRe On December 15, 2016, our equity method investee, KaylaRe Holdings Ltd. ("KaylaRe") completed an initial capital raise of $620.0 million . As of December 31, 2017 , we have an approximate 48.2% ownership interest in KaylaRe. We have recorded the investment in KaylaRe using the equity method basis of accounting, pursuant to the conclusion that we are not required to consolidate following an analysis based on the guidance in ASC 810 - Consolidation . Our investment in KaylaRe was carried at $309.8 million and $294.6 million in other assets on our consolidated balance sheet as at December 31, 2017 and December 31, 2016 , respectively. In connection with our investment in KaylaRe, we entered into a shareholders agreement with the other shareholders in KaylaRe, including the Trident funds and HH KaylaRe Holdings, Ltd., an affiliate of Hillhouse Capital Management (“Hillhouse”). The Shareholders Agreement (i) provides us with the right to appoint one member to the KaylaRe Board of Directors until the date that we own less than 1,250,000 common shares, (ii) includes a five year lock-up period on common shares of KaylaRe (unless KaylaRe completes an initial public offering before the expiry of this five year lock-up period) and (iii) provides customary tag-along rights and rights of first refusal in the case of certain proposed transfers by any other shareholder and customary preemptive rights in the event of a proposed new issuance of equity securities by KaylaRe. In the event that KaylaRe has not consummated an initial public offering by March 31, 2021, the Trident funds have the right to require us and Hillhouse to purchase on a pro rata basis all of their common shares in KaylaRe at the then-current fair market value. Subsequent to December 31, 2017, we announced that we have entered into an agreement to purchase the remaining 51.8% of KaylaRe from the existing shareholders. In exchange for the shareholdings in KaylaRe, we will issue $398.3 million of ordinary shares. In the transaction, Hillhouse will increase its overall economic interest in Enstar from 9.98% to 17.1% and its voting interest from 3.2% to 9.7% , and Stone Point will increase its economic interest from 6.9% to 7.6% and its voting interest from 8.2% to 9.1% . In addition, the shareholders agreement described above among Enstar and the other KaylaRe shareholders will be effectively terminated . The transaction is subject to regulatory approval and is expected to close during the first quarter of 2018. Our subsidiary, Enstar Limited, acts as insurance and reinsurance manager to KaylaRe's subsidiary, KaylaRe Ltd., for which it received fee income of $8.7 million during the year ended December 31, 2017 ( 2016 : $6.8 million ). Affiliates of Enstar have also entered into various reinsurance agreements with KaylaRe Ltd., and KaylaRe Ltd. will also have the opportunity to participate in future Enstar legacy transactions. We also provide administrative services to KaylaRe and KaylaRe Ltd. Through a Quota Share Agreement dated December 31, 2017 (the "KaylaRe-StarStone QS"), several of our StarStone affiliates have entered into a Quota Share Treaty with KaylaRe Ltd. pursuant to which KaylaRe Ltd. reinsures 35% of all business written by these StarStone affiliates for risks attaching from January 1, 2016, net of the StarStone affiliates’ reinsurance programs. During the year ended December 31, 2017 , StarStone ceded $234.1 million ( 2016 : $117.6 million ) of premium earned, $155.4 million ( 2016 : $75.7 million ) of net incurred losses and LAE and $99.5 million ( 2016 : $42.5 million ) of acquisition costs to KaylaRe Ltd. under the KaylaRe-StarStone QS. The amounts in 2016 were recorded in the aggregate as net incurred losses and LAE of $1.4 million in our consolidated statement of earnings for the year ended December 31, 2017 in accordance with retroactive reinsurance accounting. The amounts in 2017 were recorded in their appropriate category on our consolidated statement of earnings in accordance with prospective reinsurance accounting. In addition, Fitzwilliam Insurance Limited ("Fitzwilliam"), one of our non-life run-off subsidiaries, ceded $nil (2016: $177.2 million ) of loss reserves to KaylaRe Ltd. during the year ended December 31, 2017 , on a funds held basis. Under the terms of this reinsurance agreement, Fitzwilliam is entitled to receive a profit commission calculated with reference to reserve savings made during the currency of this agreement. During the year ended December 31, 2017 , Fitzwilliam recognized $18.8 million of profit commission ( 2016 : $7.1 million ), recorded as fees and commission income. Our consolidated balance sheet as at December 31, 2017 included the following balances related to transactions between us and KaylaRe and KaylaRe Ltd.: reinsurance recoverable of $357.4 million ( 2016 : $242.1 million ), prepaid reinsurance premiums of $116.4 million ( 2016 : $109.0 million ), funds held of $174.2 million ( 2016 : $182.3 million ) recorded in other liabilities, insurance and reinsurance balances payable of $232.9 million ( 2016 : $132.6 million ), and ceded acquisition costs of $36.1 million ( 2016 : $41.2 million ) recorded as a reduction of deferred acquisition costs. Hillhouse Investment funds managed by Hillhouse collectively own approximately 3.2% of Enstar’s voting ordinary shares. These funds also own non-voting ordinary shares and warrants to purchase additional non-voting ordinary shares, which together with their voting ordinary shares, represent an approximate 9.98% economic interest in Enstar. As of December 31, 2017 and December 31, 2016 , our equity method investee, KaylaRe, had investments in a fund managed by Hillhouse with a fair value of $456.7 million and $350.0 million , respectively. As of December 31, 2017 , our wholly-owned subsidiary, Cavello Bay, had transferred funds to Hillhouse of $200.0 million , which were invested on January 2, 2018. A further $50.0 million will be invested by Cavello Bay in funds managed by Hillhouse during the first quarter of 2018 .

Dividend Restrictions and Statu

Dividend Restrictions and Statutory Financial Information	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
Dividend Restrictions and Statutory Financial Information	22. DIVIDEND RESTRICTIONS AND STATUTORY FINANCIAL INFORMATION Parent Company Dividend Restrictions There were no significant restrictions on the Parent Company's ability to pay dividends from retained earnings as at December 31, 2017 . Bermuda law permits the payment of dividends if (i) we are not, or would not be after payment, unable to pay our liabilities as they become due and (ii) the realizable value of our assets is in excess of our liabilities after taking such payment into account. Enstar has not historically declared a dividend. Our strategy is to retain earnings and invest distributions from our subsidiaries back into the company. We do not currently expect to pay any dividends on our ordinary shares. The Bermuda Monetary Authority ("BMA") acts as group supervisor to Enstar. On an annual basis, we are required to file group statutory financial statements, a group statutory financial return, a group capital and solvency return, audited group financial statements and a Group Solvency Self-Assessment ("GSSA") with the BMA. The GSSA is designed to document our perspective on the capital resources necessary to achieve our business strategies and remain solvent, and to provide the BMA with insights on our risk management, governance procedures and documentation related to this process. We are required to maintain available group statutory capital and surplus in an amount that is at least equal to the group enhanced capital requirement ("Group ECR"). The BMA has also established a group target capital level equal to 120% of the Group ECR. We are in compliance with these requirements. Our ability to pay dividends to our shareholders is dependent upon the ability of our insurance and reinsurance subsidiaries to distribute capital and pay dividends to us. Our insurance and reinsurance subsidiaries are subject to certain regulatory restrictions on the distribution of capital and payment of dividends in the jurisdictions in which they operate, as described below. The restrictions are generally based on net income or levels of capital and surplus as determined in accordance with the relevant statutory accounting practices. Failure of these subsidiaries to meet their applicable regulatory requirements could result in restrictions on any distributions of capital or retained earnings or stricter regulatory oversight of the subsidiaries. Our ability to pay dividends and make other forms of distributions may also be limited by repayment obligations and financial covenants in our outstanding loan facility agreements. Subsidiary Statutory Financial Information and Dividend Restrictions Our insurance and reinsurance subsidiaries prepare their statutory financial statements in accordance with statutory accounting practices prescribed or permitted by local regulators. Statutory accounting differs from U.S. GAAP, including in the treatment of investments, acquisition costs and deferred income taxes, amongst other items. The statutory capital and surplus amounts for the years ended December 31, 2017 and 2016 and statutory net income amounts for the years ended December 31, 2017 , 2016 and 2015 for our insurance and reinsurance subsidiaries based in Bermuda, the United Kingdom, Australia, the United States and Continental Europe were as follows: Statutory Capital and Surplus Required Actual Statutory Income 2017 2016 2017 2016 2017 2016 2015 Bermuda $ 1,556,644 $ 792,652 $ 2,802,653 $ 2,131,308 $ 390,752 $ 339,548 $ 147,883 U.K. $ 453,160 $ 532,132 $ 699,798 $ 805,170 $ 77,900 $ 131,619 $ 113,296 U.S. $ 195,855 $ 209,283 $ 589,029 $ 662,942 $ (5,065 ) $ (1,439 ) $ 14,964 Europe $ 253,981 $ 240,107 $ 444,870 $ 286,039 $ (4,245 ) $ 31,075 $ 1,856 As at December 31, 2017 , the total amount of net assets of our consolidated subsidiaries that were restricted was $2.5 billion . Certain material aspects of these laws and regulations as they relate to solvency, dividends and capital and surplus are summarized below. Bermuda Our Bermuda-based insurance and reinsurance subsidiaries are registered under the Insurance Act 1978 of Bermuda and related regulations, as amended (the "Insurance Act"). The Insurance Act imposes certain solvency and liquidity standards and auditing and reporting requirements and grants the BMA powers to supervise, investigate, require information and the production of documents and intervene in the affairs of insurance companies. The Insurance Act requires that our Bermuda-based insurance and reinsurance subsidiaries maintain certain solvency and liquidity standards. The minimum liquidity ratio requires that the value of relevant assets not be less than 75% of the amount of relevant liabilities. The minimum solvency margin, which varies depending on the class of the insurer, is determined as a percentage of either net reserves for losses and LAE or premiums or pursuant to a risk-based capital measure. Our Bermuda subsidiaries with commercial insurance licenses are required to maintain a minimum statutory capital and surplus (Enhanced Capital Requirement or "ECR") at least equal to the greater of a minimum solvency margin or the Bermuda Solvency Capital Requirement ("BSCR"). The BSCR is calculated based on a standardized risk-based capital model. Each of our regulated Bermuda insurance and reinsurance subsidiaries would be prohibited from declaring or paying any dividends if it were in breach of its minimum solvency margin (which is a function of outstanding losses) or liquidity ratio (which is a function of relevant assets) or if the declaration or payment of such dividends would cause it to fail to meet such margin or ratio. In addition, each of our regulated Bermuda insurance and reinsurance subsidiaries is prohibited, without the prior approval of the BMA, from reducing by 15% or more its total statutory capital as set out in its previous year’s statutory financial statements. Our Bermuda insurance companies that are in run-off are required to seek regulatory approval for any dividends or distributions. As of December 31, 2017 and 2016 , each of our Bermuda-based insurance and reinsurance subsidiaries exceeded their respective minimum solvency and liquidity requirements. The Bermuda insurance and reinsurance subsidiaries in aggregate exceeded minimum solvency requirements by $1.2 billion as of December 31, 2017 ( 2016 : $1.3 billion ) and were in compliance with their liquidity requirements. United Kingdom U.K. Insurance Companies (non-Lloyd's) Our U.K. based insurance subsidiaries are regulated by the U.K. Prudential Regulatory Authority (the "PRA") and the Financial Conduct Authority (the "FCA", together with the PRA, the "U.K. Regulator"). Our U.K.-based insurance subsidiaries are required to maintain adequate financial resources in accordance with the requirements of the U.K. Regulator. The calculation of the minimum capital resources requirements in any particular case depends on, among other things, the type and amount of insurance business written and claims paid by the insurance company. As at December 31, 2017 and 2016 , all of our U.K. insurance subsidiaries maintained capital in excess of the minimum capital resources requirements and complied with the relevant U.K. Regulator requirements. The U.K.-based insurance subsidiaries, in aggregate, maintained capital in excess of the minimum capital resources requirements by $246.6 million and $273.0 million as of December 31, 2017 and 2016 , respectively. The Solvency II framework directive took effect on January 1, 2016. Solvency II sets out E.U.-wide requirements on capital adequacy and risk management for insurers with the aim of further increasing policyholder protection, instilling greater risk awareness and improving the international competitiveness of E.U. insurers. Insurers must comply with a Solvency Capital Requirement ("SCR"), which is calculated using either the Solvency II standard formula or a bespoke internal model. Our non-Lloyd's U.K. companies use the standard formula. The U.K. Regulator’s rules require our U.K. insurance subsidiaries to obtain regulatory approval for any proposed or actual payment of a dividend. From January 1, 2016, the U.K. Regulator has used the SCR, among other tests, when assessing requests to make distributions. Lloyd’s As of December 31, 2017 , we participated in the Lloyd’s market through our interests in: (i) Atrium’s Syndicate 609, which is managed by Atrium Underwriters Limited, a Lloyd's managing agent, and the Atrium corporate member; (ii) StarStone’s Syndicate 1301, which is managed by StarStone Underwriting Limited ("SUL"), a Lloyd’s managing agent, and the StarStone corporate member; and (iii) Syndicate 2008, a wholly aligned syndicate that has permission to underwrite RITC business and other run-off or discontinued business type transactions with other Lloyd’s syndicates, and its corporate member. During 2015, SUL assumed the role of managing agent for Syndicate 2008 in place of Shelbourne Syndicate Services Limited as we streamlined our organizational structure and combined Shelbourne and StarStone resources into one agency. For the 2017 underwriting year, participation in all three syndicates has been through a common corporate member. The underwriting capacity of a member of Lloyd’s is supported by providing Funds at Lloyd’s, as described in Note 6 - "Investments" . Business plans, including maximum underwriting capacity, for Lloyd’s syndicates requires annual approval by the Lloyd’s Franchise Board, which may require changes to any business plan or additional capital to support underwriting plans. The Lloyd’s market has applied the Solvency II internal model under Lloyd’s supervision, and our Lloyd’s operations are required to meet Solvency II standards. Effective January 1, 2016, Lloyd's received approval from the PRA to use its internal model under the Solvency II regime. United States Our U.S. non-life run-off and active underwriting insurance and reinsurance subsidiaries are subject to the insurance laws and regulations of the states in which they are domiciled, licensed and/or eligible to conduct business. These laws restrict the amount of dividends the subsidiaries can pay to us. The restrictions are generally based on statutory net income and/or certain levels of statutory surplus as determined in accordance with the relevant statutory accounting requirements of the individual domiciliary states or states in which any of the insurance or reinsurance subsidiaries are domiciled. Generally, prior regulatory approval must be obtained before an insurer may pay a dividend or make a distribution above a specified level. For all of our U.S. insurance and reinsurance subsidiaries, with the exception of one subsidiary which has a permitted accounting practice to treat an adverse development cover reinsurance agreement as prospective reinsurance, there are no prescribed or permitted statutory accounting practices that differ significantly from the statutory accounting principles established by the National Association of Insurance Commissioners ("NAIC"). The U.S. insurance and reinsurance subsidiaries are also required to maintain minimum levels of solvency and liquidity as determined by law, and to comply with risk-based capital requirements and licensing rules. As of December 31, 2017 , all of our U.S. non-life insurance and reinsurance subsidiaries exceeded their required levels of risk-based capital. On an aggregate basis, our U.S. non-life insurance and reinsurance subsidiaries exceeded their minimum levels of risk-based capital as of December 31, 2017 by $385.4 million ( December 31, 2016 : $402.0 million ). Our remaining regulated life subsidiary files financial statements with state insurance regulatory authorities and the NAIC in the United States. Our life company is subject to certain Risk-Based Capital ("RBC") requirements as specified by the NAIC. RBC is used to evaluate the adequacy of capital and surplus maintained by our life company in relation to risks associated with: (i) asset risk; (ii) insurance risk; (iii) interest rate risk and (iv) business risk. As of December 31, 2017 and 2016 , our life subsidiary exceeded their minimum RBC requirements by $7.8 million ( 2016 : $51.6 million ). This subsidiary is restricted by state laws and regulations as to the amount of dividends they may pay. Any dividends in excess of limits are deemed "extraordinary" and require approval. As of December 31, 2017 and 2016 , the maximum dividend payout which may be made without prior approval is $ nil ( 2016 : $nil ). Europe Our Swiss insurance subsidiary, Harper Insurance Limited, is regulated by the Swiss Financial Market Supervisory Authority ("FINMA") pursuant to the Insurance Supervisory Act 2004. This subsidiary is obligated to maintain a minimum solvency margin based on the Swiss Solvency Test regulations ("SST") as stipulated by the Insurance Supervisory Act. From January 1, 2016, Switzerland has been granted full Solvency II equivalence by the European Commission. As of December 31, 2017 and 2016 , this subsidiary exceeded the SST requirements by $44.0 million ( 2016 : $6.1 million ). The amount of dividends that this subsidiary is permitted to distribute is restricted to freely distributable reserves, which consist of retained earnings, the current year profit and legal reserves. Any dividend exceeding the current year profit requires FINMA’s approval. The solvency and capital requirements must continue to be met following any distribution. Our Liechtenstein insurance subsidiary (StarStone Insurance SE) is regulated by the Liechtenstein Financial Market Authority ("FMA") pursuant to the Liechtenstein Insurance Supervisory Act. This subsidiary is obligated to maintain a minimum solvency margin based on the Solvency II regulations. As of December 31, 2017 , this subsidiary exceeded th e Solvency II requirements by $146.8 million ( 2016 : $12.8 million). The amount of dividends that this subsidiary is permitted to distribute is restricted to freely distributable reserves, which consist of retained earnings, the current year profit and legal reserves. Any dividend exceeding the current year profit requires the FMA’s approval. Solvency and capital requirements for this subsidiary are based on the Solvency II framework and must continue to be met following any distribution. Our Belgian life insurance subsidiary files financial statements and returns with the National Bank of Belgium. This subsidiary was in compliance with its solvency and capital requirements under Solvency II.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	23. COMMITMENTS AND CONTINGENCIES Concentration of Credit Risk We believe that there are no significant concentrations of credit risk associated with our cash and cash equivalents, fixed maturity investments, or other investments. Cash, cash equivalents and fixed maturity investments are managed pursuant to guidelines that follow prudent standards of diversification and limit the allowable holdings of a single issue and issuers. Other investments are managed pursuant to guidelines that emphasize diversification and liquidity. Pursuant to these guidelines, we manage and monitor risk across a variety of investment funds and vehicles, markets and counterparties. We are also subject to custodial credit risk on our fixed maturity and equity investments, which we manage by diversifying our holdings amongst large financial institutions that are highly regulated. We have exposure to credit risk on certain of our assets pledged to ceding companies under insurance contracts. In addition, we are potentially exposed should any insurance intermediaries be unable to fulfill their contractual obligations with respect to payments of balances owed to and by us. Credit risk exists in relation to our insurance and reinsurance balances recoverable. We remain liable to the extent that counterparties do not meet their contractual obligations and, therefore, we evaluate and monitor concentration of credit risk among our insurers and reinsurers. Amounts recoverable from reinsurers are described Note 10 - "Reinsurance Balances Recoverable" . We are also subject to credit risk in relation to funds held by reinsured companies. Under funds held arrangements, the reinsured company has retained funds that would otherwise have been remitted to our reinsurance subsidiaries. The funds may be placed into trust or subject to other security arrangements. The funds balance is credited with investment income and losses payable are deducted. We are subject to credit risk if the reinsured company is unable to honor the value of the funds held balances, such as in the event of insolvency. However, we generally have the contractual ability to offset any shortfall in the payment of the funds held balances with amounts owed by us to the reinsured for losses payable and other amounts contractually due. We routinely monitor the creditworthiness of reinsured companies with whom we have funds held arrangements. We have a significant concentration of $1.0 billion to one reinsured company which has financial strength credit ratings of A+ from A.M. Best and AA from Standard & Poor's, as well as to KaylaRe as described in Note 21 - "Related Party Transactions" . We limit the amount of credit exposure to any one counterparty and none of our counterparty credit exposures, excluding U.S. Government instruments and the counterparties noted above, exceeded 10% of shareholders’ equity as of December 31, 2017 . Our credit exposure to the U.S. government was $810.9 million as at December 31, 2017 . Operating Leases We lease office space under operating leases expiring in various years through 2028. The leases are renewable at our option under certain circumstances. The following is a schedule of future minimum rental payments on non-cancelable leases as of December 31, 2017 : 2018 $ 11,023 2019 9,217 2020 9,310 2021 7,137 2022 5,647 2023 and beyond 20,461 $ 62,795 Rent expense for the years ended December 31, 2017 , 2016 and 2015 was $9.5 million , $9.7 million and $11.1 million , respectively. Legal Proceedings We are, from time to time, involved in various legal proceedings in the ordinary course of business, including litigation and arbitration regarding claims. Estimated losses relating to claims arising in the ordinary course of business, including the anticipated outcome of any pending arbitration or litigation are included in the liability for losses and LAE in our consolidated balance sheets. In addition to claims litigation, we may be subject to other lawsuits and regulatory actions in the normal course of business, which may involve, among other things, allegations of underwriting errors or omissions, employment claims or regulatory activity. We do not believe that the resolution of any currently pending legal proceedings, either individually or taken as a whole, will have a material effect on our business, results of operations or financial condition. We anticipate that, similar to the rest of the insurance and reinsurance industry, we will continue to be subject to litigation and arbitration proceedings in the ordinary course of business, including litigation generally related to the scope of coverage with respect to asbestos and environmental and other claims. Unfunded Investment Commitments As at December 31, 2017 , we had unfunded commitments to investment funds of $164.7 million . Guarantees As at December 31, 2017 and 2016 , parental guarantees supporting subsidiaries' insurance obligations were $795.7 million and $625.7 million , respectively. The increase relates to new transactions during 2017 as described in Note 3 - "Acquisitions" and Note 4 - "Significant New Business" , and includes $165.0 million for letters of credit issued under a Funds at Lloyd's facility as described in Note 6 - "Investments" . On February 8, 2018, we amended and restated the FAL Facility to issue up to $325.0 million of letters of credit, with a provision to increase the facility up to $400.0 million . The FAL Facility is available to satisfy our Funds at Lloyd’s requirements and expires in 2022. Significant New Business On December 20, 2017, we entered into a reinsurance-to-close transaction with Neon's Syndicate 2468. On January 29, 2018, we entered into a reinsurance-to-close transaction with Novae's Syndicate 2007. On February 22, 2018, we entered into a reinsurance agreement with Zurich Insurance Group. These agreements are described in Note 4 - "Significant New Business" . Asbestos Personal Injury Liabilities We acquired Dana Companies, LLC ("Dana") on December 30, 2016, as described in Note 3 - "Acquisitions" . Dana continues to process asbestos personal injury claims in the normal course of business and is separately managed. Other liabilities included $205.7 million and $220.5 million for indemnity and defense costs for pending and future claims at December 31, 2017 and 2016 , respectively , determined using standard actuarial techniques for asbestos-related exposures. Other liabilities also included $2.2 million and $2.3 million for environmental liabilities associated with Dana properties at December 31, 2017 and 2016 , respectively . Other assets included $122.3 million and $133.0 million at December 31, 2017 and 2016 , respectively, for estimated insurance recoveries relating to these liabilities. The recorded asset represents our assessment of the capacity of the insurance agreements to provide for the payment of anticipated defense and indemnity costs for pending claims and projected future demands. The recognition of these recoveries is based on an assessment of the right to recover under the respective contracts and on the financial strength of the insurers. The recorded asset does not represent the limits of our insurance coverage, but rather the amount we would expect to recover if the accrued indemnity and defense costs were paid in full. Redeemable Noncontrolling Interest We have the right to purchase the RNCI interests from the RNCI holders at certain times in the future (each such right, a "call right") and the RNCI holders have the right to sell their RNCI interests to us at certain times in the future (each such right, a "put right"). The RNCI rights held by Trident are described in Note 21 - "Related Party Transactions" . Dowling has a right to participate if Trident exercises its put right.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Information	24. SEGMENT INFORMATION In the second half of 2017, following the completion of the sale of our Laguna and Pavonia businesses, which significantly reduced the size of our life and annuities business, we undertook a review of our reportable segments. Following this review we determined that we have three reportable segments of business that are each managed, operated and reported on separately: (i) Non-life Run-off; (ii) Atrium; and (iii) StarStone. Our other activities, which do not qualify as a reportable segment, include our corporate expenses, debt servicing costs, holding company income and expenses, foreign exchange, our remaining life business and other miscellaneous items. The change in reportable segments had no impact on our previously reported historical consolidated financial positions, results of operations or cash flows. These segments are described in Note 1 - "Description of Business" . The Non-life Run-off segment comprises the operations and financial results of those insurance and reinsurance companies and portfolios in run-off that have been acquired by us. Atrium and StarStone, our active underwriting operations, are reported as separate segments because they are managed and operated in separate and distinct manners. Atrium’s senior management runs its day-to-day operations with limited involvement of our senior management, whereas our senior management and employees are involved in StarStone’s day-to-day operations. Atrium employees are not involved in the management or strategy of StarStone, nor are StarStone employees involved in the management or strategy of Atrium. Atrium and StarStone are monitored and reported upon separately and distinctly and their strategies and business plans are determined independently of each other. The following tables set forth selected and consolidated statement of earnings results by segment for the years ended December 31, 2017 , 2016 , 2015 : 2017 Non-Life Run-Off Atrium StarStone Other Total Gross premiums written $ 14,102 $ 153,472 $ 895,160 $ 5,719 $ 1,068,453 Net premiums written $ 6,482 $ 134,214 $ 464,901 $ 4,793 $ 610,390 Net premiums earned $ 14,162 $ 134,747 $ 459,403 $ 4,809 $ 613,121 Net incurred losses and LAE 190,674 (69,419 ) (314,806 ) — (193,551 ) Life and Annuity Policy Benefits — — — (4,015 ) (4,015 ) Acquisition costs (328 ) (47,688 ) (48,012 ) (878 ) (96,906 ) Operating expenses (132,235 ) (17,444 ) (135,558 ) — (285,237 ) Underwriting income (loss) 72,273 196 (38,973 ) (84 ) 33,412 Net investment income 166,678 4,218 27,706 10,187 208,789 Net realized and unrealized gains (losses) 179,545 1,117 16,613 (6,941 ) 190,334 Fees and commission income (expense) 43,849 22,788 632 (1,166 ) 66,103 Other income 27,061 230 570 648 28,509 Corporate expenses (101,592 ) (12,142 ) — (37,014 ) (150,748 ) Interest income (expense) (28,970 ) (559 ) (1,902 ) 3,329 (28,102 ) Net foreign exchange losses (7,347 ) (5,060 ) (926 ) (4,204 ) (17,537 ) Loss on sale of subsidiary — — — (16,349 ) (16,349 ) EARNINGS (LOSS) BEFORE INCOME TAXES 351,497 10,788 3,720 (51,594 ) 314,411 INCOME TAXES 6,990 (1,593 ) 988 10 6,395 NET EARNINGS (LOSS) FROM CONTINUING OPERATIONS 358,487 9,195 4,708 (51,584 ) 320,806 NET EARNINGS FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE — — — 10,993 10,993 Net earnings attributable to noncontrolling interest (14,687 ) (3,772 ) (1,882 ) — (20,341 ) NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED $ 343,800 $ 5,423 $ 2,826 $ (40,591 ) $ 311,458 Underwriting ratios: Loss ratio (1) 51.5 % 68.5 % Acquisition expense ratio (1) 35.4 % 10.5 % Operating expense ratio (1) 13.0 % 29.5 % Combined ratio (1) 99.9 % 108.5 % 2016 Non-Life Run-Off Atrium StarStone Other Total Gross premiums written $ 17,316 $ 143,170 $ 854,699 $ 7,157 $ 1,022,342 Net premiums written $ 9,202 $ 140,437 $ 648,036 $ 6,261 $ 803,936 Net premiums earned $ 16,755 $ 124,416 $ 676,608 $ 5,735 $ 823,514 Net incurred losses and LAE 285,881 (58,387 ) (401,593 ) — (174,099 ) Life and Annuity Policy Benefits — — — 2,038 2,038 Acquisition costs (4,198 ) (44,670 ) (138,822 ) 1,121 (186,569 ) Operating expenses (151,316 ) (14,233 ) (124,239 ) — (289,788 ) Underwriting income 147,122 7,126 11,954 8,894 175,096 Net investment income 145,237 2,940 22,221 15,065 185,463 Net realized and unrealized gains (losses) 77,685 (601 ) 5,728 (4,994 ) 77,818 Fees and commission income (expense) 17,447 18,189 5,102 (1,374 ) 39,364 Other income 2,497 206 740 1,393 4,836 Corporate expenses (61,583 ) (10,899 ) — (61,464 ) (133,946 ) Interest income (expense) (22,268 ) (198 ) (47 ) 1,871 (20,642 ) Net foreign exchange gains (losses) 1,684 (3,310 ) 754 207 (665 ) EARNINGS (LOSS) BEFORE INCOME TAXES 307,821 13,453 46,452 (40,402 ) 327,324 INCOME TAXES (28,577 ) (2,573 ) (3,693 ) (31 ) (34,874 ) NET EARNINGS (LOSS) FROM CONTINUING OPERATIONS 279,244 10,880 42,759 (40,433 ) 292,450 NET EARNINGS FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE — — — 11,963 11,963 Net earnings attributable to noncontrolling interest (17,600 ) (4,464 ) (17,542 ) — (39,606 ) NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED $ 261,644 $ 6,416 $ 25,217 $ (28,470 ) $ 264,807 Underwriting ratios: Loss ratio (1) 46.9 % 59.4 % Acquisition expense ratio (1) 35.9 % 20.5 % Operating expense ratio (1) 11.5 % 18.3 % Combined ratio (1) 94.3 % 98.2 % 2015 Non-Life Run-Off Atrium StarStone Other Total Gross premiums written $ 38,704 $ 149,082 $ 824,714 $ 2,883 $ 1,015,383 Net premiums written $ 22,594 $ 134,580 $ 628,427 $ 1,553 $ 787,154 Net premiums earned $ 44,369 $ 134,675 $ 573,146 $ 1,554 $ 753,744 Net incurred losses and LAE 270,830 (47,479 ) (327,684 ) — (104,333 ) Life and Annuity Policy Benefits — — — 546 546 Acquisition costs (8,860 ) (45,509 ) (109,347 ) — (163,716 ) Operating expenses (158,821 ) (18,499 ) (128,544 ) — (305,864 ) Underwriting income 147,518 23,188 7,571 2,100 180,377 Net investment income 88,999 2,225 15,937 15,403 122,564 Net realized and unrealized gains (losses) (31,383 ) 252 (9,784 ) (608 ) (41,523 ) Fees and commission income (expense) 22,264 28,352 — (11,269 ) 39,347 Other income (expense) 29,294 359 3,088 (2,413 ) 30,328 Corporate expenses (54,213 ) (13,111 ) — (15,971 ) (83,295 ) Interest income (expense) (33,599 ) (4,264 ) (6 ) 18,466 (19,403 ) Net foreign exchange gains (losses) (4,372 ) (213 ) 480 732 (3,373 ) EARNINGS BEFORE INCOME TAXES 164,508 36,788 17,286 6,440 225,022 INCOME TAXES (12,570 ) (5,968 ) 5,888 — (12,650 ) NET EARNINGS FROM CONTINUING OPERATIONS 151,938 30,820 23,174 6,440 212,372 NET LOSSES FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE — — — (2,031 ) (2,031 ) Net (earnings) losses attributable to noncontrolling interest 33,722 (14,262 ) (9,510 ) — 9,950 NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED $ 185,660 $ 16,558 $ 13,664 $ 4,409 $ 220,291 Underwriting ratios: Loss ratio (1) 35.3 % 57.2 % Acquisition expense ratio (1) 33.8 % 19.1 % Operating expense ratio (1) 13.7 % 22.4 % Combined ratio (1) 82.8 % 98.7 % (1) Refer to "Underwriting Ratios" for a description of how these ratios are calculated. Gross Premiums Written by Geographical Area The following table summarizes our gross premiums written for the year ended December 31, 2017 by geographic area. Geographic distribution in subsequent years is subject to variation based upon market conditions and business strategies. Non-life Run-off Atrium StarStone Other Total Total % Total % Total % Total % Total % (In thousands of U.S. dollars, except percentages) United States $ 9,639 68.3 % $ 81,438 53.1 % $ 546,223 61.0 % $ — — % $ 637,300 59.6 % United Kingdom 4,271 30.3 % 11,203 7.3 % 97,745 10.9 % 1,346 23.5 % 114,565 10.7 % Europe 192 1.4 % 10,684 7.0 % 151,106 16.9 % 4,373 76.5 % 166,355 15.6 % Asia — — % 4,739 3.1 % 48,839 5.5 % — — % 53,578 5.0 % Rest of World — — % 45,408 29.5 % 51,247 5.7 % — — % 96,655 9.1 % Total $ 14,102 100.0 % $ 153,472 100.0 % $ 895,160 100.0 % $ 5,719 100.0 % $ 1,068,453 100.0 % Assets by Segment Invested assets are managed on a subsidiary by subsidiary basis, and investment income and realized and unrealized gains on investments are recognized in each segment as earned. Our total assets as at December 31, 2017 and 2016 by segment were as follows (the elimination items include the elimination of intersegment assets): 2017 2016 Assets by Segment: Non-life Run-off $ 10,368,105 $ 8,233,450 Atrium 556,637 563,754 StarStone 3,128,725 2,968,316 Other (447,045 ) 1,100,224 Total assets $ 13,606,422 $ 12,865,744

Unaudited Condensed Quarterly F

Unaudited Condensed Quarterly Financial Data	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Unaudited Condensed Quarterly Financial Data	25. UNAUDITED CONDENSED QUARTERLY FINANCIAL DATA December 31, September 30, June 30, March 31, 2017 2016 2017 2016 2017 2016 2017 2016 INCOME Net premiums earned $ 160,627 $ 216,188 $ 148,025 $ 205,730 $ 155,571 $ 208,709 $ 148,898 $ 192,887 Fees and commission income 19,627 13,266 15,895 9,187 18,667 10,487 11,914 6,424 Net investment income 58,605 42,229 52,028 48,022 49,417 44,932 48,739 50,280 Net realized and unrealized gains (losses) 50,637 (61,570 ) 29,301 66,608 51,877 34,503 58,519 38,277 Other income (losses) 9,303 (1,277 ) (3,848 ) 414 10,856 3,289 12,198 2,410 298,799 208,836 241,401 329,961 286,388 301,920 280,268 290,278 EXPENSES Net incurred losses and loss adjustment expenses 30,327 1,321 75,712 (6,902 ) 9,620 96,462 77,892 83,218 Life and annuity policy benefits (1,033 ) (2,265 ) 1,060 1,682 4,289 (1,613 ) (301 ) 158 Acquisition costs 21,449 47,619 24,281 50,074 30,355 43,847 20,821 45,029 General and administrative expenses 126,702 123,497 100,325 103,097 106,490 104,206 102,468 92,934 Interest expense 7,251 4,796 6,410 5,027 7,573 5,421 6,868 5,398 Net foreign exchange losses (gains) 1,925 (1,527 ) 4,775 2,276 7,122 (1,856 ) 3,715 1,772 Loss on sale of subsidiary — — 6,740 — 9,609 — — — 186,621 173,441 219,303 155,254 175,058 246,467 211,463 228,509 EARNINGS BEFORE INCOME TAXES 112,178 35,395 22,098 174,707 111,330 55,453 68,805 61,769 INCOME TAXES 9,629 (11,228 ) (1,432 ) (8,227 ) (4,731 ) (8,050 ) 2,929 (7,369 ) NET EARNINGS FROM CONTINUING OPERATIONS 121,807 24,167 20,666 166,480 106,599 47,403 71,734 54,400 NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE 11,998 5,483 3,495 3,897 (4,871 ) 2,378 371 205 NET EARNINGS 133,805 29,650 24,161 170,377 101,728 49,781 72,105 54,605 Net losses (earnings) attributable to noncontrolling interest (6,206 ) (7,005 ) 14,832 (14,329 ) (11,542 ) (9,187 ) (17,425 ) (9,085 ) NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED $ 127,599 $ 22,645 $ 38,993 $ 156,048 $ 90,186 $ 40,594 $ 54,680 $ 45,520 EARNINGS PER SHARE — BASIC: Net earnings from continuing operations $ 5.96 $ 0.91 $ 1.83 $ 7.89 $ 4.90 $ 1.98 $ 2.80 $ 2.34 Net earnings (loss) from discontinuing operations $ 0.62 $ 0.26 $ 0.18 $ 0.20 $ (0.25 ) $ 0.12 $ 0.02 $ 0.02 Net earnings per ordinary share attributable to Enstar Group Limited shareholders $ 6.58 $ 1.17 $ 2.01 $ 8.09 $ 4.65 $ 2.10 $ 2.82 $ 2.36 EARNINGS PER SHARE — DILUTED: Net earnings from continuing operations $ 5.90 $ 0.90 $ 1.81 $ 7.82 $ 4.87 $ 1.97 $ 2.78 $ 2.33 Net earnings (loss) from discontinuing operations $ 0.61 $ 0.26 $ 0.18 $ 0.20 $ (0.25 ) $ 0.12 $ 0.02 $ 0.02 Net earnings per ordinary share attributable to Enstar Group Limited shareholders $ 6.51 $ 1.16 $ 1.99 $ 8.02 $ 4.62 $ 2.09 $ 2.80 $ 2.35

Schedule I - Summary of Investm

Schedule I - Summary of Investments Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2017
Summary of Investments, Other than Investments in Related Parties [Abstract]
Schedule I - Summary of Investments Other Than Investments in Related Parties	SCHEDULE I ENSTAR GROUP LIMITED SUMMARY OF INVESTMENTS OTHER THAN INVESTMENTS IN RELATED PARTIES As of December 31, 2017 (Expressed in thousands of U.S. Dollars) Type of investment Cost (1) Fair Value Amount at which shown in the balance sheet (2) Fixed maturity securities and short-term investments — Trading: U.S. government and agency $ 557,273 $ 554,036 $ 554,036 Non-U.S. government 580,280 607,132 607,132 Corporate 3,299,982 3,363,060 3,363,060 Municipal 98,153 100,221 100,221 Residential mortgage-backed 285,312 288,713 288,713 Commercial mortgage-backed 427,469 421,548 421,548 Asset-backed 534,893 541,574 541,574 Total 5,783,362 5,876,284 5,876,284 Fixed maturity securities and short-term investments — Available-for-sale: U.S. government and agency 4,210 4,187 4,187 Non-U.S. government 84,776 85,437 85,437 Corporate 113,561 115,121 115,121 Municipal 5,146 5,136 5,136 Residential mortgage-backed 31 31 31 Asset-backed 373 373 373 Total 208,097 210,285 210,285 Equities (3) 64,197 84,543 84,543 Other investments, at fair value (4) 630,058 630,058 630,058 Other investments, at cost 125,621 131,896 125,621 Total $ 6,811,335 $ 6,933,066 $ 6,926,791 (1) Original cost of fixed maturity securities is reduced by repayments and adjusted for amortization of premiums or accretion of discounts. (2) The table above excludes businesses held for sale. Refer to Note 5 - "Divestitures, Held-for-Sale Businesses and Discontinuing Operations" of the notes to the consolidated financial statements. (3) The difference in the amount of equities shown at fair value and the equities shown in our consolidated balance sheet relates to the fair value of $22.1 million as of December 31, 2017 for our investment in a registered investment company affiliated with entities owned by Trident. Refer to Note 21 - "Related Party Transactions" of the notes to the consolidated financial statements. (4) The difference in the amount of other investments shown at fair value and the other investments shown in our consolidated balance sheet relates to the fair value of $283.3 million as of December 31, 2017 for our other investments in funds or companies owned by or affiliated with certain related parties. Refer to Note 21 - "Related Party Transactions" of the notes to the consolidated financial statements.

Schedule II - Condensed Financi

Schedule II - Condensed Financial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule II - Condensed Financial Statements	SCHEDULE II ENSTAR GROUP LIMITED CONDENSED FINANCIAL INFORMATION OF REGISTRANT Balance Sheets - Parent Company Only As of December 31, 2017 and 2016 2017 2016 (in thousands of U.S. dollars, except share data) ASSETS Cash and cash equivalents $ 2,458 $ 4,884 Balances due from subsidiaries 23,635 35,563 Investments in subsidiaries 3,917,830 3,400,401 Other assets 2,877 8,533 TOTAL ASSETS $ 3,946,800 $ 3,449,381 LIABILITIES Debt obligations $ 646,689 $ 488,103 Balances due to subsidiaries 148,410 153,843 Other liabilities 15,017 5,123 TOTAL LIABILITIES 810,116 647,069 COMMITMENTS AND CONTINGENCIES SHAREHOLDERS’ EQUITY Share capital authorized, issued and fully paid, par value $1 each (authorized 2017 and 2016: 156,000,000): Ordinary shares (issued and outstanding 2017: 16,402,279; 2016: 16,175,250) 16,402 16,175 Non-voting convertible ordinary shares: Series C (issued and outstanding 2017: 2,599,672; 2016: 2,792,157) 2,600 2,792 Series E (issued and outstanding 2017 and 2016: 404,771) 405 405 Series C Preferred Shares (issued and outstanding 2017 and 2016: 388,571) 389 389 Treasury shares at cost (Preferred shares 2017 and 2016: 388,571) (421,559 ) (421,559 ) Additional paid-in capital 1,395,067 1,380,109 Accumulated other comprehensive income (loss) 10,468 (23,549 ) Retained earnings 2,132,912 1,847,550 Total Enstar Group Limited Shareholders’ Equity 3,136,684 2,802,312 TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY $ 3,946,800 $ 3,449,381 See accompanying notes to the Condensed Financial Information of Registrant SCHEDULE II ENSTAR GROUP LIMITED CONDENSED FINANCIAL INFORMATION OF REGISTRANT - CONTINUED Statements of Earnings - Parent Company Only For the Years Ended December 31, 2017 , 2016 and 2015 2017 2016 2015 (in thousands of U.S. dollars) INCOME Net investment income $ 80 $ 44 $ 14,965 Other income 1,050 — — Dividend income from subsidiaries 249,055 361,675 1,000 250,185 361,719 15,965 EXPENSES General and administrative expenses 87,596 59,755 50,349 Interest expense 23,138 10,109 8,693 Net foreign exchange losses (gains) 6,135 (318 ) 213 116,869 69,546 59,255 EARNINGS (LOSSES) BEFORE EQUITY IN UNDISTRIBUTED EARNINGS OF SUBSIDIARIES 133,316 292,173 (43,290 ) EQUITY IN UNDISTRIBUTED EARNINGS (LOSSES) OF SUBSIDIARIES - CONTINUING OPERATIONS 167,149 (39,329 ) 265,612 EQUITY IN UNDISTRIBUTED EARNINGS (LOSSES) OF SUBSIDIARIES - DISCONTINUING OPERATIONS 10,993 11,963 (2,031 ) NET EARNINGS $ 311,458 $ 264,807 $ 220,291 Statements of Comprehensive Income - Parent Company Only For the Years Ended December 31, 2017 , 2016 and 2015 2017 2016 2015 (in thousands of U.S. dollars) NET EARNINGS $ 311,458 $ 264,807 $ 220,291 OTHER COMPREHENSIVE INCOME (LOSS) RELATING TO SUBSIDIARIES, NET OF TAX 34,016 11,613 (22,476 ) COMPREHENSIVE INCOME $ 345,474 $ 276,420 $ 197,815 See accompanying notes to the Condensed Financial Information of Registrant SCHEDULE II ENSTAR GROUP LIMITED CONDENSED FINANCIAL INFORMATION OF REGISTRANT - CONTINUED Statements of Cash Flows - Parent Company Only For the Years Ended December 31, 2017 , 2016 and 2015 2017 2016 2015 (in thousands of U.S. dollars) OPERATING ACTIVITIES: Net cash flows provided by (used in) operating activities $ 97,898 $ 39,185 $ (81,384 ) INVESTING ACTIVITIES: Dividends and return of capital from subsidiaries 217,450 250,117 1,000 Contributions to subsidiaries (465,650 ) (295,268 ) (218,935 ) Net cash flows used in investing activities (248,200 ) (45,151 ) (217,935 ) FINANCING ACTIVITIES: Repayment of loans (696,640 ) (426,750 ) (223,500 ) Receipt of loans 844,516 433,048 505,700 Net cash flows provided by financing activities 147,876 6,298 282,200 NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS (2,426 ) 332 (17,119 ) CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR 4,884 4,552 21,671 CASH AND CASH EQUIVALENTS, END OF YEAR $ 2,458 $ 4,884 $ 4,552 See accompanying notes to the Condensed Financial Information of Registrant Notes to the Condensed Financial Information of Registrant The Condensed Financial Information of Registrant should be read in conjunction with our consolidated financial statements and the accompanying notes thereto included in Part II - Item 8 of this Annual Report on Form 10-K. Our wholly owned and majority owned subsidiaries are recorded based upon our proportionate share of our subsidiaries' net assets (similar to presenting them on the equity method). Investing activities in the Condensed Statements of Cash Flows primarily represents the flow of funds to and from subsidiaries to provide cash on hand to fund acquisitions and significant new business. Net investment income relates to interest on loans to subsidiaries. For the years ended December 31, 2017 , 2016 , and 2015 , interest paid was $ 17.6 million , $ 15.0 million , and $ 13.0 million , respectively. During the years ended December 31, 2017 and 2016 , non-cash investing activities included $31.6 million and $111.6 million , respectively, for dividends and return of capital from subsidiaries and $148.1 million and $452.1 million , respectively, for contributions to subsidiaries. These transactions were to settle intercompany balances, resulting in a net reduction in balances due from subsidiaries and an increase in investments in subsidiaries. There were no non-cash investing activities for the year ended December 31, 2015 . As at December 31, 2017 and 2016 , parental guarantees supporting subsidiaries' insurance obligations were $795.7 million and $625.7 million , respectively. As at December 31, 2017 and 2016 , retained earnings was $2,132.9 million and $1,847.6 million , respectively, an increase of $285.4 million . The increase in retained earnings was primarily attributable to net earnings of $311.5 million .

Schedule III - Supplementary In

Schedule III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2017
Supplementary Insurance Information [Abstract]
Schedule III - Supplementary Insurance Information	SCHEDULE III ENSTAR GROUP LIMITED SUPPLEMENTARY INSURANCE INFORMATION (Expressed in thousands of U.S. Dollars) As of December 31, Year ended December 31, Deferred Acquisition Costs Reserves for Losses and Loss Adjustment Expenses Unearned Premiums Policy Benefits for Life and Annuity Contracts Net Premiums Earned Net Investment Income Losses and Loss Expenses and Policy Benefits Amortization of Deferred Acquisition Costs Other Operating Expenses Net Premiums Written 2017 Non-life run-off $ 655 $ 5,949,472 $ 14,275 $ — $ 14,162 $ 166,678 $ (190,674 ) $ 328 $ 233,827 $ 6,482 Atrium 18,385 240,873 64,877 — 134,747 4,218 69,419 47,688 29,586 134,214 StarStone 45,944 1,207,743 504,045 — 459,403 27,706 314,806 48,012 135,558 464,901 Other — — — 117,207 4,809 10,187 4,015 878 37,014 4,793 Total $ 64,984 $ 7,398,088 $ 583,197 $ 117,207 $ 613,121 $ 208,789 $ 197,566 $ 96,906 $ 435,985 $ 610,390 2016 Non-life run-off $ 1,081 $ 4,716,363 $ 15,107 $ — $ 16,755 $ 145,237 $ (285,881 ) $ 4,198 $ 212,899 $ 9,202 Atrium 16,964 212,122 61,862 — 124,416 2,940 58,387 44,670 25,132 140,437 StarStone 40,069 1,059,382 471,374 — 676,608 22,221 401,593 138,822 124,239 648,036 Other — — — 112,095 5,735 15,065 (2,038 ) (1,121 ) 61,464 6,261 Total $ 58,114 $ 5,987,867 $ 548,343 $ 112,095 $ 823,514 $ 185,463 $ 172,061 $ 186,569 $ 423,734 $ 803,936 2015 Non-life run-off $ 1,788 $ 4,585,454 $ 27,792 $ — $ 44,369 $ 88,999 $ (270,830 ) $ 8,860 $ 213,034 $ 22,594 Atrium 16,326 201,017 59,808 — 134,675 2,225 47,479 45,509 31,610 134,580 StarStone 71,009 933,678 455,171 — 573,146 15,937 327,684 109,347 128,544 628,427 Other — — — 126,321 1,554 15,403 (546 ) — 15,971 1,553 Total $ 89,123 $ 5,720,149 $ 542,771 $ 126,321 $ 753,744 $ 122,564 $ 103,787 $ 163,716 $ 389,159 $ 787,154

Schedule IV - Reinsurance

Schedule IV - Reinsurance	12 Months Ended
	Dec. 31, 2017
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
Schedule IV - Reinsurance	SCHEDULE IV ENSTAR GROUP LIMITED REINSURANCE For the Years Ended December 31, 2017 , 2016 and 2015 (Expressed in thousands of U.S. Dollars) Gross Ceded to Other Companies Assumed from Other Companies Net Amount Percentage of Amount Assumed to Net 2017 Life insurance in force $ 979,291 $ (100,189 ) $ — $ 879,102 — % Premiums earned: Property and casualty 899,226 (433,075 ) 142,161 608,312 23.4 % Life and annuities 5,900 (1,091 ) — 4,809 — % Total premiums earned $ 905,126 $ (434,166 ) $ 142,161 $ 613,121 2016 Life insurance in force $ 2,317,567 $ (585,575 ) $ — $ 1,731,992 — % Premiums earned: Property and casualty 804,141 (178,834 ) 192,472 817,779 23.5 % Life and annuities 7,220 (1,485 ) — 5,735 — % Total premiums earned $ 811,361 $ (180,319 ) $ 192,472 $ 823,514 2015 Life insurance in force $ 2,978,466 $ (777,759 ) $ — $ 2,200,707 — % Premiums earned: Property and casualty 854,856 (283,489 ) 180,823 752,190 24.0 % Life and annuities 2,884 (1,330 ) — 1,554 — % Total premiums earned $ 857,740 $ (284,819 ) $ 180,823 $ 753,744

Schedule V - Valuation and Qual

Schedule V - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule V - Valuation and Qualifying Accounts	SCHEDULE V ENSTAR GROUP LIMITED VALUATION AND QUALIFYING ACCOUNTS For the Years Ended December 31, 2017 , 2016 and 2015 (Expressed in thousands of U.S. Dollars) Balance at Beginning of Year Charged to costs and expenses Charged to other (1) Deductions (2) Balance at End of Year December 31, 2017 Reinsurance balances recoverable: Provisions for bad debt 174,516 (1,536 ) (4,191 ) (3,576 ) 165,213 Valuation allowance for deferred tax assets 290,861 (16,694 ) — (85,867 ) 188,300 December 31, 2016 Reinsurance balances recoverable: Provisions for bad debt 210,327 (13,822 ) (19,255 ) (2,734 ) 174,516 Valuation allowance for deferred tax assets 291,280 13,389 — (13,808 ) 290,861 December 31, 2015 Reinsurance balances recoverable: Provisions for bad debt 289,909 (25,271 ) (45,234 ) (9,077 ) 210,327 Valuation allowance for deferred tax assets 333,617 (17,379 ) — (24,958 ) 291,280 (1) These amounts are credited to net incurred losses and there is an offsetting debit within the same line, resulting in no impact on earnings. (2) Credited to the related asset account.

Schedule VI - Supplementary Inf

Schedule VI - Supplementary Information Concerning Property/Casualty Insurance Operations	12 Months Ended
	Dec. 31, 2017
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Schedule VI - Supplementary Information Concerning Property/Casualty Insurance Operations	SCHEDULE VI ENSTAR GROUP LIMITED SUPPLEMENTARY INFORMATION CONCERNING PROPERTY/CASUALTY INSURANCE OPERATIONS As of and for the years ended December 31, 2017 , 2016 and 2015 (Expressed in thousands of U.S. Dollars) As of December 31, Year ended December 31, Affiliation with Registrant Deferred Acquisition Costs Reserves for Unpaid Losses and Loss Adjustment Expenses Unearned Premiums Net Premiums Earned Net Investment Income Net Losses and Loss Expenses Incurred Net Paid Losses and Loss Expenses Amortization of Deferred Acquisition Costs Net Premiums Written Current Year Prior Year Consolidated Subsidiaries 2017 $ 64,984 $ 7,398,088 $ 583,197 $ 608,312 $ 198,602 $ 437,853 $ (244,302 ) $ (945,194 ) $ 96,028 $ 605,597 2016 58,114 5,987,867 548,343 817,779 170,398 493,016 (318,917 ) (833,057 ) 187,690 797,675 2015 89,123 5,720,149 542,771 752,190 107,161 476,364 (372,031 ) (781,889 ) 163,716 785,601

Significant Accounting Polici39

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Preparation	The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America ("U.S. GAAP").
Basis of Consolidation	The consolidated financial statements include our assets, liabilities and results of operations as of December 31, 2017 and 2016 and for the years ended December 31, 2017 , 2016 and 2015 . Results of operations for acquired subsidiaries are included from the date of acquisition. All significant intercompany transactions and balances have been eliminated.
New Accounting Standards Adopted and Recently Issued Accounting Pronouncements Not Yet Adopted	New Accounting Standards Adopted in 2017 Accounting Standards Update (“ASU”) 2017-12, Targeted Improvements to Accounting for Hedging Activities In August 2017, the Financial Accounting Standards Board (the "FASB") issued ASU 2017-12, which amends the hedge accounting recognition and presentation requirements in Accounting Standards Codification (“ASC”) 815 - Derivatives and Hedging. The guidance (1) improves the transparency and understandability of information conveyed to financial statement users about an entity’s risk management activities by better aligning the entity’s financial reporting for hedging relationships with those risk management activities, and (2) reduces the complexity of and simplify the application of hedge accounting by preparers. We early adopted this guidance and that adoption did not have an impact on our consolidated financial statements and disclosures. ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities In March 2017, the FASB issued ASU 2017-08, which amends the amortization period for certain purchased callable debt securities held at a premium, shortening such period to the earliest call date. The adoption of this guidance did not have a material impact on our consolidated financial statements. ASU 2017-04, Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued ASU 2017-04, which simplifies the accounting for goodwill impairments by eliminating Step 2 from the goodwill impairment test. Instead, if the carrying amount of a reporting unit exceeds its fair value, an impairment loss shall be recognized in an amount equal to that excess, limited to the total amount of goodwill allocated to that reporting unit. We early adopted this guidance and that adoption did not have an impact on our consolidated financial statements and disclosures. ASU 2017-01, Clarifying the Definition of a Business In January 2017, the FASB issued ASU 2017-01 to clarify the definition of a business in ASC 805 - Business Combinations, with the intent of making the application of the guidance more consistent and cost-efficient. This clarification is expected to result in fewer acquired sets of assets and liabilities being identified as businesses. We early adopted this guidance and that adoption did not have an impact on our consolidated financial statements and disclosures. ASU 2016-09, Improvements to Employee Share-Based Payment Accounting In March 2016, the FASB issued ASU 2016-09, which simplifies several aspects of the accounting for employee share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The impact of adopting this guidance on our consolidated financial statements was a cumu lative-effect adjustment of $4.9 million to opening retained earnings for the year ended December 31, 2017 for the excess tax benefit not previously recognized. ASU 2016-07, Simplifying the Transition to the Equity Method of Accounting In March 2016, the FASB issued ASU 2016-07, which simplifies the equity method of accounting by eliminating the requirement to retrospectively apply the equity method to an investment that subsequently qualifies for such accounting as a result of an increase in the level of ownership interest or degree of influence. Entities are therefore required to apply the guidance prospectively to increases in the level of ownership interest or degree of influence occurring after the ASU’s effective date. The ASU further requires that unrealized holding gains or losses in accumulated other comprehensive income related to an available-for-sale security that becomes eligible for the equity method be recognized in earnings as of the date on which the investment qualifies for the equity method. The adoption of this guidance did not have any impact on our consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In February 2018, the FASB issued ASU 2018-02, which gives entities the option to reclassify to retained earnings tax effects related to items in accumulated other comprehensive income (“AOCI”) that are deemed stranded in AOCI as a result of the Tax Cuts and Jobs Act ("Tax Act") enacted in the United States at the end of 2017. The amendments in this guidance eliminate the stranded tax effects resulting from the Tax Act and will improve the usefulness of information reported to financial statement users. The ASU is effective for interim and annual reporting periods beginning after December 15, 2018 but early adoption is permitted in any interim or annual period for which financial statements have not yet been issued. Entities also have the option of applying the ASU either (1) in the period of adoption or (2) retrospectively to each period in which the income tax effects of the Tax Act related to items in AOCI, are recognized. The adoption of this guidance is not expected to have a material impact on our consolidated financial statements and disclosures. ASU 2017-09, Stock Compensation - Scope of Modification Accounting In May 2017, the FASB issued ASU 2017-09, which amends the scope of modification accounting for share-based payment arrangements. The ASU provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting under ASC 718. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions, and classification of the awards are the same immediately before and after the modification. The ASU’s amendments are effective for interim and annual reporting periods beginning after December 15, 2017, although early adoption is permitted. The adoption of this guidance is not expected to have a material impact on our consolidated financial statements and disclosures. ASU 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost In March 2017, the FASB issued ASU 2017-07, which amends the requirements in ASC 715 related to the income statement presentation of the components of net periodic benefit cost for an entity’s sponsored defined benefit pension and other postretirement plans. The ASU requires entities to (1) disaggregate the current-service-cost component from the other components of net benefit cost (the “other components”) and present it with other current compensation costs for related employees in the statement of earnings, and (2) present the other components elsewhere in the statement of earnings and outside of income from operations if such a subtotal is presented. The ASU also requires entities to disclose the captions within the statement of earnings that contain the other components if they are not presented on appropriately described separate lines. In addition, only the service-cost component of the net benefit cost is eligible for capitalization, which is a change from current practice, under which entities capitalize the aggregate net benefit cost when applicable. The ASU’s amendments are effective for interim and annual reporting periods beginning after December 15, 2017, although early adoption is permitted. The adoption of this guidance is not expected to have a material impact on our consolidated financial statements and disclosures. ASU 2017-05, Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets In February 2017, the FASB issued ASU 2017-05 to clarify the scope of the Board’s guidance on nonfinancial asset derecognition (ASC 610-20) as well as the accounting for partial sales of nonfinancial assets. The ASU conforms the derecognition on nonfinancial assets with the model for transactions in the new revenue standard (ASC 606, as amended). The ASU clarifies that ASC 610-20 applies to the derecognition of all nonfinancial assets and in-substance nonfinancial assets. The ASU also requires an entity to derecognize the nonfinancial asset or in-substance nonfinancial asset in a partial sale transaction when (1) the entity ceases to have a controlling financial interest in a subsidiary pursuant to ASC 810, and (2) control of the asset is transferred in accordance with ASC 606. The ASU is effective for interim and annual reporting periods beginning after December 15, 2017. We expect to adopt this guidance on January 1, 2018 using the modified retrospective approach. We do not expect this adoption to have a material impact on our consolidated financial statements and disclosures. ASU 2016-16, Intra-Entity Transfers of Assets Other Than Inventory In October 2016, the FASB issued ASU 2016-16, which requires immediate recognition of the tax consequences of many intercompany asset transfers other than inventory. The ASU is effective for interim and annual reporting periods beginning after December 15, 2017, however early adoption is permitted. The adoption of this guidance is not expected to have a material impact on our consolidated financial statements and disclosures. ASU 2016-15, Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments In August 2016, the FASB issued ASU 2016-15, which amends the guidance on the classification of certain cash receipts and payments in the statement of cash flows. The ASU is effective for interim and annual reporting periods beginning after December 15, 2017, however early adoption is permitted. The adoption of this guidance is not expected to have a material impact on our consolidated financial statements and disclosures. ASU 2016-13, Financial Instruments - Credit Losses - Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued ASU 2016-13, which amends the guidance on impairment of financial instruments and significantly changes how entities will measure credit losses for most financial assets and certain other financial instruments including reinsurance balances recoverable that are not measured at fair value through net income. The ASU will replace the existing “incurred loss” approach, with an “expected loss” model for instruments measured at amortized cost and require entities to record allowances for available-for-sale debt securities rather than reduce the carrying amount under the existing OTTI model. The ASU also simplifies the accounting model for purchased credit-impaired debt securities and loans. The ASU is effective for interim and annual reporting periods beginning after December 15, 2019. We expect to adopt the new guidance on January 1, 2020 and upon adoption the OTTI approach we currently use for our available-for-sale securities whereby any credit losses are presented as write-downs on individual securities will be replaced by an approach whereby any credit losses are instead presented as an allowance against each security. This revised approach records the full effect of reversals of any credit losses in current period earnings, compared to current U.S. GAAP which amortizes the reversal of credit losses over the lifetime of the security. The length of time an available for sale security has been in an unrealized loss position will no longer be considered in determining whether to record a credit loss. In addition, the historical and implied volatility of the fair value of an available for sale security and recoveries or declines in fair value after the balance sheet date will no longer be considered when making a determination of whether a credit loss exists. For our reinsurance balances recoverable, the ASU will require us to determine a provision for credit losses associated with our reinsurers based on an “expected loss” approach which will likely differ from the provisions for uncollectible reinsurance balances recoverable that we have currently recorded, based on the “incurred loss” approach under existing guidance. We are continuing to review all our financial instruments as well as assets that are subject to credit risk, primarily our reinsurance balance recoverables and available-for-sale debt securities to determine the provisions for credit losses on the instruments and to quantify the impact of adopting the “expected loss” approach required by the ASU. While we anticipate an increase in our allowances for credit losses for the financial instruments and assets that are within the scope of the ASU in view of the objective of the new guidance, the magnitude of any increase will depend largely on the composition of our investment portfolio at the date of adoption of the ASU as well as on the prevailing economic conditions and forecasts at the time of adoption . ASU 2016-02, Leases In February 2016, the FASB issued ASU 2016-02, which amends the guidance on the classification, measurement and disclosure of leases for both lessors and lessees. The ASU requires lessees to recognize a right-of-use asset and a lease liability on the balance sheet and to disclose qualitative and quantitative information about leasing arrangements. The ASU is effective for interim and annual reporting periods beginning after December 15, 2018. We expect to adopt the new standard on January 1, 2019 and will recognize and measure our leasing arrangements at the beginning of the earliest period presented using the modified retrospective approach permitted by the ASU. The modified retrospective approach includes a number of specific optional practical expedients which we intend to elect on adoption of the ASU, relating to, (1) the identification and classification of leases that commenced before the effective date, (2) initial direct costs for leases that commenced before the effective date, and (3) the ability to use hindsight in evaluating lessee options to extend or terminate a lease. The election of these practical expedients will allow us to in effect, continue to account for leases that commence before the effective date in accordance with the previous U.S. GAAP unless the lease is modified. The only exception would be that we will be required to recognize a right-of-use asset and a lease liability for all our existing operating leases at each reporting date based on the present value of the remaining minimum lease rental payments that we are disclosing under current U.S. GAAP. We are continuing to review all our operating lease arrangements to quantify the right-of-use asset and the offsetting lease liability to be recorded on our Consolidated Balance Sheet upon adoption of this guidance. We however, do not anticipate that the adoption of the ASU will have a material impact on our consolidated financial statements and related disclosures. ASU 2016-01, Recognition and Measurement of Financial Instruments In January 2016, the FASB issued ASU 2016-01, which amends the guidance on the classification and measurement of financial instruments. Although the ASU retains many of the current requirements, it significantly revises an entity’s accounting related to (1) the classification and measurement of investments in equity securities, and (2) the presentation of certain fair value changes for financial liabilities measured at fair value. The ASU also amends certain disclosure requirements associated with the fair value of financial instruments. The ASU is effective for interim and annual reporting periods beginning after December 15, 2017. Based on our current review, while the ASU will impact the financial liabilities that we have assumed through loss portfolio transfer reinsurance agreements for which we have elected the fair value option, substantially all of our assets are not within the scope of the new guidance. We expect to adopt this guidance on January 1, 2018 using the modified retrospective approach, however we do not expect that adoption to have a material impact on our consolidated financial statements and related disclosures. ASUs 2014-09, 2016-08, 2016-10, 2016-12, Revenue from Contracts with Customers In May 2014, the FASB issued ASU 2014-09, which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The ASU applies to all contracts with customers except those that are within the scope of other topics in the FASB ASC including ASC 944 - Insurance. However, while contracts within the scope of ASC 944 are excluded from the scope of the ASU, certain insurance-related contracts should be accounted for under the ASU, for example contracts under which service providers charge their customers fixed fees in exchange for an agreement to provide services for an uncertain future event. Certain of the ASU’s provisions also apply to transfers of non-financial assets and include guidance on recognition and measurement. In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers - Principal versus Agent Considerations , which clarifies the implementation guidance for principal versus agent considerations in ASU 2014-09. In April 2016, the FASB issued ASU 2016-10, Revenue from Contracts with Customers - Identifying Performance Obligations and Licensing , which amends the guidance in ASU 2014-09 related to identifying performance obligations and accounting for licenses of intellectual property. In May 2016, the FASB issued ASU 2016-12, Revenue from Contracts with Customers - Narrow-Scope Improvements and Practical Expedients , which clarifies the following aspects in ASU 2014-09 - (1) collectability, (2) presentation of sales taxes and other similar taxes collected from customers, (3) noncash considerations, (4) contract modifications at transition, (5) completed contracts at transition, and (6) technical correction. We are required to adopt ASU 2016-08, ASU 2016-10 and ASU 2016-12 together with ASU 2014-09, which is effective for interim and annual reporting periods beginning after December 15, 2017. We adopted this guidance on January 1, 2018. The two permitted transition methods under the new revenue standard are the full retrospective method, in which case the guidance would be applied to each prior reporting period presented, or the modified retrospective method, in which case the cumulative effect of applying the standard would be recognized at the date of initial adoption. We expect to adopt the guidance using the modified retrospective method.
Use of Estimates	The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amount of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Our actual results could differ materially from our estimates. Accounting policies that we believe are most dependent on assumptions and estimates are considered to be our critical accounting policies and are related to the determination of: • liability for losses and loss adjustment expenses ("LAE"); • liability for policy benefits for life and annuity contracts; • reinsurance balances recoverable; • gross and net premiums written and net premiums earned; • impairment charges, including other-than-temporary impairments on investment securities classified as available-for-sale, and impairments on goodwill, intangible assets and deferred charges; • fair value measurements of investments; • fair value estimates associated with accounting for acquisitions; • fair value estimates associated with loss portfolio transfer reinsurance agreements for which we have elected the fair value option; and • redeemable noncontrolling interests.
Premiums	Non-Life Non-life premiums written are earned on a pro-rata basis over the period the coverage is provided. Reinsurance premiums are recorded at the inception of the policy, are based upon contractual terms and, for certain business, are estimated based on underlying contracts or from information provided by insureds and/or brokers. Changes in reinsurance premium estimates are expected and may result in adjustments in future periods. Any subsequent differences arising on such estimates are recorded as premiums written in the period in which they are determined. Certain non-life contracts are retrospectively rated and provide for a final adjustment to the premium based on the final settlement of all losses. Premiums on such contracts are adjusted based upon contractual terms, and management judgme nt is involved with respect to the estimate of the amount of losses that we expect to incur. Additional premiums are recognized at the time loss thresholds specified in the contract are exceeded and are earned over the coverage period, or are earned immediately if the period of risk coverage has passed. Life and Annuities Prior to going into run-off, our life and annuities subsidiaries wrote life insurance, including credit life and disability insurance, term life insurance, assumed life reinsurance and annuities. We will continue to recognize premiums on term life insurance, assumed life reinsurance and credit life and disability insurance. These premiums are generally recognized as revenue when due from policyholders. The policies include contracts with fixed and guaranteed premiums and benefits. Benefits and expenses are matched with such revenue to result in the recognition of profit over the life of the contracts. Premiums receivable Premiums receivable represent amounts currently due and amounts not yet due on insurance and reinsurance policies. Premiums for insurance policies are generally due at inception. Premiums for reinsurance policies generally become due over the period of coverage based on the policy terms. We monitor the credit risk associated with premiums receivable, taking into consideration the impact of our contractual right to offset loss obligations or unearned premiums against premiums receivable. Amounts deemed uncollectible are charged to net earnings in the period they are determined. Changes in the estimates of premiums written will result in an adjustment to premiums receivable in the period they are determined. Unearned premiums and prepaid reinsurance premiums Unearned premiums represent the portion of premiums written that relate to the unexpired terms of policies in force. Premiums ceded are similarly pro-rated over the period the coverage is provided with the unearned portion being deferred as prepaid reinsurance premiums.
Acquisition Costs	Acquisition costs, consisting principally of commissions and brokerage expenses and certain premium taxes and fees incurred at the time a contract or policy is issued and that vary with and are directly related to the successful efforts of acquiring new insurance contracts or renewing existing insurance contracts, are deferred and amortized over the period in which the related premiums are earned. Deferred acquisition costs are limited to their estimated realizable value by line of business based on the related unearned premiums, anticipated claims and claim expenses and anticipated investment income.
Losses and LAE	Non-life Run-off The liability for losses and LAE in the Non-life Run-off segment includes an amount determined from reported claims and an amount, based on historical loss experience and industry statistics, for losses incurred but not reported ("IBNR") determined using a variety of actuarial methods. These estimates are continually reviewed and are necessarily subject to the impact of future changes in factors such as claim severity and frequency, changes in economic conditions including the impact of inflation, legal and judicial developments, and medical cost trends. While we believe that the amount is adequate, the ultimate liability may be in excess of, or less than, the amounts provided. Adjustments will be reflected as part of net increase or reduction in losses and LAE liabilities in the periods in which they become known. Premium and commission adjustments may be triggered by incurred losses, and any amounts are recorded in the same period that the related incurred loss is recognized. Commutations of acquired companies’ exposures have the effect of accelerating the payout of claims compared to the probability-weighted ranges of actuarially projected cash flows that we apply when estimating the fair values of assets and liabilities at the time of acquisition. Any material acceleration of payout together with the impact of any material loss reserve savings in any period will also accelerate the amortization of fair value adjustments in that period. Gains or losses on settlement of losses and LAE liabilities by way of commutation or policy buy-back are recognized upon execution of a commutation or policy buyback with the insured or reinsured. Our insurance and reinsurance subsidiaries also establish provisions for LAE relating to run-off costs for the estimated duration of the run-off, which are included in losses and LAE. These provisions are assessed at each reporting date, and provisions relating to future periods are adjusted to reflect any changes in estimates of the periodic run-off costs or the duration of the run-off, including the impact of any acceleration of the run-off period that may be caused by commutations. Provisions relating to the current period together with any adjustment to future run-off provisions are included in net incurred losses and LAE in the consolidated statements of earnings. Atrium and StarStone The reserves for losses and LAE in the Atrium and StarStone segments include reserves for unpaid reported losses and for IBNR loss reserves. The reserves for unpaid reported losses and loss expenses are established by management based on reports from brokers, ceding companies and insureds and represent the estimated ultimate cost of events or conditions that have been reported to or specifically identified by us. The reserve for IBNR losses is established by us based on actuarially determined estimates of ultimate losses and loss expenses. Inherent in the estimate of ultimate losses and loss expenses are expected trends in claim severity and frequency and other factors which may vary significantly as claims are settled. Accordingly, ultimate losses and loss expenses may differ from the amounts recorded in the consolidated financial statements. These estimates are reviewed regularly and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments, if any, will be recorded in earnings in the period in which they become known. Prior period development arises from changes to loss estimates recognized in the current year that relate to loss reserves established in prev ious calendar years.
Policy Benefits for Life and Annuity Contracts	Policy benefits for life and annuity contracts (“policy benefits”) are calculated using the net level premium method and are derived using locked-in assumptions. Policy benefits are established and maintained at a level that we estimate will, when taken together with future premium payments and investment income expected to be earn ed on associated premiums, be sufficient to support all future cash flow benefit obligations and third-party servicing obligations as they become payable. We review policy benefits regularly and perform loss recognition testing based upon cash flow projections. Since the development of the policy benefits is based upon projections of future cash flows, we are required to make assumptions for mortality, longevity and morbidity rates, lapse rates, expenses and investment income. The assumptions used to determine policy benefits are determined at the inception of the contracts, reviewed and adjusted at the point of acquisition, as required, and are locked-in throughout the life of the contract unless a premium deficiency develops. These locked-in assumptions are based on a best estimate view of experience at the time they are established and may include a provision for adverse deviation. Assumptions are established based upon a combination of historical and industry experience, when available, and management judgment. Actual results could differ from these estimates. Policy benefit liabilities are reviewed periodically to determine whether a premium deficiency exists. Management reviews emerging experience and updates best estimate assumptions where appropriate. If existing policy benefit reserves, reduced by unamortized acquisition costs, together with the present value of future gross premiums using current best estimate assumptions, are insufficient in covering the present value of future benefits, settlement, and maintenance costs using current best estimate assumptions, a premium deficiency is deemed to exist. To remediate, unamortized acquisition costs are reduced until the premium deficiency has been eliminated. If unamortized acquisition costs have been entirely written off and a premium deficiency still exists, locked-in assumptions are revised and a charge for policy benefits is recognized. Because of the many assumptions and estimates used in establishing policy benefits and the long-term nature of the contracts, the reserving process, while based on actua rial techniques, is inherently uncertain.
Reinsurance Recoverable, Funds Held, and Fair Value Option	In our Non-life Run-off segment we have elected to apply the fair value option for certain loss portfolio transfer reinsurance transactions. This is an irrevocable election that applies to all balances under the insurance contract, including funds held assets, reinsurance balances recoverable, and the liability for losses and loss adjustment expenses. We use an internal model to calculate the fair value of the liability for losses and loss adjustment expenses and the reinsurance balances recoverable asset. Note 8 - "Fair Value Measurements" describes the internal model, including the observable and unobservable inputs used in the model Reinsurance Balances Recoverable Amounts billed to, and due from, reinsurers resulting from paid movements in the underlying business are calculated in accordance with the terms of the individual reinsurance contracts. Similarly, reinsurance balances recoverable related to our case reserves are calculated by applying the terms of any applicable reinsurance coverage to movements in the underlying case reserves. Our estimate of reinsurance balances recoverable related to IBNR reserves is recognized on a basis consistent with the underlying IBNR reserves. Our reinsurance balances recoverable are presented net of a provision for uncollectible amounts, reflecting the amount deemed not collectible due to credit quality, collection problems due to the location of the reinsurer, contractual disputes with reinsurers over individual contentious claims, contract language or coverage issues. Under funds held arrangements, the reinsured company has retained funds that would otherwise have been remitted to our reinsurance subsidiaries. The funds balance is credited with investment income and losses payable are deducted. Funds held are shown under two categories on the consolidated balance sheets, where funds held upon which we receive the underlying portfolio economics are shown as "Funds held - directly managed", and funds held where we receive a fixed crediting rate are shown as "Funds held by reinsured companies". Funds held by reinsured companies are carried at cost. Funds held - directly managed, carried at fair value, represents the aggregate of funds held at cost and the value of an embedded derivative. The embedded derivative relates to our contractual right to receive the return on the underlying investment portfolio economics. The investment returns on both categories of funds held are recognized in net investment income and net realized and unrealized gains (losses). The revaluation of the embedded derivative is included in net unrealized gains (losses).
Investments	Short-term investments and fixed maturity investments Short-term investments comprise investments with a maturity greater than three months up to one year from the date of purchase. Fixed maturities comprise investments with a maturity of greater than one year from the date of purchase. Short-term and fixed maturity investments classified as trading are carried at fair value, with realized and unrealized holding gains and losses included in net earnings and reported as net realized and unrealized gains and losses. Short-term and fixed maturity investments classified as available-for-sale are carried at fair value, with unrealized gains and losses excluded from net earnings and reported as a separate component of accumulated other comprehensive income. Realized gains and losses on sales of investments classified as available-for-sale are recognized in the consolidated statements of earnings. The costs of short-term and fixed maturity investments are adjusted for amortization of premiums and accretion of discounts, recognized using the effective yield method and included in net investment income. For mortgage-backed and asset-backed investments, and any other holdings for which there is a prepayment risk, prepayment assumptions are evaluated and reviewed on a regular basis. Investment purchases and sales are recorded on a trade-date basis. Realized gains and losses on the sale of investments are based upon specific identification of the cost of investments. Other-Than-Temporary Impairments Fixed maturity investments classified as available-for-sale are reviewed quarterly to determine if they have sustained an impairment of value that is, based on our judgment, considered to be other than temporary. The process includes reviewing each fixed maturity investment that is below cost and: (1) determining if we have the intent to sell the fixed maturity investment; (2) determining if it is more likely than not that we will be required to sell the fixed maturity investment before its anticipated recovery; and (3) assessing whether a credit loss exists, that is, whether we expect that the present value of the cash flows expected to be collected from the fixed maturity investment is less than the amortized cost basis of the investment. In assessing whether it is more likely than not that we will be required to sell a fixed maturity investment before its anticipated recovery, we consider various factors including our future cash flow requirements, legal and regulatory requirements, the level of our cash, cash equivalents, short-term investments and fixed maturity investments available-for-sale in an unrealized gain position, and other relevant factors. In evaluating credit losses, we consider a variety of factors in the assessment of a fixed maturity investment including: (1) the time period during which there has been a significant decline below cost; (2) the extent of the decline below cost and par; (3) the potential for the investment to recover in value; (4) an analysis of the financial condition of the issuer; (5) the rating of the issuer; and (6) failure of the issuer of the investment to make scheduled interest or principal payments. If we conclude that an investment is other-than-temporarily impaired ("OTTI"), then the difference between the fair value and the amortized cost of the investment is presented as an OTTI charge in the consolidated statements of earnings, with an offset for any non-credit related loss component of the OTTI charge to be recognized in other comprehensive income. Accordingly, only the credit loss component of the OTTI amount would have an impact on our earnings. Equities Equities are classified as trading and are carried at fair value with realized and unrealized holding gains and losses included in net earnings and reported as net realized and unrealized gains and losses. Other investments, at fair value Other investments include investments in limited partnerships and limited liability companies (collectively "private equities") and fixed income funds, hedge funds, equity funds, private credit funds and collateralized loan obligation ("CLO") equity funds that carry their investments at fair value, as well as direct investments in CLO equities. These other investments are stated at fair value, which ordinarily will be the most recently reported net asset value as advised by the fund manager or administrator. Many of our fund investments publish net asset values on a daily basis and provide daily liquidity; others report on a monthly basis. Private equities typically report quarterly. The change in fair value is included in net realized and unrealized gains and losses on investments and recognized in net earnings. Other investments, at cost Investments in life settlements are recorded as other investments, at cost, and are accounted for under the investment method whereby we recognize our initial investment in the life settlement contracts at the transaction price plus all initial direct external costs. Continuing costs to keep the policy in force, primarily life insurance premiums, increase the carrying amount of the investment. We recognize income on individual investments in life settlements when the insured dies, at an amount equal to the excess of the investment proceeds over the carrying amount of the investment at that time. The investments are subject to quarterly impairment review on a contract-by-contract basis. An investment in life settlements is considered impaired if the undiscounted cash flows resulting from the expected proceeds from the investment in life settlements are not sufficient to recover the current carrying amount for the investment in life settlements plus anticipated undiscounted future premiums and other capitalizable future costs, if any. Impaired contracts are written down to their estimated fair value, which is determined on a discounted cash flow basis using current market longevity assumptions and market yields, with any impairment charges included within net realized and unrealized gains (losses).
Cash and cash equivalents	Cash and cash equivalents Cash equivalents includes all highly liquid debt instruments purchased with an original maturity of three months or less.
Fees and Commission Income	Fees and commission income primarily includes profit commissions earned from managed Lloyd's syndicates as well as fees earned under fronting and consulting arrangements with third- party clients, which are recorded on an accrual basis.
Foreign Exchange	Our reporting currency is the U.S. dollar. Assets and liabilities of entities whose functional currency is not the U.S. dollar are translated at period end exchange rates. Revenues and expenses of such foreign entities are translated at average exchange rates during the year. The effect of the currency translation adjustments for these foreign entities is included in accumulated other comprehensive income (loss). Other foreign currency assets and liabilities that are considered monetary items are translated at exchange rates in effect at the balance sheet date. Foreign currency revenues and expenses are translated at transaction date exchange rates. These exchange gains and losses are recognized in net earnings.
Share-based Compensation	We have primarily used three types of share-based compensation: (i) restricted shares, restricted share units and performance share units, (ii) cash-settled stock appreciation rights ("SARs") and (iii) shares issued under our employee share purchase plans. With the exception of SARs and the incentive plan awards issued to certain employees of Atrium, our share-based compensation awards qualify for equity classification. The fair value of the compensation cost is measured at the grant date and is expensed over the service period of the award. The SARs and the Atrium incentive plan awards are classified as liability awards. Liability classified awards are recorded at fair value within other liabilities in the consolidated balance sheet with changes in fair value relating to the vested portion of the award recorded within general and administrative expenses in the consolidated statements of earnings.
Derivative Instruments
Income Taxes	Certain of our subsidiaries and branches operate in jurisdictions where they are subject to taxation. Current and deferred income taxes are charged or credited to net income, or, in certain cases, to accumulated other comprehensive income, based upon enacted tax laws and rates applicable in the relevant jurisdiction in the period in which the tax becomes accruable or realizable. Deferred income taxes are provided for all temporary differences between the bases of assets and liabilities used in the financial statements and those used in the various jurisdictional tax returns. When our assessment indicates that it is more likely than not that all or some portion of deferred income tax assets will not be realized, a valuation allowance is recorded against the deferred tax assets. We recognize a tax benefit relating to uncertain tax positions only where the position is more likely than not to be sustained assuming examination by tax authorities. A liability is recognized for any tax benefit (along with any interest and penalty, if applicable) claimed in a tax return in excess of the amount allowed to be recognized in the financial statements under U.S. GAAP. Any changes in amounts recognized are recorded in the period in which they are determined.
Earnings Per Share	Basic earnings per share is based on the weighted average number of ordinary shares outstanding and excludes potentially dilutive securities such as restricted shares, restricted share units, warrants, options and convertible securities. Diluted earnings per share is based on the weighted average number of ordinary and ordinary share equivalents outstanding calculated using the treasury stock method for all potentially dilutive securities. When the effect of dilutive securities would be anti-dilutive, these securities are excluded from the calculation of diluted earnings per share.
Acquisitions	The acquisition method is used to account for all business acquisitions. This method requires that we record the acquired assets and liabilities at their estimated fair value. The fair values of each of the acquired reinsurance assets and liabilities are derived from probability-weighted ranges of the associated projected cash flows, based on actuarially prepared information and management’s run-off strategy. Our run-off strategy, as well as that of other run-off market participants, is expected to be different from the seller's as generally sellers are not specialized in running off insurance and reinsurance liabilities whereas we and other market participants do specialize in such run-offs. The key assumptions used by us and, we believe, by other run-off market participants in the fair valuation of acquired companies are (i) the projected payout, timing and amount of claims liabilities; (ii) the related projected timing and amount of reinsurance collections; (iii) an appropriate discount rate, which is applied to determine the present value of the future cash flows; (iv) the estimated unallocated LAE to be incurred over the life of the run-off; (v) the impact of any accelerated run-off strategy; and (vi) an appropriate risk margin.
Acquisitions, Fair Value Adjustment	The difference between the original carrying value of reinsurance liabilities and reinsurance assets acquired at the date of acquisition and their fair value is recorded as an intangible asset or other liability, which we refer to as the fair value adjustment ("FVA"). The FVA is amortized over the estimated payout period of outstanding losses and loss expenses acquired. To the extent the actual payout experience after the acquisition is materially faster or slower than anticipated at the time of the acquisition, there is an adjustment to the estimated ultimate loss reserves, or there are changes in bad debt provisions or in estimates of future run-off costs following accelerated payouts, then the amortization of the FVA is adjusted to reflect such changes.
Goodwill	The difference between the fair value of net assets acquired and the purchase price is recorded as a goodwill asset or as a gain from bargain purchase in the consolidated statements of earnings. Goodwill is established initially upon acquisition and assessed at least annually for impairment. If the goodwill asset is determined to be impaired it is written down in the period in which the determination is made.
Intangible Assets	Intangible assets represent the fair value adjustments related to unpaid losses and LAE, reinsurance balances recoverable and policy benefits for life and annuity contracts along with the intangible assets arising from the acquisitions of Atrium and StarStone. Definite-lived intangible assets are amortized over their useful lives. Amortization of intangible assets is recognized in the consolidated statement of earnings. Indefinite-lived intangible assets are not subject to amortization. The carrying values of intangible assets are reviewed for indicators of impairment at least annually. Impairment is recognized if the carrying values of the definite-lived intangible assets are not recoverable from their undiscounted cash flows and are measured as the difference between the carrying value and the fair value.
Retroactive Reinsurance and Deferred Charges	Retroactive reinsurance policies provide indemnification of losses and LAE with respect to past loss events. In our Non-life Run-off segment we use the balance sheet accounting approach for assumed loss portfolio transfers, whereby at the inception of the contract there are no premiums or losses recorded in earnings. At the inception of a contract, a deferred charge asset is recorded for the excess, if any, of the estimated ultimate losses payable over the premiums received. Deferred charges, recorded in other assets, are amortized over the estimated claim payment period of the related contract with the periodic amortization reflected in earnings as a component of losses and LAE. Deferred charges amortization is adjusted at each reporting period to reflect new estimates of the amount and timing of remaining loss payments. Changes in the estimated amount and the timing of payments of unpaid losses may have an effect on the unamortized deferred charges and the amount of periodic amortization. Deferred charges are assessed at each reporting period for impairment. If the asset is determined to be impaired, it is written down in the period in which the determination is made. In our Non-life Run-off and StarStone segments we have ceded business to KaylaRe Ltd., an affiliated reinsurer, as described in Note 21 - "Related Party Transactions" . The reinsurance ceded by StarStone to KaylaRe Ltd. during the year ended December 31, 2016 was mostly recognized as retroactive reinsurance, except for the unearned ceded premium as at December 31, 2016 which was recognized as prospective reinsurance. The reinsurance ceded by StarStone to KaylaRe Ltd. from January 1, 2017 was recognized as prospective reinsurance.
Redeemable Noncontrolling Interest	In connection with the acquisitions of Arden, Atrium and StarStone, certain subsidiaries issued shares to noncontrolling interests. These shares provide certain redemption rights to the holders, which may be settled in our own shares or cash or a combination of cash and shares, at our option. Redeemable noncontrolling interest with redemption features that are not solely within our control are classified within temporary equity in the consolidated balance sheets and carried at the redemption value, which is fair value. Change in the fair value is recognized through retained earnings as if the balance sheet date were also the redemption date.
Internal-use Software	Direct internal and external costs to acquire or develop internal-use software have been capitalized. We only capitalize costs incurred after the preliminary project stage has been completed, and when management has authorized and committed to funding the project and it is probable that the project will be completed and the software will be used to perform the functions intended. Capitalized costs related to internal-use software are amortized on a straight-line basis over the estimated useful lives of the assets. These capitalized costs are also assessed for impairment when impairment indicators exist.
Held-for-sale Business and Discontinued Operations	We report a business as held-for-sale when certain criteria are met which include, (1) management either approving the sale or receiving approval to sell the business and is committed to a formal plan to sell the business, (2) the business is available for immediate sale in its present condition, (3) the business is being actively marketed for sale at a price that is reasonable in relation to its current fair value, (4) the sale is anticipated to occur during the next 12 months, among other specified criteria. A business classified as held for sale is recorded at the lower of its carrying amount or estimated fair value less costs to sell. If the carrying amount of the business exceeds its estimated fair value, a loss is recognized. Assets and liabilities related to the businesses classified as held-for-sale are separately reported in our Consolidated Balance Sheets beginning in the period in which the business is classified as held-for-sale. Refer to Note 5 for further information regarding our held-for-sale business. The Pavonia business was also classified as a discontinued operation whose results were aggregated and presented within one line in the consolidated statements of earnings.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2017
Dana Companies
Business Acquisition [Line Items]
Purchase Price and Fair Value of Assets Acquired	The total consideration for the transaction was $88.5 million . Purchase price $ 88,500 Net assets acquired at fair value $ 88,500 Excess of purchase price over fair value of net assets acquired $ —
Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed as of Date of Acquisition	The following table summarizes the fair values of the assets acquired and liabilities assumed at the acquisition date, recorded in our Non-life Run-off segment. Total ASSETS Short-term investments, trading, at fair value $ 22,747 Fixed maturities, trading, at fair value 61,389 Other investments, at fair value 46,589 Total investments 130,725 Cash and cash equivalents 58,430 Restricted cash and cash equivalents 1,692 Other assets - Insurance balances recoverable 133,032 Other assets 5,383 TOTAL ASSETS 329,262 LIABILITIES Other liabilities - Asbestos related 220,496 Other liabilities 20,266 TOTAL LIABILITIES 240,762 NET ASSETS ACQUIRED AT FAIR VALUE $ 88,500
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements
Business Acquisition [Line Items]
Pro Forma Condensed Combined Statement of Earnings	The following unaudited pro forma condensed combined statement of earnings for the year ended December 31, 2015 combines our historical consolidated statements of earnings with those of Sussex, Alpha and Wilton Re, giving effect to the business combinations and related transactions as if they had occurred on January 1, 2015. For the year ended December 31, 2015, the operating results of Sussex, Alpha and Wilton Re have been included in the consolidated financial statements from each of their respective dates of acquisition. The unaudited pro forma financial information presented below is for informational purposes only and is not necessarily indicative of the results of operations that would have been achieved if the acquisitions of Sussex, Alpha and Wilton Re and related transactions had taken place at the beginning of each period presented, nor is it indicative of future results. Enstar Group Unaudited 2015 Sussex Alpha Wilton Re Pro forma Enstar Total income $ 904,460 $ 29,990 $ 31,884 $ 5,793 $ 9,494 $ 981,621 Total expenses (694,119 ) (39,860 ) (47,026 ) (3,628 ) 5,894 (778,739 ) Total noncontrolling interest 9,950 — — — — 9,950 Net earnings (loss) $ 220,291 $ (9,870 ) $ (15,142 ) $ 2,165 $ 15,388 $ 212,832
Summary of Pro Forma Adjustments to Pro Forma Condensed Statement of Earnings	Summary of the Pro Forma Adjustments to the Pro Forma Condensed Consolidated Statement of Earnings for the Twelve Months Ended December 31, 2015 (Unaudited): Income: (a) Reversal of amortization of fair value adjustments related to unearned premium included in Enstar Group results but reflected in 2014 pro formas 13,344 (b) Adjustment to recognize amortization of fair value adjustments related to unearned premium (3,850 ) 9,494 Expenses: (a) Adjustment to interest expense to reflect financing costs of the acquisition for the period (1,098 ) (b) Adjustment to recognize amortization of fair value adjustments related to acquired losses and LAE liabilities and reinsurance balances recoverable (451 ) (c) Reversal of amortization of fair value adjustments related to acquisition costs included in Enstar Group results but reflected in 2014 pro formas 16,173 (d) Adjustment to income taxes for pro forma adjustments (8,730 ) 5,894
Nationale Suisse Assurance S.A.
Business Acquisition [Line Items]
Purchase Price and Fair Value of Assets Acquired	The total consideration for the transaction was €32.8 million (or $35.2 million ). Purchase price $ 35,225 Net assets acquired at fair value $ 35,225 Excess of purchase price over fair value of net assets acquired $ —
Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed as of Date of Acquisition	The following table summarizes the fair values of the assets acquired and liabilities assumed in the Alpha transaction at the acquisition date, allocated between our Non-life Run-off segment and our other activities. Non-life Other Total ASSETS Short-term investments, trading, at fair value $ 8,644 $ — $ 8,644 Short-term investments, available-for-sale, at fair value — 6,687 6,687 Fixed maturities, trading, at fair value 31,350 — 31,350 Fixed maturities, available-for-sale, at fair value — 96,656 96,656 Other investments, at fair value 1,339 — 1,339 Total investments 41,333 103,343 144,676 Cash and cash equivalents 39,451 25,258 64,709 Reinsurance balances recoverable — reserves 4,041 302 4,343 Reinsurance balances recoverable — paid 10,831 1,320 12,151 Prepaid reinsurance premiums 3,213 — 3,213 Other assets 3,097 2,298 5,395 TOTAL ASSETS 101,966 132,521 234,487 LIABILITIES Losses and LAE 56,021 117,188 173,209 Funds withheld 473 — 473 Insurance and reinsurance balances payable 6,212 779 6,991 Unearned premium 5,969 — 5,969 Other liabilities 9,745 2,875 12,620 TOTAL LIABILITIES 78,420 120,842 199,262 NET ASSETS ACQUIRED AT FAIR VALUE $ 23,546 $ 11,679 $ 35,225
Wilton Re
Business Acquisition [Line Items]
Purchase Price and Fair Value of Assets Acquired	Purchase price $ 173,058 Net assets acquired at fair value $ 173,058 Excess of purchase price over fair value of net assets acquired $ —
Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed as of Date of Acquisition	The following table summarizes the fair values of the assets acquired and liabilities assumed at the acquisition date. ASSETS Other investments $ 142,182 Cash and cash equivalents 5,043 Other assets 26,376 TOTAL ASSETS $ 173,601 TOTAL LIABILITIES 543 NET ASSETS ACQUIRED AT FAIR VALUE $ 173,058
Sussex Insurance Company
Business Acquisition [Line Items]
Purchase Price and Fair Value of Assets Acquired	Purchase price $ 218,000 Net assets acquired at fair value $ 218,000 Excess of purchase price over fair value of net assets acquired $ —
Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed as of Date of Acquisition	The following table summarizes the fair values of the assets acquired and liabilities assumed at the acquisition date. ASSETS Short-term investments, trading, at fair value $ 85,309 Fixed maturities, trading, at fair value 523,227 Equities, trading, at fair value 31,439 Total investments 639,975 Cash and cash equivalents 358,458 Restricted cash and cash equivalents 15,279 Accrued interest receivable 3,984 Premiums receivable 37,190 Reinsurance balances recoverable 483,816 Prepaid reinsurance premiums 28,751 Other assets 43,939 TOTAL ASSETS 1,611,392 LIABILITIES Losses and LAE 1,257,205 Insurance and reinsurance balances payable 3,030 Unearned premium 79,293 Funds withheld 42,090 Other liabilities 11,774 TOTAL LIABILITIES 1,393,392 NET ASSETS ACQUIRED AT FAIR VALUE $ 218,000

Divestitures, Held-For-Sale B41

Divestitures, Held-For-Sale Businesses and Discontinuing Operations (Tables)	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Financial Information of Held-For-Sale Business	The following table summarizes the components of assets and liabilities held-for-sale on our consolidated balance sheet as at December 31, 2017 and 2016 in relation to Pavonia: December 31, December 31, Assets: Fixed maturities, trading, at fair value $ 20,770 $ 326,382 Fixed maturities, held-to-maturity, at amortized cost — 765,554 Equities, trading, at fair value 765 4,428 Other investments, at fair value — 15,114 Cash and cash equivalents 6,314 18,018 Restricted cash and cash equivalents 13 5,202 Deferred tax assets — 31,500 Reinsurance balances recoverable 1,728 18,029 Other assets 269 60,229 Assets of businesses held for sale 29,859 1,244,456 Less: Accrual of loss on sale (5,508 ) — Total assets held for sale $ 24,351 $ 1,244,456 Liabilities: Policy benefits for life and annuity contracts $ 10,666 $ 1,144,850 Other liabilities 605 5,937 Total liabilities held for sale $ 11,271 $ 1,150,787 The following table summarizes the components of net earnings (losses) from discontinued operations on the consolidated statements of earnings for the years ended December 31, 2017 , 2016 and 2015 : December 31, December 31, December 31, Operations: INCOME Net premiums earned $ 55,906 $ 69,089 $ 85,327 Net investment income 41,117 38,140 35,404 Net realized and unrealized gains 577 4,263 271 Other income 1,564 1,912 7,690 $ 99,164 $ 113,404 $ 128,692 EXPENSES Life and annuity policy benefits 84,029 76,594 97,472 Acquisition costs 9,025 9,836 13,712 General and administrative expenses 12,813 14,416 13,886 Other expenses (26 ) 199 486 $ 105,841 $ 101,045 $ 125,556 EARNINGS (LOSS) BEFORE INCOME TAXES (6,677 ) 12,359 3,136 INCOME TAXES (3,190 ) $ (396 ) (5,167 ) NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS BEFORE GAIN ON SALE $ (9,867 ) $ 11,963 $ (2,031 ) Disposal: Consideration received $ 120,000 — — Less: Carrying value of subsidiary 86,961 — — Less: Cumulative currency translation adjustment previously recorded in accumulated other comprehensive income 12,179 — — Gain on sale of subsidiary $ 20,860 $ — $ — NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS $ 10,993 $ 11,963 $ (2,031 ) The following table presents the cash flows of Pavonia whilst under our ownership for the years ended December 31, 2017 , 2016 and 2015 : December 31, December 31, December 31, Operating activities $ 75,714 $ (71,521 ) $ (5,893 ) Investing activities 42,542 56,646 (24,766 ) Change in cash of businesses held for sale $ 118,256 $ (14,875 ) $ (30,659 )

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Estimated Fair Values of Investments in Fixed Maturity Investments, Short-Term Investments and Equities, Trading Securities	The fair values of our fixed maturity investments, short-term investments and equities classified as trading were as follows: December 31, December 31, U.S. government and agency $ 554,036 $ 840,274 Non-U.S. government 607,132 267,363 Corporate 3,363,060 2,387,322 Municipal 100,221 47,181 Residential mortgage-backed 288,713 373,528 Commercial mortgage-backed 421,548 217,212 Asset-backed 541,574 478,280 Total fixed maturity and short-term investments 5,876,284 4,611,160 Equities — U.S. 106,363 95,047 Equities — International 240 — $ 5,982,887 $ 4,706,207
Summary of Amortized Cost and Estimated Fair Value of Fixed Maturity and Short-term Investments by Contractual Maturity	The contractual maturities of our fixed maturity and short-term investments classified as trading are shown below. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call o r prepayment penalties. As at December 31, 2017 Amortized Cost Fair Value % of Total Fair Value One year or less $ 398,054 $ 398,083 6.8 % More than one year through two years 340,531 341,753 5.8 % More than two years through five years 1,283,898 1,286,527 21.9 % More than five years through ten years 1,235,079 1,249,887 21.3 % More than ten years 1,278,126 1,348,199 22.9 % Residential mortgage-backed 285,312 288,713 4.9 % Commercial mortgage-backed 427,469 421,548 7.2 % Asset-backed 534,893 541,574 9.2 % $ 5,783,362 $ 5,876,284 100.0 % The contractual maturities of our fixed maturity and short-term investments classified as available-for-sale are shown below. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. As at December 31, 2017 Amortized Cost Fair Value % of Total Fair Value One year or less $ 50,135 $ 49,828 23.7 % More than one year through two years 17,549 17,427 8.3 % More than two years through five years 53,690 54,355 25.8 % More than five years through ten years 46,743 47,735 22.7 % More than ten years 39,576 40,536 19.3 % Residential mortgage-backed 31 31 — % Asset-backed 373 373 0.2 % $ 208,097 $ 210,285 100.0 %
Amortized Cost and Estimated Fair Values of Company's Fixed Maturity and Short-Term Investments Classified as Available-for-Sale	The amortized cost and fair values of our fixed maturity and short-term investments classified as available-for-sale were as follows: As at December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Non-OTTI Fair Value U.S. government and agency $ 4,210 $ — $ (23 ) $ 4,187 Non-U.S. government 84,776 1,249 (588 ) 85,437 Corporate 113,561 2,436 (876 ) 115,121 Municipal 5,146 8 (18 ) 5,136 Residential mortgage-backed 31 — — 31 Asset-backed 373 — — 373 $ 208,097 $ 3,693 $ (1,505 ) $ 210,285 As at December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Non-OTTI Fair Value U.S. government and agency $ 12,784 $ 32 $ (106 ) $ 12,710 Non-U.S. government 86,897 1,303 (2,777 ) 85,423 Corporate 159,243 2,040 (2,628 ) 158,655 Municipal 6,585 12 (21 ) 6,576 Residential mortgage-backed 488 39 — 527 Asset-backed 3,867 9 — 3,876 $ 269,864 $ 3,435 $ (5,532 ) $ 267,767
Summary of Investments Classified as Available-for-Sale in Unrealized Loss Position as Well as Aggregate Fair Value and Gross Unrealized Loss by Length of Time	The following tables summarize our fixed maturity and short-term investments classified as available-for-sale in a gross unrealized loss position: 12 Months or Greater Less Than 12 Months Total As at December 31, 2017 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fixed maturity investments, at fair value U.S. government and agency $ 2,344 $ (16 ) $ 1,842 $ (7 ) $ 4,186 $ (23 ) Non-U.S. government 11,101 (373 ) 20,965 (215 ) 32,066 (588 ) Corporate 9,177 (807 ) 24,200 (69 ) 33,377 (876 ) Municipal 369 (5 ) 3,605 (13 ) 3,974 (18 ) Total fixed maturity investments $ 22,991 $ (1,201 ) $ 50,612 $ (304 ) $ 73,603 $ (1,505 ) 12 Months or Greater Less Than 12 Months Total As at December 31, 2016 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fixed maturity and short-term investments, at fair value U.S. government and agency $ — $ — $ 10,743 $ (106 ) $ 10,743 $ (106 ) Non-U.S. government 8,316 (1,794 ) 30,086 (983 ) 38,402 (2,777 ) Corporate 8,003 (1,800 ) 42,304 (828 ) 50,307 (2,628 ) Municipal — — 3,132 (21 ) 3,132 (21 ) Total fixed maturity and short-term investments $ 16,319 $ (3,594 ) $ 86,265 $ (1,938 ) $ 102,584 $ (5,532 )
Credit Ratings Company's Fixed Maturity and Short-Term Investments Available-for-Sale	The following table sets forth the credit ratings of our fixed maturity and short-term investments as of December 31, 2017 : Amortized Cost Fair Value % of Total Investments AAA Rated AA Rated A Rated BBB Rated Non- Investment Grade Not Rated U.S. government and agency $ 561,483 $ 558,223 9.2 % $ 556,859 $ 1,364 $ — $ — $ — $ — Non-U.S. government 665,056 692,569 11.4 % 134,619 409,315 79,030 62,964 6,641 — Corporate 3,413,543 3,478,181 57.2 % 123,059 375,252 1,854,503 932,238 188,237 4,892 Municipal 103,299 105,357 1.7 % 26,313 62,605 12,864 3,575 — — Residential mortgage-backed 285,343 288,744 4.7 % 166,386 7,425 14,204 678 98,997 1,054 Commercial mortgage-backed 427,469 421,548 6.9 % 222,656 38,176 77,811 59,358 9,555 13,992 Asset-backed 535,266 541,947 8.9 % 272,784 43,539 68,489 69,116 88,019 — Total $ 5,991,459 6,086,569 100.0 % 1,502,676 937,676 2,106,901 1,127,929 391,449 19,938 % of total fair value 24.7 % 15.4 % 34.6 % 18.6 % 6.4 % 0.3 %
Other Investments	The following table summarizes our other investments carried at fair value: December 31, December 31, Private equities and private equity funds $ 289,556 $ 300,529 Fixed income funds 229,999 249,023 Fixed income hedge funds 63,773 85,976 Equity funds 249,475 223,571 CLO equities 56,765 61,565 CLO equity funds 12,840 15,440 Private credit funds 10,156 — Other 828 943 $ 913,392 $ 937,047
Schedule of Life Settlement Contracts, Investment Method	The following table presents further information regarding our investments in life settlements as of December 31, 2017 and 2016 . December 31, 2017 December 31, 2016 Number of Contracts Carrying Face Value (Death Benefits) Number of Contracts Carrying Face Value (Death Benefits) Remaining Life Expectancy of Insureds: 0 – 1 year — $ — $ — 2 $ 461 $ 700 1 – 2 years 11 17,655 29,471 7 11,396 18,337 2 – 3 years 10 7,524 19,906 11 15,338 29,715 3 – 4 years 20 16,119 32,411 17 17,013 32,189 4 – 5 years 13 13,960 32,730 16 10,377 23,302 Thereafter 162 70,363 390,843 181 77,066 431,034 Total 216 $ 125,621 $ 505,361 234 $ 131,651 $ 535,277
Realized Gain (Loss) on Investments	Components of net realized and unrealized gains (losses) for the years ended December 31, 2017 , 2016 and 2015 were as follows: 2017 2016 2015 Net realized gains (losses) on sale: Gross realized gains on fixed maturity securities, available-for-sale $ 616 $ 405 $ 396 Gross realized (losses) on fixed maturity securities, available-for-sale securities (125 ) (21 ) (130 ) Net realized investment gains (losses) on fixed maturity securities, trading 4,695 1,848 (4,291 ) Net realized investment gains on equity securities, trading 701 5,348 19,884 Net realized investment losses on funds held - directly managed (4,219 ) (14,616 ) — Total net realized gains (losses) on sale 1,668 (7,036 ) 15,859 Net unrealized gains (losses): Fixed maturity securities, trading 35,878 36,314 (52,918 ) Equity securities, trading 16,498 6,561 (21,875 ) Other investments 102,388 70,296 17,411 Change in fair value of embedded derivative on funds held – directly managed 32,928 (28,317 ) — Change in value of fair value option on funds held - directly managed 974 — — Total net unrealized gains (losses) 188,666 84,854 (57,382 ) Net realized and unrealized gains (losses) $ 190,334 $ 77,818 $ (41,523 )
Unrealized Gain (Loss) on Investments	Components of net realized and unrealized gains (losses) for the years ended December 31, 2017 , 2016 and 2015 were as follows: 2017 2016 2015 Net realized gains (losses) on sale: Gross realized gains on fixed maturity securities, available-for-sale $ 616 $ 405 $ 396 Gross realized (losses) on fixed maturity securities, available-for-sale securities (125 ) (21 ) (130 ) Net realized investment gains (losses) on fixed maturity securities, trading 4,695 1,848 (4,291 ) Net realized investment gains on equity securities, trading 701 5,348 19,884 Net realized investment losses on funds held - directly managed (4,219 ) (14,616 ) — Total net realized gains (losses) on sale 1,668 (7,036 ) 15,859 Net unrealized gains (losses): Fixed maturity securities, trading 35,878 36,314 (52,918 ) Equity securities, trading 16,498 6,561 (21,875 ) Other investments 102,388 70,296 17,411 Change in fair value of embedded derivative on funds held – directly managed 32,928 (28,317 ) — Change in value of fair value option on funds held - directly managed 974 — — Total net unrealized gains (losses) 188,666 84,854 (57,382 ) Net realized and unrealized gains (losses) $ 190,334 $ 77,818 $ (41,523 )
Schedule of Carrying Value of Restricted Investments	The carrying value of our restricted assets, including restricted cash of $257.7 million and $363.8 million , as of December 31, 2017 and 2016 , respectively, was as follows: December 31, December 31, Collateral in trust for third party agreements $ 3,118,892 $ 1,975,022 Assets on deposit with regulatory authorities 599,829 882,400 Collateral for secured letter of credit facilities 151,467 177,263 Funds at Lloyd's (1) 234,833 220,328 $ 4,105,021 $ 3,255,013 (1) Our underwriting businesses include three Lloyd's syndicates. Lloyd's determines the required capital principally through the annual business plan of each syndicate. This capital is referred to as "Funds at Lloyd's" and will be drawn upon in the event that a syndicate has a loss that cannot be funded from other sources. As at December 31, 2017 , our combined Funds at Lloyd's were comprised of cash and investments of $234.8 million and unsecured letters of credit of $165.0 million . At December 31, 2017 , we had an unsecured letter of credit agreement for Funds at Lloyd’s purposes ("FAL Facility") to issue up to $165.0 million of letters of credit, with a provision to increase the facility up to $200.0 million . On February 8, 2018, we amended and restated the FAL Facility to issue up to $325.0 million of letters of credit, with a provision to increase the facility up to $400.0 million . The FAL Facility is available to satisfy our Funds at Lloyd’s requirements and expires in 2022.

Funds Held - Directly Managed (

Funds Held - Directly Managed (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Carrying Values of Assets and Liabilities Underlying Funds Held - Directly Managed	The following table presents the fair values of assets and liabilities underlying the funds held - directly managed account as at December 31, 2017 and 2016 : December 31, December 31, Fixed maturity investments: U.S. government and agency $ 69,850 $ 47,885 Non-U.S. government 2,926 5,961 Corporate 695,490 663,556 Municipal 58,930 38,927 Residential mortgage-backed 29,439 — Commercial mortgage-backed 211,186 151,395 Asset-backed 97,565 79,806 Total fixed maturity investments $ 1,165,386 $ 987,530 Other assets 14,554 7,135 $ 1,179,940 $ 994,665
Contractual Maturities of Fixed Maturity Investments Underlying Funds Held - Directly Managed	The contractual maturities of our fixed maturity investments underlying the funds held - directly managed account are shown below. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. As at December 31, 2017 Amortized Cost Fair Value % of Total Fair Value One year or less $ 49,093 $ 49,007 4.2 % More than one year through two years 54,447 54,204 4.7 % More than two years through five years 230,872 230,256 19.8 % More than five years through ten years 248,525 248,675 21.3 % More than ten years 234,556 245,054 21.0 % Residential mortgage-backed 29,544 29,439 2.5 % Commercial mortgage-backed 215,603 211,186 18.1 % Asset-backed 97,160 97,565 8.4 % $ 1,159,800 $ 1,165,386 100.0 %
Funds Held - Directly Managed, by Credit Rating	The following table sets forth the credit ratings of our fixed maturity investments underlying the funds held - directly managed account as of December 31, 2017 : Amortized Cost Fair Value % of Total Investments AAA Rated AA Rated A Rated BBB Rated U.S. government and agency $ 69,754 $ 69,850 6.0 % $ 69,850 $ — $ — $ — Non-U.S. government 2,977 2,926 0.3 % — — 2,926 — Corporate 688,239 695,490 59.6 % 7,754 25,418 315,385 346,933 Municipal 56,523 58,930 5.1 % — 20,921 30,449 7,560 Residential mortgage-backed 29,544 29,439 2.5 % 29,439 — — — Commercial mortgage-backed 215,603 211,186 18.1 % 202,608 6,576 2,002 — Asset-backed 97,160 97,565 8.4 % 93,849 3,716 — — Total $ 1,159,800 $ 1,165,386 100.0 % $ 403,500 $ 56,631 $ 350,762 $ 354,493 % of total fair value 34.6 % 4.9 % 30.1 % 30.4 %
Funds Held, Directly Managed, Investment Income [Table Text Block]	Major categories of net investment income underlying the funds held - directly managed account for the year ended December 31, 2017 and 2016 are summarized as follows: 2017 2016 Fixed maturity investments $ 33,558 $ 5,705 Short-term investments and cash and cash equivalents 292 64 Gross investment income 33,850 5,769 Investment expenses (1,371 ) — Investment income on funds held - directly managed $ 32,479 $ 5,769
Net Realized and Unrealized Investment (Losses) Gains	Net realized gains (losses) and change in fair value for the year ended December 31, 2017 and 2016 are summarized as follows: 2017 2016 Net realized losses on fixed maturity securities $ (4,219 ) $ (14,616 ) Change in fair value of embedded derivative 32,928 (28,317 ) Change in value of fair value option on funds held- directly managed 974 — Net realized gains (losses) and change in fair value of funds held- directly managed $ 29,683 $ (42,933 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Categorized Investments Recorded at Fair Value among Levels	We have categorized our investments that are recorded at fair value on a recurring basis among levels based on the observability of inputs, or at fair value using NAV per share (or its equivalent) as follows: December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value Based on NAV as Practical Expedient Total Fair Value Investments: Fixed maturity investments: U.S. government and agency $ — $ 558,223 $ — $ — $ 558,223 Non-U.S. government — 692,569 — — 692,569 Corporate — 3,411,003 67,178 — 3,478,181 Municipal — 105,357 — — 105,357 Residential mortgage-backed — 285,664 3,080 — 288,744 Commercial mortgage-backed — 400,054 21,494 — 421,548 Asset-backed — 514,055 27,892 — 541,947 $ — $ 5,966,925 $ 119,644 $ — $ 6,086,569 Equities: Equities — U.S. $ 103,652 $ 2,711 $ — $ — $ 106,363 Equities — International — 240 — — 240 $ 103,652 $ 2,951 $ — $ — $ 106,603 Other investments: Private equities and private equity funds $ — $ — $ — $ 289,556 $ 289,556 Fixed income funds — 202,570 — 27,429 229,999 Fixed income hedge funds — — — 63,773 63,773 Equity funds — 121,046 — 128,429 249,475 CLO equities — — 56,765 — 56,765 CLO equity funds — — — 12,840 12,840 Private credit funds — — — 10,156 10,156 Other — — 314 514 828 $ — $ 323,616 $ 57,079 $ 532,697 $ 913,392 Total Investments $ 103,652 $ 6,293,492 $ 176,723 $ 532,697 $ 7,106,564 Funds Held - Directly Managed: U.S. government and agency $ — $ 69,850 $ — $ — $ 69,850 Non-U.S. government — 2,926 — — 2,926 Corporate — 695,490 — — 695,490 Municipal — 58,930 — — 58,930 Residential mortgage-backed — 29,439 — — 29,439 Commercial mortgage-backed — 211,186 — — 211,186 Asset-backed — 97,565 — — 97,565 Other assets — 14,554 — — 14,554 $ — $ 1,179,940 $ — $ — $ 1,179,940 Reinsurance balances recoverable: $ — $ — $ 542,224 $ — $ 542,224 Other Assets: Derivative Instruments $ — $ 319 $ — $ — $ 319 $ — $ 319 $ — $ — $ 319 Losses and LAE: $ — $ — $ 1,794,669 $ — $ 1,794,669 Other Liabilities: Derivative Instruments $ — $ 7,246 $ — $ — $ 7,246 $ — $ 7,246 $ — $ — $ 7,246 December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value Based on NAV as Practical Expedient Total Fair Value Investments: Fixed maturity investments: U.S. government and agency $ — $ 852,984 $ — $ — $ 852,984 Non-U.S. government — 352,786 — — 352,786 Corporate — 2,471,444 74,534 — 2,545,978 Municipal — 53,757 — — 53,757 Residential mortgage-backed — 374,055 — — 374,055 Commercial mortgage-backed — 204,999 12,213 — 217,212 Asset-backed — 467,463 14,692 — 482,155 $ — $ 4,777,488 $ 101,439 $ — $ 4,878,927 Equities: Equities — U.S. $ 91,287 $ 3,760 $ — $ — $ 95,047 $ 91,287 $ 3,760 $ — $ — $ 95,047 Other investments: Private equities and private equity funds $ — $ — $ 15,000 $ 285,529 $ 300,529 Fixed income funds — 223,636 — 25,387 249,023 Fixed income hedge funds — — — 85,976 85,976 Equity funds — 133,802 — 89,769 223,571 CLO equities — — 61,565 — 61,565 CLO equity funds — — — 15,440 15,440 Other — — 313 630 943 $ — $ 357,438 $ 76,878 $ 502,731 $ 937,047 Total Investments $ 91,287 $ 5,138,686 $ 178,317 $ 502,731 $ 5,911,021 Funds Held - Directly Managed: U.S. government and agency $ — $ 47,885 $ — $ — $ 47,885 Non-U.S. government — 5,961 — — 5,961 Corporate — 663,556 — — 663,556 Municipal — 38,927 — — 38,927 Commercial mortgage-backed — 151,395 — — 151,395 Asset-backed — 79,806 — — 79,806 Other assets — 7,135 — — 7,135 $ — $ 994,665 $ — $ — $ 994,665 Other Assets: Derivative Instruments $ — $ 2,930 $ — $ — $ 2,930 $ — $ 2,930 $ — $ — $ 2,930 Other Liabilities: Derivative Instruments $ — $ 74 $ — $ — $ 74 $ — $ 74 $ — $ — $ 74
Reconciliation of Beginning and Ending Balances for All Investments Measured at Fair Value on Recurring Basis	The following table presents a reconciliation of the beginning and ending balances for all investments measured at fair value on a recurring basis using Level 3 inputs during the years ended December 31, 2017 and 2016 : 2017 Corporate Residential mortgage-backed Commercial mortgage-backed Asset-backed Other Investments Total Beginning fair value $ 74,534 $ — $ 12,213 $ 14,692 $ 76,878 — $ 178,317 Purchases 28,872 711 21,306 9,749 435 — 61,073 Sales (37,941 ) (37 ) (424 ) (20,795 ) (12,350 ) — (71,547 ) Total realized and unrealized gains (losses) 249 (16 ) (434 ) 205 (7,884 ) — (7,880 ) Transfer into Level 3 from Level 2 24,431 3,085 18,974 56,074 — — 102,564 Transfer out of Level 3 into Level 2 (22,967 ) (663 ) (30,141 ) (32,033 ) — — (85,804 ) Ending fair value $ 67,178 $ 3,080 $ 21,494 $ 27,892 $ 57,079 — $ 176,723 2016 Corporate Residential mortgage-backed Commercial mortgage-backed Asset-backed Other Investments Total Beginning fair value $ — $ — $ 26,704 $ 120,440 $ 77,016 $ 224,160 Purchases 24,586 — 14,216 19,750 6,885 65,437 Sales (11,011 ) (2,178 ) (14,071 ) (25,581 ) (12,933 ) (65,774 ) Total realized and unrealized gains (losses) (841 ) (24 ) (460 ) (1,897 ) 5,910 2,688 Transfer into Level 3 from Level 2 64,134 2,781 23,628 31,778 — 122,321 Transfer out of Level 3 into Level 2 (2,334 ) (579 ) (37,804 ) (129,798 ) — (170,515 ) Ending fair value $ 74,534 $ — $ 12,213 $ 14,692 $ 76,878 $ 178,317

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Foreign Currency Forward Exchange Contracts	The following table presents the gross notional amounts and the estimated fair values recorded within other assets and liabilities related to our qualifying foreign currency forward exchange rate contracts as at December 31, 2017 and 2016 : December 31, 2017 December 31, 2016 Fair Value Fair Value Gross Notional Amount Assets Liabilities Gross Notional Amount Assets Liabilities Foreign exchange forward - AUD $ 32,810 $ — $ 965 $ 45,467 $ 2,753 $ 74 Foreign exchange forward - CAD 27,141 11 512 37,175 177 — Total qualifying hedges $ 59,951 $ 11 $ 1,477 $ 82,642 $ 2,930 $ 74 The following table presents the amounts of the net gains and losses deferred in the currency translation adjustment ("CTA") account, which is a component of AOCI, in shareholders' equity, related to our qualifying foreign currency forward exchange rate contracts for the years ended December 31, 2017 and 2016 : Amount of Gains (Losses) Deferred in AOCI 2017 2016 Foreign exchange forward - AUD $ (1,247 ) $ 2,568 Foreign exchange forward - CAD — 1,186 Total qualifying hedges $ (1,247 ) $ 3,754 The following table presents the gross notional amounts, estimated fair values recorded within other assets and liabilities and the amounts included in net earnings related to our non-qualifying foreign currency forward exchange rate hedging relationships as at December 31, 2017 . December 31, 2017 Fair Value 2017 Gross Notional Amount Assets Liabilities Losses on non-qualifying Foreign exchange forward - AUD $ 57,028 $ — $ 1,002 $ (1,002 ) Foreign exchange forward - GBP 207,323 262 4,312 (6,367 ) Foreign exchange forward - EUR 19,235 46 455 (971 ) Total non-qualifying hedges $ 283,586 $ 308 $ 5,769 $ (8,340 )

Reinsurance Balances Recovera46

Reinsurance Balances Recoverable (Tables)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Summary of Reinsurance Reserves Recoverable	The following table shows our reinsurance balances recoverable by rating of reinsurer and our provisions for uncollectible reinsurance balances recoverable ("provisions for bad debt") as at December 31, 2017 and 2016 . The provisions for bad debt all relate to the Non-life Run-off segment. 2017 2016 Gross Provisions for Bad Debt Net Provisions as a Gross Provisions for Bad Debt Net Provisions as a Reinsurers rated A- or above $ 1,252,887 $ 51,115 $ 1,201,772 4.1 % $ 892,776 $ 35,184 $ 857,592 3.9 % Reinsurers rated below A-, secured 771,097 — 771,097 — % 544,894 — 544,894 — % Reinsurers rated below A-, unsecured 162,259 114,098 48,161 70.3 % 197,589 139,332 58,257 70.5 % Total $ 2,186,243 $ 165,213 $ 2,021,030 7.6 % $ 1,635,259 $ 174,516 $ 1,460,743 10.7 % The following tables provide a summary of net premiums written and earned for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Premiums Written Premiums Earned Premiums Written Premiums Earned Premiums Written Premiums Earned Non-life Run-off Gross $ 14,102 $ 23,950 $ 17,316 $ 25,989 $ 38,704 $ 116,494 Ceded (7,620 ) (9,788 ) (8,114 ) (9,234 ) (16,110 ) (72,125 ) Net $ 6,482 $ 14,162 $ 9,202 $ 16,755 $ 22,594 $ 44,369 Atrium Gross $ 153,472 $ 152,278 $ 143,170 $ 140,438 $ 149,082 $ 149,310 Ceded (19,258 ) (17,531 ) (2,733 ) (16,022 ) (14,502 ) (14,635 ) Net $ 134,214 $ 134,747 $ 140,437 $ 124,416 $ 134,580 $ 134,675 StarStone Gross $ 895,160 $ 865,159 $ 854,699 $ 830,186 $ 824,714 $ 769,875 Ceded (430,259 ) (405,756 ) (206,663 ) (153,578 ) (196,287 ) (196,729 ) Net $ 464,901 $ 459,403 $ 648,036 $ 676,608 $ 628,427 $ 573,146 Other Gross $ 5,719 $ 5,900 $ 7,157 $ 7,220 $ 2,883 $ 2,884 Ceded (926 ) (1,091 ) (896 ) (1,485 ) (1,330 ) (1,330 ) Net $ 4,793 $ 4,809 $ 6,261 $ 5,735 $ 1,553 $ 1,554 Total Gross $ 1,068,453 $ 1,047,287 $ 1,022,342 $ 1,003,833 $ 1,015,383 $ 1,038,563 Ceded (458,063 ) (434,166 ) (218,406 ) (180,319 ) (228,229 ) (284,819 ) Net $ 610,390 $ 613,121 $ 803,936 $ 823,514 $ 787,154 $ 753,744	The following table provides the total reinsurance balances recoverable as at December 31, 2017 and 2016 : 2017 Non-life Run-off Atrium StarStone Other Total Recoverable from reinsurers on unpaid: Outstanding losses $ 932,284 $ 7,472 $ 211,650 $ 16 $ 1,151,422 IBNR 590,154 31,476 242,620 — 864,250 Fair value adjustments (12,970 ) 1,583 (2,253 ) — (13,640 ) Fair value adjustments - fair value option (131,983 ) — — — (131,983 ) Total reinsurance reserves recoverable 1,377,485 40,531 452,017 16 1,870,049 Paid losses recoverable 128,253 (451 ) 23,179 — 150,981 $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 Reconciliation to Consolidated Balance Sheet: Reinsurance balances recoverable $ 963,514 $ 40,080 $ 475,196 $ 16 $ 1,478,806 Reinsurance balances recoverable - fair value option 542,224 — — — 542,224 Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 2016 Non-life Run-off Atrium StarStone Other Total Recoverable from reinsurers on unpaid: Outstanding losses $ 621,288 $ 6,438 $ 182,478 $ 190 $ 810,394 IBNR 393,550 21,753 178,259 — 593,562 Fair value adjustments (13,885 ) 1,818 (3,506 ) — (15,573 ) Total reinsurance reserves recoverable 1,000,953 30,009 357,231 190 1,388,383 Paid losses recoverable 47,160 (1,081 ) 25,512 769 72,360 $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743
Reinsurance Balances Recoverable by Reinsurer	Top Ten Reinsurers December 31, 2017 December 31, 2016 Non-life Atrium StarStone Other Total % of Non-life Atrium StarStone Other Total % of Top ten reinsurers $ 1,166,057 $ 22,422 $ 328,257 $ — $ 1,516,736 75.0 % $ 737,074 $ 23,245 $ 226,283 $ — $ 986,602 67.6 % Other reinsurers > $1 million 322,722 16,631 144,336 — 483,689 24.0 % 301,856 4,827 152,341 — 459,024 31.4 % Other reinsurers < $1 million 16,959 1,027 2,603 16 20,605 1.0 % 9,183 856 4,119 959 15,117 1.0 % Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 100.0 % $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743 100.0 %

Losses and Loss Adjustment Ex47

Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Total Losses and Loss Adjustment Expense Liabilities, and Reconciliation of Beginning and Ending Balances	The following table summarizes the liability for losses and LAE by segment as at December 31, 2017 and 2016 : 2017 2016 Non-life Run-off Atrium StarStone Total Non-life Atrium StarStone Total Outstanding losses $ 3,185,703 $ 78,363 $ 590,977 $ 3,855,043 $ 2,697,736 $ 67,379 $ 502,115 $ 3,267,230 IBNR 2,903,927 150,508 599,221 3,653,656 1,935,659 130,118 541,305 2,607,082 Fair value adjustments (125,998 ) 9,547 (555 ) (117,006 ) (135,368 ) 12,503 (863 ) (123,728 ) Fair value adjustments - fair value option (314,748 ) — — (314,748 ) — — — — ULAE 300,588 2,455 18,100 321,143 218,336 2,122 16,825 237,283 Total $ 5,949,472 $ 240,873 $ 1,207,743 $ 7,398,088 $ 4,716,363 $ 212,122 $ 1,059,382 $ 5,987,867 Reconciliation to Consolidated Balance Sheet: Losses and loss adjustment expenses $ 5,603,419 $ 5,987,867 Losses and loss adjustment expenses, at fair value 1,794,669 — Total $ 7,398,088 $ 5,987,867 The overall increase in the liability for losses and LAE between December 31, 2016 and December 31, 2017 was primarily attributable to the assumed reinsurance agreements with RSA and QBE in our Non-life Run-off segment, for which we have elected the fair value option, as described in Note 4 - "Significant New Business" . The table below provides a consolidated reconciliation of the beginning and ending liability for losses and LAE for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Balance as at January 1 $ 5,987,867 $ 5,720,149 $ 4,509,421 Less: reinsurance reserves recoverable 1,388,193 1,360,382 1,154,196 Less: deferred charges on retroactive reinsurance 94,551 255,911 — Net balance as at January 1 4,505,123 4,103,856 3,355,225 Net incurred losses and LAE: Current period 437,853 493,016 476,364 Prior periods (244,302 ) (318,917 ) (372,031 ) Total net incurred losses and LAE 193,551 174,099 104,333 Net paid losses: Current period (82,273 ) (79,579 ) (99,933 ) Prior periods (862,921 ) (753,478 ) (681,956 ) Total net paid losses (945,194 ) (833,057 ) (781,889 ) Effect of exchange rate movement 158,429 (46,903 ) (65,069 ) Acquired on purchase of subsidiaries 10,251 10,019 878,815 Assumed business 1,525,703 1,340,444 612,441 Ceded business — (243,335 ) — Net balance as at December 31 5,447,863 4,505,123 4,103,856 Plus: reinsurance reserves recoverable 1,870,033 1,388,193 1,360,382 Plus: deferred charges on retroactive reinsurance 80,192 94,551 255,911 Balance as at December 31 $ 7,398,088 $ 5,987,867 $ 5,720,149 The table below provides a reconciliation of the beginning and ending reserves for losses and LAE for the years ended December 31, 2017 , 2016 and 2015 for the Non-life Run-off segment: 2017 2016 2015 Balance as at January 1 $ 4,716,363 $ 4,585,454 $ 3,435,010 Less: reinsurance reserves recoverable 1,000,953 1,034,747 800,709 Less: deferred charges on retroactive reinsurance 94,551 255,911 — Net balance as at January 1 3,620,859 3,294,796 2,634,301 Net incurred losses and LAE: Current period 5,866 5,829 39,924 Prior periods (196,540 ) (291,710 ) (310,754 ) Total net incurred losses and LAE (190,674 ) (285,881 ) (270,830 ) Net paid losses: Current period (2,835 ) (3,869 ) (16,049 ) Prior periods (578,888 ) (529,937 ) (501,246 ) Total net paid losses (581,723 ) (533,806 ) (517,295 ) Effect of exchange rate movement 138,772 (27,478 ) (42,636 ) Acquired on purchase of subsidiaries 10,251 10,019 878,815 Assumed business 1,494,310 1,340,444 612,441 Ceded business — (177,235 ) — Net balance as at December 31 4,491,795 3,620,859 3,294,796 Plus: reinsurance reserves recoverable 1,377,485 1,000,953 1,034,747 Plus: deferred charges on retroactive reinsurance 80,192 94,551 255,911 Balance as at December 31 $ 5,949,472 $ 4,716,363 $ 4,585,454 The table below provides a reconciliation of the beginning and ending liability for losses and LAE for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Balance as at January 1 $ 212,122 $ 201,017 $ 212,611 Less: reinsurance reserves recoverable 30,009 25,852 28,278 Net balance as at January 1 182,113 175,165 184,333 Net incurred losses and LAE: Current period 90,359 71,358 69,400 Prior periods (20,940 ) (12,971 ) (21,921 ) Total net incurred losses and LAE 69,419 58,387 47,479 Net paid losses: Current period (24,571 ) (23,582 ) (21,145 ) Prior periods (31,107 ) (24,416 ) (30,890 ) Total net paid losses (55,678 ) (47,998 ) (52,035 ) Effect of exchange rate movement 4,488 (3,441 ) (4,612 ) Net balance as at December 31 200,342 182,113 175,165 Plus: reinsurance reserves recoverable 40,531 30,009 25,852 Balance as at December 31 $ 240,873 $ 212,122 $ 201,017
Schedule of Incurred Losses	The tables below provide the components of net incurred losses and LAE by segment for the years ended December 31, 2017 , 2016 and 2015 : Year Ended December 31, 2017 Non-life Atrium StarStone Total Net losses paid $ 581,723 $ 55,678 $ 307,793 $ 945,194 Net change in case and LAE reserves (381,053 ) 8,338 31,685 (341,030 ) Net change in IBNR reserves (390,727 ) 7,679 (23,540 ) (406,588 ) Amortization of deferred charges 14,359 — — 14,359 Increase (reduction) in estimates of net ultimate losses (175,698 ) 71,695 315,938 211,935 Reduction in provisions for bad debt (1,536 ) 159 — (1,377 ) Increase (reduction) in provisions for unallocated LAE (53,810 ) 285 (187 ) (53,712 ) Amortization of fair value adjustments 10,114 (2,720 ) (945 ) 6,449 Changes in fair value - fair value option 30,256 — — 30,256 Net incurred losses and LAE $ (190,674 ) $ 69,419 $ 314,806 $ 193,551 Year Ended December 31, 2016 Non-life Run-off Atrium StarStone Total Net losses paid $ 533,806 $ 47,998 $ 251,253 $ 833,057 Net change in case and LAE reserves (608,785 ) (148 ) 73,049 (535,884 ) Net change in IBNR reserves (347,384 ) 13,700 75,643 (258,041 ) Amortization of deferred charges 168,827 — — 168,827 Increase (reduction) in estimates of net ultimate losses (253,536 ) 61,550 399,945 207,959 Reduction in provisions for bad debt (13,822 ) — — (13,822 ) Increase (reduction) in provisions for unallocated LAE (43,955 ) 145 3,543 (40,267 ) Amortization of fair value adjustments 25,432 (3,308 ) (1,895 ) 20,229 Net incurred losses and LAE $ (285,881 ) $ 58,387 $ 401,593 $ 174,099 Year Ended December 31, 2015 Non-life Atrium StarStone Total Net losses paid $ 517,295 $ 52,035 $ 212,559 $ 781,889 Net change in case and LAE reserves (355,335 ) (709 ) 77,219 (278,825 ) Net change in IBNR reserves (364,774 ) 2,844 37,904 (324,026 ) Amortization of deferred charges 15,265 — — 15,265 Increase (reduction) in estimates of net ultimate losses (187,549 ) 54,170 327,682 194,303 Increase in provisions for bad debt (25,271 ) — — (25,271 ) Reduction in provisions for unallocated LAE (62,653 ) (83 ) 3,537 (59,199 ) Amortization of fair value adjustments 4,643 (6,608 ) (3,535 ) (5,500 ) Net incurred losses and LAE $ (270,830 ) $ 47,479 $ 327,684 $ 104,333 Net incurred losses and LAE in the Non-life Run-off segment for the years ended December 31, 2017 , 2016 and 2015 were as follows: 2017 2016 2015 Prior Period Current Period Total Prior Period Current Period Total Prior Period Current Period Total Net losses paid $ 578,888 $ 2,835 $ 581,723 $ 529,937 $ 3,869 $ 533,806 $ 501,246 $ 16,049 $ 517,295 Net change in case and LAE reserves (381,450 ) 397 (381,053 ) (608,168 ) (617 ) (608,785 ) (366,262 ) 10,927 (355,335 ) Net change in IBNR reserves (393,100 ) 2,373 (390,727 ) (349,726 ) 2,342 (347,384 ) (377,722 ) 12,948 (364,774 ) Amortization of deferred charges 14,359 — 14,359 168,827 — 168,827 15,265 — 15,265 Increase (reduction) in estimates of net ultimate losses (181,303 ) 5,605 (175,698 ) (259,130 ) 5,594 (253,536 ) (227,473 ) 39,924 (187,549 ) Reduction in provisions for bad debt (1,536 ) — (1,536 ) (13,822 ) — (13,822 ) (25,271 ) — (25,271 ) Increase (reduction) in provisions for unallocated LAE (54,071 ) 261 (53,810 ) (44,190 ) 235 (43,955 ) (62,653 ) — (62,653 ) Amortization of fair value adjustments 10,114 — 10,114 25,432 — 25,432 4,643 — 4,643 Changes in fair value - fair value option 30,256 — 30,256 — — — — — — Net incurred losses and LAE $ (196,540 ) $ 5,866 $ (190,674 ) $ (291,710 ) $ 5,829 $ (285,881 ) $ (310,754 ) $ 39,924 $ (270,830 ) Net incurred losses and LAE in the Atrium segment for the years ended December 31, 2017 , 2016 and 2015 were as follows: 2017 2016 2015 Prior Period Current Period Total Prior Period Current Period Total Prior Period Current Period Total Net losses paid $ 31,107 $ 24,571 $ 55,678 $ 24,416 $ 23,582 $ 47,998 $ 30,890 $ 21,145 $ 52,035 Net change in case and LAE reserves (13,324 ) 21,662 8,338 (13,115 ) 12,967 (148 ) (18,213 ) 17,504 (709 ) Net change in IBNR reserves (35,650 ) 43,329 7,679 (20,543 ) 34,243 13,700 (27,382 ) 30,226 2,844 Increase (reduction) in estimates of net ultimate losses (17,867 ) 89,562 71,695 (9,242 ) 70,792 61,550 (14,705 ) 68,875 54,170 Reduction (increase) in provisions for bad debt 89 70 159 — — — — — — Increase (reduction) in provisions for unallocated LAE (442 ) 727 285 (421 ) 566 145 (608 ) 525 (83 ) Amortization of fair value adjustments (2,720 ) — (2,720 ) (3,308 ) — (3,308 ) (6,608 ) — (6,608 ) Net incurred losses and LAE $ (20,940 ) $ 90,359 $ 69,419 $ (12,971 ) $ 71,358 $ 58,387 (21,921 ) $ 69,400 $ 47,479 Net incurred losses and LAE for the years ended December 31, 2017 , 2016 and 2015 were as follows: 2017 2016 2015 Prior Current Total Prior Current Total Prior Current Total Net losses paid $ 252,926 $ 54,867 $ 307,793 $ 199,125 $ 52,128 $ 251,253 $ 149,820 $ 62,739 $ 212,559 Net change in case and LAE reserves (63,785 ) 95,470 31,685 (51,309 ) 124,358 73,049 15,772 61,447 77,219 Net change in IBNR reserves (208,244 ) 184,704 (23,540 ) (156,546 ) 232,189 75,643 (200,730 ) 238,634 37,904 Increase (reduction) in estimates of net ultimate losses (19,103 ) 335,041 315,938 (8,730 ) 408,675 399,945 (35,138 ) 362,820 327,682 Increase (reduction) in provisions for unallocated LAE (6,774 ) 6,587 (187 ) (3,611 ) 7,154 3,543 (683 ) 4,220 3,537 Amortization of fair value adjustments (945 ) — (945 ) (1,895 ) — (1,895 ) (3,535 ) — (3,535 ) Net incurred losses and LAE $ (26,822 ) $ 341,628 $ 314,806 $ (14,236 ) $ 415,829 $ 401,593 $ (39,356 ) $ 367,040 $ 327,684
Schedule of Gross and Net Losses and LAE Reserves by Category	The following tables provides a breakdown of the gross and net losses and LAE reserves by line of business as at December 31, 2017 and 2016 : 2017 2017 Gross Net OLR IBNR Total OLR IBNR Total (in thousands of U.S. dollars) Asbestos $ 366,446 $ 1,434,598 $ 1,801,044 $ 341,355 $ 1,337,467 $ 1,678,822 Environmental 95,801 95,259 191,060 91,049 93,345 184,394 General casualty 344,425 266,526 610,951 276,791 194,747 471,538 Workers' compensation/personal accident 1,458,430 748,949 2,207,379 889,265 371,161 1,260,426 Marine, aviation and transit 109,102 56,284 165,386 90,101 51,904 142,005 Construction defect 28,701 135,608 164,309 27,406 122,307 149,713 Professional indemnity/Directors & Officers 214,803 40,265 255,068 181,027 39,591 220,618 Other 567,995 126,438 694,433 356,424 103,251 459,675 $ 3,185,703 $ 2,903,927 $ 6,089,630 $ 2,253,418 $ 2,313,773 $ 4,567,191 Fair value adjustments (125,998 ) (113,028 ) Fair value adjustments - fair value option (314,748 ) (182,764 ) Deferred charge on retroactive reinsurance — (80,192 ) $ 5,648,884 $ 4,191,207 ULAE 300,588 300,588 Total $ 5,949,472 $ 4,491,795 2016 2016 Gross Net OLR IBNR Total OLR IBNR Total (in thousands of U.S. dollars) Asbestos $ 265,144 $ 584,757 $ 849,901 $ 246,030 $ 569,736 $ 815,766 Environmental 100,128 71,722 171,850 94,311 69,740 164,051 General casualty 428,210 317,613 745,823 300,650 195,393 496,043 Workers' compensation/personal accident 1,389,097 701,616 2,090,713 1,007,528 484,863 1,492,391 Marine, aviation and transit 54,025 35,744 89,769 48,469 35,607 84,076 Construction defect 40,446 121,551 161,997 33,591 90,977 124,568 Professional indemnity/Directors & Officers 110,208 61,663 171,871 92,716 60,626 153,342 Other 310,478 40,993 351,471 253,154 35,166 288,320 $ 2,697,736 $ 1,935,659 $ 4,633,395 $ 2,076,449 $ 1,542,108 $ 3,618,557 Fair value adjustments (135,368 ) (121,483 ) Deferred charge on retroactive reinsurance — (94,551 ) $ 4,498,027 $ 3,402,523 ULAE 218,336 218,336 Total $ 4,716,363 $ 3,620,859
Incurred and Paid Loss Development Information, and IBNR Liabilities and Cumulative Loss Frequency	Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, As of December 31, 2017 Accident Year 2008 (unaudited) 2009 (unaudited) 2010 (unaudited) 2011 (unaudited) 2012 (unaudited) 2013 (unaudited) 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 IBNR (1) Cumulative Number of Claims 2008 $ 20,277 $ 24,456 $ 45,420 $ 51,927 $ 59,142 $ 63,437 $ 64,982 $ 69,784 $ 66,160 $ 84,811 $ 10,162 3,543 2009 20,081 27,612 48,009 66,202 84,596 86,618 92,084 94,550 112,799 10,570 3,497 2010 34,527 55,916 68,142 93,817 177,344 201,813 215,279 230,288 20,143 5,365 2011 40,109 42,977 68,439 83,854 87,625 86,727 92,802 16,825 3,864 2012 65,494 72,203 82,667 73,218 88,743 104,284 16,766 3,929 2013 60,121 76,526 50,524 53,597 72,586 13,387 2,529 2014 35,789 23,657 25,197 37,628 7,883 1,447 2015 9,478 9,891 14,003 5,500 516 2016 2,319 1,281 868 103 2017 141 115 26 Total $ 750,623 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, Accident Year 2008 (unaudited) 2009 (unaudited) 2010 (unaudited) 2011 (unaudited) 2012 (unaudited) 2013 (unaudited) 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 2008 $ 5,752 $ 12,512 $ 20,372 $ 30,193 $ 40,909 $ 45,447 $ 52,416 $ 54,510 $ 57,625 $ 62,930 2009 4,834 11,384 22,986 41,723 55,455 66,001 73,154 80,004 85,802 2010 6,108 14,462 26,943 41,340 97,854 150,681 179,633 195,858 2011 8,353 17,573 26,839 43,189 55,998 60,809 64,789 2012 12,435 17,787 31,031 42,991 58,717 71,372 2013 2,449 14,311 20,416 29,342 39,996 2014 1,740 5,070 10,300 19,672 2015 744 1,505 3,188 2016 81 147 2017 17 Total $ 543,771 All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance 264,686 Total outstanding liabilities for unpaid losses and LAE, net of reinsurance $ 471,538 (1) Total of IBNR plus expected development on reported losses. Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, As of December 31, 2017 Accident Year 2008 (unaudited) 2009 (unaudited) 2010 (unaudited) 2011 (unaudited) 2012 (unaudited) 2013 (unaudited) 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 IBNR (1) Cumulative Number of Claims 2008 $ 4,149 $ 23,865 $ 53,480 $ 58,806 $ 80,673 $ 86,120 $ 83,578 $ 77,421 $ 128,985 $ 128,410 $ 3,666 — 2009 1,205 14,027 25,782 48,547 54,345 58,429 62,705 59,906 57,076 2,238 — 2010 — — — — 793 463 454 485 (3 ) 520 2011 — — — 39,854 43,180 41,508 40,602 1,500 2,003 2012 — — 59,123 69,319 67,098 65,893 3,254 2,281 2013 — 47,164 62,259 57,983 61,785 8,724 1,922 2014 7,374 4,903 5,496 3,760 2,417 439 2015 198 4,925 8,789 2,216 26 2016 42 — — 1 2017 58 — 2 $ 366,858 (1) Total of IBNR plus expected development on reported losses. Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, Accident Year 2008 (unaudited) 2009 (unaudited) 2010 (unaudited) 2011 (unaudited) 2012 (unaudited) 2013 (unaudited) 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 2008 $ 179 $ 3,157 $ 11,350 $ 26,799 $ 33,932 $ 40,045 $ 44,913 $ 53,018 $ 107,854 $ 109,032 2009 88 2,604 7,784 17,040 26,023 33,246 37,708 41,053 46,209 2010 — — — — 462 463 456 490 2011 — — — 28,221 32,366 35,061 36,236 2012 — — 33,687 44,410 51,396 54,208 2013 — 18,678 31,063 35,219 44,337 2014 430 717 1,075 1,127 2015 29 198 1,821 2016 — — 2017 37 Total $ 293,497 All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance 147,257 Total outstanding liabilities for unpaid losses and LAE, net of reinsurance $ 220,618 (1) Total of IBNR plus expected development on reported losses. The following table provides a breakdown of the liability for losses and LAE by line of business for the years ended December 31, 2017 and 2016 for the Atrium segment: 2017 2016 OLR IBNR Total OLR IBNR Total (in thousands of U.S. dollars) Marine, Aviation and Transit $ 24,581 $ 46,138 $ 70,719 $ 25,565 $ 49,369 $ 74,934 Binding Authorities 26,115 51,896 78,011 21,543 41,603 63,146 Reinsurance 14,381 34,489 48,870 11,485 22,178 33,663 Accident and Health 3,716 5,518 9,234 2,913 5,625 8,538 Non-Marine Direct and Facultative 9,570 12,467 22,037 5,873 11,343 17,216 Total $ 78,363 $ 150,508 $ 228,871 $ 67,379 $ 130,118 $ 197,497 Fair value adjustments 9,547 12,503 ULAE 2,455 2,122 Total $ 240,873 $ 212,122 The following tables set forth information about incurred and paid loss development information for the Atrium segment as at December 31, 2017 . The information related to incurred and paid loss development for the years ended December 31, 2008 through 2016 is presented as supplementary information and is therefore unaudited. Information about total IBNR reserves and cumulative loss frequency as at December 31, 2017 , including expected development on reported losses included within the net incurred losses and allocated LAE amounts for the Atrium segment, are set forth in the table below. Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, As of December 31, 2017 Accident Year 2008 (unaudited) 2009 (unaudited) 2010 (unaudited) 2011 (unaudited) 2012 (unaudited) 2013 (unaudited) 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 IBNR (1) Cumulative Number of Claims 2008 $ 46,002 $ 60,309 $ 60,742 $ 73,128 $ 68,943 $ 67,201 $ 66,701 $ 65,311 $ 63,552 $ 63,081 $ 2,478 266 2009 28,071 40,847 57,959 52,744 51,888 50,246 47,715 46,929 46,542 1,705 294 2010 27,139 65,704 58,465 55,666 50,078 47,871 47,128 45,478 1,900 376 2011 87,325 85,580 78,981 75,384 72,380 70,537 69,341 2,642 561 2012 70,930 64,633 60,804 57,126 54,416 52,995 3,536 756 2013 69,241 71,302 62,166 57,415 53,632 3,985 1,132 2014 70,008 70,275 66,825 61,211 8,570 1,835 2015 70,336 72,234 64,178 15,047 3,070 2016 74,001 76,208 25,036 4,899 2017 91,129 56,376 5,197 Total $ 623,795 (1) Total of IBNR plus expected development on reported losses. Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, Accident Year 2008 (unaudited) 2009 (unaudited) 2010 (unaudited) 2011 (unaudited) 2012 (unaudited) 2013 (unaudited) 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 2008 $ 15,492 $ 37,939 $ 48,558 $ 53,307 $ 56,311 $ 58,193 $ 59,439 $ 60,018 $ 59,546 $ 59,738 2009 12,145 28,002 35,047 38,591 40,631 41,849 42,542 42,833 43,093 2010 11,599 25,421 32,600 36,968 39,486 40,526 41,137 41,713 2011 17,314 40,413 53,018 59,270 63,237 64,607 65,904 2012 11,357 31,762 38,324 42,499 44,807 45,710 2013 14,731 32,383 40,890 43,984 45,884 2014 17,754 34,763 42,114 47,441 2015 12,147 30,009 39,430 2016 13,878 34,988 2017 14,473 Total $ 438,374 All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance 3,369 Total outstanding liabilities for unpaid losses and LAE, net of reinsurance $ 188,790 Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, As of December 31, 2017 Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 IBNR (1) Cumulative Number of Claims 2008 $ — $ — $ — $ — $ — — 2009 — — — — — — 2010 — — — — — — 2011 — — — — — — 2012 — — — — — — 2013 — — — — — — 2014 15,607 17,199 18,291 15,662 2,129 1,061 2015 54,978 55,505 50,102 9,583 2,510 2016 54,630 46,866 12,550 2,468 2017 27,261 17,659 1,783 Total $ 139,891 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 2008 $ — $ — $ — $ — 2009 — — — — 2010 — — — — 2011 — — — — 2012 — — — — 2013 — — — — 2014 1,491 6,079 9,279 11,431 2015 6,361 20,194 30,439 2016 8,092 21,329 2017 3,560 Total $ 66,759 All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance — Total outstanding liabilities for unpaid losses and LAE, net of reinsurance $ 73,132 (1) Total of IBNR plus expected development on reported losses Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, As of December 31, 2017 Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 IBNR (1) Cumulative Number of Claims 2008 $ 7,114 $ 7,105 $ 7,112 $ 7,113 $ — 486 2009 10,653 10,554 10,526 10,539 — 657 2010 26,257 23,478 23,344 23,471 211 1,087 2011 25,459 23,838 23,503 23,631 243 2,082 2012 49,820 53,365 53,309 52,110 667 2,498 2013 63,366 56,191 54,163 55,122 249 2,318 2014 52,740 53,415 49,624 56,212 5,439 4,298 2015 73,237 71,311 81,587 7,131 5,868 2016 63,694 61,926 11,258 6,751 2017 87,925 44,629 5,487 Total $ 459,636 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 2008 $ 7,081 $ 7,092 $ 7,108 $ 7,108 2009 10,529 10,542 10,523 10,530 2010 20,427 22,482 22,562 22,530 2011 20,185 21,245 22,237 22,484 2012 39,975 44,127 46,028 46,820 2013 29,985 39,370 43,538 45,993 2014 11,146 25,533 33,311 37,794 2015 11,038 31,483 51,454 2016 11,102 34,452 2017 16,527 Total $ 295,692 All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance — Total outstanding liabilities for unpaid losses and LAE, net of reinsurance $ 163,944 (1) Total of IBNR plus expected development on reported losses The following table provides a breakdown of the liability for losses and LAE reserves by line of business as at December 31, 2017 and 2016 : 2017 2016 OLR IBNR Total OLR IBNR Total (in thousands of U.S. dollars) Casualty $ 139,200 $ 282,789 $ 421,989 $ 101,897 $ 279,823 $ 381,720 Marine 130,962 118,375 249,337 102,957 94,396 197,353 Property 208,777 89,963 298,740 182,480 57,184 239,664 Aerospace 63,920 26,070 89,990 66,190 30,921 97,111 Workers' Compensation 48,118 82,024 130,142 48,591 78,981 127,572 Total $ 590,977 $ 599,221 $ 1,190,198 $ 502,115 $ 541,305 $ 1,043,420 Fair value adjustments (555 ) (863 ) ULAE 18,100 16,825 Total $ 1,207,743 $ 1,059,382 The following tables set forth information about incurred and paid loss development, total IBNR reserves and cumulative loss frequency related to all the individual lines of business within the StarStone segment as at December 31, 2017 . The information related to incurred and paid loss development for the years ended December 31, 2014 through 2016 is presented as supplementary information and is therefore unaudited. The information within the tables below is presented on a prospective basis from the date of our acquisition of StarStone on April 1, 2014 since providing pre-acquisition incurred and paid losses by accident year for years prior to 2014 was determined to be impracticable due to significant data limitations. Casualty Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, As of December 31, 2017 Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 IBNR (1) Cumulative Number of Claims 2008 $ 7,759 $ 7,734 $ 7,740 $ 7,733 $ — 491 2009 21,096 21,158 21,158 21,162 — 496 2010 15,972 18,026 18,113 18,974 178 734 2011 20,964 23,948 24,665 25,211 713 2,043 2012 57,413 48,530 44,003 39,388 2,381 3,100 2013 74,312 69,537 79,689 78,573 7,002 4,952 2014 92,236 93,687 93,325 90,663 18,892 5,336 2015 108,762 112,430 111,582 36,723 3,950 2016 103,057 100,301 49,588 3,722 2017 96,294 73,042 3,594 Total $ 589,881 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 2008 $ 7,759 $ 7,734 $ 7,740 $ 7,733 2009 21,096 21,158 21,158 21,162 2010 15,809 18,026 18,113 18,796 2011 15,850 21,200 23,930 24,497 2012 18,514 29,613 32,805 34,074 2013 23,210 30,675 50,427 54,989 2014 5,803 22,041 37,793 51,012 2015 8,779 28,230 50,072 2016 4,856 34,214 2017 6,761 Total $ 303,310 All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance 18 Total outstanding liabilities for unpaid losses and LAE, net of reinsurance $ 286,589 (1) Total of IBNR plus expected development on reported losses Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, As of December 31, 2017 Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 IBNR (1) Cumulative Number of Claims 2008 $ 48,894 $ 49,135 $ 49,163 $ 49,158 $ — 740 2009 28,946 28,417 28,826 29,070 — 1,100 2010 75,670 74,491 73,332 73,395 — 1,698 2011 92,107 90,708 90,646 90,364 — 1,688 2012 65,529 62,398 61,594 62,332 284 1,574 2013 76,665 66,079 65,885 65,146 868 1,946 2014 63,673 44,317 44,955 45,382 1,927 2,114 2015 79,339 77,695 71,391 1,717 5,563 2016 74,134 80,379 3,698 6,525 2017 105,672 30,785 6,036 Total $ 672,289 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 2008 $ 48,894 $ 49,135 $ 49,163 $ 49,158 2009 28,382 28,420 28,829 29,070 2010 70,293 73,213 73,332 73,395 2011 88,327 89,561 90,103 90,364 2012 48,588 52,705 55,061 56,079 2013 31,433 46,983 51,915 54,040 2014 5,537 18,998 33,199 36,213 2015 10,467 29,060 55,956 2016 23,386 49,730 2017 24,715 Total $ 518,720 All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance 858 Total outstanding liabilities for unpaid losses and LAE, net of reinsurance $ 154,427 (1) Total of IBNR plus expected development on reported losses Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, As of December 31, 2017 Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 IBNR (1) Cumulative Number of Claims 2008 $ — $ — $ — $ — $ — — 2009 — — — — — — 2010 18,269 18,430 18,741 19,258 66 569 2011 58,954 57,436 57,833 58,268 192 2,173 2012 56,144 55,765 56,586 56,552 172 2,393 2013 72,762 70,535 70,820 75,228 348 2,324 2014 65,526 54,077 53,751 52,593 1,087 2,380 2015 66,078 69,843 73,125 2,642 2,252 2016 30,718 35,540 4,141 1,725 2017 19,036 8,407 882 Total $ 389,600 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For The Years Ended December 31, Accident Year 2014 (unaudited) 2015 (unaudited) 2016 (unaudited) 2017 2008 $ — $ — $ — $ — 2009 — — — — 2010 15,743 16,890 17,497 18,566 2011 53,956 55,321 56,002 56,584 2012 46,219 49,665 52,502 53,982 2013 51,098 60,118 63,723 69,071 2014 17,375 31,309 38,605 40,865 2015 32,415 52,407 61,081 2016 10,193 24,904 2017 6,711 Total $ 331,764 All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance — Total outstanding liabilities for unpaid losses and LAE, net of reinsurance $ 57,836 (1) Total of IBNR plus expected development on reported losses
Reconciliation of Incurred and Paid Loss Development to Liability for Unpaid Losses and LAE	The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the year ended December 31, 2017 is set forth below: December 31, 2017 Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 1,260,426 Reinsurance recoverable on unpaid losses 946,953 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 2,207,379 The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the year ended December 31, 2017 is set forth below: December 31, 2017 Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 471,538 Reinsurance recoverable on unpaid losses 139,413 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 610,951 The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the year ended December 31, 2017 is set forth below: December 31, Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 220,618 Reinsurance recoverable on unpaid losses 34,450 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 255,068 The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the Atrium segment for the year ended December 31, 2017 is set forth below: December 31, 2017 Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 188,790 Reinsurance recoverable on unpaid losses 40,081 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 228,871 The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the year ended December 31, 2017 is set forth below: December 31, 2017 Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 286,589 Reinsurance recoverable on unpaid losses 135,400 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 421,989 The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the year ended December 31, 2017 is set forth below: December 31, 2017 Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 163,944 Reinsurance recoverable on unpaid losses 85,393 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 249,337 The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the year ended December 31, 2017 is set forth below: December 31, 2017 Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 73,132 Reinsurance recoverable on unpaid losses 57,010 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 130,142 The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the year ended December 31, 2017 is set forth below: December 31, 2017 Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 57,836 Reinsurance recoverable on unpaid losses 32,154 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 89,990 The table below provides a reconciliation of the beginning and ending liability for losses and LAE for the years ended December 31, 2017 , 2016 and 2015: 2017 2016 2015 Balance as at January 1 $ 1,059,382 $ 933,678 $ 861,800 Less: reinsurance reserves recoverable 357,231 299,783 325,209 Net balance as at January 1 702,151 633,895 536,591 Net incurred losses and LAE: Current period 341,628 415,829 367,040 Prior periods (26,822 ) (14,236 ) (39,356 ) Total net incurred losses and LAE 314,806 401,593 327,684 Net paid losses: Current period (54,867 ) (52,128 ) (62,739 ) Prior periods (252,926 ) (199,125 ) (149,820 ) Total net paid losses (307,793 ) (251,253 ) (212,559 ) Effect of exchange rate movement 15,169 (15,984 ) (17,821 ) Acquired on purchase of subsidiaries — — — Assumed business 31,393 — — Ceded business — (66,100 ) — Net balance as at December 31 755,726 702,151 633,895 Plus: reinsurance reserves recoverable 452,017 357,231 299,783 Balance as at December 31 $ 1,207,743 $ 1,059,382 $ 933,678 The reconciliation of incurred and paid loss development to the liability for unpaid losses and LAE as presented in the tables above for the year ended December 31, 2017 is set forth below: December 31, 2017 Liabilities for unpaid losses and allocated LAE, net of reinsurance $ 154,427 Reinsurance recoverable on unpaid losses 144,313 Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses and fair value adjustments $ 298,740
Average Annual Duration of Claims	The following is unaudited supplementary information for average annual historical duration of claims: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Professional indemnity/ Directors & Officers 15.1 % 4.1 % 12.7 % 10.5 % 11.4 % 5.7 % 4.8 % 6.4 % 9.0 % 0.9 % The following is unaudited supplementary information for average annual historical duration of claims: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Workers' compensation 18.1 % 23.1 % 17.3 % 12.3 % 5.4 % 4.2 % 3.0 % 2.5 % 1.1 % 1.8 % The following is unaudited supplementary information for average annual historical duration of claims within the Atrium segment: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Atrium 23.2 % 37.09 % 15.11 % 8.02 % 4.72 % 2.31 % 1.67 % 0.94 % 0.56 % 0.3 % The following is unaudited supplementary information for average annual historical duration of claims: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Casualty 6.6 % 21.5 % 15.5 % 22.4 % 11.9 % 8.7 % 1.0 % 1.1 % 0.1 % — % The following is unaudited supplementary information for average annual historical duration of claims: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Marine 16.8 % 29.5 % 18.4 % 7.8 % 4.2 % 4.8 % 0.5 % — % 0.1 % — % The following is unaudited supplementary information for average annual historical duration of claims: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Property 22.4 % 29.5 % 30.9 % 6.9 % 2.8 % 2.1 % 0.2 % 0.7 % 0.4 % — % The following is unaudited supplementary information for average annual historical duration of claims: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Aerospace 36.1 % 31.7 % 12.6 % 5.1 % 4.8 % 3.2 % 1.4 % 1.8 % — % — % The following is unaudited supplementary information for average annual historical duration of claims: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Workers' compensation 14.3 % 28.4 % 13.6 % 4.6 % — % — % — % — % — % — %	The following is unaudited supplementary information for average annual historical duration of claims: Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 General casualty 6.64 % 8.29 % 10.25 % 14.39 % 15.49 % 10.99 % 7.85 % 5.2 % 4.41 % 6.26 %
Carrying Amount of Liability and Aggregate Amount of Discount	The following table includes the carrying amount of the liability for unpaid losses and LAE, net of reinsurance reported at fair value, the discount rates used to discount the liabilities and the related aggregate amount of the discount as at December 31, 2017 and the interest accretion for the year ended December 31, 2017 , recorded within net incurred losses and LAE in our consolidated statements of earnings: As at December 31, 2017 For the Year Ended December 31, 2017 Line of business Carrying value Discount rate Aggregate amount of discount Interest Accretion Asbestos $ 712,890 2.3% $ 222,138 $ 18,637 Environmental 1,003 2.0% 122 10 General casualty 120,480 2.8% 28,233 3,751 Workers' compensation/personal accident 69,266 3.0% 19,497 4,142 Marine, aviation and transit 71,138 2.0% 9,520 799 Construction defect 38,819 2.9% 5,513 1,171 Other 145,013 2.0% 18,827 1,716 ULAE 93,836 3.0% 25,953 3,621 Total $ 1,252,445 $ 329,803 $ 33,847

Premiums Written and Earned (Ta

Premiums Written and Earned (Tables)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Schedule of Net Premiums Written and Earned	The following table shows our reinsurance balances recoverable by rating of reinsurer and our provisions for uncollectible reinsurance balances recoverable ("provisions for bad debt") as at December 31, 2017 and 2016 . The provisions for bad debt all relate to the Non-life Run-off segment. 2017 2016 Gross Provisions for Bad Debt Net Provisions as a Gross Provisions for Bad Debt Net Provisions as a Reinsurers rated A- or above $ 1,252,887 $ 51,115 $ 1,201,772 4.1 % $ 892,776 $ 35,184 $ 857,592 3.9 % Reinsurers rated below A-, secured 771,097 — 771,097 — % 544,894 — 544,894 — % Reinsurers rated below A-, unsecured 162,259 114,098 48,161 70.3 % 197,589 139,332 58,257 70.5 % Total $ 2,186,243 $ 165,213 $ 2,021,030 7.6 % $ 1,635,259 $ 174,516 $ 1,460,743 10.7 % The following tables provide a summary of net premiums written and earned for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Premiums Written Premiums Earned Premiums Written Premiums Earned Premiums Written Premiums Earned Non-life Run-off Gross $ 14,102 $ 23,950 $ 17,316 $ 25,989 $ 38,704 $ 116,494 Ceded (7,620 ) (9,788 ) (8,114 ) (9,234 ) (16,110 ) (72,125 ) Net $ 6,482 $ 14,162 $ 9,202 $ 16,755 $ 22,594 $ 44,369 Atrium Gross $ 153,472 $ 152,278 $ 143,170 $ 140,438 $ 149,082 $ 149,310 Ceded (19,258 ) (17,531 ) (2,733 ) (16,022 ) (14,502 ) (14,635 ) Net $ 134,214 $ 134,747 $ 140,437 $ 124,416 $ 134,580 $ 134,675 StarStone Gross $ 895,160 $ 865,159 $ 854,699 $ 830,186 $ 824,714 $ 769,875 Ceded (430,259 ) (405,756 ) (206,663 ) (153,578 ) (196,287 ) (196,729 ) Net $ 464,901 $ 459,403 $ 648,036 $ 676,608 $ 628,427 $ 573,146 Other Gross $ 5,719 $ 5,900 $ 7,157 $ 7,220 $ 2,883 $ 2,884 Ceded (926 ) (1,091 ) (896 ) (1,485 ) (1,330 ) (1,330 ) Net $ 4,793 $ 4,809 $ 6,261 $ 5,735 $ 1,553 $ 1,554 Total Gross $ 1,068,453 $ 1,047,287 $ 1,022,342 $ 1,003,833 $ 1,015,383 $ 1,038,563 Ceded (458,063 ) (434,166 ) (218,406 ) (180,319 ) (228,229 ) (284,819 ) Net $ 610,390 $ 613,121 $ 803,936 $ 823,514 $ 787,154 $ 753,744	The following table provides the total reinsurance balances recoverable as at December 31, 2017 and 2016 : 2017 Non-life Run-off Atrium StarStone Other Total Recoverable from reinsurers on unpaid: Outstanding losses $ 932,284 $ 7,472 $ 211,650 $ 16 $ 1,151,422 IBNR 590,154 31,476 242,620 — 864,250 Fair value adjustments (12,970 ) 1,583 (2,253 ) — (13,640 ) Fair value adjustments - fair value option (131,983 ) — — — (131,983 ) Total reinsurance reserves recoverable 1,377,485 40,531 452,017 16 1,870,049 Paid losses recoverable 128,253 (451 ) 23,179 — 150,981 $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 Reconciliation to Consolidated Balance Sheet: Reinsurance balances recoverable $ 963,514 $ 40,080 $ 475,196 $ 16 $ 1,478,806 Reinsurance balances recoverable - fair value option 542,224 — — — 542,224 Total $ 1,505,738 $ 40,080 $ 475,196 $ 16 $ 2,021,030 2016 Non-life Run-off Atrium StarStone Other Total Recoverable from reinsurers on unpaid: Outstanding losses $ 621,288 $ 6,438 $ 182,478 $ 190 $ 810,394 IBNR 393,550 21,753 178,259 — 593,562 Fair value adjustments (13,885 ) 1,818 (3,506 ) — (15,573 ) Total reinsurance reserves recoverable 1,000,953 30,009 357,231 190 1,388,383 Paid losses recoverable 47,160 (1,081 ) 25,512 769 72,360 $ 1,048,113 $ 28,928 $ 382,743 $ 959 $ 1,460,743

Goodwill, Intangible Assets a49

Goodwill, Intangible Assets and Deferred Charges (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill and Intangible Assets	The gross carrying value, accumulated amortization and net carrying value of intangible assets by type and deferred charge at December 31, 2017 and 2016 were as follows: 2017 2016 Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Intangible assets with a definite life: Fair value adjustments: Losses and LAE liabilities $ 462,455 $ (345,449 ) $ 117,006 $ 458,202 $ (334,475 ) $ 123,727 Reinsurance balances recoverable (179,219 ) 165,579 (13,640 ) (175,924 ) 160,350 (15,574 ) Other Assets (48,840 ) 440 (48,400 ) (48,840 ) — (48,840 ) Other Liabilities 85,845 (418 ) 85,427 85,845 — 85,845 Total $ 320,241 $ (179,848 ) $ 140,393 $ 319,283 $ (174,125 ) $ 145,158 Other: Distribution channel $ 20,000 $ (5,444 ) $ 14,556 $ 20,000 $ (4,111 ) $ 15,889 Technology 15,000 (13,210 ) 1,790 15,000 (10,978 ) 4,022 Brand 7,000 (2,859 ) 4,141 7,000 (2,158 ) 4,842 Total $ 42,000 $ (21,513 ) $ 20,487 $ 42,000 $ (17,247 ) $ 24,753 Intangible assets with an indefinite life: Lloyd’s syndicate capacity $ 37,031 $ — $ 37,031 $ 37,031 $ — $ 37,031 Licenses 19,900 — 19,900 19,900 — 19,900 Management contract 30,100 — 30,100 30,100 — 30,100 Total $ 87,031 $ — $ 87,031 $ 87,031 $ — $ 87,031 Deferred charges on retroactive reinsurance $ 278,643 $ (198,451 ) $ 80,192 $ 278,643 $ (184,092 ) $ 94,551 The following tables present a reconciliation of the beginning and ending goodwill, intangible assets and deferred charges for the years ended December 31, 2017 and 2016 : 2017 Goodwill Intangible assets with a definite life - Other Intangible assets with an indefinite life Total Intangible assets with a definite life - FVA Other assets - Deferred Charges Balance as at January 1, 2017 $ 73,071 $ 24,753 $ 87,031 $ 184,855 $ 145,158 $ 94,551 Acquired during the year — — — — 958 — Amortization — (4,266 ) — (4,266 ) (5,723 ) (14,359 ) Balance as at December 31, 2017 $ 73,071 $ 20,487 $ 87,031 $ 180,589 $ 140,393 $ 80,192 2016 Goodwill Intangible assets with a definite life - Other Intangible assets with an indefinite life Total Intangible assets with a definite life - FVA Other assets - Deferred Charges Balance as at January 1, 2016 $ 73,071 $ 31,202 $ 87,031 $ 191,304 $ 127,170 $ 255,911 Acquired during the year — — — — 37,005 7,467 Amortization — (6,449 ) — (6,449 ) (19,017 ) (168,827 ) Balance as at December 31, 2016 $ 73,071 $ 24,753 $ 87,031 $ 184,855 $ 145,158 $ 94,551
Summary of Estimated Amortization Expense of Intangible Assets	The estimated amortization expense for each of the five succeeding fiscal years related to our intangible assets with a definite life is as follows: Year Non-life Run-off Atrium StarStone Total 2018 $ 8,082 $ (463 ) $ 255 $ 7,874 2019 $ 7,927 $ (69 ) $ (401 ) $ 7,457 2020 $ 7,634 $ 760 $ (246 ) $ 8,148 2021 $ 7,169 $ 1,254 $ (166 ) $ 8,257 2022 $ 6,559 $ 1,506 $ (108 ) $ 7,957

Debt Obligations (Tables)

Debt Obligations (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Amounts of Loans Payable Outstanding, and Accrued Interest	Under these facilities, debt obligations as of December 31, 2017 and 2016 were as follows: Facility Origination Date Term 2017 2016 Senior Notes March 10, 2017 5 years $ 350,000 $ — Unamortized debt issuance costs (2,484 ) — Total Senior Notes 347,516 — EGL Revolving Credit Facility September 16, 2014 5 years 225,110 535,103 Sussex Facility December 24, 2014 4 years — 63,500 EGL Term Loan Facility November 18, 2016 3 years 74,063 75,000 Total debt obligations $ 646,689 $ 673,603

Noncontrolling Interest (Tables

Noncontrolling Interest (Tables)	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Carrying Amount of Equity Attributable to Noncontrolling Interest	The following is a reconciliation of the beginning and ending carrying amount of the equity attributable to the RNCI for the years ended December 31, 2017 and 2016 : 2017 2016 Balance at beginning of year $ 454,522 $ 417,663 Dividends paid (27,458 ) — Net earnings attributable to RNCI 19,619 40,639 Accumulated other comprehensive income attributable to RNCI 1,945 651 Change in redemption value of RNCI 30,978 (4,431 ) Balance at end of year $ 479,606 $ 454,522

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Comparison of Basic and Diluted Earnings per Share	The following table sets forth the computation of basic and diluted earnings per share for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Numerator: Net earnings from continuing operations $ 300,465 $ 252,844 $ 222,322 Net earnings (losses) from discontinuing operations 10,993 11,963 (2,031 ) Net earnings attributable to Enstar Group Limited $ 311,458 $ 264,807 $ 220,291 Denominator: Weighted-average ordinary shares outstanding — basic 19,388,621 19,299,426 19,252,072 Effect of dilutive securities: Share-based compensation plans 62,732 48,428 76,801 Warrants 76,238 99,387 78,883 Weighted-average ordinary shares outstanding — diluted 19,527,591 19,447,241 19,407,756 Earnings per share attributable to Enstar Group Limited: Basic: Net earnings from continuing operations $ 15.50 $ 13.10 $ 11.55 Net earnings (loss) from discontinuing operations 0.56 0.62 (0.11 ) Net earnings per ordinary share $ 16.06 $ 13.72 $ 11.44 Diluted: Net earnings from continuing operations $ 15.39 $ 13.00 $ 11.46 Net earnings (loss) from discontinuing operations 0.56 0.62 (0.11 ) Net earnings per ordinary share $ 15.95 $ 13.62 $ 11.35

Share-Based Compensation and 53

Share-Based Compensation and Pensions (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Restricted Shares, Restricted Share Units and Performance Share Units	The following table summarizes the activity related to PSUs during 2017 : Number of Shares Weighted- Average Share Price of Award Nonvested — January 1 — $ — Granted 128,196 188.15 Forfeited (1,443 ) 196.11 Nonvested — December 31 126,753 188.06 The following ta ble summarizes the activity related to restricted shares and restricted share awards during 2017 : Number of Shares Weighted- Average Share Price of Award Nonvested — January 1 78,992 $ 165.94 Granted 56,333 202.82 Vested (31,199 ) 163.75 Forfeited (4,821 ) 159.93 Nonvested — December 31 99,305 187.84
PSUs Vesting - Award Terms	The number of shares to vest will be determined by a performance adjustment based on the change in fully diluted book value per share ("FDBVPS") over three years , based upon the following award terms: Grant Year PSU's Granted at Target Nonvested Units Change in FDBVPS (3 - year) at December 31, 2017 Threshold Target Maximum 2017 36,321 34,878 20.00 % 30.00 % 40.00 % 2017 91,875 91,875 30.30 % 35.70 % 41.00 % 128,196 126,753
Summary of SARs Activity	The following t able summarizes the activity related to SARs during 2017: Number of SARs Weighted- Average Exercise Price of SARs Weighted Average Expected Term (in years) Aggregate Intrinsic Value (1) Balance, beginning of year 941,168 $ 140.70 Exercised (630,301 ) 140.39 Balance, end of year 310,867 141.30 1.58 $ 18,471 (1) The aggregate intrinsic value is calculated as the pre-tax difference between the exercise price of the underlying share awards and the closing price per share of our ordinary shares of $200.75 on December 31, 2017 .
Assumptions Used to Estimate Fair Value of SARs Using Black-Scholes Option Valuation Model	The following table sets forth the assumptions used to estimate the fair value of the SARs using the Black-Scholes option valuation model as at December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Weighted-average fair value per SAR $ 75.38 $ 62.39 $ 29.02 Weighted-average volatility 19.44 % 19.82 % 22.08 % Weighted-average risk-free interest rate 1.65 % 1.12 % 1.29 % Dividend yield 0.00 % 0.00 % 0.00 %

Taxation (Tables)

Taxation (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Earnings before Income Taxes	The following table presents earnings before income taxes by jurisdiction from continuing operations : 2017 2016 2015 Domestic (Bermuda) $ 167,263 $ 191,647 $ 61,695 Foreign 147,148 135,677 163,327 Total earnings before income tax on continuing operations $ 314,411 $ 327,324 $ 225,022
Tax Expense for Income Taxes	The following table presents our current and deferred income tax expense (benefit) from continuing operations by jurisdiction: 2017 2016 2015 Current: Domestic (Bermuda) $ — $ — $ — Foreign 10,299 21,485 30,028 10,299 21,485 30,028 Deferred: Domestic (Bermuda) — — — Foreign (16,694 ) 13,389 (17,378 ) (16,694 ) 13,389 (17,378 ) Total tax expense (benefit) on continuing operations $ (6,395 ) $ 34,874 $ 12,650
Reconciliation of Earnings before Income Taxes Computed by Applying Effective Rate	The actual income tax rate differs from the amount computed by applying the effective rate of 0% under Bermuda law to earnings from continuing operations before income taxes as shown in the following reconciliation: 2017 2016 2015 Earnings before income tax $ 314,411 $ 327,324 $ 225,022 Bermuda income taxes at statutory rate 0.0 % 0.0 % 0.0 % Foreign income tax rate differential 13.1 % 8.8 % 17.6 % Change in valuation allowance (34.9 )% (0.1 )% (10.5 )% Effect of change in foreign (U.S.) tax rate 20.3 % — % — % Other (0.5 )% 2.0 % (1.5 )% Effective tax rate (2.0 )% 10.7 % 5.6 %
Components of Deferred Tax Assets and Deferred Tax Liabilities	Significant components of the deferred tax assets and deferred tax liabilities related to our continuing operations were as follows: December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 177,695 $ 262,271 Tax credits and other carryforwards — 7,487 Insurance reserves 9,082 19,265 Unearned premiums 1,690 8,760 Lloyd's underwriting losses taxable in future periods 9,131 6,581 Provisions for bad debt 6,371 16,018 Other deferred tax assets 1,944 7,946 Gross deferred tax assets 205,913 328,328 Valuation allowance (188,300 ) (290,861 ) Deferred tax assets 17,613 37,467 Deferred tax liabilities: Unrealized gains on investments (3,798 ) (12,804 ) Intangible assets — (20,615 ) Other deferred tax liabilities (16,076 ) (21,030 ) Deferred tax liabilities (19,874 ) (54,449 ) Net deferred tax liability $ (2,261 ) $ (16,982 ) The change in the deferred tax liability during the year ended December 31, 2017 differs from deferred tax expense for 2017 primarily due to reclassification of our deferred tax asset to other assets in relation to Alternative Minimum Tax ("AMT") recoverable as described below in relation to U.S. Tax Reform, partially offset by the adoption of ASU 2016-09 which resulted in a reduction of our deferred tax liability and an increase in retaining earnings on the consolidated statement of changes in shareholders' equity. Net Deferred Tax Liability balance for continuing operations by major jurisdiction: December 31, 2017 2016 Net Deferred Tax Asset / (Liability) Net Deferred Tax Asset / (Liability) United States $ 4,947 $ (513 ) United Kingdom (5,150 ) (12,297 ) Other (2,058 ) (4,172 ) Total $ (2,261 ) $ (16,982 )
Summary of Operating Loss Carryforwards	As of December 31, 2017 , we had net operating loss carryforwards that could be available to offset future taxable income, as follows: Tax Jurisdiction Loss Carryforwards Tax effect Expiration Operating and Capital Loss Carryforwards: United States - Net operating loss $ 528,226 $ 110,927 2030-2036 United States - Capital loss 14,339 3,011 2021-2022 United Kingdom 324,784 62,521 None Other 19,105 1,236 None
Summary of Income Tax Examinations	Listed below are the tax years that remain subject to examination by a major tax jurisdiction as of December 31, 2017 : Major Tax Jurisdiction Open Tax Years United States 2014-2016 United Kingdom 2014-2016 Australia 2012-2016

Dividend Restrictions and Sta55

Dividend Restrictions and Statutory Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
Summary of Statutory Capital and Surplus	The statutory capital and surplus amounts for the years ended December 31, 2017 and 2016 and statutory net income amounts for the years ended December 31, 2017 , 2016 and 2015 for our insurance and reinsurance subsidiaries based in Bermuda, the United Kingdom, Australia, the United States and Continental Europe were as follows: Statutory Capital and Surplus Required Actual Statutory Income 2017 2016 2017 2016 2017 2016 2015 Bermuda $ 1,556,644 $ 792,652 $ 2,802,653 $ 2,131,308 $ 390,752 $ 339,548 $ 147,883 U.K. $ 453,160 $ 532,132 $ 699,798 $ 805,170 $ 77,900 $ 131,619 $ 113,296 U.S. $ 195,855 $ 209,283 $ 589,029 $ 662,942 $ (5,065 ) $ (1,439 ) $ 14,964 Europe $ 253,981 $ 240,107 $ 444,870 $ 286,039 $ (4,245 ) $ 31,075 $ 1,856

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments on Non-Cancellable Leases	The following is a schedule of future minimum rental payments on non-cancelable leases as of December 31, 2017 : 2018 $ 11,023 2019 9,217 2020 9,310 2021 7,137 2022 5,647 2023 and beyond 20,461 $ 62,795

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Summary of Operations by Segment	The following tables set forth selected and consolidated statement of earnings results by segment for the years ended December 31, 2017 , 2016 , 2015 : 2017 Non-Life Run-Off Atrium StarStone Other Total Gross premiums written $ 14,102 $ 153,472 $ 895,160 $ 5,719 $ 1,068,453 Net premiums written $ 6,482 $ 134,214 $ 464,901 $ 4,793 $ 610,390 Net premiums earned $ 14,162 $ 134,747 $ 459,403 $ 4,809 $ 613,121 Net incurred losses and LAE 190,674 (69,419 ) (314,806 ) — (193,551 ) Life and Annuity Policy Benefits — — — (4,015 ) (4,015 ) Acquisition costs (328 ) (47,688 ) (48,012 ) (878 ) (96,906 ) Operating expenses (132,235 ) (17,444 ) (135,558 ) — (285,237 ) Underwriting income (loss) 72,273 196 (38,973 ) (84 ) 33,412 Net investment income 166,678 4,218 27,706 10,187 208,789 Net realized and unrealized gains (losses) 179,545 1,117 16,613 (6,941 ) 190,334 Fees and commission income (expense) 43,849 22,788 632 (1,166 ) 66,103 Other income 27,061 230 570 648 28,509 Corporate expenses (101,592 ) (12,142 ) — (37,014 ) (150,748 ) Interest income (expense) (28,970 ) (559 ) (1,902 ) 3,329 (28,102 ) Net foreign exchange losses (7,347 ) (5,060 ) (926 ) (4,204 ) (17,537 ) Loss on sale of subsidiary — — — (16,349 ) (16,349 ) EARNINGS (LOSS) BEFORE INCOME TAXES 351,497 10,788 3,720 (51,594 ) 314,411 INCOME TAXES 6,990 (1,593 ) 988 10 6,395 NET EARNINGS (LOSS) FROM CONTINUING OPERATIONS 358,487 9,195 4,708 (51,584 ) 320,806 NET EARNINGS FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE — — — 10,993 10,993 Net earnings attributable to noncontrolling interest (14,687 ) (3,772 ) (1,882 ) — (20,341 ) NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED $ 343,800 $ 5,423 $ 2,826 $ (40,591 ) $ 311,458 Underwriting ratios: Loss ratio (1) 51.5 % 68.5 % Acquisition expense ratio (1) 35.4 % 10.5 % Operating expense ratio (1) 13.0 % 29.5 % Combined ratio (1) 99.9 % 108.5 % 2016 Non-Life Run-Off Atrium StarStone Other Total Gross premiums written $ 17,316 $ 143,170 $ 854,699 $ 7,157 $ 1,022,342 Net premiums written $ 9,202 $ 140,437 $ 648,036 $ 6,261 $ 803,936 Net premiums earned $ 16,755 $ 124,416 $ 676,608 $ 5,735 $ 823,514 Net incurred losses and LAE 285,881 (58,387 ) (401,593 ) — (174,099 ) Life and Annuity Policy Benefits — — — 2,038 2,038 Acquisition costs (4,198 ) (44,670 ) (138,822 ) 1,121 (186,569 ) Operating expenses (151,316 ) (14,233 ) (124,239 ) — (289,788 ) Underwriting income 147,122 7,126 11,954 8,894 175,096 Net investment income 145,237 2,940 22,221 15,065 185,463 Net realized and unrealized gains (losses) 77,685 (601 ) 5,728 (4,994 ) 77,818 Fees and commission income (expense) 17,447 18,189 5,102 (1,374 ) 39,364 Other income 2,497 206 740 1,393 4,836 Corporate expenses (61,583 ) (10,899 ) — (61,464 ) (133,946 ) Interest income (expense) (22,268 ) (198 ) (47 ) 1,871 (20,642 ) Net foreign exchange gains (losses) 1,684 (3,310 ) 754 207 (665 ) EARNINGS (LOSS) BEFORE INCOME TAXES 307,821 13,453 46,452 (40,402 ) 327,324 INCOME TAXES (28,577 ) (2,573 ) (3,693 ) (31 ) (34,874 ) NET EARNINGS (LOSS) FROM CONTINUING OPERATIONS 279,244 10,880 42,759 (40,433 ) 292,450 NET EARNINGS FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE — — — 11,963 11,963 Net earnings attributable to noncontrolling interest (17,600 ) (4,464 ) (17,542 ) — (39,606 ) NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED $ 261,644 $ 6,416 $ 25,217 $ (28,470 ) $ 264,807 Underwriting ratios: Loss ratio (1) 46.9 % 59.4 % Acquisition expense ratio (1) 35.9 % 20.5 % Operating expense ratio (1) 11.5 % 18.3 % Combined ratio (1) 94.3 % 98.2 % 2015 Non-Life Run-Off Atrium StarStone Other Total Gross premiums written $ 38,704 $ 149,082 $ 824,714 $ 2,883 $ 1,015,383 Net premiums written $ 22,594 $ 134,580 $ 628,427 $ 1,553 $ 787,154 Net premiums earned $ 44,369 $ 134,675 $ 573,146 $ 1,554 $ 753,744 Net incurred losses and LAE 270,830 (47,479 ) (327,684 ) — (104,333 ) Life and Annuity Policy Benefits — — — 546 546 Acquisition costs (8,860 ) (45,509 ) (109,347 ) — (163,716 ) Operating expenses (158,821 ) (18,499 ) (128,544 ) — (305,864 ) Underwriting income 147,518 23,188 7,571 2,100 180,377 Net investment income 88,999 2,225 15,937 15,403 122,564 Net realized and unrealized gains (losses) (31,383 ) 252 (9,784 ) (608 ) (41,523 ) Fees and commission income (expense) 22,264 28,352 — (11,269 ) 39,347 Other income (expense) 29,294 359 3,088 (2,413 ) 30,328 Corporate expenses (54,213 ) (13,111 ) — (15,971 ) (83,295 ) Interest income (expense) (33,599 ) (4,264 ) (6 ) 18,466 (19,403 ) Net foreign exchange gains (losses) (4,372 ) (213 ) 480 732 (3,373 ) EARNINGS BEFORE INCOME TAXES 164,508 36,788 17,286 6,440 225,022 INCOME TAXES (12,570 ) (5,968 ) 5,888 — (12,650 ) NET EARNINGS FROM CONTINUING OPERATIONS 151,938 30,820 23,174 6,440 212,372 NET LOSSES FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE — — — (2,031 ) (2,031 ) Net (earnings) losses attributable to noncontrolling interest 33,722 (14,262 ) (9,510 ) — 9,950 NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED $ 185,660 $ 16,558 $ 13,664 $ 4,409 $ 220,291 Underwriting ratios: Loss ratio (1) 35.3 % 57.2 % Acquisition expense ratio (1) 33.8 % 19.1 % Operating expense ratio (1) 13.7 % 22.4 % Combined ratio (1) 82.8 % 98.7 %
Schedule of Revenue from External Customers	The following table summarizes our gross premiums written for the year ended December 31, 2017 by geographic area. Geographic distribution in subsequent years is subject to variation based upon market conditions and business strategies. Non-life Run-off Atrium StarStone Other Total Total % Total % Total % Total % Total % (In thousands of U.S. dollars, except percentages) United States $ 9,639 68.3 % $ 81,438 53.1 % $ 546,223 61.0 % $ — — % $ 637,300 59.6 % United Kingdom 4,271 30.3 % 11,203 7.3 % 97,745 10.9 % 1,346 23.5 % 114,565 10.7 % Europe 192 1.4 % 10,684 7.0 % 151,106 16.9 % 4,373 76.5 % 166,355 15.6 % Asia — — % 4,739 3.1 % 48,839 5.5 % — — % 53,578 5.0 % Rest of World — — % 45,408 29.5 % 51,247 5.7 % — — % 96,655 9.1 % Total $ 14,102 100.0 % $ 153,472 100.0 % $ 895,160 100.0 % $ 5,719 100.0 % $ 1,068,453 100.0 %
Summary of Company's Assets by Segment	Invested assets are managed on a subsidiary by subsidiary basis, and investment income and realized and unrealized gains on investments are recognized in each segment as earned. Our total assets as at December 31, 2017 and 2016 by segment were as follows (the elimination items include the elimination of intersegment assets): 2017 2016 Assets by Segment: Non-life Run-off $ 10,368,105 $ 8,233,450 Atrium 556,637 563,754 StarStone 3,128,725 2,968,316 Other (447,045 ) 1,100,224 Total assets $ 13,606,422 $ 12,865,744

Unaudited Condensed Quarterly58

Unaudited Condensed Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Unaudited Condensed Quarterly Financial Data	December 31, September 30, June 30, March 31, 2017 2016 2017 2016 2017 2016 2017 2016 INCOME Net premiums earned $ 160,627 $ 216,188 $ 148,025 $ 205,730 $ 155,571 $ 208,709 $ 148,898 $ 192,887 Fees and commission income 19,627 13,266 15,895 9,187 18,667 10,487 11,914 6,424 Net investment income 58,605 42,229 52,028 48,022 49,417 44,932 48,739 50,280 Net realized and unrealized gains (losses) 50,637 (61,570 ) 29,301 66,608 51,877 34,503 58,519 38,277 Other income (losses) 9,303 (1,277 ) (3,848 ) 414 10,856 3,289 12,198 2,410 298,799 208,836 241,401 329,961 286,388 301,920 280,268 290,278 EXPENSES Net incurred losses and loss adjustment expenses 30,327 1,321 75,712 (6,902 ) 9,620 96,462 77,892 83,218 Life and annuity policy benefits (1,033 ) (2,265 ) 1,060 1,682 4,289 (1,613 ) (301 ) 158 Acquisition costs 21,449 47,619 24,281 50,074 30,355 43,847 20,821 45,029 General and administrative expenses 126,702 123,497 100,325 103,097 106,490 104,206 102,468 92,934 Interest expense 7,251 4,796 6,410 5,027 7,573 5,421 6,868 5,398 Net foreign exchange losses (gains) 1,925 (1,527 ) 4,775 2,276 7,122 (1,856 ) 3,715 1,772 Loss on sale of subsidiary — — 6,740 — 9,609 — — — 186,621 173,441 219,303 155,254 175,058 246,467 211,463 228,509 EARNINGS BEFORE INCOME TAXES 112,178 35,395 22,098 174,707 111,330 55,453 68,805 61,769 INCOME TAXES 9,629 (11,228 ) (1,432 ) (8,227 ) (4,731 ) (8,050 ) 2,929 (7,369 ) NET EARNINGS FROM CONTINUING OPERATIONS 121,807 24,167 20,666 166,480 106,599 47,403 71,734 54,400 NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE 11,998 5,483 3,495 3,897 (4,871 ) 2,378 371 205 NET EARNINGS 133,805 29,650 24,161 170,377 101,728 49,781 72,105 54,605 Net losses (earnings) attributable to noncontrolling interest (6,206 ) (7,005 ) 14,832 (14,329 ) (11,542 ) (9,187 ) (17,425 ) (9,085 ) NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED $ 127,599 $ 22,645 $ 38,993 $ 156,048 $ 90,186 $ 40,594 $ 54,680 $ 45,520 EARNINGS PER SHARE — BASIC: Net earnings from continuing operations $ 5.96 $ 0.91 $ 1.83 $ 7.89 $ 4.90 $ 1.98 $ 2.80 $ 2.34 Net earnings (loss) from discontinuing operations $ 0.62 $ 0.26 $ 0.18 $ 0.20 $ (0.25 ) $ 0.12 $ 0.02 $ 0.02 Net earnings per ordinary share attributable to Enstar Group Limited shareholders $ 6.58 $ 1.17 $ 2.01 $ 8.09 $ 4.65 $ 2.10 $ 2.82 $ 2.36 EARNINGS PER SHARE — DILUTED: Net earnings from continuing operations $ 5.90 $ 0.90 $ 1.81 $ 7.82 $ 4.87 $ 1.97 $ 2.78 $ 2.33 Net earnings (loss) from discontinuing operations $ 0.61 $ 0.26 $ 0.18 $ 0.20 $ (0.25 ) $ 0.12 $ 0.02 $ 0.02 Net earnings per ordinary share attributable to Enstar Group Limited shareholders $ 6.51 $ 1.16 $ 1.99 $ 8.02 $ 4.62 $ 2.09 $ 2.80 $ 2.35

Description of Business - Addit

Description of Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017Segment
Segment Reporting Information [Line Items]
Number of segments	3
Atrium
Segment Reporting Information [Line Items]
Syndicate underwriting capacity percentage	25.00%

Significant Accounting Polici60

Significant Accounting Policies (Details) - Retained Earnings - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle	$ 4,882	$ 0	$ 0
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle		$ 4,900

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) € in Millions	Dec. 30, 2016USD ($)	May 05, 2016USD ($)	Nov. 13, 2015USD ($)	Nov. 13, 2015EUR (€)	May 05, 2015USD ($)Companyinstallment	Jan. 27, 2015USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Wilton Re | CPPIB and Management of Wilton Re
Business Acquisition [Line Items]
Ownership interest held by parent					100.00%		100.00%
Dana Companies
Business Acquisition [Line Items]
Acquisition consideration	$ 88,500,000
Net earnings (losses) of acquiree since acquisition date								$ 0
Nationale Suisse Assurance S.A.
Business Acquisition [Line Items]
Acquisition consideration			$ 35,200,000	€ 32.8
Net earnings (losses) of acquiree since acquisition date									$ (100,000)
Earned premiums of acquiree since acquisition date									0
Net incurred losses and LAE of acquiree since acquisition date									0
Wilton Re
Business Acquisition [Line Items]
Acquisition consideration					$ 173,058,000
Net earnings (losses) of acquiree since acquisition date									16,500,000
Number of payment installments | installment					2
Cash payments for acquisition		$ 83,900,000			$ 89,100,000
Number of companies acquired | Company					2
Sussex Insurance Company
Business Acquisition [Line Items]
Acquisition consideration						$ 218,000,000
Percentage of consideration financed through bank loan facility						50.00%
Percentage of consideration paid from cash on hand						50.00%
Fair value adjustment to net unearned premiums acquired						$ (34,600,000)
Unamortized unearned premium fair value adjustment							$ 2,500,000
Sussex Insurance Company | Non-life Run-off
Business Acquisition [Line Items]
Net earnings (losses) of acquiree since acquisition date									(42,400,000)
Earned premiums of acquiree since acquisition date									43,200,000
Net incurred losses and LAE of acquiree since acquisition date									$ 44,400,000
Sussex Insurance Company | Acquisition costs
Business Acquisition [Line Items]
Amortization of fair value adjustment to net unearned premiums acquired							16,100,000
Sussex Insurance Company | Net premiums earned
Business Acquisition [Line Items]
Amortization of fair value adjustment to net unearned premiums acquired							$ 16,000,000

Acquisitions - Purchase Price a

Acquisitions - Purchase Price and Fair Value of Assets Acquired (Detail) $ in Thousands, € in Millions	Dec. 30, 2016USD ($)	Nov. 13, 2015USD ($)	Nov. 13, 2015EUR (€)	May 05, 2015USD ($)	Jan. 27, 2015USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Business Acquisition [Line Items]
Excess of purchase price over fair value of net assets acquired						$ 73,071	$ 73,071	$ 73,071
Dana Companies
Business Acquisition [Line Items]
Purchase price	$ 88,500
Net assets acquired at fair value	88,500
Excess of purchase price over fair value of net assets acquired	$ 0
Nationale Suisse Assurance S.A.
Business Acquisition [Line Items]
Purchase price		$ 35,200	€ 32.8
Net assets acquired at fair value		35,225
Excess of purchase price over fair value of net assets acquired		$ 0
Wilton Re
Business Acquisition [Line Items]
Purchase price				$ 173,058
Net assets acquired at fair value				173,058
Excess of purchase price over fair value of net assets acquired				$ 0
Sussex Insurance Company
Business Acquisition [Line Items]
Purchase price					$ 218,000
Net assets acquired at fair value					218,000
Excess of purchase price over fair value of net assets acquired					$ 0

Acquisitions - Summary of Estim

Acquisitions - Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed as of Date of Acquisition (Detail) - USD ($) $ in Thousands	Dec. 30, 2016	Nov. 13, 2015	May 05, 2015	Jan. 27, 2015
Dana Companies
LIABILITIES
NET ASSETS ACQUIRED AT FAIR VALUE	$ 88,500
Dana Companies | Non-life Run-off Segment
ASSETS
Other investments, at fair value	46,589
Total investments	130,725
Cash and cash equivalents	58,430
Restricted cash and cash equivalents	1,692
Reinsurance balances recoverable	133,032
Other assets	5,383
TOTAL ASSETS	329,262
LIABILITIES
Other liabilities - Asbestos related	220,496
Other liabilities	20,266
TOTAL LIABILITIES	240,762
NET ASSETS ACQUIRED AT FAIR VALUE	88,500
Dana Companies | Non-life Run-off Segment | Short-term investments
ASSETS
Trading, at fair value	22,747
Dana Companies | Non-life Run-off Segment | Fixed maturities
ASSETS
Trading, at fair value	$ 61,389
Nationale Suisse Assurance S.A.
ASSETS
Other investments, at fair value		$ 1,339
Total investments		144,676
Cash and cash equivalents		64,709
Reinsurance balances recoverable — reserves		4,343
Reinsurance balances recoverable — paids		12,151
Prepaid reinsurance premiums		3,213
Other assets		5,395
TOTAL ASSETS		234,487
LIABILITIES
Losses and LAE		173,209
Funds withheld		473
Insurance and reinsurance balances payable		6,991
Unearned premium		5,969
Other liabilities		12,620
TOTAL LIABILITIES		199,262
NET ASSETS ACQUIRED AT FAIR VALUE		35,225
Nationale Suisse Assurance S.A. | Short-term investments
ASSETS
Trading, at fair value		8,644
Available-for-sale, at fair value		6,687
Nationale Suisse Assurance S.A. | Fixed maturities
ASSETS
Trading, at fair value		31,350
Available-for-sale, at fair value		96,656
Nationale Suisse Assurance S.A. | Other
ASSETS
Other investments, at fair value		0
Total investments		103,343
Cash and cash equivalents		25,258
Reinsurance balances recoverable — reserves		302
Reinsurance balances recoverable — paids		1,320
Prepaid reinsurance premiums		0
Other assets		2,298
TOTAL ASSETS		132,521
LIABILITIES
Losses and LAE		117,188
Funds withheld		0
Insurance and reinsurance balances payable		779
Unearned premium		0
Other liabilities		2,875
TOTAL LIABILITIES		120,842
NET ASSETS ACQUIRED AT FAIR VALUE		11,679
Nationale Suisse Assurance S.A. | Other | Short-term investments
ASSETS
Trading, at fair value		0
Available-for-sale, at fair value		6,687
Nationale Suisse Assurance S.A. | Other | Fixed maturities
ASSETS
Trading, at fair value		0
Available-for-sale, at fair value		96,656
Nationale Suisse Assurance S.A. | Non-life Run-off Segment
ASSETS
Other investments, at fair value		1,339
Total investments		41,333
Cash and cash equivalents		39,451
Reinsurance balances recoverable — reserves		4,041
Reinsurance balances recoverable — paids		10,831
Prepaid reinsurance premiums		3,213
Other assets		3,097
TOTAL ASSETS		101,966
LIABILITIES
Losses and LAE		56,021
Funds withheld		473
Insurance and reinsurance balances payable		6,212
Unearned premium		5,969
Other liabilities		9,745
TOTAL LIABILITIES		78,420
NET ASSETS ACQUIRED AT FAIR VALUE		23,546
Nationale Suisse Assurance S.A. | Non-life Run-off Segment | Short-term investments
ASSETS
Trading, at fair value		8,644
Available-for-sale, at fair value		0
Nationale Suisse Assurance S.A. | Non-life Run-off Segment | Fixed maturities
ASSETS
Trading, at fair value		31,350
Available-for-sale, at fair value		$ 0
Wilton Re
ASSETS
Other investments, at fair value			$ 142,182
Cash and cash equivalents			5,043
Other assets			26,376
TOTAL ASSETS			173,601
LIABILITIES
TOTAL LIABILITIES			543
NET ASSETS ACQUIRED AT FAIR VALUE			$ 173,058
Sussex Insurance Company
ASSETS
Equities, trading, at fair value				$ 31,439
Total investments				639,975
Cash and cash equivalents				358,458
Restricted cash and cash equivalents				15,279
Accrued interest receivable				3,984
Premiums receivable				37,190
Reinsurance balances recoverable				483,816
Prepaid reinsurance premiums				28,751
Other assets				43,939
TOTAL ASSETS				1,611,392
LIABILITIES
Losses and LAE				1,257,205
Funds withheld				42,090
Insurance and reinsurance balances payable				3,030
Unearned premium				79,293
Other liabilities				11,774
TOTAL LIABILITIES				1,393,392
NET ASSETS ACQUIRED AT FAIR VALUE				218,000
Sussex Insurance Company | Short-term investments
ASSETS
Trading, at fair value				85,309
Sussex Insurance Company | Fixed maturities
ASSETS
Trading, at fair value				$ 523,227

Acquisitions - Pro Forma Conden

Acquisitions - Pro Forma Condensed Combined Statement of Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total income	$ 298,799	$ 241,401	$ 286,388	$ 280,268	$ 208,836	$ 329,961	$ 301,920	$ 290,278	$ 1,106,856	$ 1,130,995	$ 904,460
Total expenses											(694,119)
Total noncontrolling interest	(6,206)	14,832	(11,542)	(17,425)	(7,005)	(14,329)	(9,187)	(9,085)	(20,341)	(39,606)	9,950
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED	$ 127,599	$ 38,993	$ 90,186	$ 54,680	$ 22,645	$ 156,048	$ 40,594	$ 45,520	$ 311,458	$ 264,807	220,291
Sussex Insurance Company
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total income											29,990
Total expenses											(39,860)
Total noncontrolling interest											0
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED											(9,870)
Alpha
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total income											31,884
Total expenses											(47,026)
Total noncontrolling interest											0
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED											(15,142)
Wilton Re
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total income											5,793
Total expenses											(3,628)
Total noncontrolling interest											0
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED											2,165
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements
Business Acquisition, Pro Forma Information [Abstract]
Total income											981,621
Total expenses											(778,739)
Total noncontrolling interest											9,950
Net earnings (loss)											212,832
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements | Pro forma | Income adjustment
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total income											9,494
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements | Pro forma | Expense adjustment
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total expenses											5,894
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements | Pro forma | Noncontrolling interest adjustment
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total noncontrolling interest											0
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements | Pro forma | Net earnings (loss) adjustment
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED											15,388
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements | Pro forma | Reversal of amortization of fair value adjustments related to unearned premium included in Enstar Group results but reflected in 2014 pro formas
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total income											13,344
Total expenses											16,173
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements | Pro forma | Adjustment to recognize amortization of fair value adjustments
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total income											(3,850)
Total expenses											(451)
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements | Pro forma | Adjustment to interest expense to reflect financing costs of the acquisition for the period
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total expenses											(1,098)
Sussex Insurance Company, National Suisse Assurance S.A., and Wilton Relife Settlements | Pro forma | Adjustment to income taxes for pro forma adjustments
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Total expenses											$ (8,730)

Significant New Business (Detai

Significant New Business (Detail) £ in Millions, AUD in Millions	Feb. 22, 2018AUD	Feb. 22, 2018USD ($)	Feb. 16, 2018USD ($)	Feb. 16, 2018GBP (£)	Jan. 29, 2018USD ($)	Jan. 29, 2018GBP (£)	Dec. 28, 2017USD ($)	Feb. 07, 2017USD ($)	Feb. 07, 2017GBP (£)	Jan. 11, 2017USD ($)	Nov. 15, 2016USD ($)	Nov. 15, 2016GBP (£)	Aug. 05, 2016USD ($)	Feb. 17, 2016USD ($)	Sep. 30, 2015USD ($)Agreement	May 27, 2015USD ($)Agreementtrust	Jan. 15, 2015USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Feb. 07, 2017GBP (£)	Nov. 30, 2015USD ($)	Dec. 31, 2014USD ($)
Guarantor Obligations [Line Items]
Assumed business																		$ 1,525,703,000	$ 1,340,444,000	$ 612,441,000
Cash and cash equivalents																		955,150,000	954,871,000	795,245,000
Deferred charge																		80,192,000	94,551,000	$ 255,911,000			$ 0
Reinsurance premium assumed																		175,383,000	82,073,000
Allianz
Guarantor Obligations [Line Items]
Percentage of reinsurance agreements entered														50.00%
Allianz
Guarantor Obligations [Line Items]
Assumed business, net							$ 81,400,000							$ 1,100,000,000
Funds held																		1,023,000,000	$ 994,800,000
Approximate value of additional funds transferred to trust							$ 8,100,000							$ 110,000,000
Percentage of reinsurance agreements entered							50.00%							50.00%
Reinsurance premium assumed							$ 81,400,000							$ 1,100,000,000
Funds held by reinsured companies							$ 162,800,000							2,200,000,000
Allianz | Limited parental guarantee
Guarantor Obligations [Line Items]
Limited parental guarantee obligations, initial amount (up to)														$ 270,000,000
RSA
Guarantor Obligations [Line Items]
Assumed business								$ 1,301,800,000	£ 1,046.4
Assumed business, net								1,153,900,000	£ 927.5
Reinsurance premium receivable								997,200,000													£ 801.6
Fair value adjustment on gross reserves								174,100,000
Fair value adjustment on net reserves								$ 156,700,000
QBE
Guarantor Obligations [Line Items]
Assumed business										$ 1,019,000,000
Assumed business, net										447,000,000
Reinsurance premium receivable										403,800,000
Restricted cash										227,600,000
Funds held										176,200,000
Fair value adjustment on gross reserves										180,000,000
Fair value adjustment on net reserves										$ 43,200,000
Coca-Cola
Guarantor Obligations [Line Items]
Assumed business													$ 108,800,000
Cash and cash equivalents													101,300,000
Approximate value of additional funds transferred to trust													108,800,000
Coca-Cola | Limited parental guarantee
Guarantor Obligations [Line Items]
Limited parental guarantee obligations, initial amount (up to)													27,000,000
Coca-Cola | Other assets
Guarantor Obligations [Line Items]
Deferred charge													$ 7,500,000
Shelbourne RITC
Guarantor Obligations [Line Items]
Assumed business											$ 158,000,000	£ 121.5
The Doctors Company and its affiliates | Workers' compensation
Guarantor Obligations [Line Items]
Total assets and liabilities assumed																						$ 29,500,000
Sun Life
Guarantor Obligations [Line Items]
Assumed business															$ 128,300,000
Cash and cash equivalents															122,500,000
Deferred charge															5,800,000
Approximate value of additional funds transferred to trust															30,600,000
Limited parental guarantee obligations, initial amount (up to)															$ 36,800,000
Percentage of reinsurance agreements entered															100.00%
Number of agreements entered | Agreement															2
Voya Financial
Guarantor Obligations [Line Items]
Assumed business																$ 572,400,000
Cash and cash equivalents																307,000,000
Deferred charge																265,400,000
Approximate value of additional funds transferred to trust																$ 67,200,000
Limited parental guarantee obligations, initial amount (up to)																		$ 129,100,000
Percentage of reinsurance agreements entered																100.00%
Number of agreements entered | Agreement																2
Number of reinsurance collateral trusts | trust																2
Reciprocal of America
Guarantor Obligations [Line Items]
Assumed business																	$ 162,100,000
Subsequent event | Zurich
Guarantor Obligations [Line Items]
Assumed business	AUD 350	$ 275,000,000
Subsequent event | AXIS Managing Agency Limited
Guarantor Obligations [Line Items]
Assumed business					$ 1,100,000,000	£ 840
Assumed business, net					$ 811,000,000	£ 600
Subsequent event | Neon Underwriting Limited
Guarantor Obligations [Line Items]
Assumed business			$ 543,400,000	£ 402.2
Assumed business, net			$ 456,400,000	£ 337.8

Divestitures, Held-For-Sale B66

Divestitures, Held-For-Sale Businesses and Discontinuing Operations - Additional Information (Details) $ in Thousands, € in Millions	3 Months Ended								6 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jun. 30, 2018USD ($)	Dec. 29, 2017USD ($)	Aug. 29, 2017USD ($)	Aug. 29, 2017EUR (€)	Feb. 17, 2017USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on sale of subsidiary	$ 0	$ 6,740	$ 9,609	$ 0	$ 0	$ 0	$ 0	$ 0				$ 16,349	$ 0	$ 0
Cumulative CTA adjustment												(20,751)	0	0
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS	11,998	$ 3,495	$ (4,871)	$ 371	5,483	$ 3,897	$ 2,378	$ 205				10,993	11,963	(2,031)
Pavonia | Discontinued operations, disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received	120,000				0							120,000	0	0					$ 120,000
Cumulative CTA adjustment									$ 0	$ 0		12,179
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS									$ 11,963	$ (2,031)		10,993
Pavonia | Discontinued operations, held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash, cash equivalents and restricted cash and cash equivalents																$ 135,100
Restricted investments	$ 1,400				$ 786,000							1,400	786,000
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS												(9,867)	11,963	(2,031)
Laguna | Not discontinued operations, disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on sale of subsidiary												16,300
Cumulative CTA adjustment											$ (6,300)
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS												$ (1,200)	$ 1,000	$ 1,800
Monument | Affiliated entity | Laguna | Not discontinued operations, disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received																	$ 30,800	€ 25.6
Scenario, Forecast | PLIC MI | Discontinued operations, held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received															$ 13,100

Divestitures, Held-For-Sale B67

Divestitures, Held-For-Sale Businesses and Discontinuing Operations - Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 17, 2017
Assets:
Total assets held for sale	$ 24,351				$ 1,244,456						$ 24,351	$ 1,244,456
Total assets held for sale	24,351				1,244,456						24,351	1,244,456
Liabilities:
Total liabilities held for sale	11,271				1,150,787						11,271	1,150,787
EXPENSES
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS BEFORE GAIN ON SALE	11,998	$ 3,495	$ (4,871)	$ 371	5,483	$ 3,897	$ 2,378	$ 205			10,993	11,963	$ (2,031)
Disposal:
Less: Cumulative currency translation adjustment previously recorded in accumulated other comprehensive income											(20,751)	0	0
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS	11,998	$ 3,495	$ (4,871)	$ 371	5,483	$ 3,897	$ 2,378	$ 205			10,993	11,963	(2,031)
Pavonia | Discontinued operations, held-for-sale
Assets:
Fixed maturities, trading, at fair value	20,770				326,382						20,770	326,382
Fixed maturities, held-to-maturity, at amortized cost	0				765,554						0	765,554
Equities, trading, at fair value	765				4,428						765	4,428
Other investments, at fair value	0				15,114						0	15,114
Cash and cash equivalents	6,314				18,018						6,314	18,018
Restricted cash and cash equivalents	13				5,202						13	5,202
Deferred tax assets	0				31,500						0	31,500
Reinsurance balances recoverable	1,728				18,029						1,728	18,029
Other assets	269				60,229						269	60,229
Assets of businesses held for sale	29,859				1,244,456						29,859	1,244,456
Less: Accrual of loss on sale	5,508				0						5,508	0
Total assets held for sale	24,351				1,244,456						24,351	1,244,456
Total assets held for sale	24,351				1,244,456						24,351	1,244,456
Liabilities:
Policy benefits for life and annuity contracts	10,666				1,144,850						10,666	1,144,850
Other liabilities	605				5,937						605	5,937
Total liabilities held for sale	11,271				1,150,787						11,271	1,150,787
INCOME
Net premiums earned											55,906	69,089	85,327
Net investment income											41,117	38,140	35,404
Net realized and unrealized gains											577	4,263	271
Other income											1,564	1,912	7,690
Total income											99,164	113,404	128,692
EXPENSES
Life and annuity policy benefits											84,029	76,594	97,472
Acquisition costs											9,025	9,836	13,712
General and administrative expenses											12,813	14,416	13,886
Other expenses											(26)	199	486
Total expenses											105,841	101,045	125,556
EARNINGS (LOSS) BEFORE INCOME TAXES											(6,677)	12,359	3,136
INCOME TAXES											(3,190)	(396)	(5,167)
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS BEFORE GAIN ON SALE											(9,867)	11,963	(2,031)
Disposal:
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS											(9,867)	11,963	(2,031)
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Operating activities											75,714	(71,521)	(5,893)
Investing activities											42,542	56,646	(24,766)
Change in cash of businesses held for sale											118,256	(14,875)	(30,659)
Pavonia | Discontinued operations, disposed of by sale
EXPENSES
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS BEFORE GAIN ON SALE									$ 11,963	$ (2,031)	10,993
Disposal:
Consideration received	120,000				0						120,000	0	0	$ 120,000
Less: Carrying value of subsidiary	$ 86,961				$ 0						86,961	$ 0	$ 0
Less: Cumulative currency translation adjustment previously recorded in accumulated other comprehensive income									0	0	12,179
Gain on sale of subsidiary									0	0	20,860
NET EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS									$ 11,963	$ (2,031)	$ 10,993

Investments - Fair Values of Fi

Investments - Fair Values of Fixed Maturity Investments, Short-Term Investments and Equities Classified as Trading (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	$ 5,876,284	$ 4,611,160
Equities, trading, at fair value	106,603	95,047
Trading securities	5,982,887	4,706,207
U.S. government and agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	554,036	840,274
Non-U.S. government
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	607,132	267,363
Corporate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	3,363,060	2,387,322
Municipal
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	100,221	47,181
Residential mortgage-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	288,713	373,528
Commercial mortgage-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	421,548	217,212
Asset-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	541,574	478,280
Equity securities | US
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equities, trading, at fair value	106,363	95,047
Equity securities | International
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equities, trading, at fair value	240	0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	152,400	362,900
Senior Secured Debt Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, debt	$ 68,900	$ 90,700

Investments - Contractual Matur

Investments - Contractual Maturities of Fixed Maturity and Short-term Investments Classified as Trading (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost
One year or less	$ 398,054
More than one year through two years	340,531
More than two years through five years	1,283,898
More than five years through ten years	1,235,079
More than ten years	1,278,126
Trading securities, amortized cost	5,783,362
Fair Value
One year or less	398,083
More than one year through two years	341,753
More than two years through five years	1,286,527
More than five years through ten years	1,249,887
More than ten years	1,348,199
Trading securities, debt	$ 5,876,284	$ 4,611,160
% of Total Fair Value
One year or less	6.80%
More than one year through two years	5.80%
More than two years through five years	21.90%
More than five years through ten years	21.30%
More than ten years	22.90%
Trading securities, percentage of fair value	100.00%
Residential mortgage-backed
Amortized Cost
Securities without single maturity date	$ 285,312
Fair Value
Securities without single maturity date	288,713
Trading securities, debt	$ 288,713	373,528
% of Total Fair Value
Securities without single maturity date	4.90%
Commercial mortgage-backed
Amortized Cost
Securities without single maturity date	$ 427,469
Fair Value
Securities without single maturity date	421,548
Trading securities, debt	$ 421,548	217,212
% of Total Fair Value
Securities without single maturity date	7.20%
Asset-backed
Amortized Cost
Securities without single maturity date	$ 534,893
Fair Value
Securities without single maturity date	541,574
Trading securities, debt	$ 541,574	$ 478,280
% of Total Fair Value
Securities without single maturity date	9.20%

Investments - Amortized Cost an

Investments - Amortized Cost and Fair Values of Fixed Maturity and Short-Term Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 208,097	$ 269,864
Gross Unrealized Gains	3,693	3,435
Gross Unrealized Losses Non-OTTI	(1,505)	(5,532)
Fair Value	210,285	267,767
U.S. government and agency
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,210	12,784
Gross Unrealized Gains	0	32
Gross Unrealized Losses Non-OTTI	(23)	(106)
Fair Value	4,187	12,710
Non-U.S. government
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	84,776	86,897
Gross Unrealized Gains	1,249	1,303
Gross Unrealized Losses Non-OTTI	(588)	(2,777)
Fair Value	85,437	85,423
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	113,561	159,243
Gross Unrealized Gains	2,436	2,040
Gross Unrealized Losses Non-OTTI	(876)	(2,628)
Fair Value	115,121	158,655
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,146	6,585
Gross Unrealized Gains	8	12
Gross Unrealized Losses Non-OTTI	(18)	(21)
Fair Value	5,136	6,576
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	31	488
Gross Unrealized Gains	0	39
Gross Unrealized Losses Non-OTTI	0	0
Fair Value	31	527
Asset-backed
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	373	3,867
Gross Unrealized Gains	0	9
Gross Unrealized Losses Non-OTTI	0	0
Fair Value	$ 373	$ 3,876

Investments - Contractual Mat71

Investments - Contractual Maturities of Fixed Maturity and Short-Term Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost
One year or less	$ 50,135
More than one year through two years	17,549
More than two years through five years	53,690
More than five years through ten years	46,743
More than ten years	39,576
Amortized Cost	208,097	$ 269,864
Fair Value
One year or less	49,828
More than one year through two years	17,427
More than two years through five years	54,355
More than five years through ten years	47,735
More than ten years	40,536
Fair Value	$ 210,285	267,767
% of Total Fair Value
One year or less	23.70%
More than one year through two years	8.30%
More than two years through five years	25.80%
More than five years through ten years	22.70%
More than ten years	19.30%
Percentage of Total Fair Value	100.00%
Residential mortgage-backed
Amortized Cost
Securities without single maturity date	$ 31
Amortized Cost	31	488
Fair Value
Securities without single maturity date	31
Fair Value	$ 31	527
% of Total Fair Value
Securities without single maturity date	0.00%
Asset-backed
Amortized Cost
Securities without single maturity date	$ 373
Amortized Cost	373	3,867
Fair Value
Securities without single maturity date	373
Fair Value	$ 373	$ 3,876
% of Total Fair Value
Securities without single maturity date	0.20%

Investments - Gross Unrealized

Investments - Gross Unrealized Losses (Detail) $ in Thousands	Dec. 31, 2017USD ($)Security	Dec. 31, 2016USD ($)Security
Fair Value
12 Months or Greater	$ 22,991	$ 16,319
Less Than 12 Months	50,612	86,265
Total	73,603	102,584
Gross Unrealized Losses
12 Months or Greater	(1,201)	(3,594)
Less Than 12 Months	(304)	(1,938)
Total	$ (1,505)	$ (5,532)
Number of securities classified as available-for-sale in an unrealized loss position | Security	96	156
Number of securities classified as available-for-sale in an unrealized loss position for twelve months or longer | Security	37	41
U.S. government and agency
Fair Value
12 Months or Greater	$ 2,344	$ 0
Less Than 12 Months	1,842	10,743
Total	4,186	10,743
Gross Unrealized Losses
12 Months or Greater	(16)	0
Less Than 12 Months	(7)	(106)
Total	(23)	(106)
Non-U.S. government
Fair Value
12 Months or Greater	11,101	8,316
Less Than 12 Months	20,965	30,086
Total	32,066	38,402
Gross Unrealized Losses
12 Months or Greater	(373)	(1,794)
Less Than 12 Months	(215)	(983)
Total	(588)	(2,777)
Corporate
Fair Value
12 Months or Greater	9,177	8,003
Less Than 12 Months	24,200	42,304
Total	33,377	50,307
Gross Unrealized Losses
12 Months or Greater	(807)	(1,800)
Less Than 12 Months	(69)	(828)
Total	(876)	(2,628)
Municipal
Fair Value
12 Months or Greater	369	0
Less Than 12 Months	3,605	3,132
Total	3,974	3,132
Gross Unrealized Losses
12 Months or Greater	(5)	0
Less Than 12 Months	(13)	(21)
Total	$ (18)	$ (21)

Investments - Other Than Tempor

Investments - Other Than Temporary Impairment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Other than temporary impairment losses, available-for-sale securities	$ 0	$ 0
Available-for-sale securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Credit losses	$ 0	$ 0

Investments - Credit Ratings of

Investments - Credit Ratings of Fixed Maturity and Short-Term Investments, Trading (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 5,991,459
Fair Value	6,086,569
Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 391,449
Marketable Securities Member | Portfolio Concentration Risk Member | Trading Securities and Available for Sale Securities
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	100.00%
Trading and Available for Sale Securities | Credit Rating Concentration Risk | Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	6.40%
AAA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,502,676
AAA Rated | Trading and Available for Sale Securities | Credit Rating Concentration Risk | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	24.70%
AA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 937,676
AA Rated | Trading and Available for Sale Securities | Credit Rating Concentration Risk | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	15.40%
A Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,106,901
A Rated | Trading and Available for Sale Securities | Credit Rating Concentration Risk | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	34.60%
BBB Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,127,929
BBB Rated | Trading and Available for Sale Securities | Credit Rating Concentration Risk | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	18.60%
Not Rated
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 19,938
Not Rated | Trading and Available for Sale Securities | Credit Rating Concentration Risk
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	0.30%
U.S. government and agency
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 561,483
Fair Value	558,223
U.S. government and agency | Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 0
U.S. government and agency | Marketable Securities Member | Portfolio Concentration Risk Member | Trading Securities and Available for Sale Securities
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	9.20%
U.S. government and agency | AAA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 556,859
U.S. government and agency | AA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	1,364
U.S. government and agency | A Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	0
U.S. government and agency | BBB Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	0
U.S. government and agency | Not Rated
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	0
Non-U.S. government
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	665,056
Fair Value	692,569
Non-U.S. government | Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,641
Non-U.S. government | Marketable Securities Member | Portfolio Concentration Risk Member | Trading Securities and Available for Sale Securities
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	11.40%
Non-U.S. government | AAA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 134,619
Non-U.S. government | AA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	409,315
Non-U.S. government | A Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	79,030
Non-U.S. government | BBB Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	62,964
Non-U.S. government | Not Rated
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	0
Corporate
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	3,413,543
Fair Value	3,478,181
Corporate | Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 188,237
Corporate | Marketable Securities Member | Portfolio Concentration Risk Member | Trading Securities and Available for Sale Securities
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	57.20%
Corporate | AAA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 123,059
Corporate | AA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	375,252
Corporate | A Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	1,854,503
Corporate | BBB Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	932,238
Corporate | Not Rated
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	4,892
Municipal
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	103,299
Fair Value	105,357
Municipal | Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 0
Municipal | Marketable Securities Member | Portfolio Concentration Risk Member | Trading Securities and Available for Sale Securities
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	1.70%
Municipal | AAA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 26,313
Municipal | AA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	62,605
Municipal | A Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	12,864
Municipal | BBB Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	3,575
Municipal | Not Rated
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	0
Residential mortgage-backed
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	285,343
Fair Value	288,744
Residential mortgage-backed | Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 98,997
Residential mortgage-backed | Marketable Securities Member | Portfolio Concentration Risk Member | Trading Securities and Available for Sale Securities
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	4.70%
Residential mortgage-backed | AAA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 166,386
Residential mortgage-backed | AA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	7,425
Residential mortgage-backed | A Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	14,204
Residential mortgage-backed | BBB Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	678
Residential mortgage-backed | Not Rated
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	1,054
Commercial mortgage-backed
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	427,469
Fair Value	421,548
Commercial mortgage-backed | Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 9,555
Commercial mortgage-backed | Marketable Securities Member | Portfolio Concentration Risk Member | Trading Securities and Available for Sale Securities
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	6.90%
Commercial mortgage-backed | AAA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 222,656
Commercial mortgage-backed | AA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	38,176
Commercial mortgage-backed | A Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	77,811
Commercial mortgage-backed | BBB Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	59,358
Commercial mortgage-backed | Not Rated
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	13,992
Asset-backed
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	535,266
Fair Value	541,947
Asset-backed | Non-Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 88,019
Asset-backed | Marketable Securities Member | Portfolio Concentration Risk Member | Trading Securities and Available for Sale Securities
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
% of Total Investments	8.90%
Asset-backed | AAA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 272,784
Asset-backed | AA Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	43,539
Asset-backed | A Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	68,489
Asset-backed | BBB Rated | Investment Grade
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	69,116
Asset-backed | Not Rated
Schedule of Trading Securities and Available-for-sale Securities [Line Items]
Amortized Cost	$ 0

Investments - Other Investments

Investments - Other Investments, at Fair Value (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)fund	Dec. 31, 2016USD ($)
Other Investments [Line Items]
Valuation lag period	3 months
Other investments, at fair value	$ 913,392	$ 937,047
Unfunded commitments	164,700
Private equities and private equity funds
Other Investments [Line Items]
Other investments, at fair value	289,556	300,529
Unfunded commitments	164,700
Fixed income funds
Other Investments [Line Items]
Other investments, at fair value	$ 229,999	249,023
Fixed income hedge funds
Other Investments [Line Items]
Imposed lock-up period (up to) (years)	3 years
Number of days to give notice for quarterly hedge fund redemptions	90 days
Other investments, at fair value	$ 63,773	85,976
Gates or side-pocket investments	500
Equity funds
Other Investments [Line Items]
Other investments, at fair value	249,475	223,571
CLO equities
Other Investments [Line Items]
Other investments, at fair value	$ 56,765	61,565
CLO equity funds
Other Investments [Line Items]
Number of CLO equity funds | fund	2
Other investments, at fair value	$ 12,840	15,440
Private credit funds
Other Investments [Line Items]
Other investments, at fair value	10,156	0
Other
Other Investments [Line Items]
Other investments, at fair value	828	$ 943
CLO Equity Fund One
Other Investments [Line Items]
Other investments, at fair value	$ 1,100
CLO Equity Fund One | Minimum
Other Investments [Line Items]
CLO equity fund pay out period (years)	1 year
CLO Equity Fund One | Maximum
Other Investments [Line Items]
CLO equity fund pay out period (years)	5 years
CLO Equity Fund Two
Other Investments [Line Items]
Other investments, at fair value	$ 11,700

Investments - Other Investmen76

Investments - Other Investments, at Cost (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)contract	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)contract	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)contract	Dec. 31, 2016USD ($)contract	Dec. 31, 2015USD ($)
Other Investments [Line Items]
Other investments, at cost	$ 125,621,000				$ 131,651,000				$ 125,621,000	$ 131,651,000
Amount of net investment income included in earnings attributable to investments in life settlements	$ 58,605,000	$ 52,028,000	$ 49,417,000	$ 48,739,000	$ 42,229,000	$ 48,022,000	$ 44,932,000	$ 50,280,000	$ 208,789,000	$ 185,463,000	$ 122,564,000
Number of Contracts
0 – 1 year | contract	0				2				0	2
1 – 2 years | contract	11				7				11	7
2 – 3 years | contract	10				11				10	11
3 – 4 years | contract	20				17				20	17
4 – 5 years | contract	13				16				13	16
Thereafter | contract	162				181				162	181
Total | contract	216				234				216	234
Carrying Value
0 – 1 year	$ 0				$ 461,000				$ 0	$ 461,000
1 – 2 years	17,655,000				11,396,000				17,655,000	11,396,000
2 – 3 years	7,524,000				15,338,000				7,524,000	15,338,000
3 – 4 years	16,119,000				17,013,000				16,119,000	17,013,000
4 – 5 years	13,960,000				10,377,000				13,960,000	10,377,000
Thereafter	70,363,000				77,066,000				70,363,000	77,066,000
Total	125,621,000				131,651,000				125,621,000	131,651,000
Face Value (Death Benefits)
0 – 1 year	0				700,000				0	700,000
1 – 2 years	29,471,000				18,337,000				29,471,000	18,337,000
2 – 3 years	19,906,000				29,715,000				19,906,000	29,715,000
3 – 4 years	32,411,000				32,189,000				32,411,000	32,189,000
4 – 5 years	32,730,000				23,302,000				32,730,000	23,302,000
Thereafter	390,843,000				431,034,000				390,843,000	431,034,000
Total	505,361,000				535,277,000				505,361,000	535,277,000
Life Settlement Contracts, Investment Method, Premiums to be Paid, Fiscal Year Maturity [Abstract]
Life insurance premiums payable in 2018	17,800,000								17,800,000
Life insurance premiums payable in 2019	17,700,000								17,700,000
Life insurance premiums payable in 2020	16,600,000								16,600,000
Life insurance premiums payable in 2021	15,700,000								15,700,000
Life insurance premiums payable in 2022	15,200,000								15,200,000
Life Settlements
Other Investments [Line Items]
Amount of net investment income included in earnings attributable to investments in life settlements									13,800,000	18,000,000
Impairment charges recognized in the period									7,200,000	5,300,000
Carrying Value | Life Settlement
Other Investments [Line Items]
Other investments, at cost	$ 125,600,000				$ 131,700,000				$ 125,600,000	$ 131,700,000

Investments - Net Investment In

Investments - Net Investment Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Investment Income [Line Items]
Gross investment income									$ 219,823	$ 193,308	$ 131,902
Funds Held, Directly Managed, Investment Income [Table Text Block]									Major categories of net investment income underlying the funds held - directly managed account for the year ended December 31, 2017 and 2016 are summarized as follows: 2017 2016 Fixed maturity investments $ 33,558 $ 5,705 Short-term investments and cash and cash equivalents 292 64 Gross investment income 33,850 5,769 Investment expenses (1,371 ) — Investment income on funds held - directly managed $ 32,479 $ 5,769
Investment expenses									$ (11,034)	(7,845)	(9,338)
Net investment income	$ 58,605	$ 52,028	$ 49,417	$ 48,739	$ 42,229	$ 48,022	$ 44,932	$ 50,280	208,789	185,463	122,564
Fixed maturities
Net Investment Income [Line Items]
Gross investment income									144,367	114,885	87,512
Short-term investments and cash and cash equivalents
Net Investment Income [Line Items]
Gross investment income									9,314	4,491	5,993
Funds held
Net Investment Income [Line Items]
Gross investment income									601	22,583	234
Funds held – directly managed
Net Investment Income [Line Items]
Gross investment income									$ 33,850	5,769	0
Funds Held, Directly Managed, Investment Income [Table Text Block]									32,479,000
Investment expenses									$ (1,371)	0
Net investment income										5,769
Investment income from fixed maturities and cash and cash equivalents
Net Investment Income [Line Items]
Gross investment income									186,761	147,728	93,739
Equity securities
Net Investment Income [Line Items]
Gross investment income									4,355	4,874	5,580
Other investments
Net Investment Income [Line Items]
Gross investment income									14,337	22,515	11,712
Life settlements and other
Net Investment Income [Line Items]
Gross investment income									14,370	18,191	20,871
Investment income from equities and other investments
Net Investment Income [Line Items]
Gross investment income									$ 33,062	$ 45,580	$ 38,163

Investments - Net Realized and

Investments - Net Realized and Unrealized Gains (Losses) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Total net realized gains (losses) on sale									$ 1,668	$ (7,036)	$ 15,859
Change in fair value of embedded derivative									102,388	70,296	17,411
Total net unrealized gains (losses)									188,666	84,854	(57,382)
Net realized gains (losses) and change in fair value of funds held- directly managed	$ 50,637	$ 29,301	$ 51,877	$ 58,519	$ (61,570)	$ 66,608	$ 34,503	$ 38,277	190,334	77,818	(41,523)
Proceeds from sales of available-for-sale securities									40,800	41,300	95,100
Fixed maturity investments
Gain (Loss) on Investments [Line Items]
Gross realized gains on fixed maturity securities, available-for-sale									616	405	396
Gross realized (losses) on fixed maturity securities, available-for-sale									(125)	(21)	(130)
Net realized gains (losses) on trading securities									4,695	1,848	(4,291)
Net unrealized gains (losses) on trading securities									35,878	36,314	(52,918)
Equity securities
Gain (Loss) on Investments [Line Items]
Net realized gains (losses) on trading securities									701	5,348	19,884
Net unrealized gains (losses) on trading securities									16,498	6,561	(21,875)
Funds held – directly managed
Gain (Loss) on Investments [Line Items]
Net realized gains (losses) on trading securities									(4,219)	(14,616)	0
Change in value of fair value option on funds held - directly managed									32,928	(28,317)	0
Change in value of fair value option on funds held- directly managed									974	0	$ 0
Net realized gains (losses) and change in fair value of funds held- directly managed									$ 29,683	$ (42,933)

Investments - Restricted Assets

Investments - Restricted Assets (Detail)	Feb. 08, 2018USD ($)	Dec. 31, 2017USD ($)syndicate	Dec. 31, 2016USD ($)	Nov. 30, 2016USD ($)	Dec. 31, 2015USD ($)
Investments, Debt and Equity Securities [Abstract]
Restricted cash and cash equivalents		$ 257,686,000	$ 363,774,000		$ 499,924,000
Collateral in trust for third party agreements		3,118,892,000	1,975,022,000
Assets on deposit with regulatory authorities		599,829,000	882,400,000
Assets on deposit with regulatory authorities		151,467,000	177,263,000
Funds at Lloyd's		234,833,000	220,328,000
Restricted assets, total		$ 4,105,021,000	$ 3,255,013,000
Number of syndicates | syndicate		3
Cash and investments		$ 234,800,000
FAL Facility | Loan facilities | Letters of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity				$ 165,000,000
Higher borrowing capacity option				$ 200,000,000
Subsequent event | FAL Facility | Loan facilities | Letters of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 325,000,000
Higher borrowing capacity option	$ 400,000,000

Funds Held - Directly Managed -

Funds Held - Directly Managed - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jan. 11, 2017	Dec. 31, 2016
Net Investment Income [Line Items]
Funds held - directly managed	$ 1,179,940		$ 994,665
Trading securities, amortized cost	5,783,362
Trading, at fair value	5,876,284		4,611,160
Funds held – directly managed
Net Investment Income [Line Items]
Trading securities, amortized cost	1,159,800
Trading, at fair value	1,165,386		987,530
Allianz
Net Investment Income [Line Items]
Funds held - directly managed, carrying value	1,023,000		994,800
Funds held - directly managed, embedded derivative, fair value	4,700		(28,300)
Funds held - directly managed	$ 999,500		$ 994,700
QBE
Net Investment Income [Line Items]
Funds held - directly managed, carrying value		$ 176,200

Funds Held - Directly Managed81

Funds Held - Directly Managed - Carrying Values of Assets and Liabilities Underlying Funds Held - Directly Managed (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	$ 5,876,284	$ 4,611,160
Funds held - directly managed	1,179,940	994,665
U.S. government and agency
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	554,036	840,274
Non-U.S. government
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	607,132	267,363
Corporate
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	3,363,060	2,387,322
Municipal
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	100,221	47,181
Residential mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	288,713	373,528
Commercial mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	421,548	217,212
Asset-backed
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	541,574	478,280
Funds held – directly managed
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	1,165,386	987,530
Funds held - directly managed, other assets	14,554	7,135
Funds held – directly managed | U.S. government and agency
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	69,850	47,885
Funds held – directly managed | Non-U.S. government
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	2,926	5,961
Funds held – directly managed | Corporate
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	695,490	663,556
Funds held – directly managed | Municipal
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	58,930	38,927
Funds held – directly managed | Residential mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	29,439	0
Funds held – directly managed | Commercial mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	211,186	151,395
Funds held – directly managed | Asset-backed
Schedule of Funds Held, Directly Managed [Line Items]
Trading securities, debt	$ 97,565	$ 79,806

Funds Held - Directly Managed82

Funds Held - Directly Managed - Contractual Maturities of Fixed Maturity Investments Underlying Funds Held - Directly Managed (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost
One year or less	$ 398,054
More than one year through two years	340,531
More than two years through five years	1,283,898
More than five years through ten years	1,235,079
More than ten years	1,278,126
Trading securities, amortized cost	5,783,362
Fair Value
One year or less	398,083
More than one year through two years	341,753
More than two years through five years	1,286,527
More than five years through ten years	1,249,887
More than ten years	1,348,199
Trading securities, debt	$ 5,876,284	$ 4,611,160
% of Total Fair Value
One year or less	6.80%
More than one year through two years	5.80%
More than two years through five years	21.90%
More than five years through ten years	21.30%
More than ten years	22.90%
Trading securities, percentage of fair value	100.00%
Residential mortgage-backed
Amortized Cost
Securities without single maturity date	$ 285,312
Fair Value
Securities without single maturity date	288,713
Trading securities, debt	$ 288,713	373,528
% of Total Fair Value
Securities without single maturity date	4.90%
Commercial mortgage-backed
Amortized Cost
Securities without single maturity date	$ 427,469
Fair Value
Securities without single maturity date	421,548
Trading securities, debt	$ 421,548	217,212
% of Total Fair Value
Securities without single maturity date	7.20%
Asset-backed
Amortized Cost
Securities without single maturity date	$ 534,893
Fair Value
Securities without single maturity date	541,574
Trading securities, debt	$ 541,574	478,280
% of Total Fair Value
Securities without single maturity date	9.20%
Funds held – directly managed
Amortized Cost
One year or less	$ 49,093
More than one year through two years	54,447
More than two years through five years	230,872
More than five years through ten years	248,525
More than ten years	234,556
Trading securities, amortized cost	1,159,800
Fair Value
One year or less	49,007
More than one year through two years	54,204
More than two years through five years	230,256
More than five years through ten years	248,675
More than ten years	245,054
Trading securities, debt	$ 1,165,386	987,530
% of Total Fair Value
One year or less	4.20%
More than one year through two years	4.70%
More than two years through five years	19.80%
More than five years through ten years	21.30%
More than ten years	21.00%
Trading securities, percentage of fair value	100.00%
Funds held – directly managed | Residential mortgage-backed
Amortized Cost
Securities without single maturity date	$ 29,544
Trading securities, amortized cost	29,544
Fair Value
Securities without single maturity date	29,439
Trading securities, debt	$ 29,439	0
% of Total Fair Value
Securities without single maturity date	2.50%
Funds held – directly managed | Commercial mortgage-backed
Amortized Cost
Securities without single maturity date	$ 215,603
Trading securities, amortized cost	215,603
Fair Value
Securities without single maturity date	211,186
Trading securities, debt	$ 211,186	151,395
% of Total Fair Value
Securities without single maturity date	18.10%
Funds held – directly managed | Asset-backed
Amortized Cost
Securities without single maturity date	$ 97,160
Trading securities, amortized cost	97,160
Fair Value
Securities without single maturity date	97,565
Trading securities, debt	$ 97,565	$ 79,806
% of Total Fair Value
Securities without single maturity date	8.40%

Funds Held - Directly Managed83

Funds Held - Directly Managed - Funds Held - Directly Managed, by Credit Rating (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 5,783,362
Fair Value	5,982,887	$ 4,706,207
Funds held – directly managed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	1,159,800
Fair Value	1,165,386
Funds held – directly managed | U.S. government and agency
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	69,754
Fair Value	69,850
Funds held – directly managed | Non-U.S. government
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	2,977
Fair Value	2,926
Funds held – directly managed | Corporate
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	688,239
Fair Value	695,490
Funds held – directly managed | Municipal
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	56,523
Fair Value	58,930
Funds held – directly managed | Residential mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	29,544
Fair Value	$ 29,439
% of Total Investments	2.50%
Funds held – directly managed | Commercial mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 215,603
Fair Value	211,186
Funds held – directly managed | Asset-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	97,160
Fair Value	$ 97,565
Funds held – directly managed | Trading securities | Portfolio Concentration Risk Member
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	100.00%
Funds held – directly managed | Trading securities | Portfolio Concentration Risk Member | U.S. government and agency
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	6.00%
Funds held – directly managed | Trading securities | Portfolio Concentration Risk Member | Non-U.S. government
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	0.30%
Funds held – directly managed | Trading securities | Portfolio Concentration Risk Member | Corporate
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	59.60%
Funds held – directly managed | Trading securities | Portfolio Concentration Risk Member | Municipal
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	5.10%
Funds held – directly managed | Trading securities | Portfolio Concentration Risk Member | Commercial mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	18.10%
Funds held – directly managed | Trading securities | Portfolio Concentration Risk Member | Asset-backed
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	8.40%
Funds held – directly managed | AAA Rated | Investment Grade
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 403,500
Funds held – directly managed | AAA Rated | Investment Grade | U.S. government and agency
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	69,850
Funds held – directly managed | AAA Rated | Investment Grade | Non-U.S. government
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | AAA Rated | Investment Grade | Corporate
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	7,754
Funds held – directly managed | AAA Rated | Investment Grade | Municipal
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | AAA Rated | Investment Grade | Residential mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	29,439
Funds held – directly managed | AAA Rated | Investment Grade | Commercial mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	202,608
Funds held – directly managed | AAA Rated | Investment Grade | Asset-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 93,849
Funds held – directly managed | AAA Rated | Trading securities | Investment Grade | Credit Rating Concentration Risk
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	34.60%
Funds held – directly managed | AA Rated | Investment Grade
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 56,631
Funds held – directly managed | AA Rated | Investment Grade | U.S. government and agency
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | AA Rated | Investment Grade | Non-U.S. government
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | AA Rated | Investment Grade | Corporate
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	25,418
Funds held – directly managed | AA Rated | Investment Grade | Municipal
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	20,921
Funds held – directly managed | AA Rated | Investment Grade | Residential mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | AA Rated | Investment Grade | Commercial mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	6,576
Funds held – directly managed | AA Rated | Investment Grade | Asset-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 3,716
Funds held – directly managed | AA Rated | Trading securities | Investment Grade | Credit Rating Concentration Risk
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	4.90%
Funds held – directly managed | A Rated | Investment Grade
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 350,762
Funds held – directly managed | A Rated | Investment Grade | U.S. government and agency
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | A Rated | Investment Grade | Non-U.S. government
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	2,926
Funds held – directly managed | A Rated | Investment Grade | Corporate
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	315,385
Funds held – directly managed | A Rated | Investment Grade | Municipal
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	30,449
Funds held – directly managed | A Rated | Investment Grade | Residential mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | A Rated | Investment Grade | Commercial mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	2,002
Funds held – directly managed | A Rated | Investment Grade | Asset-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 0
Funds held – directly managed | A Rated | Trading securities | Investment Grade | Credit Rating Concentration Risk
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	30.10%
Funds held – directly managed | BBB Rated | Investment Grade
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 354,493
Funds held – directly managed | BBB Rated | Investment Grade | U.S. government and agency
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | BBB Rated | Investment Grade | Non-U.S. government
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | BBB Rated | Investment Grade | Corporate
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	346,933
Funds held – directly managed | BBB Rated | Investment Grade | Municipal
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	7,560
Funds held – directly managed | BBB Rated | Investment Grade | Residential mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | BBB Rated | Investment Grade | Commercial mortgage-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	0
Funds held – directly managed | BBB Rated | Investment Grade | Asset-backed
Schedule of Funds Held, Directly Managed [Line Items]
Amortized Cost	$ 0
Funds held – directly managed | BBB Rated | Trading securities | Investment Grade | Credit Rating Concentration Risk
Schedule of Funds Held, Directly Managed [Line Items]
% of Total Investments	30.40%

Funds Held - Directly Managed84

Funds Held - Directly Managed - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Investment Income [Line Items]
Gross investment income									$ 219,823	$ 193,308	$ 131,902
Investment expenses									$ (11,034)	(7,845)	(9,338)
Funds Held, Directly Managed, Investment Income [Table Text Block]									Major categories of net investment income underlying the funds held - directly managed account for the year ended December 31, 2017 and 2016 are summarized as follows: 2017 2016 Fixed maturity investments $ 33,558 $ 5,705 Short-term investments and cash and cash equivalents 292 64 Gross investment income 33,850 5,769 Investment expenses (1,371 ) — Investment income on funds held - directly managed $ 32,479 $ 5,769
Investment income on funds held - directly managed	$ 58,605	$ 52,028	$ 49,417	$ 48,739	$ 42,229	$ 48,022	$ 44,932	$ 50,280	$ 208,789	185,463	122,564
Funds held – directly managed
Net Investment Income [Line Items]
Gross investment income									33,850	5,769	0
Investment expenses									$ (1,371)	0
Funds Held, Directly Managed, Investment Income [Table Text Block]									32,479,000
Investment income on funds held - directly managed										5,769
Fixed maturities
Net Investment Income [Line Items]
Gross investment income									$ 144,367	114,885	87,512
Short-term investments and cash and cash equivalents
Net Investment Income [Line Items]
Gross investment income									9,314	4,491	$ 5,993
Short-term investments and cash and cash equivalents | Funds held – directly managed
Net Investment Income [Line Items]
Gross investment income									292	64
Fixed maturities | Funds held – directly managed
Net Investment Income [Line Items]
Gross investment income									$ 33,558	$ 5,705

Funds Held - Directly Managed85

Funds Held - Directly Managed - Net Realized and Unrealized Investment (Losses) Gains (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Net realized gains (losses) and change in fair value of funds held- directly managed	$ 50,637	$ 29,301	$ 51,877	$ 58,519	$ (61,570)	$ 66,608	$ 34,503	$ 38,277	$ 190,334	$ 77,818	$ (41,523)
Funds held – directly managed
Gain (Loss) on Investments [Line Items]
Net realized losses on fixed maturity securities									(4,219)	(14,616)	0
Change in fair value of embedded derivative									32,928	(28,317)	0
Change in value of fair value option on funds held- directly managed									974	0	$ 0
Net realized gains (losses) and change in fair value of funds held- directly managed									$ 29,683	$ (42,933)

Fair Value Measurements - Categ

Fair Value Measurements - Categorized Investments and Assets Carried at Cost or Amortized Cost and Fair Value Among Levels (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	$ 7,106,564	$ 5,911,021
Fair Value Based on NAV as Practical Expedient	532,697	502,731
Other investments, at fair value	913,392	937,047
Trading securities, debt	5,876,284	4,611,160
Funds held - directly managed	1,179,940	994,665
Reinsurance recoverable	(131,983)
Losses and LAE	1,794,669	0
Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	5,696,073	4,388,242
Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	532,697	502,731
Other investments, at fair value	913,392	937,047
Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	1,165,386	987,530
Funds held - directly managed, other assets	14,554	7,135
U.S. government and agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	554,036	840,274
U.S. government and agency | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	69,850	47,885
Non-U.S. government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	607,132	267,363
Non-U.S. government | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	2,926	5,961
Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	3,363,060	2,387,322
Corporate | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	695,490	663,556
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	100,221	47,181
Municipal | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	58,930	38,927
Residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	288,713	373,528
Residential mortgage-backed | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	29,439	0
Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	421,548	217,212
Commercial mortgage-backed | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	211,186	151,395
Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	541,574	478,280
Asset-backed | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	97,565	79,806
Private equities and private equity funds | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	289,556	285,529
Other investments, at fair value	289,556	300,529
Fixed income funds | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	27,429	25,387
Other investments, at fair value	229,999	249,023
Fixed income hedge funds | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	63,773	85,976
Other investments, at fair value	63,773	85,976
Equity funds | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	128,429	89,769
Other investments, at fair value	249,475	223,571
CLO equities | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	0	0
Other investments, at fair value	56,765	61,565
CLO equity funds | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	12,840	15,440
Other investments, at fair value	12,840	15,440
Private credit funds | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	10,156
Other investments, at fair value	10,156
Other | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Based on NAV as Practical Expedient	514	630
Other investments, at fair value	828	943
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed, other assets		7,135
Funds held - directly managed	1,179,940	994,665
Reinsurance recoverable	542,224
Losses and LAE	1,794,669
Recurring | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	6,086,569	4,878,927
Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	106,603	95,047
Recurring | Equity securities | US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	106,363	95,047
Recurring | Equity securities | International
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	240
Recurring | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed, other assets	14,554
Recurring | Other Assets
Other Assets:
Derivative Instruments	319	2,930
Recurring | Other Liabilities
Other Liabilities:
Derivative Instruments	7,246	74
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	103,652	91,287
Funds held - directly managed, other assets		0
Funds held - directly managed	0	0
Reinsurance recoverable	0
Losses and LAE	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	103,652	91,287
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities | US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	103,652	91,287
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities | International
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed, other assets	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Assets
Other Assets:
Derivative Instruments	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Liabilities
Other Liabilities:
Derivative Instruments	0	0
Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	6,293,492	5,138,686
Funds held - directly managed, other assets		7,135
Funds held - directly managed	1,179,940	994,665
Reinsurance recoverable	0
Losses and LAE	0
Recurring | Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	5,966,925	4,777,488
Recurring | Significant Other Observable Inputs (Level 2) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	2,951	3,760
Recurring | Significant Other Observable Inputs (Level 2) | Equity securities | US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	2,711	3,760
Recurring | Significant Other Observable Inputs (Level 2) | Equity securities | International
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	240
Recurring | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	323,616	357,438
Recurring | Significant Other Observable Inputs (Level 2) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed, other assets	14,554
Recurring | Significant Other Observable Inputs (Level 2) | Other Assets
Other Assets:
Derivative Instruments	319	2,930
Recurring | Significant Other Observable Inputs (Level 2) | Other Liabilities
Other Liabilities:
Derivative Instruments	7,246	74
Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	176,723	178,317
Funds held - directly managed, other assets		0
Funds held - directly managed	0	0
Reinsurance recoverable	542,224
Losses and LAE	1,794,669
Recurring | Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	119,644	101,439
Recurring | Significant Unobservable Inputs (Level 3) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Equity securities | US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Equity securities | International
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0
Recurring | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	57,079	76,878
Recurring | Significant Unobservable Inputs (Level 3) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed, other assets	0
Recurring | Significant Unobservable Inputs (Level 3) | Other Assets
Other Assets:
Derivative Instruments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Other Liabilities
Other Liabilities:
Derivative Instruments	0	0
Recurring | U.S. government and agency | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	558,223	852,984
Recurring | U.S. government and agency | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	69,850	47,885
Recurring | U.S. government and agency | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | U.S. government and agency | Quoted Prices in Active Markets for Identical Assets (Level 1) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | U.S. government and agency | Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	558,223	852,984
Recurring | U.S. government and agency | Significant Other Observable Inputs (Level 2) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	69,850	47,885
Recurring | U.S. government and agency | Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | U.S. government and agency | Significant Unobservable Inputs (Level 3) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Non-U.S. government | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	692,569	352,786
Recurring | Non-U.S. government | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	2,926	5,961
Recurring | Non-U.S. government | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Non-U.S. government | Quoted Prices in Active Markets for Identical Assets (Level 1) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Non-U.S. government | Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	692,569	352,786
Recurring | Non-U.S. government | Significant Other Observable Inputs (Level 2) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	2,926	5,961
Recurring | Non-U.S. government | Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Non-U.S. government | Significant Unobservable Inputs (Level 3) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Corporate | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	3,478,181	2,545,978
Recurring | Corporate | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	695,490	663,556
Recurring | Corporate | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Corporate | Quoted Prices in Active Markets for Identical Assets (Level 1) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Corporate | Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	3,411,003	2,471,444
Recurring | Corporate | Significant Other Observable Inputs (Level 2) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	695,490	663,556
Recurring | Corporate | Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	67,178	74,534
Recurring | Corporate | Significant Unobservable Inputs (Level 3) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Municipal | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	105,357	53,757
Recurring | Municipal | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	58,930	38,927
Recurring | Municipal | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Municipal | Quoted Prices in Active Markets for Identical Assets (Level 1) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Municipal | Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	105,357	53,757
Recurring | Municipal | Significant Other Observable Inputs (Level 2) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	58,930	38,927
Recurring | Municipal | Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Municipal | Significant Unobservable Inputs (Level 3) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Residential mortgage-backed | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	288,744	374,055
Recurring | Residential mortgage-backed | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	29,439
Recurring | Residential mortgage-backed | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Residential mortgage-backed | Quoted Prices in Active Markets for Identical Assets (Level 1) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0
Recurring | Residential mortgage-backed | Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	285,664	374,055
Recurring | Residential mortgage-backed | Significant Other Observable Inputs (Level 2) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	29,439
Recurring | Residential mortgage-backed | Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	3,080	0
Recurring | Residential mortgage-backed | Significant Unobservable Inputs (Level 3) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0
Recurring | Commercial mortgage-backed | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	421,548	217,212
Recurring | Commercial mortgage-backed | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	211,186	151,395
Recurring | Commercial mortgage-backed | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Commercial mortgage-backed | Quoted Prices in Active Markets for Identical Assets (Level 1) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Commercial mortgage-backed | Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	400,054	204,999
Recurring | Commercial mortgage-backed | Significant Other Observable Inputs (Level 2) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	211,186	151,395
Recurring | Commercial mortgage-backed | Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	21,494	12,213
Recurring | Commercial mortgage-backed | Significant Unobservable Inputs (Level 3) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Asset-backed | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	541,947	482,155
Recurring | Asset-backed | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	97,565	79,806
Recurring | Asset-backed | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	0	0
Recurring | Asset-backed | Quoted Prices in Active Markets for Identical Assets (Level 1) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Asset-backed | Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	514,055	467,463
Recurring | Asset-backed | Significant Other Observable Inputs (Level 2) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	97,565	79,806
Recurring | Asset-backed | Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments	27,892	14,692
Recurring | Asset-backed | Significant Unobservable Inputs (Level 3) | Funds held – directly managed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, debt	0	0
Recurring | Private equities and private equity funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Private equities and private equity funds | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Private equities and private equity funds | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	15,000
Recurring | Fixed income funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Fixed income funds | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	202,570	223,636
Recurring | Fixed income funds | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Fixed income hedge funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Fixed income hedge funds | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Fixed income hedge funds | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Equity funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Equity funds | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	121,046	133,802
Recurring | Equity funds | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | CLO equities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | CLO equities | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | CLO equities | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	56,765	61,565
Recurring | CLO equity funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | CLO equity funds | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | CLO equity funds | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Private credit funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0
Recurring | Private credit funds | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0
Recurring | Private credit funds | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0
Recurring | Other | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Other | Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Recurring | Other | Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	$ 314	$ 313

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation for Investments Measured At Fair Value on Recurring Basis Level 3 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	$ 178,317	$ 224,160
Purchases	61,073	65,437
Sales	(71,547)	(65,774)
Total realized and unrealized gains (losses)	(7,880)	2,688
Transfer into Level 3 from Level 2	102,564	122,321
Transfer out of Level 3 into Level 2	(85,804)	(170,515)
Ending fair value	176,723	178,317
Corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	74,534	0
Purchases	28,872	24,586
Sales	(37,941)	(11,011)
Total realized and unrealized gains (losses)	249	(841)
Transfer into Level 3 from Level 2	24,431	64,134
Transfer out of Level 3 into Level 2	(22,967)	(2,334)
Ending fair value	67,178	74,534
Residential mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	0	0
Purchases	711	0
Sales	(37)	(2,178)
Total realized and unrealized gains (losses)	(16)	(24)
Transfer into Level 3 from Level 2	3,085	2,781
Transfer out of Level 3 into Level 2	(663)	(579)
Ending fair value	3,080	0
Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	12,213	26,704
Purchases	21,306	14,216
Sales	(424)	(14,071)
Total realized and unrealized gains (losses)	(434)	(460)
Transfer into Level 3 from Level 2	18,974	23,628
Transfer out of Level 3 into Level 2	(30,141)	(37,804)
Ending fair value	21,494	12,213
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	14,692	120,440
Purchases	9,749	19,750
Sales	(20,795)	(25,581)
Total realized and unrealized gains (losses)	205	(1,897)
Transfer into Level 3 from Level 2	56,074	31,778
Transfer out of Level 3 into Level 2	(32,033)	(129,798)
Ending fair value	27,892	14,692
Other Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	76,878	77,016
Purchases	435	6,885
Sales	(12,350)	(12,933)
Total realized and unrealized gains (losses)	(7,884)	5,910
Transfer into Level 3 from Level 2	0	0
Transfer out of Level 3 into Level 2	0	0
Ending fair value	$ 57,079	$ 76,878

Fair Value Measurements - Asset

Fair Value Measurements - Assets Carried at Cost or Amortized Cost (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value | Life Settlement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Life settlements	$ 131.9	$ 129.5

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Measurements - Insurance Contracts - Fair Value Option (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reinsurance balances recoverable
Beginning fair value	$ 178,317	$ 224,160
Assumed business	61,073	65,437
Changes in fair value:
Ending fair value	176,723	178,317
Reinsurance balances recoverable
Reinsurance balances recoverable
Beginning fair value	0
Assumed business	565,824
Changes in nominal amounts:
Net incurred losses and LAE	(1,848)
Paid losses	(56,256)
Changes in fair value:
Discounted cash flows	29,785
Risk margin	(6,034)
Effect of exchange rate movements	10,753
Ending fair value	542,224	0
Losses And Loss Adjustment Expense Liabilities [Member]
Liability for losses and LAE
Beginning fair value	0
Assumed business	1,966,843
Changes in nominal amounts:
Net incurred losses and LAE	(122,797)
Paid losses	(197,102)
Changes in fair value:
Discounted cash flows	78,046
Risk margin	(24,039)
Effect of exchange rate movements	93,718
Ending fair value	$ 1,794,669	$ 0

Fair Value Measurements Fair 90

Fair Value Measurements Fair Value Measurements - Quantitative Information (Details) - Internal Model - Recurring	12 Months Ended
	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit spread for non-performance risk (U)	0.20%
Risk cost of capital	5.00%
Weighted average cost of capital (U)	8.50%
Losses and LAE liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, duration	11 years 4 months 29 days
Reinsurance balances recoverable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs, duration	11 years 7 months 29 days

Fair Value Measurements Fair 91

Fair Value Measurements Fair Value Measurements - Fair Values for Financial Instruments Carried At Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Mar. 10, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments, at cost	$ 125,621		$ 131,651
Carrying value of debt	646,689		673,603
Life Settlement | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments, at cost	125,600		131,700
Life Settlement | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life settlements	$ 131,900		129,500
Senior Notes | Senior Notes Due 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate	4.50%	4.50%
Carrying value of debt	$ 347,516		$ 0
Fair value of debt	$ 357,400

Derivative Instruments (Details

Derivative Instruments (Details) € in Millions	Dec. 29, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017EUR (€)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017EUR (€)	Dec. 31, 2016EUR (€)
Derivative [Line Items]
Repayment of loans		$ 912,140,000		$ 493,250,000	$ 377,500,000
Realized gain				5,400,000
Net Investment Hedging
Derivative [Line Items]
Gross Notional Amount		60,100,000		88,500,000		€ 50	€ 75
Repayment of loans		29,500,000	€ 25
Foreign exchange losses		(1,100,000)
Foreign Exchange Forward
Derivative [Line Items]
Cumulative losses reclassified into earnings	$ 1,100,000
Designated as Hedging Instrument | Foreign Exchange Forward
Derivative [Line Items]
Gross Notional Amount		59,951,000		82,642,000
Assets		11,000		2,930,000
Liabilities		1,477,000		74,000
Amount of Gains Deferred in AOCI (Effective Portion)		(1,247,000)		3,754,000
Designated as Hedging Instrument | Foreign Exchange Forward | Australia, Dollars
Derivative [Line Items]
Gross Notional Amount		32,810,000		45,467,000
Assets		0		2,753,000
Liabilities		965,000		74,000
Amount of Gains Deferred in AOCI (Effective Portion)		(1,247,000)		2,568,000
Designated as Hedging Instrument | Foreign Exchange Forward | Canada, Dollars
Derivative [Line Items]
Gross Notional Amount		27,141,000		37,175,000
Assets		11,000		177,000
Liabilities		512,000		0
Amount of Gains Deferred in AOCI (Effective Portion)		0		1,186,000
Not Designated as Hedging Instrument | Foreign Exchange Forward
Derivative [Line Items]
Gross Notional Amount		283,586,000
Assets		308,000
Liabilities		5,769,000
Losses on non-qualifying hedges charged to earnings		(8,340,000)
Not Designated as Hedging Instrument | Foreign Exchange Forward | Australia, Dollars
Derivative [Line Items]
Gross Notional Amount		57,028,000
Assets		0
Liabilities		1,002,000
Losses on non-qualifying hedges charged to earnings		(1,002,000)
Not Designated as Hedging Instrument | Foreign Exchange Forward | United Kingdom, Pounds
Derivative [Line Items]
Gross Notional Amount		207,323,000
Assets		262,000
Liabilities		4,312,000
Losses on non-qualifying hedges charged to earnings		(6,367,000)
Not Designated as Hedging Instrument | Foreign Exchange Forward | Euro Member Countries, Euro
Derivative [Line Items]
Gross Notional Amount		19,235,000
Assets		46,000
Liabilities		455,000
Losses on non-qualifying hedges charged to earnings		(971,000)
Not Designated as Hedging Instrument | Equity Option
Derivative [Line Items]
Equities at cost		$ 0		$ 5,500,000

Reinsurance Balances Recovera93

Reinsurance Balances Recoverable - Summary of Reinsurance Reserves Recoverable (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effects of Reinsurance [Line Items]
Outstanding losses	$ 1,151,422	$ 810,394
IBNR	864,250	593,562
Fair value adjustments	(13,640)	(15,573)
Fair value adjustments - fair value option	(131,983)
Total reinsurance reserves recoverable	1,870,049	1,388,383
Paid losses recoverable	150,981	72,360
Net	2,021,030	1,460,743
Reinsurance balances recoverable	1,478,806	1,460,743
Reinsurance balances recoverable - fair value option	542,224	0
Non-life Run-off
Effects of Reinsurance [Line Items]
Outstanding losses	932,284	621,288
IBNR	590,154	393,550
Fair value adjustments	(12,970)	(13,885)
Fair value adjustments - fair value option	(131,983)
Total reinsurance reserves recoverable	1,377,485	1,000,953	$ 1,034,747	$ 800,709
Paid losses recoverable	128,253	47,160
Net	1,505,738	1,048,113
Reinsurance balances recoverable	963,514
Reinsurance balances recoverable - fair value option	542,224
Atrium
Effects of Reinsurance [Line Items]
Outstanding losses	7,472	6,438
IBNR	31,476	21,753
Fair value adjustments	1,583	1,818
Fair value adjustments - fair value option	0
Total reinsurance reserves recoverable	40,531	30,009	25,852	28,278
Paid losses recoverable	(451)	(1,081)
Net	40,080	28,928
Reinsurance balances recoverable	40,080
Reinsurance balances recoverable - fair value option	0
StarStone
Effects of Reinsurance [Line Items]
Outstanding losses	211,650	182,478
IBNR	242,620	178,259
Fair value adjustments	(2,253)	(3,506)
Fair value adjustments - fair value option	0
Total reinsurance reserves recoverable	452,017	357,231	$ 299,783	$ 325,209
Paid losses recoverable	23,179	25,512
Net	475,196	382,743
Reinsurance balances recoverable	475,196
Reinsurance balances recoverable - fair value option	0
Other
Effects of Reinsurance [Line Items]
Outstanding losses	16	190
IBNR	0	0
Fair value adjustments	0	0
Fair value adjustments - fair value option	0
Total reinsurance reserves recoverable	16	190
Paid losses recoverable	0	769
Net	16	$ 959
Reinsurance balances recoverable	16
Reinsurance balances recoverable - fair value option	$ 0

Reinsurance Balances Recovera94

Reinsurance Balances Recoverable - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)reinsurer	Dec. 31, 2016USD ($)reinsurer	Dec. 31, 2015USD ($)
Effects of Reinsurance [Line Items]
Reinsurance balances recoverable	$ 2,021,030	$ 1,460,743
Increase (decrease) in reinsurance recoverable	$ 530,857	$ 21,866	$ (391,182)
Reinsurer concentration risk
Effects of Reinsurance [Line Items]
Number of external reinsurers | reinsurer		10
Reinsurer concentration risk | Top Ten Reinsurers, Rated A Minus Or Higher
Effects of Reinsurance [Line Items]
Number of external reinsurers | reinsurer	6	6
Reinsurer concentration risk | Top Ten Reinsurers, Four Non-Rated Reinsurers
Effects of Reinsurance [Line Items]
Number of external reinsurers | reinsurer	4	4
Reinsurer concentration risk | Three non-rated reinsurers
Effects of Reinsurance [Line Items]
Reinsurance balances recoverable	$ 687,600	$ 512,200
Reinsurer concentration risk | Top Ten Reinsurers, Kayla Re
Effects of Reinsurance [Line Items]
Reinsurance balances recoverable	357,400	242,100
Reinsurer concentration risk | Reinsurance balances recoverable
Effects of Reinsurance [Line Items]
Reinsurance balances recoverable	$ 2,021,030	$ 1,460,743
Gross premiums written (percent)	100.00%	100.00%
Reinsurer concentration risk | Reinsurance balances recoverable | Two Reinsurers Accounting for More than 10% of Total Reinsurance Balances Receivable
Effects of Reinsurance [Line Items]
Gross premiums written (percent)	10.00%
Non-Life Run-Off
Effects of Reinsurance [Line Items]
Increase (decrease) in reinsurance recoverable	$ 560,300
Equity method investee | Reinsurer concentration risk | Hannover Ruck SE [Member]
Effects of Reinsurance [Line Items]
Reinsurance balances recoverable	$ 320,000	$ 67,300

Reinsurance Balances Recovera95

Reinsurance Balances Recoverable - Reinsurance Balances Recoverable by Reinsurer (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	$ 2,021,030	$ 1,460,743
Reinsurance balances recoverable | Reinsurer concentration risk
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	$ 2,021,030	$ 1,460,743
% of Total	100.00%	100.00%
Reinsurance balances recoverable | Reinsurer concentration risk | Top Ten Reinsurers
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	$ 1,516,736	$ 986,602
% of Total	75.00%	67.60%
Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Greater Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	$ 483,689	$ 459,024
% of Total	24.00%	31.40%
Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Less Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	$ 20,605	$ 15,117
% of Total	1.00%	1.00%
Non-life Run-off
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	$ 1,505,738	$ 1,048,113
Non-life Run-off | Reinsurance balances recoverable | Reinsurer concentration risk
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	1,505,738	1,048,113
Non-life Run-off | Reinsurance balances recoverable | Reinsurer concentration risk | Top Ten Reinsurers
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	1,166,057	737,074
Non-life Run-off | Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Greater Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	322,722	301,856
Non-life Run-off | Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Less Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	16,959	9,183
Atrium
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	40,080	28,928
Atrium | Reinsurance balances recoverable | Reinsurer concentration risk
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	40,080	28,928
Atrium | Reinsurance balances recoverable | Reinsurer concentration risk | Top Ten Reinsurers
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	22,422	23,245
Atrium | Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Greater Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	16,631	4,827
Atrium | Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Less Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	1,027	856
StarStone
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	475,196	382,743
StarStone | Reinsurance balances recoverable | Reinsurer concentration risk
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	475,196	382,743
StarStone | Reinsurance balances recoverable | Reinsurer concentration risk | Top Ten Reinsurers
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	328,257	226,283
StarStone | Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Greater Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	144,336	152,341
StarStone | Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Less Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	2,603	4,119
Other
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	16	959
Other | Reinsurance balances recoverable | Reinsurer concentration risk
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	16	959
Other | Reinsurance balances recoverable | Reinsurer concentration risk | Top Ten Reinsurers
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	0	0
Other | Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Greater Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	0	0
Other | Reinsurance balances recoverable | Reinsurer concentration risk | Other Reinsurers' Balances Less Than $1 Million
Ceded Credit Risk [Line Items]
Reinsurance balances recoverable	$ 16	$ 959

Reinsurance Balances Recovera96

Reinsurance Balances Recoverable - Summary of Provisions for Uncollectible Reinsurance Balances Recoverable by Rating of Reinsurer (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Effects of Reinsurance [Line Items]
Gross	$ 2,186,243	$ 1,635,259
Provisions for Bad Debt	165,213	174,516
Net	$ 2,021,030	$ 1,460,743
Provisions as a % of Gross	7.60%	10.70%
Reinsurers rated A- or above
Effects of Reinsurance [Line Items]
Gross	$ 1,252,887	$ 892,776
Provisions for Bad Debt	51,115	35,184
Net	$ 1,201,772	$ 857,592
Provisions as a % of Gross	4.10%	3.90%
Secured | Reinsurers Rated Below A-
Effects of Reinsurance [Line Items]
Gross	$ 771,097	$ 544,894
Provisions for Bad Debt	0	0
Net	$ 771,097	$ 544,894
Provisions as a % of Gross	0.00%	0.00%
Unsecured | Reinsurers Rated Below A-
Effects of Reinsurance [Line Items]
Gross	$ 162,259	$ 197,589
Provisions for Bad Debt	114,098	139,332
Net	$ 48,161	$ 58,257
Provisions as a % of Gross	70.30%	70.50%

Losses and Loss Adjustment Ex97

Losses and Loss Adjustment Expenses - Total Losses and Loss Adjustment Expense Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense [Line Items]
Outstanding losses	$ 3,855,043	$ 3,267,230
IBNR	3,653,656	2,607,082
Fair value adjustments	(117,006)	(123,728)
Fair value adjustments - fair value option	(314,748)	0
ULAE	321,143	237,283
Total gross liability for unpaid losses and LAE	7,398,088	5,987,867	$ 5,720,149	$ 4,509,421
Losses and loss adjustment expenses	5,603,419	5,987,867
Losses and loss adjustment expenses, fair value	1,794,669	0
Non-life Run-off
Liability for Claims and Claims Adjustment Expense [Line Items]
Outstanding losses	3,185,703	2,697,736
IBNR	2,903,927	1,935,659
Fair value adjustments	(125,998)	(135,368)
Fair value adjustments - fair value option	(314,748)	0
ULAE	300,588	218,336
Total gross liability for unpaid losses and LAE	5,949,472	4,716,363	4,585,454	3,435,010
Atrium
Liability for Claims and Claims Adjustment Expense [Line Items]
Outstanding losses	78,363	67,379
IBNR	150,508	130,118
Fair value adjustments	9,547	12,503
Fair value adjustments - fair value option	0	0
ULAE	2,455	2,122
Total gross liability for unpaid losses and LAE	240,873	212,122	201,017	212,611
StarStone
Liability for Claims and Claims Adjustment Expense [Line Items]
Outstanding losses	590,977	502,115
IBNR	599,221	541,305
Fair value adjustments	(555)	(863)
Fair value adjustments - fair value option	0	0
ULAE	18,100	16,825
Total gross liability for unpaid losses and LAE	$ 1,207,743	$ 1,059,382	$ 933,678	$ 861,800

Losses and Loss Adjustment Ex98

Losses and Loss Adjustment Expenses - Reconciliation of Beginning and Ending Reserves for Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1				$ 5,987,867				$ 5,720,149	$ 5,987,867	$ 5,720,149	$ 4,509,421
Less: reinsurance reserves recoverable				1,388,383					1,388,383
Less: deferred charges on retroactive reinsurance				94,551				255,911	94,551	255,911	0
Net balance as at January 1				4,505,123				4,103,856	4,505,123	4,103,856	3,355,225
Net incurred losses and LAE:
Current period									437,853	493,016	476,364
Prior periods									(244,302)	(318,917)	(372,031)
Total net incurred losses and LAE	$ 30,327	$ 75,712	$ 9,620	77,892	$ 1,321	$ (6,902)	$ 96,462	83,218	193,551	174,099	104,333
Net paid losses:
Current period									(82,273)	79,579	(99,933)
Prior periods									862,921	753,478	681,956
Total net paid losses									(945,194)	(833,057)	(781,889)
Effect of exchange rate movement									158,429	46,903	65,069
Acquired on purchase of subsidiaries									10,251	10,019	878,815
Assumed business									1,525,703	1,340,444	612,441
Ceded business									0	243,335	0
Net balance as at December 31	5,447,863				4,505,123				5,447,863	4,505,123	4,103,856
Plus: reinsurance reserves recoverable	1,870,049				1,388,383				1,870,049	1,388,383
Plus: deferred charges on retroactive reinsurance	80,192				94,551				80,192	94,551	255,911
Balance as at December 31	7,398,088				5,987,867				7,398,088	5,987,867	5,720,149
Non-Life Run-off Segment, Atrium Segment, and Starstone Segment
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less: reinsurance reserves recoverable				1,388,193				1,360,382	1,388,193	1,360,382	1,154,196
Net paid losses:
Plus: reinsurance reserves recoverable	1,870,033				1,388,193				1,870,033	1,388,193	1,360,382
Non-life Run-off
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1				4,716,363				4,585,454	4,716,363	4,585,454	3,435,010
Less: reinsurance reserves recoverable				1,000,953				1,034,747	1,000,953	1,034,747	800,709
Less: deferred charges on retroactive reinsurance				94,551				255,911	94,551	255,911	0
Net balance as at January 1				3,620,859				3,294,796	3,620,859	3,294,796	2,634,301
Net incurred losses and LAE:
Current period									5,866	5,829	39,924
Prior periods									(196,540)	(291,710)	(310,754)
Total net incurred losses and LAE									(190,674)	(285,881)	(270,830)
Net paid losses:
Current period									(2,835)	(3,869)	(16,049)
Prior periods									(578,888)	(529,937)	(501,246)
Total net paid losses									(581,723)	(533,806)	(517,295)
Effect of exchange rate movement									138,772	(27,478)	(42,636)
Acquired on purchase of subsidiaries									10,251	10,019	878,815
Assumed business									1,494,310	1,340,444	612,441
Ceded business									0	(177,235)	0
Net balance as at December 31	4,491,795				3,620,859				4,491,795	3,620,859	3,294,796
Plus: reinsurance reserves recoverable	1,377,485				1,000,953				1,377,485	1,000,953	1,034,747
Plus: deferred charges on retroactive reinsurance	80,192				94,551				80,192	94,551	255,911
Balance as at December 31	5,949,472				4,716,363				5,949,472	4,716,363	4,585,454
Total liability excluding unallocated loss adjustment expenses	6,089,630				4,633,395				6,089,630	4,633,395
Atrium
Liability for Claims and Claims Adjustment Expense [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	188,790								188,790
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	40,081								40,081
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1				212,122				201,017	212,122	201,017	212,611
Less: reinsurance reserves recoverable				30,009				25,852	30,009	25,852	28,278
Net balance as at January 1				182,113				175,165	182,113	175,165	184,333
Net incurred losses and LAE:
Current period									90,359	71,358	69,400
Prior periods									(20,940)	(12,971)	(21,921)
Total net incurred losses and LAE									69,419	58,387	47,479
Net paid losses:
Current period									(24,571)	(23,582)	(21,145)
Prior periods									(31,107)	(24,416)	(30,890)
Total net paid losses									(55,678)	(47,998)	(52,035)
Effect of exchange rate movement									4,488	(3,441)	(4,612)
Net balance as at December 31	200,342				182,113				200,342	182,113	175,165
Plus: reinsurance reserves recoverable	40,531				30,009				40,531	30,009	25,852
Balance as at December 31	240,873				212,122				240,873	212,122	201,017
Total liability excluding unallocated loss adjustment expenses	228,871				197,497				228,871	197,497
StarStone
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1				1,059,382				933,678	1,059,382	933,678	861,800
Less: reinsurance reserves recoverable				357,231				299,783	357,231	299,783	325,209
Net balance as at January 1				$ 702,151				$ 633,895	702,151	633,895	536,591
Net incurred losses and LAE:
Current period									341,628	415,829	367,040
Prior periods									(26,822)	(14,236)	(39,356)
Total net incurred losses and LAE									314,806	401,593	327,684
Net paid losses:
Current period									(54,867)	(52,128)	(62,739)
Prior periods									(252,926)	(199,125)	(149,820)
Total net paid losses									(307,793)	(251,253)	(212,559)
Effect of exchange rate movement									15,169	(15,984)	(17,821)
Acquired on purchase of subsidiaries									0	0	0
Assumed business									31,393	0	0
Ceded business									0	(66,100)	0
Net balance as at December 31	755,726				702,151				755,726	702,151	633,895
Plus: reinsurance reserves recoverable	452,017				357,231				452,017	357,231	299,783
Balance as at December 31	1,207,743				1,059,382				1,207,743	1,059,382	$ 933,678
Total liability excluding unallocated loss adjustment expenses	1,190,198				1,043,420				1,190,198	1,043,420
General casualty | Non-life Run-off
Liability for Claims and Claims Adjustment Expense [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	471,538								471,538
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	139,413								139,413
Net paid losses:
Total liability excluding unallocated loss adjustment expenses	610,951				745,823				610,951	745,823
General casualty | StarStone
Liability for Claims and Claims Adjustment Expense [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	286,589								286,589
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	135,400								135,400
Net paid losses:
Total liability excluding unallocated loss adjustment expenses	$ 421,989				$ 381,720				$ 421,989	$ 381,720

Losses and Loss Adjustment Ex99

Losses and Loss Adjustment Expenses - Net (Reduction) Increase in Ultimate Losses and Loss Adjustment Expense Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Prior Period
Net losses paid, prior period									$ (862,921)	$ (753,478)	$ (681,956)
Prior periods									(244,302)	(318,917)	(372,031)
Current Period
Net losses paid, current period									82,273	(79,579)	99,933
Net incurred losses and LAE, current period									437,853	493,016	476,364
Total
Net losses paid									945,194	833,057	781,889
Net change in case and LAE reserves									(341,030)	(535,884)	(278,825)
Net change in IBNR reserves									(406,588)	(258,041)	(324,026)
Amortization of deferred charges									14,359	168,827	15,265
Increase (reduction) in estimates of net ultimate losses									211,935	207,959	194,303
Increase (reduction) in provisions for bad debt									(1,377)	(13,822)	(25,271)
Increase (reduction) in provisions for unallocated LAE									(53,712)	(40,267)	(59,199)
Amortization of fair value adjustments									6,449	20,229	(5,500)
Total changes in fair value - fair value option									30,256
Total net incurred losses and LAE	$ 30,327	$ 75,712	$ 9,620	$ 77,892	$ 1,321	$ (6,902)	$ 96,462	$ 83,218	193,551	174,099	104,333
Non-life Run-off
Prior Period
Net losses paid, prior period									578,888	529,937	501,246
Net change in case and LAE reserves, prior period									(381,450)	(608,168)	(366,262)
Net change in IBNR reserves, prior period									(393,100)	(349,726)	(377,722)	$ 262,400
Amortization of deferred charges, prior period									14,359	168,827	15,265
Increase (reduction) in estimates of net ultimate losses, prior period									(181,303)	(259,130)	(227,473)
Increase (reduction) in provisions for bad debt, prior period									(1,536)	(13,822)	(25,271)
Increase (reduction) in provisions for unallocated LAE, prior period									(54,071)	(44,190)	(62,653)
Amortization of fair value adjustments, prior period									10,114	25,432	4,643
Changes in fair value - fair value option, prior period									30,256	0	0
Prior periods									(196,540)	(291,710)	(310,754)
Current Period
Net losses paid, current period									2,835	3,869	16,049
Net change in case and LAE reserves, current period									397	(617)	10,927
Net change in IBNR reserves, current period									2,373	2,342	12,948
Amortization of deferred charges, current period									0	0	0
Increase (reduction) in estimates of net ultimate losses, current period									5,605	5,594	39,924
Increase (reduction) in provisions for bad debt, current period									0	0	0
Increase (reduction) in provisions for unallocated LAE, current period									261	235	0
Amortization of fair value adjustments, current period									0	0	0
Changes in fair value - fair value option, current period									0	0	0
Net incurred losses and LAE, current period									5,866	5,829	39,924
Total
Net losses paid									581,723	533,806	517,295
Net change in case and LAE reserves									(381,053)	(608,785)	(355,335)
Net change in IBNR reserves									(390,727)	(347,384)	(364,774)
Amortization of deferred charges									14,359	168,827	15,265
Increase (reduction) in estimates of net ultimate losses									(175,698)	(253,536)	(187,549)
Increase (reduction) in provisions for bad debt									(1,536)	(13,822)	(25,271)
Increase (reduction) in provisions for unallocated LAE									(53,810)	(43,955)	(62,653)
Amortization of fair value adjustments									10,114	25,432	4,643
Total changes in fair value - fair value option									30,256	0	0
Total net incurred losses and LAE									(190,674)	(285,881)	(270,830)
Atrium
Prior Period
Net losses paid, prior period									31,107	24,416	30,890
Net change in case and LAE reserves, prior period									(13,324)	(13,115)	(18,213)
Net change in IBNR reserves, prior period									(35,650)	(20,543)	(27,382)
Increase (reduction) in estimates of net ultimate losses, prior period									(17,867)	(9,242)	(14,705)
Increase (reduction) in provisions for bad debt, prior period									89	0	0
Increase (reduction) in provisions for unallocated LAE, prior period									(442)	(421)	(608)
Amortization of fair value adjustments, prior period									(2,720)	(3,308)	(6,608)
Prior periods									(20,940)	(12,971)	(21,921)
Current Period
Net losses paid, current period									24,571	23,582	21,145
Net change in case and LAE reserves, current period									21,662	12,967	17,504
Net change in IBNR reserves, current period									43,329	34,243	30,226
Increase (reduction) in estimates of net ultimate losses, current period									89,562	70,792	68,875
Increase (reduction) in provisions for bad debt, current period									70	0	0
Increase (reduction) in provisions for unallocated LAE, current period									727	566	525
Amortization of fair value adjustments, current period									0	0	0
Net incurred losses and LAE, current period									90,359	71,358	69,400
Total
Net losses paid									55,678	47,998	52,035
Net change in case and LAE reserves									8,338	(148)	(709)
Net change in IBNR reserves									7,679	13,700	2,844
Amortization of deferred charges									0	0	0
Increase (reduction) in estimates of net ultimate losses									71,695	61,550	54,170
Increase (reduction) in provisions for bad debt									159	0	0
Increase (reduction) in provisions for unallocated LAE									285	145	(83)
Amortization of fair value adjustments									(2,720)	(3,308)	(6,608)
Total changes in fair value - fair value option									0
Total net incurred losses and LAE									69,419	58,387	47,479
StarStone
Prior Period
Net losses paid, prior period									252,926	199,125	149,820
Net change in case and LAE reserves, prior period									(63,785)	(51,309)	15,772
Net change in IBNR reserves, prior period									(208,244)	(156,546)	(200,730)
Increase (reduction) in estimates of net ultimate losses, prior period									(19,103)	(8,730)	(35,138)
Increase (reduction) in provisions for unallocated LAE, prior period									(6,774)	(3,611)	(683)
Amortization of fair value adjustments, prior period									(945)	(1,895)	(3,535)
Prior periods									(26,822)	(14,236)	(39,356)
Current Period
Net losses paid, current period									54,867	52,128	62,739
Net change in case and LAE reserves, current period									95,470	124,358	61,447
Net change in IBNR reserves, current period									184,704	232,189	238,634
Increase (reduction) in estimates of net ultimate losses, current period									335,041	408,675	362,820
Increase (reduction) in provisions for unallocated LAE, current period									6,587	7,154	4,220
Amortization of fair value adjustments, current period									0	0	0
Net incurred losses and LAE, current period									341,628	415,829	367,040
Total
Net losses paid									307,793	251,253	212,559
Net change in case and LAE reserves									31,685	73,049	77,219
Net change in IBNR reserves									(23,540)	75,643	37,904
Amortization of deferred charges									0	0	0
Increase (reduction) in estimates of net ultimate losses									315,938	399,945	327,682
Increase (reduction) in provisions for bad debt									0	0	0
Increase (reduction) in provisions for unallocated LAE									(187)	3,543	3,537
Amortization of fair value adjustments									(945)	(1,895)	(3,535)
Total changes in fair value - fair value option									0
Total net incurred losses and LAE									314,806	401,593	327,684
Environmental liabilities | Non-life Run-off
Prior Period
Net change in IBNR reserves, prior period									7,500	35,500	1,600	6,200
Reserve for General Casualty Loss | Non-life Run-off
Prior Period
Net change in IBNR reserves, prior period									7,200	800	3,000	62,500
Workers' compensation liabilities | Non-life Run-off
Prior Period
Net change in IBNR reserves, prior period									156,200	333,200	243,400	63,600
Other liabilities | Non-life Run-off
Prior Period
Net change in IBNR reserves, prior period									152,200	90,600	97,700	70,700
Asbestos liabilities | Non-life Run-off
Prior Period
Net change in IBNR reserves, prior period									$ 70,000	$ 39,400	$ 32,000	$ 59,400

Losses and Loss Adjustment E100

Losses and Loss Adjustment Expenses - Incurred and Paid Loss Development, IBNR, Claims Counts and Payout Percentages (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	$ 3,855,043	$ 3,267,230
IBNR	3,653,656	2,607,082
Fair value adjustments	(117,006)	(123,728)
Total gross liability for unpaid losses and LAE	7,398,088	5,987,867	$ 5,720,149	$ 4,509,421
StarStone
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	590,977	502,115
IBNR	599,221	541,305
Total liability excluding unallocated loss adjustment expenses	1,190,198	1,043,420
Fair value adjustments	(555)	(863)
ULAE	18,100	16,825
Total gross liability for unpaid losses and LAE	1,207,743	1,059,382	933,678	861,800
StarStone | Casualty
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	139,200	101,897
IBNR	282,789	279,823
Total liability excluding unallocated loss adjustment expenses	421,989	381,720
StarStone | Marine
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	130,962	102,957
IBNR	118,375	94,396
Total liability excluding unallocated loss adjustment expenses	249,337	197,353
StarStone | Property
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	208,777	182,480
IBNR	89,963	57,184
Total liability excluding unallocated loss adjustment expenses	298,740	239,664
StarStone | Aerospace
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	63,920	66,190
IBNR	26,070	30,921
Total liability excluding unallocated loss adjustment expenses	89,990	97,111
StarStone | Workers' compensation
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	48,118	48,591
IBNR	82,024	78,981
Total liability excluding unallocated loss adjustment expenses	130,142	127,572
Atrium
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	78,363	67,379
IBNR	150,508	130,118
Total liability excluding unallocated loss adjustment expenses	228,871	197,497
Fair value adjustments	9,547	12,503
ULAE	2,455	2,122
Total gross liability for unpaid losses and LAE	240,873	212,122	201,017	212,611
Atrium | Marine, aviation and transit
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	24,581	25,565
IBNR	46,138	49,369
Total liability excluding unallocated loss adjustment expenses	70,719	74,934
Atrium | Binding Authorities
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	26,115	21,543
IBNR	51,896	41,603
Total liability excluding unallocated loss adjustment expenses	78,011	63,146
Atrium | Reinsurance
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	14,381	11,485
IBNR	34,489	22,178
Total liability excluding unallocated loss adjustment expenses	48,870	33,663
Atrium | Accident and Health
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	3,716	2,913
IBNR	5,518	5,625
Total liability excluding unallocated loss adjustment expenses	9,234	8,538
Atrium | Non-Marine Direct and Facultative
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	9,570	5,873
IBNR	12,467	11,343
Total liability excluding unallocated loss adjustment expenses	22,037	17,216
Non-life Run-off
Liability for Claims and Claims Adjustment Expense [Line Items]
OLR	3,185,703	2,697,736
IBNR	2,903,927	1,935,659
Total liability excluding unallocated loss adjustment expenses	6,089,630	4,633,395
Fair value adjustments	(125,998)	(135,368)
Total gross liability for unpaid losses and LAE	5,949,472	4,716,363	$ 4,585,454	$ 3,435,010
Non-life Run-off | Casualty
Liability for Claims and Claims Adjustment Expense [Line Items]
Total liability excluding unallocated loss adjustment expenses	610,951	745,823
Non-life Run-off | Marine, aviation and transit
Liability for Claims and Claims Adjustment Expense [Line Items]
Total liability excluding unallocated loss adjustment expenses	165,386	89,769
Non-life Run-off | Workers' compensation
Liability for Claims and Claims Adjustment Expense [Line Items]
Total liability excluding unallocated loss adjustment expenses	$ 2,207,379	$ 2,090,713

Losses and Loss Adjustment E101

Losses and Loss Adjustment Expenses - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)commutation	Dec. 31, 2016USD ($)commutation	Dec. 31, 2015USD ($)commutation	Dec. 31, 2014USD ($)
Effects of Reinsurance [Line Items]
Net incurred losses and loss adjustment expenses	$ 30,327	$ 75,712	$ 9,620	$ 77,892	$ 1,321	$ (6,902)	$ 96,462	$ 83,218	$ 193,551	$ 174,099	$ 104,333
Net incurred losses and LAE, current period									437,853	493,016	476,364
Net incurred losses and LAE, prior period									(244,302)	(318,917)	(372,031)
Amortization of deferred charges									14,359	168,827	15,265
Net losses paid, prior period									(862,921)	(753,478)	(681,956)
Increase in asbestos and environmental reserves, gross									970,400	545,200
Increase in asbestos and environmental reserves, net									$ 883,400	545,100
Percent of underwriting capacity and capital owned									25.00%
Non-life Run-off
Effects of Reinsurance [Line Items]
Net incurred losses and loss adjustment expenses									$ (190,674)	(285,881)	(270,830)
Net incurred losses and LAE, current period									5,866	5,829	39,924
Net incurred losses and LAE, prior period									(196,540)	(291,710)	(310,754)
Increase (reduction) in estimates of net ultimate losses, prior period									(181,303)	(259,130)	(227,473)
Increase (reduction) in provisions for bad debt, prior period									(1,536)	(13,822)	(25,271)
Increase (reduction) in provisions for unallocated LAE, prior period									(54,071)	(44,190)	(62,653)
Amortization of fair value adjustments, prior period									10,114	25,432	4,643
Changes in fair value, fair value option									30,256	0	0
Amortization of deferred charges									14,359	168,827	15,265
Net change in IBNR reserves, prior period									(393,100)	(349,726)	(377,722)	$ 262,400
Net incurred loss development									$ 211,800	$ 90,600	$ 150,200
Total number of commutations | commutation									59	56	79
Net change in case and LAE reserves, prior period									$ (381,450)	$ (608,168)	$ (366,262)
Net losses paid, prior period									578,888	529,937	501,246
Net incurred liabilities settled by way of commutation									7,400	14,700	56,600
Ceded incurred reinsurance recoverables									15,800	24,400	83,700
Assumed incurred liabilities									23,200	39,100	140,300
Current period net earned premium										7,100	43,300
Estimate of net ultimate liability for asbestos and environmental claims	1,863,200				979,800				1,863,200	979,800
Estimate of gross ultimate liability for asbestos and environmental claims	$ 1,992,100				$ 1,021,800				1,992,100	1,021,800
Non-life Run-off | Asbestos liabilities
Effects of Reinsurance [Line Items]
Net change in IBNR reserves, prior period									70,000	39,400	32,000	59,400
Non-life Run-off | Environmental liabilities
Effects of Reinsurance [Line Items]
Net change in IBNR reserves, prior period									7,500	35,500	1,600	6,200
Non-life Run-off | General casualty liabilities
Effects of Reinsurance [Line Items]
Net change in IBNR reserves, prior period									7,200	800	3,000	62,500
Non-life Run-off | Workers' compensation liabilities
Effects of Reinsurance [Line Items]
Net change in IBNR reserves, prior period									156,200	333,200	243,400	63,600
Non-life Run-off | Other liabilities
Effects of Reinsurance [Line Items]
Net change in IBNR reserves, prior period									152,200	90,600	97,700	$ 70,700
Atrium Segment
Effects of Reinsurance [Line Items]
Net incurred losses and loss adjustment expenses									69,419	58,387	47,479
Net incurred losses and LAE, current period									90,359	71,358	69,400
Net incurred losses and LAE, prior period									(20,940)	(12,971)	(21,921)
Increase (reduction) in estimates of net ultimate losses, prior period									(17,867)	(9,242)	(14,705)
Increase (reduction) in provisions for bad debt, prior period									89	0	0
Increase (reduction) in provisions for unallocated LAE, prior period									(442)	(421)	(608)
Amortization of fair value adjustments, prior period									(2,720)	(3,308)	(6,608)
Amortization of deferred charges									0	0	0
Net change in IBNR reserves, prior period									(35,650)	(20,543)	(27,382)
Net change in case and LAE reserves, prior period									(13,324)	(13,115)	(18,213)
Net losses paid, prior period									31,107	24,416	30,890
StarStone
Effects of Reinsurance [Line Items]
Net incurred losses and loss adjustment expenses									314,806	401,593	327,684
Net incurred losses and LAE, current period									341,628	415,829	367,040
Net incurred losses and LAE, prior period									(26,822)	(14,236)	(39,356)
Increase (reduction) in estimates of net ultimate losses, prior period									(19,103)	(8,730)	(35,138)
Increase (reduction) in provisions for unallocated LAE, prior period									(6,774)	(3,611)	(683)
Amortization of fair value adjustments, prior period									(945)	(1,895)	(3,535)
Amortization of deferred charges									0	0	0
Net change in IBNR reserves, prior period									(208,244)	(156,546)	(200,730)
Net change in case and LAE reserves, prior period									(63,785)	(51,309)	15,772
Net losses paid, prior period									$ 252,926	$ 199,125	$ 149,820
Product Concentration Risk | Liability for Unpaid Claims and Claims Adjustment Expense | Non-life Run-off
Effects of Reinsurance [Line Items]
% of Total									80.00%	83.00%
Product Concentration Risk | Liability for Unpaid Claims and Claims Adjustment Expense | Non-life Run-off | Marine, Aviation, Transit and Construction Defect
Effects of Reinsurance [Line Items]
% of Total									3.00%
Product Concentration Risk | Liability for Unpaid Claims and Claims Adjustment Expense, Net | Non-life Run-off
Effects of Reinsurance [Line Items]
% of Total									80.00%	82.00%
Product Concentration Risk | Liability for Unpaid Claims and Claims Adjustment Expense, Net | Non-life Run-off | Asbestos and Environmental Lines
Effects of Reinsurance [Line Items]
% of Total									41.00%
Segment Concentration Risk | Liability Claims and Claims Adjustment Expense | Atrium Segment
Effects of Reinsurance [Line Items]
% of Total									3.30%

Losses and Loss Adjustment E102

Losses and Loss Adjustment Expenses - Breakdown of Gross and Net Losses and LAE Reserves by Major Category (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gross
Fair value adjustments	$ (117,006)	$ (123,728)
Fair value adjustments - fair value option	(314,748)	0
Total gross liability for unpaid losses and LAE	7,398,088	5,987,867	$ 5,720,149	$ 4,509,421
Net
ULAE	321,143	237,283
Total net liability for unpaid losses and LAE	5,447,863	4,505,123	4,103,856	3,355,225
Non-life Run-off
Gross
OLR	3,185,703	2,697,736
IBNR	2,903,927	1,935,659
Total	6,089,630	4,633,395
Fair value adjustments	(125,998)	(135,368)
Fair value adjustments - fair value option	(314,748)	0
Deferred charge on retroactive reinsurance	0	0
Total gross liability for unpaid losses excluding ULAE	5,648,884	4,498,027
ULAE	300,588	218,336
Total gross liability for unpaid losses and LAE	5,949,472	4,716,363	4,585,454	3,435,010
Net
OLR	2,253,418	2,076,449
IBNR	2,313,773	1,542,108
Total	4,567,191	3,618,557
Fair value adjustments	(113,028)	(121,483)
Fair value adjustments - fair value option	(182,764)
Deferred charge on retroactive reinsurance	(80,192)	(94,551)
Total net liability for unpaid losses excluding ULAE	4,191,207	3,402,523
ULAE	300,588	218,336
Total net liability for unpaid losses and LAE	4,491,795	3,620,859	$ 3,294,796	$ 2,634,301
Non-life Run-off | Asbestos
Gross
OLR	366,446	265,144
IBNR	1,434,598	584,757
Total	1,801,044	849,901
Net
OLR	341,355	246,030
IBNR	1,337,467	569,736
Total	1,678,822	815,766
Non-life Run-off | Environmental
Gross
OLR	95,801	100,128
IBNR	95,259	71,722
Total	191,060	171,850
Net
OLR	91,049	94,311
IBNR	93,345	69,740
Total	184,394	164,051
Non-life Run-off | General casualty
Gross
OLR	344,425	428,210
IBNR	266,526	317,613
Total	610,951	745,823
Net
OLR	276,791	300,650
IBNR	194,747	195,393
Total	471,538	496,043
Non-life Run-off | Workers' compensation/personal accident
Gross
OLR	1,458,430	1,389,097
IBNR	748,949	701,616
Total	2,207,379	2,090,713
Net
OLR	889,265	1,007,528
IBNR	371,161	484,863
Total	1,260,426	1,492,391
Non-life Run-off | Marine, aviation and transit
Gross
OLR	109,102	54,025
IBNR	56,284	35,744
Total	165,386	89,769
Net
OLR	90,101	48,469
IBNR	51,904	35,607
Total	142,005	84,076
Non-life Run-off | Construction defect
Gross
OLR	28,701	40,446
IBNR	135,608	121,551
Total	164,309	161,997
Net
OLR	27,406	33,591
IBNR	122,307	90,977
Total	149,713	124,568
Non-life Run-off | Professional indemnity/Directors & Officers
Gross
OLR	214,803	110,208
IBNR	40,265	61,663
Total	255,068	171,871
Net
OLR	181,027	92,716
IBNR	39,591	60,626
Total	220,618	153,342
Non-life Run-off | Other
Gross
OLR	567,995	310,478
IBNR	126,438	40,993
Total	694,433	351,471
Net
OLR	356,424	253,154
IBNR	103,251	35,166
Total	$ 459,675	$ 288,320

Losses and Loss Adjustment E103

Losses and Loss Adjustment Expenses - Incurred and Paid Loss Development Information, and IBNR Liabilities and Cumulative Loss Frequency (Details) $ in Thousands	Dec. 31, 2017USD ($)claim	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)	Dec. 31, 2008USD ($)
Non-life Run-off | Casualty
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 750,623
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	543,771
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	264,686
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	471,538
Non-life Run-off | Casualty | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	84,811	$ 66,160	$ 69,784	$ 64,982	$ 63,437	$ 59,142	$ 51,927	$ 45,420	$ 24,456	$ 20,277
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	62,930	57,625	54,510	52,416	45,447	40,909	30,193	20,372	12,512	5,752
IBNR losses and loss expenses, net of reinsurance	$ 10,162
Cumulative number of reported claims | claim	3,543
Non-life Run-off | Casualty | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 112,799	94,550	92,084	86,618	84,596	66,202	48,009	27,612	20,081
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	85,802	80,004	73,154	66,001	55,455	41,723	22,986	11,384	4,834
IBNR losses and loss expenses, net of reinsurance	$ 10,570
Cumulative number of reported claims | claim	3,497
Non-life Run-off | Casualty | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 230,288	215,279	201,813	177,344	93,817	68,142	55,916	34,527
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	195,858	179,633	150,681	97,854	41,340	26,943	14,462	6,108
IBNR losses and loss expenses, net of reinsurance	$ 20,143
Cumulative number of reported claims | claim	5,365
Non-life Run-off | Casualty | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 92,802	86,727	87,625	83,854	68,439	42,977	40,109
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	64,789	60,809	55,998	43,189	26,839	17,573	8,353
IBNR losses and loss expenses, net of reinsurance	$ 16,825
Cumulative number of reported claims | claim	3,864
Non-life Run-off | Casualty | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 104,284	88,743	73,218	82,667	72,203	65,494
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	71,372	58,717	42,991	31,031	17,787	12,435
IBNR losses and loss expenses, net of reinsurance	$ 16,766
Cumulative number of reported claims | claim	3,929
Non-life Run-off | Casualty | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 72,586	53,597	50,524	76,526	60,121
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	39,996	29,342	20,416	14,311	2,449
IBNR losses and loss expenses, net of reinsurance	$ 13,387
Cumulative number of reported claims | claim	2,529
Non-life Run-off | Casualty | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 37,628	25,197	23,657	35,789
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	19,672	10,300	5,070	1,740
IBNR losses and loss expenses, net of reinsurance	$ 7,883
Cumulative number of reported claims | claim	1,447
Non-life Run-off | Casualty | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 14,003	9,891	9,478
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	3,188	1,505	744
IBNR losses and loss expenses, net of reinsurance	$ 5,500
Cumulative number of reported claims | claim	516
Non-life Run-off | Casualty | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 1,281	2,319
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	147	81
IBNR losses and loss expenses, net of reinsurance	$ 868
Cumulative number of reported claims | claim	103
Non-life Run-off | Casualty | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 141
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	17
IBNR losses and loss expenses, net of reinsurance	$ 115
Cumulative number of reported claims | claim	26
Non-life Run-off | Workers' compensation/personal accident
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 1,719,076
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	1,363,013
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	904,363
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	1,260,426
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	360,478	344,352	340,547	344,977	338,214	327,727	329,516	315,753	295,970	265,540
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	324,480	317,946	313,936	306,607	293,874	278,088	255,550	219,202	164,145	83,344
IBNR losses and loss expenses, net of reinsurance	$ 13,587
Cumulative number of reported claims | claim	43,430
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 312,309	322,864	316,540	308,837	301,191	294,104	288,464	275,932	236,790
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	275,573	283,407	275,620	270,693	254,348	233,516	198,214	146,631	76,071
IBNR losses and loss expenses, net of reinsurance	$ 16,599
Cumulative number of reported claims | claim	41,928
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 354,173	348,008	344,619	337,680	326,852	309,258	291,649	257,331
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	299,285	288,933	275,286	264,329	252,732	218,846	163,231	85,367
IBNR losses and loss expenses, net of reinsurance	$ 25,476
Cumulative number of reported claims | claim	46,023
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 250,915	251,575	257,374	253,525	224,479	215,605	201,011
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	199,292	185,650	162,444	134,487	153,192	110,189	44,931
IBNR losses and loss expenses, net of reinsurance	$ 26,894
Cumulative number of reported claims | claim	46,698
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 231,740	223,991	227,214	232,410	200,200	191,946
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	156,579	134,993	92,588	57,070	89,004	37,848
IBNR losses and loss expenses, net of reinsurance	$ 41,832
Cumulative number of reported claims | claim	44,448
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 104,942	107,511	116,744	133,563	99,594
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	45,909	21,187	(17,142)	(41,452)	18,305
IBNR losses and loss expenses, net of reinsurance	$ 35,061
Cumulative number of reported claims | claim	31,945
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 82,084	81,227	87,181	75,905
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	49,884	35,025	13,896	8,385
IBNR losses and loss expenses, net of reinsurance	$ 18,062
Cumulative number of reported claims | claim	10,925
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 18,465	18,038	23,973
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	11,432	8,944	4,602
IBNR losses and loss expenses, net of reinsurance	$ 2,895
Cumulative number of reported claims | claim	2,885
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 1,055	981
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	420	184
IBNR losses and loss expenses, net of reinsurance	$ 652
Cumulative number of reported claims | claim	38
Non-life Run-off | Workers' compensation/personal accident | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 2,915
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	159
IBNR losses and loss expenses, net of reinsurance	$ 2,307
Cumulative number of reported claims | claim	8
Non-life Run-off | Professional indemnity/Directors & Officers
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 366,858
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	293,497
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	147,257
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	220,618
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	128,410	128,985	77,421	83,578	86,120	80,673	58,806	53,480	23,865	4,149
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	109,032	107,854	53,018	44,913	40,045	33,932	26,799	11,350	3,157	179
IBNR losses and loss expenses, net of reinsurance	$ 3,666
Cumulative number of reported claims | claim	0
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 57,076	59,906	62,705	58,429	54,345	48,547	25,782	14,027	1,205
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	46,209	41,053	37,708	33,246	26,023	17,040	7,784	2,604	88
IBNR losses and loss expenses, net of reinsurance	$ 2,238
Cumulative number of reported claims | claim	0
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 485	454	463	793	0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	490	456	463	462	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ (3)
Cumulative number of reported claims | claim	520
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 40,602	41,508	43,180	39,854	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	36,236	35,061	32,366	28,221	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 1,500
Cumulative number of reported claims | claim	2,003
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 65,893	67,098	69,319	59,123	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	54,208	51,396	44,410	33,687	0	0
IBNR losses and loss expenses, net of reinsurance	$ 3,254
Cumulative number of reported claims | claim	2,281
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 61,785	57,983	62,259	47,164	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	44,337	35,219	31,063	18,678	0
IBNR losses and loss expenses, net of reinsurance	$ 8,724
Cumulative number of reported claims | claim	1,922
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 3,760	5,496	4,903	7,374
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	1,127	1,075	717	430
IBNR losses and loss expenses, net of reinsurance	$ 2,417
Cumulative number of reported claims | claim	439
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 8,789	4,925	198
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	1,821	198	29
IBNR losses and loss expenses, net of reinsurance	$ 2,216
Cumulative number of reported claims | claim	26
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 0	42
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	1
Non-life Run-off | Professional indemnity/Directors & Officers | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 58
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	37
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	2
Atrium
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 623,795
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	438,374
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	3,369
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	188,790
Atrium | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	63,081	63,552	65,311	66,701	67,201	68,943	73,128	60,742	60,309	46,002
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	59,738	59,546	60,018	59,439	58,193	56,311	53,307	48,558	37,939	$ 15,492
IBNR losses and loss expenses, net of reinsurance	$ 2,478
Cumulative number of reported claims | claim	266
Atrium | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 46,542	46,929	47,715	50,246	51,888	52,744	57,959	40,847	28,071
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	43,093	42,833	42,542	41,849	40,631	38,591	35,047	28,002	$ 12,145
IBNR losses and loss expenses, net of reinsurance	$ 1,705
Cumulative number of reported claims | claim	294
Atrium | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 45,478	47,128	47,871	50,078	55,666	58,465	65,704	27,139
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	41,713	41,137	40,526	39,486	36,968	32,600	25,421	$ 11,599
IBNR losses and loss expenses, net of reinsurance	$ 1,900
Cumulative number of reported claims | claim	376
Atrium | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 69,341	70,537	72,380	75,384	78,981	85,580	87,325
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	65,904	64,607	63,237	59,270	53,018	40,413	$ 17,314
IBNR losses and loss expenses, net of reinsurance	$ 2,642
Cumulative number of reported claims | claim	561
Atrium | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 52,995	54,416	57,126	60,804	64,633	70,930
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	45,710	44,807	42,499	38,324	31,762	$ 11,357
IBNR losses and loss expenses, net of reinsurance	$ 3,536
Cumulative number of reported claims | claim	756
Atrium | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 53,632	57,415	62,166	71,302	69,241
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	45,884	43,984	40,890	32,383	$ 14,731
IBNR losses and loss expenses, net of reinsurance	$ 3,985
Cumulative number of reported claims | claim	1,132
Atrium | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 61,211	66,825	70,275	70,008
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	47,441	42,114	34,763	17,754
IBNR losses and loss expenses, net of reinsurance	$ 8,570
Cumulative number of reported claims | claim	1,835
Atrium | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 64,178	72,234	70,336
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	39,430	30,009	12,147
IBNR losses and loss expenses, net of reinsurance	$ 15,047
Cumulative number of reported claims | claim	3,070
Atrium | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 76,208	74,001
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	34,988	13,878
IBNR losses and loss expenses, net of reinsurance	$ 25,036
Cumulative number of reported claims | claim	4,899
Atrium | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 91,129
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	14,473
IBNR losses and loss expenses, net of reinsurance	$ 56,376
Cumulative number of reported claims | claim	5,197
StarStone | Casualty
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 589,881
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	303,310
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	18
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	286,589
StarStone | Casualty | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	7,733	7,740	7,734	7,759
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	7,733	7,740	7,734	7,759
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	491
StarStone | Casualty | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 21,162	21,158	21,158	21,096
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	21,162	21,158	21,158	21,096
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	496
StarStone | Casualty | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 18,974	18,113	18,026	15,972
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	18,796	18,113	18,026	15,809
IBNR losses and loss expenses, net of reinsurance	$ 178
Cumulative number of reported claims | claim	734
StarStone | Casualty | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 25,211	24,665	23,948	20,964
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	24,497	23,930	21,200	15,850
IBNR losses and loss expenses, net of reinsurance	$ 713
Cumulative number of reported claims | claim	2,043
StarStone | Casualty | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 39,388	44,003	48,530	57,413
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	34,074	32,805	29,613	18,514
IBNR losses and loss expenses, net of reinsurance	$ 2,381
Cumulative number of reported claims | claim	3,100
StarStone | Casualty | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 78,573	79,689	69,537	74,312
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	54,989	50,427	30,675	23,210
IBNR losses and loss expenses, net of reinsurance	$ 7,002
Cumulative number of reported claims | claim	4,952
StarStone | Casualty | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 90,663	93,325	93,687	92,236
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	51,012	37,793	22,041	5,803
IBNR losses and loss expenses, net of reinsurance	$ 18,892
Cumulative number of reported claims | claim	5,336
StarStone | Casualty | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 111,582	112,430	108,762
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	50,072	28,230	8,779
IBNR losses and loss expenses, net of reinsurance	$ 36,723
Cumulative number of reported claims | claim	3,950
StarStone | Casualty | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 100,301	103,057
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	34,214	4,856
IBNR losses and loss expenses, net of reinsurance	$ 49,588
Cumulative number of reported claims | claim	3,722
StarStone | Casualty | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 96,294
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	6,761
IBNR losses and loss expenses, net of reinsurance	$ 73,042
Cumulative number of reported claims | claim	3,594
StarStone | Workers' compensation/personal accident
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 139,891
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	66,759
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	0
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	73,132
StarStone | Workers' compensation/personal accident | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	0
StarStone | Workers' compensation/personal accident | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	0
StarStone | Workers' compensation/personal accident | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	0
StarStone | Workers' compensation/personal accident | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	0
StarStone | Workers' compensation/personal accident | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	0
StarStone | Workers' compensation/personal accident | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	0
StarStone | Workers' compensation/personal accident | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 15,662	18,291	17,199	15,607
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	11,431	9,279	6,079	1,491
IBNR losses and loss expenses, net of reinsurance	$ 2,129
Cumulative number of reported claims | claim	1,061
StarStone | Workers' compensation/personal accident | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 50,102	55,505	54,978
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	30,439	20,194	6,361
IBNR losses and loss expenses, net of reinsurance	$ 9,583
Cumulative number of reported claims | claim	2,510
StarStone | Workers' compensation/personal accident | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 46,866	54,630
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	21,329	8,092
IBNR losses and loss expenses, net of reinsurance	$ 12,550
Cumulative number of reported claims | claim	2,468
StarStone | Workers' compensation/personal accident | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 27,261
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	3,560
IBNR losses and loss expenses, net of reinsurance	$ 17,659
Cumulative number of reported claims | claim	1,783
StarStone | Marine
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 459,636
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	295,692
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	0
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	163,944
StarStone | Marine | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	7,113	7,112	7,105	7,114
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	7,108	7,108	7,092	7,081
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	486
StarStone | Marine | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 10,539	10,526	10,554	10,653
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	10,530	10,523	10,542	10,529
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	657
StarStone | Marine | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 23,471	23,344	23,478	26,257
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	22,530	22,562	22,482	20,427
IBNR losses and loss expenses, net of reinsurance	$ 211
Cumulative number of reported claims | claim	1,087
StarStone | Marine | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 23,631	23,503	23,838	25,459
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	22,484	22,237	21,245	20,185
IBNR losses and loss expenses, net of reinsurance	$ 243
Cumulative number of reported claims | claim	2,082
StarStone | Marine | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 52,110	53,309	53,365	49,820
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	46,820	46,028	44,127	39,975
IBNR losses and loss expenses, net of reinsurance	$ 667
Cumulative number of reported claims | claim	2,498
StarStone | Marine | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 55,122	54,163	56,191	63,366
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	45,993	43,538	39,370	29,985
IBNR losses and loss expenses, net of reinsurance	$ 249
Cumulative number of reported claims | claim	2,318
StarStone | Marine | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 56,212	49,624	53,415	52,740
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	37,794	33,311	25,533	11,146
IBNR losses and loss expenses, net of reinsurance	$ 5,439
Cumulative number of reported claims | claim	4,298
StarStone | Marine | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 81,587	71,311	73,237
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	51,454	31,483	11,038
IBNR losses and loss expenses, net of reinsurance	$ 7,131
Cumulative number of reported claims | claim	5,868
StarStone | Marine | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 61,926	63,694
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	34,452	11,102
IBNR losses and loss expenses, net of reinsurance	$ 11,258
Cumulative number of reported claims | claim	6,751
StarStone | Marine | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 87,925
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	16,527
IBNR losses and loss expenses, net of reinsurance	$ 44,629
Cumulative number of reported claims | claim	5,487
StarStone | Property
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 672,289
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	518,720
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	858
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	154,427
StarStone | Property | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	49,158	49,163	49,135	48,894
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	49,158	49,163	49,135	48,894
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	740
StarStone | Property | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 29,070	28,826	28,417	28,946
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	29,070	28,829	28,420	28,382
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	1,100
StarStone | Property | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 73,395	73,332	74,491	75,670
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	73,395	73,332	73,213	70,293
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	1,698
StarStone | Property | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 90,364	90,646	90,708	92,107
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	90,364	90,103	89,561	88,327
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	1,688
StarStone | Property | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 62,332	61,594	62,398	65,529
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	56,079	55,061	52,705	48,588
IBNR losses and loss expenses, net of reinsurance	$ 284
Cumulative number of reported claims | claim	1,574
StarStone | Property | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 65,146	65,885	66,079	76,665
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	54,040	51,915	46,983	31,433
IBNR losses and loss expenses, net of reinsurance	$ 868
Cumulative number of reported claims | claim	1,946
StarStone | Property | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 45,382	44,955	44,317	63,673
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	36,213	33,199	18,998	5,537
IBNR losses and loss expenses, net of reinsurance	$ 1,927
Cumulative number of reported claims | claim	2,114
StarStone | Property | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 71,391	77,695	79,339
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	55,956	29,060	10,467
IBNR losses and loss expenses, net of reinsurance	$ 1,717
Cumulative number of reported claims | claim	5,563
StarStone | Property | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 80,379	74,134
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	49,730	23,386
IBNR losses and loss expenses, net of reinsurance	$ 3,698
Cumulative number of reported claims | claim	6,525
StarStone | Property | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 105,672
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	24,715
IBNR losses and loss expenses, net of reinsurance	$ 30,785
Cumulative number of reported claims | claim	6,036
StarStone | Aerospace
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 389,600
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	331,764
All outstanding liabilities for unpaid losses and LAE prior to 2008, net of reinsurance	0
Total outstanding liabilities for unpaid losses and LAE, net of reinsurance	57,836
StarStone | Aerospace | Accident Year - 2008
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	0
StarStone | Aerospace | Accident Year - 2009
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 0	0	0	0
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	0	0	0	0
IBNR losses and loss expenses, net of reinsurance	$ 0
Cumulative number of reported claims | claim	0
StarStone | Aerospace | Accident Year - 2010
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 19,258	18,741	18,430	18,269
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	18,566	17,497	16,890	15,743
IBNR losses and loss expenses, net of reinsurance	$ 66
Cumulative number of reported claims | claim	569
StarStone | Aerospace | Accident Year - 2011
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 58,268	57,833	57,436	58,954
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	56,584	56,002	55,321	53,956
IBNR losses and loss expenses, net of reinsurance	$ 192
Cumulative number of reported claims | claim	2,173
StarStone | Aerospace | Accident Year - 2012
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 56,552	56,586	55,765	56,144
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	53,982	52,502	49,665	46,219
IBNR losses and loss expenses, net of reinsurance	$ 172
Cumulative number of reported claims | claim	2,393
StarStone | Aerospace | Accident Year - 2013
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 75,228	70,820	70,535	72,762
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	69,071	63,723	60,118	51,098
IBNR losses and loss expenses, net of reinsurance	$ 348
Cumulative number of reported claims | claim	2,324
StarStone | Aerospace | Accident Year - 2014
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 52,593	53,751	54,077	65,526
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	40,865	38,605	31,309	$ 17,375
IBNR losses and loss expenses, net of reinsurance	$ 1,087
Cumulative number of reported claims | claim	2,380
StarStone | Aerospace | Accident Year - 2015
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 73,125	69,843	66,078
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	61,081	52,407	$ 32,415
IBNR losses and loss expenses, net of reinsurance	$ 2,642
Cumulative number of reported claims | claim	2,252
StarStone | Aerospace | Accident Year - 2016
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 35,540	30,718
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	24,904	$ 10,193
IBNR losses and loss expenses, net of reinsurance	$ 4,141
Cumulative number of reported claims | claim	1,725
StarStone | Aerospace | Accident Year - 2017
Net
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 19,036
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	6,711
IBNR losses and loss expenses, net of reinsurance	$ 8,407
Cumulative number of reported claims | claim	882

Losses and Loss Adjustment E104

Losses and Loss Adjustment Expenses - IBNR Acquired in Assumed Loss Portfolio Transfer Reinsurance Transactions (Details) - Non-life Run-off Segment - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Casualty
Liability for Claims and Claims Adjustment Expense [Line Items]
Take-On IBNR for Assume Business	$ 79,495	$ 36,501	$ 0	$ 5,263	$ 0	$ 25,703	$ 0	$ 3,633	$ 0	$ 10,740
Workers' compensation
Liability for Claims and Claims Adjustment Expense [Line Items]
Take-On IBNR for Assume Business	$ 62,192	$ 100,000	$ 0	$ 0	$ 0		$ 0	$ 5,954	$ 5,323	$ 0

Losses and Loss Adjustment E105

Losses and Loss Adjustment Expenses - Average Annual Duration of Claims (Details)	Dec. 31, 2017
Non-life Run-off | General casualty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	6.64%
Year 2	8.29%
Year 3	10.25%
Year 4	14.39%
Year 5	15.49%
Year 6	10.99%
Year 7	7.85%
Year 8	5.20%
Year 9	4.41%
Year 10	6.26%
Non-life Run-off | Workers' compensation
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	18.10%
Year 2	23.10%
Year 3	17.30%
Year 4	12.30%
Year 5	5.40%
Year 6	4.20%
Year 7	3.00%
Year 8	2.50%
Year 9	1.10%
Year 10	1.80%
Non-life Run-off | Professional indemnity/Directors & Officers
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	15.10%
Year 2	4.10%
Year 3	12.70%
Year 4	10.50%
Year 5	11.40%
Year 6	5.70%
Year 7	4.80%
Year 8	6.40%
Year 9	9.00%
Year 10	0.90%
Atrium
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	23.20%
Year 2	37.09%
Year 3	15.11%
Year 4	8.02%
Year 5	4.72%
Year 6	2.31%
Year 7	1.67%
Year 8	0.94%
Year 9	0.56%
Year 10	0.30%
StarStone | General casualty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	6.60%
Year 2	21.50%
Year 3	15.50%
Year 4	22.40%
Year 5	11.90%
Year 6	8.70%
Year 7	1.00%
Year 8	1.10%
Year 9	0.10%
Year 10	0.00%
StarStone | Workers' compensation
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	14.30%
Year 2	28.40%
Year 3	13.60%
Year 4	4.60%
Year 5	0.00%
Year 6	0.00%
Year 7	0.00%
Year 8	0.00%
Year 9	0.00%
Year 10	0.00%
StarStone | Marine
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	16.80%
Year 2	29.50%
Year 3	18.40%
Year 4	7.80%
Year 5	4.20%
Year 6	4.80%
Year 7	0.50%
Year 8	0.00%
Year 9	0.10%
Year 10	0.00%
StarStone | Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	22.40%
Year 2	29.50%
Year 3	30.90%
Year 4	6.90%
Year 5	2.80%
Year 6	2.10%
Year 7	0.20%
Year 8	0.70%
Year 9	0.40%
Year 10	0.00%
StarStone | Aerospace
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	36.10%
Year 2	31.70%
Year 3	12.60%
Year 4	5.10%
Year 5	4.80%
Year 6	3.20%
Year 7	1.40%
Year 8	1.80%
Year 9	0.00%
Year 10	0.00%

Losses and Loss Adjustment E106

Losses and Loss Adjustment Expenses - Reconciliation of Incurred and Paid Loss Development to Liability for Unpaid Losses and LAE (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Non-life Run-off
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	$ 6,089,630	$ 4,633,395
Non-life Run-off | Casualty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	471,538
Reinsurance recoverable on unpaid losses	139,413
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	610,951	745,823
Non-life Run-off | Workers' compensation/personal accident
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	1,260,426
Reinsurance recoverable on unpaid losses	946,953
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	2,207,379	2,090,713
Non-life Run-off | Professional indemnity/Directors & Officers
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	220,618
Reinsurance recoverable on unpaid losses	34,450
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	255,068	171,871
Atrium
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	188,790
Reinsurance recoverable on unpaid losses	40,081
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	228,871	197,497
StarStone
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	1,190,198	1,043,420
StarStone | Casualty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	286,589
Reinsurance recoverable on unpaid losses	135,400
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	421,989	381,720
StarStone | Workers' compensation/personal accident
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	73,132
Reinsurance recoverable on unpaid losses	57,010
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	130,142	127,572
StarStone | Marine
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	163,944
Reinsurance recoverable on unpaid losses	85,393
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	249,337	197,353
StarStone | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	154,427
Reinsurance recoverable on unpaid losses	144,313
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	298,740	239,664
StarStone | Aerospace
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and allocated LAE, net of reinsurance	57,836
Reinsurance recoverable on unpaid losses	32,154
Gross liability for unpaid losses and LAE before unallocated loss adjustment expenses	$ 89,990	$ 97,111

Losses and Loss Adjustment E107

Losses and Loss Adjustment Expenses - Carrying Amount of Liability for Unpaid Losses (Details) - Non-life Run-off $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Liability for Claims and Claims Adjustment Expense [Line Items]
Carrying value	$ 1,252,445
Aggregate amount of discount	329,803
Interest Accretion	33,847
ULAE
ULAE, carrying value	$ 93,836
ULAE, discount rate	3.00%
ULAE, aggregate amount of discount	$ 25,953
ULAE, interest accretion	3,621
Asbestos
Liability for Claims and Claims Adjustment Expense [Line Items]
Carrying value	$ 712,890
Discount rate	2.30%
Aggregate amount of discount	$ 222,138
Interest Accretion	18,637
Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Carrying value	$ 1,003
Discount rate	2.00%
Aggregate amount of discount	$ 122
Interest Accretion	10
Casualty
Liability for Claims and Claims Adjustment Expense [Line Items]
Carrying value	$ 120,480
Discount rate	2.80%
Aggregate amount of discount	$ 28,233
Interest Accretion	3,751
Workers' compensation/personal accident
Liability for Claims and Claims Adjustment Expense [Line Items]
Carrying value	$ 69,266
Discount rate	3.00%
Aggregate amount of discount	$ 19,497
Interest Accretion	4,142
Marine, Aviation and Transit
Liability for Claims and Claims Adjustment Expense [Line Items]
Carrying value	$ 71,138
Discount rate	2.00%
Aggregate amount of discount	$ 9,520
Interest Accretion	799
Construction defect
Liability for Claims and Claims Adjustment Expense [Line Items]
Carrying value	$ 38,819
Discount rate	2.90%
Aggregate amount of discount	$ 5,513
Interest Accretion	1,171
Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Carrying value	$ 145,013
Discount rate	2.00%
Aggregate amount of discount	$ 18,827
Interest Accretion	$ 1,716

Policy Benefits for Life Con108

Policy Benefits for Life Contracts - Schedule of Life and Annuity Benefits (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Policy benefits for life contracts	$ 117.2	$ 112.1

Premiums Written and Earned - S

Premiums Written and Earned - Schedule of Net Premiums Written and Earned (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effects of Reinsurance [Line Items]
Gross, premiums written									$ 1,068,453	$ 1,022,342	$ 1,015,383
Ceded, premiums written									(458,063)	(218,406)	(228,229)
Net, premiums written									610,390	803,936	787,154
Gross, premiums earned									1,047,287	1,003,833	1,038,563
Ceded, premiums earned									(434,166)	(180,319)	(284,819)
Net, premiums earned	$ 160,627	$ 148,025	$ 155,571	$ 148,898	$ 216,188	$ 205,730	$ 208,709	$ 192,887	613,121	823,514	753,744
Non-life Run-off
Effects of Reinsurance [Line Items]
Gross, premiums written									14,102	17,316	38,704
Ceded, premiums written									(7,620)	(8,114)	(16,110)
Net, premiums written									6,482	9,202	22,594
Gross, premiums earned									23,950	25,989	116,494
Ceded, premiums earned									(9,788)	(9,234)	(72,125)
Net, premiums earned									14,162	16,755	44,369
Atrium
Effects of Reinsurance [Line Items]
Gross, premiums written									153,472	143,170	149,082
Ceded, premiums written									(19,258)	(2,733)	(14,502)
Net, premiums written									134,214	140,437	134,580
Gross, premiums earned									152,278	140,438	149,310
Ceded, premiums earned									(17,531)	(16,022)	(14,635)
Net, premiums earned									134,747	124,416	134,675
StarStone
Effects of Reinsurance [Line Items]
Gross, premiums written									895,160	854,699	824,714
Ceded, premiums written									(430,259)	(206,663)	(196,287)
Net, premiums written									464,901	648,036	628,427
Gross, premiums earned									865,159	830,186	769,875
Ceded, premiums earned									(405,756)	(153,578)	(196,729)
Net, premiums earned									459,403	676,608	573,146
Other
Effects of Reinsurance [Line Items]
Gross, premiums written									5,719	7,157	2,883
Ceded, premiums written									(926)	(896)	(1,330)
Net, premiums written									4,793	6,261	1,553
Gross, premiums earned									5,900	7,220	2,884
Ceded, premiums earned									(1,091)	(1,485)	(1,330)
Net, premiums earned									$ 4,809	$ 5,735	$ 1,554

Goodwill, Intangible Assets 110

Goodwill, Intangible Assets and Deferred Charges - Schedule of Goodwill, Intangible Assets and Deferred Charges (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill, Beginning balance	$ 73,071	$ 73,071
Goodwill, Acquired during the year	0	0
Goodwill, Ending balance	73,071	73,071	$ 73,071
Finite-lived Intangible Assets [Roll Forward]
Intangible assets with a definite life, Beginning balance	24,753	31,202
Intangible assets with a definite life, Acquired during the year	0	0
Intangible assets with a definite life, Amortization	(4,266)	(6,449)
Intangible assets with a definite life, Ending balance	20,487	24,753	31,202
Indefinite-lived Intangible Assets [Roll Forward]
Intangible assets with an indefinite life, Beginning balance	87,031	87,031
Intangible assets with an indefinite life, Acquired during the year	0	0
Intangible assets with an indefinite life, Ending balance	87,031	87,031	87,031
Goodwill and Intangible Assets [Roll Forward]
Goodwill and intangible assets, Beginning Balance	184,855	191,304
Goodwill and intangible assets, Acquired during the year	0	0
Intangible assets with a definite life, Amortization	(4,266)	(6,449)
Goodwill and intangible assets, Ending balance	180,589	184,855	191,304
Movement in Intangible Assets Arising from Insurance Contracts Acquired in Business Combination [Roll Forward] (Deprecated 2017-01-31)
Intangible assets with a definite life - FVA, Beginning balance	145,158	127,170
Intangible assets with a definite life - FVA, Acquired during the period	958	37,005
Intangible assets with a definite life - FVA, Amortization	(5,723)	(19,017)	5,600
Intangible assets with a definite life - FVA, Ending balance	140,393	145,158	127,170
Deferred Charges [Roll Forward]
Less: deferred charges on retroactive reinsurance	94,551	255,911	0
Other assets - Deferred Charge, Acquired during the year	0	7,467
Amortization of deferred charges	14,359	168,827	15,265
Plus: deferred charges on retroactive reinsurance	$ 80,192	$ 94,551	$ 255,911

Goodwill, Intangible Assets 111

Goodwill, Intangible Assets and Deferred Charge - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Goodwill	$ 73,071,000	$ 73,071,000	$ 73,071,000
Impairment of goodwill	0
Amortization of intangible assets	4,300,000	6,400,000	9,800,000
Impairment of intangible assets with a definite life		4,000,000
Intangible assets FVA amortization (accretion)	5,723,000	19,017,000	(5,600,000)
Amortization of deferred charges - related to reduction in liability for losses and LAE	14,400,000	130,200,000
Amortization of deferred charges - primarily related to change in expected return on underlying assets	0	38,600,000
Intangible assets with a definite life, fair value adjustments	140,393,000	145,158,000	$ 127,170,000
Discontinued operations, held-for-sale | Pavonia
Segment Reporting Information [Line Items]
Intangible assets FVA amortization (accretion)	6,100,000	7,000,000
Fair value adjustments, policy benefits for life and annuity contracts
Segment Reporting Information [Line Items]
Intangible assets with a definite life, fair value adjustments	$ 2,700,000	46,500,000
Minimum
Segment Reporting Information [Line Items]
Intangible assets useful life	4 years
Maximum
Segment Reporting Information [Line Items]
Intangible assets useful life	15 years
Non-life Run-off
Segment Reporting Information [Line Items]
Goodwill	$ 21,200,000	21,200,000
Atrium Segment
Segment Reporting Information [Line Items]
Goodwill	38,900,000	38,900,000
StarStone
Segment Reporting Information [Line Items]
Goodwill	$ 13,000,000	$ 13,000,000

Goodwill, Intangible Assets 112

Goodwill, Intangible Assets and Deferred Charge - Summary of Gross Carrying Value, Accumulated Amortization and Net Carrying Value of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Indefinite-lived Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	$ 87,031	$ 87,031	$ 87,031
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value, Fair value adjustments	320,241	319,283
Accumulated Amortization, Fair value adjustments	(179,848)	(174,125)
Net Carrying Value, Fair value adjustments	140,393	145,158	127,170
Gross Carrying Value	42,000	42,000
Accumulated Amortization	(21,513)	(17,247)
Intangible assets with a definite life, Net Carrying Value	20,487	24,753	31,202
Deferred charge on retroactive reinsurance, Gross Carrying Value	278,643	278,643
Deferred charge on retroactive reinsurance, Accumulated Amortization	(198,451)	(184,092)
Deferred charge on retroactive reinsurance, Net Carrying Value	80,192	94,551	$ 255,911	$ 0
Lloyd’s syndicate capacity
Indefinite-lived Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	37,031	37,031
Licenses
Indefinite-lived Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	19,900	19,900
Management contract
Indefinite-lived Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	30,100	30,100
Losses and LAE liabilities
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value, Fair value adjustments	462,455	458,202
Accumulated Amortization, Fair value adjustments	(345,449)	(334,475)
Net Carrying Value, Fair value adjustments	117,006	123,727
Reinsurance balances recoverable
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value, Fair value adjustments	(179,219)	(175,924)
Accumulated Amortization, Fair value adjustments	165,579	160,350
Net Carrying Value, Fair value adjustments	(13,640)	(15,574)
Other Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value, Fair value adjustments	(48,840)	(48,840)
Accumulated Amortization, Fair value adjustments	440	0
Net Carrying Value, Fair value adjustments	(48,400)	(48,840)
Other Liabilities
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value, Fair value adjustments	85,845	85,845
Accumulated Amortization, Fair value adjustments	(418)	0
Net Carrying Value, Fair value adjustments	85,427	85,845
Distribution channel
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	20,000	20,000
Accumulated Amortization	(5,444)	(4,111)
Intangible assets with a definite life, Net Carrying Value	14,556	15,889
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	15,000	15,000
Accumulated Amortization	(13,210)	(10,978)
Intangible assets with a definite life, Net Carrying Value	1,790	4,022
Brand
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	7,000	7,000
Accumulated Amortization	(2,859)	(2,158)
Intangible assets with a definite life, Net Carrying Value	4,141	4,842
Fair value adjustments, policy benefits for life and annuity contracts
Finite-Lived Intangible Assets [Line Items]
Net Carrying Value, Fair value adjustments	$ 2,700	$ 46,500

Goodwill, Intangible Assets 113

Goodwill, Intangible Assets and Deferred Charge - Summary of Estimated Amortization Expense of Intangible Assets (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Segment Reporting Information [Line Items]
2,018	$ 7,874
2,019	7,457
2,020	8,148
2,021	8,257
2,022	7,957
Non-life Run-off
Segment Reporting Information [Line Items]
2,018	8,082
2,019	7,927
2,020	7,634
2,021	7,169
2,022	6,559
Atrium
Segment Reporting Information [Line Items]
2,018	(463)
2,019	(69)
2,020	760
2,021	1,254
2,022	1,506
StarStone
Segment Reporting Information [Line Items]
2,018	255
2,019	(401)
2,020	(246)
2,021	(166)
2,022	$ (108)

Debt Obligations - Amounts of O

Debt Obligations - Amounts of Outstanding and Accrued Interest (Detail) - USD ($) $ in Thousands	Mar. 10, 2017	Nov. 18, 2016	Dec. 24, 2014	Sep. 16, 2014	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Total debt obligations					$ 646,689	$ 673,603
Senior Notes | Senior Notes Due 2022
Line of Credit Facility [Line Items]
Term	5 years
Long-term debt					350,000	0
Unamortized debt issuance costs					(2,484)	0
Total debt obligations					347,516	0
Loan facilities | EGL Revolving Credit Facility
Line of Credit Facility [Line Items]
Term				5 years
Total debt obligations					225,110	535,103
Loan facilities | Sussex Facility
Line of Credit Facility [Line Items]
Term			4 years
Total debt obligations					0	63,500
Loan facilities | EGL Term Loan Facility
Line of Credit Facility [Line Items]
Term		3 years
Total debt obligations					$ 74,063	$ 75,000

Debt Obligations - Additional I

Debt Obligations - Additional Information (Detail) € in Millions	Mar. 10, 2017USD ($)	Nov. 18, 2016USD ($)	Aug. 05, 2016USD ($)	Dec. 24, 2014USD ($)financial_institution	Sep. 16, 2014	Feb. 28, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017EUR (€)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017EUR (€)	Mar. 20, 2017USD ($)	Dec. 31, 2016EUR (€)
Line of Credit Facility [Line Items]
Receipt of loans															$ 874,100,000		$ 571,048,000	$ 657,700,000
Repayment of loans															912,140,000		493,250,000	377,500,000
Interest expense							$ 7,251,000	$ 6,410,000	$ 7,573,000	$ 6,868,000	$ 4,796,000	$ 5,027,000	$ 5,421,000	$ 5,398,000	28,102,000		20,642,000	19,403,000
Currency translation gain (loss)															30,174,000		4,793,000	(24,694,000)
Net Investment Hedging
Line of Credit Facility [Line Items]
Repayment of loans															29,500,000	€ 25
Gross notional amount							60,100,000				$ 88,500,000				60,100,000		88,500,000		€ 50		€ 75
Currency translation gain (loss)															9,400,000		6,000,000
Foreign exchange losses															(1,100,000)
Loan facilities
Line of Credit Facility [Line Items]
Receipt of loans															874,100,000
Repayment of loans															912,100,000
Interest expense															26,000,000		$ 20,300,000	$ 19,300,000
Loan facilities | EGL Revolving Credit Facility
Line of Credit Facility [Line Items]
Facility term					5 years
Maximum borrowing capacity																				$ 831,300,000
Available unutilized capacity							$ 607,200,000								607,200,000
Frequency of interest payments (at least)			6 months
Covenant compliance, consolidated indebtedness to total capitalization (not greater than)			0.35
Covenant compliance, net income (loss) threshold			$ 1,500,000,000
Covenant compliance, net income threshold percent			50.00%
Covenant compliance, percentage of proceeds of common stock issuance			75.00%
Loan facilities | EGL Revolving Credit Facility | Subsequent event
Line of Credit Facility [Line Items]
Receipt of loans						$ 307,400,000
Repayment of loans						132,000,000
Available unutilized capacity						$ 431,800,000
Loan facilities | Sussex Facility
Line of Credit Facility [Line Items]
Receipt of loans				$ 109,000,000
Facility term				4 years
Number of financial institutions | financial_institution				2
Percentage of consideration payable for acquisition				50.00%
Loan facilities | EGL Term Loan Facility
Line of Credit Facility [Line Items]
Facility term		3 years
Maximum borrowing capacity		$ 75,000,000
Frequency of interest payments (at least)		3 months
Repayments of debt															$ 900,000
Debt instrument, covenant compliance, capital resources multiplier for solvency requirements		1.1
Senior Notes | Senior Notes Due 2022
Line of Credit Facility [Line Items]
Aggregate principal amount	$ 350,000,000
Interest rate	4.50%						4.50%								4.50%				4.50%
Redemption price, percentage of principal amount	100.00%
Debt issuance costs	$ 2,900,000
Facility term	5 years

Noncontrolling Interest - Redee

Noncontrolling Interest - Redeemable Noncontrolling Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Balance at beginning of year	$ 454,522	$ 417,663
Dividends paid	(27,458)	0
Net earnings attributable to RNCI	19,619	40,639
Accumulated other comprehensive income attributable to RNCI	1,945	651
Change in redemption value of RNCI	30,978	(4,431)
Balance at end of year	$ 479,606	$ 454,522
Atrium | Northshore
Redeemable Noncontrolling Interest [Line Items]
Ownership interest held by parent	100.00%
Arden | Northshore
Redeemable Noncontrolling Interest [Line Items]
Ownership interest held by parent	100.00%
Starstone | StarStone Holdings
Redeemable Noncontrolling Interest [Line Items]
Ownership interest held by parent	100.00%
Subsidiaries | Trident
Redeemable Noncontrolling Interest [Line Items]
Ownership interest held by noncontrolling owners	39.30%
Subsidiaries | Dowling
Redeemable Noncontrolling Interest [Line Items]
Ownership interest held by noncontrolling owners	1.70%

Noncontrolling Interest - Nonco

Noncontrolling Interest - Noncontrolling Interest (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Abstract]
Noncontrolling interest	$ 9,264	$ 8,520

Share Capital (Detail)

Share Capital (Detail)	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2016$ / sharesshares	Mar. 31, 2017shares	Dec. 31, 2016$ / sharesshares	Dec. 31, 2015shares	Dec. 31, 2017vote$ / sharesshares
Class of Stock [Line Items]
Common shares, authorized (shares)	111,000,000		111,000,000		111,000,000
Common shares, par value (dollars per share) | $ / shares	$ 1		$ 1		$ 1
Preference shares, authorized (shares)	45,000,000		45,000,000		45,000,000
Preferred shares, par value (dollars per share) | $ / shares	$ 1		$ 1		$ 1
Warrants exercised (shares)	164,919
Voting ordinary shares
Class of Stock [Line Items]
Common shares, par value (dollars per share) | $ / shares	$ 1		$ 1		$ 1
Common stock, number of votes | vote					1
Percentage ownership (or more) of voting ordinary shares entitled to less than one vote per share					9.50%
Ordinary shares, issued (shares)	16,175,250		16,175,250		16,402,279
Ordinary shares, outstanding (shares)	16,175,250		16,175,250		16,402,279
Series C non-voting convertible ordinary shares
Class of Stock [Line Items]
Conversion ratio, issued upon conversion (shares)					1
Aggregate voting power of Company's issued share capital (percent) (not to exceed)					0.01%
Ordinary shares, issued (shares)	2,792,157		2,792,157		2,599,672
Ordinary shares, outstanding (shares)	2,792,157		2,792,157		2,599,672
Warrants outstanding (shares)					175,901
Warrants, exercise price (dollars per share) | $ / shares					$ 115
Stock issued upon exercise of Warrants (shares)	66,520
Stock issued upon conversion (shares)		192,485
Series B non-voting convertible ordinary shares
Class of Stock [Line Items]
Ordinary shares, issued (shares)					0
Ordinary shares, outstanding (shares)					0
Series D non-voting convertible ordinary shares
Class of Stock [Line Items]
Ordinary shares, issued (shares)					0
Ordinary shares, outstanding (shares)					0
Series E non-voting convertible ordinary shares
Class of Stock [Line Items]
Ordinary shares, issued (shares)	404,771		404,771	714,015	404,771
Ordinary shares, outstanding (shares)	404,771		404,771	714,015	404,771
Conversion of stock, shares converted (shares)			309,244
Non-voting ordinary shares
Class of Stock [Line Items]
Common shares, par value (dollars per share) | $ / shares	$ 1		$ 1		$ 1
Series C non-voting preferred shares
Class of Stock [Line Items]
Preferred shares, issued (shares)	388,571		388,571		388,571
Preferred shares, liquidation preference (dollars per share) | $ / shares					$ 0.001
Series B non-voting preferred shares
Class of Stock [Line Items]
Stock issued upon conversion (shares)				(714,015)

Earnings Per Share - Comparison

Earnings Per Share - Comparison of Basic and Diluted Earnings per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net earnings from continuing operations									$ 300,465	$ 252,844	$ 222,322
Net earnings (losses) from discontinuing operations									10,993	11,963	(2,031)
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED	$ 127,599	$ 38,993	$ 90,186	$ 54,680	$ 22,645	$ 156,048	$ 40,594	$ 45,520	$ 311,458	$ 264,807	$ 220,291
Denominator:
Weighted-average ordinary shares outstanding — basic (shares)									19,388,621	19,299,426	19,252,072
Effect of dilutive securities:
Share-based compensation plans (shares)									62,732	48,428	76,801
Warrants (in shares)									76,238	99,387	78,883
Diluted (shares)									19,527,591	19,447,241	19,407,756
Basic:
Net earnings from continuing operations (dollars per share)	$ 5.96	$ 1.83	$ 4.90	$ 2.80	$ 0.91	$ 7.89	$ 1.98	$ 2.34	$ 15.50	$ 13.10	$ 11.55
Net earnings (loss) from discontinuing operations (dollars per share)	0.62	0.18	(0.25)	0.02	0.26	0.20	0.12	0.02	0.56	0.62	(0.11)
Net earnings per ordinary share (dollars per share)	6.58	2.01	4.65	2.82	1.17	8.09	2.10	2.36	16.06	13.72	11.44
Diluted:
Net earnings from continuing operations (dollars per share)	5.90	1.81	4.87	2.78	0.90	7.82	1.97	2.33	15.39	13	11.46
Net earnings (loss) from discontinuing operations (dollars per share)	0.61	0.18	(0.25)	0.02	0.26	0.20	0.12	0.02	0.56	0.62	(0.11)
Net earnings per ordinary share (dollars per share)	$ 6.51	$ 1.99	$ 4.62	$ 2.80	$ 1.16	$ 8.02	$ 2.09	$ 2.35	$ 15.95	$ 13.62	$ 11.35

Share-Based Compensation and120

Share-Based Compensation and Pensions - Restricted Shares and Restricted Share Units (Detail) - Restricted shares and restricted share awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Nonvested — January 1	78,992
Granted (shares)	56,333
Vested (shares)	(31,199)
Forfeited (shares)	(4,821)
Nonvested — December 31	99,305	78,992
Weighted- Average Share Price of Award
Nonvested - January 1 (dollars per share)	$ 165.94
Granted (dollars per share)	202.82
Vested (dollars per share)	163.75
Forfeited (dollars per share)	159.93
Nonvested - December 31 (dollars per share)	$ 187.84	$ 165.94
Compensation costs	$ 7.3	$ 3	$ 6.1
Unrecognized compensation cost	$ 11.7
Unrecognized compensation cost, period of recognition	1 year 9 months 1 day
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years

Share-Based Compensation and121

Share-Based Compensation and Pensions - Cash-Settled Stock Appreciation Rights (Detail) - Cash-Settled Stock Appreciation Rights - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance, beginning of year, Number of SARs (shares)	941,168
Exercised, Number of SARs (shares)	(630,301)
Balance, end of year, Number of SARs (shares)	310,867	941,168
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Balance, beginning of year, Weighted Average Exercise Price of SARs (dollars per share)	$ 140.70
Exercised, Weighted Average Exercise Price of SARS (dollars per share)	140.39
Balance, end of year, Weighted Average Exercise Price of SARs (dollars per share)	$ 141.30	$ 140.70
Balance, end of year, Weighted Average Remaining Contractual Term (in years)	1 year 7 months
Balance, end of year, Aggregate Intrinsic Value	$ 18,471
Closing price per share, ordinary shares (dollars per share)	$ 200.75
Compensation costs	$ 8,900	$ 35,600	$ 8,900
Unrecognized compensation cost	$ 200
Unrecognized compensation cost, period of recognition	7 months 8 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Granted (dollars per share)	$ 75.38	$ 62.39	$ 29.02
Weighted-average volatility	19.44%	19.82%	22.08%
Weighted-average risk-free interest rate	1.65%	1.12%	1.29%
Dividend yield	0.00%	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise period	4 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise period	10 years

Share-Based Compensation and122

Share-Based Compensation and Pensions - Performance Share Units (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Performance share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
PSU's Granted at Target (shares)	128,196
Nonvested Units (shares)	0	0		126,753
Number of Shares
Nonvested — January 1	0
Granted (shares)	128,196
Forfeited (shares)	(1,443)
Nonvested — December 31	126,753	0
Weighted- Average Share Price of Award
Nonvested - January 1 (dollars per share)	$ 0
Granted (dollars per share)	188.15
Forfeited (dollars per share)	196.11
Nonvested - December 31 (dollars per share)	$ 188.06	$ 0
Compensation costs	$ 5.8	$ 0	$ 0
Unrecognized compensation cost				$ 18
Unrecognized compensation cost, period of recognition	2 years 3 months 2 days
Performance share units | Performance Target One | Minimum
Weighted- Average Share Price of Award
Share settlement percentage	100.00%
Performance share units | Performance Target One | Maximum
Weighted- Average Share Price of Award
Share settlement percentage	150.00%
Performance share units | Performance Target Two | Minimum
Weighted- Average Share Price of Award
Share settlement percentage	50.00%
Performance share units | Performance Target Two | Maximum
Weighted- Average Share Price of Award
Share settlement percentage	100.00%
Performance share units | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSU's Granted at Target (shares)	36,321
Nonvested Units (shares)	34,878			34,878
Change in FDBVPS (3 - year)
Threshold	20.00%
Target	30.00%
Maximum	40.00%
Number of Shares
Granted (shares)	36,321
Nonvested — December 31	34,878
Performance share units | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSU's Granted at Target (shares)	91,875
Nonvested Units (shares)	91,875			91,875
Change in FDBVPS (3 - year)
Threshold	30.30%
Target	35.70%
Maximum	41.00%
Number of Shares
Granted (shares)	91,875
Nonvested — December 31	91,875
Stock Appreciation Rights (SARs)
Weighted- Average Share Price of Award
Granted (dollars per share)	$ 75.38	$ 62.39	$ 29.02
Compensation costs	$ 8.9	$ 35.6	$ 8.9
Unrecognized compensation cost				$ 0.2
Unrecognized compensation cost, period of recognition	7 months 8 days

Share-Based Compensation and123

Share-Based Compensation and Pensions - Other Share-Based Compensation Plans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)directorshares	Dec. 31, 2015USD ($)shares
Long-term incentive plans | Time-based restricted shares
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Compensation costs	$ 3.2	$ 2.8	$ 3.9
Unrecognized compensation cost	$ 5.4
Unrecognized compensation cost, period of recognition	1 year 10 months 12 days
Long-term incentive plans | Minimum | Time-based restricted shares
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period	2 years
Long-term incentive plans | Maximum | Time-based restricted shares
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period	3 years
Deferred compensation plan | Director | Share-based compensation plans
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Restricted share units credited to the accounts of non-employee directors (shares) | shares	3,852	4,298	5,174
Expenses related to the restricted share units	$ 0.8	$ 0.7	$ 1
Deferred compensation plan | Director | Share-based compensation plans | Share-based compensation plans
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Deferred compensation arrangement, shares converted | shares		2,393
Number of directors | director		2
Employee share purchase plan | Employee stock
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Compensation costs	$ 0.4	$ 0.3	$ 0.3
Stock issued to employees (shares) | shares	12,401	12,234	11,998

Share-Based Compensation and124

Share-Based Compensation and Pensions - Pension Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan expense	$ 12.2	$ 10.8	$ 10.3
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pension expense	1.9	2.3	$ 0.6
Unfunded liability	9.4	10.3
Accrued liability	$ 9.4	$ 10.3

Taxation - Additional Informati

Taxation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Bermuda income taxes at statutory rate	0.00%	0.00%	0.00%
Valuation allowance	$ 188,300,000	$ 290,861,000
Increase (decrease) in valuation allowance	(102,600,000)
Accrued interest and penalties related to unrecognized tax benefits	0	0	$ 0
Unrecognized tax benefits	$ 0	$ 0	$ 0

Taxation - Earnings before Inco

Taxation - Earnings before Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic (Bermuda)									$ 167,263	$ 191,647	$ 61,695
Foreign									147,148	135,677	163,327
EARNINGS BEFORE INCOME TAXES	$ 112,178	$ 22,098	$ 111,330	$ 68,805	$ 35,395	$ 174,707	$ 55,453	$ 61,769	$ 314,411	$ 327,324	$ 225,022

Taxation - Tax Expense for Inco

Taxation - Tax Expense for Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Domestic (Bermuda)									$ 0	$ 0	$ 0
Foreign									10,299	21,485	30,028
Total current tax expense									10,299	21,485	30,028
Deferred:
Domestic (Bermuda)									0	0	0
Foreign									(16,694)	13,389	(17,378)
Total deferred tax expense									(16,694)	13,389	(17,378)
Total tax expense (benefit) on continuing operations	$ 9,629	$ (1,432)	$ (4,731)	$ 2,929	$ (11,228)	$ (8,227)	$ (8,050)	$ (7,369)	$ 6,395	$ (34,874)	$ (12,650)

Taxation - Reconciliation of Ea

Taxation - Reconciliation of Earnings before Income Taxes Computed by Applying Effective Rate (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Earnings before income tax	$ 112,178	$ 22,098	$ 111,330	$ 68,805	$ 35,395	$ 174,707	$ 55,453	$ 61,769	$ 314,411	$ 327,324	$ 225,022
Bermuda income taxes at statutory rate									0.00%	0.00%	0.00%
Foreign income tax rate differential									13.10%	8.80%	17.60%
Change relating to US Tax Reform									20.30%	0.00%	0.00%
Change in valuation allowance									(34.90%)	(0.10%)	(10.50%)
Other									(0.50%)	2.00%	(1.50%)
Effective tax rate									(2.00%)	10.70%	5.60%

Taxation - Components of Deferr

Taxation - Components of Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 177,695	$ 262,271
Tax credits and other carryforwards	0	7,487
Insurance reserves	9,082	19,265
Unearned premiums	1,690	8,760
Lloyd's underwriting losses taxable in future periods	9,131	6,581
Provisions for bad debt	6,371	16,018
Other deferred tax assets	1,944	7,946
Gross deferred tax assets	205,913	328,328
Valuation allowance	(188,300)	(290,861)
Deferred tax assets	17,613	37,467
Deferred tax liabilities:
Unrealized gains on investments	(3,798)	(12,804)
Intangible assets	0	(20,615)
Other deferred tax liabilities	(16,076)	(21,030)
Deferred tax liabilities	(19,874)	(54,449)
Net deferred tax liability	$ (2,261)	$ (16,982)

Taxation - Net Operating Loss C

Taxation - Net Operating Loss Carryforwards (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Tax effect of operating loss carryforward	$ 177,695	$ 262,271
Foreign Tax Authority | United States
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	528,226
Tax effect of operating loss carryforward	110,927
Foreign Tax Authority | United Kingdom
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	324,784
Tax effect of operating loss carryforward	62,521
Foreign Tax Authority | Other
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	19,105
Tax effect of operating loss carryforward	1,236
Capital loss carryforward | Foreign Tax Authority | United States
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	14,339
Tax effect of capital loss carryforward	$ 3,011

Taxation Taxation - Deferred Ta

Taxation Taxation - Deferred Tax Ending Balance (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net Deferred Tax Asset / (Liability)	$ (2,261)	$ (16,982)
United States
Segment Reporting Information [Line Items]
Deferred Tax Assets, Net	4,947
Net Deferred Tax Asset / (Liability)		(513)
United Kingdom
Segment Reporting Information [Line Items]
Net Deferred Tax Asset / (Liability)	(5,150)	(12,297)
Other
Segment Reporting Information [Line Items]
Net Deferred Tax Asset / (Liability)	$ (2,058)	$ (4,172)

Taxation Taxation - Impact of U

Taxation Taxation - Impact of US Tax Reform (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Income Tax Disclosure [Abstract]
Reduction to valuation allowance and reclass to DTA	$ 63.8
Deferred tax assets	$ 7.4

Related Party Transactions - St

Related Party Transactions - Stone Point Capital LLC (Details) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Jul. 31, 2012shares	Dec. 31, 2017USD ($)Investment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Nov. 06, 2013general_partner
Related Party Transaction [Line Items]
Redeemable noncontrolling interest	$ 479,606				$ 454,522					$ 479,606	$ 454,522	$ 417,663
Investments in funds	913,392				937,047					913,392	937,047
Investment in registered investment company	106,603				95,047					106,603	95,047
Net realized and unrealized gains (losses)	50,637	$ 29,301	$ 51,877	$ 58,519	(61,570)	$ 66,608	$ 34,503	$ 38,277		190,334	77,818	$ (41,523)
Affiliated entity
Related Party Transaction [Line Items]
Investments in funds	283,300									283,300
Sound Point Capital
Related Party Transaction [Line Items]
Separate account assets	$ 63,600				61,200					$ 63,600	61,200
Trident | Affiliated entity
Related Party Transaction [Line Items]
Voting ordinary shares acquired (shares) | shares									1,350,000
Voting ordinary shares acquired, percent	8.20%									8.20%
Number of newly elected board of directors | general_partner													1
Number of general partners | general_partner													4
Agreement period										90 days
Redeemable noncontrolling interest	$ 459,600				435,600					$ 459,600	435,600
Investments in funds	255,900				232,100					255,900	232,100
Investment in registered investment company	22,100				20,900					22,100	20,900
Trident | Affiliated entity | Fund Investments
Related Party Transaction [Line Items]
Net realized and unrealized gains (losses)										22,300	(17,200)
Trident | Affiliated entity | Registered Investment Company
Related Party Transaction [Line Items]
Net realized and unrealized gains (losses)										(2,900)	(400)
Interest income										2,500	3,100
Eagle Point Credit and PRIMA Capital Advisors | Affiliated entity
Related Party Transaction [Line Items]
Separate account assets	183,400				215,000					183,400	215,000
Sound Point Capital | Affiliated entity
Related Party Transaction [Line Items]
Investments in funds	27,400				25,400					27,400	25,400
Net realized and unrealized gains (losses)										$ 2,000	1,900
Number of invested funds | Investment										2
Sound Point Capital | Affiliated entity | Management fees
Related Party Transaction [Line Items]
Management fees										$ 300	500
CLO equities
Related Party Transaction [Line Items]
Investments in funds	56,765				61,565					56,765	61,565
CLO equities | Sound Point Capital | Affiliated entity
Related Party Transaction [Line Items]
Investments in funds	$ 17,800				$ 20,300					17,800	20,300
Net realized and unrealized gains (losses)										2,500	(2,100)
Interest income										$ 4,300	$ 6,700

Related Party Transactions - CP

Related Party Transactions - CPPIB (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016	May 05, 2015
CPPIB and Management of Wilton Re | Affiliated entity
Related Party Transaction [Line Items]
Voting ordinary shares acquired, percent			9.10%
Economic ownership percentage			16.00%
Reinsurance balances recoverable	$ 7	$ 9.4
Wilton Re | CPPIB and Management of Wilton Re
Related Party Transaction [Line Items]
Ownership interest held by parent	100.00%			100.00%

Related Party Transactions - Ka

Related Party Transactions - KaylaRe (Details) $ in Thousands	Dec. 15, 2016USD ($)	Feb. 28, 2018USD ($)	Dec. 31, 2017USD ($)membershares	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)membershares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Mar. 01, 2018
Related Party Transaction [Line Items]
Related party fee income											$ 8,700	$ 6,800
Ceded, premiums earned											434,166	180,319	$ 284,819
Net incurred losses and LAE			$ 30,327	$ 75,712	$ 9,620	$ 77,892	$ 1,321	$ (6,902)	$ 96,462	$ 83,218	193,551	174,099	104,333
Acquisition costs			21,449	24,281	30,355	20,821	47,619	50,074	43,847	45,029	96,906	186,569	163,716
Fees and commission income			19,627	$ 15,895	$ 18,667	$ 11,914	13,266	$ 9,187	$ 10,487	$ 6,424	66,103	39,364	$ 39,347
Reinsurance recoverable			2,021,030				1,460,743				2,021,030	1,460,743
Ceded unearned premium			13,700								13,700
Reinsurance balances payable			236,697				394,021				236,697	394,021
KaylaRe
Related Party Transaction [Line Items]
Initial capital raise	$ 620,000
KaylaRe | Fitzwilliam | Subsidiaries
Related Party Transaction [Line Items]
Ceded reinsurance receivables			$ 0				177,200				0	177,200
Fees and commission income											$ 18,800	7,100
KaylaRe | Starstone
Related Party Transaction [Line Items]
Percentage reinsured of certain businesses											35.00%
Ceded, premiums earned											$ 234,100	117,600
Net incurred losses and LAE											155,400	75,700
Acquisition costs											$ 99,500	42,500
Equity method investee | KaylaRe
Related Party Transaction [Line Items]
Shareholders Agreement, right to appoint board members, number of members | member			1								1
Shareholders Agreement, minimum number of shares owned for right to appoint board members | shares			1,250,000								1,250,000
Shareholders Agreement, lock-up period on common shares	5 years
Reinsurance recoverable			$ 357,400				242,100				$ 357,400	242,100
Ceded unearned premium			116,400				109,000				116,400	109,000
Funds held			174,200				182,300				174,200	182,300
Reinsurance balances payable			232,900				132,600				232,900	132,600
Ceded acquisition costs			$ 36,100				41,200				$ 36,100	41,200
Affiliated entity | Hillhouse Affiliates
Related Party Transaction [Line Items]
Economic ownership percentage			9.98%								9.98%
Voting ordinary shares acquired, percent			3.20%								3.20%
Affiliated entity | Stone Point
Related Party Transaction [Line Items]
Economic ownership percentage			6.90%								6.90%
Voting ordinary shares acquired, percent			8.20%								8.20%
KaylaRe
Related Party Transaction [Line Items]
Equity method investment ownership percentage			48.20%								48.20%
Equity method investment			$ 309,800				$ 294,600				$ 309,800	294,600
Net incurred losses and LAE												$ 1,400
Subsequent event | Equity method investee | KaylaRe
Related Party Transaction [Line Items]
Ownership percentage acquired														51.80%
Value of ordinary shares issued		$ 398,300
Subsequent event | Affiliated entity | Hillhouse Affiliates
Related Party Transaction [Line Items]
Economic ownership percentage														17.10%
Voting ordinary shares acquired, percent														9.70%
Subsequent event | Affiliated entity | Stone Point
Related Party Transaction [Line Items]
Economic ownership percentage														7.60%
Voting ordinary shares acquired, percent														9.10%

Related Party Transactions - Hi

Related Party Transactions - Hillhouse (Details) - USD ($) $ in Thousands	Jan. 02, 2018	Mar. 31, 2018	Mar. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Investments in funds				$ 913,392	$ 937,047
Affiliated entity
Related Party Transaction [Line Items]
Investments in funds				$ 283,300
Hillhouse Affiliates | Affiliated entity
Related Party Transaction [Line Items]
Voting ordinary shares acquired, percent				3.20%
Economic ownership percentage				9.98%
Hillhouse | KaylaRe | Affiliated entity
Related Party Transaction [Line Items]
Investments in funds				$ 456,700	$ 350,000
Subsequent event | Hillhouse Affiliates | Affiliated entity
Related Party Transaction [Line Items]
Voting ordinary shares acquired, percent			9.70%
Economic ownership percentage			17.10%
Subsequent event | Subsidiaries | Hillhouse | Cavello Bay
Related Party Transaction [Line Items]
Payments for investments	$ 200,000
Scenario, Forecast | Subsidiaries | Hillhouse | Cavello Bay
Related Party Transaction [Line Items]
Payments for investments		$ 50,000

Related Party Transactions - Mo

Related Party Transactions - Monument (Details) € in Millions, $ in Millions	15 Months Ended
	Dec. 31, 2017USD ($)	Aug. 29, 2017USD ($)	Aug. 29, 2017EUR (€)	Dec. 31, 2016USD ($)
Monument | Laguna | Not discontinued operations, disposed of by sale | Affiliated entity
Related Party Transaction [Line Items]
Consideration received		$ 30.8	€ 25.6
Monument
Related Party Transaction [Line Items]
Investment in common and preferred shares	$ 16
Equity method investment ownership percentage	26.60%
Equity method investment	$ 16			$ 0.2

Related Party Transactions - Cl

Related Party Transactions - Clear Spring (Details) - USD ($) $ in Thousands	Jan. 01, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Capitalized amount	$ 56,000
Ceded, premiums earned										$ 434,166	$ 180,319	$ 284,819
Ceded business										0	243,335	0
Acquisition costs		$ 21,449	$ 24,281	$ 30,355	$ 20,821	$ 47,619	$ 50,074	$ 43,847	$ 45,029	96,906	186,569	163,716
Reinsurance recoverable		2,021,030				1,460,743				2,021,030	1,460,743
Ceded unearned premium		13,700								13,700
Ceded other liabilities		14,000								14,000
Premiums earned, assumed										142,161	192,472	180,823
Net incurred losses and loss adjustment expenses		30,327	$ 75,712	$ 9,620	$ 77,892	1,321	$ (6,902)	$ 96,462	$ 83,218	193,551	174,099	104,333
Liability for losses and LAE		7,398,088				5,987,867				7,398,088	5,987,867	$ 5,720,149	$ 4,509,421
Unearned premiums		583,197				548,343				583,197	548,343
Funds held by reinsured companies		$ 175,383				$ 82,073				$ 175,383	82,073
Equity method investee | Clear Spring
Related Party Transaction [Line Items]
Equity method investment ownership percentage		20.00%								20.00%
Reinsurance recoverable		$ 9,100								$ 9,100
Ceded acquisition costs		3,200								3,200
Starstone | Clear Spring
Related Party Transaction [Line Items]
Equity method investment		10,600								10,600
Percentage reinsured of certain businesses	33.30%
Ceded, premiums earned										14,300
Ceded business										(9,500)
Acquisition costs										6,700
Cavello Bay | Clear Spring
Related Party Transaction [Line Items]
Percentage reinsured of certain businesses	25.00%
Acquisition costs										1,700
Premiums earned, assumed										3,600
Net incurred losses and loss adjustment expenses											$ 1,200
Liability for losses and LAE		2,200								2,200
Unearned premiums		3,400								3,400
Funds held by reinsured companies		$ 5,100								$ 5,100

Dividend Restrictions and St139

Dividend Restrictions and Statutory Financial Information - Summary of Statutory Capital and Surplus (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Bermuda
Statutory Accounting Practices [Line Items]
Minimum required statutory capital and surplus	$ 1,556,644	$ 792,652
Actual statutory capital and surplus	2,802,653	2,131,308
Statutory income	390,752	339,548	$ 147,883
United Kingdom
Statutory Accounting Practices [Line Items]
Minimum required statutory capital and surplus	453,160	532,132
Actual statutory capital and surplus	699,798	805,170
Statutory income	77,900	131,619	113,296
United States
Statutory Accounting Practices [Line Items]
Minimum required statutory capital and surplus	195,855	209,283
Actual statutory capital and surplus	589,029	662,942
Statutory income	(5,065)	(1,439)	14,964
Europe
Statutory Accounting Practices [Line Items]
Minimum required statutory capital and surplus	253,981	240,107
Actual statutory capital and surplus	444,870	286,039
Statutory income	$ (4,245)	$ 31,075	$ 1,856

Dividend Restrictions and St140

Dividend Restrictions and Statutory Financial Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)syndicate	Dec. 31, 2016USD ($)
Statutory Accounting Practices [Line Items]
Restricted net assets of consolidated subsidiaries	$ 2,500,000,000
Number of syndicates | syndicate	3
Bermuda
Statutory Accounting Practices [Line Items]
Target statutory capital and surplus percent	120.00%
Minimum liquidity ratio percent (not less than)	75.00%
Maximum percentage reduction in total statutory capital without prior approval of Bermuda regulator (percent) (or more)	15.00%
Minimum solvency requirement	$ 1,200,000,000	$ 1,300,000,000
United Kingdom
Statutory Accounting Practices [Line Items]
Minimum capital requirements	246,600,000	273,000,000
United States
Statutory Accounting Practices [Line Items]
Minimum levels of risk-based capital	385,400,000	402,000,000
United States and Canada
Statutory Accounting Practices [Line Items]
Minimum levels of risk-based capital	7,800,000	51,600,000
Maximum dividend payout without prior approval	0	0
Switzerland
Statutory Accounting Practices [Line Items]
Minimum Swiss solvency test margin	44,000,000	6,100,000
Liechtenstein
Statutory Accounting Practices [Line Items]
Minimum solvency requirement	$ 146,800,000	$ 12,800,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 08, 2018	Nov. 30, 2016
Business Acquisition [Line Items]
Rent expense	$ 9,500,000	$ 9,700,000	$ 11,100,000
Commitments, unfunded	164,700,000
Concentration Risk [Line Items]
Funds held by reinsured companies	175,383,000	82,073,000
Guarantor Obligations [Line Items]
Collateral for line of credit facility	165,000,000
Limited parental guarantee
Guarantor Obligations [Line Items]
Total parental guarantees	795,700,000	625,700,000
Reinsurer concentration risk | Reinsurance balances recoverable
Concentration Risk [Line Items]
Funds held by reinsured companies	1,000,000,000
United States
Concentration Risk [Line Items]
Exposure to government	810,900,000
FAL Facility | Loan facilities | Letters of Credit
Guarantor Obligations [Line Items]
Maximum borrowing capacity					$ 165,000,000
Higher borrowing capacity option					$ 200,000,000
FAL Facility | Loan facilities | Letters of Credit | Subsequent event
Guarantor Obligations [Line Items]
Maximum borrowing capacity				$ 325,000,000
Higher borrowing capacity option				$ 400,000,000
Dana Companies
Business Acquisition [Line Items]
Loss contingency accrual	205,700,000	220,500,000
Accrual for environmental liabilities	2,200,000	2,300,000
Insurance recoveries receivable	$ 122,300,000	$ 133,000,000

Commitments and Contingencie142

Commitments and Contingencies - Schedule of Future Minimum Rental Payments on Non-Cancellable Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 11,023
2,019	9,217
2,020	9,310
2,021	7,137
2,022	5,647
2023 and beyond	20,461
Total	$ 62,795

Segment Information - Additiona

Segment Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017Segment
Segment Reporting [Abstract]
Number of segments	3

Segment Information - Summary o

Segment Information - Summary of Operations by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Gross premiums written									$ 1,068,453	$ 1,022,342	$ 1,015,383
Net premiums written									610,390	803,936	787,154
Net premiums earned	$ 160,627	$ 148,025	$ 155,571	$ 148,898	$ 216,188	$ 205,730	$ 208,709	$ 192,887	613,121	823,514	753,744
Net incurred losses and LAE	(30,327)	(75,712)	(9,620)	(77,892)	(1,321)	6,902	(96,462)	(83,218)	(193,551)	(174,099)	(104,333)
Life and Annuity Policy Benefits									(4,015)	2,038	546
Acquisition costs	(21,449)	(24,281)	(30,355)	(20,821)	(47,619)	(50,074)	(43,847)	(45,029)	(96,906)	(186,569)	(163,716)
Operating expenses									(285,237)	(289,788)	(305,864)
Underwriting income (loss)									33,412	175,096	180,377
Net investment income	58,605	52,028	49,417	48,739	42,229	48,022	44,932	50,280	208,789	185,463	122,564
Net realized and unrealized gains (losses)	50,637	29,301	51,877	58,519	(61,570)	66,608	34,503	38,277	190,334	77,818	(41,523)
Fees and commission income	19,627	15,895	18,667	11,914	13,266	9,187	10,487	6,424	66,103	39,364	39,347
Other income	9,303	(3,848)	10,856	12,198	(1,277)	414	3,289	2,410	28,509	4,836	30,328
Corporate expenses									(150,748)	(133,946)	(83,295)
Interest expense	(7,251)	(6,410)	(7,573)	(6,868)	(4,796)	(5,027)	(5,421)	(5,398)	(28,102)	(20,642)	(19,403)
Net foreign exchange losses (gains)	1,925	4,775	7,122	3,715	(1,527)	2,276	(1,856)	1,772	17,537	665	3,373
Loss on sale of subsidiary	0	6,740	9,609	0	0	0	0	0	16,349	0	0
EARNINGS BEFORE INCOME TAXES	112,178	22,098	111,330	68,805	35,395	174,707	55,453	61,769	314,411	327,324	225,022
INCOME TAXES	9,629	(1,432)	(4,731)	2,929	(11,228)	(8,227)	(8,050)	(7,369)	6,395	(34,874)	(12,650)
NET EARNINGS FROM CONTINUING OPERATIONS	121,807	20,666	106,599	71,734	24,167	166,480	47,403	54,400	320,806	292,450	212,372
NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE	11,998	3,495	(4,871)	371	5,483	3,897	2,378	205	10,993	11,963	(2,031)
Net loss (earnings) attributable to noncontrolling interest	(6,206)	14,832	(11,542)	(17,425)	(7,005)	(14,329)	(9,187)	(9,085)	(20,341)	(39,606)	9,950
NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED	$ 127,599	$ 38,993	$ 90,186	$ 54,680	$ 22,645	$ 156,048	$ 40,594	$ 45,520	311,458	264,807	220,291
Non-life Run-off
Segment Reporting Information [Line Items]
Gross premiums written									14,102	17,316	38,704
Net premiums written									6,482	9,202	22,594
Net premiums earned									14,162	16,755	44,369
Net incurred losses and LAE									190,674	285,881	270,830
Life and Annuity Policy Benefits									0	0	0
Acquisition costs									(328)	(4,198)	(8,860)
Operating expenses									(132,235)	(151,316)	(158,821)
Underwriting income (loss)									72,273	147,122	147,518
Net investment income									166,678	145,237	88,999
Net realized and unrealized gains (losses)									179,545	77,685	(31,383)
Fees and commission income									43,849	17,447	22,264
Other income									27,061	2,497	29,294
Corporate expenses									(101,592)	(61,583)	(54,213)
Interest expense									(28,970)	(22,268)	(33,599)
Net foreign exchange losses (gains)									7,347	(1,684)	(4,372)
Loss on sale of subsidiary									0
EARNINGS BEFORE INCOME TAXES									351,497	307,821	164,508
INCOME TAXES									6,990	28,577	(12,570)
NET EARNINGS FROM CONTINUING OPERATIONS									358,487	279,244	151,938
NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE									0	0	0
Net loss (earnings) attributable to noncontrolling interest									(14,687)	(17,600)	33,722
NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED									343,800	261,644	185,660
Atrium
Segment Reporting Information [Line Items]
Gross premiums written									153,472	143,170	149,082
Net premiums written									134,214	140,437	134,580
Net premiums earned									134,747	124,416	134,675
Net incurred losses and LAE									(69,419)	(58,387)	(47,479)
Life and Annuity Policy Benefits									0	0	0
Acquisition costs									(47,688)	(44,670)	(45,509)
Operating expenses									(17,444)	(14,233)	(18,499)
Underwriting income (loss)									196	7,126	23,188
Net investment income									4,218	2,940	2,225
Net realized and unrealized gains (losses)									1,117	(601)	252
Fees and commission income									22,788	18,189	28,352
Other income									230	206	359
Corporate expenses									(12,142)	(10,899)	(13,111)
Interest expense									(559)	(198)	(4,264)
Net foreign exchange losses (gains)									5,060	3,310	(213)
Loss on sale of subsidiary									0
EARNINGS BEFORE INCOME TAXES									10,788	13,453	36,788
INCOME TAXES									(1,593)	2,573	(5,968)
NET EARNINGS FROM CONTINUING OPERATIONS									9,195	10,880	30,820
NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE									0	0	0
Net loss (earnings) attributable to noncontrolling interest									(3,772)	(4,464)	(14,262)
NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED									$ 5,423	$ 6,416	$ 16,558
Underwriting ratios:
Loss ratio									51.50%	46.90%	35.30%
Acquisition expense ratio									35.40%	35.90%	33.80%
Other operating expense ratio									13.00%	11.50%	13.70%
Combined ratio									99.90%	94.30%	82.80%
StarStone
Segment Reporting Information [Line Items]
Gross premiums written									$ 895,160	$ 854,699	$ 824,714
Net premiums written									464,901	648,036	628,427
Net premiums earned									459,403	676,608	573,146
Net incurred losses and LAE									(314,806)	(401,593)	(327,684)
Life and Annuity Policy Benefits									0	0	0
Acquisition costs									(48,012)	(138,822)	(109,347)
Operating expenses									(135,558)	(124,239)	(128,544)
Underwriting income (loss)									(38,973)	11,954	7,571
Net investment income									27,706	22,221	15,937
Net realized and unrealized gains (losses)									16,613	5,728	(9,784)
Fees and commission income									632	5,102	0
Other income									570	740	3,088
Corporate expenses									0	0	0
Interest expense									(1,902)	(47)	(6)
Net foreign exchange losses (gains)									926	(754)	480
Loss on sale of subsidiary									0
EARNINGS BEFORE INCOME TAXES									3,720	46,452	17,286
INCOME TAXES									988	3,693	5,888
NET EARNINGS FROM CONTINUING OPERATIONS									4,708	42,759	23,174
NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE									0	0	0
Net loss (earnings) attributable to noncontrolling interest									(1,882)	(17,542)	(9,510)
NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED									$ 2,826	$ 25,217	$ 13,664
Underwriting ratios:
Loss ratio									68.50%	59.40%	57.20%
Acquisition expense ratio									10.50%	20.50%	19.10%
Other operating expense ratio									29.50%	18.30%	22.40%
Combined ratio									108.50%	98.20%	98.70%
Other
Segment Reporting Information [Line Items]
Gross premiums written									$ 5,719	$ 7,157	$ 2,883
Net premiums written									4,793	6,261	1,553
Net premiums earned									4,809	5,735	1,554
Net incurred losses and LAE									0	0	0
Life and Annuity Policy Benefits									(4,015)	2,038	546
Acquisition costs									(878)	1,121	0
Operating expenses									0	0	0
Underwriting income (loss)									(84)	8,894	2,100
Net investment income									10,187	15,065	15,403
Net realized and unrealized gains (losses)									(6,941)	(4,994)	(608)
Fees and commission income									(1,166)	(1,374)	(11,269)
Other income									648	1,393	(2,413)
Corporate expenses									(37,014)	(61,464)	(15,971)
Interest expense									3,329	1,871	18,466
Net foreign exchange losses (gains)									4,204	(207)	732
Loss on sale of subsidiary									16,349
EARNINGS BEFORE INCOME TAXES									(51,594)	(40,402)	6,440
INCOME TAXES									10	31	0
NET EARNINGS FROM CONTINUING OPERATIONS									(51,584)	(40,433)	6,440
NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE									10,993	11,963	(2,031)
Net loss (earnings) attributable to noncontrolling interest									0	0	0
NET EARNINGS (LOSS) ATTRIBUTABLE TO ENSTAR GROUP LIMITED									$ (40,591)	$ (28,470)	$ 4,409

Segment Information - Gross Pre

Segment Information - Gross Premiums Written by Geographical Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Gross, premiums written	$ 1,068,453	$ 1,022,342	$ 1,015,383
Non-life Run-off
Segment Reporting Information [Line Items]
Gross, premiums written	14,102	17,316	38,704
Atrium
Segment Reporting Information [Line Items]
Gross, premiums written	153,472	143,170	149,082
StarStone
Segment Reporting Information [Line Items]
Gross, premiums written	895,160	$ 854,699	$ 824,714
Other
Segment Reporting Information [Line Items]
Gross, premiums written	5,719
United States
Segment Reporting Information [Line Items]
Gross, premiums written	637,300
United States | Non-life Run-off
Segment Reporting Information [Line Items]
Gross, premiums written	9,639
United States | Atrium
Segment Reporting Information [Line Items]
Gross, premiums written	81,438
United States | StarStone
Segment Reporting Information [Line Items]
Gross, premiums written	546,223
United States | Other
Segment Reporting Information [Line Items]
Gross, premiums written	0
United Kingdom
Segment Reporting Information [Line Items]
Gross, premiums written	114,565
United Kingdom | Non-life Run-off
Segment Reporting Information [Line Items]
Gross, premiums written	4,271
United Kingdom | Atrium
Segment Reporting Information [Line Items]
Gross, premiums written	11,203
United Kingdom | StarStone
Segment Reporting Information [Line Items]
Gross, premiums written	97,745
United Kingdom | Other
Segment Reporting Information [Line Items]
Gross, premiums written	1,346
Europe
Segment Reporting Information [Line Items]
Gross, premiums written	166,355
Europe | Non-life Run-off
Segment Reporting Information [Line Items]
Gross, premiums written	192
Europe | Atrium
Segment Reporting Information [Line Items]
Gross, premiums written	10,684
Europe | StarStone
Segment Reporting Information [Line Items]
Gross, premiums written	151,106
Europe | Other
Segment Reporting Information [Line Items]
Gross, premiums written	4,373
Asia
Segment Reporting Information [Line Items]
Gross, premiums written	53,578
Asia | Non-life Run-off
Segment Reporting Information [Line Items]
Gross, premiums written	0
Asia | Atrium
Segment Reporting Information [Line Items]
Gross, premiums written	4,739
Asia | StarStone
Segment Reporting Information [Line Items]
Gross, premiums written	48,839
Asia | Other
Segment Reporting Information [Line Items]
Gross, premiums written	0
Rest of World
Segment Reporting Information [Line Items]
Gross, premiums written	96,655
Rest of World | Non-life Run-off
Segment Reporting Information [Line Items]
Gross, premiums written	0
Rest of World | Atrium
Segment Reporting Information [Line Items]
Gross, premiums written	45,408
Rest of World | StarStone
Segment Reporting Information [Line Items]
Gross, premiums written	51,247
Rest of World | Other
Segment Reporting Information [Line Items]
Gross, premiums written	$ 0
Geographic concentration risk | Gross premiums written
Segment Reporting Information [Line Items]
Gross premiums written (percent)	100.00%
Geographic concentration risk | Gross premiums written | Non-life Run-off
Segment Reporting Information [Line Items]
Gross premiums written (percent)	100.00%
Geographic concentration risk | Gross premiums written | Atrium
Segment Reporting Information [Line Items]
Gross premiums written (percent)	100.00%
Geographic concentration risk | Gross premiums written | StarStone
Segment Reporting Information [Line Items]
Gross premiums written (percent)	100.00%
Geographic concentration risk | Gross premiums written | Other
Segment Reporting Information [Line Items]
Gross premiums written (percent)	100.00%
Geographic concentration risk | Gross premiums written | United States
Segment Reporting Information [Line Items]
Gross premiums written (percent)	59.60%
Geographic concentration risk | Gross premiums written | United States | Non-life Run-off
Segment Reporting Information [Line Items]
Gross premiums written (percent)	68.30%
Geographic concentration risk | Gross premiums written | United States | Atrium
Segment Reporting Information [Line Items]
Gross premiums written (percent)	53.10%
Geographic concentration risk | Gross premiums written | United States | StarStone
Segment Reporting Information [Line Items]
Gross premiums written (percent)	61.00%
Geographic concentration risk | Gross premiums written | United States | Other
Segment Reporting Information [Line Items]
Gross premiums written (percent)	0.00%
Geographic concentration risk | Gross premiums written | United Kingdom
Segment Reporting Information [Line Items]
Gross premiums written (percent)	10.70%
Geographic concentration risk | Gross premiums written | United Kingdom | Non-life Run-off
Segment Reporting Information [Line Items]
Gross premiums written (percent)	30.30%
Geographic concentration risk | Gross premiums written | United Kingdom | Atrium
Segment Reporting Information [Line Items]
Gross premiums written (percent)	7.30%
Geographic concentration risk | Gross premiums written | United Kingdom | StarStone
Segment Reporting Information [Line Items]
Gross premiums written (percent)	10.90%
Geographic concentration risk | Gross premiums written | United Kingdom | Other
Segment Reporting Information [Line Items]
Gross premiums written (percent)	23.50%
Geographic concentration risk | Gross premiums written | Europe
Segment Reporting Information [Line Items]
Gross premiums written (percent)	15.60%
Geographic concentration risk | Gross premiums written | Europe | Non-life Run-off
Segment Reporting Information [Line Items]
Gross premiums written (percent)	1.40%
Geographic concentration risk | Gross premiums written | Europe | Atrium
Segment Reporting Information [Line Items]
Gross premiums written (percent)	7.00%
Geographic concentration risk | Gross premiums written | Europe | StarStone
Segment Reporting Information [Line Items]
Gross premiums written (percent)	16.90%
Geographic concentration risk | Gross premiums written | Europe | Other
Segment Reporting Information [Line Items]
Gross premiums written (percent)	76.50%
Geographic concentration risk | Gross premiums written | Asia
Segment Reporting Information [Line Items]
Gross premiums written (percent)	5.00%
Geographic concentration risk | Gross premiums written | Asia | Non-life Run-off
Segment Reporting Information [Line Items]
Gross premiums written (percent)	0.00%
Geographic concentration risk | Gross premiums written | Asia | Atrium
Segment Reporting Information [Line Items]
Gross premiums written (percent)	3.10%
Geographic concentration risk | Gross premiums written | Asia | StarStone
Segment Reporting Information [Line Items]
Gross premiums written (percent)	5.50%
Geographic concentration risk | Gross premiums written | Asia | Other
Segment Reporting Information [Line Items]
Gross premiums written (percent)	0.00%
Geographic concentration risk | Gross premiums written | Rest of World
Segment Reporting Information [Line Items]
Gross premiums written (percent)	9.10%
Geographic concentration risk | Gross premiums written | Rest of World | Non-life Run-off
Segment Reporting Information [Line Items]
Gross premiums written (percent)	0.00%
Geographic concentration risk | Gross premiums written | Rest of World | Atrium
Segment Reporting Information [Line Items]
Gross premiums written (percent)	29.50%
Geographic concentration risk | Gross premiums written | Rest of World | StarStone
Segment Reporting Information [Line Items]
Gross premiums written (percent)	5.70%
Geographic concentration risk | Gross premiums written | Rest of World | Other
Segment Reporting Information [Line Items]
Gross premiums written (percent)	0.00%

Segment Information - Summar146

Segment Information - Summary of Company's Assets by Segment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 13,606,422	$ 12,865,744
Non-life Run-off
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	10,368,105	8,233,450
Atrium
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	556,637	563,754
StarStone
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	3,128,725	2,968,316
Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ (447,045)	$ 1,100,224

Unaudited Condensed Quarterl147

Unaudited Condensed Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INCOME
Net premiums earned	$ 160,627	$ 148,025	$ 155,571	$ 148,898	$ 216,188	$ 205,730	$ 208,709	$ 192,887	$ 613,121	$ 823,514	$ 753,744
Fees and commission income	19,627	15,895	18,667	11,914	13,266	9,187	10,487	6,424	66,103	39,364	39,347
Net investment income	58,605	52,028	49,417	48,739	42,229	48,022	44,932	50,280	208,789	185,463	122,564
Net realized and unrealized gains (losses)	50,637	29,301	51,877	58,519	(61,570)	66,608	34,503	38,277	190,334	77,818	(41,523)
Other income	9,303	(3,848)	10,856	12,198	(1,277)	414	3,289	2,410	28,509	4,836	30,328
Total income	298,799	241,401	286,388	280,268	208,836	329,961	301,920	290,278	1,106,856	1,130,995	904,460
EXPENSES
Net incurred losses and loss adjustment expenses	30,327	75,712	9,620	77,892	1,321	(6,902)	96,462	83,218	193,551	174,099	104,333
Life and annuity policy benefits	(1,033)	1,060	4,289	(301)	(2,265)	1,682	(1,613)	158	4,015	(2,038)	(546)
Acquisition costs	21,449	24,281	30,355	20,821	47,619	50,074	43,847	45,029	96,906	186,569	163,716
General and administrative expenses	126,702	100,325	106,490	102,468	123,497	103,097	104,206	92,934	435,985	423,734	389,159
Interest expense	7,251	6,410	7,573	6,868	4,796	5,027	5,421	5,398	28,102	20,642	19,403
Net foreign exchange losses	1,925	4,775	7,122	3,715	(1,527)	2,276	(1,856)	1,772	17,537	665	3,373
Loss on sale of subsidiary	0	6,740	9,609	0	0	0	0	0	16,349	0	0
Total expenses	186,621	219,303	175,058	211,463	173,441	155,254	246,467	228,509	792,445	803,671	679,438
EARNINGS BEFORE INCOME TAXES	112,178	22,098	111,330	68,805	35,395	174,707	55,453	61,769	314,411	327,324	225,022
INCOME TAXES	9,629	(1,432)	(4,731)	2,929	(11,228)	(8,227)	(8,050)	(7,369)	6,395	(34,874)	(12,650)
NET EARNINGS FROM CONTINUING OPERATIONS	121,807	20,666	106,599	71,734	24,167	166,480	47,403	54,400	320,806	292,450	212,372
NET EARNINGS (LOSS) FROM DISCONTINUING OPERATIONS, NET OF INCOME TAX EXPENSE	11,998	3,495	(4,871)	371	5,483	3,897	2,378	205	10,993	11,963	(2,031)
NET EARNINGS	133,805	24,161	101,728	72,105	29,650	170,377	49,781	54,605	331,799	304,413	210,341
Net loss (earnings) attributable to noncontrolling interest	(6,206)	14,832	(11,542)	(17,425)	(7,005)	(14,329)	(9,187)	(9,085)	(20,341)	(39,606)	9,950
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED	$ 127,599	$ 38,993	$ 90,186	$ 54,680	$ 22,645	$ 156,048	$ 40,594	$ 45,520	$ 311,458	$ 264,807	$ 220,291
EARNINGS PER SHARE — BASIC:
Net earnings from continuing operations (dollars per share)	$ 5.96	$ 1.83	$ 4.90	$ 2.80	$ 0.91	$ 7.89	$ 1.98	$ 2.34	$ 15.50	$ 13.10	$ 11.55
Net earnings (loss) from discontinuing operations (dollars per share)	0.62	0.18	(0.25)	0.02	0.26	0.20	0.12	0.02	0.56	0.62	(0.11)
Net earnings per ordinary share (dollars per share)	6.58	2.01	4.65	2.82	1.17	8.09	2.10	2.36	16.06	13.72	11.44
EARNINGS PER SHARE — DILUTED:
Net earnings from continuing operations (dollars per share)	5.90	1.81	4.87	2.78	0.90	7.82	1.97	2.33	15.39	13	11.46
Net earnings (loss) from discontinuing operations (dollars per share)	0.61	0.18	(0.25)	0.02	0.26	0.20	0.12	0.02	0.56	0.62	(0.11)
Net earnings per ordinary share (dollars per share)	$ 6.51	$ 1.99	$ 4.62	$ 2.80	$ 1.16	$ 8.02	$ 2.09	$ 2.35	$ 15.95	$ 13.62	$ 11.35

Schedule I - Summary of Inve148

Schedule I - Summary of Investments Other Than Investments in Related Parties (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 6,811,335
Fair Value	6,933,066
Amount at which shown in the balance sheet	6,926,791
Equities, trading, at fair value	106,603	$ 95,047
Fair value of other investments in funds or companies owned by or affiliated with related parties	913,392	937,047
Affiliated entity
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fair value of other investments in funds or companies owned by or affiliated with related parties	283,300
Affiliated entity | Trident
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Equities, trading, at fair value	22,100	20,900
Fair value of other investments in funds or companies owned by or affiliated with related parties	255,900	$ 232,100
Equities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	64,197
Fair Value	84,543
Amount at which shown in the balance sheet	84,543
Other investments, at fair value
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	630,058
Fair Value	630,058
Amount at which shown in the balance sheet	630,058
Other investments, at cost
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	125,621
Fair Value	131,896
Amount at which shown in the balance sheet	125,621
Trading securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5,783,362
Fair Value	5,876,284
Amount at which shown in the balance sheet	5,876,284
Trading securities | U.S. government and agency
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	557,273
Fair Value	554,036
Amount at which shown in the balance sheet	554,036
Trading securities | Non-U.S. government
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	580,280
Fair Value	607,132
Amount at which shown in the balance sheet	607,132
Trading securities | Corporate
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	3,299,982
Fair Value	3,363,060
Amount at which shown in the balance sheet	3,363,060
Trading securities | Municipal
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	98,153
Fair Value	100,221
Amount at which shown in the balance sheet	100,221
Trading securities | Residential mortgage-backed
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	285,312
Fair Value	288,713
Amount at which shown in the balance sheet	288,713
Trading securities | Commercial mortgage-backed
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	427,469
Fair Value	421,548
Amount at which shown in the balance sheet	421,548
Trading securities | Asset-backed
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	534,893
Fair Value	541,574
Amount at which shown in the balance sheet	541,574
Available-for-sale securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	208,097
Fair Value	210,285
Amount at which shown in the balance sheet	210,285
Available-for-sale securities | U.S. government and agency
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	4,210
Fair Value	4,187
Amount at which shown in the balance sheet	4,187
Available-for-sale securities | Non-U.S. government
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	84,776
Fair Value	85,437
Amount at which shown in the balance sheet	85,437
Available-for-sale securities | Corporate
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	113,561
Fair Value	115,121
Amount at which shown in the balance sheet	115,121
Available-for-sale securities | Municipal
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5,146
Fair Value	5,136
Amount at which shown in the balance sheet	5,136
Available-for-sale securities | Residential mortgage-backed
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	31
Fair Value	31
Amount at which shown in the balance sheet	31
Available-for-sale securities | Asset-backed
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	373
Fair Value	373
Amount at which shown in the balance sheet	$ 373

Schedule II - Condensed Balance

Schedule II - Condensed Balance Sheets (Detail) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 955,150	$ 954,871	$ 795,245
Other assets	831,320	842,356
TOTAL ASSETS	13,606,422	12,865,744
LIABILITIES
Debt obligations	646,689	673,603
Other liabilities	972,457	705,318
TOTAL LIABILITIES	9,980,868	9,600,390
SHAREHOLDERS’ EQUITY
Treasury shares at cost (Preferred shares 2017 and 2016: 388,571)	(421,559)	(421,559)
Additional paid-in capital	1,395,067	1,380,109
Accumulated other comprehensive income (loss)	10,468	(23,549)
Retained earnings	2,132,912	1,847,550
Total Enstar Group Limited Shareholders’ Equity	3,136,684	2,802,312
TOTAL LIABILITIES, REDEEMABLE NONCONTROLLING INTEREST AND SHAREHOLDERS’ EQUITY	$ 13,606,422	$ 12,865,744
Parenthetical Disclosures [Abstract]
Common shares, par value (dollars per share)	$ 1	$ 1
Preferred shares, par value (dollars per share)	$ 1	$ 1
Share capital, authorized (shares)	156,000,000	156,000,000
Voting ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	$ 16,402	$ 16,175
Parenthetical Disclosures [Abstract]
Common shares, par value (dollars per share)	$ 1	$ 1
Ordinary shares, shares issued (shares)	16,402,279	16,175,250
Ordinary shares, outstanding (shares)	16,402,279	16,175,250
Series C non-voting convertible ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	$ 2,600	$ 2,792
Parenthetical Disclosures [Abstract]
Ordinary shares, shares issued (shares)	2,599,672	2,792,157
Ordinary shares, outstanding (shares)	2,599,672	2,792,157
Series E non-voting convertible ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	$ 405	$ 405
Parenthetical Disclosures [Abstract]
Ordinary shares, shares issued (shares)	404,771	404,771	714,015
Ordinary shares, outstanding (shares)	404,771	404,771	714,015
Series C non-voting preferred shares
SHAREHOLDERS’ EQUITY
Series C Preferred Shares (issued and outstanding 2017 and 2016: 388,571)	$ 389	$ 389
Parenthetical Disclosures [Abstract]
Preferred shares, issued (shares)	388,571	388,571
Preferred shares, outstanding (shares)	388,571	388,571
Treasury shares (shares)	388,571	388,571
Enstar Group Limited
ASSETS
Cash and cash equivalents	$ 2,458	$ 4,884	$ 4,552	$ 21,671
Balances due from subsidiaries	23,635	35,563
Investments in subsidiaries	3,917,830	3,400,401
Other assets	2,877	8,533
TOTAL ASSETS	3,946,800	3,449,381
LIABILITIES
Debt obligations	646,689	488,103
Balances due to subsidiaries	148,410	153,843
Other liabilities	15,017	5,123
TOTAL LIABILITIES	810,116	647,069
SHAREHOLDERS’ EQUITY
Treasury shares at cost (Preferred shares 2017 and 2016: 388,571)	(421,559)	(421,559)
Additional paid-in capital	1,395,067	1,380,109
Accumulated other comprehensive income (loss)	10,468	(23,549)
Retained earnings	2,132,912	1,847,550
Total Enstar Group Limited Shareholders’ Equity	3,136,684	2,802,312
TOTAL LIABILITIES, REDEEMABLE NONCONTROLLING INTEREST AND SHAREHOLDERS’ EQUITY	$ 3,946,800	$ 3,449,381
Parenthetical Disclosures [Abstract]
Common shares, par value (dollars per share)	$ 1	$ 1
Share capital, authorized (shares)	156,000,000	156,000,000
Enstar Group Limited | Voting ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	$ 16,402	$ 16,175
Parenthetical Disclosures [Abstract]
Ordinary shares, shares issued (shares)	16,175,250	16,133,334
Ordinary shares, outstanding (shares)	16,175,250	16,133,334
Enstar Group Limited | Series A non-voting convertible ordinary shares
Parenthetical Disclosures [Abstract]
Treasury shares (shares)	0	388,571
Enstar Group Limited | Series C non-voting convertible ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	$ 2,600	$ 2,792
Parenthetical Disclosures [Abstract]
Ordinary shares, shares issued (shares)	2,792,157	2,725,637
Ordinary shares, outstanding (shares)	2,792,157	2,725,637
Enstar Group Limited | Series E non-voting convertible ordinary shares
SHAREHOLDERS’ EQUITY
Ordinary shares	$ 405	$ 405
Parenthetical Disclosures [Abstract]
Ordinary shares, shares issued (shares)	404,771	404,771
Ordinary shares, outstanding (shares)	404,771	404,771
Enstar Group Limited | Series C non-voting preferred shares
SHAREHOLDERS’ EQUITY
Series C Preferred Shares (issued and outstanding 2017 and 2016: 388,571)	$ 389	$ 389
Parenthetical Disclosures [Abstract]
Preferred shares, issued (shares)	388,571	0
Preferred shares, outstanding (shares)	388,571	0
Treasury shares (shares)	388,571	0

Schedule II - Condensed Stateme

Schedule II - Condensed Statements of Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INCOME
Net investment income	$ 58,605	$ 52,028	$ 49,417	$ 48,739	$ 42,229	$ 48,022	$ 44,932	$ 50,280	$ 208,789	$ 185,463	$ 122,564
Other income	9,303	(3,848)	10,856	12,198	(1,277)	414	3,289	2,410	28,509	4,836	30,328
Total income	298,799	241,401	286,388	280,268	208,836	329,961	301,920	290,278	1,106,856	1,130,995	904,460
EXPENSES
General and administrative expenses	126,702	100,325	106,490	102,468	123,497	103,097	104,206	92,934	435,985	423,734	389,159
Interest expense	7,251	6,410	7,573	6,868	4,796	5,027	5,421	5,398	28,102	20,642	19,403
Net foreign exchange losses (gains)	1,925	4,775	7,122	3,715	(1,527)	2,276	(1,856)	1,772	17,537	665	3,373
Total expenses	186,621	219,303	175,058	211,463	173,441	155,254	246,467	228,509	792,445	803,671	679,438
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED	$ 127,599	$ 38,993	$ 90,186	$ 54,680	$ 22,645	$ 156,048	$ 40,594	$ 45,520	311,458	264,807	220,291
Enstar Group Limited
INCOME
Net investment income									80	44	14,965
Other income									1,050	0	0
Dividend income from subsidiaries									249,055	361,675	1,000
Total income									250,185	361,719	15,965
EXPENSES
General and administrative expenses									87,596	59,755	50,349
Interest expense									23,138	10,109	8,693
Net foreign exchange losses (gains)									6,135	(318)	213
Total expenses									116,869	69,546	59,255
EARNINGS (LOSSES) BEFORE EQUITY IN UNDISTRIBUTED EARNINGS OF SUBSIDIARIES									133,316	292,173	(43,290)
EQUITY IN UNDISTRIBUTED EARNINGS (LOSSES) OF SUBSIDIARIES - CONTINUING OPERATIONS									167,149	(39,329)	265,612
EQUITY IN UNDISTRIBUTED EARNINGS (LOSSES) OF SUBSIDIARIES - DISCONTINUING OPERATIONS									10,993	11,963	(2,031)
NET EARNINGS ATTRIBUTABLE TO ENSTAR GROUP LIMITED									$ 311,458	$ 264,807	$ 220,291

Schedule II - Comprehensive Inc

Schedule II - Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Statement of Income Captions [Line Items]
NET EARNINGS	$ 127,599	$ 38,993	$ 90,186	$ 54,680	$ 22,645	$ 156,048	$ 40,594	$ 45,520	$ 311,458	$ 264,807	$ 220,291
COMPREHENSIVE INCOME ATTRIBUTABLE TO ENSTAR GROUP LIMITED									345,474	276,420	197,815
Enstar Group Limited
Condensed Statement of Income Captions [Line Items]
NET EARNINGS									311,458	264,807	220,291
OTHER COMPREHENSIVE INCOME (LOSS) RELATING TO SUBSIDIARIES, NET OF TAX									34,016	11,613	(22,476)
COMPREHENSIVE INCOME ATTRIBUTABLE TO ENSTAR GROUP LIMITED									$ 345,474	$ 276,420	$ 197,815

Schedule II - Condensed Stat152

Schedule II - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES:
Net cash flows provided by (used in) operating activities	$ (343,107)	$ (202,689)	$ (265,152)
INVESTING ACTIVITIES:
Net cash flows provided by investing activities	293,262	156,709	19,885
FINANCING ACTIVITIES:
Repayment of loans	(912,140)	(493,250)	(377,500)
Receipt of loans	874,100	571,048	657,700
Net cash flows provided by (used in) financing activities	(65,476)	83,441	129,347
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF YEAR	954,871	795,245
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, END OF YEAR	955,150	954,871	795,245
Enstar Group Limited
OPERATING ACTIVITIES:
Net cash flows provided by (used in) operating activities	97,898	39,185	(81,384)
INVESTING ACTIVITIES:
Dividends and return of capital from subsidiaries	217,450	250,117	1,000
Contributions to subsidiaries	(465,650)	(295,268)	(218,935)
Net cash flows provided by investing activities	(248,200)	(45,151)	(217,935)
FINANCING ACTIVITIES:
Repayment of loans	(696,640)	(426,750)	(223,500)
Receipt of loans	844,516	433,048	505,700
Net cash flows provided by (used in) financing activities	147,876	6,298	282,200
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(2,426)	332	(17,119)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF YEAR	4,884	4,552	21,671
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, END OF YEAR	$ 2,458	$ 4,884	$ 4,552

Schedule II - Narrative (Detail

Schedule II - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Interest paid									$ 21,487	$ 19,451	$ 19,395
Dividends and return of capital from subsidiaries, non-cash									31,600	111,600
Contributions to subsidiaries, non-cash									148,100	452,100
Retained earnings	$ 2,132,912				$ 1,847,550				2,132,912	1,847,550
Net earnings attributable to Enstar Group Limited	127,599	$ 38,993	$ 90,186	$ 54,680	22,645	$ 156,048	$ 40,594	$ 45,520	311,458	264,807	220,291
Limited parental guarantee
Condensed Financial Statements, Captions [Line Items]
Total parental guarantees	795,700				625,700				795,700	625,700
Enstar Group Limited
Condensed Financial Statements, Captions [Line Items]
Interest paid									17,600	15,000	13,000
Retained earnings	2,132,912				1,847,550				2,132,912	1,847,550
Increase in retained earnings									285,400
Net earnings attributable to Enstar Group Limited									311,458	264,807	$ 220,291
Enstar Group Limited | Limited parental guarantee
Condensed Financial Statements, Captions [Line Items]
Total parental guarantees	$ 795,700				$ 625,700				$ 795,700	$ 625,700

Schedule III - Supplementary154

Schedule III - Supplementary Insurance Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	$ 64,984	$ 58,114	$ 89,123
Reserves for Losses and Loss Adjustment Expenses	7,398,088	5,987,867	5,720,149
Unearned Premiums	583,197	548,343	542,771
Policy Benefits for Life and Annuity Contracts	117,207	112,095	126,321
Net Premiums Earned	613,121	823,514	753,744
Net Investment Income	208,789	185,463	122,564
Losses and Loss Expenses and Policy Benefits	197,566	172,061	103,787
Amortization of Deferred Acquisition Costs	96,906	186,569	163,716
Other Operating Expenses	435,985	423,734	389,159
Net Premiums Written	610,390	803,936	787,154
Non-life Run-off
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	655	1,081	1,788
Reserves for Losses and Loss Adjustment Expenses	5,949,472	4,716,363	4,585,454
Unearned Premiums	14,275	15,107	27,792
Policy Benefits for Life and Annuity Contracts	0	0	0
Net Premiums Earned	14,162	16,755	44,369
Net Investment Income	166,678	145,237	88,999
Losses and Loss Expenses and Policy Benefits	(190,674)	(285,881)	(270,830)
Amortization of Deferred Acquisition Costs	328	4,198	8,860
Other Operating Expenses	233,827	212,899	213,034
Net Premiums Written	6,482	9,202	22,594
Atrium
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	18,385	16,964	16,326
Reserves for Losses and Loss Adjustment Expenses	240,873	212,122	201,017
Unearned Premiums	64,877	61,862	59,808
Policy Benefits for Life and Annuity Contracts	0	0	0
Net Premiums Earned	134,747	124,416	134,675
Net Investment Income	4,218	2,940	2,225
Losses and Loss Expenses and Policy Benefits	69,419	58,387	47,479
Amortization of Deferred Acquisition Costs	47,688	44,670	45,509
Other Operating Expenses	29,586	25,132	31,610
Net Premiums Written	134,214	140,437	134,580
StarStone
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	45,944	40,069	71,009
Reserves for Losses and Loss Adjustment Expenses	1,207,743	1,059,382	933,678
Unearned Premiums	504,045	471,374	455,171
Policy Benefits for Life and Annuity Contracts	0	0	0
Net Premiums Earned	459,403	676,608	573,146
Net Investment Income	27,706	22,221	15,937
Losses and Loss Expenses and Policy Benefits	314,806	401,593	327,684
Amortization of Deferred Acquisition Costs	48,012	138,822	109,347
Other Operating Expenses	135,558	124,239	128,544
Net Premiums Written	464,901	648,036	628,427
Other
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	0	0	0
Reserves for Losses and Loss Adjustment Expenses	0	0	0
Unearned Premiums	0	0	0
Policy Benefits for Life and Annuity Contracts	117,207	112,095	126,321
Net Premiums Earned	4,809	5,735	1,554
Net Investment Income	10,187	15,065	15,403
Losses and Loss Expenses and Policy Benefits	4,015	(2,038)	(546)
Amortization of Deferred Acquisition Costs	878	(1,121)	0
Other Operating Expenses	37,014	61,464	15,971
Net Premiums Written	$ 4,793	$ 6,261	$ 1,553

Schedule IV - Reinsurance (Deta

Schedule IV - Reinsurance (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Life insurance in force, gross	$ 979,291				$ 2,317,567				$ 979,291	$ 2,317,567	$ 2,978,466
Life insurance in force, ceded	(100,189)				(585,575)				(100,189)	(585,575)	(777,759)
Life insurance in force, assumed	0				0				0	0	0
Life insurance in force, net	$ 879,102				$ 1,731,992				$ 879,102	$ 1,731,992	$ 2,200,707
Life insurance in force, percentage of amount assumed to net	0.00%				0.00%				0.00%	0.00%	0.00%
Premiums earned, gross									$ 905,126	$ 811,361	$ 857,740
Premiums earned, ceded									(434,166)	(180,319)	(284,819)
Premiums earned, assumed									142,161	192,472	180,823
Net, premiums earned	$ 160,627	$ 148,025	$ 155,571	$ 148,898	$ 216,188	$ 205,730	$ 208,709	$ 192,887	613,121	823,514	753,744
Property and casualty
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums earned, gross									899,226	804,141	854,856
Premiums earned, ceded									(433,075)	(178,834)	(283,489)
Premiums earned, assumed									142,161	192,472	180,823
Net, premiums earned									$ 608,312	$ 817,779	$ 752,190
Premiums earned, percentage of amount assumed to net									23.40%	23.50%	24.00%
Life and annuities
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums earned, gross									$ 5,900	$ 7,220	$ 2,884
Premiums earned, ceded									(1,091)	(1,485)	(1,330)
Premiums earned, assumed									0	0	0
Net, premiums earned									$ 4,809	$ 5,735	$ 1,554
Premiums earned, percentage of amount assumed to net									0.00%	0.00%	0.00%

Schedule V - Valuation and Q156

Schedule V - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance balances recoverable, provisions for bad debt
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 165,213	$ 174,516	$ 210,327	$ 289,909
Charged to costs and expenses	(1,536)	(13,822)	(25,271)
Charged to other accounts	(4,191)	(19,255)	(45,234)
Deductions	(3,576)	(2,734)	(9,077)
Balance at End of Year	165,213	174,516	210,327
Valuation allowance for deferred tax assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	188,300	290,861	291,280	$ 333,617
Charged to costs and expenses	(16,694)	13,389	(17,379)
Charged to other accounts	0	0	0
Deductions	(85,867)	(13,808)	(24,958)
Balance at End of Year	$ 188,300	$ 290,861	$ 291,280

Schedule VI - Supplementary 157

Schedule VI - Supplementary Information Concerning Property/Casualty Insurance Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Deferred Acquisition Costs	$ 64,984	$ 58,114	$ 89,123
Reserves for Unpaid Losses and Loss Adjustment Expenses	7,398,088	5,987,867	5,720,149
Unearned Premiums	583,197	548,343	542,771
Net Premiums Earned	608,312	817,779	752,190
Net Investment Income	198,602	170,398	107,161
Net Losses and Loss Expenses Incurred - Current Year	437,853	493,016	476,364
Net Loses and Loss Expenses Incurred - Prior Year	(244,302)	(318,917)	(372,031)
Net Paid Losses and Loss Expenses	(945,194)	(833,057)	(781,889)
Amortization of Deferred Acquisition Costs	96,028	187,690	163,716
Net Premiums Written	$ 605,597	$ 797,675	$ 785,601