Arch Capital (ACGL) 10-Q 3 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 31, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	ARCH CAPITAL GROUP LTD.
Entity Central Index Key	947,484
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		130,874,024

Unaudited Consolidated Balance

Unaudited Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investments:
Fixed maturities available for sale, at fair value (amortized cost: $13,722,581 and $13,522,671)	$ 13,792,903	$ 13,426,577
Short-term investments available for sale, at fair value (amortized cost: $1,645,873 and $611,878)	1,646,036	612,005
Collateral received under securities lending, at fair value (amortized cost: $543,243 and $762,554)	543,252	762,565
Equity securities available for sale, at fair value (cost: $401,674 and $475,085)	477,143	518,041
Other investments available for sale, at fair value (cost: $205,828 and $149,077)	260,339	167,970
Investments accounted for using the fair value option	4,249,634	3,421,220
Investments accounted for using the equity method	962,574	811,273
Total investments	21,931,881	19,719,651
Cash	862,361	842,942
Accrued investment income	101,104	124,483
Securities pledged under securities lending, at fair value (amortized cost: $529,700 and $746,409)	528,212	744,980
Premiums receivable	1,269,678	1,072,435
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	2,506,015	2,114,138
Contractholder receivables	1,864,348	1,717,436
Ceded unearned premiums	947,135	859,567
Deferred acquisition costs	531,196	447,560
Receivable for securities sold	385,952	58,284
Goodwill and intangible assets	684,405	781,553
Other assets	1,012,510	889,080
Total assets	32,624,797	29,372,109
Liabilities
Reserve for losses and loss adjustment expenses	11,351,267	10,200,960
Unearned premiums	3,751,550	3,406,870
Reinsurance balances payable	352,006	300,407
Contractholder payables	1,864,348	1,717,436
Collateral held for insured obligations	345,726	301,406
Senior notes	1,732,726	1,732,258
Revolving credit agreement borrowings	826,242	756,650
Securities lending payable	543,243	762,554
Payable for securities purchased	1,091,464	76,183
Other liabilities	788,354	806,260
Total liabilities	22,646,926	20,060,984
Commitments and Contingencies
Redeemable noncontrolling interests	205,829	205,553
Shareholders' Equity
Non-cumulative preferred shares	772,555	772,555
Convertible non-voting common equivalent preferred shares	489,627	1,101,304
Common shares ($0.0033 par, shares issued: 182,924,882 and 174,644,101)	610	582
Additional paid-in capital	1,212,960	531,687
Retained earnings	8,359,354	7,996,701
Accumulated other comprehensive income (loss), net of deferred income tax	129,682	(114,541)
Common shares held in treasury, at cost (shares: 52,058,509 and 51,856,584)	(2,053,644)	(2,034,570)
Total shareholders' equity available to Arch	8,911,144	8,253,718
Non-redeemable noncontrolling interests	860,898	851,854
Total shareholders' equity	9,772,042	9,105,572
Total liabilities, noncontrolling interests and shareholders' equity	$ 32,624,797	$ 29,372,109

Unaudited Consolidated Balance3

Unaudited Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fixed maturities available for sale, at amortized cost	$ 13,722,581	$ 13,522,671
Short-term investments available for sale, at amortized cost	1,645,873	611,878
Collateral received under securities lending, at amortized cost	543,243	762,554
Equity securities available for sale, at cost	401,674	475,085
Other investments available for sale, at cost	205,828	149,077
Securities pledged under securities lending, at amortized cost	$ 529,700	$ 746,409
Common shares, par value per share	$ 0.0033	$ 0.0033
Common shares issued (shares)	182,924,882	174,644,101
Common shares held in treasury (shares)	52,058,509	51,856,584

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Net premiums written	$ 1,325,403	$ 1,014,278	$ 3,850,358	$ 3,159,076
Change in unearned premiums	(63,517)	(55,875)	(230,581)	(243,109)
Net premiums earned	1,261,886	958,403	3,619,777	2,915,967
Net investment income	116,459	93,618	345,457	275,691
Net realized gains (losses)	66,275	125,105	122,163	230,647
Other-than-temporary impairment losses	(1,878)	(3,867)	(5,415)	(16,999)
Less investment impairments recognized in other comprehensive income, before taxes	0	0	0	150
Net impairment losses recognized in earnings	(1,878)	(3,867)	(5,415)	(16,849)
Other underwriting income	6,064	7,980	15,519	38,251
Equity in net income (loss) of investment funds accounted for using the equity method	31,090	16,662	111,884	32,054
Other income (loss)	(342)	(400)	(3,118)	(432)
Total revenues	1,479,554	1,197,501	4,206,267	3,475,329
Expenses
Losses and loss adjustment expenses	1,046,141	524,183	2,288,571	1,631,724
Acquisition expenses	193,854	161,267	566,579	501,782
Other operating expenses	170,127	153,286	514,827	460,748
Corporate expenses	17,098	18,485	69,766	45,068
Amortization of intangible assets	31,824	4,865	93,942	14,493
Interest expense	29,510	15,943	86,935	47,713
Net foreign exchange losses (gains)	28,028	2,621	86,975	1,525
Total expenses	1,516,582	880,650	3,707,595	2,703,053
Income (loss) before income taxes	(37,028)	316,851	498,672	772,276
Income tax expense	(8,189)	(13,231)	(70,755)	(43,672)
Net income (loss)	(45,217)	303,620	427,917	728,604
Net (income) loss attributable to noncontrolling interests	11,561	(50,748)	(23,279)	(109,879)
Net income (loss) available to Arch	(33,656)	252,872	404,638	618,725
Preferred dividends	(12,369)	(5,484)	(34,936)	(16,453)
Loss on redemption of preferred shares	(6,735)	0	(6,735)	0
Net income (loss) available to Arch common shareholders	$ (52,760)	$ 247,388	$ 362,967	$ 602,272
Net income per common share
Basic (per share)	$ (0.39)	$ 2.05	$ 2.70	$ 4.99
Diluted (per share)	$ (0.39)	$ 1.98	$ 2.61	$ 4.84
Weighted average common shares and common share equivalents outstanding
Basic (shares)	134,885,451	120,938,916	134,472,129	120,656,420
Diluted (shares)	134,885,451	124,931,653	139,222,324	124,528,174

Unaudited Consolidated Stateme5

Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Comprehensive Income
Net income (loss)	$ (45,217)	$ 303,620	$ 427,917	$ 728,604
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during period	66,462	16,281	260,223	251,722
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0	0	0	(150)
Reclassification of net realized (gains) losses, net of income taxes, included in net income (loss)	(23,912)	(54,992)	(46,180)	(109,309)
Foreign currency translation adjustments	8,280	(5,312)	29,701	(6,150)
Comprehensive income	5,613	259,597	671,661	864,717
Net (income) loss attributable to noncontrolling interests	11,561	(50,748)	(23,279)	(109,879)
Foreign currency translation adjustments attributable to noncontrolling interests	411	(59)	479	141
Comprehensive income available to Arch	$ 17,585	$ 208,790	$ 648,861	$ 754,979

Unaudited Consolidated Stateme6

Unaudited Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Non-cumulative preferred shares	Common shares	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss), net of deferred income tax	Unrealized appreciation (decline) in value of available-for-sale securities, net of deferred income tax	Foreign currency translation adjustments	Common shares held in treasury, at cost	Convertible non-voting common equivalent preferred shares
Cumulative effect of an accounting change					$ 0
Balance at beginning of year, as adjusted					7,332,032
Balance at beginning of year at Dec. 31, 2015		$ 325,000	$ 577	$ 467,339	7,332,032	$ (16,502)	$ 50,085	$ (66,587)	$ (1,941,904)	$ 0
Preferred shares issued		450,000
Preferred shares redeemed		0
Preferred shares converted to common shares				0						0
Common shares issued, net			5
Issue costs on preferred shares				(15,101)
Loss on redemption of preferred shares	$ 0			0	0
All other				63,966
Net income (loss)	728,604				728,604
Net (income) loss attributable to noncontrolling interests	(109,879)				(109,879)
Preferred share dividends	(16,453)				(16,453)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							142,413
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(150)						(150)
Foreign currency translation adjustments	(6,150)							(6,150)
Foreign currency translation adjustments attributable to noncontrolling interests								141
Shares repurchased for treasury									(89,955)
Balance at end of period at Sep. 30, 2016	7,313,983	775,000	582	516,204	7,934,304	119,752	192,348	(72,596)	(2,031,859)	0
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2016	834,808
Total shareholders’ equity at Sep. 30, 2016	8,148,791
Loss on redemption of preferred shares	0
Net income (loss)	303,620
Net (income) loss attributable to noncontrolling interests	(50,748)
Preferred share dividends	(5,484)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0
Foreign currency translation adjustments	(5,312)
Balance at end of period at Sep. 30, 2016	7,313,983	775,000	582	516,204	7,934,304	119,752	192,348	(72,596)	(2,031,859)	0
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2016	834,808
Total shareholders’ equity at Sep. 30, 2016	8,148,791
Cumulative effect of an accounting change					(314)
Balance at beginning of year, as adjusted					7,996,387
Balance at beginning of year at Dec. 31, 2016	8,253,718	772,555	582	531,687	7,996,701	(114,541)	(27,641)	(86,900)	(2,034,570)	1,101,304
Preferred shares issued		230,000
Preferred shares redeemed		(230,000)
Preferred shares converted to common shares				611,653						(611,677)
Common shares issued, net			28
Issue costs on preferred shares				(7,946)
Loss on redemption of preferred shares	(6,735)			6,735	(6,735)
All other				70,831
Net income (loss)	427,917				427,917
Net (income) loss attributable to noncontrolling interests	(23,279)				(23,279)
Preferred share dividends	(34,936)				(34,936)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							214,043
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0						0
Foreign currency translation adjustments	29,701							29,701
Foreign currency translation adjustments attributable to noncontrolling interests								479
Shares repurchased for treasury									(19,074)
Balance at end of period at Sep. 30, 2017	8,911,144	772,555	610	1,212,960	8,359,354	129,682	186,402	(56,720)	(2,053,644)	489,627
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2017	860,898
Total shareholders’ equity at Sep. 30, 2017	9,772,042
Loss on redemption of preferred shares	(6,735)
Net income (loss)	(45,217)
Net (income) loss attributable to noncontrolling interests	11,561
Preferred share dividends	(12,369)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0
Foreign currency translation adjustments	8,280
Balance at end of period at Sep. 30, 2017	8,911,144	$ 772,555	$ 610	$ 1,212,960	$ 8,359,354	$ 129,682	$ 186,402	$ (56,720)	$ (2,053,644)	$ 489,627
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2017	860,898
Total shareholders’ equity at Sep. 30, 2017	$ 9,772,042

Unaudited Consolidated Stateme7

Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating Activities
Net income (loss)	$ 427,917	$ 728,604
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized (gains) losses	(141,944)	(262,112)
Net impairment losses recognized in earnings	5,415	16,849
Equity in net income or loss of investment funds accounted for using the equity method and other income or loss	(63,784)	8,157
Amortization of intangible assets	93,942	14,493
Share-based compensation	58,308	46,311
Changes in:
Reserve for losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable	602,652	277,277
Unearned premiums, net of ceded unearned premiums	230,581	243,109
Premiums receivable	(167,143)	(198,909)
Deferred acquisition costs	(73,631)	(40,906)
Reinsurance balances payable	37,528	49,198
Other items, net	71,293	155,068
Net Cash Provided By Operating Activities	1,081,134	1,037,139
Investing Activities
Purchases of fixed maturity investments	(28,079,129)	(27,840,555)
Purchases of equity securities	(667,135)	(377,767)
Purchases of other investments	(1,406,528)	(1,008,774)
Proceeds from sales of fixed maturity investments	27,629,474	26,731,924
Proceeds from sales of equity securities	751,873	464,904
Proceeds from sales, redemptions and maturities of other investments	938,581	879,330
Proceeds from redemptions and maturities of fixed maturity investments	747,621	540,823
Net settlements of derivative instruments	(20,952)	23,396
Net (purchases) sales of short-term investments	(964,653)	(604,162)
Change in cash collateral related to securities lending	148,692	(27,935)
Acquisitions, net of cash	(27,709)	(20,911)
Purchases of fixed assets	(16,862)	(11,565)
Other	86,145	(3,816)
Net Cash Provided By (Used For) Investing Activities	(880,582)	(1,255,108)
Financing Activities
Proceeds from issuance of preferred shares, net	222,054	434,899
Redemption of preferred shares	(230,000)	0
Purchases of common shares under share repurchase program	0	(75,256)
Proceeds from common shares issued, net	(7,484)	(3,785)
Proceeds from borrowings	238,915	46,000
Repayments of borrowings	(172,000)	(179,171)
Change in cash collateral related to securities lending	(148,692)	27,935
Dividends paid to redeemable noncontrolling interests	(13,491)	(13,491)
Other	(49,280)	33,113
Preferred dividends paid	(34,936)	(16,453)
Net Cash Provided By (Used For) Financing Activities	(194,914)	253,791
Effects of exchange rate changes on foreign currency cash	13,781	(10,332)
Increase (decrease) in cash	19,419	25,490
Cash beginning of year	842,942	553,326
Cash end of period	862,361	578,816
Income taxes paid	47,907	40,742
Interest paid	$ 64,613	$ 35,234

General

General	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General	General Arch Capital Group Ltd. (“ACGL”) is a Bermuda public limited liability company which provides insurance, reinsurance and mortgage insurance on a worldwide basis through its wholly-owned subsidiaries. As used herein, the “Company” means ACGL and its subsidiaries. The Company’s consolidated financial statements include the results of Watford Holdings Ltd. and its wholly owned subsidiaries. See Note 3 . On December 31, 2016, the Company completed the acquisition of United Guaranty Corporation, a North Carolina corporation (“UGC”) pursuant to a stock purchase agreement with American International Group, Inc. (“AIG”). The acquisition of UGC (“UGC acquisition”) expanded the scale of Arch’s existing mortgage insurance businesses by combining UGC’s position as the market leader in the U.S. private mortgage insurance industry with Arch’s financial strength and history of innovation, further diversifying the Company’s business profile and customer base. The interim consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). All significant intercompany transactions and balances have been eliminated in consolidation. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts 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. Actual results could differ from those estimates and assumptions. In the opinion of management, the accompanying unaudited interim consolidated financial statements reflect all adjustments (consisting of normally recurring accruals) necessary for a fair statement of results on an interim basis. The results of any interim period are not necessarily indicative of the results for a full year or any future periods. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted; however, management believes that the disclosures are adequate to make the information presented not misleading. This report should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2016 (“2016 Form 10-K”), including the Company’s audited consolidated financial statements and related notes. The Company has reclassified the presentation of certain prior year information to conform to the current presentation, including the presentation of ‘amortization of intangible assets’ on its consolidated statements of income to split out such item (previously reflected in acquisition expenses and/or other operating expenses). Such reclassifications had no effect on the Company’s net income, comprehensive income, shareholders’ equity or cash flows. Tabular amounts are in U.S. Dollars in thousands, except share amounts, unless otherwise noted.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Issued Accounting Standards Adopted The Company adopted Financial Accounting Standards Board (“FASB”) Accounting Standard Update (“ASU”) 2016-09, “Compensation - Stock Compensation (Topic 718) - Improvements to Employee Share-Based Payment Accounting,” effective January 1, 2017 . This ASU was issued in the 2016 first quarter to improve and simplify the accounting for employee share-based payment transactions. This ASU provides simplifications with respect to income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows for these types of transactions. With respect to the forfeiture accounting policy election, the Company has elected to account for forfeitures as they occur, which did not result in a material cumulative effect adjustment. With respect to the change in presentation in the statement of cash flows related to excess tax benefits, the Company has applied the guidance prospectively and prior periods have not been adjusted. Recently Issued Accounting Standards Not Yet Adopted ASU 2014-09, “Revenue from Contracts with Customers (Topic 606),” was issued in the 2014 second quarter and updated through various ASUs in 2016. This ASU (and as updated in 2016) creates a new comprehensive revenue recognition standard that will serve as a single source of revenue guidance for all companies in all industries. The guidance applies to all companies that either enter into contracts with customers to transfer goods or services or enter into contracts for the transfer of non-financial assets, unless those contracts are within the scope of other standards, such as insurance contracts or financial instruments.The ASU also requires enhanced disclosures about revenue. The ASU is effective in the 2018 first quarter and the Company intends on adopting the ASU using the modified retrospective method, whereby the cumulative effect of adoption will be recognized as an adjustment to retained earnings at the date of initial application. The adoption of this ASU will not impact the Company's insurance premium revenues or revenues from its investment portfolio, which represent a substantial portion of consolidated revenues, but may have an impact on the Company's other revenues. Based on the Company’s evaluation of the impacted revenue streams, the ASU is not expected to have a material effect on the Company’s consolidated financial statements and the cumulative effect adjustment to retained earnings at the date of initial application is not expected to be material. ASU 2016-01, “Financial Instruments - Overall (Subtopic 825-10) - Recognition and Measurement of Financial Assets and Financial Liabilities, ” was issued in the 2016 first quarter to enhance the reporting model for financial instruments and to provide improved financial information to readers of the financial statements. Among other provisions focused on improving the recognition and measurement of financial instruments, the ASU requires that equity investments be measured at fair value on the balance sheet with changes in fair value reported in the income statement and that an exit price notion be used when measuring the fair value of financial instruments for disclosure purposes. The ASU is effective in the 2018 first quarter and, aside from limited situations, cannot be early adopted. The Company is currently assessing the impact the implementation of this ASU will have on its consolidated financial statements. The adoption of this ASU is not expected to have a material impact on the Company's financial position, cash flows, or total comprehensive income, but will have a material impact on the Company's results of operations as changes in fair value of equity instruments will be presented in net income rather than other comprehensive income. ASU 2016-18, "Statement of Cash Flows (Topic 230) - Restricted Cash " was issued in the 2016 fourth quarter. The ASU requires that restricted cash and restricted cash equivalents be included with cash and cash equivalents in the reconciliation of beginning and ending cash on the statements of cash flows. As a result, transfers between cash and cash equivalents and restricted cash and restricted cash equivalents will no longer be presented on the statement of cash flows. The ASU is effective, with retrospective adoption, for interim and annual periods beginning after December 15, 2017, with early adoption permitted. The Company is currently assessing the impact the implementation of this ASU will have on its consolidated financial statements. The adoption of this ASU is not expected to have a material effect on the Company’s results of operations, financial position, comprehensive income or net cash provided from operating activities. ASU 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities,” was issued in the 2017 first quarter. The ASU amends the amortization period for certain purchased callable debt securities held at a premium by shortening the amortization period for the premium to the earliest call date. The ASU will be effective for the Company on January 1, 2019 and is required to be applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The Company is currently assessing the impact the implementation of this ASU will have on its consolidated financial statements. The adoption of this ASU is not expected to have a material effect on the Company’s results of operations, financial position or cash flows . ASU 2017-09, “Compensation - Stock Compensation (Topic 718) - Scope of Modification Accounting ” was issued in the 2017 second quarter. The ASU provides updated guidance to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The ASU is effective prospectively for all companies for annual periods beginning on or after December 15, 2017, with early adoption permitted. The adoption of this ASU is not expected to have a material effect on the Company’s results of operations, financial position or cash flows .

Variable Interest Entities and

Variable Interest Entities and Noncontrolling Interests	9 Months Ended
	Sep. 30, 2017
Noncontrolling Interest [Abstract]
Variable Interest Entity and Noncontrolling Interests	Variable Interest Entities and Noncontrolling Interests A variable interest entity (“VIE”) refers to an entity that has characteristics such as (i) insufficient equity at risk to allow the entity to finance its activities without additional financial support or (ii) instances where the equity investors, as a group, do not have characteristics of a controlling financial interest. The primary beneficiary of a VIE is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (i) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (ii) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. If a company is determined to be the primary beneficiary, it is required to consolidate the VIE in its financial statements. Watford Holdings Ltd. In March 2014, the Company invested $100.0 million and acquired approximately 11% of Watford Holdings Ltd.’s common equity and a warrant to purchase additional common equity. Watford Holdings Ltd. is the parent of Watford Re Ltd., a multi-line Bermuda reinsurance company (together with Watford Holdings Ltd., “Watford Re”). Watford Re is considered a VIE and the Company concluded that it is the primary beneficiary of Watford Re. As such, the results of Watford Re are included in the Company’s consolidated financial statements. The Company does not guarantee or provide credit support for Watford Re, and the Company’s financial exposure to Watford Re is limited to its investment in Watford Re’s common and preferred shares and counterparty credit risk (mitigated by collateral) arising from reinsurance transactions. The following table provides the carrying amount and balance sheet caption in which the assets and liabilities of Watford Re are reported: September 30, December 31, 2017 2016 Assets Investments accounted for using the fair value option $ 2,457,365 $ 1,857,623 Cash 57,151 74,893 Accrued investment income 13,718 17,017 Premiums receivable 209,985 189,911 Reinsurance recoverable on unpaid and paid losses and LAE 37,575 24,420 Ceded unearned premiums 23,538 12,145 Deferred acquisition costs 87,692 86,379 Receivable for securities sold 74,051 1,326 Goodwill and intangible assets 7,650 7,650 Other assets 132,796 111,386 Total assets of consolidated VIE $ 3,101,521 $ 2,382,750 Liabilities Reserves for losses and loss adjustment expenses $ 735,132 $ 510,809 Unearned premiums 344,060 293,480 Reinsurance balances payable 22,487 12,289 Revolving credit agreement borrowings 426,242 256,650 Payable for securities purchased 211,065 42,922 Other liabilities 174,472 88,976 Total liabilities of consolidated VIE $ 1,913,458 $ 1,205,126 Redeemable noncontrolling interests $ 220,529 $ 220,253 For the nine months ended September 30, 2017 , Watford Re generated $221.9 million of cash provided by operating activities, $394.4 million of cash used for investing activities and $152.5 million of cash provided by financing activities, compared to $207.0 million of cash provided by operating activities, $124.0 million of cash used for investing activities and $119.6 million of cash used for financing activities for the nine months ended September 30, 2016 . Non-redeemable noncontrolling interests The Company accounts for the portion of Watford Re’s common equity attributable to third party investors in the shareholders’ equity section of its consolidated balance sheets. The noncontrolling ownership in Watford Re’s common shares was approximately 89% at September 30, 2017 . The portion of Watford Re’s income or loss attributable to third party investors is recorded in the consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests.’ The following table sets forth activity in the non-redeemable noncontrolling interests: September 30, 2017 2016 Three Months Ended Balance, beginning of period $ 877,456 $ 788,589 Amounts attributable to noncontrolling interests (16,147 ) 46,160 Foreign currency translation adjustments attributable to noncontrolling interests (411 ) 59 Balance, end of period $ 860,898 $ 834,808 Nine Months Ended Balance, beginning of year $ 851,854 $ 738,831 Amounts attributable to noncontrolling interests 9,523 96,118 Foreign currency translation adjustments attributable to noncontrolling interests (479 ) (141 ) Balance, end of period $ 860,898 $ 834,808 Redeemable noncontrolling interests The Company accounts for redeemable noncontrolling interests in the mezzanine section of its consolidated balance sheets in accordance with applicable accounting guidance. Such redeemable noncontrolling interests relate to the 9,065,200 cumulative redeemable preference shares (“Watford Preference Shares”) issued in March 2014 with a par value of $0.01 per share and a liquidation preference of $25.00 per share. Preferred dividends, including the accretion of the discount and issuance costs, are included in ‘net (income) loss attributable to noncontrolling interests’ in the Company’s consolidated statements of income. The following table sets forth activity in the redeemable non-controlling interests: September 30, 2017 2016 Three Months Ended Balance, beginning of period $ 205,736 $ 205,366 Accretion of preference share issuance costs 93 93 Balance, end of period $ 205,829 $ 205,459 Nine Months Ended Balance, beginning of year $ 205,553 $ 205,182 Accretion of preference share issuance costs 276 277 Balance, end of period $ 205,829 $ 205,459 The portion of Watford Re’s income or loss attributable to third party investors, recorded in the Company’s consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests,’ are summarized in the table below: September 30, 2017 2016 Three Months Ended Amounts attributable to non-redeemable noncontrolling interests $ 16,147 $ (46,160 ) Dividends attributable to redeemable noncontrolling interests (4,586 ) (4,588 ) Net (income) loss attributable to noncontrolling interests $ 11,561 $ (50,748 ) Nine Months Ended Amounts attributable to non-redeemable noncontrolling interests $ (9,523 ) $ (96,118 ) Dividends attributable to redeemable noncontrolling interests (13,756 ) (13,761 ) Net (income) loss attributable to noncontrolling interests $ (23,279 ) $ (109,879 ) Bellemeade Re I and II Upon closing of the UGC acquisition, the Company acquired the rights and obligations related to aggregate excess of loss reinsurance agreements with Bellemeade Re I Ltd. (“Bellemeade I”), entered into in July 2015, and with Bellemeade Re II Ltd. (“Bellemeade II”), entered into in May 2016 (the “Bellemeade Agreements”). Bellemeade I and Bellemeade II are special purpose reinsurance companies domiciled in Bermuda, each of which provided for up to approximately $300 million of aggregate excess of loss reinsurance coverage at inception for new delinquencies on portfolios of in-force policies issued. As a result of the evaluation of the Bellemeade Agreements, the Company concluded that both Bellemeade I and Bellemeade II are VIEs. However, given that the ceding insurers do not have the unilateral power to direct those activities that are significant to the economic performance of Bellemeade I and Bellemeade II, the Company does not consolidate Bellemeade I and Bellemeade II in its consolidated financial statements. The following table presents total assets of Bellemeade I and Bellemeade II as well as the Company’s maximum exposure to loss associated with these VIEs: Maximum Exposure to Loss Total VIE Assets On-Balance Sheet Off-Balance Sheet Total Bellemeade I $ 112,090 $ 533 $ 1,009 $ 1,542 Bellemeade II 191,387 (53 ) 746 693 Total $ 303,477 $ 480 $ 1,755 $ 2,235 See note 18 , “Subsequent Event.” Irving Partners Limited Partnership Upon closing of the UGC acquisition, the Company acquired a limited partnership interest in Irving Partners Limited Partnership (“Irving Partners”), which owns and operates an office building in Greensboro, North Carolina in which the Company is the main tenant. The Company concluded that Irving Partners is a VIE but that it is not the primary beneficiary. During the 2017 third quarter, the Company’s ownership in Irving Partners was sold to a third party for approximately $14.5 million .

Earnings Per Common Share

Earnings Per Common Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings (Loss) Per Common Share Due to the net loss recorded in the 2017 third quarter, diluted weighted average common shares and common share equivalents outstanding for the 2017 third quarter do not include the effect of 4.7 million otherwise dilutive securities since the inclusion of such securities is anti-dilutive to per share results. Since the Company reported net income for the other periods presented, the computation of diluted average shares outstanding includes dilutive securities for such periods. The following table sets forth the computation of basic and diluted earnings (loss) per common share: Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Numerator: Net income (loss) $ (45,217 ) $ 303,620 $ 427,917 $ 728,604 Amounts attributable to noncontrolling interests 11,561 (50,748 ) (23,279 ) (109,879 ) Net income (loss) available to Arch (33,656 ) 252,872 404,638 618,725 Preferred dividends (12,369 ) (5,484 ) (34,936 ) (16,453 ) Loss on redemption of preferred shares (6,735 ) — (6,735 ) — Net income (loss) available to Arch common shareholders $ (52,760 ) $ 247,388 $ 362,967 $ 602,272 Denominator: Weighted average common shares outstanding 129,211,251 120,938,916 124,526,611 120,656,420 Series D preferred shares (1) 5,674,200 — 9,945,518 — Weighted average common shares and common share equivalents outstanding — basic 134,885,451 120,938,916 134,472,129 120,656,420 Effect of dilutive common share equivalents: Nonvested restricted shares — 1,313,025 1,459,879 1,295,825 Stock options (2) — 2,679,712 3,290,316 2,575,929 Weighted average common shares and common share equivalents outstanding — diluted (3) 134,885,451 124,931,653 139,222,324 124,528,174 Earnings (loss) per common share: Basic $ (0.39 ) $ 2.05 $ 2.70 $ 4.99 Diluted $ (0.39 ) $ 1.98 $ 2.61 $ 4.84 (1) Such shares are convertible non-voting common equivalent preferred shares issued in connection with the UGC acquisition. (2) Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2017 third quarter and 2016 third quarter , the number of stock options excluded were nil and 334,203 , respectively. For the nine months ended September 30, 2017 and 2016 , the number of stock options excluded were 838,868 and 842,105 , respectively.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Segment Information	Segment Information The Company classifies its businesses into three underwriting segments — insurance, reinsurance and mortgage — and two other operating segments — ‘other’ and corporate (non-underwriting). The Company determined its reportable segments using the management approach described in accounting guidance regarding disclosures about segments of an enterprise and related information. The accounting policies of the segments are the same as those used for the preparation of the Company’s consolidated financial statements. Intersegment business is allocated to the segment accountable for the underwriting results. The Company’s insurance, reinsurance and mortgage segments each have managers who are responsible for the overall profitability of their respective segments and who are directly accountable to the Company’s chief operating decision makers, the Chairman and Chief Executive Officer, the President and Chief Operating Officer, and the Chief Financial Officer of ACGL. The chief operating decision makers do not assess performance, measure return on equity or make resource allocation decisions on a line of business basis. Management measures segment performance for its three underwriting segments based on underwriting income or loss. The Company does not manage its assets by underwriting segment, with the exception of goodwill and intangible assets, and, accordingly, investment income is not allocated to each underwriting segment. The insurance segment consists of the Company’s insurance underwriting units which offer specialty product lines on a worldwide basis. Product lines include: construction and national accounts; excess and surplus casualty; lenders products; professional lines; programs; property, energy, marine and aviation; travel, accident and health; and other (consisting of alternative markets, excess workers' compensation and surety business). The reinsurance segment consists of the Company’s reinsurance underwriting units which offer specialty product lines on a worldwide basis. Product lines include: casualty; marine and aviation; other specialty; property catastrophe; property excluding property catastrophe (losses on a single risk, both excess of loss and pro rata); and other (consisting of life reinsurance, casualty clash and other). The mortgage segment includes the Company’s U.S. and international mortgage insurance and reinsurance operations as well as government sponsored enterprise (“GSE”) credit-risk sharing transactions. Arch Mortgage Insurance Company, United Guaranty Residential Insurance Company and United Guaranty Mortgage Indemnity Company (combined “Arch MI U.S.”) are approved as eligible mortgage insurers by Federal National Mortgage Association (“Fannie Mae”) and Federal Home Loan Mortgage Corporation (“Freddie Mac”), each a GSE. The corporate (non-underwriting) segment results include net investment income, other income (loss), corporate expenses, UGC transaction costs and other, interest expense, items related to the Company’s non-cumulative preferred shares, net realized gains or losses, net impairment losses included in earnings, equity in net income or loss of investment funds accounted for using the equity method, net foreign exchange gains or losses and income taxes. Such amounts exclude the results of the ‘other’ segment. The ‘other’ segment includes the results of Watford Re (see Note 3 ). Watford Re has its own management and board of directors that is responsible for the overall profitability of the ‘other’ segment. For the ‘other’ segment, performance is measured based on net income or loss. The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income or loss to net income available to common shareholders: Three Months Ended September 30, 2017 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 787,447 $ 422,083 $ 347,951 $ 1,557,179 $ 166,198 $ 1,648,246 Premiums ceded (222,516 ) (105,389 ) (57,900 ) (385,503 ) (12,471 ) (322,843 ) Net premiums written 564,931 316,694 290,051 1,171,676 153,727 1,325,403 Change in unearned premiums (29,766 ) 6,879 (15,533 ) (38,420 ) (25,097 ) (63,517 ) Net premiums earned 535,165 323,573 274,518 1,133,256 128,630 1,261,886 Other underwriting income (loss) — 1,728 3,599 5,327 737 6,064 Losses and loss adjustment expenses (568,795 ) (318,609 ) (35,156 ) (922,560 ) (123,581 ) (1,046,141 ) Acquisition expenses (82,638 ) (57,340 ) (21,803 ) (161,781 ) (32,073 ) (193,854 ) Other operating expenses (90,875 ) (36,214 ) (34,770 ) (161,859 ) (8,268 ) (170,127 ) Underwriting income (loss) $ (207,143 ) $ (86,862 ) $ 186,388 (107,617 ) (34,555 ) (142,172 ) Net investment income 94,127 22,332 116,459 Net realized gains (losses) 64,104 2,171 66,275 Net impairment losses recognized in earnings (1,878 ) — (1,878 ) Equity in net income (loss) of investment funds accounted for using the equity method 31,090 — 31,090 Other income (loss) (342 ) — (342 ) Corporate expenses (2) (14,108 ) — (14,108 ) UGC transaction costs and other (2) (2,990 ) — (2,990 ) Amortization of intangible assets (31,824 ) — (31,824 ) Interest expense (26,264 ) (3,246 ) (29,510 ) Net foreign exchange gains (losses) (27,785 ) (243 ) (28,028 ) Income (loss) before income taxes (23,487 ) (13,541 ) (37,028 ) Income tax (expense) benefit (8,168 ) (21 ) (8,189 ) Net income (loss) (31,655 ) (13,562 ) (45,217 ) Dividends attributable to redeemable noncontrolling interests — (4,586 ) (4,586 ) Amounts attributable to nonredeemable noncontrolling interests — 16,147 16,147 Net income (loss) available to Arch (31,655 ) (2,001 ) (33,656 ) Preferred dividends (12,369 ) — (12,369 ) Loss on redemption of preferred shares (6,735 ) — (6,735 ) Net income (loss) available to Arch common shareholders $ (50,759 ) $ (2,001 ) $ (52,760 ) Underwriting Ratios Loss ratio 106.3 % 98.5 % 12.8 % 81.4 % 96.1 % 82.9 % Acquisition expense ratio 15.4 % 17.7 % 7.9 % 14.3 % 24.9 % 15.4 % Other operating expense ratio 17.0 % 11.2 % 12.7 % 14.3 % 6.4 % 13.5 % Combined ratio 138.7 % 127.4 % 33.4 % 110.0 % 127.4 % 111.8 % Goodwill and intangible assets $ 23,445 $ 417 $ 652,893 $ 676,755 $ 7,650 $ 684,405 (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’ Three Months Ended September 30, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 758,934 $ 324,361 $ 131,726 $ 1,214,765 $ 163,736 $ 1,278,765 Premiums ceded (217,446 ) (89,551 ) (51,182 ) (357,923 ) (6,300 ) (264,487 ) Net premiums written 541,488 234,810 80,544 856,842 157,436 1,014,278 Change in unearned premiums (22,410 ) 17,117 (3,582 ) (8,875 ) (47,000 ) (55,875 ) Net premiums earned 519,078 251,927 76,962 847,967 110,436 958,403 Other underwriting income (loss) — 2,216 4,740 6,956 1,024 7,980 Losses and loss adjustment expenses (332,845 ) (105,924 ) (11,107 ) (449,876 ) (74,307 ) (524,183 ) Acquisition expenses (77,146 ) (50,192 ) (5,190 ) (132,528 ) (28,739 ) (161,267 ) Other operating expenses (86,613 ) (35,389 ) (24,249 ) (146,251 ) (7,035 ) (153,286 ) Underwriting income (loss) $ 22,474 $ 62,638 $ 41,156 126,268 1,379 127,647 Net investment income 66,282 27,336 93,618 Net realized gains (losses) 95,946 29,159 125,105 Net impairment losses recognized in earnings (3,867 ) — (3,867 ) Equity in net income (loss) of investment funds accounted for using the equity method 16,662 — 16,662 Other income (loss) (400 ) — (400 ) Corporate expenses (2) (11,343 ) — (11,343 ) UGC transaction costs and other (2) (7,142 ) — (7,142 ) Amortization of intangible assets (4,865 ) — (4,865 ) Interest expense (12,924 ) (3,019 ) (15,943 ) Net foreign exchange gains (losses) (4,232 ) 1,611 (2,621 ) Income (loss) before income taxes 260,385 56,466 316,851 Income tax (expense) benefit (13,232 ) 1 (13,231 ) Net income (loss) 247,153 56,467 303,620 Dividends attributable to redeemable noncontrolling interests — (4,588 ) (4,588 ) Amounts attributable to nonredeemable noncontrolling interests — (46,160 ) (46,160 ) Net income (loss) available to Arch 247,153 5,719 252,872 Preferred dividends (5,484 ) — (5,484 ) Net income (loss) available to Arch common shareholders $ 241,669 $ 5,719 $ 247,388 Underwriting Ratios Loss ratio 64.1 % 42.0 % 14.4 % 53.1 % 67.3 % 54.7 % Acquisition expense ratio 14.9 % 19.9 % 6.7 % 15.6 % 26.0 % 16.8 % Other operating expense ratio 16.7 % 14.0 % 31.5 % 17.2 % 6.4 % 16.0 % Combined ratio 95.7 % 75.9 % 52.6 % 85.9 % 99.7 % 87.5 % Goodwill and intangible assets $ 26,367 $ 1,228 $ 55,696 $ 83,291 $ 7,650 $ 90,941 (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’ Nine Months Ended September 30, 2017 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,313,630 $ 1,351,051 $ 1,032,800 $ 4,697,007 $ 473,131 $ 4,915,895 Premiums ceded (704,057 ) (386,743 ) (194,139 ) (1,284,465 ) (35,315 ) (1,065,537 ) Net premiums written 1,609,573 964,308 838,661 3,412,542 437,816 3,850,358 Change in unearned premiums (51,188 ) (81,182 ) (61,776 ) (194,146 ) (36,435 ) (230,581 ) Net premiums earned 1,558,385 883,126 776,885 3,218,396 401,381 3,619,777 Other underwriting income (loss) — 1,143 11,999 13,142 2,377 15,519 Losses and loss adjustment expenses (1,252,375 ) (631,669 ) (84,915 ) (1,968,959 ) (319,612 ) (2,288,571 ) Acquisition expenses (236,378 ) (154,638 ) (76,235 ) (467,251 ) (99,328 ) (566,579 ) Other operating expenses (271,268 ) (110,458 ) (108,790 ) (490,516 ) (24,311 ) (514,827 ) Underwriting income (loss) $ (201,636 ) $ (12,496 ) $ 518,944 304,812 (39,493 ) 265,319 Net investment income 282,459 62,998 345,457 Net realized gains (losses) 110,662 11,501 122,163 Net impairment losses recognized in earnings (5,415 ) — (5,415 ) Equity in net income (loss) of investment funds accounted for using the equity method 111,884 — 111,884 Other income (loss) (3,118 ) — (3,118 ) Corporate expenses (2) (48,517 ) — (48,517 ) UGC transaction costs and other (2) (21,249 ) — (21,249 ) Amortization of intangible assets (93,942 ) — (93,942 ) Interest expense (77,932 ) (9,003 ) (86,935 ) Net foreign exchange gains (losses) (85,451 ) (1,524 ) (86,975 ) Income (loss) before income taxes 474,193 24,479 498,672 Income tax (expense) benefit (70,734 ) (21 ) (70,755 ) Net income (loss) 403,459 24,458 427,917 Dividends attributable to redeemable noncontrolling interests — (13,756 ) (13,756 ) Amounts attributable to nonredeemable noncontrolling interests — (9,523 ) (9,523 ) Net income (loss) available to Arch 403,459 1,179 404,638 Preferred dividends (34,936 ) — (34,936 ) Loss on redemption of preferred shares (6,735 ) — (6,735 ) Net income (loss) available to Arch common shareholders $ 361,788 $ 1,179 $ 362,967 Underwriting Ratios Loss ratio 80.4 % 71.5 % 10.9 % 61.2 % 79.6 % 63.2 % Acquisition expense ratio 15.2 % 17.5 % 9.8 % 14.5 % 24.7 % 15.7 % Other operating expense ratio 17.4 % 12.5 % 14.0 % 15.2 % 6.1 % 14.2 % Combined ratio 113.0 % 101.5 % 34.7 % 90.9 % 110.4 % 93.1 % (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’ Nine Months Ended September 30, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,319,530 $ 1,217,804 $ 361,440 $ 3,898,025 $ 421,627 $ 4,046,667 Premiums ceded (713,110 ) (370,068 ) (62,918 ) (1,145,347 ) (15,229 ) (887,591 ) Net premiums written 1,606,420 847,736 298,522 2,752,678 406,398 3,159,076 Change in unearned premiums (46,603 ) (43,345 ) (93,283 ) (183,231 ) (59,878 ) (243,109 ) Net premiums earned 1,559,817 804,391 205,239 2,569,447 346,520 2,915,967 Other underwriting income (loss) — 22,659 12,670 35,329 2,922 38,251 Losses and loss adjustment expenses (1,011,087 ) (363,613 ) (20,102 ) (1,394,802 ) (236,922 ) (1,631,724 ) Acquisition expenses (228,806 ) (160,706 ) (16,947 ) (406,459 ) (95,323 ) (501,782 ) Other operating expenses (263,111 ) (108,561 ) (70,590 ) (442,262 ) (18,486 ) (460,748 ) Underwriting income (loss) $ 56,813 $ 194,170 $ 110,270 361,253 (1,289 ) 359,964 Net investment income 207,088 68,603 275,691 Net realized gains (losses) 168,735 61,912 230,647 Net impairment losses recognized in earnings (16,849 ) — (16,849 ) Equity in net income (loss) of investment funds accounted for using the equity method 32,054 — 32,054 Other income (loss) (432 ) — (432 ) Corporate expenses (2) (37,926 ) — (37,926 ) UGC transaction costs and other (2) (7,142 ) — (7,142 ) Amortization of intangible assets (14,493 ) — (14,493 ) Interest expense (37,983 ) (9,730 ) (47,713 ) Net foreign exchange gains (losses) (3,812 ) 2,287 (1,525 ) Income (loss) before income taxes 650,493 121,783 772,276 Income tax (expense) benefit (43,673 ) 1 (43,672 ) Net income (loss) 606,820 121,784 728,604 Dividends attributable to redeemable noncontrolling interests — (13,761 ) (13,761 ) Amounts attributable to nonredeemable noncontrolling interests — (96,118 ) (96,118 ) Net income (loss) available to Arch 606,820 11,905 618,725 Preferred dividends (16,453 ) — (16,453 ) Net income (loss) available to Arch common shareholders $ 590,367 $ 11,905 $ 602,272 Underwriting Ratios Loss ratio 64.8 % 45.2 % 9.8 % 54.3 % 68.4 % 56.0 % Acquisition expense ratio 14.7 % 20.0 % 8.3 % 15.8 % 27.5 % 17.2 % Other operating expense ratio 16.9 % 13.5 % 34.4 % 17.2 % 5.3 % 15.8 % Combined ratio 96.4 % 78.7 % 52.5 % 87.3 % 101.2 % 89.0 % (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’

Reserve for Losses and Loss Adj

Reserve for Losses and Loss Adjustment Expenses	9 Months Ended
	Sep. 30, 2017
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Reserve for losses and loss adjustment expenses	Reserve for Losses and Loss Adjustment Expenses The following table represents an analysis of losses and loss adjustment expenses and a reconciliation of the beginning and ending reserve for losses and loss adjustment expenses: Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Reserve for losses and loss adjustment expenses at beginning of period $ 10,520,511 $ 9,471,647 $ 10,200,960 $ 9,125,250 Unpaid losses and loss adjustment expenses recoverable and deferred charges 2,116,210 2,003,768 2,083,575 1,828,837 Net reserve for losses and loss adjustment expenses at beginning of period 8,404,301 7,467,879 8,117,385 7,296,413 Net incurred losses and loss adjustment expenses relating to losses occurring in: Current year 1,092,175 598,940 2,487,212 1,848,299 Prior years (45,232 ) (74,757 ) (197,839 ) (216,575 ) Discount and accretion on retroactive reinsurance (802 ) — (802 ) — Total net incurred losses and loss adjustment expenses 1,046,141 524,183 2,288,571 1,631,724 Net foreign exchange losses (gains) 61,919 1,463 168,493 (13,270 ) Net paid losses and loss adjustment expenses relating to losses occurring in: Current year (167,450 ) (128,432 ) (282,952 ) (285,468 ) Prior years (457,183 ) (304,673 ) (1,403,769 ) (1,068,979 ) Total net paid losses and loss adjustment expenses (624,633 ) (433,105 ) (1,686,721 ) (1,354,447 ) Net reserve for losses and loss adjustment expenses at end of period 8,887,728 7,560,420 8,887,728 7,560,420 Unpaid losses and loss adjustment expenses recoverable and deferred charges 2,463,539 2,049,769 2,463,539 2,049,769 Reserve for losses and loss adjustment expenses at end of period $ 11,351,267 $ 9,610,189 $ 11,351,267 $ 9,610,189 2017 Third Quarter Catastrophe Losses The Company’s 2017 third quarter results reflect estimated net losses from current accident year catastrophic events of $347.8 million , net of reinsurance and reinstatement premiums, which consisted of $133.4 million from the reinsurance segment and $214.5 million from the insurance segment. Such amounts were primarily related to Hurricanes Harvey, Irma and Maria, along with the Mexican earthquakes and other more minor global events. In addition, estimated net losses from current accident year catastrophic events for the 2017 third quarter in the ‘other’ segment were $19.8 million . Development on Prior Year Loss Reserves 2017 Third Quarter During the 2017 third quarter , the Company recorded net favorable development on prior year loss reserves of $45.2 million , which consisted of $36.5 million from the reinsurance segment, $3.0 million from the insurance segment, $21.5 million from the mortgage segment and adverse development of $15.8 million from the ‘other’ segment. The reinsurance segment’s net favorable development of $36.5 million , or 11.3 points, for the 2017 third quarter consisted of $16.9 million from short-tailed lines and $19.6 million from long-tailed and medium-tailed lines. Favorable development in short-tailed lines included $11.8 million from property catastrophe and property other than property catastrophe reserves, across most underwriting years ( i.e. , all premiums and losses attributable to contracts having an inception or renewal date within the given twelve-month period), reflecting lower levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during the period. Favorable development in long-tailed and medium-tailed lines reflected reductions in casualty reserves of $13.4 million based on varying levels of reported and paid claims activity, primarily from the 2002 to 2009 underwriting years, and favorable development in marine reserves of $4.3 million across most underwriting years. The insurance segment’s net favorable development of $3.0 million , or 0.6 points, for the 2017 third quarter consisted of $1.8 million of net favorable development in short-tailed lines and $1.2 million of net favorable development in long-tailed and medium-tailed lines. Net favorable development in short-tailed lines primarily resulted from property (including special risk other than marine) reserves from the 2011 to 2016 accident years ( i.e. , the year in which a loss occurred). Net favorable development in medium-tailed lines reflected $11.9 million from professional liability reserves across most accident years and in surety reserves with $4.2 million of favorable development. Such amounts were partially offset by $12.9 million of adverse development on a small number of programs in the 2014 to 2016 accident years. The mortgage segment’s net favorable development was $21.5 million , or 7.8 points, for the 2017 third quarter . The 2017 third quarter development was primarily driven by continued lower than expected claim emergence across most origination years and also reflected $6.1 million related to second lien and other portfolios, primarily due to subrogation recoveries. 2016 Third Quarter During the 2016 third quarter , the Company recorded net favorable development on prior year loss reserves of $74.8 million , which consisted of $59.5 million from the reinsurance segment, $13.7 million from the insurance segment, $2.5 million from the mortgage segment and adverse development of $0.9 million from the ‘other’ segment. The reinsurance segment’s net favorable development of $59.5 million , or 23.6 points, for the 2016 third quarter consisted of $27.7 million from short-tailed lines and $31.8 million from long-tailed and medium-tailed lines. Favorable development in short-tailed lines included $23.2 million from property catastrophe and property other than property catastrophe reserves, across most underwriting years, reflecting lower levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during the period. Favorable development in long-tailed lines reflected reductions in casualty reserves of $29.3 million based on varying levels of reported and paid claims activity, primarily from the 2002 to 2010 underwriting years and 2012 to 2013 underwriting years. The insurance segment’s net favorable development of $13.7 million , or 2.6 points, for the 2016 third quarter consisted of $18.2 million of net favorable development in long-tailed lines, partially offset by $2.4 million of net adverse development in short-tailed lines and $2.0 million of net adverse development in medium-tailed lines. Net favorable development in long-tailed lines reflected net reductions in executive assurance reserves from the 2008 to 2015 accident years, and net reductions in casualty reserves from the 2007 and 2008 accident years. Net adverse development in short-tailed lines primarily resulted from property (including special risk other than marine) reserves from the 2015 accident year, primarily due to a small number of attritional losses. Net adverse development in medium-tailed lines primarily resulted from an increase in programs of $6.2 million stemming in part from terminated programs, partially offset by favorable development of $4.2 million in other medium-tailed lines, primarily in professional liability and surety. The mortgage segment’s net favorable development was $2.5 million , or 3.2 points, for the 2016 third quarter . The 2016 third quarter development was primarily driven by lower than expected claim rates across most origination years. Nine Months Ended September 30, 2017 During the nine months ended September 30, 2017 , the Company recorded net favorable development on prior year loss reserves of $197.8 million , which consisted of $133.3 million from the reinsurance segment, $7.2 million from the insurance segment, $74.9 million from the mortgage segment and adverse development of $17.5 million from the ‘other’ segment. The reinsurance segment’s net favorable development of $133.3 million , or 15.1 points, for the 2017 period consisted of $85.8 million from short-tailed lines and $47.5 million from long-tailed and medium-tailed lines. Favorable development in short-tailed lines included $62.7 million from property catastrophe and property other than property catastrophe reserves, across most underwriting years, reflecting lower levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during the period. Favorable development in long-tailed and medium-tailed lines reflected reductions in casualty reserves of $28.0 million based on varying levels of reported and paid claims activity, primarily from the 2002 to 2013 underwriting years, and favorable development in marine reserves of $16.6 million across most underwriting years. The insurance segment’s net favorable development of $7.2 million , or 0.5 points, for the 2017 period consisted of $9.0 million of net favorable development in short-tailed lines and $7.4 million of net favorable development in long-tailed lines, partially offset by $9.2 million of net adverse development in medium-tailed lines. Net favorable development in short-tailed lines primarily resulted from property (including special risk other than marine) reserves from the 2011 to 2016 accident years. Net favorable development in long-tailed lines reflected net reductions in executive assurance reserves from the 2008 to 2014 accident years and reductions in healthcare reserves across various accident years, partially offset by $17.2 million of adverse development on construction reserves across various accident years. Net adverse development in medium-tailed lines primarily resulted from an increase in programs of $39.3 million stemming in part from development on a small number of programs in the 2013 to 2015 accident years, partially offset by net favorable development of $30.1 million in other medium-tailed lines, primarily in professional liability and surety. The mortgage segment’s net favorable development was $74.9 million , or 9.6 points, for the 2017 period. The development was primarily driven by continued lower than expected claim emergence across most origination years and also reflected $19.2 million related to second lien and other portfolios, primarily due to subrogation recoveries. Nine Months Ended September 30, 2016 During the nine months ended September 30, 2016 , the Company recorded net favorable development on prior year loss reserves of $216.6 million , which consisted of $176.7 million from the reinsurance segment, $24.8 million from the insurance segment, $16.3 million from the mortgage segment and adverse development of $1.2 million from the ‘other’ segment. The reinsurance segment’s net favorable development of $176.7 million , or 22.0 points, for the 2016 period consisted of $113.1 million from short-tailed lines and $63.6 million from long-tailed and medium-tailed lines. Favorable development in short-tailed lines included $92.6 million from property catastrophe and property other than property catastrophe reserves, across most underwriting years. The net reduction of loss estimates for the reinsurance segment’s short-tailed lines primarily resulted from varying levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during the period. Favorable development in long-tailed lines reflected reductions in casualty reserves of $66.4 million based on varying levels of reported and paid claims activity, primarily from the 2002 to 2013 underwriting years. Such amounts were partially offset by net adverse development on marine reserves, primarily from the 2002 and 2015 underwriting years, partially offset by favorable development from most other underwriting years. The insurance segment’s net favorable development of $24.8 million , or 1.6 points, for the 2016 period consisted of $36.2 million of net favorable development in long-tailed lines and $7.7 million of net favorable development in short-tailed lines, partially offset by $19.1 million of net adverse development in medium-tailed lines. Net favorable development in long-tailed lines reflected net reductions in executive assurance reserves from the 2008 to 2009 accident years and 2011 to 2013 accident years, and net reductions in casualty reserves across most accident years, partially offset by a large energy casualty claim from the 2015 accident year. Net favorable development in short-tailed lines primarily resulted from reductions in property (including special risk other than marine) reserves from the 2009 to 2014 accident years, primarily due to varying levels of reported claims activity. Net adverse development in medium-tailed lines primarily resulted from an increase in programs of $28.6 million stemming in part from terminated programs, partially offset by favorable development of $9.5 million in other medium-tailed lines, primarily in professional liability and surety. The mortgage segment’s net favorable development was $16.3 million , or 7.9 points, for the 2016 period. The development was primarily driven by lower than expected claim rates across most origination years.

Investment Information

Investment Information	9 Months Ended
	Sep. 30, 2017
Disclosure Investment Information [Abstract]
Investment Information	Investment Information At September 30, 2017 , total investable assets of $22.00 billion included $19.70 billion managed by the Company and $2.30 billion attributable to Watford Re. Available For Sale Investments The following table summarizes the fair value and cost or amortized cost of the Company’s investments classified as available for sale: Estimated Fair Value Gross Unrealized Gains Gross Unrealized Losses Cost or Amortized Cost OTTI Unrealized Losses (2) September 30, 2017 Fixed maturities (1): Corporate bonds $ 4,275,437 $ 49,576 $ (22,303 ) $ 4,248,164 $ (73 ) Mortgage backed securities 323,900 5,078 (2,540 ) 321,362 (2,146 ) Municipal bonds 2,353,234 31,202 (7,614 ) 2,329,646 — Commercial mortgage backed securities 584,730 3,114 (4,377 ) 585,993 — U.S. government and government agencies 3,761,612 3,303 (20,246 ) 3,778,555 — Non-U.S. government securities 1,473,819 49,570 (21,647 ) 1,445,896 — Asset backed securities 1,544,919 9,053 (4,748 ) 1,540,614 (22 ) Total 14,317,651 150,896 (83,475 ) 14,250,230 (2,241 ) Equity securities 480,607 84,755 (7,873 ) 403,725 — Other investments 260,339 54,512 (1 ) 205,828 — Short-term investments 1,646,036 667 (504 ) 1,645,873 — Total $ 16,704,633 $ 290,830 $ (91,853 ) $ 16,505,656 $ (2,241 ) December 31, 2016 Fixed maturities (1): Corporate bonds $ 4,392,373 $ 27,606 $ (46,905 ) $ 4,411,672 $ (2,285 ) Mortgage backed securities 490,093 4,794 (8,357 ) 493,656 (3,323 ) Municipal bonds 3,713,434 8,554 (29,154 ) 3,734,034 (201 ) Commercial mortgage backed securities 536,051 2,876 (6,508 ) 539,683 — U.S. government and government agencies 2,804,540 9,319 (24,437 ) 2,819,658 — Non-U.S. government securities 1,096,440 19,036 (56,872 ) 1,134,276 — Asset backed securities 1,123,987 6,897 (6,526 ) 1,123,616 (22 ) Total 14,156,918 79,082 (178,759 ) 14,256,595 (5,831 ) Equity securities 532,680 62,627 (17,517 ) 487,570 — Other investments 167,970 21,358 (2,465 ) 149,077 — Short-term investments 612,005 272 (145 ) 611,878 — Total $ 15,469,573 $ 163,339 $ (198,886 ) $ 15,505,120 $ (5,831 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” (2) Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At September 30, 2017 , the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $0.9 million , compared to a net unrealized gain of $2.8 million at December 31, 2016 . The following table summarizes, for all available for sale securities in an unrealized loss position, the fair value and gross unrealized loss by length of time the security has been in a continual unrealized loss position: Less than 12 Months 12 Months or More Total Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses September 30, 2017 Fixed maturities (1): Corporate bonds $ 1,173,096 $ (18,315 ) $ 191,382 $ (3,988 ) $ 1,364,478 $ (22,303 ) Mortgage backed securities 146,352 (2,477 ) 1,511 (63 ) 147,863 (2,540 ) Municipal bonds 745,410 (5,958 ) 110,752 (1,656 ) 856,162 (7,614 ) Commercial mortgage backed securities 282,901 (3,579 ) 17,570 (798 ) 300,471 (4,377 ) U.S. government and government agencies 3,083,239 (19,736 ) 25,894 (510 ) 3,109,133 (20,246 ) Non-U.S. government securities 1,149,528 (20,741 ) 37,655 (906 ) 1,187,183 (21,647 ) Asset backed securities 587,561 (4,404 ) 22,051 (344 ) 609,612 (4,748 ) Total 7,168,087 (75,210 ) 406,815 (8,265 ) 7,574,902 (83,475 ) Equity securities 170,937 (7,873 ) — — 170,937 (7,873 ) Other investments 725 (1 ) — — 725 (1 ) Short-term investments 110,444 (504 ) — — 110,444 (504 ) Total $ 7,450,193 $ (83,588 ) $ 406,815 $ (8,265 ) $ 7,857,008 $ (91,853 ) December 31, 2016 Fixed maturities (1): Corporate bonds $ 1,700,813 $ (43,011 ) $ 46,902 $ (3,894 ) $ 1,747,715 $ (46,905 ) Mortgage backed securities 402,699 (8,134 ) 6,105 (223 ) 408,804 (8,357 ) Municipal bonds 1,513,308 (28,504 ) 29,636 (650 ) 1,542,944 (29,154 ) Commercial mortgage backed securities 231,374 (6,331 ) 5,635 (177 ) 237,009 (6,508 ) U.S. government and government agencies 1,888,018 (24,437 ) — — 1,888,018 (24,437 ) Non-U.S. government securities 807,598 (56,872 ) — — 807,598 (56,872 ) Asset backed securities 627,557 (5,465 ) 65,723 (1,061 ) 693,280 (6,526 ) Total 7,171,367 (172,754 ) 154,001 (6,005 ) 7,325,368 (178,759 ) Equity securities 269,381 (17,517 ) — — 269,381 (17,517 ) Other investments 39,299 (2,465 ) — — 39,299 (2,465 ) Short-term investments 29,146 (145 ) — — 29,146 (145 ) Total $ 7,509,193 $ (192,881 ) $ 154,001 $ (6,005 ) $ 7,663,194 $ (198,886 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” At September 30, 2017 , on a lot level basis, approximately 2,870 security lots out of a total of approximately 7,410 security lots were in an unrealized loss position and the largest single unrealized loss from a single lot in the Company’s fixed maturity portfolio was $1.6 million . At December 31, 2016 , on a lot level basis, approximately 3,540 security lots out of a total of approximately 7,240 security lots were in an unrealized loss position and the largest single unrealized loss from a single lot in the Company’s fixed maturity portfolio was $4.6 million . The contractual maturities of the Company’s fixed maturities are shown in the following table. Expected maturities, which are management’s best estimates, will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. September 30, 2017 December 31, 2016 Maturity Estimated Fair Value Amortized Cost Estimated Amortized Cost Due in one year or less $ 537,043 $ 534,513 $ 560,830 $ 557,675 Due after one year through five years 7,547,002 7,508,674 6,158,148 6,211,099 Due after five years through 10 years 3,495,424 3,480,251 4,676,847 4,710,017 Due after 10 years 284,633 278,823 610,962 620,849 11,864,102 11,802,261 12,006,787 12,099,640 Mortgage backed securities 323,900 321,362 490,093 493,656 Commercial mortgage backed securities 584,730 585,993 536,051 539,683 Asset backed securities 1,544,919 1,540,614 1,123,987 1,123,616 Total (1) $ 14,317,651 $ 14,250,230 $ 14,156,918 $ 14,256,595 (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” Securities Lending Agreements The Company enters into securities lending agreements with financial institutions to enhance investment income whereby it loans certain of its securities to third parties, primarily major brokerage firms, for short periods of time through a lending agent. The Company maintains legal control over the securities it lends, retains the earnings and cash flows associated with the loaned securities and receives a fee from the borrower for the temporary use of the securities. An indemnification agreement with the lending agent protects the Company in the event a borrower becomes insolvent or fails to return any of the securities on loan from the Company. The Company receives collateral in the form of cash or securities. At September 30, 2017 , the fair value of the cash collateral received on securities lending was $63.8 million and the fair value of security collateral received was $479.5 million . At December 31, 2016 , the fair value of the cash collateral received on securities lending was $212.5 million , and the fair value of security collateral received was $550.1 million . Cash collateral is reinvested in short-term investments. The Company’s securities lending transactions were accounted for as secured borrowings with significant investment categories as follows: Remaining Contractual Maturity of the Agreements Overnight and Continuous Less than 30 Days 30-90 Days 90 Days or More Total September 30, 2017 U.S. government and government agencies $ 424,838 $ 8,186 $ 74,930 $ — $ 507,954 Corporate bonds 31,305 — — — 31,305 Equity securities 3,984 — — — 3,984 Total $ 460,127 $ 8,186 $ 74,930 $ — $ 543,243 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9 $ — Amounts related to securities lending not included in offsetting disclosure in Note 9 $ 543,243 December 31, 2016 U.S. government and government agencies $ 556,015 $ 31,244 $ 126,093 $ 5,140 $ 718,492 Corporate bonds 29,078 — — — 29,078 Equity securities 14,984 — — — 14,984 Total $ 600,077 $ 31,244 $ 126,093 $ 5,140 $ 762,554 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9 $ — Amounts related to securities lending not included in offsetting disclosure in Note 9 $ 762,554 Other Investments The following table summarizes the Company’s other investments, including available for sale and fair value option components: September 30, December 31, Available for sale: Asian and emerging markets $ 123,225 $ 84,778 Investment grade fixed income 53,325 33,923 Credit related funds 20,752 7,469 Other 63,037 41,800 Total available for sale 260,339 167,970 Fair value option: Term loan investments (par value: $1,378,797 and $1,208,537) 1,387,663 1,190,799 Mezzanine debt funds 172,000 127,943 Credit related funds 194,200 218,298 Investment grade fixed income 95,151 75,468 Asian and emerging markets 300,552 178,568 Other (1) 147,639 129,717 Total fair value option 2,297,205 1,920,793 Total $ 2,557,544 $ 2,088,763 (1) Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other. Certain of the Company’s other investments are in investment funds for which the Company has the option to redeem at agreed upon values as described in each investment fund’s subscription agreement. Depending on the terms of the various subscription agreements, investments in investment funds may be redeemed daily, monthly, quarterly or on other terms. Two common redemption restrictions which may impact the Company’s ability to redeem these investment funds are gates and lockups. A gate is a suspension of redemptions which may be implemented by the general partner or investment manager of the fund in order to defer, in whole or in part, the redemption request in the event the aggregate amount of redemption requests exceeds a predetermined percentage of the investment fund’s net assets which may otherwise hinder the general partner or investment manager’s ability to liquidate holdings in an orderly fashion in order to generate the cash necessary to fund extraordinarily large redemption payouts. A lockup period is the initial amount of time an investor is contractually required to hold the security before having the ability to redeem. If the investment funds are eligible to be redeemed, the time to redeem such fund can take weeks or months following the notification. Fair Value Option The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option: September 30, December 31, Fixed maturities $ 1,508,204 $ 1,099,116 Other investments 2,297,205 1,920,793 Short-term investments 349,540 373,669 Equity securities 94,685 27,642 Investments accounted for using the fair value option $ 4,249,634 $ 3,421,220 Limited partnership interests In the normal course of its activities, the Company invests in limited partnerships as part of its overall investment strategy. Such amounts are included in ‘investments accounted for using the equity method’ and ‘investments accounted for using the fair value option.’ The Company has determined that it is not required to consolidate these investments because it is not the primary beneficiary of the funds. The Company’s maximum exposure to loss with respect to these investments is limited to the investment carrying amounts reported in the Company’s consolidated balance sheet and any unfunded commitment. The following table summarizes investments in limited partnership interests where the Company has a variable interest by balance sheet line item: September 30, December 31, Investments accounted for using the equity method (1) $ 962,574 $ 800,970 Investments accounted for using the fair value option (2) 109,157 90,804 Total $ 1,071,731 $ 891,774 (1) Aggregate unfunded commitments were $850.4 million at September 30, 2017 , compared to $776.6 million at December 31, 2016 . (2) Aggregate unfunded commitments were $162.3 million at September 30, 2017 , compared to $16.7 million at December 31, 2016 . Net Investment Income The components of net investment income were derived from the following sources: September 30, 2017 2016 Three Months Ended Fixed maturities $ 96,144 $ 71,366 Equity securities 2,887 3,311 Short-term investments 2,957 1,703 Other (1) 37,957 37,466 Gross investment income 139,945 113,846 Investment expenses (23,486 ) (20,228 ) Net investment income $ 116,459 $ 93,618 Nine Months Ended Fixed maturities $ 284,807 $ 223,033 Equity securities 9,184 10,409 Short-term investments 6,732 3,015 Other (1) 111,613 98,089 Gross investment income 412,336 334,546 Investment expenses (66,879 ) (58,855 ) Net investment income $ 345,457 $ 275,691 (1) Includes income distributions from investment funds, term loan investments and other items. Net Realized Gains (Losses) Net realized gains (losses) were as follows, excluding other than-temporary impairment provision. September 30, 2017 2016 Three Months Ended Available for sale securities: Gross gains on investment sales $ 66,565 $ 84,451 Gross losses on investment sales (39,015 ) (22,985 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 4,035 43,935 Other investments 24,264 46,428 Equity securities 10,230 (52 ) Short-term investments (3,320 ) 1,150 Derivative instruments (1) 4,298 (16,964 ) Other (2) (782 ) (10,858 ) Net realized gains (losses) $ 66,275 $ 125,105 Nine Months Ended Available for sale securities: Gross gains on investment sales $ 212,470 $ 266,965 Gross losses on investment sales (152,996 ) (129,409 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 34,232 62,234 Other investments 42,149 38,016 Equity securities 16,604 385 Short-term investments 12 107 Derivative instruments (1) (9,653 ) 24,102 Other (2) (20,655 ) (31,753 ) Net realized gains (losses) $ 122,163 $ 230,647 (1) See Note 9 for information on the Company’s derivative instruments. (2) Includes the re-measurement of contingent consideration liability amounts. Equity in Net Income (Loss) of Investment Funds Accounted for Using the Equity Method The Company recorded $31.1 million of equity in net income related to investment funds accounted for using the equity method in the 2017 third quarter , compared to $16.7 million for the 2016 third quarter , and $111.9 million for the nine months ended September 30, 2017 , compared to $32.1 million for the 2016 period. In applying the equity method, investments are initially recorded at cost and are subsequently adjusted based on the Company’s proportionate share of the net income or loss of the funds (which include changes in the market value of the underlying securities in the funds). Such investments are generally recorded on a one to three month lag based on the availability of reports from the investment funds. Other-Than-Temporary Impairments The Company performs quarterly reviews of its available for sale investments in order to determine whether declines in fair value below the amortized cost basis were considered other-than-temporary in accordance with applicable guidance. The following table details the net impairment losses recognized in earnings by asset class: September 30, 2017 2016 Three Months Ended Fixed maturities: Mortgage backed securities $ (50 ) $ (233 ) Corporate bonds (82 ) — Non-U.S. government securities (178 ) (545 ) U.S. government and government agencies (426 ) — Municipal bonds (202 ) — Total (938 ) (778 ) Equity securities (940 ) (557 ) Other investments — (2,532 ) Net impairment losses recognized in earnings $ (1,878 ) $ (3,867 ) Nine Months Ended Fixed maturities: Mortgage backed securities $ (1,461 ) $ (788 ) Corporate bonds (1,484 ) (5,655 ) Non-U.S. government securities (376 ) (777 ) Asset backed securities — (2,506 ) U.S. government and government agencies (426 ) — Municipal bonds (375 ) — Total (4,122 ) (9,726 ) Equity securities (1,126 ) (3,594 ) Other investments (167 ) (3,529 ) Net impairment losses recognized in earnings $ (5,415 ) $ (16,849 ) Net impairment losses recognized in earnings in the 2017 third quarter were primarily related to equities and on fixed maturities with foreign currency fluctuations. For the nine months ended September 30, 2017 , net impairment losses recognized in earnings reflected the Company’s decision to liquidate a portfolio of mortgage backed securities in April 2017. The Company recorded impairment losses on securities in such portfolio that were in an unrealized loss position at March 31, 2017. The Company believes that the $2.2 million of OTTI included in accumulated other comprehensive income at September 30, 2017 on the securities which were considered by the Company to be impaired was due to market and sector-related factors ( i.e. , not credit losses). At September 30, 2017 , the Company did not intend to sell these securities, or any other securities which were in an unrealized loss position, and determined that it is more likely than not that the Company will not be required to sell such securities before recovery of their cost basis. The following table provides a roll forward of the amount related to credit losses recognized in earnings for which a portion of an OTTI was recognized in accumulated other comprehensive income: September 30, 2017 2016 Three Months Ended Balance at start of period $ 4,437 $ 14,847 Credit loss impairments recognized on securities not previously impaired — 38 Credit loss impairments recognized on securities previously impaired 15 60 Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security — — Reductions for securities sold during the period (689 ) (1,166 ) Balance at end of period $ 3,763 $ 13,779 Nine Months Ended Balance at start of year $ 13,138 $ 26,875 Credit loss impairments recognized on securities not previously impaired 31 1,388 Credit loss impairments recognized on securities previously impaired 210 582 Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security — — Reductions for securities sold during the period (9,616 ) (15,066 ) Balance at end of period $ 3,763 $ 13,779 Restricted Assets The Company is required to maintain assets on deposit, which primarily consist of fixed maturities, with various regulatory authorities to support its insurance and reinsurance operations. The Company’s insurance and reinsurance subsidiaries maintain assets in trust accounts as collateral for insurance and reinsurance transactions with affiliated companies and also have investments in segregated portfolios primarily to provide collateral or guarantees for letters of credit to third parties. See Note 10 for further details. The following table details the value of the Company’s restricted assets: September 30, December 31, Assets used for collateral or guarantees: Affiliated transactions $ 4,264,131 $ 3,871,971 Third party agreements 1,689,104 1,513,079 Deposits with U.S. regulatory authorities 618,136 472,890 Deposits with non-U.S. regulatory authorities 56,753 44,399 Total restricted assets $ 6,628,124 $ 5,902,339

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value	Fair Value Accounting guidance regarding fair value measurements addresses how companies should measure fair value when they are required to use a fair value measure for recognition or disclosure purposes under GAAP and provides a common definition of fair value to be used throughout GAAP. It defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly fashion between market participants at the measurement date. In addition, it establishes a three-level valuation hierarchy for the disclosure of fair value measurements. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. The level in the hierarchy within which a given fair value measurement falls is determined based on the lowest level input that is significant to the measurement (Level 1 being the highest priority and Level 3 being the lowest priority). The levels in the hierarchy are defined as follows: Level 1: Inputs to the valuation methodology are observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets Level 2: Inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets, and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument Level 3: Inputs to the valuation methodology are unobservable and significant to the fair value measurement Following is a description of the valuation methodologies used for securities measured at fair value, as well as the general classification of such securities pursuant to the valuation hierarchy. The Company reviews its securities measured at fair value and discusses the proper classification of such investments with investment advisers and others. The Company determines the existence of an active market based on its judgment as to whether transactions for the financial instrument occur in such market with sufficient frequency and volume to provide reliable pricing information. The independent pricing sources obtain market quotations and actual transaction prices for securities that have quoted prices in active markets. The Company uses quoted values and other data provided by nationally recognized independent pricing sources as inputs into its process for determining fair values of its fixed maturity investments. To validate the techniques or models used by pricing sources, the Company's review process includes, but is not limited to: (i) quantitative analysis (e.g., comparing the quarterly return for each managed portfolio to its target benchmark, with significant differences identified and investigated); (ii) a review of the average number of prices obtained in the pricing process and the range of resulting fair values; (iii) initial and ongoing evaluation of methodologies used by outside parties to calculate fair value; (iv) a comparison of the fair value estimates to the Company’s knowledge of the current market; (v) a comparison of the pricing services' fair values to other pricing services' fair values for the same investments; and (vi) periodic back-testing, which includes randomly selecting purchased or sold securities and comparing the executed prices to the fair value estimates from the pricing service. A price source hierarchy was maintained in order to determine which price source would be used (i.e. , a price obtained from a pricing service with more seniority in the hierarchy will be used over a less senior one in all cases). The hierarchy prioritizes pricing services based on availability and reliability and assigns the highest priority to index providers. Based on the above review, the Company will challenge any prices for a security or portfolio which are considered not to be representative of fair value. The Company did not adjust any of the prices obtained from the independent pricing sources at September 30, 2017 . In certain circumstances, when fair values are unavailable from these independent pricing sources, quotes are obtained directly from broker-dealers who are active in the corresponding markets. Such quotes are subject to the validation procedures noted above. Of the $21.14 billion of financial assets and liabilities measured at fair value at September 30, 2017 , approximately $242.9 million , or 1.2% , were priced using non-binding broker-dealer quotes. Of the $19.10 billion of financial assets and liabilities measured at fair value at December 31, 2016 , approximately $234.0 million , or 1.2% , were priced using non-binding broker-dealer quotes. Fixed maturities The Company uses the market approach valuation technique to estimate the fair value of its fixed maturity securities, when possible. The market approach includes obtaining prices from independent pricing services, such as index providers and pricing vendors, as well as to a lesser extent quotes from broker-dealers. The independent pricing sources obtain market quotations and actual transaction prices for securities that have quoted prices in active markets. Each source has its own proprietary method for determining the fair value of securities that are not actively traded. In general, these methods involve the use of “matrix pricing” in which the independent pricing source uses observable market inputs including, but not limited to, investment yields, credit risks and spreads, benchmarking of like securities, broker-dealer quotes, reported trades and sector groupings to determine a reasonable fair value. The following describes the significant inputs generally used to determine the fair value of the Company’s fixed maturity securities by asset class: • U.S. government and government agencies — valuations provided by independent pricing services, with all prices provided through index providers and pricing vendors. The Company determined that all U.S. Treasuries would be classified as Level 1 securities due to observed levels of trading activity, the high number of strongly correlated pricing quotes received on U.S. Treasuries and other factors. The fair values of U.S. government agency securities are generally determined using the spread above the risk-free yield curve. As the yields for the risk-free yield curve and the spreads for these securities are observable market inputs, the fair values of U.S. government agency securities are classified within Level 2. • Corporate bonds — valuations provided by independent pricing services, substantially all through index providers and pricing vendors with a small amount through broker-dealers. The fair values of these securities are generally determined using the spread above the risk-free yield curve. These spreads are generally obtained from the new issue market, secondary trading and from broker-dealers who trade in the relevant security market. As the significant inputs used in the pricing process for corporate bonds are observable market inputs, the fair value of these securities are classified within Level 2. A small number of securities are included in Level 3 due to a low level of transparency on the inputs used in the pricing process. • Mortgage-backed securities — valuations provided by independent pricing services, substantially all through pricing vendors and index providers with a small amount through broker-dealers. The fair values of these securities are generally determined through the use of pricing models (including Option Adjusted Spread) which use spreads to determine the expected average life of the securities. These spreads are generally obtained from the new issue market, secondary trading and from broker-dealers who trade in the relevant security market. The pricing services also review prepayment speeds and other indicators, when applicable. As the significant inputs used in the pricing process for mortgage-backed securities are observable market inputs, the fair value of these securities are classified within Level 2. A small number of securities are included in Level 3 due to a low level of transparency on the inputs used in the pricing process. • Municipal bonds — valuations provided by independent pricing services, with all prices provided through index providers and pricing vendors. The fair values of these securities are generally determined using spreads obtained from broker-dealers who trade in the relevant security market, trade prices and the new issue market. As the significant inputs used in the pricing process for municipal bonds are observable market inputs, the fair value of these securities are classified within Level 2. • Commercial mortgage-backed securities — valuations provided by independent pricing services, substantially all through index providers and pricing vendors with a small amount through broker-dealers. The fair values of these securities are generally determined through the use of pricing models which use spreads to determine the appropriate average life of the securities. These spreads are generally obtained from the new issue market, secondary trading and from broker-dealers who trade in the relevant security market. The pricing services also review prepayment speeds and other indicators, when applicable. As the significant inputs used in the pricing process for commercial mortgage-backed securities are observable market inputs, the fair value of these securities are classified within Level 2. A small number of securities are included in Level 3 due to a low level of transparency on the inputs used in the pricing process. • Non-U.S. government securities — valuations provided by independent pricing services, with all prices provided through index providers and pricing vendors. The fair values of these securities are generally based on international indices or valuation models which include daily observed yield curves, cross-currency basis index spreads and country credit spreads. As the significant inputs used in the pricing process for non-U.S. government securities are observable market inputs, the fair value of these securities are classified within Level 2. • Asset-backed securities — valuations provided by independent pricing services, substantially all through index providers and pricing vendors with a small amount through broker-dealers. The fair values of these securities are generally determined through the use of pricing models (including Option Adjusted Spread) which use spreads to determine the appropriate average life of the securities. These spreads are generally obtained from the new issue market, secondary trading and from broker-dealers who trade in the relevant security market. The pricing services also review prepayment speeds and other indicators, when applicable. As the significant inputs used in the pricing process for asset-backed securities are observable market inputs, the fair value of these securities are classified within Level 2. A small number of securities are included in Level 3 due to a low level of transparency on the inputs used in the pricing process. During the 2017 third quarter, the Company transferred $17.6 million of fixed maturities from Level 2 to Level 3 based on a review of the pricing of such securities, as described above. Equity securities The Company determined that exchange-traded equity securities would be included in Level 1 as their fair values are based on quoted market prices in active markets. Other equity securities are included in Level 2 of the valuation hierarchy. Other investments The Company determined that exchange-traded investments in mutual funds would be included in Level 1 as their fair values are based on quoted market prices in active markets. Other investments also include term loan investments for which fair values are estimated by using quoted prices of term loan investments with similar characteristics, pricing models or matrix pricing. Such investments are generally classified within Level 2. The fair values for certain of the Company’s other investments are determined using net asset values as advised by external fund managers. The net asset value is based on the fund manager’s valuation of the underlying holdings in accordance with the fund’s governing documents. In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. A small number of securities are included in Level 3 due to the lack of an available independent price source for such securities. During the 2017 third quarter, the Company transferred $4.8 million of other investments from Level 2 to Level 3 based on a review of the pricing of such securities, as described above. Derivative instruments The Company’s futures contracts, foreign currency forward contracts, interest rate swaps and other derivatives trade in the over-the-counter derivative market. The Company uses the market approach valuation technique to estimate the fair value for these derivatives based on significant observable market inputs from third party pricing vendors, non-binding broker-dealer quotes and/or recent trading activity. As the significant inputs used in the pricing process for these derivative instruments are observable market inputs, the fair value of these securities are classified within Level 2. Short-term investments The Company determined that certain of its short-term investments held in highly liquid money market-type funds, Treasury bills and commercial paper would be included in Level 1 as their fair values are based on quoted market prices in active markets. The fair values of other short-term investments are generally determined using the spread above the risk-free yield curve and are classified within Level 2. Contingent consideration liabilities Contingent consideration liabilities (included in ‘other liabilities’ in the consolidated balance sheets) include amounts related to the acquisition of CMG Mortgage Insurance Company and its affiliated mortgage insurance companies and other acquisitions. Such amounts are remeasured at fair value at each balance sheet date with changes in fair value recognized in ‘net realized gains (losses).’ To determine the fair value of contingent consideration liabilities, the Company estimates future payments using an income approach based on modeled inputs which include a weighted average cost of capital. The Company determined that contingent consideration liabilities would be included within Level 3. The following table presents the Company’s financial assets and liabilities measured at fair value by level at September 30, 2017 : Estimated Fair Value Measurements Using: Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets measured at fair value (1): Available for sale securities: Fixed maturities: Corporate bonds $ 4,275,437 $ — $ 4,263,446 $ 11,991 Mortgage backed securities 323,900 — 323,496 404 Municipal bonds 2,353,234 — 2,353,234 — Commercial mortgage backed securities 584,730 — 584,185 545 U.S. government and government agencies 3,761,612 3,687,126 74,486 — Non-U.S. government securities 1,473,819 — 1,473,819 — Asset backed securities 1,544,919 — 1,539,919 5,000 Total 14,317,651 3,687,126 10,612,585 17,940 Equity securities 480,607 473,908 6,699 — Short-term investments 1,646,036 1,600,885 45,151 — Other investments 84,671 83,254 1,417 — Other investments measured at net asset value (2) 175,668 Total other investments 260,339 83,254 1,417 — Derivative instruments (4) 33,141 — 33,141 — Fair value option: Corporate bonds 823,181 — 811,710 11,471 Non-U.S. government bonds 97,614 — 97,614 — Mortgage backed securities 21,218 — 21,218 — Municipal bonds 2,740 — 2,740 — Commercial mortgage backed securities 12,539 — 12,539 — Asset backed securities 63,437 — 63,437 — U.S. government and government agencies 487,475 487,475 — — Short-term investments 349,540 343,620 5,920 — Equity securities 94,685 59,332 35,353 — Other investments 1,298,198 120,212 1,146,840 31,146 Other investments measured at net asset value (2) 999,007 Total 4,249,634 1,010,639 2,197,371 42,617 Total assets measured at fair value $ 20,987,408 $ 6,855,812 $ 12,896,364 $ 60,557 Liabilities measured at fair value: Contingent consideration liabilities $ (59,248 ) $ — $ — $ (59,248 ) Securities sold but not yet purchased (3) (72,682 ) — (72,682 ) — Derivative instruments (4) (23,037 ) — (23,037 ) — Total liabilities measured at fair value $ (154,967 ) $ — $ (95,719 ) $ (59,248 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7 , “Investment Information—Securities Lending Agreements.” (2) In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. (3) Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets. (4) See Note 9 , “Derivative Instruments.” The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2016 : Estimated Fair Value Measurements Using: Estimated Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets measured at fair value (1): Available for sale securities: Fixed maturities: Corporate bonds $ 4,392,373 $ — $ 4,374,029 $ 18,344 Mortgage backed securities 490,093 — 490,093 — Municipal bonds 3,713,434 — 3,713,434 — Commercial mortgage backed securities 536,051 — 536,051 — U.S. government and government agencies 2,804,540 2,691,575 112,965 — Non-U.S. government securities 1,096,440 — 1,096,440 — Asset backed securities 1,123,987 — 1,112,698 11,289 Total 14,156,918 2,691,575 11,435,710 29,633 Equity securities 532,680 529,695 2,985 — Short-term investments 612,005 608,862 3,143 — Other investments 112,313 112,313 — — Other investments measured at net asset value (2) 55,657 Total other investments 167,970 112,313 — — Derivative instruments (4) 28,410 — 28,410 — Fair value option: Corporate bonds 790,935 — 790,935 — Non-U.S. government bonds 61,747 — 61,747 — Mortgage backed securities 18,624 — 18,624 — Asset backed securities 30,324 — 30,324 — U.S. government and government agencies 197,486 197,486 — — Short-term investments 373,669 309,127 64,542 — Equity securities 27,642 25,328 2,314 — Other investments 1,226,242 80,706 1,120,536 25,000 Other investments measured at net asset value (2) 694,551 Total 3,421,220 612,647 2,089,022 25,000 Total assets measured at fair value $ 18,919,203 $ 4,555,092 $ 13,559,270 $ 54,633 Liabilities measured at fair value: Contingent consideration liabilities $ (122,350 ) $ — $ — $ (122,350 ) Securities sold but not yet purchased (3) (33,157 ) — (33,157 ) — Derivative instruments (4) (26,049 ) — (26,049 ) — Total liabilities measured at fair value $ (181,556 ) $ — $ (59,206 ) $ (122,350 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7 , “Investment Information—Securities Lending Agreements.” (2) In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. (3) Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets. (4) See Note 9 , “Derivative Instruments.” The following table presents a reconciliation of the beginning and ending balances for all financial assets and liabilities measured at fair value on a recurring basis using Level 3 inputs: Assets Liabilities s Available For Sale Fair Value Option Structured Securities (1) Corporate Corporate Other Investments Total Contingent Consideration Liabilities Three Months Ended September 30, 2017 Balance at beginning of period $ — $ 11,570 $ — $ 25,000 $ 36,570 $ (57,246 ) Total gains or (losses) (realized/unrealized) Included in earnings (2) — — — — — (2,002 ) Included in other comprehensive income — 289 — — 289 — Purchases, issuances, sales and settlements Purchases — — — 1,348 1,348 — Issuances — — — — — — Sales — — — — — — Settlements — — — — — — Transfers in and/or out of Level 3 5,949 132 11,471 4,798 22,350 — Balance at end of period $ 5,949 $ 11,991 $ 11,471 $ 31,146 $ 60,557 $ (59,248 ) Three Months Ended September 30, 2016 Balance at beginning of period $ 49,211 $ 17,305 $ — $ — $ 66,516 $ (111,670 ) Total gains or (losses) (realized/unrealized) Included in earnings (2) — 1,667 — — 1,667 (4,795 ) Included in other comprehensive income — — — — — 88 Purchases, issuances, sales and settlements Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (22,435 ) — — — (22,435 ) — Transfers in and/or out of Level 3 — — — — — — Balance at end of period $ 26,776 $ 18,972 $ — $ — $ 45,748 $ (116,377 ) Nine Months Ended September 30, 2017 Balance at beginning of year $ 11,289 $ 18,344 $ — $ 25,000 $ 54,633 $ (122,350 ) Total gains or (losses) (realized/unrealized) Included in earnings (2) 3,779 893 — — 4,672 (9,089 ) Included in other comprehensive income — 289 — — 289 — Purchases, issuances, sales and settlements Purchases — 4,935 — 1,348 6,283 — Issuances — — — — — — Sales (13,640 ) (12,602 ) — — (26,242 ) — Settlements (1,428 ) — — — (1,428 ) 72,191 Transfers in and/or out of Level 3 5,949 132 11,471 4,798 22,350 — Balance at end of period $ 5,949 $ 11,991 $ 11,471 $ 31,146 $ 60,557 $ (59,248 ) Nine Months Ended September 30, 2016 Balance at beginning of year $ 57,500 $ 16,368 $ — $ — $ 73,868 $ (96,048 ) Total gains or (losses) (realized/unrealized) Included in earnings (2) (2,500 ) 1,828 — — (672 ) (20,916 ) Included in other comprehensive income — — — — — 51 Purchases, issuances, sales and settlements Purchases — 776 — — 776 — Issuances — — — — — — Sales — — — — — — Settlements (28,224 ) — — — (28,224 ) 536 Transfers in and/or out of Level 3 — — — — — — Balance at end of period $ 26,776 $ 18,972 $ — $ — $ 45,748 $ (116,377 ) (1) Includes asset backed securities, mortgage backed securities and commercial mortgage backed securities. (2) For the 2017 periods, gains or losses were included in net realized gains (losses). For the 2016 periods, losses on structured securities were included in net impairment losses recognized in earnings gains or losses while gains or losses on corporate bonds and contingent consideration liabilities were included in net realized gains (losses). Financial Instruments Disclosed, But Not Carried, At Fair Value The Company uses various financial instruments in the normal course of its business. The carrying values of cash, accrued investment income, receivable for securities sold, certain other assets, payable for securities purchased and certain other liabilities approximated their fair values at September 30, 2017 , due to their respective short maturities. As these financial instruments are not actively traded, their respective fair values are classified within Level 2. At September 30, 2017 , the senior notes of ACGL were carried at their cost, net of debt issuance costs, of $297.0 million and had a fair value of $406.0 million , while the senior notes of Arch Capital Group (U.S.) Inc. (“Arch-U.S.”) were carried at their cost, net of debt issuance costs, of $494.6 million and had a fair value of $566.2 million . The senior notes of Arch Capital Finance LLC due in 2026 were carried at their cost, net of debt issuance costs, of $496.0 million and had a fair value of $519.8 million , while the senior notes due in 2046 were carried at their cost, net of debt issuance costs, of $445.1 million and had a fair value of $503.5 million . The fair values of the senior notes were obtained from a third party pricing service and are based on observable market inputs. As such, the fair values of the senior notes are classified within Level 2.

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments The Company’s investment strategy allows for the use of derivative instruments. The Company’s derivative instruments are recorded on its consolidated balance sheets at fair value. The Company utilizes exchange traded U.S. Treasury note, Eurodollar and other futures contracts and commodity futures to manage portfolio duration or replicate investment positions in its portfolios and the Company routinely utilizes foreign currency forward contracts, currency options, index futures contracts and other derivatives as part of its total return objective. In addition, certain of the Company’s investments are managed in portfolios which incorporate the use of foreign currency forward contracts which are intended to provide an economic hedge against foreign currency movements. In addition, the Company purchases to-be-announced mortgage backed securities (“TBAs”) as part of its investment strategy. TBAs represent commitments to purchase a future issuance of agency mortgage backed securities. For the period between purchase of a TBA and issuance of the underlying security, the Company’s position is accounted for as a derivative. The Company purchases TBAs in both long and short positions to enhance investment performance and as part of its overall investment strategy. The following table summarizes information on the fair values and notional values of the Company’s derivative instruments: Estimated Fair Value Asset Derivatives Liability Derivatives Notional Value (1) September 30, 2017 Futures contracts (2) $ 5,351 $ (6,722 ) $ 1,524,985 Foreign currency forward contracts (2) 19,376 (5,348 ) 805,201 TBAs (3) 18,331 — 18,143 Other (2) 8,414 (10,967 ) 2,032,922 Total $ 51,472 $ (23,037 ) December 31, 2016 Futures contracts (2) $ 360 $ (9,398 ) $ 1,655,530 Foreign currency forward contracts (2) 9,354 (12,941 ) 1,186,386 TBAs (3) — — — Other (2) 20,287 (3,710 ) 1,014,863 Total $ 30,001 $ (26,049 ) (1) Represents the absolute notional value of all outstanding contracts, consisting of long and short positions. (2) The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’ (3) The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’ The Company did not hold any derivatives which were designated as hedging instruments at September 30, 2017 or December 31, 2016 . The Company’s derivative instruments can be traded under master netting agreements, which establish terms that apply to all derivative transactions with a counterparty. In the event of a bankruptcy or other stipulated event of default, such agreements provide that the non-defaulting party may elect to terminate all outstanding derivative transactions, in which case all individual derivative positions (loss or gain) with a counterparty are closed out and netted and replaced with a single amount, usually referred to as the termination amount, which is expressed in a single currency. The resulting single net amount, where positive, is payable to the party “in-the-money” regardless of whether or not it is the defaulting party, unless the parties have agreed that only the non-defaulting party is entitled to receive a termination payment where the net amount is positive and is in its favor. Contractual close-out netting reduces derivatives credit exposure from gross to net exposure. At September 30, 2017 , asset derivatives and liability derivatives of $49.4 million and $22.5 million , respectively, were subject to a master netting agreement, compared to $28.4 million and $26.0 million , respectively, at December 31, 2016 . The remaining derivatives included in the preceding table were not subject to a master netting agreement. All realized and unrealized contract gains and losses on the Company’s derivative instruments are reflected in net realized gains (losses) in the consolidated statements of income, as summarized in the following table: Derivatives not designated as September 30, hedging instruments: 2017 2016 Three Months Ended Net realized gains (losses): Futures contracts $ 4,899 $ (15,368 ) Foreign currency forward contracts (228 ) 4,583 TBAs 122 (23 ) Other (495 ) (6,156 ) Total $ 4,298 $ (16,964 ) Nine Months Ended Net realized gains (losses): Futures contracts $ 7,309 $ 45,954 Foreign currency forward contracts (12,266 ) (13,951 ) TBAs 143 311 Other (4,839 ) (8,212 ) Total $ (9,653 ) $ 24,102

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Letter of Credit and Revolving Credit Facilities ACGL repaid $100.0 million of borrowings under its unsecured revolving loan and letter of credit facility in the 2017 third quarter , offset by an increase in borrowings in the Company’s ‘other’ segment. Investment Commitments The Company’s investment commitments, which are primarily related to agreements entered into by the Company to invest in funds and separately managed accounts when called upon, were approximately $1.58 billion at September 30, 2017 , compared to $1.29 billion at December 31, 2016 .

Share Transactions

Share Transactions	9 Months Ended
	Sep. 30, 2017
Stockholders' Equity Note [Abstract]
Share Transactions	Share Transactions Share Repurchases The board of directors of ACGL has authorized the investment in ACGL’s common shares through a share repurchase program. Since the inception of the share repurchase program, ACGL has repurchased approximately 125.2 million common shares for an aggregate purchase price of $3.68 billion . For the nine months ended September 30, 2017 , the Company did not repurchase any shares under the share repurchase program, compared to 1.1 million common shares repurchased for the nine months ended September 30, 2016 with an aggregate purchase price of $75.3 million (no repurchases in the 2016 third quarter ). At September 30, 2017 , $446.5 million of share repurchases were available under the program, which may be effected from time to time in open market or privately negotiated transactions through December 31, 2019. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations. Conversion of Convertible Non-Voting Common Equivalent Preferred Shares On June 8, 2017, ACGL and AIG entered into Amendment No. 1 (the “Amendment”) to the Investor Rights Agreement (the “Investor Rights Agreement”) dated as of December 31, 2016 to amend the restrictions on transfers of the 1,276,282 shares of ACGL’s convertible non-voting common-equivalent preference shares owned by AIG (the “Convertible Preferred Shares”). The Convertible Preferred Shares were issued to AIG as part of the consideration in UGC acquisition. Pursuant to the certificate of designations for the Convertible Preferred Shares and in accordance with the terms and conditions set forth therein, each Convertible Preferred Share is convertible into ten common shares of ACGL. Pursuant to the Amendment, ACGL permitted AIG to transfer: (i) 638,141 Convertible Preferred Shares from and after June 8, 2017, and up to an additional 95,721 of the Convertible Preferred Shares to the extent that the several underwriters exercise the option to purchase additional securities expected to be granted pursuant to an underwritten secondary offering of ACGL common shares issuable upon conversion of the Convertible Preferred Shares by AIG and (ii) any and all of the Convertible Preferred Shares from and after January 15, 2018, subject to certain exceptions, and in each case subject to the terms and conditions of the Investor Rights Agreement. All other terms of the Investor Rights Agreement remain in effect. In June 2017, ACGL completed an underwritten public secondary offering of 7,088,620 common shares by AIG following transfer of 708,862 Convertible Preferred Shares. Proceeds from the sale of common shares pursuant to the public offering were received by AIG. At September 30, 2017 , 567,420 Convertible Preferred Shares were outstanding. Series F Preferred Shares In August 2017, ACGL completed a $230 million underwritten public offering of 9.2 million depositary shares (the “Depositary Shares”), each of which represents a 1/1,000th interest in a share of its 5.45% Non-Cumulative Preferred Shares, Series F, have a $0.01 par value and $25,000 liquidation preference per share (equivalent to $25 liquidation preference per Depositary Share) (the “Series F Preferred Shares”). Each Depositary Share, evidenced by a depositary receipt, entitles the holder, through the depositary, to a proportional fractional interest in all rights and preferences of the Series F Preferred Shares represented thereby (including any dividend, liquidation, redemption and voting rights). Holders of Series F Preferred Shares will be entitled to receive dividend payments only when, as and if declared by our board of directors or a duly authorized committee of the board. Any such dividends will be payable from, and including, the date of original issue on a noncumulative basis, quarterly in arrears on the last day of March, June, September and December of each year, at an annual rate of 5.45% . Dividends on the Series F Preferred Shares are not cumulative. The Company will be restricted from paying dividends on or repurchasing its common shares unless certain dividend payments are made on the Series F Preferred Shares. Except in specified circumstances relating to certain tax or corporate events, the Series F Preferred Shares are not redeemable prior to August 17, 2022 (the fifth anniversary of the issue date). On and after that date, the Series F Preferred Shares will be redeemable at the Company’s option, in whole or in part, at a redemption price of $25,000 per share of the Series F Preferred Shares (equivalent to $25 per depositary share), plus any declared and unpaid dividends, without accumulation of any undeclared dividends to, but excluding, the redemption date. The Depositary Shares will be redeemed if and to the extent the related Series F Preferred Shares are redeemed by the Company. Neither the Depositary Shares nor the Series F Preferred Shares have a stated maturity, nor will they be subject to any sinking fund or mandatory redemption. The Series F Preferred Shares are not convertible into any other securities. The Series F Preferred Shares will not have voting rights, except under limited circumstances. The net proceeds from the offering of $222.1 million and other available funds were used to redeem in part its outstanding 6.75% Series C Non-Cumulative Preferred Shares. The preferred shares were redeemed at a redemption price equal to $25 per share, plus all declared and unpaid dividends to (but excluding) the redemption date. In accordance with GAAP, following the redemption, original issuance costs related to such shares have been removed from additional paid-in capital and recorded as a “loss on redemption of preferred shares.” Such adjustment had no impact on total shareholders’ equity or cash flows.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2017
Comprehensive Income Note Disclosure [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The following tables present details about amounts reclassified from accumulated other comprehensive income and the tax effects allocated to each component of other comprehensive income (loss): Amounts Reclassified from AOCI Consolidated Statement of Income Three Months Ended Nine Months Ended Details About Line Item That Includes September 30, September 30, AOCI Components Reclassification 2017 2016 2017 2016 Unrealized appreciation on available-for-sale investments Net realized gains (losses) $ 27,550 $ 61,464 $ 59,474 $ 137,555 Other-than-temporary impairment losses (1,878 ) (3,867 ) (5,415 ) (16,999 ) Total before tax 25,672 57,597 54,059 120,556 Income tax (expense) benefit (1,760 ) (2,605 ) (7,879 ) (11,247 ) Net of tax $ 23,912 $ 54,992 $ 46,180 $ 109,309 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Three Months Ended September 30, 2017 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 69,330 $ 2,868 $ 66,462 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 25,672 1,760 23,912 Foreign currency translation adjustments 8,590 310 8,280 Other comprehensive income (loss) $ 52,248 $ 1,418 $ 50,830 Three Months Ended September 30, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 11,692 $ (4,589 ) $ 16,281 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 57,597 2,605 54,992 Foreign currency translation adjustments (5,407 ) (95 ) (5,312 ) Other comprehensive income (loss) $ (51,312 ) $ (7,289 ) $ (44,023 ) Nine Months Ended September 30, 2017 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 288,813 $ 28,590 $ 260,223 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 54,059 7,879 46,180 Foreign currency translation adjustments 30,264 563 29,701 Other comprehensive income (loss) $ 265,018 $ 21,274 $ 243,744 Nine Months Ended September 30, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 281,770 $ 30,048 $ 251,722 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (150 ) — (150 ) Less reclassification of net realized gains (losses) included in net income 120,556 11,247 109,309 Foreign currency translation adjustments (5,733 ) 417 (6,150 ) Other comprehensive income (loss) $ 155,331 $ 19,218 $ 136,113

Guarantor Financial Information

Guarantor Financial Information	9 Months Ended
	Sep. 30, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Guarantor Financial Information	Guarantor Financial Information The following tables present condensed financial information for ACGL, Arch-U.S., a 100% owned subsidiary of ACGL, and ACGL’s other subsidiaries. September 30, 2017 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 402 $ 69,671 $ 21,876,508 $ (14,700 ) $ 21,931,881 Cash 4,868 88,818 768,675 — 862,361 Investments in subsidiaries 9,214,178 4,028,493 — (13,242,671 ) — Due from subsidiaries and affiliates 81 117 1,923,941 (1,924,139 ) — Premiums receivable — — 1,863,203 (593,525 ) 1,269,678 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 7,023,836 (4,517,821 ) 2,506,015 Contractholder receivables — — 1,864,348 — 1,864,348 Ceded unearned premiums — — 2,240,129 (1,292,994 ) 947,135 Deferred acquisition costs — — 677,567 (146,371 ) 531,196 Goodwill and intangible assets — — 684,405 — 684,405 Other assets 13,357 59,734 2,146,993 (192,306 ) 2,027,778 Total assets $ 9,232,886 $ 4,246,833 $ 41,069,605 $ (21,924,527 ) $ 32,624,797 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 15,836,263 $ (4,484,996 ) $ 11,351,267 Unearned premiums — — 5,044,544 (1,292,994 ) 3,751,550 Reinsurance balances payable — — 945,530 (593,524 ) 352,006 Contractholder payables — — 1,864,348 — 1,864,348 Collateral held for insured obligations — — 345,726 345,726 Senior notes 297,030 494,596 941,100 — 1,732,726 Revolving credit agreement borrowings — — 826,242 — 826,242 Due to subsidiaries and affiliates 41 542,103 1,381,996 (1,924,140 ) — Other liabilities 24,671 100,278 2,669,614 (371,502 ) 2,423,061 Total liabilities 321,742 1,136,977 29,855,363 (8,667,156 ) 22,646,926 Redeemable noncontrolling interests — — 220,529 (14,700 ) 205,829 Shareholders’ Equity Total shareholders’ equity available to Arch 8,911,144 3,109,856 10,132,815 (13,242,671 ) 8,911,144 Non-redeemable noncontrolling interests — — 860,898 — 860,898 Total shareholders’ equity 8,911,144 3,109,856 10,993,713 (13,242,671 ) 9,772,042 Total liabilities, noncontrolling interests and shareholders’ equity $ 9,232,886 $ 4,246,833 $ 41,069,605 $ (21,924,527 ) $ 32,624,797 December 31, 2016 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 2,612 $ 41,672 $ 19,690,067 $ (14,700 ) $ 19,719,651 Cash 1,687 71,955 769,300 — 842,942 Investments in subsidiaries 8,660,586 3,716,681 — (12,377,267 ) — Due from subsidiaries and affiliates 14,297 51,298 1,866,681 (1,932,276 ) — Premiums receivable — — 1,579,865 (507,430 ) 1,072,435 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 6,114,518 (4,000,380 ) 2,114,138 Contractholder receivables — — 1,717,436 — 1,717,436 Ceded unearned premiums — — 1,985,311 (1,125,744 ) 859,567 Deferred acquisition costs — — 577,461 (129,901 ) 447,560 Goodwill and intangible assets — — 781,553 — 781,553 Other assets 15,725 49,244 1,901,786 (149,928 ) 1,816,827 Total assets $ 8,694,907 $ 3,930,850 $ 36,983,978 $ (20,237,626 ) $ 29,372,109 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 14,164,191 $ (3,963,231 ) $ 10,200,960 Unearned premiums — — 4,532,614 (1,125,744 ) 3,406,870 Reinsurance balances payable — — 807,837 (507,430 ) 300,407 Contractholder payables — — 1,717,436 — 1,717,436 Collateral held for insured obligations — — 301,406 — 301,406 Deposit accounting liabilities — — 22,150 — 22,150 Senior notes 296,957 494,525 940,776 — 1,732,258 Revolving credit agreement borrowings 100,000 — 656,650 — 756,650 Due to subsidiaries and affiliates 26,270 535,584 1,370,422 (1,932,276 ) — Other liabilities 17,962 54,823 1,867,040 (316,978 ) 1,622,847 Total liabilities 441,189 1,084,932 26,380,522 (7,845,659 ) 20,060,984 Redeemable noncontrolling interests — — 220,253 (14,700 ) 205,553 Shareholders’ Equity Total shareholders’ equity available to Arch 8,253,718 2,845,918 9,531,349 (12,377,267 ) 8,253,718 Non-redeemable noncontrolling interests — — 851,854 — 851,854 Total shareholders’ equity 8,253,718 2,845,918 10,383,203 (12,377,267 ) 9,105,572 Total liabilities, noncontrolling interests and shareholders’ equity $ 8,694,907 $ 3,930,850 $ 36,983,978 $ (20,237,626 ) $ 29,372,109 Three Months Ended September 30, 2017 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 1,261,886 $ — $ 1,261,886 Net investment income 117 151 138,784 (22,593 ) 116,459 Net realized gains (losses) — — 66,275 — 66,275 Net impairment losses recognized in earnings — — (1,878 ) — (1,878 ) Other underwriting income — — 6,064 — 6,064 Equity in net income (loss) of investment funds accounted for using the equity method — — 31,090 — 31,090 Other income (loss) (102 ) — (240 ) — (342 ) Total revenues 15 151 1,501,981 (22,593 ) 1,479,554 Expenses Losses and loss adjustment expenses — — 1,046,141 — 1,046,141 Acquisition expenses — — 193,854 — 193,854 Other operating expenses — — 170,127 — 170,127 Corporate expenses 14,576 410 2,112 — 17,098 Amortization of intangible assets — — 31,824 — 31,824 Interest expense 5,934 12,037 33,811 (22,272 ) 29,510 Net foreign exchange (gains) losses — — 20,510 7,518 28,028 Total expenses 20,510 12,447 1,498,379 (14,754 ) 1,516,582 Income (loss) before income taxes (20,495 ) (12,296 ) 3,602 (7,839 ) (37,028 ) Income tax (expense) benefit — 4,432 (12,621 ) — (8,189 ) Income (loss) before equity in net income of subsidiaries (20,495 ) (7,864 ) (9,019 ) (7,839 ) (45,217 ) Equity in net income (loss) of subsidiaries (13,161 ) 50,057 — (36,896 ) — Net income (loss) (33,656 ) 42,193 (9,019 ) (44,735 ) (45,217 ) Net (income) loss attributable to noncontrolling interests — — 11,238 323 11,561 Net income (loss) available to Arch (33,656 ) 42,193 2,219 (44,412 ) (33,656 ) Preferred dividends (12,369 ) — — — (12,369 ) Loss on redemption of preferred shares (6,735 ) — — — (6,735 ) Net income (loss) available to Arch common shareholders $ (52,760 ) $ 42,193 $ 2,219 $ (44,412 ) $ (52,760 ) Comprehensive income (loss) available to Arch $ 17,585 $ 47,676 $ 45,936 $ (93,612 ) $ 17,585 Three Months Ended September 30, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 958,403 $ — $ 958,403 Net investment income 6 803 99,654 (6,845 ) 93,618 Net realized gains (losses) — — 125,105 — 125,105 Net impairment losses recognized in earnings — — (3,867 ) — (3,867 ) Other underwriting income — — 7,980 — 7,980 Equity in net income (loss) of investment funds accounted for using the equity method — — 16,662 — 16,662 Other income (loss) 71 — (471 ) — (400 ) Total revenues 77 803 1,203,466 (6,845 ) 1,197,501 Expenses Losses and loss adjustment expenses — — 524,183 — 524,183 Acquisition expenses — — 161,267 — 161,267 Other operating expenses — — 153,286 — 153,286 Corporate expenses 18,488 608 (611 ) — 18,485 Amortization of intangible assets — — 4,865 — 4,865 Interest expense 5,948 6,627 9,890 (6,522 ) 15,943 Net foreign exchange (gains) losses — — 2,723 (102 ) 2,621 Total expenses 24,436 7,235 855,603 (6,624 ) 880,650 Income (loss) before income taxes (24,359 ) (6,432 ) 347,863 (221 ) 316,851 Income tax (expense) benefit — 2,116 (15,347 ) — (13,231 ) Income (loss) before equity in net income of subsidiaries (24,359 ) (4,316 ) 332,516 (221 ) 303,620 Equity in net income of subsidiaries 277,231 21,945 — (299,176 ) — Net income 252,872 17,629 332,516 (299,397 ) 303,620 Net (income) loss attributable to noncontrolling interests — — (51,071 ) 323 (50,748 ) Net income available to Arch 252,872 17,629 281,445 (299,074 ) 252,872 Preferred dividends (5,484 ) — — — (5,484 ) Net income available to Arch common shareholders $ 247,388 $ 17,629 $ 281,445 $ (299,074 ) $ 247,388 Comprehensive income (loss) available to Arch $ 208,790 $ 2,019 $ 237,555 $ (239,574 ) $ 208,790 Nine Months Ended September 30, 2017 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 3,619,777 $ — $ 3,619,777 Net investment income 123 1,151 410,392 (66,209 ) 345,457 Net realized gains (losses) — — 122,163 — 122,163 Net impairment losses recognized in earnings — — (5,415 ) — (5,415 ) Other underwriting income — — 15,519 — 15,519 Equity in net income of investment funds accounted for using the equity method — — 111,884 — 111,884 Other income (loss) (368 ) — (2,750 ) — (3,118 ) Total revenues (245 ) 1,151 4,271,570 (66,209 ) 4,206,267 Expenses Losses and loss adjustment expenses — — 2,288,571 — 2,288,571 Acquisition expenses — — 566,579 — 566,579 Other operating expenses — — 514,827 — 514,827 Corporate expenses 53,639 3,727 12,400 — 69,766 Amortization of intangible assets — — 93,942 — 93,942 Interest expense 18,024 35,956 98,197 (65,242 ) 86,935 Net foreign exchange losses (gains) — — 65,701 21,274 86,975 Total expenses 71,663 39,683 3,640,217 (43,968 ) 3,707,595 Income (loss) before income taxes (71,908 ) (38,532 ) 631,353 (22,241 ) 498,672 Income tax (expense) benefit — 13,374 (84,129 ) — (70,755 ) Income (loss) before equity in net income of subsidiaries (71,908 ) (25,158 ) 547,224 (22,241 ) 427,917 Equity in net income of subsidiaries 476,546 213,586 — (690,132 ) — Net income 404,638 188,428 547,224 (712,373 ) 427,917 Amounts attributable to noncontrolling interests — — (24,247 ) 968 (23,279 ) Net income available to Arch 404,638 188,428 522,977 (711,405 ) 404,638 Preferred dividends (34,936 ) — — — (34,936 ) Loss on redemption of preferred shares (6,735 ) — — — (6,735 ) Net income available to Arch common shareholders $ 362,967 $ 188,428 $ 522,977 $ (711,405 ) $ 362,967 Comprehensive income (loss) available to Arch $ 648,861 $ 240,759 $ 745,856 $ (986,615 ) $ 648,861 Nine Months Ended September 30, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 2,915,967 $ — $ 2,915,967 Net investment income 7 2,351 294,012 (20,679 ) 275,691 Net realized gains (losses) — — 230,647 — 230,647 Net impairment losses recognized in earnings — — (16,849 ) — (16,849 ) Other underwriting income — — 54,749 (16,498 ) 38,251 Equity in net income of investment funds accounted for using the equity method — — 32,054 — 32,054 Other income (loss) 270 — (702 ) — (432 ) Total revenues 277 2,351 3,509,878 (37,177 ) 3,475,329 Expenses Losses and loss adjustment expenses — — 1,631,724 — 1,631,724 Acquisition expenses — — 501,782 — 501,782 Other operating expenses — — 460,748 — 460,748 Corporate expenses 45,284 1,549 (1,765 ) — 45,068 Amortization of intangible assets — — 14,493 — 14,493 Interest expense 17,811 19,946 46,169 (36,213 ) 47,713 Net foreign exchange losses (gains) — — 5,093 (3,568 ) 1,525 Total expenses 63,095 21,495 2,658,244 (39,781 ) 2,703,053 Income (loss) before income taxes (62,818 ) (19,144 ) 851,634 2,604 772,276 Income tax (expense) benefit — 6,446 (50,118 ) — (43,672 ) Income (loss) before equity in net income of subsidiaries (62,818 ) (12,698 ) 801,516 2,604 728,604 Equity in net income of subsidiaries 681,543 64,684 — (746,227 ) — Net income 618,725 51,986 801,516 (743,623 ) 728,604 Amounts attributable to noncontrolling interests — — (110,844 ) 965 (109,879 ) Net income available to Arch 618,725 51,986 690,672 (742,658 ) 618,725 Preferred dividends (16,453 ) — — — (16,453 ) Net income available to Arch common shareholders $ 602,272 $ 51,986 $ 690,672 $ (742,658 ) $ 602,272 Comprehensive income (loss) available to Arch $ 754,979 $ 89,204 $ 830,348 $ (919,552 ) $ 754,979 Nine Months Ended September 30, 2017 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 130,715 $ 70,761 $ 1,464,701 $ (585,043 ) $ 1,081,134 Investing Activities Purchases of fixed maturity investments — — (28,079,129 ) — (28,079,129 ) Purchases of equity securities — — (667,135 ) — (667,135 ) Purchases of other investments — — (1,406,528 ) — (1,406,528 ) Proceeds from the sales of fixed maturity investments — — 27,629,474 — 27,629,474 Proceeds from the sales of equity securities — — 751,873 — 751,873 Proceeds from the sales, redemptions and maturities of other investments — — 938,581 — 938,581 Proceeds from redemptions and maturities of fixed maturity investments — — 747,621 — 747,621 Net settlements of derivative instruments — — (20,952 ) — (20,952 ) Net (purchases) sales of short-term investments 2,209 (27,998 ) (938,864 ) — (964,653 ) Change in cash collateral related to securities lending — — 148,692 — 148,692 Contributions to subsidiaries 20,641 (72,900 ) (353,588 ) 405,847 — Issuance of intercompany loans — — (47,000 ) 47,000 — Repayment of intercompany loans — 47,000 — (47,000 ) — Acquisitions, net of cash — — (27,709 ) — (27,709 ) Purchases of fixed assets (18 ) — (16,844 ) — (16,862 ) Other — — 106,786 (20,641 ) 86,145 Net Cash Provided By (Used For) Investing Activities 22,832 (53,898 ) (1,234,722 ) 385,206 (880,582 ) Financing Activities Proceeds from issuance of preferred shares, net 222,054 — — — 222,054 Redemption of preferred shares (230,000 ) — — — (230,000 ) Proceeds from common shares issued, net (7,484 ) — 405,847 (405,847 ) (7,484 ) Proceeds from intercompany borrowings — — 47,000 (47,000 ) — Proceeds from borrowings — — 238,915 — 238,915 Repayments of intercompany borrowings — — (47,000 ) 47,000 — Repayments of borrowings (100,000 ) — (72,000 ) — (172,000 ) Change in cash collateral related to securities lending — — (148,692 ) — (148,692 ) Dividends paid to redeemable noncontrolling interests — — (14,447 ) 956 (13,491 ) Dividends paid to parent (1) — — (584,087 ) 584,087 — Other — — (69,921 ) 20,641 (49,280 ) Preferred dividends paid (34,936 ) — — — (34,936 ) Net Cash Provided By (Used For) Financing Activities (150,366 ) — (244,385 ) 199,837 (194,914 ) Effects of exchange rates changes on foreign currency cash — — 13,781 — 13,781 Increase (decrease) in cash 3,181 16,863 (625 ) — 19,419 Cash beginning of year 1,687 71,955 769,300 — 842,942 Cash end of period $ 4,868 $ 88,818 $ 768,675 $ — $ 862,361 (1) Dividends received by parent are included in net cash provided by (used for) operating activities. Nine Months Ended September 30, 2016 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 94,250 $ 14,448 $ 1,096,443 $ (168,002 ) $ 1,037,139 Investing Activities Purchases of fixed maturity investments — — (27,840,555 ) — (27,840,555 ) Purchases of equity securities — — (377,767 ) — (377,767 ) Purchases of other investments — — (1,008,774 ) — (1,008,774 ) Proceeds from the sales of fixed maturity investments — — 26,731,924 — 26,731,924 Proceeds from the sales of equity securities — — 464,904 — 464,904 Proceeds from the sales, redemptions and maturities of other investments — — 879,330 — 879,330 Proceeds from redemptions and maturities of fixed maturity investments — 41,500 499,323 — 540,823 Net settlements of derivative instruments — — 23,396 — 23,396 Net (purchases) sales of short-term investments (436,830 ) (53,779 ) (113,553 ) — (604,162 ) Change in cash collateral related to securities lending — — (27,935 ) — (27,935 ) Contributions to subsidiaries (3,585 ) — (9,247 ) 12,832 — Acquisitions, net of cash — — (20,911 ) — (20,911 ) Purchases of fixed assets (8 ) — (11,557 ) — (11,565 ) Other 2,000 — (5,816 ) — (3,816 ) Net Cash Provided By (Used For) Investing Activities (438,423 ) (12,279 ) (817,238 ) 12,832 (1,255,108 ) Financing Activities Proceeds from issuance of preferred shares, net 434,899 — — — 434,899 Purchases of common shares under share repurchase program (75,256 ) — — — (75,256 ) Proceeds from common shares issued, net (3,785 ) — 12,832 (12,832 ) (3,785 ) Proceeds from borrowings — — 46,000 — 46,000 Repayments of borrowings — — (179,171 ) — (179,171 ) Change in cash collateral related to securities lending — — 27,935 — 27,935 Dividends paid to redeemable noncontrolling interests — — (14,448 ) 957 (13,491 ) Dividends paid to parent (1) — — (167,045 ) 167,045 — Other — 200 32,913 — 33,113 Preferred dividends paid (16,453 ) — — — (16,453 ) Net Cash Provided By (Used For) Financing Activities 339,405 200 (240,984 ) 155,170 253,791 Effects of exchange rates changes on foreign currency cash — — (10,332 ) — (10,332 ) Increase (decrease) in cash (4,768 ) 2,369 27,889 — 25,490 Cash beginning of year 6,809 17,023 529,494 — 553,326 Cash end of period $ 2,041 $ 19,392 $ 557,383 $ — $ 578,816 (1) Dividends received by parent are included in net cash provided by (used for) operating activities.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company’s income tax provision on income before income taxes resulted in an expense of 14.2% for the nine months ended September 30, 2017 , compared to an expense of 5.7% for the 2016 period. The Company’s effective tax rate, which is based upon the expected annual effective tax rate, may fluctuate from period to period based on the relative mix of income or loss reported by jurisdiction and the varying tax rates in each jurisdiction. For interim reporting purposes, the Company has calculated its effective tax rate for the full year of 2017 by treating any excess tax benefits that arise from the accounting for stock based compensation as a discrete item. As such, this amount is not included when projecting the Company’s full year effective tax rate but rather is accounted for at the U.S. Federal statutory rate of 35% after applying the projected full year effective tax rate to actual nine-month results before the discrete item. The impact of the discrete item resulted in a benefit of 1.5% for the nine months ended September 30, 2017 . The Company had a net deferred tax asset of $248.3 million at September 30, 2017 , compared to $221.2 million at December 31, 2016 . In addition, the Company paid $47.9 million and $40.7 million of income taxes for the nine months ended September 30, 2017 and 2016 , respectively.

Legal Proceedings

Legal Proceedings	9 Months Ended
	Sep. 30, 2017
Disclosure Legal Proceedings [Abstract]
Legal Proceedings	Legal Proceedings The Company, in common with the insurance industry in general, is subject to litigation and arbitration in the normal course of its business. As of September 30, 2017 , the Company was not a party to any litigation or arbitration which is expected by management to have a material adverse effect on the Company’s results of operations and financial condition and liquidity.

Transactions with Related Parti

Transactions with Related Parties	9 Months Ended
	Sep. 30, 2017
Related Party Transactions [Abstract]
Transactions with Related Parties	Transactions with Related Parties Kewsong Lee, a director of ACGL, is a Managing Director and Deputy Chief Investment Officer for Corporate Private Equity of Carlyle Group LP (“Carlyle”). As part of its investment philosophy, the Company invests a portion of its investment portfolio in alternative investment funds. As of September 30, 2017 , the total value of the Company’s investments in funds or other investments managed by Carlyle was approximately $248.5 million , and the Company had aggregate unfunded commitments to funds managed by Carlyle of $471.6 million . The Company may make additional commitments to funds managed by Carlyle from time to time. During the nine months ended September 30, 2017 and 2016 , the Company made aggregate capital contributions to funds managed by Carlyle of $86.0 million and $50.1 million , respectively, and received aggregate cash distributions from funds managed by Carlyle of $48.7 million and $17.9 million , respectively. Effective November 2, 2017, Mr. Lee resigned from ACGL’s Board of Directors because of the expansion of his duties at Carlyle following his recent promotion to co-CEO effective January 1, 2018.

Acquisition

Acquisition	9 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Acquisition	Acquisition On July 1, 2017, the Company completed its previously announced acquisition of AIG United Guaranty Insurance (Asia) Limited (renamed “Arch MI Asia Limited”) following the payment of $40.0 million to AIG. Arch MI Asia Limited compliments the Company’s existing private mortgage insurance businesses, which have operations in the United States, Europe and Australia. The purchase price was allocated to the acquired assets and liabilities of Arch MI Asia Limited based on estimated fair values on the acquisition date. The Company recognized other intangible assets of $2.3 million and goodwill of $0.8 million . The goodwill balance is primarily attributed to Arch MI Asia Limited’s assembled workforce and access to the mortgage insurance market. None of the goodwill recognized is expected to be deductible for income tax purposes.

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Event	Subsequent Events On October 25, 2017, the Company’s first-lien U.S. mortgage insurance subsidiaries entered into an aggregate excess of loss reinsurance agreement with Bellemeade Re 2017-1 Ltd. (“Bellemeade III”), a special purpose reinsurance company domiciled in Bermuda. The Bellemeade III agreement provides for up to $368.1 million of aggregate excess of loss reinsurance coverage at inception for new delinquencies on a portfolio of in-force policies issued between January 1, 2017 and June 30, 2017. For the coverage period, Bellemeade III will cover $368.1 million in excess of $165.7 million of aggregate losses. The coverage amount decreases over a ten-year period as the underlying covered mortgages amortize. Bellemeade III financed the coverage through the issuance of mortgage insurance-linked notes in an aggregate amount of approximately $368.1 million to unrelated investors (the “Notes”). The maturity date of the Notes is October 25, 2027. The Notes will be redeemed prior to maturity upon the occurrence of a mandatory termination event or if the ceding insurers trigger a termination of the reinsurance agreement following the occurrence of an optional termination event. All of the proceeds paid to Bellemeade III from the sale of the Notes were deposited into a reinsurance trust for the sole benefit of the ceding insurers as security for Bellemeade III’s obligations. At all times, funds in the reinsurance trust account are required to be invested in high credit quality money market funds. In October 2017, a series of wildfires burned across several California counties. With the information available, the Company has established a preliminary range of pre-tax losses of $30 million to $55 million for these wildfires, net of reinsurance and reinstatement premiums. At this time, there are significant uncertainties surrounding the numbers of claims and scope of damage for these wildfires. The Company’s preliminary estimate for the wildfires is based on currently available information derived from modeling techniques, industry assessments of exposure, preliminary claims information obtained from the Company’s clients and brokers to date and a review of in-force contracts. Actual losses from these wildfires may vary materially from the estimates due to the inherent uncertainties in making such determinations.

General (Policies)

General (Policies)	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	The interim consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). All significant intercompany transactions and balances have been eliminated in consolidation.
Use of estimates	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts 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. Actual results could differ from those estimates and assumptions. In the opinion of management, the accompanying unaudited interim consolidated financial statements reflect all adjustments (consisting of normally recurring accruals) necessary for a fair statement of results on an interim basis. The results of any interim period are not necessarily indicative of the results for a full year or any future periods.

Variable Interest Entities an27

Variable Interest Entities and Noncontrolling Interests (Tables)	9 Months Ended
	Sep. 30, 2017
Noncontrolling Interest [Abstract]
Carrying value of assets and liabilities of variable interest entity	The following table provides the carrying amount and balance sheet caption in which the assets and liabilities of Watford Re are reported: September 30, December 31, 2017 2016 Assets Investments accounted for using the fair value option $ 2,457,365 $ 1,857,623 Cash 57,151 74,893 Accrued investment income 13,718 17,017 Premiums receivable 209,985 189,911 Reinsurance recoverable on unpaid and paid losses and LAE 37,575 24,420 Ceded unearned premiums 23,538 12,145 Deferred acquisition costs 87,692 86,379 Receivable for securities sold 74,051 1,326 Goodwill and intangible assets 7,650 7,650 Other assets 132,796 111,386 Total assets of consolidated VIE $ 3,101,521 $ 2,382,750 Liabilities Reserves for losses and loss adjustment expenses $ 735,132 $ 510,809 Unearned premiums 344,060 293,480 Reinsurance balances payable 22,487 12,289 Revolving credit agreement borrowings 426,242 256,650 Payable for securities purchased 211,065 42,922 Other liabilities 174,472 88,976 Total liabilities of consolidated VIE $ 1,913,458 $ 1,205,126 Redeemable noncontrolling interests $ 220,529 $ 220,253
Activity in non-redeemable noncontrolling interests	The following table sets forth activity in the non-redeemable noncontrolling interests: September 30, 2017 2016 Three Months Ended Balance, beginning of period $ 877,456 $ 788,589 Amounts attributable to noncontrolling interests (16,147 ) 46,160 Foreign currency translation adjustments attributable to noncontrolling interests (411 ) 59 Balance, end of period $ 860,898 $ 834,808 Nine Months Ended Balance, beginning of year $ 851,854 $ 738,831 Amounts attributable to noncontrolling interests 9,523 96,118 Foreign currency translation adjustments attributable to noncontrolling interests (479 ) (141 ) Balance, end of period $ 860,898 $ 834,808
Activity in redeemable noncontrolling interests	The following table sets forth activity in the redeemable non-controlling interests: September 30, 2017 2016 Three Months Ended Balance, beginning of period $ 205,736 $ 205,366 Accretion of preference share issuance costs 93 93 Balance, end of period $ 205,829 $ 205,459 Nine Months Ended Balance, beginning of year $ 205,553 $ 205,182 Accretion of preference share issuance costs 276 277 Balance, end of period $ 205,829 $ 205,459
Portion of income or loss attributable to third party investors	The portion of Watford Re’s income or loss attributable to third party investors, recorded in the Company’s consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests,’ are summarized in the table below: September 30, 2017 2016 Three Months Ended Amounts attributable to non-redeemable noncontrolling interests $ 16,147 $ (46,160 ) Dividends attributable to redeemable noncontrolling interests (4,586 ) (4,588 ) Net (income) loss attributable to noncontrolling interests $ 11,561 $ (50,748 ) Nine Months Ended Amounts attributable to non-redeemable noncontrolling interests $ (9,523 ) $ (96,118 ) Dividends attributable to redeemable noncontrolling interests (13,756 ) (13,761 ) Net (income) loss attributable to noncontrolling interests $ (23,279 ) $ (109,879 )
Total assets and maximum exposure to loss associated with VIEs	The following table presents total assets of Bellemeade I and Bellemeade II as well as the Company’s maximum exposure to loss associated with these VIEs: Maximum Exposure to Loss Total VIE Assets On-Balance Sheet Off-Balance Sheet Total Bellemeade I $ 112,090 $ 533 $ 1,009 $ 1,542 Bellemeade II 191,387 (53 ) 746 693 Total $ 303,477 $ 480 $ 1,755 $ 2,235

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule of computation of basic and diluted earnings per common share	The following table sets forth the computation of basic and diluted earnings (loss) per common share: Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Numerator: Net income (loss) $ (45,217 ) $ 303,620 $ 427,917 $ 728,604 Amounts attributable to noncontrolling interests 11,561 (50,748 ) (23,279 ) (109,879 ) Net income (loss) available to Arch (33,656 ) 252,872 404,638 618,725 Preferred dividends (12,369 ) (5,484 ) (34,936 ) (16,453 ) Loss on redemption of preferred shares (6,735 ) — (6,735 ) — Net income (loss) available to Arch common shareholders $ (52,760 ) $ 247,388 $ 362,967 $ 602,272 Denominator: Weighted average common shares outstanding 129,211,251 120,938,916 124,526,611 120,656,420 Series D preferred shares (1) 5,674,200 — 9,945,518 — Weighted average common shares and common share equivalents outstanding — basic 134,885,451 120,938,916 134,472,129 120,656,420 Effect of dilutive common share equivalents: Nonvested restricted shares — 1,313,025 1,459,879 1,295,825 Stock options (2) — 2,679,712 3,290,316 2,575,929 Weighted average common shares and common share equivalents outstanding — diluted (3) 134,885,451 124,931,653 139,222,324 124,528,174 Earnings (loss) per common share: Basic $ (0.39 ) $ 2.05 $ 2.70 $ 4.99 Diluted $ (0.39 ) $ 1.98 $ 2.61 $ 4.84 (1) Such shares are convertible non-voting common equivalent preferred shares issued in connection with the UGC acquisition. (2) Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2017 third quarter and 2016 third quarter , the number of stock options excluded were nil and 334,203 , respectively. For the nine months ended September 30, 2017 and 2016 , the number of stock options excluded were 838,868 and 842,105 , respectively.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Analysis of underwriting income or loss by segment and reconciliation to net income available to common shareholders	The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income or loss to net income available to common shareholders: Three Months Ended September 30, 2017 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 787,447 $ 422,083 $ 347,951 $ 1,557,179 $ 166,198 $ 1,648,246 Premiums ceded (222,516 ) (105,389 ) (57,900 ) (385,503 ) (12,471 ) (322,843 ) Net premiums written 564,931 316,694 290,051 1,171,676 153,727 1,325,403 Change in unearned premiums (29,766 ) 6,879 (15,533 ) (38,420 ) (25,097 ) (63,517 ) Net premiums earned 535,165 323,573 274,518 1,133,256 128,630 1,261,886 Other underwriting income (loss) — 1,728 3,599 5,327 737 6,064 Losses and loss adjustment expenses (568,795 ) (318,609 ) (35,156 ) (922,560 ) (123,581 ) (1,046,141 ) Acquisition expenses (82,638 ) (57,340 ) (21,803 ) (161,781 ) (32,073 ) (193,854 ) Other operating expenses (90,875 ) (36,214 ) (34,770 ) (161,859 ) (8,268 ) (170,127 ) Underwriting income (loss) $ (207,143 ) $ (86,862 ) $ 186,388 (107,617 ) (34,555 ) (142,172 ) Net investment income 94,127 22,332 116,459 Net realized gains (losses) 64,104 2,171 66,275 Net impairment losses recognized in earnings (1,878 ) — (1,878 ) Equity in net income (loss) of investment funds accounted for using the equity method 31,090 — 31,090 Other income (loss) (342 ) — (342 ) Corporate expenses (2) (14,108 ) — (14,108 ) UGC transaction costs and other (2) (2,990 ) — (2,990 ) Amortization of intangible assets (31,824 ) — (31,824 ) Interest expense (26,264 ) (3,246 ) (29,510 ) Net foreign exchange gains (losses) (27,785 ) (243 ) (28,028 ) Income (loss) before income taxes (23,487 ) (13,541 ) (37,028 ) Income tax (expense) benefit (8,168 ) (21 ) (8,189 ) Net income (loss) (31,655 ) (13,562 ) (45,217 ) Dividends attributable to redeemable noncontrolling interests — (4,586 ) (4,586 ) Amounts attributable to nonredeemable noncontrolling interests — 16,147 16,147 Net income (loss) available to Arch (31,655 ) (2,001 ) (33,656 ) Preferred dividends (12,369 ) — (12,369 ) Loss on redemption of preferred shares (6,735 ) — (6,735 ) Net income (loss) available to Arch common shareholders $ (50,759 ) $ (2,001 ) $ (52,760 ) Underwriting Ratios Loss ratio 106.3 % 98.5 % 12.8 % 81.4 % 96.1 % 82.9 % Acquisition expense ratio 15.4 % 17.7 % 7.9 % 14.3 % 24.9 % 15.4 % Other operating expense ratio 17.0 % 11.2 % 12.7 % 14.3 % 6.4 % 13.5 % Combined ratio 138.7 % 127.4 % 33.4 % 110.0 % 127.4 % 111.8 % Goodwill and intangible assets $ 23,445 $ 417 $ 652,893 $ 676,755 $ 7,650 $ 684,405 (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’ Three Months Ended September 30, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 758,934 $ 324,361 $ 131,726 $ 1,214,765 $ 163,736 $ 1,278,765 Premiums ceded (217,446 ) (89,551 ) (51,182 ) (357,923 ) (6,300 ) (264,487 ) Net premiums written 541,488 234,810 80,544 856,842 157,436 1,014,278 Change in unearned premiums (22,410 ) 17,117 (3,582 ) (8,875 ) (47,000 ) (55,875 ) Net premiums earned 519,078 251,927 76,962 847,967 110,436 958,403 Other underwriting income (loss) — 2,216 4,740 6,956 1,024 7,980 Losses and loss adjustment expenses (332,845 ) (105,924 ) (11,107 ) (449,876 ) (74,307 ) (524,183 ) Acquisition expenses (77,146 ) (50,192 ) (5,190 ) (132,528 ) (28,739 ) (161,267 ) Other operating expenses (86,613 ) (35,389 ) (24,249 ) (146,251 ) (7,035 ) (153,286 ) Underwriting income (loss) $ 22,474 $ 62,638 $ 41,156 126,268 1,379 127,647 Net investment income 66,282 27,336 93,618 Net realized gains (losses) 95,946 29,159 125,105 Net impairment losses recognized in earnings (3,867 ) — (3,867 ) Equity in net income (loss) of investment funds accounted for using the equity method 16,662 — 16,662 Other income (loss) (400 ) — (400 ) Corporate expenses (2) (11,343 ) — (11,343 ) UGC transaction costs and other (2) (7,142 ) — (7,142 ) Amortization of intangible assets (4,865 ) — (4,865 ) Interest expense (12,924 ) (3,019 ) (15,943 ) Net foreign exchange gains (losses) (4,232 ) 1,611 (2,621 ) Income (loss) before income taxes 260,385 56,466 316,851 Income tax (expense) benefit (13,232 ) 1 (13,231 ) Net income (loss) 247,153 56,467 303,620 Dividends attributable to redeemable noncontrolling interests — (4,588 ) (4,588 ) Amounts attributable to nonredeemable noncontrolling interests — (46,160 ) (46,160 ) Net income (loss) available to Arch 247,153 5,719 252,872 Preferred dividends (5,484 ) — (5,484 ) Net income (loss) available to Arch common shareholders $ 241,669 $ 5,719 $ 247,388 Underwriting Ratios Loss ratio 64.1 % 42.0 % 14.4 % 53.1 % 67.3 % 54.7 % Acquisition expense ratio 14.9 % 19.9 % 6.7 % 15.6 % 26.0 % 16.8 % Other operating expense ratio 16.7 % 14.0 % 31.5 % 17.2 % 6.4 % 16.0 % Combined ratio 95.7 % 75.9 % 52.6 % 85.9 % 99.7 % 87.5 % Goodwill and intangible assets $ 26,367 $ 1,228 $ 55,696 $ 83,291 $ 7,650 $ 90,941 (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’ Nine Months Ended September 30, 2017 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,313,630 $ 1,351,051 $ 1,032,800 $ 4,697,007 $ 473,131 $ 4,915,895 Premiums ceded (704,057 ) (386,743 ) (194,139 ) (1,284,465 ) (35,315 ) (1,065,537 ) Net premiums written 1,609,573 964,308 838,661 3,412,542 437,816 3,850,358 Change in unearned premiums (51,188 ) (81,182 ) (61,776 ) (194,146 ) (36,435 ) (230,581 ) Net premiums earned 1,558,385 883,126 776,885 3,218,396 401,381 3,619,777 Other underwriting income (loss) — 1,143 11,999 13,142 2,377 15,519 Losses and loss adjustment expenses (1,252,375 ) (631,669 ) (84,915 ) (1,968,959 ) (319,612 ) (2,288,571 ) Acquisition expenses (236,378 ) (154,638 ) (76,235 ) (467,251 ) (99,328 ) (566,579 ) Other operating expenses (271,268 ) (110,458 ) (108,790 ) (490,516 ) (24,311 ) (514,827 ) Underwriting income (loss) $ (201,636 ) $ (12,496 ) $ 518,944 304,812 (39,493 ) 265,319 Net investment income 282,459 62,998 345,457 Net realized gains (losses) 110,662 11,501 122,163 Net impairment losses recognized in earnings (5,415 ) — (5,415 ) Equity in net income (loss) of investment funds accounted for using the equity method 111,884 — 111,884 Other income (loss) (3,118 ) — (3,118 ) Corporate expenses (2) (48,517 ) — (48,517 ) UGC transaction costs and other (2) (21,249 ) — (21,249 ) Amortization of intangible assets (93,942 ) — (93,942 ) Interest expense (77,932 ) (9,003 ) (86,935 ) Net foreign exchange gains (losses) (85,451 ) (1,524 ) (86,975 ) Income (loss) before income taxes 474,193 24,479 498,672 Income tax (expense) benefit (70,734 ) (21 ) (70,755 ) Net income (loss) 403,459 24,458 427,917 Dividends attributable to redeemable noncontrolling interests — (13,756 ) (13,756 ) Amounts attributable to nonredeemable noncontrolling interests — (9,523 ) (9,523 ) Net income (loss) available to Arch 403,459 1,179 404,638 Preferred dividends (34,936 ) — (34,936 ) Loss on redemption of preferred shares (6,735 ) — (6,735 ) Net income (loss) available to Arch common shareholders $ 361,788 $ 1,179 $ 362,967 Underwriting Ratios Loss ratio 80.4 % 71.5 % 10.9 % 61.2 % 79.6 % 63.2 % Acquisition expense ratio 15.2 % 17.5 % 9.8 % 14.5 % 24.7 % 15.7 % Other operating expense ratio 17.4 % 12.5 % 14.0 % 15.2 % 6.1 % 14.2 % Combined ratio 113.0 % 101.5 % 34.7 % 90.9 % 110.4 % 93.1 % (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’ Nine Months Ended September 30, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,319,530 $ 1,217,804 $ 361,440 $ 3,898,025 $ 421,627 $ 4,046,667 Premiums ceded (713,110 ) (370,068 ) (62,918 ) (1,145,347 ) (15,229 ) (887,591 ) Net premiums written 1,606,420 847,736 298,522 2,752,678 406,398 3,159,076 Change in unearned premiums (46,603 ) (43,345 ) (93,283 ) (183,231 ) (59,878 ) (243,109 ) Net premiums earned 1,559,817 804,391 205,239 2,569,447 346,520 2,915,967 Other underwriting income (loss) — 22,659 12,670 35,329 2,922 38,251 Losses and loss adjustment expenses (1,011,087 ) (363,613 ) (20,102 ) (1,394,802 ) (236,922 ) (1,631,724 ) Acquisition expenses (228,806 ) (160,706 ) (16,947 ) (406,459 ) (95,323 ) (501,782 ) Other operating expenses (263,111 ) (108,561 ) (70,590 ) (442,262 ) (18,486 ) (460,748 ) Underwriting income (loss) $ 56,813 $ 194,170 $ 110,270 361,253 (1,289 ) 359,964 Net investment income 207,088 68,603 275,691 Net realized gains (losses) 168,735 61,912 230,647 Net impairment losses recognized in earnings (16,849 ) — (16,849 ) Equity in net income (loss) of investment funds accounted for using the equity method 32,054 — 32,054 Other income (loss) (432 ) — (432 ) Corporate expenses (2) (37,926 ) — (37,926 ) UGC transaction costs and other (2) (7,142 ) — (7,142 ) Amortization of intangible assets (14,493 ) — (14,493 ) Interest expense (37,983 ) (9,730 ) (47,713 ) Net foreign exchange gains (losses) (3,812 ) 2,287 (1,525 ) Income (loss) before income taxes 650,493 121,783 772,276 Income tax (expense) benefit (43,673 ) 1 (43,672 ) Net income (loss) 606,820 121,784 728,604 Dividends attributable to redeemable noncontrolling interests — (13,761 ) (13,761 ) Amounts attributable to nonredeemable noncontrolling interests — (96,118 ) (96,118 ) Net income (loss) available to Arch 606,820 11,905 618,725 Preferred dividends (16,453 ) — (16,453 ) Net income (loss) available to Arch common shareholders $ 590,367 $ 11,905 $ 602,272 Underwriting Ratios Loss ratio 64.8 % 45.2 % 9.8 % 54.3 % 68.4 % 56.0 % Acquisition expense ratio 14.7 % 20.0 % 8.3 % 15.8 % 27.5 % 17.2 % Other operating expense ratio 16.9 % 13.5 % 34.4 % 17.2 % 5.3 % 15.8 % Combined ratio 96.4 % 78.7 % 52.5 % 87.3 % 101.2 % 89.0 % (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’

Reserve for Losses and Loss A30

Reserve for Losses and Loss Adjustment Expenses (Tables)	9 Months Ended
	Sep. 30, 2017
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Analysis of losses and loss adjustment expenses and reconciliation of beginning and ending reserve balances	The following table represents an analysis of losses and loss adjustment expenses and a reconciliation of the beginning and ending reserve for losses and loss adjustment expenses: Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Reserve for losses and loss adjustment expenses at beginning of period $ 10,520,511 $ 9,471,647 $ 10,200,960 $ 9,125,250 Unpaid losses and loss adjustment expenses recoverable and deferred charges 2,116,210 2,003,768 2,083,575 1,828,837 Net reserve for losses and loss adjustment expenses at beginning of period 8,404,301 7,467,879 8,117,385 7,296,413 Net incurred losses and loss adjustment expenses relating to losses occurring in: Current year 1,092,175 598,940 2,487,212 1,848,299 Prior years (45,232 ) (74,757 ) (197,839 ) (216,575 ) Discount and accretion on retroactive reinsurance (802 ) — (802 ) — Total net incurred losses and loss adjustment expenses 1,046,141 524,183 2,288,571 1,631,724 Net foreign exchange losses (gains) 61,919 1,463 168,493 (13,270 ) Net paid losses and loss adjustment expenses relating to losses occurring in: Current year (167,450 ) (128,432 ) (282,952 ) (285,468 ) Prior years (457,183 ) (304,673 ) (1,403,769 ) (1,068,979 ) Total net paid losses and loss adjustment expenses (624,633 ) (433,105 ) (1,686,721 ) (1,354,447 ) Net reserve for losses and loss adjustment expenses at end of period 8,887,728 7,560,420 8,887,728 7,560,420 Unpaid losses and loss adjustment expenses recoverable and deferred charges 2,463,539 2,049,769 2,463,539 2,049,769 Reserve for losses and loss adjustment expenses at end of period $ 11,351,267 $ 9,610,189 $ 11,351,267 $ 9,610,189

Investment Information (Tables)

Investment Information (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure Investment Information [Abstract]
Summary of fair value and cost or amortized cost of available for sale securities	The following table summarizes the fair value and cost or amortized cost of the Company’s investments classified as available for sale: Estimated Fair Value Gross Unrealized Gains Gross Unrealized Losses Cost or Amortized Cost OTTI Unrealized Losses (2) September 30, 2017 Fixed maturities (1): Corporate bonds $ 4,275,437 $ 49,576 $ (22,303 ) $ 4,248,164 $ (73 ) Mortgage backed securities 323,900 5,078 (2,540 ) 321,362 (2,146 ) Municipal bonds 2,353,234 31,202 (7,614 ) 2,329,646 — Commercial mortgage backed securities 584,730 3,114 (4,377 ) 585,993 — U.S. government and government agencies 3,761,612 3,303 (20,246 ) 3,778,555 — Non-U.S. government securities 1,473,819 49,570 (21,647 ) 1,445,896 — Asset backed securities 1,544,919 9,053 (4,748 ) 1,540,614 (22 ) Total 14,317,651 150,896 (83,475 ) 14,250,230 (2,241 ) Equity securities 480,607 84,755 (7,873 ) 403,725 — Other investments 260,339 54,512 (1 ) 205,828 — Short-term investments 1,646,036 667 (504 ) 1,645,873 — Total $ 16,704,633 $ 290,830 $ (91,853 ) $ 16,505,656 $ (2,241 ) December 31, 2016 Fixed maturities (1): Corporate bonds $ 4,392,373 $ 27,606 $ (46,905 ) $ 4,411,672 $ (2,285 ) Mortgage backed securities 490,093 4,794 (8,357 ) 493,656 (3,323 ) Municipal bonds 3,713,434 8,554 (29,154 ) 3,734,034 (201 ) Commercial mortgage backed securities 536,051 2,876 (6,508 ) 539,683 — U.S. government and government agencies 2,804,540 9,319 (24,437 ) 2,819,658 — Non-U.S. government securities 1,096,440 19,036 (56,872 ) 1,134,276 — Asset backed securities 1,123,987 6,897 (6,526 ) 1,123,616 (22 ) Total 14,156,918 79,082 (178,759 ) 14,256,595 (5,831 ) Equity securities 532,680 62,627 (17,517 ) 487,570 — Other investments 167,970 21,358 (2,465 ) 149,077 — Short-term investments 612,005 272 (145 ) 611,878 — Total $ 15,469,573 $ 163,339 $ (198,886 ) $ 15,505,120 $ (5,831 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” (2) Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At September 30, 2017 , the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $0.9 million , compared to a net unrealized gain of $2.8 million at December 31, 2016 .
Summary of available for sale securities in a continual unrealized loss position	The following table summarizes, for all available for sale securities in an unrealized loss position, the fair value and gross unrealized loss by length of time the security has been in a continual unrealized loss position: Less than 12 Months 12 Months or More Total Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses September 30, 2017 Fixed maturities (1): Corporate bonds $ 1,173,096 $ (18,315 ) $ 191,382 $ (3,988 ) $ 1,364,478 $ (22,303 ) Mortgage backed securities 146,352 (2,477 ) 1,511 (63 ) 147,863 (2,540 ) Municipal bonds 745,410 (5,958 ) 110,752 (1,656 ) 856,162 (7,614 ) Commercial mortgage backed securities 282,901 (3,579 ) 17,570 (798 ) 300,471 (4,377 ) U.S. government and government agencies 3,083,239 (19,736 ) 25,894 (510 ) 3,109,133 (20,246 ) Non-U.S. government securities 1,149,528 (20,741 ) 37,655 (906 ) 1,187,183 (21,647 ) Asset backed securities 587,561 (4,404 ) 22,051 (344 ) 609,612 (4,748 ) Total 7,168,087 (75,210 ) 406,815 (8,265 ) 7,574,902 (83,475 ) Equity securities 170,937 (7,873 ) — — 170,937 (7,873 ) Other investments 725 (1 ) — — 725 (1 ) Short-term investments 110,444 (504 ) — — 110,444 (504 ) Total $ 7,450,193 $ (83,588 ) $ 406,815 $ (8,265 ) $ 7,857,008 $ (91,853 ) December 31, 2016 Fixed maturities (1): Corporate bonds $ 1,700,813 $ (43,011 ) $ 46,902 $ (3,894 ) $ 1,747,715 $ (46,905 ) Mortgage backed securities 402,699 (8,134 ) 6,105 (223 ) 408,804 (8,357 ) Municipal bonds 1,513,308 (28,504 ) 29,636 (650 ) 1,542,944 (29,154 ) Commercial mortgage backed securities 231,374 (6,331 ) 5,635 (177 ) 237,009 (6,508 ) U.S. government and government agencies 1,888,018 (24,437 ) — — 1,888,018 (24,437 ) Non-U.S. government securities 807,598 (56,872 ) — — 807,598 (56,872 ) Asset backed securities 627,557 (5,465 ) 65,723 (1,061 ) 693,280 (6,526 ) Total 7,171,367 (172,754 ) 154,001 (6,005 ) 7,325,368 (178,759 ) Equity securities 269,381 (17,517 ) — — 269,381 (17,517 ) Other investments 39,299 (2,465 ) — — 39,299 (2,465 ) Short-term investments 29,146 (145 ) — — 29,146 (145 ) Total $ 7,509,193 $ (192,881 ) $ 154,001 $ (6,005 ) $ 7,663,194 $ (198,886 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”
Contractual maturities of the Company's fixed maturities and fixed maturities pledged under securities lending arrangements	The contractual maturities of the Company’s fixed maturities are shown in the following table. Expected maturities, which are management’s best estimates, will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. September 30, 2017 December 31, 2016 Maturity Estimated Fair Value Amortized Cost Estimated Amortized Cost Due in one year or less $ 537,043 $ 534,513 $ 560,830 $ 557,675 Due after one year through five years 7,547,002 7,508,674 6,158,148 6,211,099 Due after five years through 10 years 3,495,424 3,480,251 4,676,847 4,710,017 Due after 10 years 284,633 278,823 610,962 620,849 11,864,102 11,802,261 12,006,787 12,099,640 Mortgage backed securities 323,900 321,362 490,093 493,656 Commercial mortgage backed securities 584,730 585,993 536,051 539,683 Asset backed securities 1,544,919 1,540,614 1,123,987 1,123,616 Total (1) $ 14,317,651 $ 14,250,230 $ 14,156,918 $ 14,256,595 (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”
Securities lending transactions accounted for as secured borrowings, by significant investment category	The Company’s securities lending transactions were accounted for as secured borrowings with significant investment categories as follows: Remaining Contractual Maturity of the Agreements Overnight and Continuous Less than 30 Days 30-90 Days 90 Days or More Total September 30, 2017 U.S. government and government agencies $ 424,838 $ 8,186 $ 74,930 $ — $ 507,954 Corporate bonds 31,305 — — — 31,305 Equity securities 3,984 — — — 3,984 Total $ 460,127 $ 8,186 $ 74,930 $ — $ 543,243 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9 $ — Amounts related to securities lending not included in offsetting disclosure in Note 9 $ 543,243 December 31, 2016 U.S. government and government agencies $ 556,015 $ 31,244 $ 126,093 $ 5,140 $ 718,492 Corporate bonds 29,078 — — — 29,078 Equity securities 14,984 — — — 14,984 Total $ 600,077 $ 31,244 $ 126,093 $ 5,140 $ 762,554 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9 $ — Amounts related to securities lending not included in offsetting disclosure in Note 9 $ 762,554
Summary of other investments, including available for sale and fair value option components	The following table summarizes the Company’s other investments, including available for sale and fair value option components: September 30, December 31, Available for sale: Asian and emerging markets $ 123,225 $ 84,778 Investment grade fixed income 53,325 33,923 Credit related funds 20,752 7,469 Other 63,037 41,800 Total available for sale 260,339 167,970 Fair value option: Term loan investments (par value: $1,378,797 and $1,208,537) 1,387,663 1,190,799 Mezzanine debt funds 172,000 127,943 Credit related funds 194,200 218,298 Investment grade fixed income 95,151 75,468 Asian and emerging markets 300,552 178,568 Other (1) 147,639 129,717 Total fair value option 2,297,205 1,920,793 Total $ 2,557,544 $ 2,088,763 (1) Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other.
Summary of assets and liabilities accounted for using the fair value option	The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option: September 30, December 31, Fixed maturities $ 1,508,204 $ 1,099,116 Other investments 2,297,205 1,920,793 Short-term investments 349,540 373,669 Equity securities 94,685 27,642 Investments accounted for using the fair value option $ 4,249,634 $ 3,421,220
Summary of investments in limited partnership interests where the Company has a variable interest	The following table summarizes investments in limited partnership interests where the Company has a variable interest by balance sheet line item: September 30, December 31, Investments accounted for using the equity method (1) $ 962,574 $ 800,970 Investments accounted for using the fair value option (2) 109,157 90,804 Total $ 1,071,731 $ 891,774 (1) Aggregate unfunded commitments were $850.4 million at September 30, 2017 , compared to $776.6 million at December 31, 2016 . (2) Aggregate unfunded commitments were $162.3 million at September 30, 2017 , compared to $16.7 million at December 31, 2016 .
Components of net investment income	The components of net investment income were derived from the following sources: September 30, 2017 2016 Three Months Ended Fixed maturities $ 96,144 $ 71,366 Equity securities 2,887 3,311 Short-term investments 2,957 1,703 Other (1) 37,957 37,466 Gross investment income 139,945 113,846 Investment expenses (23,486 ) (20,228 ) Net investment income $ 116,459 $ 93,618 Nine Months Ended Fixed maturities $ 284,807 $ 223,033 Equity securities 9,184 10,409 Short-term investments 6,732 3,015 Other (1) 111,613 98,089 Gross investment income 412,336 334,546 Investment expenses (66,879 ) (58,855 ) Net investment income $ 345,457 $ 275,691 (1) Includes income distributions from investment funds, term loan investments and other items.
Summary of net realized gains (losses), excluding other-than-temporary impairment provisions	Net realized gains (losses) were as follows, excluding other than-temporary impairment provision. September 30, 2017 2016 Three Months Ended Available for sale securities: Gross gains on investment sales $ 66,565 $ 84,451 Gross losses on investment sales (39,015 ) (22,985 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 4,035 43,935 Other investments 24,264 46,428 Equity securities 10,230 (52 ) Short-term investments (3,320 ) 1,150 Derivative instruments (1) 4,298 (16,964 ) Other (2) (782 ) (10,858 ) Net realized gains (losses) $ 66,275 $ 125,105 Nine Months Ended Available for sale securities: Gross gains on investment sales $ 212,470 $ 266,965 Gross losses on investment sales (152,996 ) (129,409 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 34,232 62,234 Other investments 42,149 38,016 Equity securities 16,604 385 Short-term investments 12 107 Derivative instruments (1) (9,653 ) 24,102 Other (2) (20,655 ) (31,753 ) Net realized gains (losses) $ 122,163 $ 230,647 (1) See Note 9 for information on the Company’s derivative instruments. (2) Includes the re-measurement of contingent consideration liability amounts.
Summary of OTTI recognized in earnings by asset class	The following table details the net impairment losses recognized in earnings by asset class: September 30, 2017 2016 Three Months Ended Fixed maturities: Mortgage backed securities $ (50 ) $ (233 ) Corporate bonds (82 ) — Non-U.S. government securities (178 ) (545 ) U.S. government and government agencies (426 ) — Municipal bonds (202 ) — Total (938 ) (778 ) Equity securities (940 ) (557 ) Other investments — (2,532 ) Net impairment losses recognized in earnings $ (1,878 ) $ (3,867 ) Nine Months Ended Fixed maturities: Mortgage backed securities $ (1,461 ) $ (788 ) Corporate bonds (1,484 ) (5,655 ) Non-U.S. government securities (376 ) (777 ) Asset backed securities — (2,506 ) U.S. government and government agencies (426 ) — Municipal bonds (375 ) — Total (4,122 ) (9,726 ) Equity securities (1,126 ) (3,594 ) Other investments (167 ) (3,529 ) Net impairment losses recognized in earnings $ (5,415 ) $ (16,849 )
Rollforward of the amount related to credit losses recognized in earnings for which a portion was recognized in AOCI	The following table provides a roll forward of the amount related to credit losses recognized in earnings for which a portion of an OTTI was recognized in accumulated other comprehensive income: September 30, 2017 2016 Three Months Ended Balance at start of period $ 4,437 $ 14,847 Credit loss impairments recognized on securities not previously impaired — 38 Credit loss impairments recognized on securities previously impaired 15 60 Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security — — Reductions for securities sold during the period (689 ) (1,166 ) Balance at end of period $ 3,763 $ 13,779 Nine Months Ended Balance at start of year $ 13,138 $ 26,875 Credit loss impairments recognized on securities not previously impaired 31 1,388 Credit loss impairments recognized on securities previously impaired 210 582 Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security — — Reductions for securities sold during the period (9,616 ) (15,066 ) Balance at end of period $ 3,763 $ 13,779
Summary of restricted assets	The following table details the value of the Company’s restricted assets: September 30, December 31, Assets used for collateral or guarantees: Affiliated transactions $ 4,264,131 $ 3,871,971 Third party agreements 1,689,104 1,513,079 Deposits with U.S. regulatory authorities 618,136 472,890 Deposits with non-U.S. regulatory authorities 56,753 44,399 Total restricted assets $ 6,628,124 $ 5,902,339

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair value hierarchy	The following table presents the Company’s financial assets and liabilities measured at fair value by level at September 30, 2017 : Estimated Fair Value Measurements Using: Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets measured at fair value (1): Available for sale securities: Fixed maturities: Corporate bonds $ 4,275,437 $ — $ 4,263,446 $ 11,991 Mortgage backed securities 323,900 — 323,496 404 Municipal bonds 2,353,234 — 2,353,234 — Commercial mortgage backed securities 584,730 — 584,185 545 U.S. government and government agencies 3,761,612 3,687,126 74,486 — Non-U.S. government securities 1,473,819 — 1,473,819 — Asset backed securities 1,544,919 — 1,539,919 5,000 Total 14,317,651 3,687,126 10,612,585 17,940 Equity securities 480,607 473,908 6,699 — Short-term investments 1,646,036 1,600,885 45,151 — Other investments 84,671 83,254 1,417 — Other investments measured at net asset value (2) 175,668 Total other investments 260,339 83,254 1,417 — Derivative instruments (4) 33,141 — 33,141 — Fair value option: Corporate bonds 823,181 — 811,710 11,471 Non-U.S. government bonds 97,614 — 97,614 — Mortgage backed securities 21,218 — 21,218 — Municipal bonds 2,740 — 2,740 — Commercial mortgage backed securities 12,539 — 12,539 — Asset backed securities 63,437 — 63,437 — U.S. government and government agencies 487,475 487,475 — — Short-term investments 349,540 343,620 5,920 — Equity securities 94,685 59,332 35,353 — Other investments 1,298,198 120,212 1,146,840 31,146 Other investments measured at net asset value (2) 999,007 Total 4,249,634 1,010,639 2,197,371 42,617 Total assets measured at fair value $ 20,987,408 $ 6,855,812 $ 12,896,364 $ 60,557 Liabilities measured at fair value: Contingent consideration liabilities $ (59,248 ) $ — $ — $ (59,248 ) Securities sold but not yet purchased (3) (72,682 ) — (72,682 ) — Derivative instruments (4) (23,037 ) — (23,037 ) — Total liabilities measured at fair value $ (154,967 ) $ — $ (95,719 ) $ (59,248 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7 , “Investment Information—Securities Lending Agreements.” (2) In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. (3) Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets. (4) See Note 9 , “Derivative Instruments.” The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2016 : Estimated Fair Value Measurements Using: Estimated Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets measured at fair value (1): Available for sale securities: Fixed maturities: Corporate bonds $ 4,392,373 $ — $ 4,374,029 $ 18,344 Mortgage backed securities 490,093 — 490,093 — Municipal bonds 3,713,434 — 3,713,434 — Commercial mortgage backed securities 536,051 — 536,051 — U.S. government and government agencies 2,804,540 2,691,575 112,965 — Non-U.S. government securities 1,096,440 — 1,096,440 — Asset backed securities 1,123,987 — 1,112,698 11,289 Total 14,156,918 2,691,575 11,435,710 29,633 Equity securities 532,680 529,695 2,985 — Short-term investments 612,005 608,862 3,143 — Other investments 112,313 112,313 — — Other investments measured at net asset value (2) 55,657 Total other investments 167,970 112,313 — — Derivative instruments (4) 28,410 — 28,410 — Fair value option: Corporate bonds 790,935 — 790,935 — Non-U.S. government bonds 61,747 — 61,747 — Mortgage backed securities 18,624 — 18,624 — Asset backed securities 30,324 — 30,324 — U.S. government and government agencies 197,486 197,486 — — Short-term investments 373,669 309,127 64,542 — Equity securities 27,642 25,328 2,314 — Other investments 1,226,242 80,706 1,120,536 25,000 Other investments measured at net asset value (2) 694,551 Total 3,421,220 612,647 2,089,022 25,000 Total assets measured at fair value $ 18,919,203 $ 4,555,092 $ 13,559,270 $ 54,633 Liabilities measured at fair value: Contingent consideration liabilities $ (122,350 ) $ — $ — $ (122,350 ) Securities sold but not yet purchased (3) (33,157 ) — (33,157 ) — Derivative instruments (4) (26,049 ) — (26,049 ) — Total liabilities measured at fair value $ (181,556 ) $ — $ (59,206 ) $ (122,350 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7 , “Investment Information—Securities Lending Agreements.” (2) In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. (3) Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets. (4) See Note 9 , “Derivative Instruments.”
Rollforward of Level 3 investments	The following table presents a reconciliation of the beginning and ending balances for all financial assets and liabilities measured at fair value on a recurring basis using Level 3 inputs: Assets Liabilities s Available For Sale Fair Value Option Structured Securities (1) Corporate Corporate Other Investments Total Contingent Consideration Liabilities Three Months Ended September 30, 2017 Balance at beginning of period $ — $ 11,570 $ — $ 25,000 $ 36,570 $ (57,246 ) Total gains or (losses) (realized/unrealized) Included in earnings (2) — — — — — (2,002 ) Included in other comprehensive income — 289 — — 289 — Purchases, issuances, sales and settlements Purchases — — — 1,348 1,348 — Issuances — — — — — — Sales — — — — — — Settlements — — — — — — Transfers in and/or out of Level 3 5,949 132 11,471 4,798 22,350 — Balance at end of period $ 5,949 $ 11,991 $ 11,471 $ 31,146 $ 60,557 $ (59,248 ) Three Months Ended September 30, 2016 Balance at beginning of period $ 49,211 $ 17,305 $ — $ — $ 66,516 $ (111,670 ) Total gains or (losses) (realized/unrealized) Included in earnings (2) — 1,667 — — 1,667 (4,795 ) Included in other comprehensive income — — — — — 88 Purchases, issuances, sales and settlements Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (22,435 ) — — — (22,435 ) — Transfers in and/or out of Level 3 — — — — — — Balance at end of period $ 26,776 $ 18,972 $ — $ — $ 45,748 $ (116,377 ) Nine Months Ended September 30, 2017 Balance at beginning of year $ 11,289 $ 18,344 $ — $ 25,000 $ 54,633 $ (122,350 ) Total gains or (losses) (realized/unrealized) Included in earnings (2) 3,779 893 — — 4,672 (9,089 ) Included in other comprehensive income — 289 — — 289 — Purchases, issuances, sales and settlements Purchases — 4,935 — 1,348 6,283 — Issuances — — — — — — Sales (13,640 ) (12,602 ) — — (26,242 ) — Settlements (1,428 ) — — — (1,428 ) 72,191 Transfers in and/or out of Level 3 5,949 132 11,471 4,798 22,350 — Balance at end of period $ 5,949 $ 11,991 $ 11,471 $ 31,146 $ 60,557 $ (59,248 ) Nine Months Ended September 30, 2016 Balance at beginning of year $ 57,500 $ 16,368 $ — $ — $ 73,868 $ (96,048 ) Total gains or (losses) (realized/unrealized) Included in earnings (2) (2,500 ) 1,828 — — (672 ) (20,916 ) Included in other comprehensive income — — — — — 51 Purchases, issuances, sales and settlements Purchases — 776 — — 776 — Issuances — — — — — — Sales — — — — — — Settlements (28,224 ) — — — (28,224 ) 536 Transfers in and/or out of Level 3 — — — — — — Balance at end of period $ 26,776 $ 18,972 $ — $ — $ 45,748 $ (116,377 ) (1) Includes asset backed securities, mortgage backed securities and commercial mortgage backed securities. (2) For the 2017 periods, gains or losses were included in net realized gains (losses). For the 2016 periods, losses on structured securities were included in net impairment losses recognized in earnings gains or losses while gains or losses on corporate bonds and contingent consideration liabilities were included in net realized gains (losses).

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair value and notional amount of derivatives	The following table summarizes information on the fair values and notional values of the Company’s derivative instruments: Estimated Fair Value Asset Derivatives Liability Derivatives Notional Value (1) September 30, 2017 Futures contracts (2) $ 5,351 $ (6,722 ) $ 1,524,985 Foreign currency forward contracts (2) 19,376 (5,348 ) 805,201 TBAs (3) 18,331 — 18,143 Other (2) 8,414 (10,967 ) 2,032,922 Total $ 51,472 $ (23,037 ) December 31, 2016 Futures contracts (2) $ 360 $ (9,398 ) $ 1,655,530 Foreign currency forward contracts (2) 9,354 (12,941 ) 1,186,386 TBAs (3) — — — Other (2) 20,287 (3,710 ) 1,014,863 Total $ 30,001 $ (26,049 ) (1) Represents the absolute notional value of all outstanding contracts, consisting of long and short positions. (2) The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’ (3) The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’
Summary of net realized gains (losses) recorded in the consolidated statements of income	All realized and unrealized contract gains and losses on the Company’s derivative instruments are reflected in net realized gains (losses) in the consolidated statements of income, as summarized in the following table: Derivatives not designated as September 30, hedging instruments: 2017 2016 Three Months Ended Net realized gains (losses): Futures contracts $ 4,899 $ (15,368 ) Foreign currency forward contracts (228 ) 4,583 TBAs 122 (23 ) Other (495 ) (6,156 ) Total $ 4,298 $ (16,964 ) Nine Months Ended Net realized gains (losses): Futures contracts $ 7,309 $ 45,954 Foreign currency forward contracts (12,266 ) (13,951 ) TBAs 143 311 Other (4,839 ) (8,212 ) Total $ (9,653 ) $ 24,102

Other Comprehensive Income (L34

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2017
Comprehensive Income Note Disclosure [Abstract]
Details about amounts reclassified from AOCI	The following tables present details about amounts reclassified from accumulated other comprehensive income and the tax effects allocated to each component of other comprehensive income (loss): Amounts Reclassified from AOCI Consolidated Statement of Income Three Months Ended Nine Months Ended Details About Line Item That Includes September 30, September 30, AOCI Components Reclassification 2017 2016 2017 2016 Unrealized appreciation on available-for-sale investments Net realized gains (losses) $ 27,550 $ 61,464 $ 59,474 $ 137,555 Other-than-temporary impairment losses (1,878 ) (3,867 ) (5,415 ) (16,999 ) Total before tax 25,672 57,597 54,059 120,556 Income tax (expense) benefit (1,760 ) (2,605 ) (7,879 ) (11,247 ) Net of tax $ 23,912 $ 54,992 $ 46,180 $ 109,309
Schedule of comprehensive income (loss)	Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Three Months Ended September 30, 2017 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 69,330 $ 2,868 $ 66,462 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 25,672 1,760 23,912 Foreign currency translation adjustments 8,590 310 8,280 Other comprehensive income (loss) $ 52,248 $ 1,418 $ 50,830 Three Months Ended September 30, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 11,692 $ (4,589 ) $ 16,281 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 57,597 2,605 54,992 Foreign currency translation adjustments (5,407 ) (95 ) (5,312 ) Other comprehensive income (loss) $ (51,312 ) $ (7,289 ) $ (44,023 ) Nine Months Ended September 30, 2017 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 288,813 $ 28,590 $ 260,223 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 54,059 7,879 46,180 Foreign currency translation adjustments 30,264 563 29,701 Other comprehensive income (loss) $ 265,018 $ 21,274 $ 243,744 Nine Months Ended September 30, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 281,770 $ 30,048 $ 251,722 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (150 ) — (150 ) Less reclassification of net realized gains (losses) included in net income 120,556 11,247 109,309 Foreign currency translation adjustments (5,733 ) 417 (6,150 ) Other comprehensive income (loss) $ 155,331 $ 19,218 $ 136,113

Guarantor Financial Informati35

Guarantor Financial Information (Tables)	9 Months Ended
	Sep. 30, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed consolidating balance sheet	September 30, 2017 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 402 $ 69,671 $ 21,876,508 $ (14,700 ) $ 21,931,881 Cash 4,868 88,818 768,675 — 862,361 Investments in subsidiaries 9,214,178 4,028,493 — (13,242,671 ) — Due from subsidiaries and affiliates 81 117 1,923,941 (1,924,139 ) — Premiums receivable — — 1,863,203 (593,525 ) 1,269,678 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 7,023,836 (4,517,821 ) 2,506,015 Contractholder receivables — — 1,864,348 — 1,864,348 Ceded unearned premiums — — 2,240,129 (1,292,994 ) 947,135 Deferred acquisition costs — — 677,567 (146,371 ) 531,196 Goodwill and intangible assets — — 684,405 — 684,405 Other assets 13,357 59,734 2,146,993 (192,306 ) 2,027,778 Total assets $ 9,232,886 $ 4,246,833 $ 41,069,605 $ (21,924,527 ) $ 32,624,797 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 15,836,263 $ (4,484,996 ) $ 11,351,267 Unearned premiums — — 5,044,544 (1,292,994 ) 3,751,550 Reinsurance balances payable — — 945,530 (593,524 ) 352,006 Contractholder payables — — 1,864,348 — 1,864,348 Collateral held for insured obligations — — 345,726 345,726 Senior notes 297,030 494,596 941,100 — 1,732,726 Revolving credit agreement borrowings — — 826,242 — 826,242 Due to subsidiaries and affiliates 41 542,103 1,381,996 (1,924,140 ) — Other liabilities 24,671 100,278 2,669,614 (371,502 ) 2,423,061 Total liabilities 321,742 1,136,977 29,855,363 (8,667,156 ) 22,646,926 Redeemable noncontrolling interests — — 220,529 (14,700 ) 205,829 Shareholders’ Equity Total shareholders’ equity available to Arch 8,911,144 3,109,856 10,132,815 (13,242,671 ) 8,911,144 Non-redeemable noncontrolling interests — — 860,898 — 860,898 Total shareholders’ equity 8,911,144 3,109,856 10,993,713 (13,242,671 ) 9,772,042 Total liabilities, noncontrolling interests and shareholders’ equity $ 9,232,886 $ 4,246,833 $ 41,069,605 $ (21,924,527 ) $ 32,624,797 December 31, 2016 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 2,612 $ 41,672 $ 19,690,067 $ (14,700 ) $ 19,719,651 Cash 1,687 71,955 769,300 — 842,942 Investments in subsidiaries 8,660,586 3,716,681 — (12,377,267 ) — Due from subsidiaries and affiliates 14,297 51,298 1,866,681 (1,932,276 ) — Premiums receivable — — 1,579,865 (507,430 ) 1,072,435 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 6,114,518 (4,000,380 ) 2,114,138 Contractholder receivables — — 1,717,436 — 1,717,436 Ceded unearned premiums — — 1,985,311 (1,125,744 ) 859,567 Deferred acquisition costs — — 577,461 (129,901 ) 447,560 Goodwill and intangible assets — — 781,553 — 781,553 Other assets 15,725 49,244 1,901,786 (149,928 ) 1,816,827 Total assets $ 8,694,907 $ 3,930,850 $ 36,983,978 $ (20,237,626 ) $ 29,372,109 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 14,164,191 $ (3,963,231 ) $ 10,200,960 Unearned premiums — — 4,532,614 (1,125,744 ) 3,406,870 Reinsurance balances payable — — 807,837 (507,430 ) 300,407 Contractholder payables — — 1,717,436 — 1,717,436 Collateral held for insured obligations — — 301,406 — 301,406 Deposit accounting liabilities — — 22,150 — 22,150 Senior notes 296,957 494,525 940,776 — 1,732,258 Revolving credit agreement borrowings 100,000 — 656,650 — 756,650 Due to subsidiaries and affiliates 26,270 535,584 1,370,422 (1,932,276 ) — Other liabilities 17,962 54,823 1,867,040 (316,978 ) 1,622,847 Total liabilities 441,189 1,084,932 26,380,522 (7,845,659 ) 20,060,984 Redeemable noncontrolling interests — — 220,253 (14,700 ) 205,553 Shareholders’ Equity Total shareholders’ equity available to Arch 8,253,718 2,845,918 9,531,349 (12,377,267 ) 8,253,718 Non-redeemable noncontrolling interests — — 851,854 — 851,854 Total shareholders’ equity 8,253,718 2,845,918 10,383,203 (12,377,267 ) 9,105,572 Total liabilities, noncontrolling interests and shareholders’ equity $ 8,694,907 $ 3,930,850 $ 36,983,978 $ (20,237,626 ) $ 29,372,109
Condensed consolidating statement of income and comprehensive income	Three Months Ended September 30, 2017 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 1,261,886 $ — $ 1,261,886 Net investment income 117 151 138,784 (22,593 ) 116,459 Net realized gains (losses) — — 66,275 — 66,275 Net impairment losses recognized in earnings — — (1,878 ) — (1,878 ) Other underwriting income — — 6,064 — 6,064 Equity in net income (loss) of investment funds accounted for using the equity method — — 31,090 — 31,090 Other income (loss) (102 ) — (240 ) — (342 ) Total revenues 15 151 1,501,981 (22,593 ) 1,479,554 Expenses Losses and loss adjustment expenses — — 1,046,141 — 1,046,141 Acquisition expenses — — 193,854 — 193,854 Other operating expenses — — 170,127 — 170,127 Corporate expenses 14,576 410 2,112 — 17,098 Amortization of intangible assets — — 31,824 — 31,824 Interest expense 5,934 12,037 33,811 (22,272 ) 29,510 Net foreign exchange (gains) losses — — 20,510 7,518 28,028 Total expenses 20,510 12,447 1,498,379 (14,754 ) 1,516,582 Income (loss) before income taxes (20,495 ) (12,296 ) 3,602 (7,839 ) (37,028 ) Income tax (expense) benefit — 4,432 (12,621 ) — (8,189 ) Income (loss) before equity in net income of subsidiaries (20,495 ) (7,864 ) (9,019 ) (7,839 ) (45,217 ) Equity in net income (loss) of subsidiaries (13,161 ) 50,057 — (36,896 ) — Net income (loss) (33,656 ) 42,193 (9,019 ) (44,735 ) (45,217 ) Net (income) loss attributable to noncontrolling interests — — 11,238 323 11,561 Net income (loss) available to Arch (33,656 ) 42,193 2,219 (44,412 ) (33,656 ) Preferred dividends (12,369 ) — — — (12,369 ) Loss on redemption of preferred shares (6,735 ) — — — (6,735 ) Net income (loss) available to Arch common shareholders $ (52,760 ) $ 42,193 $ 2,219 $ (44,412 ) $ (52,760 ) Comprehensive income (loss) available to Arch $ 17,585 $ 47,676 $ 45,936 $ (93,612 ) $ 17,585 Three Months Ended September 30, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 958,403 $ — $ 958,403 Net investment income 6 803 99,654 (6,845 ) 93,618 Net realized gains (losses) — — 125,105 — 125,105 Net impairment losses recognized in earnings — — (3,867 ) — (3,867 ) Other underwriting income — — 7,980 — 7,980 Equity in net income (loss) of investment funds accounted for using the equity method — — 16,662 — 16,662 Other income (loss) 71 — (471 ) — (400 ) Total revenues 77 803 1,203,466 (6,845 ) 1,197,501 Expenses Losses and loss adjustment expenses — — 524,183 — 524,183 Acquisition expenses — — 161,267 — 161,267 Other operating expenses — — 153,286 — 153,286 Corporate expenses 18,488 608 (611 ) — 18,485 Amortization of intangible assets — — 4,865 — 4,865 Interest expense 5,948 6,627 9,890 (6,522 ) 15,943 Net foreign exchange (gains) losses — — 2,723 (102 ) 2,621 Total expenses 24,436 7,235 855,603 (6,624 ) 880,650 Income (loss) before income taxes (24,359 ) (6,432 ) 347,863 (221 ) 316,851 Income tax (expense) benefit — 2,116 (15,347 ) — (13,231 ) Income (loss) before equity in net income of subsidiaries (24,359 ) (4,316 ) 332,516 (221 ) 303,620 Equity in net income of subsidiaries 277,231 21,945 — (299,176 ) — Net income 252,872 17,629 332,516 (299,397 ) 303,620 Net (income) loss attributable to noncontrolling interests — — (51,071 ) 323 (50,748 ) Net income available to Arch 252,872 17,629 281,445 (299,074 ) 252,872 Preferred dividends (5,484 ) — — — (5,484 ) Net income available to Arch common shareholders $ 247,388 $ 17,629 $ 281,445 $ (299,074 ) $ 247,388 Comprehensive income (loss) available to Arch $ 208,790 $ 2,019 $ 237,555 $ (239,574 ) $ 208,790 Nine Months Ended September 30, 2017 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 3,619,777 $ — $ 3,619,777 Net investment income 123 1,151 410,392 (66,209 ) 345,457 Net realized gains (losses) — — 122,163 — 122,163 Net impairment losses recognized in earnings — — (5,415 ) — (5,415 ) Other underwriting income — — 15,519 — 15,519 Equity in net income of investment funds accounted for using the equity method — — 111,884 — 111,884 Other income (loss) (368 ) — (2,750 ) — (3,118 ) Total revenues (245 ) 1,151 4,271,570 (66,209 ) 4,206,267 Expenses Losses and loss adjustment expenses — — 2,288,571 — 2,288,571 Acquisition expenses — — 566,579 — 566,579 Other operating expenses — — 514,827 — 514,827 Corporate expenses 53,639 3,727 12,400 — 69,766 Amortization of intangible assets — — 93,942 — 93,942 Interest expense 18,024 35,956 98,197 (65,242 ) 86,935 Net foreign exchange losses (gains) — — 65,701 21,274 86,975 Total expenses 71,663 39,683 3,640,217 (43,968 ) 3,707,595 Income (loss) before income taxes (71,908 ) (38,532 ) 631,353 (22,241 ) 498,672 Income tax (expense) benefit — 13,374 (84,129 ) — (70,755 ) Income (loss) before equity in net income of subsidiaries (71,908 ) (25,158 ) 547,224 (22,241 ) 427,917 Equity in net income of subsidiaries 476,546 213,586 — (690,132 ) — Net income 404,638 188,428 547,224 (712,373 ) 427,917 Amounts attributable to noncontrolling interests — — (24,247 ) 968 (23,279 ) Net income available to Arch 404,638 188,428 522,977 (711,405 ) 404,638 Preferred dividends (34,936 ) — — — (34,936 ) Loss on redemption of preferred shares (6,735 ) — — — (6,735 ) Net income available to Arch common shareholders $ 362,967 $ 188,428 $ 522,977 $ (711,405 ) $ 362,967 Comprehensive income (loss) available to Arch $ 648,861 $ 240,759 $ 745,856 $ (986,615 ) $ 648,861 Nine Months Ended September 30, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 2,915,967 $ — $ 2,915,967 Net investment income 7 2,351 294,012 (20,679 ) 275,691 Net realized gains (losses) — — 230,647 — 230,647 Net impairment losses recognized in earnings — — (16,849 ) — (16,849 ) Other underwriting income — — 54,749 (16,498 ) 38,251 Equity in net income of investment funds accounted for using the equity method — — 32,054 — 32,054 Other income (loss) 270 — (702 ) — (432 ) Total revenues 277 2,351 3,509,878 (37,177 ) 3,475,329 Expenses Losses and loss adjustment expenses — — 1,631,724 — 1,631,724 Acquisition expenses — — 501,782 — 501,782 Other operating expenses — — 460,748 — 460,748 Corporate expenses 45,284 1,549 (1,765 ) — 45,068 Amortization of intangible assets — — 14,493 — 14,493 Interest expense 17,811 19,946 46,169 (36,213 ) 47,713 Net foreign exchange losses (gains) — — 5,093 (3,568 ) 1,525 Total expenses 63,095 21,495 2,658,244 (39,781 ) 2,703,053 Income (loss) before income taxes (62,818 ) (19,144 ) 851,634 2,604 772,276 Income tax (expense) benefit — 6,446 (50,118 ) — (43,672 ) Income (loss) before equity in net income of subsidiaries (62,818 ) (12,698 ) 801,516 2,604 728,604 Equity in net income of subsidiaries 681,543 64,684 — (746,227 ) — Net income 618,725 51,986 801,516 (743,623 ) 728,604 Amounts attributable to noncontrolling interests — — (110,844 ) 965 (109,879 ) Net income available to Arch 618,725 51,986 690,672 (742,658 ) 618,725 Preferred dividends (16,453 ) — — — (16,453 ) Net income available to Arch common shareholders $ 602,272 $ 51,986 $ 690,672 $ (742,658 ) $ 602,272 Comprehensive income (loss) available to Arch $ 754,979 $ 89,204 $ 830,348 $ (919,552 ) $ 754,979
Condensed consolidating statement of cash flows	Nine Months Ended September 30, 2017 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 130,715 $ 70,761 $ 1,464,701 $ (585,043 ) $ 1,081,134 Investing Activities Purchases of fixed maturity investments — — (28,079,129 ) — (28,079,129 ) Purchases of equity securities — — (667,135 ) — (667,135 ) Purchases of other investments — — (1,406,528 ) — (1,406,528 ) Proceeds from the sales of fixed maturity investments — — 27,629,474 — 27,629,474 Proceeds from the sales of equity securities — — 751,873 — 751,873 Proceeds from the sales, redemptions and maturities of other investments — — 938,581 — 938,581 Proceeds from redemptions and maturities of fixed maturity investments — — 747,621 — 747,621 Net settlements of derivative instruments — — (20,952 ) — (20,952 ) Net (purchases) sales of short-term investments 2,209 (27,998 ) (938,864 ) — (964,653 ) Change in cash collateral related to securities lending — — 148,692 — 148,692 Contributions to subsidiaries 20,641 (72,900 ) (353,588 ) 405,847 — Issuance of intercompany loans — — (47,000 ) 47,000 — Repayment of intercompany loans — 47,000 — (47,000 ) — Acquisitions, net of cash — — (27,709 ) — (27,709 ) Purchases of fixed assets (18 ) — (16,844 ) — (16,862 ) Other — — 106,786 (20,641 ) 86,145 Net Cash Provided By (Used For) Investing Activities 22,832 (53,898 ) (1,234,722 ) 385,206 (880,582 ) Financing Activities Proceeds from issuance of preferred shares, net 222,054 — — — 222,054 Redemption of preferred shares (230,000 ) — — — (230,000 ) Proceeds from common shares issued, net (7,484 ) — 405,847 (405,847 ) (7,484 ) Proceeds from intercompany borrowings — — 47,000 (47,000 ) — Proceeds from borrowings — — 238,915 — 238,915 Repayments of intercompany borrowings — — (47,000 ) 47,000 — Repayments of borrowings (100,000 ) — (72,000 ) — (172,000 ) Change in cash collateral related to securities lending — — (148,692 ) — (148,692 ) Dividends paid to redeemable noncontrolling interests — — (14,447 ) 956 (13,491 ) Dividends paid to parent (1) — — (584,087 ) 584,087 — Other — — (69,921 ) 20,641 (49,280 ) Preferred dividends paid (34,936 ) — — — (34,936 ) Net Cash Provided By (Used For) Financing Activities (150,366 ) — (244,385 ) 199,837 (194,914 ) Effects of exchange rates changes on foreign currency cash — — 13,781 — 13,781 Increase (decrease) in cash 3,181 16,863 (625 ) — 19,419 Cash beginning of year 1,687 71,955 769,300 — 842,942 Cash end of period $ 4,868 $ 88,818 $ 768,675 $ — $ 862,361 (1) Dividends received by parent are included in net cash provided by (used for) operating activities. Nine Months Ended September 30, 2016 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 94,250 $ 14,448 $ 1,096,443 $ (168,002 ) $ 1,037,139 Investing Activities Purchases of fixed maturity investments — — (27,840,555 ) — (27,840,555 ) Purchases of equity securities — — (377,767 ) — (377,767 ) Purchases of other investments — — (1,008,774 ) — (1,008,774 ) Proceeds from the sales of fixed maturity investments — — 26,731,924 — 26,731,924 Proceeds from the sales of equity securities — — 464,904 — 464,904 Proceeds from the sales, redemptions and maturities of other investments — — 879,330 — 879,330 Proceeds from redemptions and maturities of fixed maturity investments — 41,500 499,323 — 540,823 Net settlements of derivative instruments — — 23,396 — 23,396 Net (purchases) sales of short-term investments (436,830 ) (53,779 ) (113,553 ) — (604,162 ) Change in cash collateral related to securities lending — — (27,935 ) — (27,935 ) Contributions to subsidiaries (3,585 ) — (9,247 ) 12,832 — Acquisitions, net of cash — — (20,911 ) — (20,911 ) Purchases of fixed assets (8 ) — (11,557 ) — (11,565 ) Other 2,000 — (5,816 ) — (3,816 ) Net Cash Provided By (Used For) Investing Activities (438,423 ) (12,279 ) (817,238 ) 12,832 (1,255,108 ) Financing Activities Proceeds from issuance of preferred shares, net 434,899 — — — 434,899 Purchases of common shares under share repurchase program (75,256 ) — — — (75,256 ) Proceeds from common shares issued, net (3,785 ) — 12,832 (12,832 ) (3,785 ) Proceeds from borrowings — — 46,000 — 46,000 Repayments of borrowings — — (179,171 ) — (179,171 ) Change in cash collateral related to securities lending — — 27,935 — 27,935 Dividends paid to redeemable noncontrolling interests — — (14,448 ) 957 (13,491 ) Dividends paid to parent (1) — — (167,045 ) 167,045 — Other — 200 32,913 — 33,113 Preferred dividends paid (16,453 ) — — — (16,453 ) Net Cash Provided By (Used For) Financing Activities 339,405 200 (240,984 ) 155,170 253,791 Effects of exchange rates changes on foreign currency cash — — (10,332 ) — (10,332 ) Increase (decrease) in cash (4,768 ) 2,369 27,889 — 25,490 Cash beginning of year 6,809 17,023 529,494 — 553,326 Cash end of period $ 2,041 $ 19,392 $ 557,383 $ — $ 578,816 (1) Dividends received by parent are included in net cash provided by (used for) operating activities.

Variable Interest Entities an36

Variable Interest Entities and Noncontrolling Interests - Carrying amount of assets and liabilities of variable interest entity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Investments accounted for using the fair value option	$ 4,249,634		$ 3,421,220
Cash	862,361		842,942	$ 578,816		$ 553,326
Accrued investment income	101,104		124,483
Premiums receivable	1,269,678		1,072,435
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	2,506,015		2,114,138
Ceded unearned premiums	947,135		859,567
Deferred acquisition costs	531,196		447,560
Receivable for securities sold	385,952		58,284
Goodwill and intangible assets	684,405		781,553	90,941
Other assets	1,012,510		889,080
Total assets of consolidated VIE	32,624,797		29,372,109
Reserve for losses and loss adjustment expenses	11,351,267	$ 10,520,511	10,200,960	9,610,189	$ 9,471,647	9,125,250
Unearned premiums	3,751,550		3,406,870
Reinsurance balances payable	352,006		300,407
Revolving credit agreement borrowings	826,242		756,650
Payable for securities purchased	1,091,464		76,183
Other liabilities	788,354		806,260
Total liabilities of consolidated VIE	22,646,926		20,060,984
Redeemable noncontrolling interests	205,829		205,553
Watford Re
Variable Interest Entity [Line Items]
Redeemable noncontrolling interests	205,829	$ 205,736	205,553	$ 205,459	$ 205,366	$ 205,182
Variable Interest Entity, Primary Beneficiary | Watford Re
Variable Interest Entity [Line Items]
Investments accounted for using the fair value option	2,457,365		1,857,623
Cash	57,151		74,893
Accrued investment income	13,718		17,017
Premiums receivable	209,985		189,911
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	37,575		24,420
Ceded unearned premiums	23,538		12,145
Deferred acquisition costs	87,692		86,379
Receivable for securities sold	74,051		1,326
Goodwill and intangible assets	7,650		7,650
Other assets	132,796		111,386
Total assets of consolidated VIE	3,101,521		2,382,750
Reserve for losses and loss adjustment expenses	735,132		510,809
Unearned premiums	344,060		293,480
Reinsurance balances payable	22,487		12,289
Revolving credit agreement borrowings	426,242		256,650
Payable for securities purchased	211,065		42,922
Other liabilities	174,472		88,976
Total liabilities of consolidated VIE	1,913,458		1,205,126
Redeemable noncontrolling interests	$ 220,529		$ 220,253

Variable Interest Entities an37

Variable Interest Entities and Noncontrolling Interests - Variable interest entity (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Mar. 31, 2014	Sep. 30, 2017	Sep. 30, 2016
Variable Interest Entity [Line Items]
Net cash provided by operating activities		$ 1,081,134	$ 1,037,139
Net cash used for investing activities		(880,582)	(1,255,108)
Net cash used for financing activities		(194,914)	253,791
Variable Interest Entity, Primary Beneficiary | Watford Holdings Ltd
Variable Interest Entity [Line Items]
Initial investment contribution amount	$ 100,000
Ownership percentage	11.00%
Variable Interest Entity, Primary Beneficiary | Watford Re
Variable Interest Entity [Line Items]
Net cash provided by operating activities		221,900	207,000
Net cash used for investing activities		(394,400)	(124,000)
Net cash used for financing activities		$ 152,500	$ (119,600)

Variable Interest Entities an38

Variable Interest Entities and Noncontrolling Interests - Non-redeemable noncontrolling interests (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interests, beginning of period			$ 851,854
Amounts attributable to noncontrolling interests	$ (16,147)	$ 46,160	9,523	$ 96,118
Non-redeemable noncontrolling interests, end of period	860,898	834,808	860,898	834,808
Watford Re
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interests, beginning of period	877,456	788,589	851,854	738,831
Amounts attributable to noncontrolling interests	(16,147)	46,160	9,523	96,118
Foreign currency translation adjustments attributable to noncontrolling interests	(411)	59	(479)	(141)
Non-redeemable noncontrolling interests, end of period	$ 860,898	$ 834,808	$ 860,898	$ 834,808
Common shares | Watford Re
Noncontrolling Interest [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	89.00%		89.00%

Variable Interest Entities an39

Variable Interest Entities and Noncontrolling Interests - Redeemable noncontrolling interests (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests, beginning of period			$ 205,553
Redeemable noncontrolling interests, end of period	$ 205,829		205,829
Watford Re
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests, beginning of period	205,736	$ 205,366	205,553	$ 205,182
Accretion of preference share issuance costs	93	93	276	277
Redeemable noncontrolling interests, end of period	$ 205,829	$ 205,459	$ 205,829	$ 205,459
Cumulative redeemable preference shares | Watford Re
Redeemable Noncontrolling Interest [Line Items]
Preference shares, number of shares issued	9,065,200		9,065,200
Par value per share	$ 0.01		$ 0.01
Liquidation preference per share	$ 25		$ 25

Variable Interest Entities an40

Variable Interest Entities and Noncontrolling Interests - Income or loss attributable to third party investors (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Noncontrolling Interest [Abstract]
Amounts attributable to non-redeemable noncontrolling interests	$ 16,147	$ (46,160)	$ (9,523)	$ (96,118)
Dividends attributable to redeemable noncontrolling interests	(4,586)	(4,588)	(13,756)	(13,761)
Net (income) loss attributable to noncontrolling interests	$ 11,561	$ (50,748)	$ (23,279)	$ (109,879)

Variable Interest Entities an41

Variable Interest Entities and Noncontrolling Interests - Other variable interest entity disclosures (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 1,071,731	$ 891,774
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Total VIE Assets	303,477
Maximum Exposure to Loss	2,235
Variable Interest Entity, Not Primary Beneficiary | On-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	480
Variable Interest Entity, Not Primary Beneficiary | Off-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,755
Variable Interest Entity, Not Primary Beneficiary | Bellemeade I
Variable Interest Entity [Line Items]
Aggregate excess of loss reinsurance agreement	300,000
Total VIE Assets	112,090
Maximum Exposure to Loss	1,542
Variable Interest Entity, Not Primary Beneficiary | Bellemeade I | On-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	533
Variable Interest Entity, Not Primary Beneficiary | Bellemeade I | Off-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,009
Variable Interest Entity, Not Primary Beneficiary | Bellemeade II
Variable Interest Entity [Line Items]
Aggregate excess of loss reinsurance agreement	300,000
Total VIE Assets	191,387
Maximum Exposure to Loss	693
Variable Interest Entity, Not Primary Beneficiary | Bellemeade II | On-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	(53)
Variable Interest Entity, Not Primary Beneficiary | Bellemeade II | Off-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	746
Variable Interest Entity, Not Primary Beneficiary | Irving Partners
Variable Interest Entity [Line Items]
Proceeds from sale of limited partnership investment	$ 14,500

Earnings Per Common Share (Deta

Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income (loss)		$ (45,217)	$ 303,620	$ 427,917	$ 728,604
Net (income) loss attributable to noncontrolling interests		11,561	(50,748)	(23,279)	(109,879)
Net income available to Arch		(33,656)	252,872	404,638	618,725
Preferred dividends		(12,369)	(5,484)	(34,936)	(16,453)
Loss on redemption of preferred shares		(6,735)	0	(6,735)	0
Net income (loss) available to Arch common shareholders		$ (52,760)	$ 247,388	$ 362,967	$ 602,272
Denominator:
Weighted average common shares outstanding		129,211,251	120,938,916	124,526,611	120,656,420
Series D preferred shares		5,674,200	0	9,945,518	0
Weighted average common shares outstanding — basic		134,885,451	120,938,916	134,472,129	120,656,420
Effect of dilutive common share equivalents:
Nonvested restricted shares		0	1,313,025	1,459,879	1,295,825
Stock options	[1]	0	2,679,712	3,290,316	2,575,929
Weighted average common shares and common share equivalents outstanding — diluted		134,885,451	124,931,653	139,222,324	124,528,174
Earnings per common share:
Basic (per share)		$ (0.39)	$ 2.05	$ 2.70	$ 4.99
Diluted (per share)		$ (0.39)	$ 1.98	$ 2.61	$ 4.84
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per common share (shares)		4,700,000
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per common share (shares)		0	334,203	838,868	842,105
[1]	Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2017 third quarter and 2016 third quarter, the number of stock options excluded were nil and 334,203, respectively. For the nine months ended September 30, 2017 and 2016, the number of stock options excluded were 838,868 and 842,105, respectively.

Segment Information - Summary o

Segment Information - Summary of underwriting income or loss by segment (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Gross premiums written		$ 1,648,246		$ 1,278,765	$ 4,915,895		$ 4,046,667
Premiums ceded		(322,843)		(264,487)	(1,065,537)		(887,591)
Net premiums written		1,325,403		1,014,278	3,850,358		3,159,076
Change in unearned premiums		(63,517)		(55,875)	(230,581)		(243,109)
Net premiums earned		1,261,886		958,403	3,619,777		2,915,967
Other underwriting income		6,064		7,980	15,519		38,251
Losses and loss adjustment expenses		(1,046,141)		(524,183)	(2,288,571)		(1,631,724)
Acquisition expenses, net		(193,854)		(161,267)	(566,579)		(501,782)
Other operating expenses		(170,127)		(153,286)	(514,827)		(460,748)
Underwriting income (loss)		(142,172)		127,647	265,319		359,964
Net investment income		116,459		93,618	345,457		275,691
Net realized gains (losses)		66,275		125,105	122,163		230,647
Net impairment losses recognized in earnings		(1,878)		(3,867)	(5,415)		(16,849)
Equity in net income (loss) of investment funds accounted for using the equity method		31,090		16,662	111,884		32,054
Other income (loss)		(342)		(400)	(3,118)		(432)
Corporate expenses		(14,108)	[1]	(11,343)	(48,517)		(37,926)
UGC transaction costs and other		(2,990)	[1]	(7,142)	(21,249)	[1]	(7,142)
Amortization of intangible assets		(31,824)		(4,865)	(93,942)		(14,493)
Interest expense		(29,510)		(15,943)	(86,935)		(47,713)
Net foreign exchange gains (losses)		(28,028)		(2,621)	(86,975)		(1,525)
Income (loss) before income taxes		(37,028)		316,851	498,672		772,276
Income tax expense		(8,189)		(13,231)	(70,755)		(43,672)
Net income (loss)		(45,217)		303,620	427,917		728,604
Dividends attributable to redeemable noncontrolling interests		(4,586)		(4,588)	(13,756)		(13,761)
Amounts attributable to non-redeemable noncontrolling interests		16,147		(46,160)	(9,523)		(96,118)
Net income (loss) available to Arch		(33,656)		252,872	404,638		618,725
Preferred dividends		(12,369)		(5,484)	(34,936)		(16,453)
Loss on redemption of preferred shares		(6,735)		0	(6,735)		0
Net income (loss) available to Arch common shareholders		$ (52,760)		$ 247,388	$ 362,967		$ 602,272
Underwriting Ratios
Loss ratio		82.90%		54.70%	63.20%		56.00%
Acquisition expense ratio		15.40%		16.80%	15.70%		17.20%
Other operating expense ratio		13.50%		16.00%	14.20%		15.80%
Combined ratio		111.80%		87.50%	93.10%		89.00%
Goodwill and intangible assets		$ 684,405		$ 90,941	$ 684,405		$ 90,941	$ 781,553
Other
Segment Reporting Information [Line Items]
Gross premiums written	[2]	166,198		163,736	473,131		421,627
Premiums ceded		(12,471)		(6,300)	(35,315)		(15,229)
Net premiums written		153,727		157,436	437,816		406,398
Change in unearned premiums		(25,097)		(47,000)	(36,435)		(59,878)
Net premiums earned		128,630		110,436	401,381		346,520
Other underwriting income		737		1,024	2,377		2,922
Losses and loss adjustment expenses		(123,581)		(74,307)	(319,612)		(236,922)
Acquisition expenses, net		(32,073)		(28,739)	(99,328)		(95,323)
Other operating expenses		(8,268)		(7,035)	(24,311)		(18,486)
Underwriting income (loss)		(34,555)		1,379	(39,493)		(1,289)
Net investment income		22,332		27,336	62,998		68,603
Net realized gains (losses)		2,171		29,159	11,501		61,912
Net impairment losses recognized in earnings		0		0	0		0
Equity in net income (loss) of investment funds accounted for using the equity method		0		0	0		0
Other income (loss)		0		0	0		0
Corporate expenses		0	[1]	0	0		0
UGC transaction costs and other		0	[1]	0	0	[1]	0
Amortization of intangible assets		0		0	0		0
Interest expense		(3,246)		(3,019)	(9,003)		(9,730)
Net foreign exchange gains (losses)		(243)		1,611	(1,524)		2,287
Income (loss) before income taxes		(13,541)		56,466	24,479		121,783
Income tax expense		(21)		1	(21)		1
Net income (loss)		(13,562)		56,467	24,458		121,784
Dividends attributable to redeemable noncontrolling interests		(4,586)		(4,588)	(13,756)		(13,761)
Amounts attributable to non-redeemable noncontrolling interests		16,147		(46,160)	(9,523)		(96,118)
Net income (loss) available to Arch		(2,001)		5,719	1,179		11,905
Preferred dividends		0		0	0		0
Loss on redemption of preferred shares		0			0
Net income (loss) available to Arch common shareholders		$ (2,001)		$ 5,719	$ 1,179		$ 11,905
Underwriting Ratios
Loss ratio		96.10%		67.30%	79.60%		68.40%
Acquisition expense ratio		24.90%		26.00%	24.70%		27.50%
Other operating expense ratio		6.40%		6.40%	6.10%		5.30%
Combined ratio		127.40%		99.70%	110.40%		101.20%
Goodwill and intangible assets		$ 7,650		$ 7,650	$ 7,650		$ 7,650
Sub-Total
Segment Reporting Information [Line Items]
Gross premiums written	[2]	1,557,179		1,214,765	4,697,007		3,898,025
Premiums ceded		(385,503)		(357,923)	(1,284,465)		(1,145,347)
Net premiums written		1,171,676		856,842	3,412,542		2,752,678
Change in unearned premiums		(38,420)		(8,875)	(194,146)		(183,231)
Net premiums earned		1,133,256		847,967	3,218,396		2,569,447
Other underwriting income		5,327		6,956	13,142		35,329
Losses and loss adjustment expenses		(922,560)		(449,876)	(1,968,959)		(1,394,802)
Acquisition expenses, net		(161,781)		(132,528)	(467,251)		(406,459)
Other operating expenses		(161,859)		(146,251)	(490,516)		(442,262)
Underwriting income (loss)		(107,617)		126,268	304,812		361,253
Net investment income		94,127		66,282	282,459		207,088
Net realized gains (losses)		64,104		95,946	110,662		168,735
Net impairment losses recognized in earnings		(1,878)		(3,867)	(5,415)		(16,849)
Equity in net income (loss) of investment funds accounted for using the equity method		31,090		16,662	111,884		32,054
Other income (loss)		(342)		(400)	(3,118)		(432)
Corporate expenses		(14,108)	[1]	(11,343)	(48,517)		(37,926)
UGC transaction costs and other		(2,990)	[1]	(7,142)	(21,249)	[1]	(7,142)
Amortization of intangible assets		(31,824)		(4,865)	(93,942)		(14,493)
Interest expense		(26,264)		(12,924)	(77,932)		(37,983)
Net foreign exchange gains (losses)		(27,785)		(4,232)	(85,451)		(3,812)
Income (loss) before income taxes		(23,487)		260,385	474,193		650,493
Income tax expense		(8,168)		(13,232)	(70,734)		(43,673)
Net income (loss)		(31,655)		247,153	403,459		606,820
Dividends attributable to redeemable noncontrolling interests		0		0	0		0
Amounts attributable to non-redeemable noncontrolling interests		0		0	0		0
Net income (loss) available to Arch		(31,655)		247,153	403,459		606,820
Preferred dividends		(12,369)		(5,484)	(34,936)		(16,453)
Loss on redemption of preferred shares		(6,735)			(6,735)
Net income (loss) available to Arch common shareholders		$ (50,759)		$ 241,669	$ 361,788		$ 590,367
Underwriting Ratios
Loss ratio		81.40%		53.10%	61.20%		54.30%
Acquisition expense ratio		14.30%		15.60%	14.50%		15.80%
Other operating expense ratio		14.30%		17.20%	15.20%		17.20%
Combined ratio		110.00%		85.90%	90.90%		87.30%
Goodwill and intangible assets		$ 676,755		$ 83,291	$ 676,755		$ 83,291
Sub-Total | Insurance
Segment Reporting Information [Line Items]
Gross premiums written	[2]	787,447		758,934	2,313,630		2,319,530
Premiums ceded		(222,516)		(217,446)	(704,057)		(713,110)
Net premiums written		564,931		541,488	1,609,573		1,606,420
Change in unearned premiums		(29,766)		(22,410)	(51,188)		(46,603)
Net premiums earned		535,165		519,078	1,558,385		1,559,817
Other underwriting income		0		0	0		0
Losses and loss adjustment expenses		(568,795)		(332,845)	(1,252,375)		(1,011,087)
Acquisition expenses, net		(82,638)		(77,146)	(236,378)		(228,806)
Other operating expenses		(90,875)		(86,613)	(271,268)		(263,111)
Underwriting income (loss)		$ (207,143)		$ 22,474	$ (201,636)		$ 56,813
Underwriting Ratios
Loss ratio		106.30%		64.10%	80.40%		64.80%
Acquisition expense ratio		15.40%		14.90%	15.20%		14.70%
Other operating expense ratio		17.00%		16.70%	17.40%		16.90%
Combined ratio		138.70%		95.70%	113.00%		96.40%
Goodwill and intangible assets		$ 23,445		$ 26,367	$ 23,445		$ 26,367
Sub-Total | Reinsurance
Segment Reporting Information [Line Items]
Gross premiums written	[2]	422,083		324,361	1,351,051		1,217,804
Premiums ceded		(105,389)		(89,551)	(386,743)		(370,068)
Net premiums written		316,694		234,810	964,308		847,736
Change in unearned premiums		6,879		17,117	(81,182)		(43,345)
Net premiums earned		323,573		251,927	883,126		804,391
Other underwriting income		1,728		2,216	1,143		22,659
Losses and loss adjustment expenses		(318,609)		(105,924)	(631,669)		(363,613)
Acquisition expenses, net		(57,340)		(50,192)	(154,638)		(160,706)
Other operating expenses		(36,214)		(35,389)	(110,458)		(108,561)
Underwriting income (loss)		$ (86,862)		$ 62,638	$ (12,496)		$ 194,170
Underwriting Ratios
Loss ratio		98.50%		42.00%	71.50%		45.20%
Acquisition expense ratio		17.70%		19.90%	17.50%		20.00%
Other operating expense ratio		11.20%		14.00%	12.50%		13.50%
Combined ratio		127.40%		75.90%	101.50%		78.70%
Goodwill and intangible assets		$ 417		$ 1,228	$ 417		$ 1,228
Sub-Total | Mortgage
Segment Reporting Information [Line Items]
Gross premiums written	[2]	347,951		131,726	1,032,800		361,440
Premiums ceded		(57,900)		(51,182)	(194,139)		(62,918)
Net premiums written		290,051		80,544	838,661		298,522
Change in unearned premiums		(15,533)		(3,582)	(61,776)		(93,283)
Net premiums earned		274,518		76,962	776,885		205,239
Other underwriting income		3,599		4,740	11,999		12,670
Losses and loss adjustment expenses		(35,156)		(11,107)	(84,915)		(20,102)
Acquisition expenses, net		(21,803)		(5,190)	(76,235)		(16,947)
Other operating expenses		(34,770)		(24,249)	(108,790)		(70,590)
Underwriting income (loss)		$ 186,388		$ 41,156	$ 518,944		$ 110,270
Underwriting Ratios
Loss ratio		12.80%		14.40%	10.90%		9.80%
Acquisition expense ratio		7.90%		6.70%	9.80%		8.30%
Other operating expense ratio		12.70%		31.50%	14.00%		34.40%
Combined ratio		33.40%		52.60%	34.70%		52.50%
Goodwill and intangible assets		$ 652,893		$ 55,696	$ 652,893		$ 55,696
[1]	Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’
[2]	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

Segment Information - Narrative

Segment Information - Narrative (Details)	9 Months Ended
	Sep. 30, 2017segment
Underwriting segments
Segment Reporting Information [Line Items]
Number of segments	3
Other
Segment Reporting Information [Line Items]
Number of segments	2

Reserve for Losses and Loss A45

Reserve for Losses and Loss Adjustment Expenses - Reconciliation of beginning and ending balances of losses and loss adjustment reserves(Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Reserve for losses and loss adjustment expenses at beginning of period	$ 10,520,511	$ 9,471,647	$ 10,200,960	$ 9,125,250
Unpaid losses and loss adjustment expenses recoverable and deferred charges	2,116,210	2,003,768	2,083,575	1,828,837
Net reserve for losses and loss adjustment expenses at beginning of period	8,404,301	7,467,879	8,117,385	7,296,413
Net incurred losses and loss adjustment expenses relating to losses occurring in:
Current year	1,092,175	598,940	2,487,212	1,848,299
Prior years	(45,232)	(74,757)	(197,839)	(216,575)
Discount accretion on retroactive reinsurance	(802)	0	(802)	0
Total net incurred losses and loss adjustment expenses	1,046,141	524,183	2,288,571	1,631,724
Net foreign exchange losses (gains)	61,919	1,463	168,493	(13,270)
Net paid losses and loss adjustment expenses relating to losses occurring in:
Current year	(167,450)	(128,432)	(282,952)	(285,468)
Prior years	(457,183)	(304,673)	(1,403,769)	(1,068,979)
Total net paid losses and loss adjustment expenses	(624,633)	(433,105)	(1,686,721)	(1,354,447)
Net reserve for losses and loss adjustment expenses at end of period	8,887,728	7,560,420	8,887,728	7,560,420
Unpaid losses and loss adjustment expenses recoverable and deferred charges	2,463,539	2,049,769	2,463,539	2,049,769
Reserve for losses and loss adjustment expenses at end of period	$ 11,351,267	$ 9,610,189	$ 11,351,267	$ 9,610,189

Reserve for Losses and Loss A46

Reserve for Losses and Loss Adjustment Expenses - Catastrophe losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Current year	$ 1,092,175	$ 598,940	$ 2,487,212	$ 1,848,299
Catastrophe losses
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Current year	347,800
Underwriting segments | Reinsurance | Catastrophe losses
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Current year	133,400
Underwriting segments | Insurance | Catastrophe losses
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Current year	214,500
Underwriting segments | Other | Catastrophe losses
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Current year	$ 19,800

Reserve for Losses and Loss A47

Reserve for Losses and Loss Adjustment Expenses - Prior year development (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (45,232)	$ (74,757)	$ (197,839)	$ (216,575)
Underwriting segments | Reinsurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (36,500)	$ (59,500)	$ (133,300)	$ (176,700)
Percentage of prior year development	11.30%	23.60%	15.10%	22.00%
Underwriting segments | Reinsurance | Short Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (16,900)	$ (27,700)	$ (85,800)	$ (113,100)
Underwriting segments | Reinsurance | Short Tailed Lines | Property Catastrophe And Property Other Than Property Catastrophe
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(11,800)	(23,200)	(62,700)	(92,600)
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(19,600)	(31,800)	(47,500)	(63,600)
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines | Casualty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years		(29,300)	(28,000)
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines | Casualty | 2002-2009
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(13,400)
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines | Marine And Aviation
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(4,300)		(16,600)
Underwriting segments | Reinsurance | Long Tailed Lines | Casualty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years				(66,400)
Underwriting segments | Insurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (3,000)	$ (13,700)	$ (7,200)	$ (24,800)
Percentage of prior year development	0.60%	2.60%	0.50%	1.60%
Underwriting segments | Insurance | Short Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (1,800)	$ 2,400	$ (9,000)	$ (7,700)
Underwriting segments | Insurance | Medium Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years		2,000	9,200	19,100
Underwriting segments | Insurance | Medium Tailed Lines | Professional lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(11,900)
Underwriting segments | Insurance | Medium Tailed Lines | Surety
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(4,200)
Underwriting segments | Insurance | Medium Tailed Lines | Programs
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	12,900	6,200	39,300	28,600
Underwriting segments | Insurance | Medium Tailed Lines | Other product lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years		(4,200)	(30,100)	(9,500)
Underwriting segments | Insurance | Medium Tailed Lines | Construction
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years			17,200
Underwriting segments | Insurance | Medium Tailed And Long Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(1,200)
Underwriting segments | Insurance | Long Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years		(18,200)	(7,400)	(36,200)
Underwriting segments | Mortgage
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (21,500)	$ (2,500)	$ (74,900)	$ (16,300)
Percentage of prior year development	7.80%	3.20%	9.60%	7.90%
Underwriting segments | Mortgage | Most origination years
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (6,100)
Underwriting segments | Mortgage | Other product lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years			$ (19,200)
Underwriting segments | Other
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ 15,800	$ 900	$ 17,500	$ 1,200

Investment Information - Summar

Investment Information - Summary of available for sale securities (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2016
Available for sale securities:
Estimated Fair Value		$ 16,704,633	$ 15,469,573
Gross Unrealized Gains		290,830	163,339
Gross Unrealized Losses		(91,853)	(198,886)
Cost or Amortized Cost		16,505,656	15,505,120
OTTI Unrealized Losses	[1]	(2,241)	(5,831)
Fixed maturities
Available for sale securities:
Estimated Fair Value		14,317,651	14,156,918
Gross Unrealized Gains	[2]	150,896	79,082
Gross Unrealized Losses	[2]	(83,475)	(178,759)
Cost or Amortized Cost	[2]	14,250,230	14,256,595
OTTI Unrealized Losses	[1],[2]	(2,241)	(5,831)
Fixed maturities | Corporate bonds
Available for sale securities:
Estimated Fair Value		4,275,437	4,392,373
Gross Unrealized Gains	[2]	49,576	27,606
Gross Unrealized Losses	[2]	(22,303)	(46,905)
Cost or Amortized Cost	[2]	4,248,164	4,411,672
OTTI Unrealized Losses	[1],[2]	(73)	(2,285)
Fixed maturities | Mortgage backed securities
Available for sale securities:
Estimated Fair Value		323,900	490,093
Gross Unrealized Gains	[2]	5,078	4,794
Gross Unrealized Losses	[2]	(2,540)	(8,357)
Cost or Amortized Cost	[2]	321,362	493,656
OTTI Unrealized Losses	[1],[2]	(2,146)	(3,323)
Fixed maturities | Municipal bonds
Available for sale securities:
Estimated Fair Value		2,353,234	3,713,434
Gross Unrealized Gains	[2]	31,202	8,554
Gross Unrealized Losses	[2]	(7,614)	(29,154)
Cost or Amortized Cost	[2]	2,329,646	3,734,034
OTTI Unrealized Losses	[1],[2]	0	(201)
Fixed maturities | Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value		584,730	536,051
Gross Unrealized Gains	[2]	3,114	2,876
Gross Unrealized Losses	[2]	(4,377)	(6,508)
Cost or Amortized Cost	[2]	585,993	539,683
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | US government and government agencies
Available for sale securities:
Estimated Fair Value		3,761,612	2,804,540
Gross Unrealized Gains	[2]	3,303	9,319
Gross Unrealized Losses	[2]	(20,246)	(24,437)
Cost or Amortized Cost	[2]	3,778,555	2,819,658
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | Non-US government securities
Available for sale securities:
Estimated Fair Value		1,473,819	1,096,440
Gross Unrealized Gains	[2]	49,570	19,036
Gross Unrealized Losses	[2]	(21,647)	(56,872)
Cost or Amortized Cost	[2]	1,445,896	1,134,276
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | Asset backed securities
Available for sale securities:
Estimated Fair Value		1,544,919	1,123,987
Gross Unrealized Gains	[2]	9,053	6,897
Gross Unrealized Losses	[2]	(4,748)	(6,526)
Cost or Amortized Cost	[2]	1,540,614	1,123,616
OTTI Unrealized Losses	[1],[2]	(22)	(22)
Equity securities
Available for sale securities:
Estimated Fair Value		480,607	532,680
Gross Unrealized Gains		84,755	62,627
Gross Unrealized Losses		(7,873)	(17,517)
Cost or Amortized Cost		403,725	487,570
OTTI Unrealized Losses	[1]	0	0
Other investments
Available for sale securities:
Estimated Fair Value		260,339	167,970
Gross Unrealized Gains		54,512	21,358
Gross Unrealized Losses		(1)	(2,465)
Cost or Amortized Cost		205,828	149,077
OTTI Unrealized Losses	[1]	0	0
Short-term investments
Available for sale securities:
Estimated Fair Value		1,646,036	612,005
Gross Unrealized Gains		667	272
Gross Unrealized Losses		(504)	(145)
Cost or Amortized Cost		1,645,873	611,878
OTTI Unrealized Losses	[1]	$ 0	$ 0
[1]	Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At September 30, 2017, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $0.9 million, compared to a net unrealized gain of $2.8 million at December 31, 2016.
[2]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Aging

Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Available for sale securities:
Estimated Fair Value - Less than 12 Months		$ 7,450,193	$ 7,509,193
Gross Unrealized Losses - Less than 12 Months		(83,588)	(192,881)
Estimated Fair Value - 12 Months or More		406,815	154,001
Gross Unrealized Losses - 12 Months or More		(8,265)	(6,005)
Estimated Fair Value - Total		7,857,008	7,663,194
Gross Unrealized Losses - Total		(91,853)	(198,886)
Fixed maturities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	7,168,087	7,171,367
Gross Unrealized Losses - Less than 12 Months	[1]	(75,210)	(172,754)
Estimated Fair Value - 12 Months or More	[1]	406,815	154,001
Gross Unrealized Losses - 12 Months or More	[1]	(8,265)	(6,005)
Estimated Fair Value - Total	[1]	7,574,902	7,325,368
Gross Unrealized Losses - Total	[1]	(83,475)	(178,759)
Fixed maturities | Corporate bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,173,096	1,700,813
Gross Unrealized Losses - Less than 12 Months	[1]	(18,315)	(43,011)
Estimated Fair Value - 12 Months or More	[1]	191,382	46,902
Gross Unrealized Losses - 12 Months or More	[1]	(3,988)	(3,894)
Estimated Fair Value - Total	[1]	1,364,478	1,747,715
Gross Unrealized Losses - Total	[1]	(22,303)	(46,905)
Fixed maturities | Mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	146,352	402,699
Gross Unrealized Losses - Less than 12 Months	[1]	(2,477)	(8,134)
Estimated Fair Value - 12 Months or More	[1]	1,511	6,105
Gross Unrealized Losses - 12 Months or More	[1]	(63)	(223)
Estimated Fair Value - Total	[1]	147,863	408,804
Gross Unrealized Losses - Total	[1]	(2,540)	(8,357)
Fixed maturities | Municipal bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	745,410	1,513,308
Gross Unrealized Losses - Less than 12 Months	[1]	(5,958)	(28,504)
Estimated Fair Value - 12 Months or More	[1]	110,752	29,636
Gross Unrealized Losses - 12 Months or More	[1]	(1,656)	(650)
Estimated Fair Value - Total	[1]	856,162	1,542,944
Gross Unrealized Losses - Total	[1]	(7,614)	(29,154)
Fixed maturities | Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	282,901	231,374
Gross Unrealized Losses - Less than 12 Months	[1]	(3,579)	(6,331)
Estimated Fair Value - 12 Months or More	[1]	17,570	5,635
Gross Unrealized Losses - 12 Months or More	[1]	(798)	(177)
Estimated Fair Value - Total	[1]	300,471	237,009
Gross Unrealized Losses - Total	[1]	(4,377)	(6,508)
Fixed maturities | US government and government agencies
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	3,083,239	1,888,018
Gross Unrealized Losses - Less than 12 Months	[1]	(19,736)	(24,437)
Estimated Fair Value - 12 Months or More	[1]	25,894	0
Gross Unrealized Losses - 12 Months or More	[1]	(510)	0
Estimated Fair Value - Total	[1]	3,109,133	1,888,018
Gross Unrealized Losses - Total	[1]	(20,246)	(24,437)
Fixed maturities | Non-US government securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,149,528	807,598
Gross Unrealized Losses - Less than 12 Months	[1]	(20,741)	(56,872)
Estimated Fair Value - 12 Months or More	[1]	37,655	0
Gross Unrealized Losses - 12 Months or More	[1]	(906)	0
Estimated Fair Value - Total	[1]	1,187,183	807,598
Gross Unrealized Losses - Total	[1]	(21,647)	(56,872)
Fixed maturities | Asset backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	587,561	627,557
Gross Unrealized Losses - Less than 12 Months	[1]	(4,404)	(5,465)
Estimated Fair Value - 12 Months or More	[1]	22,051	65,723
Gross Unrealized Losses - 12 Months or More	[1]	(344)	(1,061)
Estimated Fair Value - Total	[1]	609,612	693,280
Gross Unrealized Losses - Total	[1]	(4,748)	(6,526)
Equity securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months		170,937	269,381
Gross Unrealized Losses - Less than 12 Months		(7,873)	(17,517)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		170,937	269,381
Gross Unrealized Losses - Total		(7,873)	(17,517)
Other investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months		725	39,299
Gross Unrealized Losses - Less than 12 Months		(1)	(2,465)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		725	39,299
Gross Unrealized Losses - Total		(1)	(2,465)
Short-term investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months		110,444	29,146
Gross Unrealized Losses - Less than 12 Months		(504)	(145)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		110,444	29,146
Gross Unrealized Losses - Total		$ (504)	$ (145)
[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Maturi

Investment Information - Maturity profile of available for sale securities) (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Estimated Fair Value:
Estimated fair value		$ 13,792,903	$ 13,426,577
Amortized Cost:
Amortized cost		13,722,581	13,522,671
Fixed maturities
Estimated Fair Value:
Due in one year or less		537,043	560,830
Due after one year through five years		7,547,002	6,158,148
Due after five years through 10 years		3,495,424	4,676,847
Due after 10 years		284,633	610,962
Single maturity date		11,864,102	12,006,787
Estimated fair value	[1]	14,317,651	14,156,918
Amortized Cost:
Due in one year or less		534,513	557,675
Due after one year through five years		7,508,674	6,211,099
Due after five years through 10 years		3,480,251	4,710,017
Due after 10 years		278,823	620,849
Single maturity date		11,802,261	12,099,640
Amortized cost	[1]	14,250,230	14,256,595
Fixed maturities | Mortgage backed securities
Estimated Fair Value:
Securities without single maturity date		323,900	490,093
Amortized Cost:
Securities without single maturity date		321,362	493,656
Fixed maturities | Commercial mortgage backed securities
Estimated Fair Value:
Securities without single maturity date		584,730	536,051
Amortized Cost:
Securities without single maturity date		585,993	539,683
Fixed maturities | Asset backed securities
Estimated Fair Value:
Securities without single maturity date		1,544,919	1,123,987
Amortized Cost:
Securities without single maturity date		$ 1,540,614	$ 1,123,616
[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Securi

Investment Information - Securities lending agreements (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Disclosure Investment Information [Abstract]
Fair value of cash collateral received on securities lending	$ 63,800	$ 212,500
Fair value of non-cash collateral received on securities lending	479,500	550,100
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	543,243	762,554
Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9	0	0
Amounts related to securities lending not included in offsetting disclosure in Note 9	543,243	762,554
US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	507,954	718,492
Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	31,305	29,078
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	3,984	14,984
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	460,127	600,077
Overnight and continuous | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	424,838	556,015
Overnight and continuous | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	31,305	29,078
Overnight and continuous | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	3,984	14,984
Less than 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	8,186	31,244
Less than 30 days | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	8,186	31,244
Less than 30 days | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
Less than 30 days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
30 - 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	74,930	126,093
30 - 90 days | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	74,930	126,093
30 - 90 days | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
30 - 90 days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
90 days or more
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	5,140
90 days or more | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	5,140
90 days or more | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
90 days or more | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	$ 0	$ 0

Investment Information - Other

Investment Information - Other investments (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		$ 2,557,544	$ 2,088,763
Available for sale
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		260,339	167,970
Available for sale | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		123,225	84,778
Available for sale | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		53,325	33,923
Available for sale | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		20,752	7,469
Available for sale | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		63,037	41,800
Fair value option
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		2,297,205	1,920,793
Fair value option | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		1,387,663	1,190,799
Other investments par		1,378,797	1,208,537
Fair value option | Mezzanine debt funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		172,000	127,943
Fair value option | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		300,552	178,568
Fair value option | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		95,151	75,468
Fair value option | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		194,200	218,298
Fair value option | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	[1]	$ 147,639	$ 129,717
[1]	Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other.

Investment Information - Fair v

Investment Information - Fair value option (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 4,249,634	$ 3,421,220
Fixed maturities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	1,508,204	1,099,116
Other investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	2,297,205	1,920,793
Short-term investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	349,540	373,669
Equity securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 94,685	$ 27,642

Investment Information - Limite

Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss		$ 1,071,731	$ 891,774
Aggregate unfunded commitments		1,580,000	1,290,000
Equity method investments
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[1]	962,574	800,970
Aggregate unfunded commitments		850,400	776,600
Fair value option
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[2]	109,157	90,804
Aggregate unfunded commitments		$ 162,300	$ 16,700
[1]	Aggregate unfunded commitments were $850.4 million at September 30, 2017, compared to $776.6 million at December 31, 2016.
[2]	Aggregate unfunded commitments were $162.3 million at September 30, 2017, compared to $16.7 million at December 31, 2016.

Investment Information - Net in

Investment Information - Net investment income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net investment income:
Gross investment income	$ 139,945	$ 113,846	$ 412,336	$ 334,546
Investment expenses	(23,486)	(20,228)	(66,879)	(58,855)
Net investment income	116,459	93,618	345,457	275,691
Fixed maturities
Net investment income:
Gross investment income	96,144	71,366	284,807	223,033
Equity securities (dividends)
Net investment income:
Gross investment income	2,887	3,311	9,184	10,409
Short-term investments
Net investment income:
Gross investment income	2,957	1,703	6,732	3,015
Other
Net investment income:
Gross investment income	$ 37,957	$ 37,466	$ 111,613	$ 98,089

Investment Information - Net re

Investment Information - Net realized gains and losses (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net realized gains and losses:
Available for sale securities, gross gains on investment sales		$ 66,565	$ 84,451	$ 212,470	$ 266,965
Available for sale securities, gross losses on investment sales		(39,015)	(22,985)	(152,996)	(129,409)
Derivative instruments	[1]	4,298	(16,964)	(9,653)	24,102
Other	[2]	(782)	(10,858)	(20,655)	(31,753)
Net realized gains (losses)		66,275	125,105	122,163	230,647
Fixed maturities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		4,035	43,935	34,232	62,234
Other investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		24,264	46,428	42,149	38,016
Equity securities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		10,230	(52)	16,604	385
Short-term investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		$ (3,320)	$ 1,150	$ 12	$ 107
[1]	See Note 9 for information on the Company’s derivative instruments.
[2]	Includes the re-measurement of contingent consideration liability amounts.

Investment Information - Othe57

Investment Information - Other than temporary impairments recognized in earnings (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ (1,878)	$ (3,867)	$ (5,415)	$ (16,849)
Fixed maturities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(938)	(778)	(4,122)	(9,726)
Fixed maturities | Mortgage backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(50)	(233)	(1,461)	(788)
Fixed maturities | Corporate bonds
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(82)	0	(1,484)	(5,655)
Fixed maturities | Non-US government securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(178)	(545)	(376)	(777)
Fixed maturities | Asset backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings			0	(2,506)
Fixed maturities | US government and government agencies
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(426)	0	(426)	0
Fixed maturities | Municipal bonds
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(202)	0	(375)	0
Equity securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(940)	(557)	(1,126)	(3,594)
Other investments
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ 0	$ (2,532)	$ (167)	$ (3,529)

Investment Information - Othe58

Investment Information - Other than temporary impairments rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Rollforward:
Balance at start of period	$ 4,437	$ 14,847	$ 13,138	$ 26,875
Credit loss impairments recognized on securities not previously impaired	0	38	31	1,388
Credit loss impairments recognized on securities previously impaired	15	60	210	582
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	0	0	0	0
Reductions for securities sold during the period	(689)	(1,166)	(9,616)	(15,066)
Balance at end of period	$ 3,763	$ 13,779	$ 3,763	$ 13,779

Investment Information - Restri

Investment Information - Restricted assets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Restricted Assets [Line Items]
Restricted assets	$ 6,628,124	$ 5,902,339
Collateral or guarantees - affiliated transactions
Restricted Assets [Line Items]
Restricted assets	4,264,131	3,871,971
Collateral or guarantees - third party agreements
Restricted Assets [Line Items]
Restricted assets	1,689,104	1,513,079
Deposits with US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	618,136	472,890
Deposits with non-US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	$ 56,753	$ 44,399

Investment Information - Narrat

Investment Information - Narrative (Details) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2017USD ($)lots	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)lots	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)lots
Narrative items:
Investable assets		$ 22,000,000		$ 22,000,000
Equity in net income (loss) of investment funds accounted for using the equity method		31,090	$ 16,662	111,884	$ 32,054
OTTI unrealized (losses) gains at current fair value		$ 900		$ 900		$ 2,800
Continuous unrealized loss, qualitative disclosures:
Number of positions in an unrealized loss position (lots) | lots		2,870		2,870		3,540
Total number of positions (lots) | lots		7,410		7,410		7,240
Largest single loss		$ 1,600		$ 1,600		$ 4,600
OTTI unrealized losses (gains)	[1]			$ 2,241		$ 5,831
Minimum
Narrative items:
Time lag for reporting				1 month
Maximum
Narrative items:
Time lag for reporting				3 months
Underwriting segments
Narrative items:
Investable assets		19,700,000		$ 19,700,000
Equity in net income (loss) of investment funds accounted for using the equity method		31,090	16,662	111,884	32,054
Other
Narrative items:
Investable assets		2,300,000		2,300,000
Equity in net income (loss) of investment funds accounted for using the equity method		$ 0	$ 0	$ 0	$ 0
[1]	Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At September 30, 2017, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $0.9 million, compared to a net unrealized gain of $2.8 million at December 31, 2016.

Fair Value - Fair Value Hierarc

Fair Value - Fair Value Hierarchy (Details) - Recurring - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		$ 6,855,812	$ 4,555,092
Liabilities measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Securities sold but not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[1]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		0	0
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]
Assets measured at fair value	[2]	3,687,126	2,691,575
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	3,687,126	2,691,575
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
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]
Assets measured at fair value		473,908	529,695
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,600,885	608,862
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]
Assets measured at fair value		83,254	112,313
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		83,254	112,313
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,010,639	612,647
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		487,475	197,486
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		343,620	309,127
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		59,332	25,328
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		120,212	80,706
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		12,896,364	13,559,270
Liabilities measured at fair value		(95,719)	(59,206)
Significant Other Observable Inputs (Level 2) | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		0	0
Significant Other Observable Inputs (Level 2) | Securities sold but not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[1]	(72,682)	(33,157)
Significant Other Observable Inputs (Level 2) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(23,037)	(26,049)
Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	10,612,585	11,435,710
Significant Other Observable Inputs (Level 2) | Fixed maturities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	4,263,446	4,374,029
Significant Other Observable Inputs (Level 2) | Fixed maturities | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	323,496	490,093
Significant Other Observable Inputs (Level 2) | Fixed maturities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	2,353,234	3,713,434
Significant Other Observable Inputs (Level 2) | Fixed maturities | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	584,185	536,051
Significant Other Observable Inputs (Level 2) | Fixed maturities | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	74,486	112,965
Significant Other Observable Inputs (Level 2) | Fixed maturities | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	1,473,819	1,096,440
Significant Other Observable Inputs (Level 2) | Fixed maturities | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	1,539,919	1,112,698
Significant Other Observable Inputs (Level 2) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		6,699	2,985
Significant Other Observable Inputs (Level 2) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		45,151	3,143
Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,417	0
Significant Other Observable Inputs (Level 2) | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,417	0
Significant Other Observable Inputs (Level 2) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		33,141	28,410
Significant Other Observable Inputs (Level 2) | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		2,197,371	2,089,022
Significant Other Observable Inputs (Level 2) | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		811,710	790,935
Significant Other Observable Inputs (Level 2) | Fair value option | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		21,218	18,624
Significant Other Observable Inputs (Level 2) | Fair value option | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		2,740
Significant Other Observable Inputs (Level 2) | Fair value option | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		12,539
Significant Other Observable Inputs (Level 2) | Fair value option | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Other Observable Inputs (Level 2) | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		97,614	61,747
Significant Other Observable Inputs (Level 2) | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		63,437	30,324
Significant Other Observable Inputs (Level 2) | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		5,920	64,542
Significant Other Observable Inputs (Level 2) | Fair value option | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		35,353	2,314
Significant Other Observable Inputs (Level 2) | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,146,840	1,120,536
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		60,557	54,633
Liabilities measured at fair value		(59,248)	(122,350)
Significant Unobservable Inputs (Level 3) | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(59,248)	(122,350)
Significant Unobservable Inputs (Level 3) | Securities sold but not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[1]	0	0
Significant Unobservable Inputs (Level 3) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	17,940	29,633
Significant Unobservable Inputs (Level 3) | Fixed maturities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	11,991	18,344
Significant Unobservable Inputs (Level 3) | Fixed maturities | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	404	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	545	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	5,000	11,289
Significant Unobservable Inputs (Level 3) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		42,617	25,000
Significant Unobservable Inputs (Level 3) | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		11,471	0
Significant Unobservable Inputs (Level 3) | Fair value option | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0
Significant Unobservable Inputs (Level 3) | Fair value option | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0
Significant Unobservable Inputs (Level 3) | Fair value option | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		31,146	25,000
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		20,987,408	18,919,203
Liabilities measured at fair value		(154,967)	(181,556)
Estimated Fair Value | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(59,248)	(122,350)
Estimated Fair Value | Securities sold but not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[1]	(72,682)	(33,157)
Estimated Fair Value | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(23,037)	(26,049)
Estimated Fair Value | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		14,317,651	14,156,918
Estimated Fair Value | Fixed maturities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		4,275,437	4,392,373
Estimated Fair Value | Fixed maturities | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		323,900	490,093
Estimated Fair Value | Fixed maturities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		2,353,234	3,713,434
Estimated Fair Value | Fixed maturities | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		584,730	536,051
Estimated Fair Value | Fixed maturities | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		3,761,612	2,804,540
Estimated Fair Value | Fixed maturities | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,473,819	1,096,440
Estimated Fair Value | Fixed maturities | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,544,919	1,123,987
Estimated Fair Value | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		480,607	532,680
Estimated Fair Value | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,646,036	612,005
Estimated Fair Value | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		260,339	167,970
Estimated Fair Value | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		84,671	112,313
Estimated Fair Value | Other investments measured at net asset value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	175,668	55,657
Estimated Fair Value | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		33,141	28,410
Estimated Fair Value | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		4,249,634	3,421,220
Estimated Fair Value | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		823,181	790,935
Estimated Fair Value | Fair value option | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		21,218	18,624
Estimated Fair Value | Fair value option | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		2,740
Estimated Fair Value | Fair value option | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		12,539
Estimated Fair Value | Fair value option | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		487,475	197,486
Estimated Fair Value | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		97,614	61,747
Estimated Fair Value | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		63,437	30,324
Estimated Fair Value | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		349,540	373,669
Estimated Fair Value | Fair value option | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		94,685	27,642
Estimated Fair Value | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,298,198	1,226,242
Estimated Fair Value | Fair value option | Other investments measured at net asset value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	$ 999,007	$ 694,551
[1]	Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets.
[2]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7, “Investment Information—Securities Lending Agreements.”
[3]	In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets.

Fair Value - Rollforward of Lev

Fair Value - Rollforward of Level 3 assets and liabilities (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ 36,570	$ 66,516	$ 54,633	$ 73,868
Total gains or (losses) (realized/unrealized) - included in earnings		0	1,667	4,672	(672)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		289	0	289	0
Purchases, issuances, sales and settlements
Purchases		1,348	0	6,283	776
Issuances		0	0	0	0
Sales		0	0	(26,242)	0
Settlements		0	(22,435)	(1,428)	(28,224)
Transfers in and/or out of Level 3		22,350	0	22,350	0
Balance at end of period		60,557	45,748	60,557	45,748
Contingent consideration liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		(57,246)	(111,670)	(122,350)	(96,048)
Total gains or (losses) (realized/unrealized) - included in earnings		(2,002)	(4,795)	(9,089)	(20,916)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	88	0	51
Purchases, issuances, sales and settlements
Purchases		0	0	0	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	(72,191)	536
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		(59,248)	(116,377)	(59,248)	(116,377)
Available for sale | Asset backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	[1]	0	49,211	11,289	57,500
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	3,779	(2,500)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	[1]	0	0	0	0
Purchases, issuances, sales and settlements
Purchases	[1]	0	0	0	0
Issuances	[1]	0	0	0	0
Sales	[1]	0	0	(13,640)	0
Settlements	[1]	0	(22,435)	(1,428)	(28,224)
Transfers in and/or out of Level 3	[1]	5,949	0	5,949	0
Balance at end of period	[1]	5,949	26,776	5,949	26,776
Available for sale | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		11,570	17,305	18,344	16,368
Total gains or (losses) (realized/unrealized) - included in earnings		0	1,667	893	1,828
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		289	0	289	0
Purchases, issuances, sales and settlements
Purchases		0	0	4,935	776
Issuances		0	0	0	0
Sales		0	0	(12,602)	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		132	0	132	0
Balance at end of period		11,991	18,972	11,991	18,972
Fair value option | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		0	0	0	0
Total gains or (losses) (realized/unrealized) - included in earnings		0	0	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	0	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		11,471	0	11,471	0
Balance at end of period		11,471	0	11,471	0
Fair value option | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		25,000	0	25,000	0
Total gains or (losses) (realized/unrealized) - included in earnings		0	0	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		1,348	0	1,348	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		4,798	0	4,798	0
Balance at end of period		$ 31,146	$ 0	$ 31,146	$ 0
[1]	Includes asset backed securities, mortgage backed securities and commercial mortgage backed securities.

Fair Value - Narrative (Details

Fair Value - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Total assets and liabilities measured at fair value	$ 21,140,000	$ 19,100,000
Total assets and liabilities measured at fair value priced using non-binding broker quotes	$ 242,900	$ 234,000
Total assets and liabilities measured at fair value priced using non-binding broker quotes (percentage)	1.20%	1.20%
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 1,732,726	$ 1,732,258
Reportable Legal Entities | ACGL (Parent Guarantor)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	297,030	296,957
Estimated fair value of senior notes	406,000
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	494,596	$ 494,525
Estimated fair value of senior notes	566,200
Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Transfers into Level 3	17,600
Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Transfers into Level 3	4,800
Unsecured debt | Notes due 2026
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	496,000
Estimated fair value of senior notes	519,800
Unsecured debt | Notes due 2046
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	445,100
Estimated fair value of senior notes	$ 503,500

Derivative Instruments (Details

Derivative Instruments (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016	Dec. 31, 2016
Derivative offsetting [Abstract]
Derivative assets subject to master netting agreements		$ 49,400			$ 49,400			$ 28,400
Derivative liabilities subject to master netting agreements		22,500			22,500			26,000
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	[1]	4,298		$ (16,964)	(9,653)		$ 24,102
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives - fair value		51,472			51,472			30,001
Liability derivatives - fair value		(23,037)			(23,037)			(26,049)
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		4,298		(16,964)	(9,653)		24,102
Not Designated as Hedging Instrument [Member] | Futures contracts
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	1,524,985			1,524,985			1,655,530
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		4,899		(15,368)	7,309		45,954
Not Designated as Hedging Instrument [Member] | Futures contracts | Other assets
Derivative [Line Items]
Asset derivatives - fair value		5,351	[3]		5,351	[3]		360
Not Designated as Hedging Instrument [Member] | Futures contracts | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	(6,722)			(6,722)			(9,398)
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	805,201			805,201			1,186,386
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(228)		4,583	(12,266)		(13,951)
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts | Other assets
Derivative [Line Items]
Asset derivatives - fair value	[3]	19,376			19,376			9,354
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	(5,348)			(5,348)			(12,941)
Not Designated as Hedging Instrument [Member] | TBAs
Derivative [Line Items]
Net derivatives - notional value	[2],[4]	18,143			18,143			0
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		122		(23)	143		311
Not Designated as Hedging Instrument [Member] | TBAs | Fixed maturities available for sale
Derivative [Line Items]
Asset derivatives - fair value		18,331	[4]		18,331	[4]		0
Liability derivatives - fair value	[4]	0			0			0
Not Designated as Hedging Instrument [Member] | Other
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	2,032,922			2,032,922			1,014,863
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(495)		$ (6,156)	(4,839)		$ (8,212)
Not Designated as Hedging Instrument [Member] | Other | Other assets
Derivative [Line Items]
Asset derivatives - fair value	[3]	8,414			8,414			20,287
Not Designated as Hedging Instrument [Member] | Other | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	$ (10,967)			$ (10,967)			$ (3,710)
[1]	See Note 9 for information on the Company’s derivative instruments.
[2]	Represents the absolute notional value of all outstanding contracts, consisting of long and short positions.
[3]	The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’
[4]	The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Repayments of borrowings	$ 100,000	$ 172,000	$ 179,171
Investment commitments	$ 1,580,000	$ 1,580,000		$ 1,290,000

Share Transactions - Share repu

Share Transactions - Share repurchases (Details) - Common shares - USD ($) shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Class of Stock [Line Items]
Cumulative number of shares acquired since inception of share repurchase program	125.2
Aggregate purchase price of shares acquired since inception of share repurchase program	$ 3,680
Treasury stock, shares acquired (shares)		1.1
Treasury stock, value of shares acquired		$ 75.3
Remaining authorized repurchase amount	$ 446.5

Share Transactions - Conversion

Share Transactions - Conversion of Non-voting common equivalent preferred shares (Details) - shares	1 Months Ended
	Jun. 30, 2017	Sep. 30, 2017	Jun. 08, 2017
Class of Stock [Line Items]
Number of convertible shares transferred	708,862
Number of common shares issued on conversion	7,088,620
Shares transferred
Class of Stock [Line Items]
Number of convertible shares transferred		638,141
Underwriter option
Class of Stock [Line Items]
Number of convertible shares transferred		95,721
AIG
Class of Stock [Line Items]
Preferred shares		567,420	1,276,282

Share Transactions - Series F P

Share Transactions - Series F Preferred Shares (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended	9 Months Ended
	Aug. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Class of Stock [Line Items]
Proceeds from issuance of preferred shares, net		$ 222,054	$ 434,899
Series C Preferred Shares
Class of Stock [Line Items]
Dividend rate percentage	6.75%
Redemption price per share	$ 25
Series F Preferred Shares
Class of Stock [Line Items]
Preferred stock value outstanding	$ 230,000
Number of shares outstanding	9.2
Proportionate interest per depositary share	0.10%
Dividend rate percentage	5.45%
Par value per share	$ 0.01
Liquidation preference per share	25,000
Redemption price per share	$ 25,000
Proceeds from issuance of preferred shares, net	$ 222,100
Depositary share equivalent
Class of Stock [Line Items]
Liquidation preference per share	$ 25
Redemption price per share	$ 25

Other Comprehensive Income (L69

Other Comprehensive Income (Loss) - Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses	$ (1,878)	$ (3,867)	$ (5,415)	$ (16,999)
Income (loss) before income taxes	(37,028)	316,851	498,672	772,276
Income tax expense	(8,189)	(13,231)	(70,755)	(43,672)
Net of tax	(33,656)	252,872	404,638	618,725
Reclassification out of accumulated other comprehensive income | Unrealized appreciation on available-for-sale investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses)	27,550	61,464	59,474	137,555
Other-than-temporary impairment losses	(1,878)	(3,867)	(5,415)	(16,999)
Income (loss) before income taxes	25,672	57,597	54,059	120,556
Income tax expense	(1,760)	(2,605)	(7,879)	(11,247)
Net of tax	$ 23,912	$ 54,992	$ 46,180	$ 109,309

Other Comprehensive Income (L70

Other Comprehensive Income (Loss) - Components of other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Before tax amount:
Unrealized holding gains (losses) arising during period, before tax	$ 69,330	$ 11,692	$ 288,813	$ 281,770
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), before tax	0	0	0	(150)
Less reclassification of net realized gains included in net income, before tax	25,672	57,597	54,059	120,556
Foreign currency translation adjustments, before tax	8,590	(5,407)	30,264	(5,733)
Other comprehensive income (loss), before tax	52,248	(51,312)	265,018	155,331
Tax expense (benefit):
Unrealized holding gains (losses) arising during period, tax	2,868	(4,589)	28,590	30,048
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), tax	0	0	0	0
Less reclassification of net realized gains included in net income, tax	1,760	2,605	7,879	11,247
Foreign currency translation adjustments, tax	310	(95)	563	417
Other comprehensive income (loss), tax	1,418	(7,289)	21,274	19,218
Net of tax amount:
Unrealized holding gains (losses) arising during period, net of tax	66,462	16,281	260,223	251,722
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), net of tax	0	0	0	(150)
Less reclassification of net realized gains included in net income, net of tax	23,912	54,992	46,180	109,309
Foreign currency translation adjustments, net of tax	8,280	(5,312)	29,701	(6,150)
Net current period other comprehensive income (loss)	$ 50,830	$ (44,023)	$ 243,744	$ 136,113

Guarantor Financial Informati71

Guarantor Financial Information - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Assets
Total investments	$ 21,931,881		$ 19,719,651
Cash	862,361		842,942	$ 578,816		$ 553,326
Investments in subsidiaries	0		0
Due from subsidiaries and affiliates	0		0
Premiums receivable	1,269,678		1,072,435
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	2,506,015		2,114,138
Contractholder receivables	1,864,348		1,717,436
Ceded unearned premiums	947,135		859,567
Deferred acquisition costs	531,196		447,560
Goodwill and intangible assets	684,405		781,553	90,941
Other assets	2,027,778		1,816,827
Total assets	32,624,797		29,372,109
Liabilities
Reserve for losses and loss adjustment expenses	11,351,267	$ 10,520,511	10,200,960	9,610,189	$ 9,471,647	9,125,250
Unearned premiums	3,751,550		3,406,870
Reinsurance balances payable	352,006		300,407
Contractholder payables	1,864,348		1,717,436
Collateral held for insured obligations	345,726		301,406
Deposit accounting liabilities			22,150
Senior notes	1,732,726		1,732,258
Revolving credit agreement borrowings	826,242		756,650
Due to subsidiaries and affiliates	0		0
Other liabilities	2,423,061		1,622,847
Total liabilities	22,646,926		20,060,984
Redeemable noncontrolling interests	205,829		205,553
Shareholders' Equity
Total shareholders’ equity available to Arch	8,911,144		8,253,718	7,313,983
Non-redeemable noncontrolling interests	860,898		851,854	834,808
Total shareholders’ equity	9,772,042		9,105,572	8,148,791
Total liabilities, noncontrolling interests and shareholders’ equity	32,624,797		29,372,109
Reportable Legal Entities | ACGL (Parent Guarantor)
Assets
Total investments	402		2,612
Cash	4,868		1,687	2,041		6,809
Investments in subsidiaries	9,214,178		8,660,586
Due from subsidiaries and affiliates	81		14,297
Premiums receivable	0		0
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	0		0
Contractholder receivables	0		0
Ceded unearned premiums	0		0
Deferred acquisition costs	0		0
Goodwill and intangible assets	0		0
Other assets	13,357		15,725
Total assets	9,232,886		8,694,907
Liabilities
Reserve for losses and loss adjustment expenses	0		0
Unearned premiums	0		0
Reinsurance balances payable	0		0
Contractholder payables	0		0
Collateral held for insured obligations	0		0
Deposit accounting liabilities			0
Senior notes	297,030		296,957
Revolving credit agreement borrowings	0		100,000
Due to subsidiaries and affiliates	41		26,270
Other liabilities	24,671		17,962
Total liabilities	321,742		441,189
Redeemable noncontrolling interests	0		0
Shareholders' Equity
Total shareholders’ equity available to Arch	8,911,144		8,253,718
Non-redeemable noncontrolling interests	0		0
Total shareholders’ equity	8,911,144		8,253,718
Total liabilities, noncontrolling interests and shareholders’ equity	9,232,886		8,694,907
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Assets
Total investments	69,671		41,672
Cash	88,818		71,955	19,392		17,023
Investments in subsidiaries	4,028,493		3,716,681
Due from subsidiaries and affiliates	117		51,298
Premiums receivable	0		0
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	0		0
Contractholder receivables	0		0
Ceded unearned premiums	0		0
Deferred acquisition costs	0		0
Goodwill and intangible assets	0		0
Other assets	59,734		49,244
Total assets	4,246,833		3,930,850
Liabilities
Reserve for losses and loss adjustment expenses	0		0
Unearned premiums	0		0
Reinsurance balances payable	0		0
Contractholder payables	0		0
Collateral held for insured obligations	0		0
Deposit accounting liabilities			0
Senior notes	494,596		494,525
Revolving credit agreement borrowings	0		0
Due to subsidiaries and affiliates	542,103		535,584
Other liabilities	100,278		54,823
Total liabilities	1,136,977		1,084,932
Redeemable noncontrolling interests	0		0
Shareholders' Equity
Total shareholders’ equity available to Arch	3,109,856		2,845,918
Non-redeemable noncontrolling interests	0		0
Total shareholders’ equity	3,109,856		2,845,918
Total liabilities, noncontrolling interests and shareholders’ equity	$ 4,246,833		3,930,850
Percentage Ownership of Subsidiary	100.00%
Reportable Legal Entities | Other ACGL Subsidiaries
Assets
Total investments	$ 21,876,508		19,690,067
Cash	768,675		769,300	557,383		529,494
Investments in subsidiaries	0		0
Due from subsidiaries and affiliates	1,923,941		1,866,681
Premiums receivable	1,863,203		1,579,865
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	7,023,836		6,114,518
Contractholder receivables	1,864,348		1,717,436
Ceded unearned premiums	2,240,129		1,985,311
Deferred acquisition costs	677,567		577,461
Goodwill and intangible assets	684,405		781,553
Other assets	2,146,993		1,901,786
Total assets	41,069,605		36,983,978
Liabilities
Reserve for losses and loss adjustment expenses	15,836,263		14,164,191
Unearned premiums	5,044,544		4,532,614
Reinsurance balances payable	945,530		807,837
Contractholder payables	1,864,348		1,717,436
Collateral held for insured obligations	345,726		301,406
Deposit accounting liabilities			22,150
Senior notes	941,100		940,776
Revolving credit agreement borrowings	826,242		656,650
Due to subsidiaries and affiliates	1,381,996		1,370,422
Other liabilities	2,669,614		1,867,040
Total liabilities	29,855,363		26,380,522
Redeemable noncontrolling interests	220,529		220,253
Shareholders' Equity
Total shareholders’ equity available to Arch	10,132,815		9,531,349
Non-redeemable noncontrolling interests	860,898		851,854
Total shareholders’ equity	10,993,713		10,383,203
Total liabilities, noncontrolling interests and shareholders’ equity	41,069,605		36,983,978
Consolidating Adjustments and Eliminations
Assets
Total investments	(14,700)		(14,700)
Cash	0		0	$ 0		$ 0
Investments in subsidiaries	(13,242,671)		(12,377,267)
Due from subsidiaries and affiliates	(1,924,139)		(1,932,276)
Premiums receivable	(593,525)		(507,430)
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	(4,517,821)		(4,000,380)
Contractholder receivables	0		0
Ceded unearned premiums	(1,292,994)		(1,125,744)
Deferred acquisition costs	(146,371)		(129,901)
Goodwill and intangible assets	0		0
Other assets	(192,306)		(149,928)
Total assets	(21,924,527)		(20,237,626)
Liabilities
Reserve for losses and loss adjustment expenses	(4,484,996)		(3,963,231)
Unearned premiums	(1,292,994)		(1,125,744)
Reinsurance balances payable	(593,524)		(507,430)
Contractholder payables	0		0
Collateral held for insured obligations			0
Deposit accounting liabilities			0
Senior notes	0		0
Revolving credit agreement borrowings	0		0
Due to subsidiaries and affiliates	(1,924,140)		(1,932,276)
Other liabilities	(371,502)		(316,978)
Total liabilities	(8,667,156)		(7,845,659)
Redeemable noncontrolling interests	(14,700)		(14,700)
Shareholders' Equity
Total shareholders’ equity available to Arch	(13,242,671)		(12,377,267)
Non-redeemable noncontrolling interests	0		0
Total shareholders’ equity	(13,242,671)		(12,377,267)
Total liabilities, noncontrolling interests and shareholders’ equity	$ (21,924,527)		$ (20,237,626)

Guarantor Financial Informati72

Guarantor Financial Information - Condensed consolidating statement of income and comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Net premiums earned	$ 1,261,886	$ 958,403	$ 3,619,777	$ 2,915,967
Net investment income	116,459	93,618	345,457	275,691
Net realized gains (losses)	66,275	125,105	122,163	230,647
Net impairment losses recognized in earnings	(1,878)	(3,867)	(5,415)	(16,849)
Other underwriting income	6,064	7,980	15,519	38,251
Equity in net income (loss) of investment funds accounted for using the equity method	31,090	16,662	111,884	32,054
Other income (loss)	(342)	(400)	(3,118)	(432)
Total revenues	1,479,554	1,197,501	4,206,267	3,475,329
Expenses
Losses and loss adjustment expenses	1,046,141	524,183	2,288,571	1,631,724
Acquisition expenses	193,854	161,267	566,579	501,782
Other operating expenses	170,127	153,286	514,827	460,748
Corporate expenses	17,098	18,485	69,766	45,068
Amortization of intangible assets	31,824	4,865	93,942	14,493
Interest expense	29,510	15,943	86,935	47,713
Net foreign exchange (gains) losses	28,028	2,621	86,975	1,525
Total expenses	1,516,582	880,650	3,707,595	2,703,053
Income (loss) before income taxes	(37,028)	316,851	498,672	772,276
Income tax (expense) benefit	(8,189)	(13,231)	(70,755)	(43,672)
Income (loss) before equity in net income of subsidiaries	(45,217)	303,620	427,917	728,604
Equity in net income of subsidiaries	0	0	0	0
Net income (loss)	(45,217)	303,620	427,917	728,604
Net (income) loss attributable to noncontrolling interests	11,561	(50,748)	(23,279)	(109,879)
Net income available to Arch	(33,656)	252,872	404,638	618,725
Preferred dividends	(12,369)	(5,484)	(34,936)	(16,453)
Loss on redemption of preferred shares	(6,735)	0	(6,735)	0
Net income (loss) available to Arch common shareholders	(52,760)	247,388	362,967	602,272
Comprehensive income (loss) available to Arch	17,585	208,790	648,861	754,979
Reportable Legal Entities | ACGL (Parent Guarantor)
Revenues
Net premiums earned	0	0	0	0
Net investment income	117	6	123	7
Net realized gains (losses)	0	0	0	0
Net impairment losses recognized in earnings	0	0	0	0
Other underwriting income	0	0	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	0	0	0	0
Other income (loss)	(102)	71	(368)	270
Total revenues	15	77	(245)	277
Expenses
Losses and loss adjustment expenses	0	0	0	0
Acquisition expenses	0	0	0	0
Other operating expenses	0	0	0	0
Corporate expenses	14,576	18,488	53,639	45,284
Amortization of intangible assets	0	0	0	0
Interest expense	5,934	5,948	18,024	17,811
Net foreign exchange (gains) losses	0	0	0	0
Total expenses	20,510	24,436	71,663	63,095
Income (loss) before income taxes	(20,495)	(24,359)	(71,908)	(62,818)
Income tax (expense) benefit	0	0	0	0
Income (loss) before equity in net income of subsidiaries	(20,495)	(24,359)	(71,908)	(62,818)
Equity in net income of subsidiaries	(13,161)	277,231	476,546	681,543
Net income (loss)	(33,656)	252,872	404,638	618,725
Net (income) loss attributable to noncontrolling interests	0	0	0	0
Net income available to Arch	(33,656)	252,872	404,638	618,725
Preferred dividends	(12,369)	(5,484)	(34,936)	(16,453)
Loss on redemption of preferred shares	(6,735)		(6,735)
Net income (loss) available to Arch common shareholders	(52,760)	247,388	362,967	602,272
Comprehensive income (loss) available to Arch	17,585	208,790	648,861	754,979
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Revenues
Net premiums earned	0	0	0	0
Net investment income	151	803	1,151	2,351
Net realized gains (losses)	0	0	0	0
Net impairment losses recognized in earnings	0	0	0	0
Other underwriting income	0	0	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	0	0	0	0
Other income (loss)	0	0	0	0
Total revenues	151	803	1,151	2,351
Expenses
Losses and loss adjustment expenses	0	0	0	0
Acquisition expenses	0	0	0	0
Other operating expenses	0	0	0	0
Corporate expenses	410	608	3,727	1,549
Amortization of intangible assets	0	0	0	0
Interest expense	12,037	6,627	35,956	19,946
Net foreign exchange (gains) losses	0	0	0	0
Total expenses	12,447	7,235	39,683	21,495
Income (loss) before income taxes	(12,296)	(6,432)	(38,532)	(19,144)
Income tax (expense) benefit	4,432	2,116	13,374	6,446
Income (loss) before equity in net income of subsidiaries	(7,864)	(4,316)	(25,158)	(12,698)
Equity in net income of subsidiaries	50,057	21,945	213,586	64,684
Net income (loss)	42,193	17,629	188,428	51,986
Net (income) loss attributable to noncontrolling interests	0	0	0	0
Net income available to Arch	42,193	17,629	188,428	51,986
Preferred dividends	0	0	0	0
Loss on redemption of preferred shares	0		0
Net income (loss) available to Arch common shareholders	42,193	17,629	188,428	51,986
Comprehensive income (loss) available to Arch	47,676	2,019	240,759	89,204
Reportable Legal Entities | Other ACGL Subsidiaries
Revenues
Net premiums earned	1,261,886	958,403	3,619,777	2,915,967
Net investment income	138,784	99,654	410,392	294,012
Net realized gains (losses)	66,275	125,105	122,163	230,647
Net impairment losses recognized in earnings	(1,878)	(3,867)	(5,415)	(16,849)
Other underwriting income	6,064	7,980	15,519	54,749
Equity in net income (loss) of investment funds accounted for using the equity method	31,090	16,662	111,884	32,054
Other income (loss)	(240)	(471)	(2,750)	(702)
Total revenues	1,501,981	1,203,466	4,271,570	3,509,878
Expenses
Losses and loss adjustment expenses	1,046,141	524,183	2,288,571	1,631,724
Acquisition expenses	193,854	161,267	566,579	501,782
Other operating expenses	170,127	153,286	514,827	460,748
Corporate expenses	2,112	(611)	12,400	(1,765)
Amortization of intangible assets	31,824	4,865	93,942	14,493
Interest expense	33,811	9,890	98,197	46,169
Net foreign exchange (gains) losses	20,510	2,723	65,701	5,093
Total expenses	1,498,379	855,603	3,640,217	2,658,244
Income (loss) before income taxes	3,602	347,863	631,353	851,634
Income tax (expense) benefit	(12,621)	(15,347)	(84,129)	(50,118)
Income (loss) before equity in net income of subsidiaries	(9,019)	332,516	547,224	801,516
Equity in net income of subsidiaries	0	0	0	0
Net income (loss)	(9,019)	332,516	547,224	801,516
Net (income) loss attributable to noncontrolling interests	11,238	(51,071)	(24,247)	(110,844)
Net income available to Arch	2,219	281,445	522,977	690,672
Preferred dividends	0	0	0	0
Loss on redemption of preferred shares	0		0
Net income (loss) available to Arch common shareholders	2,219	281,445	522,977	690,672
Comprehensive income (loss) available to Arch	45,936	237,555	745,856	830,348
Consolidating Adjustments and Eliminations
Revenues
Net premiums earned	0	0	0	0
Net investment income	(22,593)	(6,845)	(66,209)	(20,679)
Net realized gains (losses)	0	0	0	0
Net impairment losses recognized in earnings	0	0	0	0
Other underwriting income	0	0	0	(16,498)
Equity in net income (loss) of investment funds accounted for using the equity method	0	0	0	0
Other income (loss)	0	0	0	0
Total revenues	(22,593)	(6,845)	(66,209)	(37,177)
Expenses
Losses and loss adjustment expenses	0	0	0	0
Acquisition expenses	0	0	0	0
Other operating expenses	0	0	0	0
Corporate expenses	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	(22,272)	(6,522)	(65,242)	(36,213)
Net foreign exchange (gains) losses	7,518	(102)	21,274	(3,568)
Total expenses	(14,754)	(6,624)	(43,968)	(39,781)
Income (loss) before income taxes	(7,839)	(221)	(22,241)	2,604
Income tax (expense) benefit	0	0	0	0
Income (loss) before equity in net income of subsidiaries	(7,839)	(221)	(22,241)	2,604
Equity in net income of subsidiaries	(36,896)	(299,176)	(690,132)	(746,227)
Net income (loss)	(44,735)	(299,397)	(712,373)	(743,623)
Net (income) loss attributable to noncontrolling interests	323	323	968	965
Net income available to Arch	(44,412)	(299,074)	(711,405)	(742,658)
Preferred dividends	0	0	0	0
Loss on redemption of preferred shares	0		0
Net income (loss) available to Arch common shareholders	(44,412)	(299,074)	(711,405)	(742,658)
Comprehensive income (loss) available to Arch	$ (93,612)	$ (239,574)	$ (986,615)	$ (919,552)

Guarantor Financial Informati73

Guarantor Financial Information - Condensed consolidating statement of cash flows (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Operating Activities
Net Cash Provided by (Used in) Operating Activities			$ 1,081,134	$ 1,037,139
Investing Activities
Purchases of fixed maturity investments			(28,079,129)	(27,840,555)
Purchases of equity securities			(667,135)	(377,767)
Purchases of other investments			(1,406,528)	(1,008,774)
Proceeds from sales of fixed maturity investments			27,629,474	26,731,924
Proceeds from sales of equity securities			751,873	464,904
Proceeds from sales, redemptions and maturities of other investments			938,581	879,330
Proceeds from redemptions and maturities of fixed maturity investments			747,621	540,823
Net settlements of derivative instruments			(20,952)	23,396
Net (purchases) sales of short-term investments			(964,653)	(604,162)
Change in cash collateral related to securities lending			148,692	(27,935)
Contributions to subsidiaries			0	0
Issuance of intercompany loans			0
Repayment of intercompany loans			0
Acquisitions, net of cash			(27,709)	(20,911)
Purchases of fixed assets			(16,862)	(11,565)
Other			86,145	(3,816)
Net Cash Provided By (Used For) Investing Activities			(880,582)	(1,255,108)
Financing Activities
Proceeds from issuance of preferred shares, net			222,054	434,899
Redemption of preferred shares			(230,000)	0
Purchases of common shares under share repurchase program			0	(75,256)
Proceeds from common shares issued, net			(7,484)	(3,785)
Proceeds from intercompany borrowings			0
Proceeds from borrowings			238,915	46,000
Repayments of Intercompany Debt Financing Activities			0
Repayments of borrowings		$ (100,000)	(172,000)	(179,171)
Change in cash collateral related to securities lending			(148,692)	27,935
Dividends paid to redeemable noncontrolling interests			(13,491)	(13,491)
Dividends paid to parent	[1]		0	0
Other			(49,280)	33,113
Preferred dividends paid			(34,936)	(16,453)
Net Cash Provided By (Used For) Financing Activities			(194,914)	253,791
Effects of exchange rate changes on foreign currency cash			13,781	(10,332)
Increase (decrease) in cash			19,419	25,490
Cash beginning of year			842,942	553,326
Cash end of period		862,361	862,361	578,816
Reportable Legal Entities | ACGL (Parent Guarantor)
Operating Activities
Net Cash Provided by (Used in) Operating Activities			130,715	94,250
Investing Activities
Purchases of fixed maturity investments			0	0
Purchases of equity securities			0	0
Purchases of other investments			0	0
Proceeds from sales of fixed maturity investments			0	0
Proceeds from sales of equity securities			0	0
Proceeds from sales, redemptions and maturities of other investments			0	0
Proceeds from redemptions and maturities of fixed maturity investments			0	0
Net settlements of derivative instruments			0	0
Net (purchases) sales of short-term investments			2,209	(436,830)
Change in cash collateral related to securities lending			0	0
Contributions to subsidiaries			20,641	(3,585)
Issuance of intercompany loans			0
Repayment of intercompany loans			0
Acquisitions, net of cash			0	0
Purchases of fixed assets			(18)	(8)
Other			0	2,000
Net Cash Provided By (Used For) Investing Activities			22,832	(438,423)
Financing Activities
Proceeds from issuance of preferred shares, net			222,054	434,899
Redemption of preferred shares			(230,000)
Purchases of common shares under share repurchase program				(75,256)
Proceeds from common shares issued, net			(7,484)	(3,785)
Proceeds from intercompany borrowings			0
Proceeds from borrowings			0	0
Repayments of Intercompany Debt Financing Activities			0
Repayments of borrowings			(100,000)	0
Change in cash collateral related to securities lending			0	0
Dividends paid to redeemable noncontrolling interests			0	0
Dividends paid to parent	[1]		0	0
Other			0	0
Preferred dividends paid			(34,936)	(16,453)
Net Cash Provided By (Used For) Financing Activities			(150,366)	339,405
Effects of exchange rate changes on foreign currency cash			0	0
Increase (decrease) in cash			3,181	(4,768)
Cash beginning of year			1,687	6,809
Cash end of period		4,868	4,868	2,041
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Operating Activities
Net Cash Provided by (Used in) Operating Activities			70,761	14,448
Investing Activities
Purchases of fixed maturity investments			0	0
Purchases of equity securities			0	0
Purchases of other investments			0	0
Proceeds from sales of fixed maturity investments			0	0
Proceeds from sales of equity securities			0	0
Proceeds from sales, redemptions and maturities of other investments			0	0
Proceeds from redemptions and maturities of fixed maturity investments			0	41,500
Net settlements of derivative instruments			0	0
Net (purchases) sales of short-term investments			(27,998)	(53,779)
Change in cash collateral related to securities lending			0	0
Contributions to subsidiaries			(72,900)	0
Issuance of intercompany loans			0
Repayment of intercompany loans			47,000
Acquisitions, net of cash			0	0
Purchases of fixed assets			0	0
Other			0	0
Net Cash Provided By (Used For) Investing Activities			(53,898)	(12,279)
Financing Activities
Proceeds from issuance of preferred shares, net			0	0
Redemption of preferred shares			0
Purchases of common shares under share repurchase program				0
Proceeds from common shares issued, net			0	0
Proceeds from intercompany borrowings			0
Proceeds from borrowings			0	0
Repayments of Intercompany Debt Financing Activities			0
Repayments of borrowings			0	0
Change in cash collateral related to securities lending			0	0
Dividends paid to redeemable noncontrolling interests			0	0
Dividends paid to parent	[1]		0	0
Other			0	200
Preferred dividends paid			0	0
Net Cash Provided By (Used For) Financing Activities			0	200
Effects of exchange rate changes on foreign currency cash			0	0
Increase (decrease) in cash			16,863	2,369
Cash beginning of year			71,955	17,023
Cash end of period		88,818	88,818	19,392
Reportable Legal Entities | Other ACGL Subsidiaries
Operating Activities
Net Cash Provided by (Used in) Operating Activities			1,464,701	1,096,443
Investing Activities
Purchases of fixed maturity investments			(28,079,129)	(27,840,555)
Purchases of equity securities			(667,135)	(377,767)
Purchases of other investments			(1,406,528)	(1,008,774)
Proceeds from sales of fixed maturity investments			27,629,474	26,731,924
Proceeds from sales of equity securities			751,873	464,904
Proceeds from sales, redemptions and maturities of other investments			938,581	879,330
Proceeds from redemptions and maturities of fixed maturity investments			747,621	499,323
Net settlements of derivative instruments			(20,952)	23,396
Net (purchases) sales of short-term investments			(938,864)	(113,553)
Change in cash collateral related to securities lending			148,692	(27,935)
Contributions to subsidiaries			(353,588)	(9,247)
Issuance of intercompany loans			(47,000)
Repayment of intercompany loans			0
Acquisitions, net of cash			(27,709)	(20,911)
Purchases of fixed assets			(16,844)	(11,557)
Other			106,786	(5,816)
Net Cash Provided By (Used For) Investing Activities			(1,234,722)	(817,238)
Financing Activities
Proceeds from issuance of preferred shares, net			0	0
Redemption of preferred shares			0
Purchases of common shares under share repurchase program				0
Proceeds from common shares issued, net			405,847	12,832
Proceeds from intercompany borrowings			47,000
Proceeds from borrowings			238,915	46,000
Repayments of Intercompany Debt Financing Activities			(47,000)
Repayments of borrowings			(72,000)	(179,171)
Change in cash collateral related to securities lending			(148,692)	27,935
Dividends paid to redeemable noncontrolling interests			(14,447)	(14,448)
Dividends paid to parent	[1]		(584,087)	(167,045)
Other			(69,921)	32,913
Preferred dividends paid			0	0
Net Cash Provided By (Used For) Financing Activities			(244,385)	(240,984)
Effects of exchange rate changes on foreign currency cash			13,781	(10,332)
Increase (decrease) in cash			(625)	27,889
Cash beginning of year			769,300	529,494
Cash end of period		768,675	768,675	557,383
Consolidating Adjustments and Eliminations
Operating Activities
Net Cash Provided by (Used in) Operating Activities			(585,043)	(168,002)
Investing Activities
Purchases of fixed maturity investments			0	0
Purchases of equity securities			0	0
Purchases of other investments			0	0
Proceeds from sales of fixed maturity investments			0	0
Proceeds from sales of equity securities			0	0
Proceeds from sales, redemptions and maturities of other investments			0	0
Proceeds from redemptions and maturities of fixed maturity investments			0	0
Net settlements of derivative instruments			0	0
Net (purchases) sales of short-term investments			0	0
Change in cash collateral related to securities lending			0	0
Contributions to subsidiaries			405,847	12,832
Issuance of intercompany loans			47,000
Repayment of intercompany loans			(47,000)
Acquisitions, net of cash			0	0
Purchases of fixed assets			0	0
Other			(20,641)	0
Net Cash Provided By (Used For) Investing Activities			385,206	12,832
Financing Activities
Proceeds from issuance of preferred shares, net			0	0
Redemption of preferred shares			0
Purchases of common shares under share repurchase program				0
Proceeds from common shares issued, net			(405,847)	(12,832)
Proceeds from intercompany borrowings			(47,000)
Proceeds from borrowings			0	0
Repayments of Intercompany Debt Financing Activities			47,000
Repayments of borrowings			0	0
Change in cash collateral related to securities lending			0	0
Dividends paid to redeemable noncontrolling interests			956	957
Dividends paid to parent	[1]		584,087	167,045
Other			20,641	0
Preferred dividends paid			0	0
Net Cash Provided By (Used For) Financing Activities			199,837	155,170
Effects of exchange rate changes on foreign currency cash			0	0
Increase (decrease) in cash			0	0
Cash beginning of year			0	0
Cash end of period		$ 0	$ 0	$ 0
[1]	Dividends received by parent are included in net cash provided by (used for) operating activities

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective tax rate on income before income taxes (percentage)	14.20%	5.70%
Statutory federal tax rate	35.00%
Tax benefit on share-based compensation	1.50%
Net deferred tax assets	$ 248.3		$ 221.2
Income taxes paid	$ 47.9	$ 40.7

Transactions with Related Par75

Transactions with Related Parties (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Investment commitments	$ 1,580,000		$ 1,290,000
Purchases of other investments	1,406,528	$ 1,008,774
Common director | The Carlyle Group
Related Party Transaction [Line Items]
Investments, value	248,500
Unfunded commitments	471,600
Purchases of other investments	86,000	50,100
Aggregate cash distributions received	$ 48,700	$ 17,900

Acquisition (Details)

Acquisition (Details) - AIG United Guaranty Insurance (Asia) Limited $ in Millions	Jul. 01, 2017USD ($)
Business Acquisition [Line Items]
Payment to acquire businesses	$ 40
Intangible assets acquired	2.3
Goodwill	$ 0.8

Subsequent Event (Details)

Subsequent Event (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Oct. 25, 2017
Subsequent Event [Line Items]
Incurred claims		$ 1,092,175	$ 598,940	$ 2,487,212	$ 1,848,299
Subsequent event | Variable Interest Entity, Not Primary Beneficiary | Bellemeade Re 2017-1 Ltd
Subsequent Event [Line Items]
Aggregate excess of loss reinsurance agreement						$ 368,100
Aggregate losses						165,700
Mortgage insurance-linked notes issued						$ 368,100
Subsequent event | California Wildfires [Member] | Minimum
Subsequent Event [Line Items]
Incurred claims	$ 30,000
Subsequent event | California Wildfires [Member] | Maximum
Subsequent Event [Line Items]
Incurred claims	$ 55,000