Arch Capital (ACGL) 10-K 26 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Feb. 23, 2016	Jun. 30, 2015
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	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		122,078,177
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 7,890

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Investments:
Fixed maturities available for sale, at fair value (amortized cost: $10,515,440 and $10,701,557)	$ 10,459,353	$ 10,750,770
Short-term investments available for sale, at fair value (amortized cost: $591,141 and $801,758)	587,904	797,226
Collateral received under securities lending, at fair value (amortized cost: $385,984 and $40,473)	389,336	44,301
Equity securities available for sale, at fair value (cost: $543,767 and $562,534)	618,405	658,182
Other investments available for sale, at fair value (cost: $261,343 and $264,747)	300,476	296,224
Investments accounted for using the fair value option	2,894,494	2,425,053
Investments accounted for using the equity method	592,973	349,014
Total investments	15,842,941	15,320,770
Cash	553,326	485,702
Accrued investment income	87,206	74,316
Securities pledged under securities lending, at fair value (amortized cost: $386,411 and $52,076)	384,081	50,802
Premiums receivable	983,443	948,695
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	1,867,373	1,812,845
Contractholder receivables	1,486,296	1,309,192
Prepaid reinsurance premiums	427,609	377,078
Deferred acquisition costs, net	433,477	414,525
Receivable for securities sold	45,505	78,170
Goodwill and intangible assets	97,531	109,539
Other assets	968,482	1,024,447
Total assets	23,177,270	22,006,081
Liabilities
Reserve for losses and loss adjustment expenses	9,125,250	9,036,448
Unearned premiums	2,333,932	2,231,578
Reinsurance balances payable	224,120	219,312
Contractholder payables	1,486,296	1,309,192
Collateral held for insured obligations	248,982	184,219
Deposit accounting liabilities	260,364	327,384
Senior notes	791,306	791,141
Revolving credit agreement borrowings	530,434	100,000
Securities lending payable	393,844	50,529
Payable for securities purchased	64,996	128,413
Other liabilities	568,852	509,219
Total liabilities	$ 16,028,376	$ 14,887,435
Commitments and Contingencies
Redeemable noncontrolling interests	$ 205,182	$ 219,512
Shareholders’ Equity
Non-cumulative preferred shares	325,000	325,000
Common shares ($0.0033 par, shares issued: 173,107,849 and 171,672,408)	577	572
Additional paid-in capital	467,339	383,073
Retained earnings	7,370,371	6,854,571
Accumulated other comprehensive income (loss), net of deferred income tax	(16,502)	128,856
Common shares held in treasury, at cost (shares: 50,480,066 and 44,304,474)	(1,941,904)	(1,562,019)
Total shareholders' equity available to Arch	6,204,881	6,130,053
Non-redeemable noncontrolling interests	738,831	769,081
Total shareholders' equity	6,943,712	6,899,134
Total liabilities, noncontrolling interests and shareholders' equity	$ 23,177,270	$ 22,006,081

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fixed maturities available for sale, at amortized cost	$ 10,515,440	$ 10,701,557
Short-term investments available for sale, at amortized cost	591,141	801,758
Collateral received under securities lending agreements, at amortized cost	385,984	40,473
Equity securities available for sale, at cost	543,767	562,534
Other investments available for sale, at cost	261,343	264,747
Securities pledged under securities lending, at amortized cost	$ 386,411	$ 52,076
Common shares, par value per share	$ 0.0033	$ 0.0033
Common shares issued (shares)	173,107,849	171,672,408
Common shares held in treasury (shares)	50,480,066	44,304,474

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues
Net premiums written	$ 3,817,531	$ 3,891,938	$ 3,351,367
Change in unearned premiums	(83,626)	(298,190)	(205,415)
Net premiums earned	3,733,905	3,593,748	3,145,952
Net investment income	348,090	302,585	267,219
Net realized gains (losses)	(185,842)	102,917	74,018
Other-than-temporary impairment losses	(26,152)	(30,470)	(3,961)
Less investment impairments recognized in other comprehensive income, before taxes	6,036	320	175
Net impairment losses recognized in earnings	(20,116)	(30,150)	(3,786)
Other underwriting income	35,497	10,142	7,639
Equity in net income of investment funds accounted for using the equity method	25,455	19,883	35,701
Other income (loss)	(399)	(10,252)	(586)
Total revenues	3,936,590	3,988,873	3,526,157
Expenses
Losses and loss adjustment expenses	2,050,903	1,919,250	1,679,424
Acquisition expenses	681,476	657,262	564,103
Other operating expenses	657,261	606,224	500,730
Interest expense	45,874	45,634	27,060
Net foreign exchange (gains) losses	(66,118)	(83,744)	12,335
Total expenses	3,369,396	3,144,626	2,783,652
Income (loss) before income taxes	567,194	844,247	742,505
Current tax expense	44,194	30,550	32,696
Deferred tax (benefit) expense	(3,582)	(7,563)	78
Income tax expense	40,612	22,987	32,774
Net income	526,582	821,260	709,731
Net (income) loss attributable to noncontrolling interests	11,156	13,095	0
Net income available to Arch	537,738	834,355	709,731
Preferred dividends	(21,938)	(21,938)	(21,938)
Net income available to Arch common shareholders	$ 515,800	$ 812,417	$ 687,793
Net income per common share
Basic (per share)	$ 4.24	$ 6.21	$ 5.24
Diluted (per share)	$ 4.09	$ 6.02	$ 5.07
Weighted average common shares and common share equivalents outstanding
Basic (shares)	121,786,127	130,817,610	131,355,392
Diluted (shares)	126,038,743	134,922,322	135,777,183

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Comprehensive Income
Net income (loss)	$ 526,582	$ 821,260	$ 709,731
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during period	(77,244)	146,330	(176,403)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(6,036)	(320)	(175)
Reclassification of net realized gains, net of income taxes, included in net income	(28,233)	(65,104)	(32,686)
Foreign currency translation adjustments	(34,110)	(27,014)	(2,789)
Comprehensive income	380,959	875,152	497,678
Net (income) loss attributable to noncontrolling interests	11,156	13,095	0
Other comprehensive (income) loss attributable to noncontrolling interests	265	0	0
Comprehensive income available to Arch	$ 392,380	$ 888,247	$ 497,678

Consolidated Statements of Chan

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)	Unrealized Appreciation on Available-For-Sale Investments	Foreign Currency Translation Adjustments	Common shares held in treasury, at cost
Balance at beginning of year at Dec. 31, 2012		$ 325,000	$ 561	$ 227,778	$ 5,354,361	$ 287,017	$ 289,956	$ (2,939)	$ (1,025,839)
Common shares issued, net			4	8,237
Exercise of stock options				10,561
Amortization of share-based compensation				49,237
Other				3,704
Net income (loss)	$ 709,731				709,731
Net (income) loss attributable to noncontrolling interests	0				0
Preferred dividends	(21,938)				(21,938)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							(209,089)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax							(175)
Foreign currency translation adjustments	(2,789)							(2,789)
Foreign currency translation adjustments attributable to noncontrolling interests								0
Shares repurchased for treasury									(68,865)
Balance at end of year at Dec. 31, 2013	5,647,496	325,000	565	299,517	6,042,154	74,964	80,692	(5,728)	(1,094,704)
Non-redeemable noncontrolling interests	0
Total shareholders' equity	5,647,496
Common shares issued, net			7	9,590
Exercise of stock options				18,662
Amortization of share-based compensation				54,789
Other				515
Net income (loss)	821,260				821,260
Net (income) loss attributable to noncontrolling interests	13,095				13,095
Preferred dividends	(21,938)				(21,938)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							81,226
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax							(320)
Foreign currency translation adjustments	(27,014)							(27,014)
Foreign currency translation adjustments attributable to noncontrolling interests								0
Shares repurchased for treasury									(467,315)
Balance at end of year at Dec. 31, 2014	6,130,053	325,000	572	383,073	6,854,571	128,856	161,598	(32,742)	(1,562,019)
Non-redeemable noncontrolling interests	769,081
Total shareholders' equity	6,899,134
Common shares issued, net			5	10,576
Exercise of stock options				15,926
Amortization of share-based compensation				56,096
Other				1,668
Net income (loss)	526,582				526,582
Net (income) loss attributable to noncontrolling interests	11,156				11,156
Preferred dividends	(21,938)				(21,938)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							(105,477)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax							(6,036)
Foreign currency translation adjustments	(34,110)							(34,110)
Foreign currency translation adjustments attributable to noncontrolling interests								265
Shares repurchased for treasury									(379,885)
Balance at end of year at Dec. 31, 2015	6,204,881	$ 325,000	$ 577	$ 467,339	$ 7,370,371	$ (16,502)	$ 50,085	$ (66,587)	$ (1,941,904)
Non-redeemable noncontrolling interests	738,831
Total shareholders' equity	$ 6,943,712

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net income (loss)	$ 526,582	$ 821,260	$ 709,731
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized losses (gains)	149,961	(127,511)	(78,084)
Net impairment losses recognized in earnings	20,116	30,150	3,786
Equity in net income or loss of investment funds accounted for using the equity method and other income or loss	3,857	13,340	52,824
Share-based compensation	56,096	54,789	49,237
Changes in:
Reserve for losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable	181,658	156,211	(29,393)
Unearned premiums, net of prepaid reinsurance premiums	83,626	298,190	205,415
Premiums receivable	(26,783)	(217,035)	(60,224)
Deferred acquisition costs, net	(29,008)	(81,584)	(75,948)
Reinsurance balances payable	(5,885)	26,699	6,830
Other liabilities	45,223	101,757	(29,989)
Other items, net	(7,537)	(39,136)	96,683
Net Cash Provided By Operating Activities	997,906	1,037,130	850,868
Investing Activities
Purchases of fixed maturity investments	(29,451,873)	(28,745,279)	(18,174,988)
Purchases of equity securities	(515,413)	(520,817)	(535,857)
Purchases of other investments	(1,749,525)	(1,590,648)	(994,185)
Proceeds from the sale of fixed maturity investments	28,094,047	26,823,189	17,194,635
Proceeds from the sale of equity securities	564,011	411,362	462,787
Proceeds from sales, redemptions and maturities of other investments	1,250,883	941,798	817,648
Proceeds from redemptions and maturities of fixed maturity investments	748,529	762,995	731,708
Net settlements of derivative instruments	(5,056)	34,372	14,494
Proceeds from investment in joint venture	40,000	0	0
Net sales (purchases) of short-term investments	169,095	577,126	(750,613)
Change in cash collateral related to securities lending	(6,662)	57,470	(55,643)
Purchase of business, net of cash acquired	818	(237,106)	0
Purchases of fixed assets	(15,736)	(19,883)	(17,499)
Change in other assets	(36,993)	0	0
Net Cash Used For Investing Activities	(913,875)	(1,505,421)	(1,307,513)
Financing Activities
Purchases of common shares under share repurchase program	(365,383)	(454,137)	(57,796)
Proceeds from common shares issued, net	4,861	6,827	3,051
Proceeds from borrowings	431,362	0	494,228
Change in cash collateral related to securities lending	6,662	(57,470)	55,643
Third party investment in non-redeemable noncontrolling interests	0	796,903	0
Third party investment in redeemable noncontrolling interests	0	219,233	0
Dividends paid to redeemable noncontrolling interests	(18,307)	(14,448)	0
Other	(41,913)	64,973	50,830
Preferred dividends paid	(21,938)	(21,938)	(21,938)
Net Cash Provided By (Used For) Financing Activities	(4,656)	539,943	524,018
Effects of exchange rate changes on foreign currency cash	(11,751)	(20,007)	(4,357)
Increase in cash	67,624	51,645	63,016
Cash beginning of year	485,702	434,057	371,041
Cash end of year	553,326	485,702	434,057
Income taxes paid	40,273	20,923	15,288
Interest paid	$ 52,728	$ 46,429	$ 23,733

General

General	12 Months Ended
	Dec. 31, 2015
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 and reinsurance on a worldwide basis through its wholly owned subsidiaries. ACGL was formed in September 2000 and became the sole shareholder of Arch Capital Group (U.S.) Inc. (“Arch-U.S.”) pursuant to an internal reorganization transaction completed in November 2000. In October 2001, ACGL launched an underwriting initiative to meet current and future demand in the global insurance and reinsurance markets that included the recruitment of new management teams and an equity capital infusion of $763.2 million . As used herein, the “Company” means ACGL and its subsidiaries. Similarly, “Common Shares” means the common shares, par value $0.0033 , of ACGL. The Company’s consolidated financial statements include the results of Watford Holdings Ltd., and its wholly owned subsidiaries (“Watford Re”). See Note 4 . The Company has reclassified the presentation of certain prior year information to conform to the current presentation. Such reclassifications had no effect on the Company’s net income, shareholders’ equity or cash flows. Tabular amounts are in U.S. Dollars in thousands, except share amounts, unless otherwise noted.

Business Acquired

Business Acquired	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Business Acquired	Businesses Acquired Gulf Re Holdings Limited In May 2008, the Company provided $100.0 million of funding to Gulf Reinsurance Limited, a wholly owned subsidiary of Gulf Re Holdings Limited (collectively, “Gulf Re”), pursuant to the joint venture agreement with Gulf Investment Corporation GSC (“GIC”). Under the agreement, Arch Re Bermuda and GIC each owned 50% of Gulf Re. The Company entered into a number of strategic initiatives related to Gulf Re in the 2014 fourth quarter, including an agreement to acquire complete ownership and effective control of Gulf Re. Such agreement was approved by the Dubai Financial Services Authority in April 2015 and the transaction closed on May 14, 2015. Pursuant to the agreement, Gulf Re distributed $130.6 million in total to the Company and GIC, and Gulf Re maintained $50.7 million of equity capital. The Company purchased GIC’s remaining investment in Gulf Re for $25.6 million through a transfer of fixed maturity investments. GIC will continue to participate equally with the Company in the financial results of Gulf Re and have the ability to purchase shares in Gulf Re over the next seven years . The acquisition resulted in no goodwill or other intangible assets as the fair value of Gulf Re was equal to its book value at closing. Mortgage Insurance Operations On January 30, 2014, the Company’s U.S.-based subsidiaries completed the acquisition of CMG Mortgage Insurance Company and its affiliated mortgage insurance companies (the “CMG Entities”) through a stock purchase agreement (“SPA”) from its previous owners, PMI Mortgage Insurance Co., in Rehabilitation (“PMI”) and CMFG Life Insurance Company (“CUNA Mutual”). In addition, the Company entered into a distribution agreement with CUNA Mutual and a reinsurance agreement with an affiliate of CUNA Mutual. CMG Mortgage Insurance Company has been renamed “Arch Mortgage Insurance Company” (“Arch MI U.S.”). As part of the transaction, Arch MI U.S. obtained approval as an eligible mortgage insurer from Federal National Mortgage Association and Federal Home Loan Mortgage Corporation (each a government sponsored enterprise or “GSE”), subject to maintaining certain ongoing requirements. In addition, through an asset purchase agreement (“APA”) with PMI, the Company acquired the mortgage insurance operating platform of PMI, 100% of the capital stock of PMI Mortgage Assurance Co., a mortgage insurance company licensed in all 50 states (renamed Arch Mortgage Guaranty Company), and entered into a quota share reinsurance agreement pursuant to which Arch Reinsurance Ltd. (“Arch Re Bermuda”) agreed to provide 100% quota share indemnity reinsurance to PMI for all certificates of insurance that were issued by PMI between and including January 1, 2009 and December 31, 2011 that were not in default as of an agreed upon effective date. Other than this quota share, no PMI legacy exposures were assumed in the transaction. As part of the transaction, the Company entered into a services agreement with PMI to provide certain necessary operational services to administer the run-off of PMI’s legacy business at the direction of PMI. Arch MI U.S. also entered into a quota share reinsurance agreement whereby it will cede to an affiliate of PMI 20% of all new primary flow mortgage insurance business post-closing (both credit union and non-credit union business) on the first $25 billion in original loan amounts, on a funds-withheld basis. The completion of the SPA and APA transactions enabled the Company to enter the U.S. mortgage insurance marketplace and serve all lenders nationwide. The arrangements with CUNA Mutual also provided a seamless transition and enabled the Company to provide uninterrupted access and services to the credit union marketplace. At closing, the Company paid aggregate consideration of $160.6 million ( 80% of the actual closing date book value of the CMG Entities) under the SPA and $84.6 million under the APA. Additionally, the SPA contains provisions for contingent consideration payments, subject to an overall maximum payment of 150% of closing book value of the pre-closing portfolio of the CMG Entities as re-calculated over an earn-out period and payable at the third, fifth and sixth anniversaries after closing (subject to a one time extension period of one to three years at the sellers’ discretion). The maximum amount of contingent consideration payments is $136.9 million . To the extent that the adjusted book value of the CMG Entities drops below the cumulative amount paid by the Company, no additional payments would be due. To determine the fair value of the contingent consideration liability, the Company estimated future payments using a weighted average cost of capital approach at a rate of return of 15% which reflects the industry-weighted average rate of return on debt and equity as required by market participants. The fair value of the contingent consideration liability was $41.8 million at closing. The contingent consideration liability, which is included in ‘other liabilities’ in the consolidated balance sheets, is remeasured at fair value at each balance sheet date ( $95.0 million at December 31, 2015 ) until the contingency is resolved with changes in fair value recognized in ‘net realized gains (losses).’ The following table summarizes the fair value of net assets acquired and allocation of purchase price, measured as of the acquisition date: Total Useful Life Purchase price Cash paid $ 245,157 Contingent consideration liability 41,762 Total purchase price (a) $ 286,919 Assets acquired Cash $ 9,579 Investments, at fair value 312,093 Intangible asset -- acquired insurance contracts 46,473 5 years Intangible asset -- operating platform 29,900 5 years Intangible asset -- favorable lease contract 1,056 5 years Intangible asset -- insurance licenses 16,858 Indefinite Other assets acquired 21,691 Total assets acquired 437,650 Liabilities acquired Reserves for losses and loss adjustment expenses $ 121,572 Unearned premiums 26,261 Intangible liability -- unfavorable service contract 9,533 9 years Other liabilities acquired 7,217 Total liabilities acquired 164,583 Net assets acquired (b) $ 273,067 Goodwill (a)-(b) $ 13,852 From the acquisition date to December 31, 2014, the Company recorded amortization expense of $20.1 million related to net intangible assets acquired. The Company recognized goodwill of $13.9 million that is primarily attributed to PMI’s assembled workforce, access to the mortgage insurance market and additional synergies to be realized in the future. Under U.S. tax principles, which differentiate between taxable and non-taxable business combinations, the Company estimated that $48.0 million of goodwill was expected to be deductible for tax purposes at December 31, 2014. The Company includes the operations of Arch MI U.S. in its mortgage segment (see Note 5 ).

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Significant accounting policies	Significant Accounting Policies (a) Basis of Presentation The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of ACGL and its subsidiaries, including Arch Re Bermuda, Arch Reinsurance Company (“Arch Re U.S.”), Arch-U.S., Arch Insurance Company, Arch Specialty Insurance Company, Arch Excess & Surplus Insurance Company, Arch Indemnity Insurance Company, Arch Insurance Canada Ltd. (“Arch Insurance Canada”), Alternative Re Limited, Arch Reinsurance Europe Underwriting Designated Activity Company (“Arch Re Europe”), Arch MI U.S., Arch Mortgage Guaranty Company, Arch Mortgage Insurance Designated Activity Company (“Arch MI Europe”), Arch Insurance Company (Europe) Limited (“Arch Insurance Company Europe”), Lloyd’s of London syndicate 2012 and related companies (“Arch Syndicate 2012”), Gulf Re and Watford Re. 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. (b) Premium Revenues and Related Expenses Insurance. Insurance premiums written are generally recorded at the policy inception and are primarily earned on a pro rata basis over the terms of the policies for all products, usually 12 months . Premiums written include estimates in the Company’s programs, specialty lines, lenders products business and for participation in involuntary pools. Such premium estimates are derived from multiple sources which include the historical experience of the underlying business, similar business and available industry information. Unearned premium reserves represent the portion of premiums written that relates to the unexpired terms of in-force insurance policies. Reinsurance. Reinsurance premiums written include amounts reported by brokers and ceding companies, supplemented by the Company’s own estimates of premiums where reports have not been received. The determination of premium estimates requires a review of the Company’s experience with the ceding companies, familiarity with each market, the timing of the reported information, an analysis and understanding of the characteristics of each line of business, and management’s judgment of the impact of various factors, including premium or loss trends, on the volume of business written and ceded to the Company. On an ongoing basis, the Company’s underwriters review the amounts reported by these third parties for reasonableness based on their experience and knowledge of the subject class of business, taking into account the Company’s historical experience with the brokers or ceding companies. In addition, reinsurance contracts under which the Company assumes business generally contain specific provisions which allow the Company to perform audits of the ceding company to ensure compliance with the terms and conditions of the contract, including accurate and timely reporting of information. Based on a review of all available information, management establishes premium estimates where reports have not been received. Premium estimates are updated when new information is received and differences between such estimates and actual amounts are recorded in the period in which estimates are changed or the actual amounts are determined. Reinsurance premiums written are recorded based on the type of contracts the Company writes. Premiums on the Company’s excess of loss and pro rata reinsurance contracts are estimated when the business is underwritten. For excess of loss contracts, premiums are recorded as written based on the terms of the contract. Estimates of premiums written under pro rata contracts are recorded in the period in which the underlying risks are expected to incept and are based on information provided by the brokers and the ceding companies. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term. Reinstatement premiums for the Company’s insurance and reinsurance operations are recognized at the time a loss event occurs, where coverage limits for the remaining life of the contract are reinstated under pre-defined contract terms. Reinstatement premiums, if obligatory, are fully earned when recognized. The accrual of reinstatement premiums is based on an estimate of losses and loss adjustment expenses, which reflects management’s judgment. Premium estimates are reviewed by management at least quarterly. Such review includes a comparison of actual reported premiums to expected ultimate premiums along with a review of the aging and collection of premium estimates. Based on management’s review, the appropriateness of the premium estimates is evaluated, and any adjustment to these estimates is recorded in the period in which it becomes known. Adjustments to premium estimates could be material and such adjustments could directly and significantly impact earnings favorably or unfavorably in the period they are determined because the estimated premium may be fully or substantially earned. A significant portion of amounts included as premiums receivable, which represent estimated premiums written, net of commissions, are not currently due based on the terms of the underlying contracts. Reinsurance premiums written, irrespective of the class of business, are generally earned on a pro rata basis over the terms of the underlying policies or reinsurance contracts. Contracts and policies written on a “losses occurring” basis cover claims that may occur during the term of the contract or policy, which is typically 12 months . Accordingly, the premium is earned evenly over the term. Contracts which are written on a “risks attaching” basis cover claims which attach to the underlying insurance policies written during the terms of such contracts. Premiums earned on such contracts usually extend beyond the original term of the reinsurance contract, typically resulting in recognition of premiums earned over a 24 -month period. Certain of the Company’s reinsurance contracts include provisions that adjust premiums or acquisition expenses based upon the experience under the contracts. Premiums written and earned, as well as related acquisition expenses, are recorded based upon the projected experience under such contracts. The Company also writes certain reinsurance business that is intended to provide insurers with risk management solutions that complement traditional reinsurance. Under these contracts, the Company assumes a measured amount of insurance risk in exchange for an anticipated margin, which is typically lower than on traditional reinsurance contracts. The terms and conditions of these contracts may include additional or return premiums based on loss experience, loss corridors, sublimits and caps. Examples of such business include aggregate stop-loss coverages, financial quota share coverages and multi-year retrospectively rated excess of loss coverages. If these contracts are deemed to transfer risk, they are accounted for as reinsurance. Mortgage. Mortgage guaranty insurance policies are contracts that are generally non-cancelable by the insurer, are renewable at a fixed price, and provide for payment of premiums on a monthly, annual or single basis. Upon renewal, the Company is not able to re-underwrite or re-price its policies. Consistent with industry accounting practices, premiums written on a monthly basis are earned as coverage is provided. Premiums written on an annual basis are amortized on a monthly pro rata basis over the year of coverage. Primary mortgage insurance premiums written on policies covering more than one year are referred to as single premiums. A portion of the revenue from single premiums is recognized in premiums earned in the current period, and the remaining portion is deferred as unearned premiums and earned over the estimated expiration of risk of the policy. If single premium policies related to insured loans are canceled due to repayment by the borrower and the policy is a non-refundable product, the remaining unearned premium related to each canceled policy is recognized as earned premium upon notification of the cancellation. Unearned premiums represent the portion of premiums written that is applicable to the estimated unexpired risk of insured loans. A portion of premium payments may be refundable if the insured cancels coverage, which generally occurs when the loan is repaid, the loan amortizes to a sufficiently low amount to trigger a lender permitted or legally required cancellation, or the value of the property has increased sufficiently in accordance with the terms of the contract. Premium refunds reduce premiums earned in the consolidated statements of income. Generally, only unearned premiums are refundable. However, when the Company pays a claim on a delinquent loan, all servicer paid premiums received on the delinquent loan covering any period after the default date will be refunded, in accordance with the terms of the contract. Acquisition Costs. Acquisition expenses and other expenses related to the Company’s underwriting operations that vary with, and are directly related to, the successful acquisition or renewal of business are deferred and amortized based on the type of contract. For property and casualty insurance and reinsurance contracts, deferred acquisition costs are amortized over the period in which the related premiums are earned. Consistent with mortgage insurance industry accounting practice, amortization of acquisition costs related to the mortgage insurance contracts for each underwriting year’s book of business is recorded in proportion to estimated gross profits. Estimated gross profits are comprised of earned premiums and losses and loss adjustment expenses. For each underwriting year, the Company estimates the rate of amortization to reflect actual experience and any changes to persistency or loss development. Acquisition expenses, net of ceding commissions received from reinsurers, consist principally of commissions and premium taxes paid to obtain the Company’s business. Other operating expenses also include expenses that vary with, and are directly related to, the successful acquisition of business. Deferred acquisition costs are carried at their estimated realizable value and take into account anticipated losses and loss adjustment expenses, based on historical and current experience, and anticipated investment income. A premium deficiency occurs if the sum of anticipated losses and loss adjustment expenses, unamortized acquisition costs and maintenance costs exceed unearned premiums (including expected future premiums) and anticipated investment income. A premium deficiency reserve (“PDR”) is recorded by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. To assess the need for a PDR on mortgage exposures, the Company develops loss projections based on modeled loan defaults related to its current policies in force. This projection is based on recent trends in default experience, severity and rates of defaulted loans moving to claim, as well as recent trends in the rate at which loans are prepaid. Evaluating the expected profitability of the Company’s existing mortgage insurance business and the need for a PDR for its mortgage business involves significant reliance upon assumptions and estimates with regard to the likelihood, magnitude and timing of potential losses and premium revenues. No premium deficiency charges were recorded by the Company during 2015 , 2014 or 2013 . (c) Deposit Accounting Certain assumed reinsurance contracts that are deemed not to transfer insurance risk, are accounted for using the deposit method of accounting. However, it is possible that the Company could incur financial losses on such contracts. Management exercises significant judgment in the assumptions used in determining whether assumed contracts should be accounted for as reinsurance contracts or deposit contracts. For those contracts that contain only significant underwriting risk, the estimated profit margin is deferred and amortized over the contract period and such amount is included in the Company’s underwriting results. When the estimated profit margin is explicit, the margin is reflected as other underwriting income and any adverse financial results on such contracts are reflected as incurred losses. When the estimated profit margin is implicit, the margin is reflected as an offset to paid losses and any adverse financial results on such contracts are reflected as incurred losses. Additional judgments are required when applying the accounting guidance with respect to the revenue recognition criteria for contracts deemed to transfer only significant underwriting risk. For those contracts that contain only significant timing risk, an accretion rate is established at inception of the contract based on actuarial estimates whereby the deposit accounting liability is increased to the estimated amount payable over the contract term. The accretion on the deposit is based on the expected rate of return required to fund the expected future payment obligations. Periodically the Company reassesses the estimated ultimate liability and the related expected rate of return. The accretion of the deposit accounting liability as well as changes to the estimated ultimate liability and the accretion rate would be reflected as part of interest expense in the Company’s results of operations. Any negative accretion in a deposit accounting liability is shown in other underwriting income in the Company’s results of operations. Deposit accounting liabilities totaled $260.4 million and $327.4 million , respectively, at December 31, 2015 and 2014 . Under some of these contracts, the ceding company retains the related assets on a funds-held basis. In those instances, the Company records the asset as a deposit accounting asset. Deposit accounting assets of $234.5 million and $284.4 million , respectively, at December 31, 2015 and 2014 are included in “Other assets” on the Company’s balance sheet. Interest income produced by those assets are recorded as part of net investment income in the Company's results of operations. (d) Retroactive Accounting Retroactive reinsurance reimburses a ceding company for liabilities incurred as a result of past insurable events covered by the underlying policies reinsured. In certain instances, reinsurance contracts cover losses both on a prospective basis and on a retroactive basis and, accordingly, the Company bifurcates the prospective and retrospective elements of these reinsurance contracts and accounts for each element separately where practical. Underwriting income generated in connection with retroactive reinsurance contracts is deferred and amortized into income over the settlement period while losses are charged to income immediately. Subsequent changes in estimated or actual cash flows under such retroactive reinsurance contracts are accounted for by adjusting the previously deferred amount to the balance that would have existed had the revised estimate been available at the inception of the reinsurance transaction, with a corresponding charge or credit to income. (e) Reinsurance Ceded In the normal course of business, the Company purchases reinsurance to increase capacity and to limit the impact of individual losses and events on its underwriting results by reinsuring certain levels of risk with other insurance enterprises or reinsurers. The Company uses pro rata, excess of loss and facultative reinsurance contracts. Reinsurance ceding commissions are recognized as a reduction to acquisition costs on a pro rata basis over the period of risk while the portion of such commissions that will be earned in the future is deferred. The accompanying consolidated statement of income reflects premiums and losses and loss adjustment expenses and acquisition costs, net of reinsurance ceded. See Note 7 for information on the Company's reinsurance usage. Ceded unearned premiums are reported as prepaid reinsurance premiums and estimated amounts of reinsurance recoverable on unpaid losses are reported as unpaid losses and loss adjustment expenses recoverable. Reinsurance premiums ceded and unpaid losses and loss adjustment expenses recoverable are estimated in a manner consistent with that of the original policies issued and the terms of the reinsurance contracts. If the reinsurers are unable to satisfy their obligations under the agreements, the Company’s insurance or reinsurance subsidiaries would be liable for such defaulted amounts. (f) Cash Cash includes cash equivalents, which are investments with original maturities of three months or less that are not managed by external or internal investment advisors. (g) Investments The Company currently classifies substantially all of its fixed maturity investments, equity securities and short-term investments as “available for sale” and, accordingly, they are carried at estimated fair value (also known as fair value) with the changes in fair value recorded as an unrealized gain or loss component of accumulated other comprehensive income in shareholders’ equity. The fair value of fixed maturity securities and equity securities is generally determined from quotations received from nationally recognized pricing services, or when such prices are not available, by reference to broker or underwriter bid indications. Short-term investments comprise securities due to mature within one year of the date of issue. Short-term investments include certain cash equivalents which are part of investment portfolios under the management of external and internal investment managers. The Company participates in a securities lending program as a mechanism for generating additional interest income on its fixed income portfolio. Under the security lending agreements, certain of its fixed income portfolio securities are loaned to third parties, primarily major brokerage firms, for short periods of time through a lending agent. Such securities have been reclassified as “Fixed maturities and short-term investments pledged under securities lending agreements, at fair value.” 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. Collateral received is required at a rate of 102% or greater of the fair value of the loaned securities including accrued investment income and is monitored and maintained by the lending agent. Such collateral is reflected as “Collateral received under securities lending agreements, at fair value.” The Company’s investment portfolio includes certain funds that, due to their ownership structure, are accounted for by the Company using the equity method. In applying the equity method, these 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 fair 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. Changes in the carrying value of such investments are recorded in net income as “Equity in net income (loss) of investment funds accounted for using the equity method.” As such, fluctuations in the carrying value of the investment funds accounted for using the equity method may increase the volatility of the Company’s reported results of operations. Other investments include funds and separately managed accounts with holdings in Asian and emerging markets, fixed maturities, term loans and other investment strategies. The fair value for certain of the Company’s other investments are determined using net asset values (“NAVs”) as advised by external fund managers. The NAV is based on the fund manager’s valuation of the underlying holdings in accordance with the fund’s governing documents. Certain of the funds are accounted for as available for sale equity securities, regardless of the nature of the investments held within the fund. The Company elected to carry certain fixed maturity securities, equity securities and other investments at fair value under the fair value option afforded by accounting guidance regarding the fair value option for financial assets and liabilities. Changes in fair value of investments accounted for using the fair value option are included in “Net realized gains (losses).” The primary reasons for electing the fair value option were to address simplification and cost-benefit considerations. The Company invests in limited partner interests and shares of limited liability companies. Such amounts are included in investments accounted for using the equity method, other investments available for sale and investments accounted for using the fair value option. These investments can often have characteristics of a variable interest entity (“VIE”). A VIE refers to entities that have 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 the characteristic of a controlling financial interest. If the Company is determined to be the primary beneficiary, it is required to consolidate the VIE. The primary beneficiary 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. At inception of the VIE as well as on an ongoing basis, the Company determines whether it is the primary beneficiary based on an analysis of the Company’s level of involvement in the VIE, the contractual terms, and the overall structure of the VIE. 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 Company performs quarterly reviews of its investments to determine whether declines in fair value below the cost basis are considered other-than-temporary in accordance with applicable accounting guidance regarding the recognition and presentation of other-than-temporary impairments (“OTTI”). The process of determining whether a security is other-than-temporarily impaired requires judgment and involves analyzing many factors. These factors include (i) an analysis of the liquidity, business prospects and overall financial condition of the issuer, (ii) the time period in which there was a significant decline in value, (iii) the significance of the decline and (iv) the analysis of specific credit events. The Company evaluates the unrealized losses of its equity securities by issuer and forecasts a reasonable period of time by which the fair value of the securities would increase and the Company would recover its cost. If the Company is unable to forecast a reasonable period of time in which to recover the cost of its equity securities, a net impairment loss in earnings equivalent to the entire unrealized loss is recognized. When there are credit-related losses associated with debt securities for which the Company does not have an intent to sell and it is more likely than not that it will not be required to sell the security before recovery of its cost basis, the amount of the OTTI related to a credit loss is recognized in earnings and the amount of the OTTI related to other factors ( e.g. , interest rates, market conditions, etc.) is recorded as a component of other comprehensive income (loss). The amount of the credit loss of an impaired debt security is the difference between the amortized cost and the greater of (i) the present value of expected future cash flows and (ii) the fair value of the security. In instances where no credit loss exists but it is more likely than not that the Company will have to sell the debt security prior to the anticipated recovery, the decline in fair value below amortized cost is recognized as an OTTI in earnings. In periods after the recognition of an OTTI on debt securities, the Company accounts for such securities as if they had been purchased on the measurement date of the OTTI at an amortized cost basis equal to the previous amortized cost basis less the OTTI recognized in earnings. For debt securities for which OTTI were recognized in earnings, the difference between the new amortized cost basis and the cash flows expected to be collected will be accreted or amortized into net investment income. See Note 8 , “Investment Information—Other-Than-Temporary Impairments” for additional information. Net investment income includes interest and dividend income together with amortization of market premiums and discounts and is net of investment management and custody fees. Anticipated prepayments and expected maturities are used in applying the interest method for certain investments such as mortgage and other asset-backed securities. When actual prepayments differ significantly from anticipated prepayments, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The net investment in such securities is adjusted to the amount that would have existed had the new effective yield been applied since the acquisition of the security. Such adjustments, if any, are included in net investment income when determined. Investment gains or losses realized on the sale of investments, except for certain fund investments, are determined on a first-in, first-out basis and are reflected in net income. Investments gains or losses realized on the sale of certain fund investments are determined on an average cost basis. Unrealized appreciation or decline in the value of available for sale securities, which are carried at fair value, is excluded from net income and recorded as a separate component of accumulated other comprehensive income, net of applicable deferred income tax. (h) Derivative Instruments The Company recognizes all derivative instruments, including embedded derivative instruments, at fair value in the Consolidated Balance Sheets. The Company employs the use of derivative instruments within its operations to mitigate risks arising from assets and liabilities held in foreign currencies as well as part of its overall investment strategy. For such instruments, changes in assets and liabilities measured at fair value are recorded as “Net realized gains” in the consolidated statements of income. In addition, the Company’s derivative instruments include amounts related to underwriting activities where an insurance or reinsurance contract meets the accounting definition of a derivative instrument. For such contracts, changes in fair value are reflected in “Other underwriting income” in the consolidated statements of income as the underlying contract originates from the Company’s underwriting operations. For the periods ended 2015 , 2014 , and 2013 , the Company did not designate any derivative instruments as hedges under the relevant accounting guidance. See Note 10 for information on the Company’s derivative instruments. (i) Reserves for Losses and Loss Adjustment Expenses Insurance and Reinsurance. The reserve for losses and loss adjustment expenses consists of estimates of unpaid reported losses and loss adjustment expenses and estimates for losses incurred but not reported. The reserve for unpaid reported losses and loss adjustment expenses, established by management based on reports from ceding companies and claims from insureds, excludes estimates of amounts related to losses under high deductible policies, and represents the estimated ultimate cost of events or conditions that have been reported to or specifically identified by the Company. Such reserves are supplemented by management’s estimates of reserves for losses incurred for which reports or claims have not been received. The Company’s reserves are based on a combination of reserving methods, incorporating both Company and industry loss development patterns. The Company selects the initial expected loss and loss adjustment expense ratios based on information derived by its underwriters and actuaries during the initial pricing of the business, supplemented by industry data where appropriate. Such ratios consider, among other things, rate changes and changes in terms and conditions that have been observed in the market. These estimates are reviewed regularly and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments, if any, are reflected in income in the period in which they are determined. As actual loss information has been reported, the Company has developed its own loss experience and its reserving methods include other actuarial techniques. Over time, such techniques have been given further weight in its reserving process based on the continuing maturation of the Company’s reserves. Inherent in the estimates of ultimate losses and loss adjustment expenses are expected trends in claims severity and frequency and other factors which may vary significantly as claims are settled. Accordingly, ultimate losses and loss adjustment expenses may differ materially from the amounts recorded in the accompanying consolidated financial statements. Losses and loss adjustment expenses are recorded on an undiscounted basis, except for excess workers’ compensation and employers’ liability business written by the Company’s insurance operations. Mortgage. The reserves for mortgage guaranty insurance losses and loss adjustment expenses are the estimated claim settlement costs on notices of default that have been received by the Company, as well as loan defaults that have been incurred but have not been reported by the lenders. Consistent with primary mortgage insurance industry accounting practice, the Company does not establish loss reserves for future claims on insured loans that are not currently in default (defined as two consecutive missed payments). The Company establishes loss reserves on a case-by-case basis when insured loans are identified as currently in default using estimated claim rates and average claim sizes for each report year, net of any salvage recoverable. The Company also reserves for defaults that have occurred but have not yet been reported to the Company prior to the close of an accounting period. To determine this reserve, the Company estimates the number of defaults not yet reported using historical information regarding late reported delinquencies and applies estimated claim rates and claim sizes for the estimated defaults not yet reported. The establishment of reserves across the Company’s segments is an inherently uncertain process, are necessarily based on estimates, and the ultimate net cost may vary from such estimates. The methods for making such estimates and for establishing the resulting liability are reviewed and updated using the most current information available. Any resulting adjustments, which may be material, are reflected in current operations. (j) Contractholder Receivables and Payables and Collateral Held for Insured Obligations Certain insurance policies written by the Company’s insurance operations feature large deductibles, primarily in its construction and national accounts lines of business. Under such contracts, the Company is obligated to pay the claimant for the full amount of the claim. The Company is subsequently reimbursed by the policyholder for the deductible amount. These amounts are include

Variable Interest Entity and No

Variable Interest Entity and Noncontrolling Interests	12 Months Ended
	Dec. 31, 2015
Variable Interest Entity and Noncontrolling Interest Disclosure [Abstract]
Variable Interest Entity and Noncontrolling Interests	Variable Interest Entity and Noncontrolling Interests Variable interest entity A 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. In March 2014, Watford Re raised approximately $1.1 billion of capital consisting of $907.3 million in common equity ( $895.6 million net of issuance costs) and $226.6 million in preference equity ( $219.2 million net of issuance costs and discount). 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. Arch Underwriters Ltd. (“AUL”), a subsidiary of the Company, acts as Watford Re’s reinsurance underwriting manager, and Highbridge Principal Strategies, LLC (“Highbridge”), a subsidiary of JPMorgan Chase & Co., manages Watford Re’s investment assets, each under separate long term services agreements. In connection with the capital raise at Watford Re, warrants to purchase a total of 1.7 million common shares were issued to the Company and Highbridge. The warrants are only exercisable if Watford Re has consummated an initial public offering of its common shares or otherwise effected a listing of its common shares on a U.S. national securities exchange and certain targeted returns are achieved for existing common shareholders. The warrants expire on March 25, 2020. John Rathgeber, previously Vice Chairman of Arch Worldwide Reinsurance Group, was named CEO of Watford Re. In addition, Marc Grandisson, President and COO of ACGL, and Nicolas Papadopoulo, CEO Reinsurance Group, were appointed to the board of directors of Watford Re. The Company concluded that Watford Re is a VIE due to both the reinsurance management services agreement with AUL and the investment management agreement with Highbridge. Both of these agreements provide for services for an extended period of time with limited termination rights by Watford Re. In addition, these agreements allow for both AUL and Highbridge to participate in the favorable results of Watford Re in the form of performance fees. To determine if the Company is the primary beneficiary of Watford Re, the Company concluded that the most significant activity of Watford Re pertains to the insurance activities arising from the reinsurance management services agreement. In addition, the Company factored into its analysis qualitative aspects of its relationship with Watford Re that are indicative of power to direct the insurance activities. As such, the Company concluded that it is the primary beneficiary of Watford Re and includes the results of Watford Re in its consolidated financial statements. The Company concluded that Watford Re represents a separate operating segment and provides the income statement and total investable assets, total assets and total liabilities of Watford Re within Note 5 . At December 31, 2015 , Watford Re’s liabilities included unearned premiums of $250.0 million and reserves for losses and loss adjustment expenses of $291.0 million , some of which is related to transactions with the Company, along with $430.4 million of revolving credit agreement borrowings (see Note 15 ). During 2015, Watford Re generated $293.7 million of cash provided by operating activities and $361.9 million of cash provided by financing activities, partially offset by $556.8 million of cash used for investing activities. At December 31, 2014, Watford Re’s liabilities included unearned premiums of $180.0 million and reserves for losses and loss adjustment expenses of $66.3 million , some of which is related to transactions with the Company. During 2014, Watford Re generated $39.3 million of cash provided by operating activities and $1.16 billion of cash provided by financing activities, partially offset by $1.18 billion of cash used for investing activities. Because Watford Re is an independent company, the assets of Watford Re can be used only to settle obligations of Watford Re and Watford Re is solely responsible for its own liabilities and commitments. The Company’s financial exposure to Watford Re is limited to its investment in Watford Re’s common shares and counterparty credit risk (mitigated by collateral) arising from the reinsurance transactions. 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 December 31, 2015 . 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: December 31, 2015 2014 Balance, beginning of year $ 769,081 $ — Sale of shares to noncontrolling interests — 796,904 Amounts attributable to noncontrolling interests (29,984 ) (27,823 ) Foreign currency translation adjustments (266 ) — Balance, end of year $ 738,831 $ 769,081 Redeemable noncontrolling interests The Company accounts for redeemable noncontrolling interests in the mezzanine section of its consolidated balance sheet. Such redeemable noncontrolling interests relate to the 9,065,200 cumulative redeemable preference shares (“Watford Preference Shares”) issued in late March 2014 with a par value of $0.01 per share and a liquidation preference of $25.00 per share. The Watford Preference Shares were issued at a discounted amount of $24.50 per share. Holders of the Watford Preference Shares will be entitled to receive, if declared by Watford Re’s board, quarterly cash dividends on the last day of March, June, September, and December. Dividends will accrue from the closing date to June 30, 2019 at a fixed rate of 8.5% per annum. From June 30, 2019 and subsequent, dividends will accrue based on a floating rate equal to the 3 month U.S. dollar LIBOR (with a 1% floor) plus a margin based on the difference between the fixed rate and the 5 year mid swap rate to the floating rate as set out on the Bloomberg Screen IRSB 18. The Watford Preference Shares may be redeemed by Watford Re on or after June 30, 2019 or at the option of the preferred shareholders at any time on or after June 30, 2034. Because the redemption features are not solely within the control of Watford Re, the Company accounts for the redeemable noncontrolling interests in the Watford Preference Shares in the mezzanine section of its consolidated balance sheets. Preferred dividends on the Watford Preference Shares, including the accretion of the discount and issuance costs, totaled $19.6 million for 2015 . Preferred dividends, including the accretion of the discount and issuance costs, are included in ‘amounts attributable to noncontrolling interests’ in the Company’s consolidated statements of income. The following table sets forth activity in the redeemable non-controlling interests: December 31, 2015 2014 Balance, beginning of year $ 219,512 $ — Sale of shares to noncontrolling interests — 219,233 Shares acquired by the Company (1) (14,700 ) — Accretion of preference share issuance costs 370 279 Balance, end of year $ 205,182 $ 219,512 (1) During the 2015 second quarter, the Company acquired Gulf Re, which owns 600,000 Watford Preference Shares. Such shares, net of a discount, along with related dividends and accretion of the discount, are eliminated in consolidation. 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’ as summarized in the table below: December 31, 2015 2014 Amounts attributable to non-redeemable noncontrolling interests $ 29,984 $ 27,823 Dividends attributable to redeemable noncontrolling interests (18,828 ) (14,728 ) Net (income) loss attributable to noncontrolling interests $ 11,156 $ 13,095

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2015
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 of ACGL, the President and Chief Operating Officer of ACGL 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 results of Arch MI U.S. and Arch MI Europe, leading providers of mortgage insurance products and services to the U.S. and European markets, respectively. Arch MI U.S. is approved as an eligible mortgage insurer by Federal National Mortgage Association (“Fannie Mae”) and Federal Home Loan Mortgage Corporation (“Freddie Mac”), each a government sponsored enterprise, or “GSE.” The mortgage segment also includes GSE credit risk-sharing transactions and mortgage reinsurance for the U.S. and Australian markets. The corporate (non-underwriting) segment results include net investment income, other income (loss), other expenses incurred by the Company, interest expense, 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, income taxes and items related to the Company’s non-cumulative preferred shares. Such amounts exclude the results of the ‘other’ segment. The ‘other’ segment includes the results of Watford Re (see Note 4 ). 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 Arch common shareholders, summary information regarding net premiums written and earned by major line of business and net premiums written by location: Year Ended December 31, 2015 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,944,018 $ 1,419,022 $ 295,557 $ 4,656,723 $ 488,899 $ 4,797,163 Premiums ceded (898,347 ) (380,614 ) (28,064 ) (1,305,151 ) (22,940 ) (979,632 ) Net premiums written 2,045,671 1,038,408 267,493 3,351,572 465,959 3,817,531 Change in unearned premiums (863 ) 38,727 (53,383 ) (15,519 ) (68,107 ) (83,626 ) Net premiums earned 2,044,808 1,077,135 214,110 3,336,053 397,852 3,733,905 Other underwriting income 1,993 10,606 18,430 31,029 4,468 35,497 Losses and loss adjustment expenses (1,292,647 ) (440,350 ) (40,247 ) (1,773,244 ) (277,659 ) (2,050,903 ) Acquisition expenses, net (299,317 ) (223,632 ) (45,076 ) (568,025 ) (113,451 ) (681,476 ) Other operating expenses (354,416 ) (155,811 ) (82,370 ) (592,597 ) (14,919 ) (607,516 ) Underwriting income (loss) $ 100,421 $ 267,948 $ 64,847 433,216 (3,709 ) 429,507 Net investment income 271,680 76,410 348,090 Net realized gains (losses) (99,133 ) (86,709 ) (185,842 ) Net impairment losses recognized in earnings (20,116 ) — (20,116 ) Equity in net income (loss) of investment funds accounted for using the equity method 25,455 — 25,455 Other income (loss) (399 ) — (399 ) Other expenses (49,745 ) — (49,745 ) Interest expense (41,518 ) (4,356 ) (45,874 ) Net foreign exchange gains (losses) 62,624 3,494 66,118 Income (loss) before income taxes 582,064 (14,870 ) 567,194 Income tax expense (40,612 ) — (40,612 ) Net income (loss) 541,452 (14,870 ) 526,582 Dividends attributable to redeemable noncontrolling interests — (18,828 ) (18,828 ) Amounts attributable to noncontrolling interests — 29,984 29,984 Net income (loss) available to Arch 541,452 (3,714 ) 537,738 Preferred dividends (21,938 ) — (21,938 ) Net income (loss) available to Arch common shareholders $ 519,514 $ (3,714 ) $ 515,800 Underwriting Ratios Loss ratio 63.2 % 40.9 % 18.8 % 53.2 % 69.8 % 54.9 % Acquisition expense ratio 14.6 % 20.8 % 21.1 % 17.0 % 28.5 % 18.3 % Other operating expense ratio 17.3 % 14.5 % 38.5 % 17.8 % 3.7 % 16.3 % Combined ratio 95.1 % 76.2 % 78.4 % 88.0 % 102.0 % 89.5 % Goodwill and intangible assets $ 28,810 $ 1,875 $ 66,846 $ 97,531 $ — $ 97,531 Total investable assets $ 14,644,831 $ 1,696,107 $ 16,340,938 Total assets 21,054,938 2,122,332 23,177,270 Total liabilities 14,956,274 1,072,102 16,028,376 (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. Year Ended December 31, 2014 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 3,008,669 $ 1,527,245 $ 227,356 $ 4,760,394 $ 288,627 $ 4,840,616 Premiums ceded (862,015 ) (261,254 ) (22,519 ) (1,142,912 ) (14,171 ) (948,678 ) Net premiums written 2,146,654 1,265,991 204,837 3,617,482 274,456 3,891,938 Change in unearned premiums (129,284 ) 13,337 (11,264 ) (127,211 ) (170,979 ) (298,190 ) Net premiums earned 2,017,370 1,279,328 193,573 3,490,271 103,477 3,593,748 Other underwriting income 2,135 3,167 4,840 10,142 — 10,142 Losses and loss adjustment expenses (1,260,953 ) (532,450 ) (55,674 ) (1,849,077 ) (70,173 ) (1,919,250 ) Acquisition expenses, net (316,308 ) (261,438 ) (49,400 ) (627,146 ) (30,116 ) (657,262 ) Other operating expenses (335,157 ) (147,964 ) (66,891 ) (550,012 ) (6,268 ) (556,280 ) Underwriting income (loss) $ 107,087 $ 340,643 $ 26,448 474,178 (3,080 ) 471,098 Net investment income 284,336 18,249 302,585 Net realized gains (losses) 133,384 (30,467 ) 102,917 Net impairment losses recognized in earnings (30,150 ) — (30,150 ) Equity in net income (loss) of investment funds accounted for using the equity method 19,883 — 19,883 Other income (loss) (10,252 ) — (10,252 ) Other expenses (47,615 ) (2,329 ) (49,944 ) Interest expense (45,634 ) — (45,634 ) Net foreign exchange gains (losses) 82,658 1,086 83,744 Income (loss) before income taxes 860,788 (16,541 ) 844,247 Income tax expense (22,987 ) — (22,987 ) Net income (loss) 837,801 (16,541 ) 821,260 Dividends attributable to redeemable noncontrolling interests — (14,728 ) (14,728 ) Amounts attributable to noncontrolling interests — 27,823 27,823 Net income (loss) available to Arch 837,801 (3,446 ) 834,355 Preferred dividends (21,938 ) — (21,938 ) Net income (loss) available to Arch common shareholders $ 815,863 $ (3,446 ) $ 812,417 Underwriting Ratios Loss ratio 62.5 % 41.6 % 28.8 % 53.0 % 67.8 % 53.4 % Acquisition expense ratio 15.7 % 20.4 % 25.5 % 18.0 % 29.1 % 18.3 % Other operating expense ratio 16.6 % 11.6 % 34.6 % 15.8 % 6.1 % 15.5 % Combined ratio 94.8 % 73.6 % 88.9 % 86.8 % 103.0 % 87.2 % Goodwill and intangible assets $ 28,331 $ 3,333 $ 77,875 $ 109,539 $ — $ 109,539 Total investable assets $ 14,599,490 $ 1,163,240 $ 15,762,730 Total assets 20,523,565 1,482,516 22,006,081 Total liabilities 14,488,775 398,660 14,887,435 (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. Year Ended December 31, 2013 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,712,509 $ 1,399,621 $ 89,570 $ 4,196,623 $ — $ 4,196,623 Premiums ceded (763,713 ) (86,620 ) — (845,256 ) — (845,256 ) Net premiums written 1,948,796 1,313,001 89,570 3,351,367 — 3,351,367 Change in unearned premiums (72,782 ) (94,329 ) (38,304 ) (205,415 ) — (205,415 ) Net premiums earned 1,876,014 1,218,672 51,266 3,145,952 — 3,145,952 Other underwriting income 2,122 5,258 259 7,639 — 7,639 Losses and loss adjustment expenses (1,188,445 ) (486,236 ) (4,743 ) (1,679,424 ) — (1,679,424 ) Acquisition expenses, net (311,904 ) (234,373 ) (17,826 ) (564,103 ) — (564,103 ) Other operating expenses (315,387 ) (134,563 ) (8,377 ) (458,327 ) — (458,327 ) Underwriting income (loss) $ 62,400 $ 368,758 $ 20,579 451,737 — 451,737 Net investment income 267,219 — 267,219 Net realized gains (losses) 74,018 — 74,018 Net impairment losses recognized in earnings (3,786 ) — (3,786 ) Equity in net income (loss) of investment funds accounted for using the equity method 35,701 — 35,701 Other income (loss) (586 ) — (586 ) Other expenses (42,403 ) — (42,403 ) Interest expense (27,060 ) — (27,060 ) Net foreign exchange gains (losses) (12,335 ) — (12,335 ) Income (loss) before income taxes 742,505 — 742,505 Income tax benefit (32,774 ) — (32,774 ) Net income (loss) 709,731 — 709,731 Dividends attributable to redeemable noncontrolling interests — — — Amounts attributable to noncontrolling interests — — — Net income (loss) available to Arch 709,731 — 709,731 Preferred dividends (21,938 ) — (21,938 ) Net income (loss) available to Arch common shareholders $ 687,793 $ — $ 687,793 Underwriting Ratios Loss ratio 63.3 % 39.9 % 9.3 % 53.4 % — 53.4 % Acquisition expense ratio 16.6 % 19.2 % 34.8 % 17.9 % — 17.9 % Other operating expense ratio 16.8 % 11.0 % 16.3 % 14.6 % — 14.6 % Combined ratio 96.7 % 70.1 % 60.4 % 85.9 % — 85.9 % Goodwill and intangible assets $ 20,419 $ 6,900 $ — $ 27,319 $ — $ 27,319 Total investable assets $ 14,049,525 $ — $ 14,049,525 Total assets 19,557,054 — 19,557,054 Total liabilities 13,909,558 — 13,909,558 (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. The following tables provide summary information regarding net premiums written and earned by major line of business and net premiums written by location: INSURANCE SEGMENT Year Ended December 31, 2015 2014 2013 Net premiums written (1) Professional lines (2) $ 434,024 $ 476,604 $ 476,193 Programs 423,157 480,580 419,673 Construction and national accounts 299,463 286,994 271,110 Excess and surplus casualty (3) 204,856 212,519 149,286 Property, energy, marine and aviation 203,186 244,640 280,551 Travel, accident and health 160,132 145,732 104,903 Lenders products 106,916 100,407 101,576 Other (4) 213,937 199,178 145,504 Total $ 2,045,671 $ 2,146,654 $ 1,948,796 Net premiums earned (1) Professional lines (2) $ 424,968 $ 456,508 $ 491,791 Programs 446,512 460,392 386,840 Construction and national accounts 296,828 277,811 250,729 Excess and surplus casualty (3) 208,091 182,024 118,395 Property, energy, marine and aviation 216,127 244,974 304,294 Travel, accident and health 153,578 127,691 97,135 Lenders products 90,906 94,438 99,847 Other (4) 207,798 173,532 126,983 Total $ 2,044,808 $ 2,017,370 $ 1,876,014 Net premiums written by client location (1) United States $ 1,710,918 $ 1,726,181 $ 1,526,156 Europe 187,020 240,136 226,254 Asia and Pacific 64,638 79,564 95,970 Other 83,095 100,773 100,416 Total $ 2,045,671 $ 2,146,654 $ 1,948,796 Net premiums written by underwriting location (1) United States $ 1,673,867 $ 1,688,887 $ 1,478,930 Europe 317,998 394,430 389,763 Other 53,806 63,337 80,103 Total $ 2,045,671 $ 2,146,654 $ 1,948,796 (1) Insurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions. (2) Includes professional liability, executive assurance and healthcare business. (3) Includes casualty and contract binding business. (4) Includes alternative markets, excess workers' compensation and surety business. REINSURANCE SEGMENT Year Ended December 31, 2015 2014 2013 Net premiums written (1) Casualty (2) $ 303,093 $ 317,996 $ 306,304 Other specialty (3) 298,794 405,126 417,865 Property excluding property catastrophe (4) 280,511 343,043 292,536 Property catastrophe 91,620 137,471 220,749 Marine and aviation 50,834 50,444 64,380 Other (5) 13,556 11,911 11,167 Total $ 1,038,408 $ 1,265,991 $ 1,313,001 Net premiums earned (1) Casualty (2) $ 310,249 $ 327,518 $ 241,774 Other specialty (3) 311,307 424,725 387,630 Property excluding property catastrophe (4) 295,487 303,496 274,719 Property catastrophe 96,865 150,761 232,423 Marine and aviation 50,808 61,118 70,105 Other (5) 12,419 11,710 12,021 Total $ 1,077,135 $ 1,279,328 $ 1,218,672 Net premiums written (1) Pro rata $ 537,556 $ 663,135 $ 692,024 Excess of loss 500,852 602,856 620,977 Total $ 1,038,408 $ 1,265,991 $ 1,313,001 Net premiums earned (1) Pro rata $ 563,585 $ 686,201 $ 608,586 Excess of loss 513,550 593,127 610,086 Total $ 1,077,135 $ 1,279,328 $ 1,218,672 Net premiums written by client location (1) United States $ 470,484 $ 589,255 $ 706,388 Europe 307,165 355,735 327,059 Asia and Pacific 94,609 142,626 94,252 Bermuda 80,888 77,620 87,047 Other 85,262 100,755 98,255 Total $ 1,038,408 $ 1,265,991 $ 1,313,001 Net premiums written by underwriting location (1) United States $ 439,190 $ 492,891 $ 507,183 Bermuda 281,985 394,351 459,467 Europe 298,790 343,823 309,129 Other 18,443 34,926 37,222 Total $ 1,038,408 $ 1,265,991 $ 1,313,001 (1) Reinsurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions. (2) Includes executive assurance, professional liability, workers’ compensation, excess motor, healthcare and other. (3) Includes proportional motor, surety, accident and health, workers’ compensation catastrophe, agriculture, trade credit and other. (4) Includes facultative business. (5) Includes life, casualty clash and other. Year Ended December 31, MORTGAGE SEGMENT 2015 2014 2013 Net premiums written by client location United States $ 193,617 $ 184,333 $ 63,692 Other 73,876 20,504 25,878 Total $ 267,493 $ 204,837 $ 89,570 Net premiums written by underwriting location United States $ 125,317 $ 98,809 $ — Other 142,176 106,028 89,570 Total $ 267,493 $ 204,837 $ 89,570 Net premiums earned by client location United States $ 202,930 $ 187,194 $ 49,045 Other 11,180 6,379 2,221 Total $ 214,110 $ 193,573 $ 51,266 Net premiums earned by underwriting location United States $ 113,062 $ 92,236 $ — Other 101,048 101,337 51,266 Total $ 214,110 $ 193,573 $ 51,266 OTHER SEGMENT Year Ended December 31, 2015 2014 2013 Net premiums written (1) Casualty (2) $ 320,619 $ 179,054 $ — Other specialty (3) 112,666 66,524 — Property catastrophe 12,441 9,280 — Property excluding property catastrophe 2,892 564 — Marine and aviation 1,256 1,251 — Other (4) 16,085 17,783 — Total $ 465,959 $ 274,456 $ — Net premiums earned (1) Casualty (2) $ 275,708 $ 72,395 $ — Other specialty (3) 101,588 24,157 — Property catastrophe 12,540 5,115 — Property excluding property catastrophe 1,340 182 — Marine and aviation 1,585 789 — Other (4) 5,091 839 — Total $ 397,852 $ 103,477 $ — Net premiums written by client location (1) United States $ 350,228 $ 186,795 $ — Europe 67,279 54,131 — Bermuda 39,414 27,977 — Other 9,038 5,553 — Total $ 465,959 $ 274,456 $ — (1) Other segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions. (2) Includes professional liability, excess motor, programs and other. (3) Includes proportional motor and other. (4) Includes mortgage and other.

Reserve for Losses and Loss Adj

Reserve for Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2015
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: Year Ended December 31, 2015 2014 2013 Reserve for losses and loss adjustment expenses at beginning of year $ 9,036,448 $ 8,824,696 $ 8,933,292 Unpaid losses and loss adjustment expenses recoverable 1,778,303 1,748,250 1,829,070 Net reserve for losses and loss adjustment expenses at beginning of year 7,258,145 7,076,446 7,104,222 Net incurred losses and loss adjustment expenses relating to losses occurring in: Current year 2,336,026 2,246,152 1,943,466 Prior years (285,123 ) (326,902 ) (264,042 ) Total net incurred losses and loss adjustment expenses 2,050,903 1,919,250 1,679,424 Net losses and loss adjustment expense reserves of acquired business (1) 262 120,671 — Foreign exchange (gains) losses (143,653 ) (160,486 ) 1,617 Net paid losses and loss adjustment expenses relating to losses occurring in: Current year (454,179 ) (347,270 ) (288,114 ) Prior years (1,415,065 ) (1,350,466 ) (1,420,703 ) Total net paid losses and loss adjustment expenses (1,869,244 ) (1,697,736 ) (1,708,817 ) Net reserve for losses and loss adjustment expenses at end of year 7,296,413 7,258,145 7,076,446 Unpaid losses and loss adjustment expenses recoverable 1,828,837 1,778,303 1,748,250 Reserve for losses and loss adjustment expenses at end of year $ 9,125,250 $ 9,036,448 $ 8,824,696 (1) 2014 amount relates to the Company’s acquisition of Arch MI U.S. 2015 Prior Year Reserve Development During 2015, the Company recorded estimated net favorable development on prior year loss reserves of $285.1 million , which consisted of $224.8 million from the reinsurance segment, $47.2 million from the insurance segment, $12.3 million from the mortgage segment and $0.8 million from the ‘other’ segment. The reinsurance segment’s net favorable development of $224.8 million , or 20.9 points of net earned premium, consisted of $107.6 million from short-tailed lines and $117.2 million of net favorable development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines included $80.9 million from property catastrophe and property other than property catastrophe reserves, primarily from the 2011 to 2014 underwriting years ( i.e. , losses attributable to contracts having an inception or renewal date within the given twelve-month period). Contained within this release was favorable development of $11.8 million from the 2005 to 2014 named catastrophic events. 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 2015 . Net favorable development of $117.2 million in medium-tailed and long-tailed lines included reductions in casualty reserves of $99.7 million , primarily from the 2003 to 2006 underwriting years and the 2008 and 2009 underwriting years, and marine and aviation reserves of $11.7 million , primarily from the 2008 to 2012 underwriting years. The balance of net favorable development was spread across various lines and underwriting years. The insurance segment’s net favorable development of $47.2 million , or 2.3 points of net earned premium, consisted of $27.3 million of net favorable development from short-tailed lines and $19.9 million of net favorable development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines predominantly consisted of $32.4 million of net favorable development in property lines, primarily from the 2011 to 2014 accident years ( i.e. , the year in which a loss occurred). Contained within this short tail release was favorable development of $5.7 million from 2005 to 2014 named catastrophic events. Net favorable development in medium-tailed and long-tailed lines of $19.9 million included $29.7 million of net favorable development on professional lines, primarily from the 2005 to 2010 accident years, partially offset by $15.0 million of net adverse development in program business, primarily from the 2013 and 2014 accident years. The adverse development in program business was driven by a few programs that were non-renewed in 2015 and early in 2016. The mortgage segment’s net favorable development of $12.3 million , or 5.7 points of net earned premium, included $11.1 million of favorable development on Arch MI U.S. business, reflecting a decrease in the number of delinquent loans and a lower claim rate on such loans. Such development was primarily from the 2003 to 2008 origination years. The mortgage segment also experienced net favorable development of $1.2 million on U.S. mortgage reinsurance business. 2014 Prior Year Reserve Development During 2014 , the Company recorded estimated net favorable development on prior year loss reserves of $326.9 million , which consisted of $267.3 million from the reinsurance segment, $58.7 million from the insurance segment and $0.9 million from the mortgage segment. The reinsurance segment’s net favorable development of $267.3 million , or 20.9 points of net earned premium, consisted of $146.7 million from short-tailed lines and $120.6 million of net favorable development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines included $107.6 million from property catastrophe and property other than property catastrophe reserves, primarily from the 2011 to 2013 underwriting years. Contained within this release was favorable development of $23.3 million from the 2005 to 2013 named catastrophic events. 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 2014 . Net favorable development of $120.6 million in medium-tailed and long-tailed lines included reductions in casualty reserves of $101.6 million , primarily from the 2003 to 2006 underwriting years and the 2009 and 2010 underwriting years, and marine and aviation reserves of $14.7 million , primarily from the 2008 to 2012 underwriting years. The balance of net favorable development was spread across various lines and underwriting years. The insurance segment’s net favorable development of $58.7 million , or 2.9 points of net earned premium, consisted of $73.5 million of net favorable development from short-tailed lines, partially offset by $14.8 million of net adverse development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines predominantly consisted of $60.5 million of net favorable development in property lines, primarily from the 2008 to 2013 accident years, with the balance emanating from lenders products, primarily from the 2012 accident year, and travel and accident, primarily from the 2012 and 2013 accident years. Contained within this short tail release was favorable development of $7.9 million from 2005 to 2013 named catastrophic events. Net adverse development in medium-tailed and long-tailed lines of $14.8 million included a net increase of $41.3 million in construction reserves, primarily from the 2009 to 2013 accident years. The adverse development in construction was largely driven by general liability claims involving New York labor law matters. In addition, the insurance segment experienced $26.2 million of net adverse development in program business, primarily from the 2011 and 2012 accident years. Such amounts were partially offset by $39.0 million of net favorable development on professional lines, primarily from the 2003 to 2011 accident years, and $7.8 million of net favorable development on surety business, primarily from the 2011 to 2013 accident years. 2013 Prior Year Reserve Development During 2013 , the Company recorded estimated net favorable development on prior year loss reserves of $264.0 million , which consisted of $217.9 million from the reinsurance segment, $45.1 million from the insurance segment and $1.0 million from the mortgage segment. The reinsurance segment’s net favorable development of $217.9 million , or 17.9 points of net earned premium, consisted of $111.1 million from short-tailed lines and $106.8 million of net favorable development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines included $110.1 million from property catastrophe and property other than property catastrophe reserves, primarily from the 2009 to 2012 underwriting years. Contained within this release was favorable development of $28.6 million from the 2005 to 2012 named catastrophic events. 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 2013 . Net favorable development of $106.8 million in medium-tailed and long-tailed lines included reductions in casualty reserves of $98.8 million , primarily from the 2003 to 2009 underwriting years, and marine and aviation reserves of $8.1 million , primarily from the 2007 and 2009 underwriting years. The balance of net favorable development was spread across various lines and underwriting years. The insurance segment’s net favorable development of $45.1 million , or 2.4 points of net earned premium, consisted of $67.0 million of net favorable development from short-tailed lines, partially offset by $21.9 million of net adverse development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines predominantly consisted of $62.4 million of net favorable development in property lines from the 2008 to 2011 accident years, with the balance emanating from lenders products, primarily from the 2011 and 2012 accident years, and travel and accident, primarily from the 2009 and 2010 accident years. Contained within this short tail release was favorable development of $15.9 million from 2005 to 2012 named catastrophic events. Net adverse development in medium-tailed and long-tailed lines of $21.9 million included a net increase of $28.0 million in specialty casualty reserves. Such development primarily stemmed from losses in two captive programs written by the insurance segment's Canadian operation, which was partially offset by favorable development in non-captive business, and from three large excess casualty claims in the insurance segment's U.S. operation, all of the above in the more recent accident years. In addition, the insurance segment experienced $26.2 million of net adverse development in program business, with nearly 90% of this development emanating from a single canceled program whose last inception year was 2011. Such amounts were partially offset by net favorable development spread across various lines and accident years.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2015
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance In the normal course of business, the Company’s insurance subsidiaries cede a portion of their premium through pro rata and excess of loss reinsurance agreements on a treaty or facultative basis. The Company’s reinsurance subsidiaries participate in “common account” retrocessional arrangements for certain pro rata treaties. Such arrangements reduce the effect of individual or aggregate losses to all companies participating on such treaties, including the reinsurers, such as the Company’s reinsurance subsidiaries, and the ceding company. In addition, the Company’s reinsurance subsidiaries may purchase retrocessional coverage as part of their risk management program. Reinsurance recoverables are recorded as assets, predicated on the reinsurers’ ability to meet their obligations under the reinsurance agreements. If the reinsurers are unable to satisfy their obligations under the agreements, the Company’s insurance or reinsurance subsidiaries would be liable for such defaulted amounts. The effects of reinsurance on the Company’s written and earned premiums and losses and loss adjustment expenses with unaffiliated reinsurers were as follows: Year Ended December 31, 2015 2014 2013 Premiums Written Direct $ 3,086,919 $ 3,100,946 $ 2,754,582 Assumed 1,710,244 1,739,670 1,442,041 Ceded (979,632 ) (948,678 ) (845,256 ) Net $ 3,817,531 $ 3,891,938 $ 3,351,367 Premiums Earned Direct $ 3,002,508 $ 2,914,755 $ 2,666,104 Assumed 1,659,456 1,574,049 1,296,048 Ceded (928,059 ) (895,056 ) (816,200 ) Net $ 3,733,905 $ 3,593,748 $ 3,145,952 Losses and Loss Adjustment Expenses Direct $ 1,830,785 $ 1,763,492 $ 1,603,369 Assumed 752,304 621,346 450,618 Ceded (532,186 ) (465,588 ) (374,563 ) Net $ 2,050,903 $ 1,919,250 $ 1,679,424 The Company monitors the financial condition of its reinsurers and attempts to place coverages only with substantial, financially sound carriers. At December 31, 2015 , approximately 77.9% of the Company’s reinsurance recoverables on paid and unpaid losses (not including prepaid reinsurance premiums) of $1.87 billion were due from carriers which had an A.M. Best rating of “A-” or better while 22.0% were from companies not rated, a substantial portion of which was collateralized through reinsurance trusts or letters of credit. The largest reinsurance recoverables from any one carrier was approximately 3.4% of the Company’s total shareholders’ equity at December 31, 2015 . At December 31, 2014 , approximately 83.0% of the Company’s reinsurance recoverables on paid and unpaid losses (not including prepaid reinsurance premiums) of $1.81 billion were due from carriers which had an A.M. Best rating of “A-” or better while 17.0% were from companies not rated, a substantial portion of which was collateralized through reinsurance trusts or letters of credit. The largest reinsurance recoverables from any one carrier was approximately 3.7% of the Company’s total shareholders’ equity at December 31, 2014 . Although the Company has not experienced any material credit losses to date, an inability of its reinsurers or retrocessionaires to meet their obligations to it over the relevant exposure periods for any reason could have a material adverse effect on its financial condition and results of operations.

Investment Information

Investment Information	12 Months Ended
	Dec. 31, 2015
Disclosure Investment Information [Abstract]
Investment Information	Investment Information At December 31, 2015 , total investable assets of $16.34 billion included $14.64 billion managed by the Company and $1.70 billion attributable to Watford Re. Available For Sale Securities The following table summarizes the fair value and cost or amortized cost of the Company’s securities classified as available for sale: Estimated Gross Gross Cost or OTTI Fair Unrealized Unrealized Amortized Unrealized Value Gains Losses Cost Losses (2) December 31, 2015 Fixed maturities (1): Corporate bonds $ 2,725,729 $ 15,978 $ (60,508 ) $ 2,770,259 $ (3,553 ) Mortgage backed securities 754,870 9,872 (5,334 ) 750,332 (3,350 ) Municipal bonds 1,626,281 27,014 (1,534 ) 1,600,801 — Commercial mortgage backed securities 764,152 3,269 (6,978 ) 767,861 — U.S. government and government agencies 2,423,455 6,228 (9,978 ) 2,427,205 — Non-U.S. government securities 917,664 10,414 (39,122 ) 946,372 — Asset backed securities 1,620,506 3,307 (12,951 ) 1,630,150 (22 ) Total 10,832,657 76,082 (136,405 ) 10,892,980 (6,925 ) Equity securities 629,182 94,341 (17,796 ) 552,637 — Other investments 300,476 43,798 (4,665 ) 261,343 — Short-term investments 587,904 187 (3,425 ) 591,142 — Total $ 12,350,219 $ 214,408 $ (162,291 ) $ 12,298,102 $ (6,925 ) December 31, 2014 Fixed maturities (1): Corporate bonds $ 3,108,513 $ 37,928 $ (38,974 ) $ 3,109,559 $ (317 ) Mortgage backed securities 943,343 18,843 (3,842 ) 928,342 (3,307 ) Municipal bonds 1,494,122 31,227 (1,044 ) 1,463,939 — Commercial mortgage backed securities 1,114,528 14,594 (3,822 ) 1,103,756 — U.S. government and government agencies 1,447,972 8,345 (1,760 ) 1,441,387 — Non-U.S. government securities 1,015,153 21,311 (37,203 ) 1,031,045 — Asset backed securities 1,677,941 8,425 (6,089 ) 1,675,605 (22 ) Total 10,801,572 140,673 (92,734 ) 10,753,633 (3,646 ) Equity securities 658,182 109,012 (13,364 ) 562,534 — Other investments 296,224 31,839 (362 ) 264,747 — Short-term investments 797,226 738 (5,270 ) 801,758 — Total $ 12,553,204 $ 282,262 $ (111,730 ) $ 12,382,672 $ (3,646 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments 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 December 31, 2015 , the net unrealized loss related to securities for which a non-credit OTTI was recognized in AOCI was $1.4 million , compared to a net unrealized gain of $0.9 million at December 31, 2014 . 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 Estimated Gross Estimated Gross Fair Unrealized Fair Unrealized Fair Unrealized Value Losses Value Losses Value Losses December 31, 2015 Fixed maturities (1): Corporate bonds $ 1,810,988 $ (37,445 ) $ 129,896 $ (23,063 ) $ 1,940,884 $ (60,508 ) Mortgage backed securities 487,018 (4,508 ) 48,991 (826 ) 536,009 (5,334 ) Municipal bonds 269,015 (1,303 ) 9,692 (231 ) 278,707 (1,534 ) Commercial mortgage backed securities 511,261 (6,639 ) 20,596 (339 ) 531,857 (6,978 ) U.S. government and government agencies 1,991,163 (9,978 ) — — 1,991,163 (9,978 ) Non-U.S. government securities 458,414 (13,494 ) 138,792 (25,628 ) 597,206 (39,122 ) Asset backed securities 1,217,163 (9,328 ) 134,841 (3,623 ) 1,352,004 (12,951 ) Total 6,745,022 (82,695 ) 482,808 (53,710 ) 7,227,830 (136,405 ) Equity securities 232,275 (17,796 ) — — 232,275 (17,796 ) Other investments 93,614 (4,665 ) — — 93,614 (4,665 ) Short-term investments 30,625 (3,425 ) — — 30,625 (3,425 ) Total $ 7,101,536 $ (108,581 ) $ 482,808 $ (53,710 ) $ 7,584,344 $ (162,291 ) December 31, 2014 Fixed maturities (1): Corporate bonds $ 1,309,637 $ (32,903 ) $ 148,963 $ (6,071 ) $ 1,458,600 $ (38,974 ) Mortgage backed securities 293,624 (1,476 ) 59,107 (2,366 ) 352,731 (3,842 ) Municipal bonds 210,614 (588 ) 13,643 (456 ) 224,257 (1,044 ) Commercial mortgage backed securities 232,147 (770 ) 125,894 (3,052 ) 358,041 (3,822 ) U.S. government and government agencies 618,381 (1,626 ) 3,438 (134 ) 621,819 (1,760 ) Non-U.S. government securities 510,766 (31,172 ) 46,910 (6,031 ) 557,676 (37,203 ) Asset backed securities 612,950 (2,486 ) 243,452 (3,603 ) 856,402 (6,089 ) Total 3,788,119 (71,021 ) 641,407 (21,713 ) 4,429,526 (92,734 ) Equity securities 181,002 (13,364 ) — — 181,002 (13,364 ) Other investments 59,638 (362 ) — — 59,638 (362 ) Short-term investments 79,271 (5,270 ) — — 79,271 (5,270 ) Total $ 4,108,030 $ (90,017 ) $ 641,407 $ (21,713 ) $ 4,749,437 $ (111,730 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged. See “—Securities Lending Agreements.” At December 31, 2015 , on a lot level basis, approximately 3,560 security lots out of a total of approximately 5,550 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 $3.1 million . At December 31, 2014 , on a lot level basis, approximately 1,900 security lots out of a total of approximately 4,790 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 $2.9 million . The contractual maturities of the Company’s fixed maturities and fixed maturities pledged under securities lending agreements 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. December 31, 2015 December 31, 2014 Maturity Estimated Fair Value Amortized Cost Estimated Fair Value Amortized Cost Due in one year or less $ 337,898 $ 341,595 $ 235,930 $ 233,794 Due after one year through five years 4,644,516 4,677,230 4,074,562 4,077,408 Due after five years through 10 years 2,214,413 2,228,638 2,475,726 2,461,356 Due after 10 years 496,302 497,174 279,542 273,372 7,693,129 7,744,637 7,065,760 7,045,930 Mortgage backed securities 754,870 750,332 943,343 928,342 Commercial mortgage backed securities 764,152 767,861 1,114,528 1,103,756 Asset backed securities 1,620,506 1,630,150 1,677,941 1,675,605 Total $ 10,832,657 $ 10,892,980 $ 10,801,572 $ 10,753,633 Securities Lending Agreements From time to time, the Company enters into securities lending agreements with financial institutions to enhance investment income. The Company 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 to the Company. At December 31, 2015 , the fair value and amortized cost of securities pledged under securities lending agreements were $384.1 million and $386.4 million , respectively, compared to $50.8 million and $52.1 million at December 31, 2014 , respectively. At December 31, 2015 , the portfolio of collateral backing the Company’s securities lending program included approximately $3.0 million of sub-prime securities, compared to $5.8 million at December 31, 2014 . The Company receives collateral in the form of cash or securities. Cash collateral primarily consists of short-term investments. At December 31, 2015 , the fair value of the cash collateral received on securities lending was $52.7 million , which included $3.0 million that was reinvested in sub-prime mortgage backed securities, and the fair value of security collateral received was $336.6 million . At December 31, 2014 , the fair value of the cash collateral received on securities lending was $44.3 million , which included $5.8 million that was reinvested in sub-prime mortgage backed securities, and the fair value of security collateral received was nil . The Company’s securities lending transactions were accounted for as secured borrowings with significant investment categories as follows: December 31, 2015 Remaining Contractual Maturity of the Agreements Securities Lending Transactions Overnight and Continuous Less than 30 Days 30-90 Days 90 Days or More Total U.S. government and government agencies $ 235,728 $ — $ 82,286 $ 9,598 $ 327,612 Corporate bonds 55,086 — — — 55,086 Equity securities 6,722 4,424 — — 11,146 Total $ 297,536 $ 4,424 $ 82,286 $ 9,598 $ 393,844 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 10 $ — Amounts related to securities lending not included in offsetting disclosure in Note 10 $ 393,844 Other Investments The following table summarizes the Company’s other investments, including available for sale and fair value option components: December 31, 2015 2014 Available for sale securities: Asian and emerging markets $ 206,861 $ 236,586 Investment grade fixed income 31,370 59,638 Credit related funds 22,512 — Other 39,733 — Total available for sale 300,476 296,224 Fair value option: Term loan investments (par value: $1,197,143 and $1,094,337) 1,108,017 1,073,649 Mezzanine debt funds 121,589 121,341 Credit related funds 219,049 114,436 Investment grade fixed income 63,053 69,108 Asian and emerging markets 34,761 25,800 Other (1) 124,502 137,094 Total fair value option 1,670,971 1,541,428 Total $ 1,971,447 $ 1,837,652 (1) Includes fund investments with strategies in mortgage servicing rights, transportation and infrastructure assets 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: December 31, 2015 2014 Fixed maturities $ 936,802 $ 632,024 Other investments 1,670,971 1,541,428 Short-term investments 285,923 251,601 Equity securities 798 — Investments accounted for using the fair value option $ 2,894,494 $ 2,425,053 Net Investment Income The components of net investment income were derived from the following sources: Year Ended December 31, 2015 2014 2013 Fixed maturities $ 283,998 $ 265,219 $ 249,833 Term loan investments 71,120 39,940 20,608 Equity securities (dividends) 13,534 13,005 8,919 Short-term investments 669 1,888 1,259 Other (1) 41,807 28,869 19,710 Gross investment income 411,128 348,921 300,329 Investment expenses (63,038 ) (46,336 ) (33,110 ) Net investment income $ 348,090 $ 302,585 $ 267,219 (1) Includes income distributions from investment funds and other items. Net Realized Gains (Losses) Net realized gains (losses) were as follows, excluding the other-than-temporary impairment provisions: Year Ended December 31, 2015 2014 2013 Available for sale securities: Gross gains on investment sales $ 281,786 $ 248,031 $ 239,421 Gross losses on investment sales (218,970 ) (145,808 ) (203,077 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities (84,620 ) (20,743 ) 54 Other investments (122,171 ) 2,672 17,503 Equity securities (85 ) — 704 Short-term investments 1,462 (395 ) — Derivative instruments (1) (7,114 ) 43,934 20,912 Other (2) (36,130 ) (24,774 ) (1,499 ) Net realized gains (losses) $ (185,842 ) $ 102,917 $ 74,018 (1) See Note 10 for information on the Company’s derivative instruments. (2) Includes the re-measurement of contingent consideration liability amounts. 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: Year Ended December 31, 2015 2014 2013 Fixed maturities: Mortgage backed securities $ (1,794 ) $ (1,525 ) $ (295 ) Corporate bonds (10,841 ) (2,062 ) (88 ) Commercial mortgage backed securities — (7 ) — Asset backed securities — (40 ) (128 ) Total (12,635 ) (3,634 ) (511 ) Short-term investments (2,341 ) — — Equity securities (4,206 ) (1,106 ) (3,275 ) Other investments (934 ) (25,410 ) — Net impairment losses recognized in earnings $ (20,116 ) $ (30,150 ) $ (3,786 ) A description of the methodology and significant inputs used to measure the amount of net impairment losses recognized in earnings in 2015 is as follows: • Corporate bonds – the Company reviewed the business prospects, credit ratings, estimated loss given default factors, foreign currency impacts and information received from asset managers and rating agencies for certain corporate bonds. Approximately 57% of the impairment losses for 2015 resulted from non-investment grade corporate bonds predominantly in the energy sector, reflecting current market conditions, with the remaining 43% related to foreign currency fluctuations on non-U.S. Dollar denominated investments based on the remaining time to maturity. The amortized cost basis of the corporate bonds were adjusted down, if required, to the expected recovery value calculated in the OTTI review process; • Equity securities – the Company utilized information received from asset managers on common stocks, including the business prospects, recent events, industry and market data and other factors. For certain equities which were in an unrealized loss position and where the Company determined that it did not have the intent or ability to hold such securities for a reasonable period of time by which the fair value of the securities would increase and the Company would recover its cost, the cost basis of such securities was adjusted down accordingly; • Other investments – the Company utilized information received from fund managers and positive and negative evidence, including the business prospects, recent events, industry and market data and other factors. Net impairment losses for 2015 primarily related to a reduction in the carrying value of one fund investment; • Mortgage backed securities – the Company utilized underlying data provided by asset managers, cash flow projections and additional information from credit agencies in order to determine an expected recovery value for each security. The analysis includes expected cash flow projections under base case and stress case scenarios which modify the expected default expectations and loss severities and slow down prepayment assumptions. The significant inputs in the models include the expected default rates, delinquency rates and foreclosure costs. The amortized cost basis of the mortgage backed securities were adjusted down, if required, to the expected recovery value calculated in the OTTI review process; • Short-term investments – net impairment losses related to a reduction in the carrying value of a Euro-denominated investment in an unrealized loss position due to the decline of the Euro against the U.S. Dollar. Due to the short time to maturity, the Company recorded an OTTI on such security. The Company believes that the $6.9 million of OTTI included in accumulated other comprehensive income at December 31, 2015 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 December 31, 2015 , 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: Year Ended December 31, 2015 2014 2013 Balance at start of year $ 20,196 $ 60,062 $ 62,001 Credit loss impairments recognized on securities not previously impaired 12,777 691 423 Credit loss impairments recognized on securities previously impaired 1,673 162 88 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 (7,771 ) (40,719 ) (2,450 ) Balance at end of year $ 26,875 $ 20,196 $ 60,062 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 15 for further details. The following table details the value of the Company’s restricted assets: December 31, 2015 2014 Assets used for collateral or guarantees: Affiliated transactions $ 3,810,104 $ 4,138,527 Third party agreements 1,181,087 970,120 Deposits with U.S. regulatory authorities 391,458 337,981 Deposits with non-U.S. regulatory authorities 38,230 — Trust funds 105,170 72,461 Total restricted assets $ 5,526,049 $ 5,519,089 In addition, because Watford Re is an independent company, the assets of Watford Re can be used only to settle obligations of Watford Re and Watford Re is solely responsible for its own liabilities and commitments. See Note 5 , for information on Watford Re’s assets and liabilities. Investment Funds Accounted For Using the Equity Method The Company recorded equity in net income related to investment funds accounted for using the equity method of $25.5 million for 2015 , compared to $19.9 million for 2014 and $35.7 million for 2013 . Due to the ownership structure of these investment funds ( e.g. , limited partnership), the Company uses the equity method where it does not have a controlling interest and is not the primary beneficiary. In applying the equity method, these 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 fair value of the underlying securities in the funds). Such investments are generally recorded on a one month lag with some investments reported on a three month lag based on the availability of reports from the investment funds. Changes in the carrying value of such investments are recorded in net income as “Equity in net income (loss) of investment funds accounted for using the equity method.” As such, fluctuations in the carrying value of the investment funds accounted for using the equity method may increase the volatility of the Company’s reported results of operations. Investment funds accounted for using the equity method totaled $593.0 million at December 31, 2015 , compared to $349.0 million at December 31, 2014 .

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2015
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 Fair Value Measurements on a Recurring Basis 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 December 31, 2015 . 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 $15.40 billion of financial assets and liabilities measured at fair value at December 31, 2015 , approximately $317.8 million , or 2.1% , were priced using non-binding broker-dealer quotes. Of the $15.06 billion of financial assets and liabilities measured at fair value at December 31, 2014 , approximately $260.8 million , or 1.7% , were priced using non-binding broker-dealer quotes. The Company reviews its securities measured at fair value and discusses the proper classification of such investments with investment advisors and others. A discussion of the general classification of the Company’s financial instruments follows: 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. • 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. • 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. • 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 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. During 2015 , the Company transferred $44.6 million of U.S. government agency securities from Level 1 to Level 2 based on a review of the pricing of such securities, as described above. In addition, the Company transferred $16.4 million of corporate bonds from Level 2 to Level 3 which indicated a low level of transparency on the inputs used in the pricing process on one corporate bond. 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. During 2015 , the Company transferred $99.7 million of other investments from Level 2 to Level 1 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 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) includes 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 December 31, 2015 : Fair Value Measurement 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: Available for sale securities: Fixed maturities (1): Corporate bonds $ 2,725,729 $ — $ 2,709,361 $ 16,368 Mortgage backed securities 754,870 — 754,870 — Municipal bonds 1,626,281 — 1,626,281 — Commercial mortgage backed securities 764,152 — 764,152 — U.S. government and government agencies 2,423,455 2,378,662 44,793 — Non-U.S. government securities 917,664 — 917,664 — Asset backed securities 1,620,506 — 1,563,006 57,500 Total 10,832,657 2,378,662 8,380,127 73,868 Equity securities 629,182 627,441 1,741 — Short-term investments 587,904 572,604 15,300 — Other investments 99,159 99,159 — — Other investments measured at net asset value (2) 201,317 Total other investments 300,476 99,159 — — Derivative instruments (4) 20,022 — 20,022 — Fair value option: Corporate bonds 771,733 — 771,733 — Non-U.S. government bonds 81,824 — 81,824 — Mortgage backed securities 57,687 — 57,687 — Asset backed securities 25,444 — 25,444 — U.S. government and government agencies 114 114 — — Short-term investments 285,923 285,923 — — Equity securities 798 798 — — Other investments 1,176,312 68,295 1,108,017 — Other investments measured at net asset value (2) 494,659 Total 2,894,494 355,130 2,044,705 — Total assets measured at fair value $ 15,264,735 $ 4,032,996 $ 10,461,895 $ 73,868 Liabilities measured at fair value: Contingent consideration liabilities $ (96,048 ) $ — $ — $ (96,048 ) Securities sold but not yet purchased (3) (30,583 ) — (30,583 ) — Derivative instruments (4) (11,863 ) — (11,863 ) — Total liabilities measured at fair value $ (138,494 ) $ — $ (42,446 ) $ (96,048 ) (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 8 , “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 10 , “Derivative Instruments.” The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2014 : Fair Value Measurement 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: Available for sale securities: Fixed maturities (1): Corporate bonds $ 3,108,513 $ — $ 3,108,513 $ — Mortgage backed securities 943,343 — 943,343 — Municipal bonds 1,494,122 — 1,494,122 — Commercial mortgage backed securities 1,114,528 — 1,114,528 — U.S. government and government agencies 1,447,972 1,447,972 — — Non-U.S. government securities 1,015,153 — 1,015,153 — Asset backed securities 1,677,941 — 1,620,441 57,500 Total 10,801,572 1,447,972 9,296,100 57,500 Equity securities 658,182 658,182 — — Short-term investments 797,226 759,621 37,605 — Other investments 97,372 — 97,372 — Other investments measured at net asset value (2) 198,852 Total other investments 296,224 — 97,372 — Derivative instruments (3) 15,876 — 15,876 — Fair value option: Corporate bonds 497,101 — 497,101 — Non-U.S. government bonds 88,411 — 88,411 — Mortgage backed securities 22,190 — 22,190 — Asset backed securities 24,322 — 24,322 — Short-term investments 251,601 250,580 1,021 — Other investments 1,140,266 — 1,140,266 — Other investments measured at net asset value (2) 401,162 Total 2,425,053 250,580 1,773,311 — Total assets measured at fair value $ 14,994,133 $ 3,116,355 $ 11,220,264 $ 57,500 Liabilities measured at fair value: Contingent consideration liabilities $ (61,845 ) $ — $ — $ (61,845 ) Derivative instruments (3) (5,397 ) — (5,397 ) — Total liabilities measured at fair value $ (67,242 ) $ — $ (5,397 ) $ (61,845 ) (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 8 , “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) See Note 10 , “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 for 2015 , 2014 and 2013 : Assets Liabilities Available for sale Fair value option Asset Backed Securities Corporate Bonds Other Investments Other Investments Total Contingent Consideration Liabilities Year Ended December 31, 2015 Balance at beginning of year $ 57,500 $ — $ — $ — $ 57,500 $ (61,845 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — — — — — (33,135 ) Included in other comprehensive income — — — — — — Purchases, issuances, sales and settlements Purchases — — — — — — Issuances — — — — — (1,068 ) Sales — — — — — — Settlements — — — — — — Transfers in and/or out of Level 3 — 16,368 — — 16,368 — Balance at end of year $ 57,500 $ 16,368 $ — $ — $ 73,868 $ (96,048 ) Year Ended December 31, 2014 Balance at beginning of year $ — $ 2,045 $ 170,420 $ 377,525 $ 549,990 $ — Total gains or (losses) (realized/unrealized) Included in earnings (1) — — — — — (20,083 ) Included in other comprehensive income — — — — — — Purchases, issuances, sales and settlements Purchases — — — — — — Issuances — — — — — (41,762 ) Sales — (2,045 ) — — (2,045 ) — Settlements — — — — — — Transfers in and/or out of Level 3 57,500 — (170,420 ) (377,525 ) (490,445 ) — Balance at end of year $ 57,500 $ — $ — $ — $ 57,500 $ (61,845 ) (1) Gains or losses on fixed maturities available for sale were included in net realized gains (losses) while gains or losses on other investments were included in net realized gains (losses) or net investment income. Gains or losses on contingent consideration liabilities were included in net realized gains (losses). (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 transfers out of Level 3 presented in this table are intended to permit reconciliation to information previously presented. 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 December 31, 2015 , due to their respective short maturities. As these financial instruments are not actively traded, their respective fair values are classified within Level 2. At December 31, 2015 , the senior notes of ACGL were carried at their cost, net of debt issuance costs, of $296.9 million and had a fair value of $390.1 million while the senior notes of Arch-U.S. were carried at their cost, net of debt issuance costs, of $494.4 million and had a fair value of $513.9 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 value of the senior notes is classified within Level 2. Fair Value Measurements on a Non-Recurring Basis The Company measures the fair value of certain assets on a non-recurring basis, generally quarterly, annually, or when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. These assets include investment funds accounted for using the equity method, certain other investments, goodwill and intangible assets, and long-lived assets. The Company uses a variety of techniques to measure the fair value of these assets when appropriate, as described below: Investments accounted for using the equity method. When the Company determines that the carrying value of these assets may not be recoverable, the Company records the assets at fair value with the loss recognized in income. In such cases, the Company measures the fair value of these assets using the techniques discussed above in “—Fair Value Measurements on a Recurring Basis.” Goodwill and Intangible Assets . The Company tests goodwill and intangible assets for impairment whenever events or changes in circumstances indicate the carrying amount may not be recoverable. When the Company determines goodwill and intangible assets may be impaired, the Company uses techniques including discounted expected future cash flows, to measure fair value. Long-Lived Assets . The Company tests its long-lived assets for impairment whenever events or changes in circumstances indicate the carrying amount of a long-lived asset may not be recoverable.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2015
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 Company did not hold any derivatives which were designated as hedging instruments at December 31, 2015 or 2014 . The following table summarizes information on the fair values and notional values of the Company’s derivative instruments: Estimated Fair Value Asset Liability Derivatives Net Notional Value (1) December 31, 2015 Futures contracts (2) $ 2,816 $ (1,202 ) $ 1,614 $ 1,797,115 Foreign currency forward contracts (2) 9,336 (6,344 ) 2,992 773,619 TBAs (3) 6,525 — 6,525 6,316 Other (2) 7,870 (4,317 ) 3,553 1,694,935 Total $ 26,547 $ (11,863 ) $ 14,684 December 31, 2014 Futures contracts (2) $ 2,156 $ (1,907 ) $ 249 $ 2,549,027 Foreign currency forward contracts (2) 10,511 (1,145 ) 9,366 397,106 TBAs (3) 10,592 — 10,592 10,056 Other (2) 3,209 (2,345 ) 864 735,684 Total $ 26,468 $ (5,397 ) $ 21,071 (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.’ Such amounts include risk in force on GSE credit-risk sharing transactions that are accounted for as derivatives. (3) The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’ 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. Effectively, contractual close-out netting reduces derivatives credit exposure from gross to net exposure. At December 31, 2015 , $26.5 million and $11.9 million , respectively, of asset derivatives and liability derivatives were subject to a master netting agreement compared to $25.3 million and $5.4 million , respectively, at December 31, 2014 . The remaining derivatives included in the table above 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 hedging instruments Year Ended December 31, 2015 2014 2013 Net realized gains (losses): Futures contracts $ (21,533 ) $ 30,444 $ 10,742 Foreign currency forward contracts 16,045 13,430 9,762 TBAs 1,452 (342 ) (1,623 ) Other (3,078 ) 402 2,031 Total $ (7,114 ) $ 43,934 $ 20,912

Other Comprehensive Income

Other Comprehensive Income	12 Months Ended
	Dec. 31, 2015
Comprehensive Income Note Disclosure [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The following table presents the changes in each component of accumulated other comprehensive income (“AOCI”), net of noncontrolling interests: Unrealized Appreciation on Available-For-Sale Investments Foreign Currency Translation Adjustments Total Year Ended December 31, 2015 Beginning balance $ 161,598 $ (32,742 ) $ 128,856 Other comprehensive income (loss) before reclassifications (83,280 ) (33,845 ) (117,125 ) Amounts reclassified from accumulated other comprehensive income (28,233 ) — (28,233 ) Net current period other comprehensive income (loss) (111,513 ) (33,845 ) (145,358 ) Ending balance $ 50,085 $ (66,587 ) $ (16,502 ) Year Ended December 31, 2014 Beginning balance $ 80,692 $ (5,728 ) $ 74,964 Other comprehensive income (loss) before reclassifications 146,010 (27,014 ) 118,996 Amounts reclassified from accumulated other comprehensive income (65,104 ) — (65,104 ) Net current period other comprehensive income (loss) 80,906 (27,014 ) 53,892 Ending balance $ 161,598 $ (32,742 ) $ 128,856 Year Ended December 31, 2013 Beginning balance $ 289,956 $ (2,939 ) $ 287,017 Other comprehensive income (loss) before reclassifications (176,578 ) (2,789 ) (179,367 ) Amounts reclassified from accumulated other comprehensive income (32,686 ) — (32,686 ) Net current period other comprehensive income (loss) (209,264 ) (2,789 ) (212,053 ) Ending balance $ 80,692 $ (5,728 ) $ 74,964 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): Consolidated Statement of Income Amounts Reclassified from AOCI Details About Line Item That Includes Year Ended December 31, AOCI Components Reclassification 2015 2014 2013 Unrealized appreciation on available-for-sale investments Net realized gains $ 62,817 $ 102,223 $ 39,308 Other-than-temporary impairment losses (26,152 ) (30,470 ) (3,961 ) Total before tax 36,665 71,753 35,347 Income tax (expense) benefit (8,432 ) (6,649 ) (2,661 ) Net of tax $ 28,233 $ 65,104 $ 32,686 Following are the related tax effects allocated to each component of other comprehensive income (loss): Before Tax Tax Expense Net of Tax Amount (Benefit) Amount Year Ended December 31, 2015 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ (77,311 ) $ (67 ) $ (77,244 ) Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (6,036 ) — (6,036 ) Less reclassification of net realized gains (losses) included in net income 36,665 8,432 28,233 Foreign currency translation adjustments (35,678 ) (1,568 ) (34,110 ) Other comprehensive income (loss) $ (155,690 ) $ (10,067 ) $ (145,623 ) Year Ended December 31, 2014 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 161,685 $ 15,355 $ 146,330 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (320 ) — (320 ) Less reclassification of net realized gains (losses) included in net income 71,753 6,649 65,104 Foreign currency translation adjustments (27,014 ) — (27,014 ) Other comprehensive income (loss) $ 62,598 $ 8,706 $ 53,892 Year Ended December 31, 2013 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ (201,386 ) $ (24,983 ) $ (176,403 ) Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (175 ) — (175 ) Less reclassification of net realized gains (losses) included in net income 35,347 2,661 32,686 Foreign currency translation adjustments (2,789 ) — (2,789 ) Other comprehensive income (loss) $ (239,697 ) $ (27,644 ) $ (212,053 )

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share The calculation of basic earnings per common share excludes dilutive securities and is computed by dividing income available to Arch common shareholders by the weighted average number of Common Shares, including vested restricted shares, outstanding for the periods. The following table sets forth the computation of basic and diluted earnings per common share: Year Ended December 31, 2015 2014 2013 Numerator: Net income $ 526,582 $ 821,260 $ 709,731 Amounts attributable to noncontrolling interests 11,156 13,095 — Net income available to Arch 537,738 834,355 709,731 Preferred dividends (21,938 ) (21,938 ) (21,938 ) Net income available to Arch common shareholders $ 515,800 $ 812,417 $ 687,793 Denominator: Weighted average common shares outstanding – basic 121,786,127 130,817,610 131,355,392 Effect of dilutive common share equivalents: Nonvested restricted shares 1,253,938 1,128,540 1,090,100 Stock options (1) 2,998,678 2,976,172 3,331,691 Weighted average common shares and common share equivalents outstanding – diluted 126,038,743 134,922,322 135,777,183 Earnings per common share: Basic $ 4.24 $ 6.21 $ 5.24 Diluted $ 4.09 $ 6.02 $ 5.07 (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 2015 , 2014 and 2013 , the number of stock options excluded were 799,535 , 1,435,955 and 892,439 , respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes ACGL is incorporated under the laws of Bermuda and, under current Bermuda law, is not obligated to pay any taxes in Bermuda based upon income or capital gains. The Company has received a written undertaking from the Minister of Finance in Bermuda under the Exempted Undertakings Tax Protection Act 1966 that, in the event that any legislation is enacted in Bermuda imposing any tax computed on profits, income, gain or appreciation on any capital asset, or any tax in the nature of estate duty or inheritance tax, such tax will not be applicable to ACGL or any of its operations until March 31, 2035. This undertaking does not, however, prevent the imposition of taxes on any person ordinarily resident in Bermuda or any company in respect of its ownership of real property or leasehold interests in Bermuda. ACGL and its non-U.S. subsidiaries will be subject to U.S. federal income tax only to the extent that they derive U.S. source income that is subject to U.S. withholding tax or income that is effectively connected with the conduct of a trade or business within the U.S. and is not exempt from U.S. tax under an applicable income tax treaty with the U.S. ACGL and its non-U.S. subsidiaries will be subject to a withholding tax on dividends from U.S. investments and interest from certain U.S. payors (subject to reduction by any applicable income tax treaty). ACGL and its non-U.S. subsidiaries intend to conduct their operations in a manner that will not cause them to be treated as engaged in a trade or business in the United States and, therefore, will not be required to pay U.S. federal income taxes (other than U.S. excise taxes on insurance and reinsurance premium and withholding taxes on dividends and certain other U.S. source investment income). However, because there is uncertainty as to the activities which constitute being engaged in a trade or business within the United States, there can be no assurances that the U.S. Internal Revenue Service will not contend successfully that ACGL or its non-U.S. subsidiaries are engaged in a trade or business in the United States. If ACGL or any of its non-U.S. subsidiaries were subject to U.S. income tax, ACGL’s shareholders’ equity and earnings could be materially adversely affected. ACGL has subsidiaries and branches that operate in various jurisdictions around the world that are subject to tax in the jurisdictions in which they operate. The significant jurisdictions in which ACGL’s subsidiaries and branches are subject to tax are the United States, United Kingdom, Ireland, Canada, Switzerland and Denmark. The components of income taxes attributable to operations were as follows: Year Ended December 31, 2015 2014 2013 Current expense (benefit): United States $ 37,186 $ 29,749 $ 27,537 Non-U.S. 7,008 801 5,159 44,194 30,550 32,696 Deferred expense (benefit): United States (4,893 ) (8,168 ) 1,937 Non-U.S. 1,311 605 (1,859 ) (3,582 ) (7,563 ) 78 Income tax expense (benefit) $ 40,612 $ 22,987 $ 32,774 The Company’s income or loss before income taxes was earned in the following jurisdictions: Year Ended December 31, 2015 2014 2013 Income (Loss) Before Income Taxes: Bermuda $ 508,561 $ 794,926 $ 717,661 United States 57,527 53,055 87,032 Other 1,106 (3,734 ) (62,188 ) Total $ 567,194 $ 844,247 $ 742,505 The expected tax provision computed on pre-tax income or loss at the weighted average tax rate has been calculated as the sum of the pre-tax income in each jurisdiction multiplied by that jurisdiction’s applicable statutory tax rate. The statutory tax rates by jurisdiction were as follows: Bermuda ( 0.0% ), United States ( 35.0% ), United Kingdom ( 20.25% ), Ireland ( 12.5% ), Denmark ( 23.5% ), Canada ( 26.5% ), Gibraltar ( 10.0% ) and the Netherlands ( 25.0% ). A reconciliation of the difference between the provision for income taxes and the expected tax provision at the weighted average tax rate follows: Year Ended December 31, 2015 2014 2013 Expected income tax expense (benefit) computed on pre-tax income at weighted average income tax rate $ 20,058 $ 18,178 $ 17,506 Addition (reduction) in income tax expense (benefit) resulting from: Tax-exempt investment income (9,588 ) (8,048 ) (8,255 ) Meals and entertainment 897 711 599 State taxes, net of U.S. federal tax benefit 858 1,281 431 Foreign branch taxes 1,456 464 703 Prior year adjustment 2,510 320 2,810 Foreign exchange gains & losses 670 746 (1,254 ) Changes in applicable tax rate 40 (51 ) 2,007 Dividend withholding taxes 6,323 3,276 4,619 Change in valuation allowance 2,917 (736 ) 11,795 Contingent consideration 11,548 6,763 — Uncertain tax position 2,008 — — Other 915 83 1,813 Income tax expense (benefit) $ 40,612 $ 22,987 $ 32,774 Deferred income tax assets and liabilities reflect temporary differences based on enacted tax rates between the carrying amounts of assets and liabilities for financial reporting and income tax purposes. Significant components of the Company’s deferred income tax assets and liabilities were as follows: December 31, 2015 2014 Deferred income tax assets: Net operating loss $ 11,436 $ 12,017 AMT credit carryforward 5,304 5,309 Discounting of net loss reserves 54,373 63,880 Net unearned premium reserve 33,579 34,087 Compensation liabilities 29,069 27,765 Foreign tax credit carryforward 6,215 4,628 Interest expense 1,972 5,208 Goodwill and intangible assets 2,683 885 Tax and loss bonds 14,150 21,247 Net unrealized foreign exchange gains 1,573 — Other, net 21,273 13,408 Deferred tax assets before valuation allowance 181,627 188,434 Valuation allowance (13,816 ) (12,624 ) Deferred tax assets net of valuation allowance 167,811 175,810 Deferred income tax liabilities: Depreciation and amortization (7,368 ) (7,579 ) Deferred acquisition costs, net (164 ) (2,744 ) Deposit accounting liability (4,151 ) (4,170 ) Contingency reserve (15,289 ) (18,480 ) Net unrealized appreciation of investments (4,103 ) (11,695 ) Other, net (1,042 ) (150 ) Total deferred tax liabilities (32,117 ) (44,818 ) Net deferred income tax assets $ 135,694 $ 130,992 The Company provides a valuation allowance to reduce certain deferred tax assets to an amount which management expects to more likely than not be realized. As of December 31, 2015 , the Company’s valuation allowance was $13.8 million , compared to $12.6 million at December 31, 2014 . The valuation allowance in both periods was primarily attributable to (1) a full valuation allowance on the Company’s Canadian operations; (2) unutilized foreign tax credits; and (3) certain other deferred tax assets relating to carryforwards that have a limited use. At December 31, 2015 , the Company has net operating loss carryforwards in its U.K. operating subsidiaries of approximately $16.1 million . Additionally, the Company’s U.K. operations have a foreign tax credit carryforward of $6.2 million at December 31, 2015 . These operating losses and foreign tax credits can be carried forward without expiration. Due to uncertainty surrounding their future utilization, valuation allowances of $0.1 million and $6.2 million have been established in respect of $0.6 million U.K. operating losses and $6.2 million foreign tax credits, respectively. At December 31, 2015 , net operating loss carryforwards in Ireland were approximately $5.3 million . Although these losses may be carried forward indefinitely, a full valuation allowance of $0.6 million has been established given management’s expectation that these losses, which are specific to an individual Irish entity, will not be utilized in the future. At December 31, 2015 , net operating loss carryforwards in the U.S. were approximately $18.8 million . Such net operating loss carryforwards are currently available to offset future taxable income of the Company’s U.S. subsidiaries. Under applicable law, the U.S. net operating loss carryforwards expire between 2029 and 2035. On January 30, 2014, the Company’s U.S. mortgage operations underwent an ownership change for U.S. federal income tax purposes as a result of the Company’s acquisition of the CMG Entities. As a result of this ownership change, a limitation has been imposed upon the utilization of approximately $11.5 million of the Company’s existing U.S. net operating loss carryforwards. Utilization is limited to approximately $0.6 million per year in accordance with Section 382 of the Internal Revenue Code of 1986 as amended (“the Code”). Additionally, the Company has an alternative minimum tax (“AMT”) credit carryforward in the amount of $5.3 million which can be carried forward indefinitely. Given the Company’s U.S. mortgage operations, the Company is eligible for a tax deduction, subject to certain limitations, under Section 832(e) of the Code for amounts required by state law or regulation to be set aside in statutory contingency reserves. The deduction is allowed only to the extent that the Company purchases non-interest bearing U.S. Mortgage Guaranty Tax and Loss Bonds (“T&L Bonds”) issued by the Treasury Department in an amount equal to the tax benefit derived from deducting any portion of the statutory contingency reserves. Cumulative T&L bonds purchased and subsequent redemptions are reflected in the Company’s deferred tax asset and totaled approximately $14.2 million at December 31, 2015 , compared to $21.2 million at December 31, 2014. Deferred income tax liabilities have not been accrued with respect to all of the undistributed earnings of the Company's subsidiaries. If the earnings were to be distributed, as dividends or otherwise, such amounts may be subject to withholding tax in the jurisdiction of the paying entity. No withholding taxes have been accrued with respect to the earnings of the Company's U.S. and Canadian subsidiaries, as it is the intention that all such earnings will be permanently reinvested. Additionally, determining the amount of the related deferred income tax liability is not practicable. It is intended that earnings from the U.K. and Ireland would also be permanently reinvested. Distributions from the U.K. or Ireland would not be subject to withholding tax and no deferred income tax liability would need to be accrued. The Company recognizes interest and penalties relating to unrecognized tax benefits in the provision for income taxes. As of December 31, 2015 , the Company’s total unrecognized tax benefits, including interest and penalties, were $2.0 million . A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: December 31, 2015 2014 Balance at beginning of year $ — $ — Additions based on tax positions related to the current year 517 — Additions for tax positions of prior years 1,491 — Reductions for tax positions of prior years — — Settlements — — Balance at end of year $ 2,008 $ — The Company or its subsidiaries or branches files income tax returns in the U.S. federal jurisdiction and various state, local and foreign jurisdictions. The Company’s examination by the tax authorities in the U.S. for the 2009 through 2011 tax years closed with no change. The following table details open tax years that are potentially subject to examination by local tax authorities, in the following major jurisdictions: Jurisdiction Tax Years United States 2012-2015 United Kingdom 2010-2015 Ireland 2011-2015 Canada 2011-2015 Switzerland 2012-2015 Denmark 2012-2015 As of December 31, 2015 , the Company’s current income tax recoverable (included in “Other assets”) was $0.9 million .

Transactions with Related Parti

Transactions with Related Parties	12 Months Ended
	Dec. 31, 2015
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 The Carlyle Group (“Carlyle”). As part of its investment philosophy, the Company invests a portion of its investment portfolio in alternative investment funds. As of December 31, 2015 , the Company had aggregate commitments of $695.9 million to funds managed by Carlyle, of which $482.5 million was unfunded. The Company may make additional commitments to funds managed by Carlyle from time to time. During 2015 , 2014 and 2013 , the Company made aggregate capital contributions to funds managed by Carlyle of $116.5 million , $63.5 million and $60.8 million , respectively. During 2015 , 2014 and 2013 , the Company received aggregate cash distributions from funds managed by Carlyle of $44.6 million , $45.8 million and $15.0 million , respectively, of which $38.8 million , $34.4 million and $12.9 million , respectively, represented a return of capital. Certain directors and executive officers of the Company own common and preference shares of Watford Re. See note 4 , “Variable Interest Entity and Noncontrolling Interests,” for information about Watford Re.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Concentrations of Credit Risk The creditworthiness of a counterparty is evaluated by the Company, taking into account credit ratings assigned by independent agencies. The credit approval process involves an assessment of factors, including, among others, the counterparty, country and industry credit exposure limits. Collateral may be required, at the discretion of the Company, on certain transactions based on the creditworthiness of the counterparty. The areas where significant concentrations of credit risk may exist include unpaid losses and loss adjustment expenses recoverable, contractholder receivables, prepaid reinsurance premiums, paid losses and loss adjustment expenses recoverable net of reinsurance balances payable, investments and cash and cash equivalent balances. A credit exposure exists with respect to reinsurance recoverables as they may become uncollectible. The Company manages its credit risk in its reinsurance relationships by transacting with reinsurers that it considers financially sound and, if necessary, the Company may hold collateral in the form of funds, trust accounts and/or irrevocable letters of credit. This collateral can be drawn on for amounts that remain unpaid beyond specified time periods on an individual reinsurer basis. In addition, certain insurance policies written by the Company’s insurance operations feature large deductibles, primarily in its construction and national accounts lines of business. Under such contracts, the Company is obligated to pay the claimant for the full amount of the claim. The Company is subsequently reimbursed by the policyholder for the deductible amount. These amounts are included on a gross basis in the consolidated balance sheet in contractholder payables and contractholder receivables, respectively. In the event that the Company is unable to collect from the policyholder, the Company would be liable for such defaulted amounts. Collateral, primarily in the form of letters of credit, cash and trusts, is obtained from the policyholder to mitigate the Company’s credit risk. In the instances where the company receives collateral in the form of cash, the Company records a related liability in “Collateral held for insured obligations.” In addition, the Company underwrites a significant amount of its business through brokers and a credit risk exists should any of these brokers be unable to fulfill their contractual obligations with respect to the payments of insurance and reinsurance balances owed to the Company. During 2015 , approximately 13.1% and 15.3% of the Company’s consolidated gross written premiums were generated from or placed by Aon Corporation and its subsidiaries and Marsh & McLennan Companies and its subsidiaries, respectively, compared to approximately 13.4% and 15.0% for 2014 , respectively, and 16.0% and 17.0% for 2013 , respectively. No other broker and no one insured or reinsured accounted for more than 10% of gross premiums written for 2015 , 2014 and 2013 . The Company’s available for sale investment portfolio is managed in accordance with guidelines that have been tailored to meet specific investment strategies, including standards of diversification, which limit the allowable holdings of any single issue. There were no investments in any entity in excess of 10% of the Company’s shareholders’ equity at December 31, 2015 other than investments issued or guaranteed by the United States government or its agencies. 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 $1.11 billion at December 31, 2015 . Letter of Credit and Revolving Credit Facilities As of December 31, 2015 , ACGL and its wholly-owned subsidiaries had a $300.0 million unsecured revolving loan and letter of credit facility and a $500.0 million secured letter of credit facility (the “Credit Agreement”). Under the terms of the Credit Agreement, Arch Re U.S. and Arch Re Bermuda are limited to issuing an aggregate of $100.0 million of unsecured letters of credit as part of the $300.0 million unsecured revolving loan. Borrowings of revolving loans may be made at a variable rate based on LIBOR or an alternative base rate at the option of ACGL. Secured letters of credit are available for issuance on behalf of ACGL insurance and reinsurance subsidiaries. The Credit Agreement and related documents are structured such that each party that requests a letter of credit or borrowing does so only for itself and for only its own obligations. Issuance of letters of credit and borrowings under the Credit Agreement are subject to compliance with certain covenants and conditions, including absence of a material adverse change. These covenants require, among other things, the maintenance of a debt to total capital ratio of not greater than 0.35 to 1 and consolidated tangible net worth in excess of $3.95 billion plus 25% of future aggregate net income for each quarterly period (not including any future net losses) beginning after March 31, 2014 and 25% of future aggregate proceeds from the issuance of common or preferred equity and that ACGL’s principal insurance and reinsurance subsidiaries maintain at least a “B++” rating from A.M. Best. In addition, certain of ACGL’s subsidiaries which are party to the Credit Agreement are required to maintain minimum shareholders’ equity levels. ACGL and its’ subsidiaries which are party to the Credit Agreement were in compliance with all covenants contained in the Credit Agreement at December 31, 2015 . The Credit Agreement expires on June 30, 2019. In addition, certain of ACGL’s subsidiaries had outstanding letters of credit of $242.3 million , which were issued on a limited basis and for limited purposes (together with the secured portion of the Credit Agreement and these letter of credit facilities, the “LOC Facilities”). The principal purpose of the LOC Facilities is to issue, as required, evergreen standby letters of credit in favor of primary insurance or reinsurance counterparties with which certain of ACGL’s subsidiaries has entered into reinsurance arrangements. This is required to ensure that such counterparties are permitted to take credit for reinsurance obtained in United States jurisdictions where such subsidiaries are not licensed or otherwise admitted as an insurer, as required under insurance regulations in the United States, and to comply with requirements of Lloyd’s of London in connection with qualifying quota share and other arrangements. The amount of letters of credit issued is driven by, among other things, the timing and payment of catastrophe losses, loss development of existing reserves, the payment pattern of such reserves, the further expansion of business and the loss experience of such business. When issued, certain letters of credit are secured by a portion of the investment portfolio. ACGL and its’ subsidiaries which are party to the LOC Facilities were in compliance with all covenants contained in the LOC Facilities at December 31, 2015 . At such date, approximately $464.8 million of letters of credit under the LOC Facilities were outstanding, which were secured by investments with a fair value of $529.3 million , and $100.0 million of borrowings were outstanding under the Credit Agreement. Under the $500.0 million secured letter of credit facility, ACGL’s subsidiaries had remaining capacity of $277.5 million . Watford Re has access to a $100 million letter of credit facility expiring on May 19, 2016 and an $800 million secured credit facility expiring on June 4, 2018, that provides for borrowings and the issuance of letters of credit not to exceed $400 million of borrowings. Borrowings of revolving loans may be made by Watford Re at a variable rate based on LIBOR or an alternative base rate at the option of Watford Re. At December 31, 2015 , Watford Re had $125.6 million in outstanding letters of credit under the two facilities and $430.4 million of borrowings outstanding under the secured credit facility, backed by Watford Re’s investment portfolio. Watford Re was in compliance with all covenants contained in both of its credit facilities at December 31, 2015 . 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 the reinsurance transactions. Leases and Purchase Obligations At December 31, 2015 , the future minimum rental commitments, exclusive of escalation clauses and maintenance costs and net of rental income, for all of the Company’s operating leases are as follows: 2016 $ 25,494 2017 24,660 2018 24,337 2019 21,024 2020 18,250 Thereafter 40,361 Total $ 154,126 All of these leases are for the rental of office space, with expiration terms that range from 2016 to 2025. Rental expense, net of income from subleases, was approximately $23.8 million , $23.1 million and $18.7 million for 2015 , 2014 and 2013 , respectively. The Company has also entered into certain agreements which commit the Company to purchase goods or services, primarily related to software and computerized systems. Such purchase obligations were approximately $20.7 million and $22.2 million at December 31, 2015 and 2014 , respectively. Employment and Other Arrangements At December 31, 2015 , the Company has entered into employment agreements with certain of its executive officers for periods extending up to March 2018. Such employment arrangements provide for compensation in the form of base salary, annual bonus, share-based awards, participation in the Company’s employee benefit programs and the reimbursements of expenses.

Senior Notes

Senior Notes	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Senior Notes	Senior Notes On May 4, 2004, ACGL completed a public offering of $300.0 million principal amount of 7.35% senior notes due May 1, 2034 (“ACGL Senior Notes”). The ACGL Senior Notes are ACGL’s senior unsecured obligations and rank equally with all of its existing and future senior unsecured indebtedness. Interest payments on the ACGL Senior Notes are due on May 1st and November 1st of each year. ACGL may redeem the ACGL Senior Notes at any time and from time to time, in whole or in part, at a “make-whole” redemption price. The fair value of the ACGL Senior Notes at December 31, 2015 and 2014 was $390.1 million and $462.4 million , respectively. On December 13, 2013, Arch-U.S., a wholly-owned subsidiary of ACGL, completed a public offering of $500.0 million principal amount of 5.144% senior notes due November 1, 2043 (“Arch-U.S. Senior Notes”), fully and unconditionally guaranteed by ACGL (the “Guarantee”). The Arch-U.S. Senior Notes are unsecured and unsubordinated obligations of Arch-U.S. and ACGL, respectively, and rank equally and ratably with the other unsecured and unsubordinated indebtedness of Arch-U.S. and ACGL, respectively. Interest payments on the Arch-U.S. Senior Notes are due on May 1st and November 1st of each year. Arch-U.S. may redeem the Arch-U.S. Senior Notes at any time and from time to time, in whole or in part, at a “make-whole” redemption price. The fair value of the Arch-U.S. Senior Notes at December 31, 2015 and 2014 was $513.9 million and $609.9 million , respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets The following table shows an analysis of goodwill and intangible assets: Goodwill Intangible assets with an indefinite life Intangible assets with finite life Total Net balance at December 31, 2013 $ — $ 16,666 $ 10,653 $ 27,319 Acquisitions 14,965 16,858 76,435 108,258 Amortization — — (25,520 ) (25,520 ) Foreign currency translation adjustment (19 ) — (499 ) (518 ) Net balance at December 31, 2014 14,946 33,524 61,069 109,539 Acquisitions 663 — 10,844 11,507 Amortization — — (22,968 ) (22,968 ) Foreign currency translation adjustment (73 ) — (474 ) (547 ) Net balance at December 31, 2015 $ 15,536 $ 33,524 $ 48,471 $ 97,531 Gross balance at December 31, 2015 $ 15,628 $ 33,524 $ 135,752 $ 184,904 Accumulated amortization — — (86,407 ) (86,407 ) Foreign currency translation adjustment (92 ) — (874 ) (966 ) Net balance at December 31, 2015 $ 15,536 $ 33,524 $ 48,471 $ 97,531 The following table presents the components of intangible assets: Gross Balance Accumulated Foreign Currency Translation Adjustment Net Balance December 31, 2015 Acquired insurance contracts $ 85,032 $ (62,377 ) $ (152 ) $ 22,503 Operating platform 29,900 (11,462 ) — 18,438 Customer relationships 29,296 (16,355 ) (722 ) 12,219 Goodwill 15,628 — (92 ) 15,536 Insurance licenses 33,524 — — 33,524 Unfavorable service contract (9,533 ) 4,192 — (5,341 ) Other 1,057 (405 ) — 652 Total $ 184,904 $ (86,407 ) $ (966 ) $ 97,531 December 31, 2014 Acquired insurance contracts $ 77,574 $ (47,710 ) $ (107 ) $ 29,757 Operating platform 29,900 (5,482 ) — 24,418 Customer relationships 25,910 (12,283 ) (293 ) 13,334 Goodwill 14,965 — (19 ) 14,946 Insurance licenses 33,524 — — 33,524 Unfavorable service contract $ (9,533 ) $ 2,229 $ — (7,304 ) Other $ 1,057 $ (193 ) $ — 864 Total $ 173,397 $ (63,439 ) $ (419 ) $ 109,539 The expected remaining amortization expense for intangible assets with a finite life is $19.3 million for 2016 , $15.3 million for 2017 , $11.9 million for 2018 , $3.1 million for 2019 and $0.1 million for 2020 . The estimated remaining useful lives of these assets range from two to seven years at December 31, 2015 . The Company’s impairment reviews for goodwill and intangible assets did not result in the recognition of impairment losses for 2015, 2014 and 2013.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders’ Equity Authorized and Issued The authorized share capital of ACGL consists of 600 million Common Shares, par value of $0.0033 per share, and 50 million Preferred Shares, par value of $0.01 per share. Common Shares The following table presents a roll-forward of changes in ACGL’s issued and outstanding Common Shares: Year Ended December 31, 2015 2014 2013 Common Shares: Shares issued and outstanding, beginning of year 171,672,408 169,560,591 168,255,572 Shares issued (1) 1,001,667 1,493,524 811,732 Restricted shares issued, net of cancellations 433,774 618,293 493,287 Shares issued, end of year 173,107,849 171,672,408 169,560,591 Common shares in treasury, end of year (50,480,066 ) (44,304,474 ) (35,885,707 ) Shares issued and outstanding, end of year 122,627,783 127,367,934 133,674,884 (1) Includes shares issued from the exercise of stock options and stock appreciation rights, and shares issued from the employee share purchase plan. Share Repurchases The board of directors of ACGL has authorized the investment in ACGL’s common shares through a share repurchase program. Authorizations have consisted of a $1.0 billion authorization in February 2007, a $500.0 million authorization in May 2008, a $1.0 billion authorization in November 2009, a $1.0 billion authorization in February 2011 and a $629.2 million authorization in November 2014. Since the inception of the share repurchase program through December 31, 2015 , ACGL has repurchased approximately 124.1 million common shares for an aggregate purchase price of $3.61 billion . During 2015 , ACGL repurchased 5.9 million common shares for an aggregate purchase price of $365.4 million , compared to 8.2 million common shares for an aggregate purchase price of $454.1 million during 2014 and 1.3 million common shares for an aggregate purchase price of $57.8 million during 2013 . At December 31, 2015 , approximately $521.8 million of share repurchases were available under the program. Repurchases under the program may be effected from time to time in open market or privately negotiated transactions. 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. Treasury Shares In May 2010, ACGL’s shareholders approved amendments to the bye-laws to permit ACGL to hold its own acquired shares as treasury shares in lieu of cancellation, as determined by ACGL’s board of directors. From May 5, 2010 to December 31, 2015 , all repurchases of ACGL’s common shares in connection with the share repurchase plan noted above and other share-based transactions were held in the treasury under the cost method, and the cost of the common shares acquired is included in ‘Common shares held in treasury, at cost.’ At December 31, 2015 , ACGL held 50.5 million shares for an aggregate cost of $1.94 billion in treasury, at cost. Preferred Shares On April 2, 2012, ACGL completed the underwritten public offering of $325.0 million of its 6.75% Series C non-cumulative preferred shares (“Preferred Shares”). Except in specified circumstances relating to certain tax or corporate events, the Preferred Shares are not redeemable prior to April 2, 2017. The net proceeds from the offering of $315.8 million and other available funds were used to redeem all of ACGL’s $200.0 million of 8.0% Series A preferred shares and $125.0 million of 7.875% Series B preferred shares on May 2, 2012. The Series A preferred shares and Series B preferred shares were redeemed at a redemption price equal to $25.00 per share, plus all declared and unpaid dividends to (but excluding) the redemption date. Dividends on the Preferred Shares are non-cumulative. Consequently, in the event dividends are not declared on the Preferred Shares for any dividend period, holders of Preferred Shares will not be entitled to receive a dividend for such period, and such undeclared dividend will not accrue and will not be payable. Holders of Preferred Shares will be entitled to receive dividend payments only when, as and if declared by ACGL’s board of directors or a duly authorized committee of the board of directors. Any such dividends will be payable from the date of original issue on a non-cumulative basis, quarterly in arrears. To the extent declared, these dividends will accumulate, with respect to each dividend period, in an amount per share equal to 6.75% of the $25.00 liquidation preference per annum. In 2015 , 2014 and 2013 , ACGL paid dividends of $21.9 million to holders of ACGL’s preferred shares.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation Long Term Incentive and Share Award Plans The 2015 Long Term Incentive and Share Award Plan (the (“2015 Plan”) became effective as of May 7, 2015 following approval by shareholders of the Company. The purposes of the 2015 Plan are to advance the interests of ACGL and its shareholders by providing a means to attract, retain, and motivate employees and directors of ACGL and its subsidiaries. The 2015 Plan is intended to provide for competitive compensation opportunities, to encourage long-term service, to recognize individual contributions and reward achievement of performance goals, and to promote the creation of long-term value for shareholders by aligning the interests of such persons with those of shareholders. Officers, other employees and directors of ACGL and its subsidiaries will be eligible for grants of awards under the 2015 Plan. The 2015 Plan will terminate as to future awards on February 26, 2025. The number of common shares reserved for grants of awards under the 2015 Plan, subject to anti-dilution adjustments in the event of certain changes in the Company’s capital structure is 4,300,000 . In addition, no more than 50% of such common shares may be issued in connection with full value awards ( i.e. , awards other than stock options or SARs) and no more than 2,000,000 common shares may be issued as incentive stock options under Section 422 of the Code. At December 31, 2015, 3,242,692 shares are available for future issuance. The 2012 Long Term Incentive and Share Award Plan (the “2012 Plan”) became effective as of May 9, 2012 (the “Effective Date”) following approval by shareholders of the Company. The 2012 Plan is intended to provide for competitive compensation opportunities, to encourage long-term service, to recognize individual contributions and reward achievement of performance goals and to promote the creation of long-term value for shareholders by aligning the interests of such persons with those of shareholders. The 2012 Plan provides for the grant to eligible employees and directors stock options, stock appreciation rights (“SARs”), restricted shares, restricted share units payable in common shares or cash, share awards in lieu of cash awards, dividend equivalents and other share-based awards. The 2012 Plan also provides the Company’s non-employee directors with the opportunity to receive the annual retainer fee for Board service in common shares. The 2012 Plan will terminate as to future awards on February 28, 2022. The 2007 Long Term Incentive and Share Award Plan (the “2007 Plan”) was merged with and into the 2012 Plan as of the Effective Date. As of the Effective Date, the 3,153,924 remaining shares available for issuance under the 2007 Plan were transferred into the 2012 Plan and as of such date no additional grants may be made under the 2007 Plan. Grants which were outstanding under the 2007 Plan as of the Effective Date will continue in accordance with their original terms (subject to such amendments as the compensation committee determines appropriate, consistent with the terms of the 2007 Plan) and will be issued or transferred under the 2012 Plan. The number of common shares reserved for grants of awards under the 2012 Plan, subject to anti-dilution adjustments in the event of certain changes in the Company’s capital structure is 7,433,924 which is the sum of (i) 4,280,000 and (ii) 3,153,924 shares remaining available for grants under the 2007 Plan. In addition, no more than 50% of such common shares may be issued in connection with full value awards ( i.e., awards other than stock options or SARs) and no more than 2,000,000 common shares may be issued as incentive stock options under Section 422 of the Code. At December 31, 2015 , 950,307 shares are available for grant under the 2012 Plan. On May 11, 2007, following shareholder approval, the Company adopted the 2007 Employee Share Purchase Plan (the “ESPP”). The purpose of the ESPP is to give employees of ACGL and its subsidiaries an opportunity to purchase common shares through payroll deductions, thereby encouraging employees to share in the economic growth and success of ACGL and its subsidiaries. The ESPP is designed to qualify as an “employee share purchase plan” under Section 423 of the Code. A total of 2,250,000 common shares are reserved for issuance under the ESPP. At December 31, 2015 , approximately 563,259 shares remain available for issuance. The ESPP provides for consecutive six-month offering periods (or other periods of not more than 27 months as determined by the compensation committee) under which participating employees can elect to have up to 20% of their total compensation withheld and applied to the purchase of common shares of the Company at the end of the period. Unless otherwise determined by the compensation committee before an offering period commences, (1) the purchase price will be 85% of the fair market value of the common shares at the beginning of the offering period; and (2) the maximum number of common shares that may be purchased by an employee in any offering period is 3,000 shares. In addition, applicable Code limitations specify, in general, that a participant’s right to purchase stock under the ESPP cannot accumulate at a rate in excess of $25,000 (based on the value at the beginning of the applicable offering periods) per calendar year. The Company recorded $1.7 million of share-based compensation expense, net of a tax benefit of $0.2 million , related to the ESPP for 2015 , compared to $1.6 million , net of a tax benefit of $0.1 million , for 2014 and $1.4 million , net of a tax benefit of $0.1 million , for 2013 . With respect to certain subsidiaries, the Company may withhold, or require a participant to remit to the Company, an amount sufficient to satisfy any federal, state or local withholding tax requirements associated with awards under the Company’s share award plans. This includes the authority to withhold or receive shares or other property and to make cash payments in respect thereof. Stock Options and Stock Appreciation Rights The Company generally issues stock options and SARs to eligible employees, with exercise prices equal to the fair market values of the Company’s Common Shares on the grant dates. Such grants generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. In addition, in November 2012 the Company issued off-cycle stock options and SARs to certain employees, which will cliff vest on the fifth anniversary of the grant date. Option awards and SARs have a 10 year contractual life. Refer to Note 3 (m) for details related to the Company’s accounting for stock options and SARs. The Company recorded after-tax share-based compensation expense of $10.5 million related to stock options and SARs for 2015 , net of a tax benefit of $2.2 million , compared to $12.5 million for 2014 , net of a tax benefit of $2.1 million , and $10.6 million for 2013 , net of a tax benefit of $2.0 million . As of December 31, 2015 , there was approximately $12.0 million of unrecognized compensation cost related to nonvested stock options and SARs. Such cost is expected to be recognized over a weighted average period of 1.3 years. For purposes of determining estimated market value, the Company has computed the estimated market values of share-based compensation related to stock options and SARs using the Black-Scholes option valuation model and has applied the assumptions set forth in the following table. As described above, stock options and SARs generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. The expected life assumption ( i.e. , the estimated period of time between the date an option or SAR is granted and the date the option or SAR is exercised) was based on an expected term analysis which incorporated the Company’s historical exercise experience. The Company based its estimate of expected volatility for stock options and SARs granted during 2015 on daily historical trading data of its common shares from September 20, 2002, the date marking the completion of the Company’s transition as a worldwide insurance and reinsurance company. For stock options and SARs granted during 2014 and 2013 , the Company based its volatility estimate under the same method used for 2015 , using the period from September 20, 2002 through the last day of the applicable period. Year Ended December 31, 2015 2014 2013 Dividend yield 0.0 % 0.0 % 0.0 % Expected volatility 22.1 % 22.8 % 23.6 % Risk free interest rate 1.8 % 1.9 % 1.0 % Expected option life 6.0 years 6.0 years 6.0 years The Black-Scholes option pricing model requires the input of highly subjective assumptions. Because the Company’s employee stock options and SARs have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of its employee stock options and SARs. In addition, management will continue to assess the assumptions and methodologies used to calculate estimated fair value of share-based compensation. Circumstances may change and additional data may become available over time, which could result in changes to these assumptions and methodologies, and which could materially impact the Company’s fair value determination. A summary of stock option and SAR activity under the Company’s Long Term Incentive and Share Award Plans during 2015 is presented below: Year Ended December 31, 2015 Number of Options / SARs Weighted Average Exercise Price Outstanding, beginning of year 7,804,033 $ 34.52 Granted 693,107 $ 61.93 Exercised (926,958 ) $ 24.91 Forfeited or expired (87,720 ) $ 50.09 Outstanding, end of year 7,482,462 $ 38.07 Exercisable, end of year 5,429,047 $ 32.88 The weighted average grant-date fair value of stock options and SARs granted during 2015 , 2014 and 2013 was $15.90 , $14.77 and $12.96 , respectively. The aggregate intrinsic value of stock options and SARs exercised during 2015 , 2014 and 2013 was approximately $38.6 million , $58.4 million , and $21.7 million , respectively and represents the difference between the exercise price of the stock options and SARs and the closing market price of the Company’s common shares on the exercise dates. Shares issued upon exercise of stock options and SARs were from the Company’s authorized but unissued share capital pool. The aggregate intrinsic value of the Company’s outstanding and exercisable stock options and SARs at December 31, 2015 was $237.1 million and $200.2 million , respectively. The weighted average remaining contractual life of the Company’s outstanding and exercisable stock options and SARs at December 31, 2015 was 5.4 years and 4.4 years , respectively. During 2015 , the Company received proceeds of $9.4 million from the exercise of stock options and recognized a tax benefit of $8.0 million from the exercise of stock options and SARs. Restricted Common Shares and Restricted Units The Company also issues restricted share and unit awards to eligible employees and directors, for which the fair value is equal to the fair market values of the Company’s Common Shares on the grant dates. Restricted share and unit awards generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. In addition, in November 2012 the Company issued off-cycle restricted share and unit awards to certain employees, which will cliff vest on the fifth anniversary of the grant date. Refer to Note 3 (m) for details related to the Company’s accounting for restricted share and unit awards. The Company recorded $32.9 million of share-based compensation expense, net of a tax benefit of $8.6 million , related to restricted share and unit awards for 2015 , compared to $30.0 million , net of a tax benefit of $8.4 million , for 2014 and $27.4 million , net of a tax benefit of $7.8 million , for 2013 . As of December 31, 2015 , there was $39.9 million and $6.2 million , respectively, of unrecognized compensation costs related to unvested restricted share and unit awards, which are expected to be recognized over a weighted average period of 1.3 years and 1.3 years , respectively. A summary of unvested restricted share and unit activity under the Company’s Long Term Incentive and Share Award Plans for 2015 is presented below: Year Ended December 31, 2015 Restricted Common Shares Restricted Unit Awards Unvested Shares: Unvested balance, beginning of year 1,969,842 305,133 Granted 502,638 69,340 Vested (603,023 ) (88,916 ) Forfeited (68,864 ) (20,928 ) Unvested balance, end of year 1,800,593 264,629 Weighted Average Grant Date Fair Value: Unvested balance, beginning of year $ 48.47 $ 48.49 Granted $ 62.70 $ 62.61 Vested $ 49.75 $ 50.94 Forfeited $ 50.45 $ 48.97 Unvested balance, end of year $ 51.94 $ 51.33 During 2015 , 2014 and 2013 , the Company granted an aggregate of 571,978 , 767,469 and 590,118 restricted share and restricted unit awards, respectively, with weighted average grant date fair values of $62.69 , $56.97 and $53.21 , respectively. During 2015 , 2014 and 2013 , the aggregate fair value of restricted shares and units that vested was $43.8 million , $38.6 million and $41.0 million , respectively. The aggregate intrinsic value of restricted units outstanding at December 31, 2015 was $28.8 million , and the aggregate intrinsic value of restricted units vested and deferred was $10.4 million . The issuance of share-based awards and amortization thereon has no effect on the Company’s consolidated shareholders’ equity.

Retirement Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Retirement Plans	Retirement Plans For purposes of providing employees with retirement benefits, the Company maintains defined contribution retirement plans. Contributions are based on the participants’ eligible compensation. For 2015 , 2014 and 2013 , the Company expensed $29.7 million , $26.8 million and $21.5 million , respectively, related to these retirement plans.

Legal Proceedings

Legal Proceedings	12 Months Ended
	Dec. 31, 2015
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 December 31, 2015 , 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.

Statutory Information

Statutory Information	12 Months Ended
	Dec. 31, 2015
Disclosure Statutory Information [Abstract]
Statutory Information	Statutory Information The Company’s insurance and reinsurance subsidiaries are subject to insurance and/or reinsurance laws and regulations in the jurisdictions in which they operate. These regulations include certain restrictions on the amount of dividends or other distributions available to shareholders without prior approval of the insurance regulatory authorities. The actual and required statutory capital and surplus for the Company’s principal operating subsidiaries at December 31, 2015 and 2014 was as follows: December 31, 2015 December 31, 2014 Actual (1) Required (1) Actual (1) Required (1) Statutory capital and surplus (1): Bermuda $ 6,397,010 $ 2,129,064 $ 6,447,803 $ 2,209,757 Ireland 559,996 459,271 553,561 463,877 United States 1,564,056 488,794 1,454,282 467,797 United Kingdom 404,821 321,462 384,525 307,596 Canada 67,436 36,360 79,123 58,837 (1) Such amounts include ownership interests in affiliated insurance and reinsurance subsidiaries. The statutory net income (loss) for the Company’s principal operating subsidiaries for 2015 , 2014 and 2013 was as follows: Year Ended December 31, 2015 2014 2013 Statutory net income (loss): Bermuda $ 514,151 $ 692,676 $ 719,267 Ireland 29,041 43,197 (24,410 ) United States 76,604 46,110 62,605 United Kingdom 3,285 13,016 (11,353 ) Canada (1,098 ) 1,517 (36,203 ) Statutory accounting differs from U.S. GAAP in the reporting of certain items such as acquisition costs, deferred income taxes and investments. Bermuda Under The Insurance Act 1978, as amended, and related regulations of Bermuda (the “Insurance Act”), Arch Re Bermuda, the Company’s Bermuda reinsurance and insurance subsidiary, is registered as a Class 4 insurer and long-term insurer and is required to annually prepare and file statutory financial statements and a statutory financial return with the Bermuda Monetary Authority (“BMA”). The Insurance Act also requires Arch Re Bermuda to maintain minimum share capital and must ensure that the value of its general business assets exceeds the amount of its general business liabilities by an amount greater than the prescribed minimum solvency margins and enhanced capital requirement pertaining to its general business. At December 31, 2015 , all such requirements were met. Arch Re Bermuda is also required to file a regulatory risk based capital model that measures risks and determines enhanced capital requirements and a target capital level. In addition, all Class 4 Bermuda insurers must prepare and file with the BMA audited GAAP basis annual financial statements, which must be made publicly available. Declarations of dividends from retained earnings and distributions from additional paid-in-capital are subject to these requirements being met. For all applicable periods presented herein, Arch Re Bermuda satisfied these requirements. The Bermuda Companies Act 1981 (the “Companies Act”) limits Arch Re Bermuda’s ability to pay dividends and distributions to shareholders if there are reasonable grounds for believing that: (a) Arch Re Bermuda is, or would after the payment be, unable to pay its liabilities as they become due; or (b) the realizable value of Arch Re Bermuda’s assets would thereby be less than the aggregate of its liabilities and its issued share capital and share premium accounts. Under the Insurance Act, Arch Re Bermuda is restricted with respect to the payment of dividends. Arch Re Bermuda is prohibited from declaring or paying in any financial year dividends of more than 25% of its total statutory capital and surplus (as shown on its previous financial year’s statutory balance sheet) unless it files, at least seven days before payment of such dividends, with the Bermuda Monetary Authority an affidavit stating that it will continue to meet the required margins. In addition, Arch Re Bermuda is prohibited, without prior approval of the Bermuda Monetary Authority, from reducing by 15% or more its total statutory capital, as set out in its previous year’s statutory financial statements. Accordingly, Arch Re Bermuda can pay approximately $1.36 billion to ACGL during 2016 without providing an affidavit to the BMA. Watford Re is registered as a Class 4 insurer and is required to annually prepare and file statutory financial statements and a statutory financial return with the BMA. The Insurance Act also requires Watford Re to maintain minimum share capital and must ensure that the value of its general business assets exceeds the amount of its general business liabilities by an amount greater than the prescribed minimum solvency margins and enhanced capital requirement pertaining to its general business. At December 31, 2015 , all such requirements were met. Ireland Arch Re Europe was licensed and authorized by the Central Bank of Ireland (“CBOI”) as a non-life reinsurer in October 2008 and as a life reinsurer in November 2009 while Arch MI Europe was authorized as a non-life insurer in Ireland in December 2011. Irish authorized reinsurers and insurers, such as Arch Re Europe and Arch MI Europe, are also subject to the general body of Irish laws and regulations including the provisions of the Companies Act 2014. Arch Re Europe and Arch MI Europe are subject to the supervision of the CBOI and must comply with Irish insurance acts and regulations as well as with directions and guidance issued by the CBOI. Arch Re Europe and Arch MI Europe are required to maintain reserves, particularly in respect of underwriting liabilities and a solvency margin. Assets constituting statutory reserves must comply with certain principles including obligations to secure sufficiency, liquidity, security, quality, profitability and currency matching of investments. Statutory reserves must be actuarially certified annually. Under Irish company law, Arch Re Europe and Arch MI Europe are permitted to make distributions only out of profits available for distribution. A company’s profits available for distribution are its accumulated, realized profits, so far as not previously utilized by distribution or capitalization, less its accumulated, realized losses, so far as not previously written off in a reduction or reorganization of capital duly made. Further, the CBOI has powers to intervene if a dividend payment were to lead to a breach of regulatory capital requirements. Dividends or distributions, if any, made by Arch Re Europe would result in an increase in available capital at Arch Re Bermuda. United States The Company’s U.S. insurance and reinsurance subsidiaries file financial statements prepared in accordance with statutory accounting practices prescribed or permitted by insurance regulators. Statutory net income and statutory surplus, as reported to the insurance regulatory authorities, differ in certain respects from the amounts prepared in accordance with GAAP. The main differences between statutory net income and GAAP net income relate to deferred acquisition costs and deferred income taxes. In addition to deferred acquisition costs and deferred income tax assets, other differences between statutory surplus and GAAP shareholder’s equity are unrealized appreciation or decline in value of investments and non-admitted assets. The Company’s U.S. insurance and reinsurance subsidiaries are subject to insurance laws and regulations in the jurisdictions in which they operate. The ability of the Company’s regulated insurance subsidiaries to pay dividends or make distributions is dependent on their ability to meet applicable regulatory standards. These regulations include restrictions that limit the amount of dividends or other distributions, such as loans or cash advances, available to shareholders without prior approval of the insurance regulatory authorities. Dividends or distributions, if any, made by Arch Re U.S. would result in an increase in available capital at Arch-U.S., the Company’s U.S. holding company. Arch Re U.S. can declare a maximum of approximately $120 million of dividends during 2016 subject to the approval of the Commissioner of the Delaware Department of Insurance (“Commissioner”). In addition, with respect to dividends in excess of the $120 million (extraordinary dividend), no payment can be made until (1) 30 days after the Commissioner has received notice of the declaration thereof and has not within such period disapproved such payments; or (2) the Commissioner shall have approved the payment within the 30 -day period. Delaware insurance laws also require that the statutory surplus of Arch Re U.S. following any dividend or distribution be reasonable in relation to its outstanding liabilities and adequate to its financial needs. Arch MI U.S. is subject to detailed regulation both by its domiciliary and primary regulator, the Wisconsin Office of the Commissioner of Insurance, and by state insurance departments in each state in which it is licensed. In addition, Arch MI U.S. is currently approved by the GSEs as an eligible mortgage insurer. In April 2015, the GSEs published comprehensive, revised requirements, known as the Private Mortgage Insurer Eligibility Requirements or “PMIERs.” The PMIERs became effective December 31, 2015 and apply to Arch MI U.S., which is a GSE-approved mortgage insurer. In addition to extensive requirements relating to the operation of the Company’s mortgage insurance business, the PMIERs include revised financial requirements for mortgage insurers. These financial requirements require a mortgage insurer’s available assets, which generally include only the most liquid assets of an insurer, to meet or exceed “minimum required assets” as of each quarter end. Minimum required assets are calculated from PMIERs tables with several risk dimensions (including origination year, original loan-to-value and original credit score of performing loans, and the delinquency status of non-performing loans) and are subject to a minimum amount. Under the PMIERs, Arch MI U.S. is deemed to be a “newly-approved insurer.” As a result of this status, until January 2017, Arch MI U.S. is subject to additional PMIER requirements, including that it is prohibited from paying dividends to affiliates or making any investment, contribution or loan to any affiliate until such date. United Kingdom The Company’s European insurance operations are conducted on two platforms: Arch Insurance Company Europe and Arch Syndicate 2012 (collectively, the insurance operations are referred to as “Arch Insurance Europe”). Arch Insurance Company Europe was licensed and authorized by the Financial Services Authority (“FSA”) to underwrite all classes of general insurance in the U.K. in May 2004. In 2009, AUAL was licensed and authorized by the FSA and the Lloyd’s Franchise Board. AUAL holds the relevant permissions for the classes of insurance business which are underwritten in the U.K. by Arch Syndicate 2012. Arch Syndicate 2012 has one member, Arch Syndicate Investments Ltd. The FSA was replaced by the Prudential Regulatory Authority (“PRA”) and the Financial Conduct Authority (“FCA”) in 2013. The PRA has responsibility for the prudential regulation of banks and insurers, while the FCA has responsibility for the conduct of business regulation in the wholesale and retail markets. All U.K. companies are also subject to a range of statutory provisions, including the laws and regulations of the Companies Acts 2006 (as amended) (the “U.K. Companies Acts”). Arch Insurance Company Europe and AUAL (on behalf of itself, Arch Syndicate 2012 and ASIL) are each required to demonstrate the adequacy of its financial assets to the PRA. On a periodic basis, Arch Insurance Europe is required to provide the PRA and Lloyd’s with its own risk-based assessment of its capital needs, taking into account comprehensive risk factors, including market, credit, operational, liquidity and group risks to generate a revised calculation of its expected liabilities which, in turn, enables the PRA and Lloyd’s to provide individual capital guidance and requirements to Arch Insurance Europe. Arch Insurance Europe’s surplus is above the risk-based capital threshold allowed by the PRA's individual capital assessment of Arch Insurance Europe. The PRA requires that Arch Insurance Europe maintain a margin of solvency calculation based on the classes of business for which it is authorized and within its premium income projections applied to its worldwide general business. Under U.K. law, all U.K. companies are restricted from declaring a dividend to their shareholders unless they have “profits available for distribution.” The calculation as to whether a company has sufficient profits is based on its accumulated realized profits minus its accumulated realized losses. U.K. insurance regulatory laws do not prohibit the payment of dividends, but the PRA or FCA, as applicable, requires that insurance companies and insurance intermediaries maintain certain solvency margins and may restrict the payment of a dividend by Arch Insurance Company Europe, AUAL and ASIL. Dividends or distributions, if any, made by Arch Insurance Europe would result in an increase in available capital at Arch Re Europe, a subsidiary of Arch Re Bermuda. Canada Arch Insurance Canada, which commenced underwriting on January 1, 2013, and the Canadian branch of Arch Re U.S. (“Arch Re Canada”), which commenced underwriting on January 1, 2015, are subject to federal, as well as provincial and territorial, regulation in Canada. The Office of the Superintendent of Financial Institutions (“OSFI”) is the federal regulatory body that, under the Insurance Companies Act (Canada), regulates federal Canadian and non-Canadian insurance companies operating in Canada. Arch Insurance Canada and Arch Re Canada are subject to regulation in the provinces and territories in which they underwrite insurance/reinsurance, and the primary goal of insurance/reinsurance regulation at the provincial and territorial levels is to govern the market conduct of insurance/reinsurance companies. Arch Insurance Canada is licensed to carry on insurance business by OSFI and in each province and territory. Arch Re Canada is licensed to carry-on reinsurance business by OSFI and in the provinces of Ontario and Quebec. Under the Insurance Companies Act (Canada), Arch Insurance Canada is required to maintain an adequate amount of capital in Canada, calculated in accordance with a test promulgated by OSFI called the Minimum Capital Test (“MCT”), and Arch Re Canada is required to maintain an adequate margin of assets over liabilities in Canada, calculated in accordance with a test promulgated by OSFI called the Branch Adequacy of Assets Test. Dividends or distributions, if any, made by Arch Insurance Canada would result in an increase in available capital at Arch Insurance Company (see “—United States” section). Dubai Gulf Re is incorporated in the Dubai International Financial Centre (“DIFC”), a free zone specializing in wholesale financial services. The DIFC is situated in the Emirate of Dubai in the United Arab Emirates. Gulf Re is licensed to “Carry out Contracts of (Re)insurance” and “Effect Contracts of (Re)insurance” in respect of general insurance lines. Gulf Re is overseen by the DFSA and is subject to the laws of the DIFC. Gulf Re is not subject to insurance or financial regulation by the United Arab Emirates. As a (re)insurer licensed in the DIFC (a wholesale financial services market), Gulf Re is authorized to insure direct risks situated in the DIFC, but can only reinsure risks situated in the rest of the United Arab Emirates. In respect of risks situated outside of the United Arab Emirates, Gulf Re is authorized to insure or reinsure risks provided that doing so is not in breach of local regulation. Dividends or distributions, if any, made by Gulf Re would result in an increase in available capital at Arch Re Bermuda.

Unaudited Condensed Quarterly F

Unaudited Condensed Quarterly Financial Information	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Unaudited Condensed Quarterly Financial Information	Unaudited Condensed Quarterly Financial Information The following table summarizes the 2015 and 2014 unaudited condensed quarterly financial information: Fourth Quarter Third Quarter Second Quarter First Quarter Year Ended December 31, 2015 Net premiums written $ 834,984 $ 971,972 $ 943,580 $ 1,066,995 Net premiums earned 943,520 936,683 943,438 910,264 Net investment income 95,900 86,233 86,963 78,994 Net realized gains (losses) (143,767 ) (89,698 ) (35,725 ) 83,348 Net impairment losses recognized in earnings (7,336 ) (5,868 ) (1,113 ) (5,799 ) Underwriting income 113,143 94,779 105,114 116,471 Net income 58,579 80,033 115,790 283,336 Preferred dividends (5,485 ) (5,484 ) (5,485 ) (5,484 ) Net income available to Arch common shareholders 53,094 74,549 110,305 277,852 Net income per common share -- basic $ 0.44 $ 0.62 $ 0.91 $ 2.24 Net income per common share -- diluted $ 0.42 $ 0.60 $ 0.88 $ 2.16 Year Ended December 31, 2014 Net premiums written $ 895,481 $ 959,539 $ 971,928 $ 1,064,990 Net premiums earned 923,165 903,651 907,152 859,780 Net investment income 82,496 80,105 72,990 66,994 Net realized gains (losses) 10,561 18,515 54,144 19,697 Net impairment losses recognized in earnings (3,837 ) (8,593 ) (14,749 ) (2,971 ) Underwriting income 113,464 101,087 124,091 132,456 Net income 215,164 228,675 208,016 182,500 Preferred dividends (5,485 ) (5,484 ) (5,485 ) (5,484 ) Net income available to Arch common shareholders 209,679 223,191 202,531 177,016 Net income per common share -- basic $ 1.65 $ 1.69 $ 1.53 $ 1.34 Net income per common share -- diluted $ 1.60 $ 1.64 $ 1.48 $ 1.30

Guarantor Financial Information

Guarantor Financial Information	12 Months Ended
	Dec. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Guarantor Financial Information	Guarantor Financial Information The following tables present condensed consolidating balance sheets at December 31, 2015 and 2014 and condensed consolidating statements of income, comprehensive income and cash flows for 2015 , 2014 and 2013 for ACGL, Arch-U.S., a 100% owned subsidiary of ACGL, and ACGL's other subsidiaries. December 31, 2015 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 50 $ 42,210 $ 15,815,381 $ (14,700 ) $ 15,842,941 Cash 6,809 17,023 529,494 — 553,326 Investments in subsidiaries 6,609,174 1,712,757 — (8,321,931 ) — Due from subsidiaries and affiliates 23 48,811 384,469 (433,303 ) — Premiums receivable — — 1,376,310 (392,867 ) 983,443 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 5,783,452 (3,916,079 ) 1,867,373 Contractholder receivables — — 1,486,296 — 1,486,296 Prepaid reinsurance premiums — — 1,511,795 (1,084,186 ) 427,609 Deferred acquisition costs, net — — 433,477 — 433,477 Other assets 4,138 45,522 2,119,279 (586,134 ) 1,582,805 Total assets $ 6,620,194 $ 1,866,323 $ 29,439,953 $ (14,749,200 ) $ 23,177,270 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 13,010,608 $ (3,885,358 ) $ 9,125,250 Unearned premiums — — 3,418,118 (1,084,186 ) 2,333,932 Reinsurance balances payable — — 603,586 (379,466 ) 224,120 Contractholder payables — — 1,486,296 — 1,486,296 Collateral held for insured obligations 248,982 248,982 Deposit accounting liabilities — — 463,507 (203,143 ) 260,364 Senior notes 296,874 494,432 — — 791,306 Revolving credit agreement borrowings 100,000 — 430,434 — 530,434 Due to subsidiaries and affiliates 26 35,000 398,277 (433,303 ) — Other liabilities 18,413 50,890 1,385,500 (427,111 ) 1,027,692 Total liabilities 415,313 580,322 21,445,308 (6,412,567 ) 16,028,376 Redeemable noncontrolling interests — — 219,882 (14,700 ) 205,182 Shareholders' Equity Total shareholders' equity available to Arch 6,204,881 1,286,001 7,035,932 (8,321,933 ) 6,204,881 Non-redeemable noncontrolling interests — — 738,831 — 738,831 Total shareholders' equity 6,204,881 1,286,001 7,774,763 (8,321,933 ) 6,943,712 Total liabilities, noncontrolling interests and shareholders' equity $ 6,620,194 $ 1,866,323 $ 29,439,953 $ (14,749,200 ) $ 23,177,270 December 31, 2014 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 107 $ 62,867 $ 15,257,796 $ — $ 15,320,770 Cash 3,218 2,787 479,697 — 485,702 Investments in subsidiaries 6,536,644 1,685,185 — (8,221,829 ) — Due from subsidiaries and affiliates 48 7,517 370,429 (377,994 ) — Premiums receivable — — 1,331,511 (382,816 ) 948,695 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 5,584,973 (3,772,128 ) 1,812,845 Contractholder receivables — — 1,309,192 — 1,309,192 Prepaid reinsurance premiums — — 1,373,008 (995,930 ) 377,078 Deferred acquisition costs, net — — 414,525 — 414,525 Other assets 4,386 43,921 1,705,546 (416,579 ) 1,337,274 Total assets $ 6,544,403 $ 1,802,277 $ 27,826,677 $ (14,167,276 ) $ 22,006,081 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 12,784,030 $ (3,747,582 ) $ 9,036,448 Unearned premiums — — 3,227,508 (995,930 ) 2,231,578 Reinsurance balances payable — — 589,289 (369,977 ) 219,312 Contractholder payables — — 1,309,192 — 1,309,192 Collateral held for insured obligations 184,219 184,219 Deposit accounting liabilities — — 587,050 (259,666 ) 327,384 Senior notes 296,796 494,345 — — 791,141 Revolving credit agreement borrowings 100,000 — — — 100,000 Due to subsidiaries and affiliates 417 7,505 370,072 (377,994 ) — Other liabilities 17,137 49,403 815,919 (194,298 ) 688,161 Total liabilities 414,350 551,253 19,867,279 (5,945,447 ) 14,887,435 Redeemable noncontrolling interests — — 219,512 — 219,512 Shareholders' Equity Total shareholders' equity available to Arch 6,130,053 1,251,024 6,970,805 (8,221,829 ) 6,130,053 Non-redeemable noncontrolling interests — — 769,081 — 769,081 Total shareholders' equity 6,130,053 1,251,024 7,739,886 (8,221,829 ) 6,899,134 Total liabilities, noncontrolling interests and shareholders' equity $ 6,544,403 $ 1,802,277 $ 27,826,677 $ (14,167,276 ) $ 22,006,081 Year Ended December 31, 2015 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 $ — $ — $ 3,733,905 $ — $ 3,733,905 Net investment income 1 2,342 368,413 (22,666 ) 348,090 Net realized gains (losses) — 1 (185,843 ) — (185,842 ) Net impairment losses recognized in earnings — — (20,116 ) — (20,116 ) Other underwriting income — — 35,739 (242 ) 35,497 Equity in net income (loss) of investment funds accounted for using the equity method — — 25,455 — 25,455 Other income (loss) — — (399 ) — (399 ) Total revenues 1 2,343 3,957,154 (22,908 ) 3,936,590 Expenses Losses and loss adjustment expenses — — 2,050,903 — 2,050,903 Acquisition expenses — — 681,476 — 681,476 Other operating expenses 48,107 3,689 605,465 — 657,261 Interest expense 23,450 26,502 18,024 (22,102 ) 45,874 Net foreign exchange (gains) losses — — (41,622 ) (24,496 ) (66,118 ) Total expenses 71,557 30,191 3,314,246 (46,598 ) 3,369,396 Income (loss) before income taxes (71,556 ) (27,848 ) 642,908 23,690 567,194 Income tax (expense) benefit — 9,732 (50,344 ) — (40,612 ) Income (loss) before equity in net income of subsidiaries (71,556 ) (18,116 ) 592,564 23,690 526,582 Equity in net income of subsidiaries 609,294 50,156 — (659,450 ) — Net income 537,738 32,040 592,564 (635,760 ) 526,582 Net (income) loss attributable to noncontrolling interests — — 10,351 805 11,156 Net income available to Arch 537,738 32,040 602,915 (634,955 ) 537,738 Preferred dividends (21,938 ) — — — (21,938 ) Net income available to Arch common shareholders $ 515,800 $ 32,040 $ 602,915 $ (634,955 ) $ 515,800 Comprehensive income (loss) available to Arch $ 392,380 $ 838 $ 482,047 $ (482,885 ) $ 392,380 Year Ended December 31, 2014 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 $ — $ — $ 3,593,748 $ — $ 3,593,748 Net investment income — — 326,831 (24,246 ) 302,585 Net realized gains (losses) — 5 102,912 — 102,917 Net impairment losses recognized in earnings — — (30,150 ) — (30,150 ) Other underwriting income — — 10,142 — 10,142 Equity in net income (loss) of investment funds accounted for using the equity method — — 19,883 — 19,883 Other income (loss) — — (10,252 ) — (10,252 ) Total revenues — 5 4,013,114 (24,246 ) 3,988,873 Expenses Losses and loss adjustment expenses — — 1,919,250 — 1,919,250 Acquisition expenses — — 657,262 — 657,262 Other operating expenses 46,074 3,387 556,763 — 606,224 Interest expense 23,423 25,817 20,640 (24,246 ) 45,634 Net foreign exchange (gains) losses — — (53,222 ) (30,522 ) (83,744 ) Total expenses 69,497 29,204 3,100,693 (54,768 ) 3,144,626 Income (loss) before income taxes (69,497 ) (29,199 ) 912,421 30,522 844,247 Income tax (expense) benefit — 10,125 (33,112 ) — (22,987 ) Income (loss) before equity in net income of subsidiaries (69,497 ) (19,074 ) 879,309 30,522 821,260 Equity in net income of subsidiaries 903,852 53,584 — (957,436 ) — Net income 834,355 34,510 879,309 (926,914 ) 821,260 Net (income) loss attributable to noncontrolling interests — — 13,095 — 13,095 Net income available to Arch 834,355 34,510 892,404 (926,914 ) 834,355 Preferred dividends (21,938 ) — — — (21,938 ) Net income available to Arch common shareholders $ 812,417 $ 34,510 $ 892,404 $ (926,914 ) $ 812,417 Comprehensive income (loss) available to Arch $ 888,247 $ 33,671 $ 976,821 $ (1,010,492 ) $ 888,247 Year Ended December 31, 2013 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 $ — $ — $ 3,145,952 $ — $ 3,145,952 Net investment income — 31 307,449 (40,261 ) 267,219 Net realized gains (losses) — — 74,018 — 74,018 Net impairment losses recognized in earnings — — (3,786 ) — (3,786 ) Other underwriting income — — 7,639 — 7,639 Equity in net income (loss) of investment funds accounted for using the equity method — — 35,701 — 35,701 Other income (loss) — — (586 ) — (586 ) Total revenues — 31 3,566,387 (40,261 ) 3,526,157 Expenses Losses and loss adjustment expenses — — 1,679,424 — 1,679,424 Acquisition expenses — — 564,103 — 564,103 Other operating expenses 38,702 2,691 459,337 — 500,730 Interest expense 23,272 1,316 42,733 (40,261 ) 27,060 Net foreign exchange (gains) losses — — 2,145 10,190 12,335 Total expenses 61,974 4,007 2,747,742 (30,071 ) 2,783,652 Income (loss) before income taxes (61,974 ) (3,976 ) 818,645 (10,190 ) 742,505 Income tax (expense) benefit — 1,383 (34,157 ) — (32,774 ) Income (loss) before equity in net income of subsidiaries (61,974 ) (2,593 ) 784,488 (10,190 ) 709,731 Equity in net income of subsidiaries 771,705 25,644 — (797,349 ) — Net income 709,731 23,051 784,488 (807,539 ) 709,731 Net (income) loss attributable to noncontrolling interests — — — — — Net income available to Arch 709,731 23,051 784,488 (807,539 ) 709,731 Preferred dividends (21,938 ) — — — (21,938 ) Net income available to Arch common shareholders $ 687,793 $ 23,051 $ 784,488 $ (807,539 ) $ 687,793 Comprehensive income (loss) available to Arch $ 497,678 $ (28,330 ) $ 562,245 $ (533,915 ) $ 497,678 Year Ended December 31, 2015 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 $ 404,144 $ 5,505 $ 1,074,021 $ (485,764 ) $ 997,906 Investing Activities Purchases of fixed maturity investments — (3,505 ) (29,448,368 ) — (29,451,873 ) Purchases of equity securities (8,070 ) — (507,343 ) — (515,413 ) Purchases of other investments — — (1,749,525 ) — (1,749,525 ) Proceeds from the sales of fixed maturity investments — 24,507 28,069,540 — 28,094,047 Proceeds from the sales of equity securities — — 564,011 — 564,011 Proceeds from the sales, redemptions and maturities of other investments — — 1,250,883 — 1,250,883 Proceeds from redemptions and maturities of fixed maturity investments — — 748,529 — 748,529 Net settlements of derivative instruments — — (5,056 ) — (5,056 ) Proceeds from investment in joint venture — — 40,000 — 40,000 Net (purchases) sales of short-term investments 57 (338 ) 169,376 — 169,095 Change in cash collateral related to securities lending — — (6,662 ) — (6,662 ) Contributions to subsidiaries (10,000 ) — (49,348 ) 59,348 — Intercompany loans issued — (39,500 ) (27,500 ) 67,000 — Purchase of business, net of cash acquired — — 818 — 818 Purchases of fixed assets (80 ) — (15,656 ) — (15,736 ) Change in other assets — — (36,993 ) — (36,993 ) Net Cash Provided By (Used For) Investing Activities (18,093 ) (18,836 ) (1,003,294 ) 126,348 (913,875 ) Financing Activities Purchases of common shares under share repurchase program (365,383 ) — — — (365,383 ) Proceeds from common shares issued, net 4,861 — 59,348 (59,348 ) 4,861 Proceeds from intercompany borrowings — 27,500 39,500 (67,000 ) — Proceeds from borrowings — — 431,362 — 431,362 Change in cash collateral related to securities lending — — 6,662 — 6,662 Dividends paid to redeemable noncontrolling interests — — (19,263 ) 956 (18,307 ) Dividends paid to parent (1) — — (484,808 ) 484,808 — Other — 67 (41,980 ) — (41,913 ) Preferred dividends paid (21,938 ) — — — (21,938 ) Net Cash Provided By (Used For) Financing Activities (382,460 ) 27,567 (9,179 ) 359,416 (4,656 ) Effects of exchange rates changes on foreign currency cash — — (11,751 ) — (11,751 ) Increase (decrease) in cash 3,591 14,236 49,797 — 67,624 Cash beginning of year 3,218 2,787 479,697 — 485,702 Cash end of year $ 6,809 $ 17,023 $ 529,494 $ — $ 553,326 (1) Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column. Year Ended December 31, 2014 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 $ 467,091 $ 8,142 $ 1,077,597 $ (515,700 ) $ 1,037,130 Investing Activities Purchases of fixed maturity investments — (78,509 ) (28,666,770 ) — (28,745,279 ) Purchases of equity securities — — (520,817 ) — (520,817 ) Purchases of other investments — — (1,590,648 ) — (1,590,648 ) Proceeds from the sales of fixed maturity investments — 16,011 26,807,178 — 26,823,189 Proceeds from the sales of equity securities — — 411,362 — 411,362 Proceeds from the sales, redemptions and maturities of other investments — — 941,798 — 941,798 Proceeds from redemptions and maturities of fixed maturity investments — — 762,995 — 762,995 Net settlements of derivative instruments — — 34,372 — 34,372 Net (purchases) sales of short-term investments 2,423 408,591 166,112 — 577,126 Change in cash collateral related to securities lending — — 57,470 — 57,470 Contributions to subsidiaries — (341,707 ) (128,825 ) 470,532 — Intercompany loans issued — (7,500 ) 31,464 (23,964 ) — Purchase of business, net of cash acquired — — (237,106 ) — (237,106 ) Purchases of fixed assets (271 ) — (19,612 ) — (19,883 ) Net Cash Provided By (Used For) Investing Activities 2,152 (3,114 ) (1,951,027 ) 446,568 (1,505,421 ) Financing Activities Purchases of common shares under share repurchase program (454,137 ) — — — (454,137 ) Proceeds from common shares issued, net 6,827 — 470,532 (470,532 ) 6,827 Proceeds from intercompany borrowings — 7,500 7,500 (15,000 ) — Repayments of intercompany borrowings — (10,250 ) (28,714 ) 38,964 — Change in cash collateral related to securities lending — — (57,470 ) — (57,470 ) Third party investment in non-redeemable noncontrolling interests — — 796,903 — 796,903 Third party investment in redeemable noncontrolling interests — — 219,233 — 219,233 Dividends paid to redeemable noncontrolling interests — — (14,448 ) — (14,448 ) Dividends paid to parent (1) — — (515,700 ) 515,700 — Other — — 64,973 — 64,973 Preferred dividends paid (21,938 ) — — — (21,938 ) Net Cash Provided By (Used For) Financing Activities (469,248 ) (2,750 ) 942,809 69,132 539,943 Effects of exchange rates changes on foreign currency cash — — (20,007 ) — (20,007 ) Increase (decrease) in cash (5 ) 2,278 49,372 — 51,645 Cash beginning of year 3,223 509 430,325 — 434,057 Cash end of year $ 3,218 $ 2,787 $ 479,697 $ — $ 485,702 (1) Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column. Year Ended December 31, 2013 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 $ 68,562 $ (6,569 ) $ 908,375 $ (119,500 ) $ 850,868 Investing Activities Purchases of fixed maturity investments — — (18,174,988 ) — (18,174,988 ) Purchases of equity securities — — (535,857 ) — (535,857 ) Purchases of other investments — — (994,185 ) — (994,185 ) Proceeds from the sales of fixed maturity investments — — 17,194,635 — 17,194,635 Proceeds from the sales of equity securities — — 462,787 — 462,787 Proceeds from the sales, redemptions and maturities of other investments — — 817,648 — 817,648 Proceeds from redemptions and maturities of fixed maturity investments — — 731,708 — 731,708 Net settlements of derivative instruments — — 14,494 — 14,494 Net (purchases) sales of short-term investments 5,799 (400,162 ) (356,250 ) — (750,613 ) Change in cash collateral related to securities lending — — (55,643 ) — (55,643 ) Contributions to subsidiaries (160 ) (97,850 ) (20,250 ) 118,260 — Intercompany loans issued — — (10,250 ) 10,250 — Purchases of fixed assets (712 ) — (16,787 ) — (17,499 ) Net Cash Provided By (Used For) Investing Activities 4,927 (498,012 ) (942,938 ) 128,510 (1,307,513 ) Financing Activities Purchases of common shares under share repurchase program (57,796 ) — — — (57,796 ) Proceeds from common shares issued, net 3,051 — 118,260 (118,260 ) 3,051 Proceeds from intercompany borrowings — 10,250 — (10,250 ) — Proceeds from borrowings — 494,228 — — 494,228 Change in cash collateral relating to securities lending — — 55,643 — 55,643 Dividends paid to parent (1) — — (119,500 ) 119,500 — Other — — 50,830 — 50,830 Preferred dividends paid (21,938 ) — — — (21,938 ) Net Cash Provided By (Used For) Financing Activities (76,683 ) 504,478 105,233 (9,010 ) 524,018 Effects of exchange rates changes on foreign currency cash — — (4,357 ) — (4,357 ) Increase (decrease) in cash (3,194 ) (103 ) 66,313 — 63,016 Cash beginning of year 6,417 612 364,012 — 371,041 Cash end of year $ 3,223 $ 509 $ 430,325 $ — $ 434,057 (1) Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.

Schedule III - Supplementary In

Schedule III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2015
Supplementary Insurance Information [Abstract]
Supplementary Insurance Information	SCHEDULE III ARCH CAPITAL GROUP LTD. AND SUBSIDIARIES SUPPLEMENTARY INSURANCE INFORMATION (U.S. dollars in thousands) Deferred Acquisition Costs, Reserves for Losses and Loss Adjustment Expenses Unearned Premiums Net Premiums Earned Net Investment Income (1) Net Losses and Loss Adjustment Expenses Incurred Amortization of Deferred Acquisition Costs Other Operating Expenses (2) Net Premiums Written December 31, 2015 Insurance $166,771 $6,050,922 $1,217,490 $2,044,808 NM $1,292,647 $299,317 $354,416 $2,045,671 Reinsurance 138,184 2,672,044 650,138 1,077,135 NM 440,350 223,632 155,811 1,038,408 Mortgage 53,079 111,287 216,324 214,110 NM 40,247 45,076 82,370 267,493 Other 75,443 290,997 249,980 397,852 NM 277,659 113,451 14,919 465,959 Total $433,477 $9,125,250 $2,333,932 $3,733,905 NM $2,050,903 $681,476 $607,516 $3,817,531 December 31, 2014 Insurance $178,545 $6,161,500 $1,237,099 $2,017,370 NM $1,260,953 $316,308 $335,157 $2,146,654 Reinsurance 148,130 2,690,070 666,233 1,279,328 NM 532,450 261,438 147,964 1,265,991 Mortgage 38,321 118,550 148,232 193,573 NM 55,674 49,400 66,891 204,837 Other 49,529 66,328 180,014 103,477 NM 70,173 30,116 6,268 274,456 Total $414,525 $9,036,448 $2,231,578 $3,593,748 NM $1,919,250 $657,262 $556,280 $3,891,938 December 31, 2013 Insurance $158,121 $6,137,121 $1,192,188 $1,876,014 NM $1,188,445 $311,904 $315,387 $1,948,796 Reinsurance 167,642 2,680,288 612,725 1,218,672 NM 486,236 234,373 134,563 1,313,001 Mortgage 16,551 7,287 91,452 51,266 NM 4,743 17,826 8,377 89,570 Total $342,314 $8,824,696 $1,896,365 $3,145,952 NM $1,679,424 $564,103 $458,327 $3,351,367 (1) The Company does not manage its assets by segment and, accordingly, net investment income is not allocated to each underwriting segment. See Note 5 for information related to the ‘other’ segment. (2) Certain other operating expenses relate to the Company’s corporate segment (non-underwriting). Such amounts are not reflected in the table above. See Note 5 .

Schedule IV - Reinsurance

Schedule IV - Reinsurance	12 Months Ended
	Dec. 31, 2015
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
Reinsurance	SCHEDULE IV ARCH CAPITAL GROUP LTD. AND SUBSIDIARIES REINSURANCE (U.S. dollars in thousands) Gross Amount Ceded to Other Companies (1) Assumed From Other Companies (1) Net Percentage of Amount Assumed to Net Year Ended December 31, 2015 Premiums Written: Insurance $ 2,908,906 $ (898,347 ) $ 35,112 $ 2,045,671 1.7 % Reinsurance 28,510 (380,614 ) 1,390,512 1,038,408 133.9 % Mortgage 137,338 (28,064 ) 158,219 267,493 59.1 % Other 12,165 (22,940 ) 476,734 465,959 102.3 % Total $ 3,086,919 $ (979,632 ) $ 1,710,244 $ 3,817,531 44.8 % Year Ended December 31, 2014 Premiums Written: Insurance $ 2,974,996 $ (862,015 ) $ 33,673 $ 2,146,654 1.6 % Reinsurance 22,405 (261,255 ) 1,504,841 1,265,991 118.9 % Mortgage 103,545 (22,519 ) 123,811 204,837 60.4 % Other — (14,171 ) 288,627 274,456 105.2 % Total $ 3,100,946 $ (948,678 ) $ 1,739,670 $ 3,891,938 44.7 % Year Ended December 31, 2013 Premiums Written: Insurance $ 2,682,446 $ (763,713 ) $ 30,063 $ 1,948,796 1.5 % Reinsurance 72,136 (86,620 ) 1,327,485 1,313,001 101.1 % Mortgage — — 89,570 89,570 100.0 % Total $ 2,754,582 $ (845,256 ) $ 1,442,041 $ 3,351,367 43.0 % (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions and are included in the gross premiums written of each segment. 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.

Schedule VI - Supplementary Inf

Schedule VI - Supplementary Information For Property and Casualty Insurance Underwriters	12 Months Ended
	Dec. 31, 2015
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Supplementary Information for Property and Casualty Insurance Underwriters	SCHEDULE VI ARCH CAPITAL GROUP LTD. AND SUBSIDIARIES SUPPLEMENTARY INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS (U.S. dollars in thousands) Column A Column B Column C Column D Column E Column F Column G Column H Column I Column J Column K Affiliation with Registrant Deferred Acquisition Costs, Reserves for Losses and Loss Adjustment Expenses Discount, if any, deducted in Column C Unearned Premiums Net Net Investment Income Net Losses and Loss Adjustment Expenses Incurred Related to Amortization Net Paid Losses and Loss Adjustment Expenses Net (a) Current Year (b) Prior Years Consolidated Subsidiaries 2015 $ 433,477 $ 9,125,250 $ 16,789 $ 2,333,932 $ 3,733,905 $ 348,090 $ 2,336,026 $ (285,123 ) $ 681,476 $ 1,869,244 $ 3,817,531 2014 414,525 9,036,448 14,732 2,231,578 3,593,748 302,585 2,246,152 (326,902 ) 657,262 1,697,736 3,891,938 2013 342,314 8,824,696 12,539 1,896,365 3,145,952 267,219 1,943,466 (264,042 ) 564,103 1,708,817 3,351,367

Significant Accounting Polici35

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Basis of presentation	The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of ACGL and its subsidiaries, including Arch Re Bermuda, Arch Reinsurance Company (“Arch Re U.S.”), Arch-U.S., Arch Insurance Company, Arch Specialty Insurance Company, Arch Excess & Surplus Insurance Company, Arch Indemnity Insurance Company, Arch Insurance Canada Ltd. (“Arch Insurance Canada”), Alternative Re Limited, Arch Reinsurance Europe Underwriting Designated Activity Company (“Arch Re Europe”), Arch MI U.S., Arch Mortgage Guaranty Company, Arch Mortgage Insurance Designated Activity Company (“Arch MI Europe”), Arch Insurance Company (Europe) Limited (“Arch Insurance Company Europe”), Lloyd’s of London syndicate 2012 and related companies (“Arch Syndicate 2012”), Gulf Re and Watford Re. 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.
Premium revenues	Insurance. Insurance premiums written are generally recorded at the policy inception and are primarily earned on a pro rata basis over the terms of the policies for all products, usually 12 months . Premiums written include estimates in the Company’s programs, specialty lines, lenders products business and for participation in involuntary pools. Such premium estimates are derived from multiple sources which include the historical experience of the underlying business, similar business and available industry information. Unearned premium reserves represent the portion of premiums written that relates to the unexpired terms of in-force insurance policies. Reinsurance. Reinsurance premiums written include amounts reported by brokers and ceding companies, supplemented by the Company’s own estimates of premiums where reports have not been received. The determination of premium estimates requires a review of the Company’s experience with the ceding companies, familiarity with each market, the timing of the reported information, an analysis and understanding of the characteristics of each line of business, and management’s judgment of the impact of various factors, including premium or loss trends, on the volume of business written and ceded to the Company. On an ongoing basis, the Company’s underwriters review the amounts reported by these third parties for reasonableness based on their experience and knowledge of the subject class of business, taking into account the Company’s historical experience with the brokers or ceding companies. In addition, reinsurance contracts under which the Company assumes business generally contain specific provisions which allow the Company to perform audits of the ceding company to ensure compliance with the terms and conditions of the contract, including accurate and timely reporting of information. Based on a review of all available information, management establishes premium estimates where reports have not been received. Premium estimates are updated when new information is received and differences between such estimates and actual amounts are recorded in the period in which estimates are changed or the actual amounts are determined. Reinsurance premiums written are recorded based on the type of contracts the Company writes. Premiums on the Company’s excess of loss and pro rata reinsurance contracts are estimated when the business is underwritten. For excess of loss contracts, premiums are recorded as written based on the terms of the contract. Estimates of premiums written under pro rata contracts are recorded in the period in which the underlying risks are expected to incept and are based on information provided by the brokers and the ceding companies. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term. Reinstatement premiums for the Company’s insurance and reinsurance operations are recognized at the time a loss event occurs, where coverage limits for the remaining life of the contract are reinstated under pre-defined contract terms. Reinstatement premiums, if obligatory, are fully earned when recognized. The accrual of reinstatement premiums is based on an estimate of losses and loss adjustment expenses, which reflects management’s judgment. Premium estimates are reviewed by management at least quarterly. Such review includes a comparison of actual reported premiums to expected ultimate premiums along with a review of the aging and collection of premium estimates. Based on management’s review, the appropriateness of the premium estimates is evaluated, and any adjustment to these estimates is recorded in the period in which it becomes known. Adjustments to premium estimates could be material and such adjustments could directly and significantly impact earnings favorably or unfavorably in the period they are determined because the estimated premium may be fully or substantially earned. A significant portion of amounts included as premiums receivable, which represent estimated premiums written, net of commissions, are not currently due based on the terms of the underlying contracts. Reinsurance premiums written, irrespective of the class of business, are generally earned on a pro rata basis over the terms of the underlying policies or reinsurance contracts. Contracts and policies written on a “losses occurring” basis cover claims that may occur during the term of the contract or policy, which is typically 12 months . Accordingly, the premium is earned evenly over the term. Contracts which are written on a “risks attaching” basis cover claims which attach to the underlying insurance policies written during the terms of such contracts. Premiums earned on such contracts usually extend beyond the original term of the reinsurance contract, typically resulting in recognition of premiums earned over a 24 -month period. Certain of the Company’s reinsurance contracts include provisions that adjust premiums or acquisition expenses based upon the experience under the contracts. Premiums written and earned, as well as related acquisition expenses, are recorded based upon the projected experience under such contracts. The Company also writes certain reinsurance business that is intended to provide insurers with risk management solutions that complement traditional reinsurance. Under these contracts, the Company assumes a measured amount of insurance risk in exchange for an anticipated margin, which is typically lower than on traditional reinsurance contracts. The terms and conditions of these contracts may include additional or return premiums based on loss experience, loss corridors, sublimits and caps. Examples of such business include aggregate stop-loss coverages, financial quota share coverages and multi-year retrospectively rated excess of loss coverages. If these contracts are deemed to transfer risk, they are accounted for as reinsurance. Mortgage. Mortgage guaranty insurance policies are contracts that are generally non-cancelable by the insurer, are renewable at a fixed price, and provide for payment of premiums on a monthly, annual or single basis. Upon renewal, the Company is not able to re-underwrite or re-price its policies. Consistent with industry accounting practices, premiums written on a monthly basis are earned as coverage is provided. Premiums written on an annual basis are amortized on a monthly pro rata basis over the year of coverage. Primary mortgage insurance premiums written on policies covering more than one year are referred to as single premiums. A portion of the revenue from single premiums is recognized in premiums earned in the current period, and the remaining portion is deferred as unearned premiums and earned over the estimated expiration of risk of the policy. If single premium policies related to insured loans are canceled due to repayment by the borrower and the policy is a non-refundable product, the remaining unearned premium related to each canceled policy is recognized as earned premium upon notification of the cancellation. Unearned premiums represent the portion of premiums written that is applicable to the estimated unexpired risk of insured loans. A portion of premium payments may be refundable if the insured cancels coverage, which generally occurs when the loan is repaid, the loan amortizes to a sufficiently low amount to trigger a lender permitted or legally required cancellation, or the value of the property has increased sufficiently in accordance with the terms of the contract. Premium refunds reduce premiums earned in the consolidated statements of income. Generally, only unearned premiums are refundable. However, when the Company pays a claim on a delinquent loan, all servicer paid premiums received on the delinquent loan covering any period after the default date will be refunded, in accordance with the terms of the contract.
Deferred acquisition costs	Acquisition Costs. Acquisition expenses and other expenses related to the Company’s underwriting operations that vary with, and are directly related to, the successful acquisition or renewal of business are deferred and amortized based on the type of contract. For property and casualty insurance and reinsurance contracts, deferred acquisition costs are amortized over the period in which the related premiums are earned. Consistent with mortgage insurance industry accounting practice, amortization of acquisition costs related to the mortgage insurance contracts for each underwriting year’s book of business is recorded in proportion to estimated gross profits. Estimated gross profits are comprised of earned premiums and losses and loss adjustment expenses. For each underwriting year, the Company estimates the rate of amortization to reflect actual experience and any changes to persistency or loss development. Acquisition expenses, net of ceding commissions received from reinsurers, consist principally of commissions and premium taxes paid to obtain the Company’s business. Other operating expenses also include expenses that vary with, and are directly related to, the successful acquisition of business. Deferred acquisition costs are carried at their estimated realizable value and take into account anticipated losses and loss adjustment expenses, based on historical and current experience, and anticipated investment income. A premium deficiency occurs if the sum of anticipated losses and loss adjustment expenses, unamortized acquisition costs and maintenance costs exceed unearned premiums (including expected future premiums) and anticipated investment income. A premium deficiency reserve (“PDR”) is recorded by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. To assess the need for a PDR on mortgage exposures, the Company develops loss projections based on modeled loan defaults related to its current policies in force. This projection is based on recent trends in default experience, severity and rates of defaulted loans moving to claim, as well as recent trends in the rate at which loans are prepaid. Evaluating the expected profitability of the Company’s existing mortgage insurance business and the need for a PDR for its mortgage business involves significant reliance upon assumptions and estimates with regard to the likelihood, magnitude and timing of potential losses and premium revenues. No premium deficiency charges were recorded by the Company during 2015 , 2014 or 2013 .
Deposit accounting	Certain assumed reinsurance contracts that are deemed not to transfer insurance risk, are accounted for using the deposit method of accounting. However, it is possible that the Company could incur financial losses on such contracts. Management exercises significant judgment in the assumptions used in determining whether assumed contracts should be accounted for as reinsurance contracts or deposit contracts. For those contracts that contain only significant underwriting risk, the estimated profit margin is deferred and amortized over the contract period and such amount is included in the Company’s underwriting results. When the estimated profit margin is explicit, the margin is reflected as other underwriting income and any adverse financial results on such contracts are reflected as incurred losses. When the estimated profit margin is implicit, the margin is reflected as an offset to paid losses and any adverse financial results on such contracts are reflected as incurred losses. Additional judgments are required when applying the accounting guidance with respect to the revenue recognition criteria for contracts deemed to transfer only significant underwriting risk. For those contracts that contain only significant timing risk, an accretion rate is established at inception of the contract based on actuarial estimates whereby the deposit accounting liability is increased to the estimated amount payable over the contract term. The accretion on the deposit is based on the expected rate of return required to fund the expected future payment obligations. Periodically the Company reassesses the estimated ultimate liability and the related expected rate of return. The accretion of the deposit accounting liability as well as changes to the estimated ultimate liability and the accretion rate would be reflected as part of interest expense in the Company’s results of operations. Any negative accretion in a deposit accounting liability is shown in other underwriting income in the Company’s results of operations. Deposit accounting liabilities totaled $260.4 million and $327.4 million , respectively, at December 31, 2015 and 2014 . Under some of these contracts, the ceding company retains the related assets on a funds-held basis. In those instances, the Company records the asset as a deposit accounting asset. Deposit accounting assets of $234.5 million and $284.4 million , respectively, at December 31, 2015 and 2014 are included in “Other assets” on the Company’s balance sheet. Interest income produced by those assets are recorded as part of net investment income in the Company's results of operations.
Retroactive accounting	Retroactive reinsurance reimburses a ceding company for liabilities incurred as a result of past insurable events covered by the underlying policies reinsured. In certain instances, reinsurance contracts cover losses both on a prospective basis and on a retroactive basis and, accordingly, the Company bifurcates the prospective and retrospective elements of these reinsurance contracts and accounts for each element separately where practical. Underwriting income generated in connection with retroactive reinsurance contracts is deferred and amortized into income over the settlement period while losses are charged to income immediately. Subsequent changes in estimated or actual cash flows under such retroactive reinsurance contracts are accounted for by adjusting the previously deferred amount to the balance that would have existed had the revised estimate been available at the inception of the reinsurance transaction, with a corresponding charge or credit to income.
Reinsurance ceded	In the normal course of business, the Company purchases reinsurance to increase capacity and to limit the impact of individual losses and events on its underwriting results by reinsuring certain levels of risk with other insurance enterprises or reinsurers. The Company uses pro rata, excess of loss and facultative reinsurance contracts. Reinsurance ceding commissions are recognized as a reduction to acquisition costs on a pro rata basis over the period of risk while the portion of such commissions that will be earned in the future is deferred. The accompanying consolidated statement of income reflects premiums and losses and loss adjustment expenses and acquisition costs, net of reinsurance ceded. See Note 7 for information on the Company's reinsurance usage. Ceded unearned premiums are reported as prepaid reinsurance premiums and estimated amounts of reinsurance recoverable on unpaid losses are reported as unpaid losses and loss adjustment expenses recoverable. Reinsurance premiums ceded and unpaid losses and loss adjustment expenses recoverable are estimated in a manner consistent with that of the original policies issued and the terms of the reinsurance contracts. If the reinsurers are unable to satisfy their obligations under the agreements, the Company’s insurance or reinsurance subsidiaries would be liable for such defaulted amounts.
Cash	Cash includes cash equivalents, which are investments with original maturities of three months or less that are not managed by external or internal investment advisors.
Investments	The Company currently classifies substantially all of its fixed maturity investments, equity securities and short-term investments as “available for sale” and, accordingly, they are carried at estimated fair value (also known as fair value) with the changes in fair value recorded as an unrealized gain or loss component of accumulated other comprehensive income in shareholders’ equity. The fair value of fixed maturity securities and equity securities is generally determined from quotations received from nationally recognized pricing services, or when such prices are not available, by reference to broker or underwriter bid indications. Short-term investments comprise securities due to mature within one year of the date of issue. Short-term investments include certain cash equivalents which are part of investment portfolios under the management of external and internal investment managers. The Company participates in a securities lending program as a mechanism for generating additional interest income on its fixed income portfolio. Under the security lending agreements, certain of its fixed income portfolio securities are loaned to third parties, primarily major brokerage firms, for short periods of time through a lending agent. Such securities have been reclassified as “Fixed maturities and short-term investments pledged under securities lending agreements, at fair value.” 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. Collateral received is required at a rate of 102% or greater of the fair value of the loaned securities including accrued investment income and is monitored and maintained by the lending agent. Such collateral is reflected as “Collateral received under securities lending agreements, at fair value.” The Company’s investment portfolio includes certain funds that, due to their ownership structure, are accounted for by the Company using the equity method. In applying the equity method, these 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 fair 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. Changes in the carrying value of such investments are recorded in net income as “Equity in net income (loss) of investment funds accounted for using the equity method.” As such, fluctuations in the carrying value of the investment funds accounted for using the equity method may increase the volatility of the Company’s reported results of operations. Other investments include funds and separately managed accounts with holdings in Asian and emerging markets, fixed maturities, term loans and other investment strategies. The fair value for certain of the Company’s other investments are determined using net asset values (“NAVs”) as advised by external fund managers. The NAV is based on the fund manager’s valuation of the underlying holdings in accordance with the fund’s governing documents. Certain of the funds are accounted for as available for sale equity securities, regardless of the nature of the investments held within the fund. The Company elected to carry certain fixed maturity securities, equity securities and other investments at fair value under the fair value option afforded by accounting guidance regarding the fair value option for financial assets and liabilities. Changes in fair value of investments accounted for using the fair value option are included in “Net realized gains (losses).” The primary reasons for electing the fair value option were to address simplification and cost-benefit considerations. The Company invests in limited partner interests and shares of limited liability companies. Such amounts are included in investments accounted for using the equity method, other investments available for sale and investments accounted for using the fair value option. These investments can often have characteristics of a variable interest entity (“VIE”). A VIE refers to entities that have 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 the characteristic of a controlling financial interest. If the Company is determined to be the primary beneficiary, it is required to consolidate the VIE. The primary beneficiary 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. At inception of the VIE as well as on an ongoing basis, the Company determines whether it is the primary beneficiary based on an analysis of the Company’s level of involvement in the VIE, the contractual terms, and the overall structure of the VIE. 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 Company performs quarterly reviews of its investments to determine whether declines in fair value below the cost basis are considered other-than-temporary in accordance with applicable accounting guidance regarding the recognition and presentation of other-than-temporary impairments (“OTTI”). The process of determining whether a security is other-than-temporarily impaired requires judgment and involves analyzing many factors. These factors include (i) an analysis of the liquidity, business prospects and overall financial condition of the issuer, (ii) the time period in which there was a significant decline in value, (iii) the significance of the decline and (iv) the analysis of specific credit events. The Company evaluates the unrealized losses of its equity securities by issuer and forecasts a reasonable period of time by which the fair value of the securities would increase and the Company would recover its cost. If the Company is unable to forecast a reasonable period of time in which to recover the cost of its equity securities, a net impairment loss in earnings equivalent to the entire unrealized loss is recognized. When there are credit-related losses associated with debt securities for which the Company does not have an intent to sell and it is more likely than not that it will not be required to sell the security before recovery of its cost basis, the amount of the OTTI related to a credit loss is recognized in earnings and the amount of the OTTI related to other factors ( e.g. , interest rates, market conditions, etc.) is recorded as a component of other comprehensive income (loss). The amount of the credit loss of an impaired debt security is the difference between the amortized cost and the greater of (i) the present value of expected future cash flows and (ii) the fair value of the security. In instances where no credit loss exists but it is more likely than not that the Company will have to sell the debt security prior to the anticipated recovery, the decline in fair value below amortized cost is recognized as an OTTI in earnings. In periods after the recognition of an OTTI on debt securities, the Company accounts for such securities as if they had been purchased on the measurement date of the OTTI at an amortized cost basis equal to the previous amortized cost basis less the OTTI recognized in earnings. For debt securities for which OTTI were recognized in earnings, the difference between the new amortized cost basis and the cash flows expected to be collected will be accreted or amortized into net investment income. See Note 8 , “Investment Information—Other-Than-Temporary Impairments” for additional information. Net investment income includes interest and dividend income together with amortization of market premiums and discounts and is net of investment management and custody fees. Anticipated prepayments and expected maturities are used in applying the interest method for certain investments such as mortgage and other asset-backed securities. When actual prepayments differ significantly from anticipated prepayments, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The net investment in such securities is adjusted to the amount that would have existed had the new effective yield been applied since the acquisition of the security. Such adjustments, if any, are included in net investment income when determined. Investment gains or losses realized on the sale of investments, except for certain fund investments, are determined on a first-in, first-out basis and are reflected in net income. Investments gains or losses realized on the sale of certain fund investments are determined on an average cost basis. Unrealized appreciation or decline in the value of available for sale securities, which are carried at fair value, is excluded from net income and recorded as a separate component of accumulated other comprehensive income, net of applicable deferred income tax.
Derivative instruments	The Company recognizes all derivative instruments, including embedded derivative instruments, at fair value in the Consolidated Balance Sheets. The Company employs the use of derivative instruments within its operations to mitigate risks arising from assets and liabilities held in foreign currencies as well as part of its overall investment strategy. For such instruments, changes in assets and liabilities measured at fair value are recorded as “Net realized gains” in the consolidated statements of income. In addition, the Company’s derivative instruments include amounts related to underwriting activities where an insurance or reinsurance contract meets the accounting definition of a derivative instrument. For such contracts, changes in fair value are reflected in “Other underwriting income” in the consolidated statements of income as the underlying contract originates from the Company’s underwriting operations. For the periods ended 2015 , 2014 , and 2013 , the Company did not designate any derivative instruments as hedges under the relevant accounting guidance. See Note 10 for information on the Company’s derivative instruments.
Reserve for losses and loss adjustment expenses	Insurance and Reinsurance. The reserve for losses and loss adjustment expenses consists of estimates of unpaid reported losses and loss adjustment expenses and estimates for losses incurred but not reported. The reserve for unpaid reported losses and loss adjustment expenses, established by management based on reports from ceding companies and claims from insureds, excludes estimates of amounts related to losses under high deductible policies, and represents the estimated ultimate cost of events or conditions that have been reported to or specifically identified by the Company. Such reserves are supplemented by management’s estimates of reserves for losses incurred for which reports or claims have not been received. The Company’s reserves are based on a combination of reserving methods, incorporating both Company and industry loss development patterns. The Company selects the initial expected loss and loss adjustment expense ratios based on information derived by its underwriters and actuaries during the initial pricing of the business, supplemented by industry data where appropriate. Such ratios consider, among other things, rate changes and changes in terms and conditions that have been observed in the market. These estimates are reviewed regularly and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments, if any, are reflected in income in the period in which they are determined. As actual loss information has been reported, the Company has developed its own loss experience and its reserving methods include other actuarial techniques. Over time, such techniques have been given further weight in its reserving process based on the continuing maturation of the Company’s reserves. Inherent in the estimates of ultimate losses and loss adjustment expenses are expected trends in claims severity and frequency and other factors which may vary significantly as claims are settled. Accordingly, ultimate losses and loss adjustment expenses may differ materially from the amounts recorded in the accompanying consolidated financial statements. Losses and loss adjustment expenses are recorded on an undiscounted basis, except for excess workers’ compensation and employers’ liability business written by the Company’s insurance operations. Mortgage. The reserves for mortgage guaranty insurance losses and loss adjustment expenses are the estimated claim settlement costs on notices of default that have been received by the Company, as well as loan defaults that have been incurred but have not been reported by the lenders. Consistent with primary mortgage insurance industry accounting practice, the Company does not establish loss reserves for future claims on insured loans that are not currently in default (defined as two consecutive missed payments). The Company establishes loss reserves on a case-by-case basis when insured loans are identified as currently in default using estimated claim rates and average claim sizes for each report year, net of any salvage recoverable. The Company also reserves for defaults that have occurred but have not yet been reported to the Company prior to the close of an accounting period. To determine this reserve, the Company estimates the number of defaults not yet reported using historical information regarding late reported delinquencies and applies estimated claim rates and claim sizes for the estimated defaults not yet reported. The establishment of reserves across the Company’s segments is an inherently uncertain process, are necessarily based on estimates, and the ultimate net cost may vary from such estimates. The methods for making such estimates and for establishing the resulting liability are reviewed and updated using the most current information available. Any resulting adjustments, which may be material, are reflected in current operations.
Contractholder receivables and payables and collateral held for insured obligations	Certain insurance policies written by the Company’s insurance operations feature large deductibles, primarily in its construction and national accounts lines of business. Under such contracts, the Company is obligated to pay the claimant for the full amount of the claim. The Company is subsequently reimbursed by the policyholder for the deductible amount. These amounts are included on a gross basis in the consolidated balance sheet in contractholder payables and contractholder receivables, respectively. In the event that the Company is unable to collect from the policyholder, the Company would be liable for such defaulted amounts. Collateral, primarily in the form of letters of credit, cash and trusts, is obtained from the policyholder to mitigate the Company’s credit risk. In the instances where the company receives collateral in the form of cash, the company reflects it in “Collateral held for insured obligations.”
Foreign exchange	Assets and liabilities of foreign operations whose functional currency is not the U.S. Dollar are translated at the prevailing exchange rates at each balance sheet date. Revenues and expenses of such foreign operations are translated at average exchange rates during the year. The net effect of the translation adjustments for foreign operations is included in accumulated other comprehensive income, net of applicable deferred income tax. Monetary assets and liabilities, such as premiums receivable and the reserve for losses and loss adjustment expenses, denominated in foreign currencies are revalued at the exchange rate in effect at the balance sheet date with the resulting foreign exchange gains and losses included in net income. Accounts that are classified as non-monetary, such as deferred acquisition costs and the unearned premium reserves, are not revalued. In the case of foreign currency denominated fixed maturity securities which are classified as “available for sale,” the change in exchange rates between the local currency in which the investments are denominated and the Company’s functional currency at each balance sheet date is included in unrealized appreciation or decline in value of securities, a component of accumulated other comprehensive income, net of applicable deferred income tax.
Income taxes	Deferred income taxes reflect the expected future tax consequences of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and amounts used for income tax purposes. A valuation allowance is recorded if it is more likely than not that some or all of a deferred tax asset may not be realized. The Company considers future taxable income and feasible tax planning strategies in assessing the need for a valuation allowance. In the event the Company determines that it will not be able to realize all or part of its deferred income tax assets in the future, an adjustment to the deferred income tax assets would be charged to income in the period in which such determination is made. In addition, if the Company subsequently assesses that the valuation allowance is no longer needed, a benefit would be recorded to income in the period in which such determination is made. See Note 13 for more information. The Company recognizes a tax benefit where it concludes that it is more likely than not that the tax benefit will be sustained on audit by the taxing authority based solely on the technical merits of the associated tax position. If the recognition threshold is met, the Company recognizes a tax benefit measured at the largest amount of the tax benefit that, in the Company’s judgment, is greater than 50% likely to be realized. The Company records interest and penalties related to unrecognized tax benefits in the provision for income taxes.
Share-based payment arrangements	The Company applies a fair value based measurement method in accounting for its share-based payment arrangements with eligible employees and directors. Compensation expense is estimated based on the fair value of the award at the grant date and is recognized in net income over the requisite service period with a corresponding increase in shareholders’ equity. No value is attributed to awards that employees forfeit because they fail to satisfy vesting conditions. As such, the number of shares granted is reduced by assumed forfeitures and adjusted based on actual forfeitures until vesting. The Company’s share-based payment arrangements generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. The share-based compensation expense associated with such awards that have graded vesting features and vest based on service conditions only is calculated on a straight-line basis over the requisite service period for the entire award. For awards granted to retirement-eligible employees where no service is required for the employee to retain the award, the grant date fair value is immediately recognized as compensation expense at the grant date because the employee is able to retain the award without continuing to provide service. For employees near retirement eligibility, attribution of compensation cost is over the period from the grant date to the retirement eligibility date. In November 2012, the Company issued off-cycle share-based awards, which will cliff vest on the fifth anniversary of the grant date. The expense for such grant is being amortized on a straight-line basis over the five -year requisite service period. The off-cycle awards have similar terms as the annual award agreements, however with respect to retirement eligible employees service is required for the employee to retain the award. Retirement-eligible employees retiring prior to the fifth anniversary of the grant date will vest in a pro-rated portion of the award commensurate with the service performed. Such employees will receive the vested portion at the end of the five -year cliff period. These charges had no impact on the Company’s cash flows or total shareholders’ equity. See Note 19 for information relating to the Company’s share-based payment awards.
Guaranty fund and other related assessments	Liabilities for guaranty fund and other related assessments in the Company’s insurance and reinsurance operations are accrued when the Company receives notice that an amount is payable, or earlier if a reasonable estimate of the assessment can be made.
Treasury shares	Treasury shares are common shares purchased by the Company and not subsequently canceled. These shares are recorded at cost and result in a reduction of the Company’s shareholders’ equity in its Consolidated Balance Sheets.
Goodwill and intangible assets	Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired and is assigned to the applicable reporting unit at acquisition. Goodwill is evaluated for impairment on an annual basis. Impairment tests may be performed more frequently if the facts and circumstances indicate a possible impairment. In performing impairment tests, the Company may first assess qualitative factors to determine whether it is more likely than not (that is, more than a 50% probability) that the fair value of a reporting unit exceeds its carrying amount as a basis for determining whether it is necessary to perform the two-step goodwill impairment test described in the accounting guidance. Indefinite-lived intangible assets, such as insurance licenses are evaluated for impairment similar to goodwill. Finite-lived intangible assets and liabilities include the value of acquired insurance and reinsurance contracts, which are estimated based on the present value of future expected cash flows and amortized in ‘acquisition expenses’ in proportion to the estimated profits expected to be realized. Other finite-lived intangible assets or liabilities, including favorable or unfavorable contracts, are amortized in ‘other operating expenses’ over their useful lives. Finite-lived intangible assets and liabilities are periodically reviewed for indicators of impairment. An impairment is recognized when the carrying amount is not recoverable from its undiscounted cash flows and is measured as the difference between the carrying amount and fair value. If goodwill or intangible assets are impaired, such assets are written down to their fair values with the related expense recorded in the Company’s results of operations. See Note 17 for information relating to the Company’s goodwill and intangible assets.
Recent accounting pronouncements	Recently Issued Accounting Standards Adopted The Company adopted accounting guidance in the 2015 second quarter which changes the accounting for repurchase and resale-to-maturity agreements by requiring that such agreements be recognized as financing arrangements, and requires that a transfer of a financial asset and a repurchase agreement entered into contemporaneously be accounted for separately. The new accounting guidance also requires additional disclosures about certain transferred financial assets accounted for as sales and certain securities lending transactions. Disclosures are not required to be presented for comparative periods before the effective date. See Note 8 , “Investment Information—Securities Lending Agreements.” The Company adopted accounting guidance in the 2015 second quarter which relates to the presentation of debt issuance costs. Such guidance requires presentation of debt issuance costs in the balance sheet as a deduction from the carrying amount of the related debt liability instead of a deferred charge. The Company previously included its debt issuance costs within ‘other assets.’ The guidance was applied retrospectively and resulted in reductions in ‘other assets’ and ‘senior notes’ at June 30, 2015 of $8.8 million , respectively, and $8.9 million at December 31, 2014, respectively. The adoption of this change in accounting principle did not impact the Company’s shareholders’ equity or net income. The Company adopted accounting guidance pertaining to the categorization within the fair value hierarchy of certain investments measured at fair value using the net asset value per share as a practical expedient. These investments are no longer required to be categorized within the fair value hierarchy but are still required to be reported in the fair value hierarchy table to permit reconciliation back to the consolidated balance sheet. Additionally, certain disclosures are no longer applicable for investments that are eligible to be measured using the practical expedient, but for which the practical expedient was not elected. The guidance was applied retrospectively and only impacted the Company’s disclosures. See Note 9 , “Fair Value.” Recently Issued Accounting Standards Not Yet Adopted An accounting standard was issued in the 2014 second quarter which will change the manner in which most companies recognize revenue. The standard requires that revenue reflect the transfer of goods or services to customers based on the consideration or payment the company expects to be entitled to in exchange for those goods or services; however, the standard does not change the accounting for insurance contracts or financial instruments. The new standard also requires enhanced disclosures about revenue. This accounting guidance is effective in the 2018 first quarter and may be applied on a full retrospective or modified retrospective approach. The Company is assessing the impact the implementation of this standard will have on its consolidated financial statements. An accounting standard was issued in the 2015 first quarter providing targeted improvements to consolidation guidance for limited partnerships and other similarly structured entities. The new standard addresses instances where a reporting entity consolidates another entity when the reporting entity is simply acting on the behalf of others, amongst other related issues. While the standard is targeted, the application is relevant for all companies that are required to assess whether or not to consolidate certain entities. The standard is effective in the 2016 first quarter and early adoption is permitted. The Company is assessing the impact the implementation of this standard will have on its consolidated financial statements. A new accounting standard was issued in the 2015 second quarter requiring new disclosures about the reserve for losses and loss adjustment expenses for short-duration insurance contracts. These disclosures will provide additional insight into an insurance entity’s ability to underwrite and anticipate costs associated with claims. This accounting guidance is effective for the 2016 annual reporting period and interim periods thereafter and should be applied retrospectively. The Company is assessing the impact the implementation of this standard will have on its financial statement disclosures. A new accounting standard 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 standard 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 standard is effective in the 2018 first quarter and, aside from limited situations, cannot be early adopted. The Company is currently assessing the impact of the implementation of this standard on its consolidated financial statements.

Business Acquired (Tables)

Business Acquired (Tables)	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Summary of fair value of net assets acquired and allocation of purchase price	The following table summarizes the fair value of net assets acquired and allocation of purchase price, measured as of the acquisition date: Total Useful Life Purchase price Cash paid $ 245,157 Contingent consideration liability 41,762 Total purchase price (a) $ 286,919 Assets acquired Cash $ 9,579 Investments, at fair value 312,093 Intangible asset -- acquired insurance contracts 46,473 5 years Intangible asset -- operating platform 29,900 5 years Intangible asset -- favorable lease contract 1,056 5 years Intangible asset -- insurance licenses 16,858 Indefinite Other assets acquired 21,691 Total assets acquired 437,650 Liabilities acquired Reserves for losses and loss adjustment expenses $ 121,572 Unearned premiums 26,261 Intangible liability -- unfavorable service contract 9,533 9 years Other liabilities acquired 7,217 Total liabilities acquired 164,583 Net assets acquired (b) $ 273,067 Goodwill (a)-(b) $ 13,852

Variable Interest Entity and 37

Variable Interest Entity and Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2015
Variable Interest Entity and Noncontrolling Interest Disclosure [Abstract]
Activity in non-redeemable noncontrolling interests	The following table sets forth activity in the non-redeemable noncontrolling interests: December 31, 2015 2014 Balance, beginning of year $ 769,081 $ — Sale of shares to noncontrolling interests — 796,904 Amounts attributable to noncontrolling interests (29,984 ) (27,823 ) Foreign currency translation adjustments (266 ) — Balance, end of year $ 738,831 $ 769,081
Activity in redeemable noncontrolling interest	The following table sets forth activity in the redeemable non-controlling interests: December 31, 2015 2014 Balance, beginning of year $ 219,512 $ — Sale of shares to noncontrolling interests — 219,233 Shares acquired by the Company (1) (14,700 ) — Accretion of preference share issuance costs 370 279 Balance, end of year $ 205,182 $ 219,512 (1) During the 2015 second quarter, the Company acquired Gulf Re, which owns 600,000 Watford Preference Shares. Such shares, net of a discount, along with related dividends and accretion of the discount, are eliminated in consolidation.
Portion of income or loss attributable to noncontrolling interests	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’ as summarized in the table below: December 31, 2015 2014 Amounts attributable to non-redeemable noncontrolling interests $ 29,984 $ 27,823 Dividends attributable to redeemable noncontrolling interests (18,828 ) (14,728 ) Net (income) loss attributable to noncontrolling interests $ 11,156 $ 13,095

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Analysis of underwriting income (loss) by segment and reconciliation to net income (loss) 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 Arch common shareholders, summary information regarding net premiums written and earned by major line of business and net premiums written by location: Year Ended December 31, 2015 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,944,018 $ 1,419,022 $ 295,557 $ 4,656,723 $ 488,899 $ 4,797,163 Premiums ceded (898,347 ) (380,614 ) (28,064 ) (1,305,151 ) (22,940 ) (979,632 ) Net premiums written 2,045,671 1,038,408 267,493 3,351,572 465,959 3,817,531 Change in unearned premiums (863 ) 38,727 (53,383 ) (15,519 ) (68,107 ) (83,626 ) Net premiums earned 2,044,808 1,077,135 214,110 3,336,053 397,852 3,733,905 Other underwriting income 1,993 10,606 18,430 31,029 4,468 35,497 Losses and loss adjustment expenses (1,292,647 ) (440,350 ) (40,247 ) (1,773,244 ) (277,659 ) (2,050,903 ) Acquisition expenses, net (299,317 ) (223,632 ) (45,076 ) (568,025 ) (113,451 ) (681,476 ) Other operating expenses (354,416 ) (155,811 ) (82,370 ) (592,597 ) (14,919 ) (607,516 ) Underwriting income (loss) $ 100,421 $ 267,948 $ 64,847 433,216 (3,709 ) 429,507 Net investment income 271,680 76,410 348,090 Net realized gains (losses) (99,133 ) (86,709 ) (185,842 ) Net impairment losses recognized in earnings (20,116 ) — (20,116 ) Equity in net income (loss) of investment funds accounted for using the equity method 25,455 — 25,455 Other income (loss) (399 ) — (399 ) Other expenses (49,745 ) — (49,745 ) Interest expense (41,518 ) (4,356 ) (45,874 ) Net foreign exchange gains (losses) 62,624 3,494 66,118 Income (loss) before income taxes 582,064 (14,870 ) 567,194 Income tax expense (40,612 ) — (40,612 ) Net income (loss) 541,452 (14,870 ) 526,582 Dividends attributable to redeemable noncontrolling interests — (18,828 ) (18,828 ) Amounts attributable to noncontrolling interests — 29,984 29,984 Net income (loss) available to Arch 541,452 (3,714 ) 537,738 Preferred dividends (21,938 ) — (21,938 ) Net income (loss) available to Arch common shareholders $ 519,514 $ (3,714 ) $ 515,800 Underwriting Ratios Loss ratio 63.2 % 40.9 % 18.8 % 53.2 % 69.8 % 54.9 % Acquisition expense ratio 14.6 % 20.8 % 21.1 % 17.0 % 28.5 % 18.3 % Other operating expense ratio 17.3 % 14.5 % 38.5 % 17.8 % 3.7 % 16.3 % Combined ratio 95.1 % 76.2 % 78.4 % 88.0 % 102.0 % 89.5 % Goodwill and intangible assets $ 28,810 $ 1,875 $ 66,846 $ 97,531 $ — $ 97,531 Total investable assets $ 14,644,831 $ 1,696,107 $ 16,340,938 Total assets 21,054,938 2,122,332 23,177,270 Total liabilities 14,956,274 1,072,102 16,028,376 (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. Year Ended December 31, 2014 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 3,008,669 $ 1,527,245 $ 227,356 $ 4,760,394 $ 288,627 $ 4,840,616 Premiums ceded (862,015 ) (261,254 ) (22,519 ) (1,142,912 ) (14,171 ) (948,678 ) Net premiums written 2,146,654 1,265,991 204,837 3,617,482 274,456 3,891,938 Change in unearned premiums (129,284 ) 13,337 (11,264 ) (127,211 ) (170,979 ) (298,190 ) Net premiums earned 2,017,370 1,279,328 193,573 3,490,271 103,477 3,593,748 Other underwriting income 2,135 3,167 4,840 10,142 — 10,142 Losses and loss adjustment expenses (1,260,953 ) (532,450 ) (55,674 ) (1,849,077 ) (70,173 ) (1,919,250 ) Acquisition expenses, net (316,308 ) (261,438 ) (49,400 ) (627,146 ) (30,116 ) (657,262 ) Other operating expenses (335,157 ) (147,964 ) (66,891 ) (550,012 ) (6,268 ) (556,280 ) Underwriting income (loss) $ 107,087 $ 340,643 $ 26,448 474,178 (3,080 ) 471,098 Net investment income 284,336 18,249 302,585 Net realized gains (losses) 133,384 (30,467 ) 102,917 Net impairment losses recognized in earnings (30,150 ) — (30,150 ) Equity in net income (loss) of investment funds accounted for using the equity method 19,883 — 19,883 Other income (loss) (10,252 ) — (10,252 ) Other expenses (47,615 ) (2,329 ) (49,944 ) Interest expense (45,634 ) — (45,634 ) Net foreign exchange gains (losses) 82,658 1,086 83,744 Income (loss) before income taxes 860,788 (16,541 ) 844,247 Income tax expense (22,987 ) — (22,987 ) Net income (loss) 837,801 (16,541 ) 821,260 Dividends attributable to redeemable noncontrolling interests — (14,728 ) (14,728 ) Amounts attributable to noncontrolling interests — 27,823 27,823 Net income (loss) available to Arch 837,801 (3,446 ) 834,355 Preferred dividends (21,938 ) — (21,938 ) Net income (loss) available to Arch common shareholders $ 815,863 $ (3,446 ) $ 812,417 Underwriting Ratios Loss ratio 62.5 % 41.6 % 28.8 % 53.0 % 67.8 % 53.4 % Acquisition expense ratio 15.7 % 20.4 % 25.5 % 18.0 % 29.1 % 18.3 % Other operating expense ratio 16.6 % 11.6 % 34.6 % 15.8 % 6.1 % 15.5 % Combined ratio 94.8 % 73.6 % 88.9 % 86.8 % 103.0 % 87.2 % Goodwill and intangible assets $ 28,331 $ 3,333 $ 77,875 $ 109,539 $ — $ 109,539 Total investable assets $ 14,599,490 $ 1,163,240 $ 15,762,730 Total assets 20,523,565 1,482,516 22,006,081 Total liabilities 14,488,775 398,660 14,887,435 (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. Year Ended December 31, 2013 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,712,509 $ 1,399,621 $ 89,570 $ 4,196,623 $ — $ 4,196,623 Premiums ceded (763,713 ) (86,620 ) — (845,256 ) — (845,256 ) Net premiums written 1,948,796 1,313,001 89,570 3,351,367 — 3,351,367 Change in unearned premiums (72,782 ) (94,329 ) (38,304 ) (205,415 ) — (205,415 ) Net premiums earned 1,876,014 1,218,672 51,266 3,145,952 — 3,145,952 Other underwriting income 2,122 5,258 259 7,639 — 7,639 Losses and loss adjustment expenses (1,188,445 ) (486,236 ) (4,743 ) (1,679,424 ) — (1,679,424 ) Acquisition expenses, net (311,904 ) (234,373 ) (17,826 ) (564,103 ) — (564,103 ) Other operating expenses (315,387 ) (134,563 ) (8,377 ) (458,327 ) — (458,327 ) Underwriting income (loss) $ 62,400 $ 368,758 $ 20,579 451,737 — 451,737 Net investment income 267,219 — 267,219 Net realized gains (losses) 74,018 — 74,018 Net impairment losses recognized in earnings (3,786 ) — (3,786 ) Equity in net income (loss) of investment funds accounted for using the equity method 35,701 — 35,701 Other income (loss) (586 ) — (586 ) Other expenses (42,403 ) — (42,403 ) Interest expense (27,060 ) — (27,060 ) Net foreign exchange gains (losses) (12,335 ) — (12,335 ) Income (loss) before income taxes 742,505 — 742,505 Income tax benefit (32,774 ) — (32,774 ) Net income (loss) 709,731 — 709,731 Dividends attributable to redeemable noncontrolling interests — — — Amounts attributable to noncontrolling interests — — — Net income (loss) available to Arch 709,731 — 709,731 Preferred dividends (21,938 ) — (21,938 ) Net income (loss) available to Arch common shareholders $ 687,793 $ — $ 687,793 Underwriting Ratios Loss ratio 63.3 % 39.9 % 9.3 % 53.4 % — 53.4 % Acquisition expense ratio 16.6 % 19.2 % 34.8 % 17.9 % — 17.9 % Other operating expense ratio 16.8 % 11.0 % 16.3 % 14.6 % — 14.6 % Combined ratio 96.7 % 70.1 % 60.4 % 85.9 % — 85.9 % Goodwill and intangible assets $ 20,419 $ 6,900 $ — $ 27,319 $ — $ 27,319 Total investable assets $ 14,049,525 $ — $ 14,049,525 Total assets 19,557,054 — 19,557,054 Total liabilities 13,909,558 — 13,909,558 (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.
Summary of information regarding net premiums written and earned by major line of business and net premiums written by location	The following tables provide summary information regarding net premiums written and earned by major line of business and net premiums written by location: INSURANCE SEGMENT Year Ended December 31, 2015 2014 2013 Net premiums written (1) Professional lines (2) $ 434,024 $ 476,604 $ 476,193 Programs 423,157 480,580 419,673 Construction and national accounts 299,463 286,994 271,110 Excess and surplus casualty (3) 204,856 212,519 149,286 Property, energy, marine and aviation 203,186 244,640 280,551 Travel, accident and health 160,132 145,732 104,903 Lenders products 106,916 100,407 101,576 Other (4) 213,937 199,178 145,504 Total $ 2,045,671 $ 2,146,654 $ 1,948,796 Net premiums earned (1) Professional lines (2) $ 424,968 $ 456,508 $ 491,791 Programs 446,512 460,392 386,840 Construction and national accounts 296,828 277,811 250,729 Excess and surplus casualty (3) 208,091 182,024 118,395 Property, energy, marine and aviation 216,127 244,974 304,294 Travel, accident and health 153,578 127,691 97,135 Lenders products 90,906 94,438 99,847 Other (4) 207,798 173,532 126,983 Total $ 2,044,808 $ 2,017,370 $ 1,876,014 Net premiums written by client location (1) United States $ 1,710,918 $ 1,726,181 $ 1,526,156 Europe 187,020 240,136 226,254 Asia and Pacific 64,638 79,564 95,970 Other 83,095 100,773 100,416 Total $ 2,045,671 $ 2,146,654 $ 1,948,796 Net premiums written by underwriting location (1) United States $ 1,673,867 $ 1,688,887 $ 1,478,930 Europe 317,998 394,430 389,763 Other 53,806 63,337 80,103 Total $ 2,045,671 $ 2,146,654 $ 1,948,796 (1) Insurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions. (2) Includes professional liability, executive assurance and healthcare business. (3) Includes casualty and contract binding business. (4) Includes alternative markets, excess workers' compensation and surety business. REINSURANCE SEGMENT Year Ended December 31, 2015 2014 2013 Net premiums written (1) Casualty (2) $ 303,093 $ 317,996 $ 306,304 Other specialty (3) 298,794 405,126 417,865 Property excluding property catastrophe (4) 280,511 343,043 292,536 Property catastrophe 91,620 137,471 220,749 Marine and aviation 50,834 50,444 64,380 Other (5) 13,556 11,911 11,167 Total $ 1,038,408 $ 1,265,991 $ 1,313,001 Net premiums earned (1) Casualty (2) $ 310,249 $ 327,518 $ 241,774 Other specialty (3) 311,307 424,725 387,630 Property excluding property catastrophe (4) 295,487 303,496 274,719 Property catastrophe 96,865 150,761 232,423 Marine and aviation 50,808 61,118 70,105 Other (5) 12,419 11,710 12,021 Total $ 1,077,135 $ 1,279,328 $ 1,218,672 Net premiums written (1) Pro rata $ 537,556 $ 663,135 $ 692,024 Excess of loss 500,852 602,856 620,977 Total $ 1,038,408 $ 1,265,991 $ 1,313,001 Net premiums earned (1) Pro rata $ 563,585 $ 686,201 $ 608,586 Excess of loss 513,550 593,127 610,086 Total $ 1,077,135 $ 1,279,328 $ 1,218,672 Net premiums written by client location (1) United States $ 470,484 $ 589,255 $ 706,388 Europe 307,165 355,735 327,059 Asia and Pacific 94,609 142,626 94,252 Bermuda 80,888 77,620 87,047 Other 85,262 100,755 98,255 Total $ 1,038,408 $ 1,265,991 $ 1,313,001 Net premiums written by underwriting location (1) United States $ 439,190 $ 492,891 $ 507,183 Bermuda 281,985 394,351 459,467 Europe 298,790 343,823 309,129 Other 18,443 34,926 37,222 Total $ 1,038,408 $ 1,265,991 $ 1,313,001 (1) Reinsurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions. (2) Includes executive assurance, professional liability, workers’ compensation, excess motor, healthcare and other. (3) Includes proportional motor, surety, accident and health, workers’ compensation catastrophe, agriculture, trade credit and other. (4) Includes facultative business. (5) Includes life, casualty clash and other. Year Ended December 31, MORTGAGE SEGMENT 2015 2014 2013 Net premiums written by client location United States $ 193,617 $ 184,333 $ 63,692 Other 73,876 20,504 25,878 Total $ 267,493 $ 204,837 $ 89,570 Net premiums written by underwriting location United States $ 125,317 $ 98,809 $ — Other 142,176 106,028 89,570 Total $ 267,493 $ 204,837 $ 89,570 Net premiums earned by client location United States $ 202,930 $ 187,194 $ 49,045 Other 11,180 6,379 2,221 Total $ 214,110 $ 193,573 $ 51,266 Net premiums earned by underwriting location United States $ 113,062 $ 92,236 $ — Other 101,048 101,337 51,266 Total $ 214,110 $ 193,573 $ 51,266 OTHER SEGMENT Year Ended December 31, 2015 2014 2013 Net premiums written (1) Casualty (2) $ 320,619 $ 179,054 $ — Other specialty (3) 112,666 66,524 — Property catastrophe 12,441 9,280 — Property excluding property catastrophe 2,892 564 — Marine and aviation 1,256 1,251 — Other (4) 16,085 17,783 — Total $ 465,959 $ 274,456 $ — Net premiums earned (1) Casualty (2) $ 275,708 $ 72,395 $ — Other specialty (3) 101,588 24,157 — Property catastrophe 12,540 5,115 — Property excluding property catastrophe 1,340 182 — Marine and aviation 1,585 789 — Other (4) 5,091 839 — Total $ 397,852 $ 103,477 $ — Net premiums written by client location (1) United States $ 350,228 $ 186,795 $ — Europe 67,279 54,131 — Bermuda 39,414 27,977 — Other 9,038 5,553 — Total $ 465,959 $ 274,456 $ — (1) Other segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions. (2) Includes professional liability, excess motor, programs and other. (3) Includes proportional motor and other. (4) Includes mortgage and other.

Reserve for Losses and Loss A39

Reserve for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2015
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: Year Ended December 31, 2015 2014 2013 Reserve for losses and loss adjustment expenses at beginning of year $ 9,036,448 $ 8,824,696 $ 8,933,292 Unpaid losses and loss adjustment expenses recoverable 1,778,303 1,748,250 1,829,070 Net reserve for losses and loss adjustment expenses at beginning of year 7,258,145 7,076,446 7,104,222 Net incurred losses and loss adjustment expenses relating to losses occurring in: Current year 2,336,026 2,246,152 1,943,466 Prior years (285,123 ) (326,902 ) (264,042 ) Total net incurred losses and loss adjustment expenses 2,050,903 1,919,250 1,679,424 Net losses and loss adjustment expense reserves of acquired business (1) 262 120,671 — Foreign exchange (gains) losses (143,653 ) (160,486 ) 1,617 Net paid losses and loss adjustment expenses relating to losses occurring in: Current year (454,179 ) (347,270 ) (288,114 ) Prior years (1,415,065 ) (1,350,466 ) (1,420,703 ) Total net paid losses and loss adjustment expenses (1,869,244 ) (1,697,736 ) (1,708,817 ) Net reserve for losses and loss adjustment expenses at end of year 7,296,413 7,258,145 7,076,446 Unpaid losses and loss adjustment expenses recoverable 1,828,837 1,778,303 1,748,250 Reserve for losses and loss adjustment expenses at end of year $ 9,125,250 $ 9,036,448 $ 8,824,696 (1) 2014 amount relates to the Company’s acquisition of Arch MI U.S.

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2015
Reinsurance Disclosures [Abstract]
Effects of reinsurance	The effects of reinsurance on the Company’s written and earned premiums and losses and loss adjustment expenses with unaffiliated reinsurers were as follows: Year Ended December 31, 2015 2014 2013 Premiums Written Direct $ 3,086,919 $ 3,100,946 $ 2,754,582 Assumed 1,710,244 1,739,670 1,442,041 Ceded (979,632 ) (948,678 ) (845,256 ) Net $ 3,817,531 $ 3,891,938 $ 3,351,367 Premiums Earned Direct $ 3,002,508 $ 2,914,755 $ 2,666,104 Assumed 1,659,456 1,574,049 1,296,048 Ceded (928,059 ) (895,056 ) (816,200 ) Net $ 3,733,905 $ 3,593,748 $ 3,145,952 Losses and Loss Adjustment Expenses Direct $ 1,830,785 $ 1,763,492 $ 1,603,369 Assumed 752,304 621,346 450,618 Ceded (532,186 ) (465,588 ) (374,563 ) Net $ 2,050,903 $ 1,919,250 $ 1,679,424

Investment Information (Tables)

Investment Information (Tables)	12 Months Ended
	Dec. 31, 2015
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 securities classified as available for sale: Estimated Gross Gross Cost or OTTI Fair Unrealized Unrealized Amortized Unrealized Value Gains Losses Cost Losses (2) December 31, 2015 Fixed maturities (1): Corporate bonds $ 2,725,729 $ 15,978 $ (60,508 ) $ 2,770,259 $ (3,553 ) Mortgage backed securities 754,870 9,872 (5,334 ) 750,332 (3,350 ) Municipal bonds 1,626,281 27,014 (1,534 ) 1,600,801 — Commercial mortgage backed securities 764,152 3,269 (6,978 ) 767,861 — U.S. government and government agencies 2,423,455 6,228 (9,978 ) 2,427,205 — Non-U.S. government securities 917,664 10,414 (39,122 ) 946,372 — Asset backed securities 1,620,506 3,307 (12,951 ) 1,630,150 (22 ) Total 10,832,657 76,082 (136,405 ) 10,892,980 (6,925 ) Equity securities 629,182 94,341 (17,796 ) 552,637 — Other investments 300,476 43,798 (4,665 ) 261,343 — Short-term investments 587,904 187 (3,425 ) 591,142 — Total $ 12,350,219 $ 214,408 $ (162,291 ) $ 12,298,102 $ (6,925 ) December 31, 2014 Fixed maturities (1): Corporate bonds $ 3,108,513 $ 37,928 $ (38,974 ) $ 3,109,559 $ (317 ) Mortgage backed securities 943,343 18,843 (3,842 ) 928,342 (3,307 ) Municipal bonds 1,494,122 31,227 (1,044 ) 1,463,939 — Commercial mortgage backed securities 1,114,528 14,594 (3,822 ) 1,103,756 — U.S. government and government agencies 1,447,972 8,345 (1,760 ) 1,441,387 — Non-U.S. government securities 1,015,153 21,311 (37,203 ) 1,031,045 — Asset backed securities 1,677,941 8,425 (6,089 ) 1,675,605 (22 ) Total 10,801,572 140,673 (92,734 ) 10,753,633 (3,646 ) Equity securities 658,182 109,012 (13,364 ) 562,534 — Other investments 296,224 31,839 (362 ) 264,747 — Short-term investments 797,226 738 (5,270 ) 801,758 — Total $ 12,553,204 $ 282,262 $ (111,730 ) $ 12,382,672 $ (3,646 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments 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 December 31, 2015 , the net unrealized loss related to securities for which a non-credit OTTI was recognized in AOCI was $1.4 million , compared to a net unrealized gain of $0.9 million at December 31, 2014 .
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 Estimated Gross Estimated Gross Fair Unrealized Fair Unrealized Fair Unrealized Value Losses Value Losses Value Losses December 31, 2015 Fixed maturities (1): Corporate bonds $ 1,810,988 $ (37,445 ) $ 129,896 $ (23,063 ) $ 1,940,884 $ (60,508 ) Mortgage backed securities 487,018 (4,508 ) 48,991 (826 ) 536,009 (5,334 ) Municipal bonds 269,015 (1,303 ) 9,692 (231 ) 278,707 (1,534 ) Commercial mortgage backed securities 511,261 (6,639 ) 20,596 (339 ) 531,857 (6,978 ) U.S. government and government agencies 1,991,163 (9,978 ) — — 1,991,163 (9,978 ) Non-U.S. government securities 458,414 (13,494 ) 138,792 (25,628 ) 597,206 (39,122 ) Asset backed securities 1,217,163 (9,328 ) 134,841 (3,623 ) 1,352,004 (12,951 ) Total 6,745,022 (82,695 ) 482,808 (53,710 ) 7,227,830 (136,405 ) Equity securities 232,275 (17,796 ) — — 232,275 (17,796 ) Other investments 93,614 (4,665 ) — — 93,614 (4,665 ) Short-term investments 30,625 (3,425 ) — — 30,625 (3,425 ) Total $ 7,101,536 $ (108,581 ) $ 482,808 $ (53,710 ) $ 7,584,344 $ (162,291 ) December 31, 2014 Fixed maturities (1): Corporate bonds $ 1,309,637 $ (32,903 ) $ 148,963 $ (6,071 ) $ 1,458,600 $ (38,974 ) Mortgage backed securities 293,624 (1,476 ) 59,107 (2,366 ) 352,731 (3,842 ) Municipal bonds 210,614 (588 ) 13,643 (456 ) 224,257 (1,044 ) Commercial mortgage backed securities 232,147 (770 ) 125,894 (3,052 ) 358,041 (3,822 ) U.S. government and government agencies 618,381 (1,626 ) 3,438 (134 ) 621,819 (1,760 ) Non-U.S. government securities 510,766 (31,172 ) 46,910 (6,031 ) 557,676 (37,203 ) Asset backed securities 612,950 (2,486 ) 243,452 (3,603 ) 856,402 (6,089 ) Total 3,788,119 (71,021 ) 641,407 (21,713 ) 4,429,526 (92,734 ) Equity securities 181,002 (13,364 ) — — 181,002 (13,364 ) Other investments 59,638 (362 ) — — 59,638 (362 ) Short-term investments 79,271 (5,270 ) — — 79,271 (5,270 ) Total $ 4,108,030 $ (90,017 ) $ 641,407 $ (21,713 ) $ 4,749,437 $ (111,730 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged. See “—Securities Lending Agreements.”
Contractual maturities of the Company's fixed maturities and fixed maturities pledged under securities lending arrangements	December 31, 2015 December 31, 2014 Maturity Estimated Fair Value Amortized Cost Estimated Fair Value Amortized Cost Due in one year or less $ 337,898 $ 341,595 $ 235,930 $ 233,794 Due after one year through five years 4,644,516 4,677,230 4,074,562 4,077,408 Due after five years through 10 years 2,214,413 2,228,638 2,475,726 2,461,356 Due after 10 years 496,302 497,174 279,542 273,372 7,693,129 7,744,637 7,065,760 7,045,930 Mortgage backed securities 754,870 750,332 943,343 928,342 Commercial mortgage backed securities 764,152 767,861 1,114,528 1,103,756 Asset backed securities 1,620,506 1,630,150 1,677,941 1,675,605 Total $ 10,832,657 $ 10,892,980 $ 10,801,572 $ 10,753,633
Summary of securities lending transactions accounted for as secured borrowings, with significant investment categories	The Company’s securities lending transactions were accounted for as secured borrowings with significant investment categories as follows: December 31, 2015 Remaining Contractual Maturity of the Agreements Securities Lending Transactions Overnight and Continuous Less than 30 Days 30-90 Days 90 Days or More Total U.S. government and government agencies $ 235,728 $ — $ 82,286 $ 9,598 $ 327,612 Corporate bonds 55,086 — — — 55,086 Equity securities 6,722 4,424 — — 11,146 Total $ 297,536 $ 4,424 $ 82,286 $ 9,598 $ 393,844 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 10 $ — Amounts related to securities lending not included in offsetting disclosure in Note 10 $ 393,844
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: December 31, 2015 2014 Available for sale securities: Asian and emerging markets $ 206,861 $ 236,586 Investment grade fixed income 31,370 59,638 Credit related funds 22,512 — Other 39,733 — Total available for sale 300,476 296,224 Fair value option: Term loan investments (par value: $1,197,143 and $1,094,337) 1,108,017 1,073,649 Mezzanine debt funds 121,589 121,341 Credit related funds 219,049 114,436 Investment grade fixed income 63,053 69,108 Asian and emerging markets 34,761 25,800 Other (1) 124,502 137,094 Total fair value option 1,670,971 1,541,428 Total $ 1,971,447 $ 1,837,652 (1) Includes fund investments with strategies in mortgage servicing rights, transportation and infrastructure assets 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: December 31, 2015 2014 Fixed maturities $ 936,802 $ 632,024 Other investments 1,670,971 1,541,428 Short-term investments 285,923 251,601 Equity securities 798 — Investments accounted for using the fair value option $ 2,894,494 $ 2,425,053
Components of net investment income	The components of net investment income were derived from the following sources: Year Ended December 31, 2015 2014 2013 Fixed maturities $ 283,998 $ 265,219 $ 249,833 Term loan investments 71,120 39,940 20,608 Equity securities (dividends) 13,534 13,005 8,919 Short-term investments 669 1,888 1,259 Other (1) 41,807 28,869 19,710 Gross investment income 411,128 348,921 300,329 Investment expenses (63,038 ) (46,336 ) (33,110 ) Net investment income $ 348,090 $ 302,585 $ 267,219 (1) Includes income distributions from investment funds and other items.
Summary of net realized gains (losses)	Net realized gains (losses) were as follows, excluding the other-than-temporary impairment provisions: Year Ended December 31, 2015 2014 2013 Available for sale securities: Gross gains on investment sales $ 281,786 $ 248,031 $ 239,421 Gross losses on investment sales (218,970 ) (145,808 ) (203,077 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities (84,620 ) (20,743 ) 54 Other investments (122,171 ) 2,672 17,503 Equity securities (85 ) — 704 Short-term investments 1,462 (395 ) — Derivative instruments (1) (7,114 ) 43,934 20,912 Other (2) (36,130 ) (24,774 ) (1,499 ) Net realized gains (losses) $ (185,842 ) $ 102,917 $ 74,018 (1) See Note 10 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 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: Year Ended December 31, 2015 2014 2013 Fixed maturities: Mortgage backed securities $ (1,794 ) $ (1,525 ) $ (295 ) Corporate bonds (10,841 ) (2,062 ) (88 ) Commercial mortgage backed securities — (7 ) — Asset backed securities — (40 ) (128 ) Total (12,635 ) (3,634 ) (511 ) Short-term investments (2,341 ) — — Equity securities (4,206 ) (1,106 ) (3,275 ) Other investments (934 ) (25,410 ) — Net impairment losses recognized in earnings $ (20,116 ) $ (30,150 ) $ (3,786 )
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: Year Ended December 31, 2015 2014 2013 Balance at start of year $ 20,196 $ 60,062 $ 62,001 Credit loss impairments recognized on securities not previously impaired 12,777 691 423 Credit loss impairments recognized on securities previously impaired 1,673 162 88 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 (7,771 ) (40,719 ) (2,450 ) Balance at end of year $ 26,875 $ 20,196 $ 60,062
Summary of restricted assets	The following table details the value of the Company’s restricted assets: December 31, 2015 2014 Assets used for collateral or guarantees: Affiliated transactions $ 3,810,104 $ 4,138,527 Third party agreements 1,181,087 970,120 Deposits with U.S. regulatory authorities 391,458 337,981 Deposits with non-U.S. regulatory authorities 38,230 — Trust funds 105,170 72,461 Total restricted assets $ 5,526,049 $ 5,519,089

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2015
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 December 31, 2015 : Fair Value Measurement 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: Available for sale securities: Fixed maturities (1): Corporate bonds $ 2,725,729 $ — $ 2,709,361 $ 16,368 Mortgage backed securities 754,870 — 754,870 — Municipal bonds 1,626,281 — 1,626,281 — Commercial mortgage backed securities 764,152 — 764,152 — U.S. government and government agencies 2,423,455 2,378,662 44,793 — Non-U.S. government securities 917,664 — 917,664 — Asset backed securities 1,620,506 — 1,563,006 57,500 Total 10,832,657 2,378,662 8,380,127 73,868 Equity securities 629,182 627,441 1,741 — Short-term investments 587,904 572,604 15,300 — Other investments 99,159 99,159 — — Other investments measured at net asset value (2) 201,317 Total other investments 300,476 99,159 — — Derivative instruments (4) 20,022 — 20,022 — Fair value option: Corporate bonds 771,733 — 771,733 — Non-U.S. government bonds 81,824 — 81,824 — Mortgage backed securities 57,687 — 57,687 — Asset backed securities 25,444 — 25,444 — U.S. government and government agencies 114 114 — — Short-term investments 285,923 285,923 — — Equity securities 798 798 — — Other investments 1,176,312 68,295 1,108,017 — Other investments measured at net asset value (2) 494,659 Total 2,894,494 355,130 2,044,705 — Total assets measured at fair value $ 15,264,735 $ 4,032,996 $ 10,461,895 $ 73,868 Liabilities measured at fair value: Contingent consideration liabilities $ (96,048 ) $ — $ — $ (96,048 ) Securities sold but not yet purchased (3) (30,583 ) — (30,583 ) — Derivative instruments (4) (11,863 ) — (11,863 ) — Total liabilities measured at fair value $ (138,494 ) $ — $ (42,446 ) $ (96,048 ) (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 8 , “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 10 , “Derivative Instruments.” The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2014 : Fair Value Measurement 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: Available for sale securities: Fixed maturities (1): Corporate bonds $ 3,108,513 $ — $ 3,108,513 $ — Mortgage backed securities 943,343 — 943,343 — Municipal bonds 1,494,122 — 1,494,122 — Commercial mortgage backed securities 1,114,528 — 1,114,528 — U.S. government and government agencies 1,447,972 1,447,972 — — Non-U.S. government securities 1,015,153 — 1,015,153 — Asset backed securities 1,677,941 — 1,620,441 57,500 Total 10,801,572 1,447,972 9,296,100 57,500 Equity securities 658,182 658,182 — — Short-term investments 797,226 759,621 37,605 — Other investments 97,372 — 97,372 — Other investments measured at net asset value (2) 198,852 Total other investments 296,224 — 97,372 — Derivative instruments (3) 15,876 — 15,876 — Fair value option: Corporate bonds 497,101 — 497,101 — Non-U.S. government bonds 88,411 — 88,411 — Mortgage backed securities 22,190 — 22,190 — Asset backed securities 24,322 — 24,322 — Short-term investments 251,601 250,580 1,021 — Other investments 1,140,266 — 1,140,266 — Other investments measured at net asset value (2) 401,162 Total 2,425,053 250,580 1,773,311 — Total assets measured at fair value $ 14,994,133 $ 3,116,355 $ 11,220,264 $ 57,500 Liabilities measured at fair value: Contingent consideration liabilities $ (61,845 ) $ — $ — $ (61,845 ) Derivative instruments (3) (5,397 ) — (5,397 ) — Total liabilities measured at fair value $ (67,242 ) $ — $ (5,397 ) $ (61,845 ) (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 8 , “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) See Note 10 , “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 for 2015 , 2014 and 2013 : Assets Liabilities Available for sale Fair value option Asset Backed Securities Corporate Bonds Other Investments Other Investments Total Contingent Consideration Liabilities Year Ended December 31, 2015 Balance at beginning of year $ 57,500 $ — $ — $ — $ 57,500 $ (61,845 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — — — — — (33,135 ) Included in other comprehensive income — — — — — — Purchases, issuances, sales and settlements Purchases — — — — — — Issuances — — — — — (1,068 ) Sales — — — — — — Settlements — — — — — — Transfers in and/or out of Level 3 — 16,368 — — 16,368 — Balance at end of year $ 57,500 $ 16,368 $ — $ — $ 73,868 $ (96,048 ) Year Ended December 31, 2014 Balance at beginning of year $ — $ 2,045 $ 170,420 $ 377,525 $ 549,990 $ — Total gains or (losses) (realized/unrealized) Included in earnings (1) — — — — — (20,083 ) Included in other comprehensive income — — — — — — Purchases, issuances, sales and settlements Purchases — — — — — — Issuances — — — — — (41,762 ) Sales — (2,045 ) — — (2,045 ) — Settlements — — — — — — Transfers in and/or out of Level 3 57,500 — (170,420 ) (377,525 ) (490,445 ) — Balance at end of year $ 57,500 $ — $ — $ — $ 57,500 $ (61,845 ) (1) Gains or losses on fixed maturities available for sale were included in net realized gains (losses) while gains or losses on other investments were included in net realized gains (losses) or net investment income. Gains or losses on contingent consideration liabilities were included in net realized gains (losses). (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 transfers out of Level 3 presented in this table are intended to permit reconciliation to information previously presented.

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2015
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 Liability Derivatives Net Notional Value (1) December 31, 2015 Futures contracts (2) $ 2,816 $ (1,202 ) $ 1,614 $ 1,797,115 Foreign currency forward contracts (2) 9,336 (6,344 ) 2,992 773,619 TBAs (3) 6,525 — 6,525 6,316 Other (2) 7,870 (4,317 ) 3,553 1,694,935 Total $ 26,547 $ (11,863 ) $ 14,684 December 31, 2014 Futures contracts (2) $ 2,156 $ (1,907 ) $ 249 $ 2,549,027 Foreign currency forward contracts (2) 10,511 (1,145 ) 9,366 397,106 TBAs (3) 10,592 — 10,592 10,056 Other (2) 3,209 (2,345 ) 864 735,684 Total $ 26,468 $ (5,397 ) $ 21,071 (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.’ Such amounts include risk in force on GSE credit-risk sharing transactions that are accounted for as derivatives. (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 hedging instruments Year Ended December 31, 2015 2014 2013 Net realized gains (losses): Futures contracts $ (21,533 ) $ 30,444 $ 10,742 Foreign currency forward contracts 16,045 13,430 9,762 TBAs 1,452 (342 ) (1,623 ) Other (3,078 ) 402 2,031 Total $ (7,114 ) $ 43,934 $ 20,912

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2015
Comprehensive Income Note Disclosure [Abstract]
Schedule of changes in each component of AOCI	The following table presents the changes in each component of accumulated other comprehensive income (“AOCI”), net of noncontrolling interests: Unrealized Appreciation on Available-For-Sale Investments Foreign Currency Translation Adjustments Total Year Ended December 31, 2015 Beginning balance $ 161,598 $ (32,742 ) $ 128,856 Other comprehensive income (loss) before reclassifications (83,280 ) (33,845 ) (117,125 ) Amounts reclassified from accumulated other comprehensive income (28,233 ) — (28,233 ) Net current period other comprehensive income (loss) (111,513 ) (33,845 ) (145,358 ) Ending balance $ 50,085 $ (66,587 ) $ (16,502 ) Year Ended December 31, 2014 Beginning balance $ 80,692 $ (5,728 ) $ 74,964 Other comprehensive income (loss) before reclassifications 146,010 (27,014 ) 118,996 Amounts reclassified from accumulated other comprehensive income (65,104 ) — (65,104 ) Net current period other comprehensive income (loss) 80,906 (27,014 ) 53,892 Ending balance $ 161,598 $ (32,742 ) $ 128,856 Year Ended December 31, 2013 Beginning balance $ 289,956 $ (2,939 ) $ 287,017 Other comprehensive income (loss) before reclassifications (176,578 ) (2,789 ) (179,367 ) Amounts reclassified from accumulated other comprehensive income (32,686 ) — (32,686 ) Net current period other comprehensive income (loss) (209,264 ) (2,789 ) (212,053 ) Ending balance $ 80,692 $ (5,728 ) $ 74,964
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): Consolidated Statement of Income Amounts Reclassified from AOCI Details About Line Item That Includes Year Ended December 31, AOCI Components Reclassification 2015 2014 2013 Unrealized appreciation on available-for-sale investments Net realized gains $ 62,817 $ 102,223 $ 39,308 Other-than-temporary impairment losses (26,152 ) (30,470 ) (3,961 ) Total before tax 36,665 71,753 35,347 Income tax (expense) benefit (8,432 ) (6,649 ) (2,661 ) Net of tax $ 28,233 $ 65,104 $ 32,686
Schedule of tax effects allocated to each component of other comprehensive income (loss)	Following are the related tax effects allocated to each component of other comprehensive income (loss): Before Tax Tax Expense Net of Tax Amount (Benefit) Amount Year Ended December 31, 2015 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ (77,311 ) $ (67 ) $ (77,244 ) Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (6,036 ) — (6,036 ) Less reclassification of net realized gains (losses) included in net income 36,665 8,432 28,233 Foreign currency translation adjustments (35,678 ) (1,568 ) (34,110 ) Other comprehensive income (loss) $ (155,690 ) $ (10,067 ) $ (145,623 ) Year Ended December 31, 2014 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 161,685 $ 15,355 $ 146,330 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (320 ) — (320 ) Less reclassification of net realized gains (losses) included in net income 71,753 6,649 65,104 Foreign currency translation adjustments (27,014 ) — (27,014 ) Other comprehensive income (loss) $ 62,598 $ 8,706 $ 53,892 Year Ended December 31, 2013 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ (201,386 ) $ (24,983 ) $ (176,403 ) Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (175 ) — (175 ) Less reclassification of net realized gains (losses) included in net income 35,347 2,661 32,686 Foreign currency translation adjustments (2,789 ) — (2,789 ) Other comprehensive income (loss) $ (239,697 ) $ (27,644 ) $ (212,053 )

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2015
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 per common share: Year Ended December 31, 2015 2014 2013 Numerator: Net income $ 526,582 $ 821,260 $ 709,731 Amounts attributable to noncontrolling interests 11,156 13,095 — Net income available to Arch 537,738 834,355 709,731 Preferred dividends (21,938 ) (21,938 ) (21,938 ) Net income available to Arch common shareholders $ 515,800 $ 812,417 $ 687,793 Denominator: Weighted average common shares outstanding – basic 121,786,127 130,817,610 131,355,392 Effect of dilutive common share equivalents: Nonvested restricted shares 1,253,938 1,128,540 1,090,100 Stock options (1) 2,998,678 2,976,172 3,331,691 Weighted average common shares and common share equivalents outstanding – diluted 126,038,743 134,922,322 135,777,183 Earnings per common share: Basic $ 4.24 $ 6.21 $ 5.24 Diluted $ 4.09 $ 6.02 $ 5.07 (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 2015 , 2014 and 2013 , the number of stock options excluded were 799,535 , 1,435,955 and 892,439 , respectively.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Components of income taxes attributable to operations	The components of income taxes attributable to operations were as follows: Year Ended December 31, 2015 2014 2013 Current expense (benefit): United States $ 37,186 $ 29,749 $ 27,537 Non-U.S. 7,008 801 5,159 44,194 30,550 32,696 Deferred expense (benefit): United States (4,893 ) (8,168 ) 1,937 Non-U.S. 1,311 605 (1,859 ) (3,582 ) (7,563 ) 78 Income tax expense (benefit) $ 40,612 $ 22,987 $ 32,774
Schedule of income or loss before income taxes by jurisdiction	The Company’s income or loss before income taxes was earned in the following jurisdictions: Year Ended December 31, 2015 2014 2013 Income (Loss) Before Income Taxes: Bermuda $ 508,561 $ 794,926 $ 717,661 United States 57,527 53,055 87,032 Other 1,106 (3,734 ) (62,188 ) Total $ 567,194 $ 844,247 $ 742,505
Reconciliation of the differences between the provision for income taxes and the expected tax provision at the weighted average tax rate	A reconciliation of the difference between the provision for income taxes and the expected tax provision at the weighted average tax rate follows: Year Ended December 31, 2015 2014 2013 Expected income tax expense (benefit) computed on pre-tax income at weighted average income tax rate $ 20,058 $ 18,178 $ 17,506 Addition (reduction) in income tax expense (benefit) resulting from: Tax-exempt investment income (9,588 ) (8,048 ) (8,255 ) Meals and entertainment 897 711 599 State taxes, net of U.S. federal tax benefit 858 1,281 431 Foreign branch taxes 1,456 464 703 Prior year adjustment 2,510 320 2,810 Foreign exchange gains & losses 670 746 (1,254 ) Changes in applicable tax rate 40 (51 ) 2,007 Dividend withholding taxes 6,323 3,276 4,619 Change in valuation allowance 2,917 (736 ) 11,795 Contingent consideration 11,548 6,763 — Uncertain tax position 2,008 — — Other 915 83 1,813 Income tax expense (benefit) $ 40,612 $ 22,987 $ 32,774
Significant components of deferred income tax assets and liabilities	Significant components of the Company’s deferred income tax assets and liabilities were as follows: December 31, 2015 2014 Deferred income tax assets: Net operating loss $ 11,436 $ 12,017 AMT credit carryforward 5,304 5,309 Discounting of net loss reserves 54,373 63,880 Net unearned premium reserve 33,579 34,087 Compensation liabilities 29,069 27,765 Foreign tax credit carryforward 6,215 4,628 Interest expense 1,972 5,208 Goodwill and intangible assets 2,683 885 Tax and loss bonds 14,150 21,247 Net unrealized foreign exchange gains 1,573 — Other, net 21,273 13,408 Deferred tax assets before valuation allowance 181,627 188,434 Valuation allowance (13,816 ) (12,624 ) Deferred tax assets net of valuation allowance 167,811 175,810 Deferred income tax liabilities: Depreciation and amortization (7,368 ) (7,579 ) Deferred acquisition costs, net (164 ) (2,744 ) Deposit accounting liability (4,151 ) (4,170 ) Contingency reserve (15,289 ) (18,480 ) Net unrealized appreciation of investments (4,103 ) (11,695 ) Other, net (1,042 ) (150 ) Total deferred tax liabilities (32,117 ) (44,818 ) Net deferred income tax assets $ 135,694 $ 130,992
Reconciliation of the beginning and ending amount of unrecognized tax benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: December 31, 2015 2014 Balance at beginning of year $ — $ — Additions based on tax positions related to the current year 517 — Additions for tax positions of prior years 1,491 — Reductions for tax positions of prior years — — Settlements — — Balance at end of year $ 2,008 $ —
Summary of open tax years potentially subject to examination, by jurisdiction	The following table details open tax years that are potentially subject to examination by local tax authorities, in the following major jurisdictions: Jurisdiction Tax Years United States 2012-2015 United Kingdom 2010-2015 Ireland 2011-2015 Canada 2011-2015 Switzerland 2012-2015 Denmark 2012-2015

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Summary of future minimum lease payments	At December 31, 2015 , the future minimum rental commitments, exclusive of escalation clauses and maintenance costs and net of rental income, for all of the Company’s operating leases are as follows: 2016 $ 25,494 2017 24,660 2018 24,337 2019 21,024 2020 18,250 Thereafter 40,361 Total $ 154,126

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Analysis of goodwill and intangible assets	The following table shows an analysis of goodwill and intangible assets: Goodwill Intangible assets with an indefinite life Intangible assets with finite life Total Net balance at December 31, 2013 $ — $ 16,666 $ 10,653 $ 27,319 Acquisitions 14,965 16,858 76,435 108,258 Amortization — — (25,520 ) (25,520 ) Foreign currency translation adjustment (19 ) — (499 ) (518 ) Net balance at December 31, 2014 14,946 33,524 61,069 109,539 Acquisitions 663 — 10,844 11,507 Amortization — — (22,968 ) (22,968 ) Foreign currency translation adjustment (73 ) — (474 ) (547 ) Net balance at December 31, 2015 $ 15,536 $ 33,524 $ 48,471 $ 97,531 Gross balance at December 31, 2015 $ 15,628 $ 33,524 $ 135,752 $ 184,904 Accumulated amortization — — (86,407 ) (86,407 ) Foreign currency translation adjustment (92 ) — (874 ) (966 ) Net balance at December 31, 2015 $ 15,536 $ 33,524 $ 48,471 $ 97,531
Summary of components of intangible assets	The following table presents the components of intangible assets: Gross Balance Accumulated Foreign Currency Translation Adjustment Net Balance December 31, 2015 Acquired insurance contracts $ 85,032 $ (62,377 ) $ (152 ) $ 22,503 Operating platform 29,900 (11,462 ) — 18,438 Customer relationships 29,296 (16,355 ) (722 ) 12,219 Goodwill 15,628 — (92 ) 15,536 Insurance licenses 33,524 — — 33,524 Unfavorable service contract (9,533 ) 4,192 — (5,341 ) Other 1,057 (405 ) — 652 Total $ 184,904 $ (86,407 ) $ (966 ) $ 97,531 December 31, 2014 Acquired insurance contracts $ 77,574 $ (47,710 ) $ (107 ) $ 29,757 Operating platform 29,900 (5,482 ) — 24,418 Customer relationships 25,910 (12,283 ) (293 ) 13,334 Goodwill 14,965 — (19 ) 14,946 Insurance licenses 33,524 — — 33,524 Unfavorable service contract $ (9,533 ) $ 2,229 $ — (7,304 ) Other $ 1,057 $ (193 ) $ — 864 Total $ 173,397 $ (63,439 ) $ (419 ) $ 109,539

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
Roll-forward of changes in issued and outstanding Common Shares	The following table presents a roll-forward of changes in ACGL’s issued and outstanding Common Shares: Year Ended December 31, 2015 2014 2013 Common Shares: Shares issued and outstanding, beginning of year 171,672,408 169,560,591 168,255,572 Shares issued (1) 1,001,667 1,493,524 811,732 Restricted shares issued, net of cancellations 433,774 618,293 493,287 Shares issued, end of year 173,107,849 171,672,408 169,560,591 Common shares in treasury, end of year (50,480,066 ) (44,304,474 ) (35,885,707 ) Shares issued and outstanding, end of year 122,627,783 127,367,934 133,674,884 (1) Includes shares issued from the exercise of stock options and stock appreciation rights, and shares issued from the employee share purchase plan.

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Valuation assumptions	Year Ended December 31, 2015 2014 2013 Dividend yield 0.0 % 0.0 % 0.0 % Expected volatility 22.1 % 22.8 % 23.6 % Risk free interest rate 1.8 % 1.9 % 1.0 % Expected option life 6.0 years 6.0 years 6.0 years
Option activity	A summary of stock option and SAR activity under the Company’s Long Term Incentive and Share Award Plans during 2015 is presented below: Year Ended December 31, 2015 Number of Options / SARs Weighted Average Exercise Price Outstanding, beginning of year 7,804,033 $ 34.52 Granted 693,107 $ 61.93 Exercised (926,958 ) $ 24.91 Forfeited or expired (87,720 ) $ 50.09 Outstanding, end of year 7,482,462 $ 38.07 Exercisable, end of year 5,429,047 $ 32.88
Unvested restricted share and unit activity	A summary of unvested restricted share and unit activity under the Company’s Long Term Incentive and Share Award Plans for 2015 is presented below: Year Ended December 31, 2015 Restricted Common Shares Restricted Unit Awards Unvested Shares: Unvested balance, beginning of year 1,969,842 305,133 Granted 502,638 69,340 Vested (603,023 ) (88,916 ) Forfeited (68,864 ) (20,928 ) Unvested balance, end of year 1,800,593 264,629 Weighted Average Grant Date Fair Value: Unvested balance, beginning of year $ 48.47 $ 48.49 Granted $ 62.70 $ 62.61 Vested $ 49.75 $ 50.94 Forfeited $ 50.45 $ 48.97 Unvested balance, end of year $ 51.94 $ 51.33

Statutory Information (Tables)

Statutory Information (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure Statutory Information [Abstract]
Summary of statutory capital, surplus and net income	The actual and required statutory capital and surplus for the Company’s principal operating subsidiaries at December 31, 2015 and 2014 was as follows: December 31, 2015 December 31, 2014 Actual (1) Required (1) Actual (1) Required (1) Statutory capital and surplus (1): Bermuda $ 6,397,010 $ 2,129,064 $ 6,447,803 $ 2,209,757 Ireland 559,996 459,271 553,561 463,877 United States 1,564,056 488,794 1,454,282 467,797 United Kingdom 404,821 321,462 384,525 307,596 Canada 67,436 36,360 79,123 58,837 (1) Such amounts include ownership interests in affiliated insurance and reinsurance subsidiaries. The statutory net income (loss) for the Company’s principal operating subsidiaries for 2015 , 2014 and 2013 was as follows: Year Ended December 31, 2015 2014 2013 Statutory net income (loss): Bermuda $ 514,151 $ 692,676 $ 719,267 Ireland 29,041 43,197 (24,410 ) United States 76,604 46,110 62,605 United Kingdom 3,285 13,016 (11,353 ) Canada (1,098 ) 1,517 (36,203 )

Unaudited Condensed Quarterly52

Unaudited Condensed Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Summary of condensed quarterly financial information	The following table summarizes the 2015 and 2014 unaudited condensed quarterly financial information: Fourth Quarter Third Quarter Second Quarter First Quarter Year Ended December 31, 2015 Net premiums written $ 834,984 $ 971,972 $ 943,580 $ 1,066,995 Net premiums earned 943,520 936,683 943,438 910,264 Net investment income 95,900 86,233 86,963 78,994 Net realized gains (losses) (143,767 ) (89,698 ) (35,725 ) 83,348 Net impairment losses recognized in earnings (7,336 ) (5,868 ) (1,113 ) (5,799 ) Underwriting income 113,143 94,779 105,114 116,471 Net income 58,579 80,033 115,790 283,336 Preferred dividends (5,485 ) (5,484 ) (5,485 ) (5,484 ) Net income available to Arch common shareholders 53,094 74,549 110,305 277,852 Net income per common share -- basic $ 0.44 $ 0.62 $ 0.91 $ 2.24 Net income per common share -- diluted $ 0.42 $ 0.60 $ 0.88 $ 2.16 Year Ended December 31, 2014 Net premiums written $ 895,481 $ 959,539 $ 971,928 $ 1,064,990 Net premiums earned 923,165 903,651 907,152 859,780 Net investment income 82,496 80,105 72,990 66,994 Net realized gains (losses) 10,561 18,515 54,144 19,697 Net impairment losses recognized in earnings (3,837 ) (8,593 ) (14,749 ) (2,971 ) Underwriting income 113,464 101,087 124,091 132,456 Net income 215,164 228,675 208,016 182,500 Preferred dividends (5,485 ) (5,484 ) (5,485 ) (5,484 ) Net income available to Arch common shareholders 209,679 223,191 202,531 177,016 Net income per common share -- basic $ 1.65 $ 1.69 $ 1.53 $ 1.34 Net income per common share -- diluted $ 1.60 $ 1.64 $ 1.48 $ 1.30

Guarantor Financial Informati53

Guarantor Financial Information (Tables)	12 Months Ended
	Dec. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed consolidating balance sheet	December 31, 2015 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 50 $ 42,210 $ 15,815,381 $ (14,700 ) $ 15,842,941 Cash 6,809 17,023 529,494 — 553,326 Investments in subsidiaries 6,609,174 1,712,757 — (8,321,931 ) — Due from subsidiaries and affiliates 23 48,811 384,469 (433,303 ) — Premiums receivable — — 1,376,310 (392,867 ) 983,443 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 5,783,452 (3,916,079 ) 1,867,373 Contractholder receivables — — 1,486,296 — 1,486,296 Prepaid reinsurance premiums — — 1,511,795 (1,084,186 ) 427,609 Deferred acquisition costs, net — — 433,477 — 433,477 Other assets 4,138 45,522 2,119,279 (586,134 ) 1,582,805 Total assets $ 6,620,194 $ 1,866,323 $ 29,439,953 $ (14,749,200 ) $ 23,177,270 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 13,010,608 $ (3,885,358 ) $ 9,125,250 Unearned premiums — — 3,418,118 (1,084,186 ) 2,333,932 Reinsurance balances payable — — 603,586 (379,466 ) 224,120 Contractholder payables — — 1,486,296 — 1,486,296 Collateral held for insured obligations 248,982 248,982 Deposit accounting liabilities — — 463,507 (203,143 ) 260,364 Senior notes 296,874 494,432 — — 791,306 Revolving credit agreement borrowings 100,000 — 430,434 — 530,434 Due to subsidiaries and affiliates 26 35,000 398,277 (433,303 ) — Other liabilities 18,413 50,890 1,385,500 (427,111 ) 1,027,692 Total liabilities 415,313 580,322 21,445,308 (6,412,567 ) 16,028,376 Redeemable noncontrolling interests — — 219,882 (14,700 ) 205,182 Shareholders' Equity Total shareholders' equity available to Arch 6,204,881 1,286,001 7,035,932 (8,321,933 ) 6,204,881 Non-redeemable noncontrolling interests — — 738,831 — 738,831 Total shareholders' equity 6,204,881 1,286,001 7,774,763 (8,321,933 ) 6,943,712 Total liabilities, noncontrolling interests and shareholders' equity $ 6,620,194 $ 1,866,323 $ 29,439,953 $ (14,749,200 ) $ 23,177,270 December 31, 2014 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 107 $ 62,867 $ 15,257,796 $ — $ 15,320,770 Cash 3,218 2,787 479,697 — 485,702 Investments in subsidiaries 6,536,644 1,685,185 — (8,221,829 ) — Due from subsidiaries and affiliates 48 7,517 370,429 (377,994 ) — Premiums receivable — — 1,331,511 (382,816 ) 948,695 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 5,584,973 (3,772,128 ) 1,812,845 Contractholder receivables — — 1,309,192 — 1,309,192 Prepaid reinsurance premiums — — 1,373,008 (995,930 ) 377,078 Deferred acquisition costs, net — — 414,525 — 414,525 Other assets 4,386 43,921 1,705,546 (416,579 ) 1,337,274 Total assets $ 6,544,403 $ 1,802,277 $ 27,826,677 $ (14,167,276 ) $ 22,006,081 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 12,784,030 $ (3,747,582 ) $ 9,036,448 Unearned premiums — — 3,227,508 (995,930 ) 2,231,578 Reinsurance balances payable — — 589,289 (369,977 ) 219,312 Contractholder payables — — 1,309,192 — 1,309,192 Collateral held for insured obligations 184,219 184,219 Deposit accounting liabilities — — 587,050 (259,666 ) 327,384 Senior notes 296,796 494,345 — — 791,141 Revolving credit agreement borrowings 100,000 — — — 100,000 Due to subsidiaries and affiliates 417 7,505 370,072 (377,994 ) — Other liabilities 17,137 49,403 815,919 (194,298 ) 688,161 Total liabilities 414,350 551,253 19,867,279 (5,945,447 ) 14,887,435 Redeemable noncontrolling interests — — 219,512 — 219,512 Shareholders' Equity Total shareholders' equity available to Arch 6,130,053 1,251,024 6,970,805 (8,221,829 ) 6,130,053 Non-redeemable noncontrolling interests — — 769,081 — 769,081 Total shareholders' equity 6,130,053 1,251,024 7,739,886 (8,221,829 ) 6,899,134 Total liabilities, noncontrolling interests and shareholders' equity $ 6,544,403 $ 1,802,277 $ 27,826,677 $ (14,167,276 ) $ 22,006,081
Condensed consolidating statement of income and comprehensive income	Year Ended December 31, 2015 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 $ — $ — $ 3,733,905 $ — $ 3,733,905 Net investment income 1 2,342 368,413 (22,666 ) 348,090 Net realized gains (losses) — 1 (185,843 ) — (185,842 ) Net impairment losses recognized in earnings — — (20,116 ) — (20,116 ) Other underwriting income — — 35,739 (242 ) 35,497 Equity in net income (loss) of investment funds accounted for using the equity method — — 25,455 — 25,455 Other income (loss) — — (399 ) — (399 ) Total revenues 1 2,343 3,957,154 (22,908 ) 3,936,590 Expenses Losses and loss adjustment expenses — — 2,050,903 — 2,050,903 Acquisition expenses — — 681,476 — 681,476 Other operating expenses 48,107 3,689 605,465 — 657,261 Interest expense 23,450 26,502 18,024 (22,102 ) 45,874 Net foreign exchange (gains) losses — — (41,622 ) (24,496 ) (66,118 ) Total expenses 71,557 30,191 3,314,246 (46,598 ) 3,369,396 Income (loss) before income taxes (71,556 ) (27,848 ) 642,908 23,690 567,194 Income tax (expense) benefit — 9,732 (50,344 ) — (40,612 ) Income (loss) before equity in net income of subsidiaries (71,556 ) (18,116 ) 592,564 23,690 526,582 Equity in net income of subsidiaries 609,294 50,156 — (659,450 ) — Net income 537,738 32,040 592,564 (635,760 ) 526,582 Net (income) loss attributable to noncontrolling interests — — 10,351 805 11,156 Net income available to Arch 537,738 32,040 602,915 (634,955 ) 537,738 Preferred dividends (21,938 ) — — — (21,938 ) Net income available to Arch common shareholders $ 515,800 $ 32,040 $ 602,915 $ (634,955 ) $ 515,800 Comprehensive income (loss) available to Arch $ 392,380 $ 838 $ 482,047 $ (482,885 ) $ 392,380 Year Ended December 31, 2014 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 $ — $ — $ 3,593,748 $ — $ 3,593,748 Net investment income — — 326,831 (24,246 ) 302,585 Net realized gains (losses) — 5 102,912 — 102,917 Net impairment losses recognized in earnings — — (30,150 ) — (30,150 ) Other underwriting income — — 10,142 — 10,142 Equity in net income (loss) of investment funds accounted for using the equity method — — 19,883 — 19,883 Other income (loss) — — (10,252 ) — (10,252 ) Total revenues — 5 4,013,114 (24,246 ) 3,988,873 Expenses Losses and loss adjustment expenses — — 1,919,250 — 1,919,250 Acquisition expenses — — 657,262 — 657,262 Other operating expenses 46,074 3,387 556,763 — 606,224 Interest expense 23,423 25,817 20,640 (24,246 ) 45,634 Net foreign exchange (gains) losses — — (53,222 ) (30,522 ) (83,744 ) Total expenses 69,497 29,204 3,100,693 (54,768 ) 3,144,626 Income (loss) before income taxes (69,497 ) (29,199 ) 912,421 30,522 844,247 Income tax (expense) benefit — 10,125 (33,112 ) — (22,987 ) Income (loss) before equity in net income of subsidiaries (69,497 ) (19,074 ) 879,309 30,522 821,260 Equity in net income of subsidiaries 903,852 53,584 — (957,436 ) — Net income 834,355 34,510 879,309 (926,914 ) 821,260 Net (income) loss attributable to noncontrolling interests — — 13,095 — 13,095 Net income available to Arch 834,355 34,510 892,404 (926,914 ) 834,355 Preferred dividends (21,938 ) — — — (21,938 ) Net income available to Arch common shareholders $ 812,417 $ 34,510 $ 892,404 $ (926,914 ) $ 812,417 Comprehensive income (loss) available to Arch $ 888,247 $ 33,671 $ 976,821 $ (1,010,492 ) $ 888,247 Year Ended December 31, 2013 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 $ — $ — $ 3,145,952 $ — $ 3,145,952 Net investment income — 31 307,449 (40,261 ) 267,219 Net realized gains (losses) — — 74,018 — 74,018 Net impairment losses recognized in earnings — — (3,786 ) — (3,786 ) Other underwriting income — — 7,639 — 7,639 Equity in net income (loss) of investment funds accounted for using the equity method — — 35,701 — 35,701 Other income (loss) — — (586 ) — (586 ) Total revenues — 31 3,566,387 (40,261 ) 3,526,157 Expenses Losses and loss adjustment expenses — — 1,679,424 — 1,679,424 Acquisition expenses — — 564,103 — 564,103 Other operating expenses 38,702 2,691 459,337 — 500,730 Interest expense 23,272 1,316 42,733 (40,261 ) 27,060 Net foreign exchange (gains) losses — — 2,145 10,190 12,335 Total expenses 61,974 4,007 2,747,742 (30,071 ) 2,783,652 Income (loss) before income taxes (61,974 ) (3,976 ) 818,645 (10,190 ) 742,505 Income tax (expense) benefit — 1,383 (34,157 ) — (32,774 ) Income (loss) before equity in net income of subsidiaries (61,974 ) (2,593 ) 784,488 (10,190 ) 709,731 Equity in net income of subsidiaries 771,705 25,644 — (797,349 ) — Net income 709,731 23,051 784,488 (807,539 ) 709,731 Net (income) loss attributable to noncontrolling interests — — — — — Net income available to Arch 709,731 23,051 784,488 (807,539 ) 709,731 Preferred dividends (21,938 ) — — — (21,938 ) Net income available to Arch common shareholders $ 687,793 $ 23,051 $ 784,488 $ (807,539 ) $ 687,793 Comprehensive income (loss) available to Arch $ 497,678 $ (28,330 ) $ 562,245 $ (533,915 ) $ 497,678
Condensed consolidating statement of cash flows	Year Ended December 31, 2015 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 $ 404,144 $ 5,505 $ 1,074,021 $ (485,764 ) $ 997,906 Investing Activities Purchases of fixed maturity investments — (3,505 ) (29,448,368 ) — (29,451,873 ) Purchases of equity securities (8,070 ) — (507,343 ) — (515,413 ) Purchases of other investments — — (1,749,525 ) — (1,749,525 ) Proceeds from the sales of fixed maturity investments — 24,507 28,069,540 — 28,094,047 Proceeds from the sales of equity securities — — 564,011 — 564,011 Proceeds from the sales, redemptions and maturities of other investments — — 1,250,883 — 1,250,883 Proceeds from redemptions and maturities of fixed maturity investments — — 748,529 — 748,529 Net settlements of derivative instruments — — (5,056 ) — (5,056 ) Proceeds from investment in joint venture — — 40,000 — 40,000 Net (purchases) sales of short-term investments 57 (338 ) 169,376 — 169,095 Change in cash collateral related to securities lending — — (6,662 ) — (6,662 ) Contributions to subsidiaries (10,000 ) — (49,348 ) 59,348 — Intercompany loans issued — (39,500 ) (27,500 ) 67,000 — Purchase of business, net of cash acquired — — 818 — 818 Purchases of fixed assets (80 ) — (15,656 ) — (15,736 ) Change in other assets — — (36,993 ) — (36,993 ) Net Cash Provided By (Used For) Investing Activities (18,093 ) (18,836 ) (1,003,294 ) 126,348 (913,875 ) Financing Activities Purchases of common shares under share repurchase program (365,383 ) — — — (365,383 ) Proceeds from common shares issued, net 4,861 — 59,348 (59,348 ) 4,861 Proceeds from intercompany borrowings — 27,500 39,500 (67,000 ) — Proceeds from borrowings — — 431,362 — 431,362 Change in cash collateral related to securities lending — — 6,662 — 6,662 Dividends paid to redeemable noncontrolling interests — — (19,263 ) 956 (18,307 ) Dividends paid to parent (1) — — (484,808 ) 484,808 — Other — 67 (41,980 ) — (41,913 ) Preferred dividends paid (21,938 ) — — — (21,938 ) Net Cash Provided By (Used For) Financing Activities (382,460 ) 27,567 (9,179 ) 359,416 (4,656 ) Effects of exchange rates changes on foreign currency cash — — (11,751 ) — (11,751 ) Increase (decrease) in cash 3,591 14,236 49,797 — 67,624 Cash beginning of year 3,218 2,787 479,697 — 485,702 Cash end of year $ 6,809 $ 17,023 $ 529,494 $ — $ 553,326 (1) Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column. Year Ended December 31, 2014 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 $ 467,091 $ 8,142 $ 1,077,597 $ (515,700 ) $ 1,037,130 Investing Activities Purchases of fixed maturity investments — (78,509 ) (28,666,770 ) — (28,745,279 ) Purchases of equity securities — — (520,817 ) — (520,817 ) Purchases of other investments — — (1,590,648 ) — (1,590,648 ) Proceeds from the sales of fixed maturity investments — 16,011 26,807,178 — 26,823,189 Proceeds from the sales of equity securities — — 411,362 — 411,362 Proceeds from the sales, redemptions and maturities of other investments — — 941,798 — 941,798 Proceeds from redemptions and maturities of fixed maturity investments — — 762,995 — 762,995 Net settlements of derivative instruments — — 34,372 — 34,372 Net (purchases) sales of short-term investments 2,423 408,591 166,112 — 577,126 Change in cash collateral related to securities lending — — 57,470 — 57,470 Contributions to subsidiaries — (341,707 ) (128,825 ) 470,532 — Intercompany loans issued — (7,500 ) 31,464 (23,964 ) — Purchase of business, net of cash acquired — — (237,106 ) — (237,106 ) Purchases of fixed assets (271 ) — (19,612 ) — (19,883 ) Net Cash Provided By (Used For) Investing Activities 2,152 (3,114 ) (1,951,027 ) 446,568 (1,505,421 ) Financing Activities Purchases of common shares under share repurchase program (454,137 ) — — — (454,137 ) Proceeds from common shares issued, net 6,827 — 470,532 (470,532 ) 6,827 Proceeds from intercompany borrowings — 7,500 7,500 (15,000 ) — Repayments of intercompany borrowings — (10,250 ) (28,714 ) 38,964 — Change in cash collateral related to securities lending — — (57,470 ) — (57,470 ) Third party investment in non-redeemable noncontrolling interests — — 796,903 — 796,903 Third party investment in redeemable noncontrolling interests — — 219,233 — 219,233 Dividends paid to redeemable noncontrolling interests — — (14,448 ) — (14,448 ) Dividends paid to parent (1) — — (515,700 ) 515,700 — Other — — 64,973 — 64,973 Preferred dividends paid (21,938 ) — — — (21,938 ) Net Cash Provided By (Used For) Financing Activities (469,248 ) (2,750 ) 942,809 69,132 539,943 Effects of exchange rates changes on foreign currency cash — — (20,007 ) — (20,007 ) Increase (decrease) in cash (5 ) 2,278 49,372 — 51,645 Cash beginning of year 3,223 509 430,325 — 434,057 Cash end of year $ 3,218 $ 2,787 $ 479,697 $ — $ 485,702 (1) Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column. Year Ended December 31, 2013 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 $ 68,562 $ (6,569 ) $ 908,375 $ (119,500 ) $ 850,868 Investing Activities Purchases of fixed maturity investments — — (18,174,988 ) — (18,174,988 ) Purchases of equity securities — — (535,857 ) — (535,857 ) Purchases of other investments — — (994,185 ) — (994,185 ) Proceeds from the sales of fixed maturity investments — — 17,194,635 — 17,194,635 Proceeds from the sales of equity securities — — 462,787 — 462,787 Proceeds from the sales, redemptions and maturities of other investments — — 817,648 — 817,648 Proceeds from redemptions and maturities of fixed maturity investments — — 731,708 — 731,708 Net settlements of derivative instruments — — 14,494 — 14,494 Net (purchases) sales of short-term investments 5,799 (400,162 ) (356,250 ) — (750,613 ) Change in cash collateral related to securities lending — — (55,643 ) — (55,643 ) Contributions to subsidiaries (160 ) (97,850 ) (20,250 ) 118,260 — Intercompany loans issued — — (10,250 ) 10,250 — Purchases of fixed assets (712 ) — (16,787 ) — (17,499 ) Net Cash Provided By (Used For) Investing Activities 4,927 (498,012 ) (942,938 ) 128,510 (1,307,513 ) Financing Activities Purchases of common shares under share repurchase program (57,796 ) — — — (57,796 ) Proceeds from common shares issued, net 3,051 — 118,260 (118,260 ) 3,051 Proceeds from intercompany borrowings — 10,250 — (10,250 ) — Proceeds from borrowings — 494,228 — — 494,228 Change in cash collateral relating to securities lending — — 55,643 — 55,643 Dividends paid to parent (1) — — (119,500 ) 119,500 — Other — — 50,830 — 50,830 Preferred dividends paid (21,938 ) — — — (21,938 ) Net Cash Provided By (Used For) Financing Activities (76,683 ) 504,478 105,233 (9,010 ) 524,018 Effects of exchange rates changes on foreign currency cash — — (4,357 ) — (4,357 ) Increase (decrease) in cash (3,194 ) (103 ) 66,313 — 63,016 Cash beginning of year 6,417 612 364,012 — 371,041 Cash end of year $ 3,223 $ 509 $ 430,325 $ — $ 434,057 (1) Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.

General (Details)

General (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Oct. 31, 2001	Dec. 31, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Proceeds from from common shares issued	$ 763.2
Common shares, par value per share		$ 0.0033	$ 0.0033

Business Acquired (Narrative) (

Business Acquired (Narrative) (Details) - USD ($) $ in Thousands	May. 14, 2015	Jan. 30, 2014	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 31, 2008
Business Acquisition [Line Items]
Amortization of intangible assets			$ 20,100	$ 22,968	$ 25,520
Goodwill			14,946	15,536	14,946	$ 0
CMG Mortgage Insurance Company
Business Acquisition [Line Items]
Quota share agreement, percentage		100.00%
Cash paid		$ 245,157
Percentage of book value		150.00%
Contingent consideration, upper bound		$ 136,900
Discount rate, percentage		15.00%
Contingent consideration liability		$ 41,762		$ 95,000
Goodwill		$ 13,852
Goodwill, deferred tax asset			$ 48,000		$ 48,000
CMG Mortgage Insurance Company | New mortgage insurance business (post closing)
Business Acquisition [Line Items]
Quota share agreement, percentage		20.00%
Quota share reinsurance agreement limit		$ 25,000,000
PMI Mortgage Assurance Co
Business Acquisition [Line Items]
Percentage of voting interests acquired		100.00%
Gulf Reinsurance Limited [Member]
Business Acquisition [Line Items]
Investment in joint venture, at cost							$ 100,000
Joint venture, ownership percentage							50.00%
Total distributions paid by investee	$ 130,600
Equity capital of investee	50,700
Transfer of fixed maturity investments	$ 25,600
Share repurchase period				7 years
Stock Purchase Agreement [Member] | CMG Mortgage Insurance Company
Business Acquisition [Line Items]
Cash paid		$ 160,600
Percentage of book value		80.00%
Stock Purchase Agreement [Member] | CMG Mortgage Insurance Company | Minimum
Business Acquisition [Line Items]
Extension period		1 year
Stock Purchase Agreement [Member] | CMG Mortgage Insurance Company | Maximum
Business Acquisition [Line Items]
Extension period		3 years
Asset Purchase Agreement [Member] | CMG Mortgage Insurance Company
Business Acquisition [Line Items]
Cash paid		$ 84,600

Business Acquired (Summary of A

Business Acquired (Summary of Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Jan. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liabilities acquired
Goodwill		$ 15,536	$ 14,946	$ 0
CMG Mortgage Insurance Company
Purchase price
Cash paid	$ 245,157
Contingent consideration liability	41,762	$ 95,000
Total purchase price	286,919
Assets acquired
Cash	9,579
Investments, at fair value	312,093
Other assets acquired	21,691
Total assets acquired	437,650
Liabilities acquired
Reserves for losses and loss adjustment expenses	121,572
Unearned premiums	26,261
Intangible liability -- unfavorable service contract	9,533
Other liabilities acquired	7,217
Total liabilities acquired	164,583
Net assets acquired	273,067
Goodwill	$ 13,852
Useful lives of acquired intangibles
Finite-lived intangible liability, useful life	9 years
CMG Mortgage Insurance Company | Insurance licenses
Assets acquired
Indefinite lived intangible asset	$ 16,858
CMG Mortgage Insurance Company | Acquired insurance contracts
Assets acquired
Finite lived intangible asset	$ 46,473
Useful lives of acquired intangibles
Finite-lived intangible asset, useful life	5 years
CMG Mortgage Insurance Company | Operating platform
Assets acquired
Finite lived intangible asset	$ 29,900
Useful lives of acquired intangibles
Finite-lived intangible asset, useful life	5 years
CMG Mortgage Insurance Company | Favorable lease contract
Assets acquired
Finite lived intangible asset	$ 1,056
Useful lives of acquired intangibles
Finite-lived intangible asset, useful life	5 years

Significant Accounting Polici57

Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Premium revenue recognition period		12 months
Deposit accounting liabilities		$ 260,364	$ 327,384
Deposit accounting assets		$ 234,500	284,400
Securities lending rate of collateral required (percentage)		102.00%
Equity method investments, time lag for reporting - low end of range		1 month
Equity method investments, time lag for reporting - high end of range		3 months
Vesting period, share-based awards		3 years
Requisite service period, share-based awards		5 years
Losses occurring
Significant Accounting Policies [Line Items]
Premium revenue recognition period		12 months
Risks attaching
Significant Accounting Policies [Line Items]
Premium revenue recognition period		24 months
Other assets | Accounting Standards Update 2015-03
Significant Accounting Policies [Line Items]
Effect of adoption of new accounting policy	$ 8,800
Senior notes | Accounting Standards Update 2015-03
Significant Accounting Policies [Line Items]
Effect of adoption of new accounting policy			$ 8,900

Variable Interest Entity and 58

Variable Interest Entity and Noncontrolling Interests - Variable interest entity (Details) - USD ($) $ in Thousands, shares in Millions	1 Months Ended		12 Months Ended
	Mar. 31, 2014	Oct. 31, 2001	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Variable Interest Entity [Line Items]
Proceeds from from common shares issued, net		$ 763,200
Proceeds on issuance of preference shares					$ 315,800
Unearned premiums			$ 2,333,932	$ 2,231,578
Reserve for losses and loss adjustment expenses			9,125,250	9,036,448	8,824,696	$ 8,933,292
Net cash provided by (used in) operating activities			997,906	1,037,130	850,868
Net cash provided by (used in) financing activities			(4,656)	539,943	524,018
Net cash provided by (used in) investing activities			(913,875)	(1,505,421)	$ (1,307,513)
Variable Interest Entity, Primary Beneficiary | Watford Re
Variable Interest Entity [Line Items]
Initial capitalization amount	$ 1,100,000
Proceeds from from common shares issued, net	907,300
Net proceeds from issuance of common shares	895,600
Proceeds on issuance of preference shares	226,600
Net proceeds on issuance of preference shares	219,200
Initial investment contribution amount	$ 100,000
Ownership percentage	11.00%
Number of warrants received in capital raising	1.7
Unearned premiums			250,000	180,000
Reserve for losses and loss adjustment expenses			291,000	66,300
Net cash provided by (used in) operating activities			293,700	39,300
Net cash provided by (used in) financing activities			361,900	1,160,000
Net cash provided by (used in) investing activities			(556,800)	$ (1,180,000)
Credit facility expiring June 2018 | Watford Re
Variable Interest Entity [Line Items]
Outstanding borrowings			$ 430,400

Variable Interest Entity and 59

Variable Interest Entity and Noncontrolling Interests - Non-redeemable noncontrolling interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interest, beginning of year	$ 769,081	$ 0
Amounts attributable to noncontrolling interests	29,984	27,823	$ 0
Non-redeemable noncontrolling interest, end of year	738,831	769,081	0
Watford Re | Noncontrolling Interest [Member]
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interest, beginning of year	769,081	0
Sale of shares to noncontrolling interests	0	796,904
Amounts attributable to noncontrolling interests	(29,984)	(27,823)
Foreign currency translation adjustments	(266)	0
Non-redeemable noncontrolling interest, end of year	$ 738,831	$ 769,081	$ 0
Common shares | Watford Re | Noncontrolling Interest [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	89.00%

Variable Interest Entity and 60

Variable Interest Entity and Noncontrolling Interests - Redeemable noncontrolling interest (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Redeemable Noncontrolling Interest [Line Items]
Balance, beginning of year		$ 219,512	$ 0
Sale of shares to noncontrolling interests		0	219,233
Shares acquired by the Company		(14,700)	0
Accretion of preference share issuance costs		370	279
Balance, end of year		$ 205,182	$ 219,512
Preferred shares, par value per share		$ 0.01
Watford Re
Redeemable Noncontrolling Interest [Line Items]
Preference shares, number of shares issued		9,065,200
Preferred shares, par value per share		$ 0.01
Liquidation preference per share		25
Issue price per share		$ 24.50
Preferred shares, dividend rate (as a percent)		8.50%
Preferred Dividends Including Accretion Of Discount And Issuance Costs		$ 19,600
3 month US dollar LIBOR | Watford Re
Redeemable Noncontrolling Interest [Line Items]
Preferred shares, dividend rate (as a percent)		1.00%
Gulf Reinsurance Limited [Member] | Watford Re
Redeemable Noncontrolling Interest [Line Items]
Noncontrolling Interest Number of Shares	600,000

Variable Interest Entity and 61

Variable Interest Entity and Noncontrolling Interests - Income or loss attributable to third party investors (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Noncontrolling Interest [Line Items]
Amounts attributable to non-redeemable noncontrolling interests	$ 29,984	$ 27,823	$ 0
Dividends attributable to redeemable noncontrolling interests	(18,828)	(14,728)	0
Net (income) loss attributable to noncontrolling interests	11,156	13,095	0
Other
Noncontrolling Interest [Line Items]
Amounts attributable to non-redeemable noncontrolling interests	29,984	27,823	0
Dividends attributable to redeemable noncontrolling interests	(18,828)	(14,728)	$ 0
Net (income) loss attributable to noncontrolling interests	$ 11,156	$ 13,095

Segment Information - Analysis

Segment Information - Analysis of underwriting income by segment and reconciliation to net income available to common shareholders (Details) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Sep. 30, 2014USD ($)	Jun. 30, 2014USD ($)	Mar. 31, 2014USD ($)	Dec. 31, 2015USD ($)segment		Dec. 31, 2014USD ($)		Dec. 31, 2013USD ($)
Segment Reporting Information [Line Items]
Gross premiums written										$ 4,797,163		$ 4,840,616		$ 4,196,623
Premiums ceded										(979,632)		(948,678)		(845,256)
Net premiums written		$ 834,984	$ 971,972	$ 943,580	$ 1,066,995	$ 895,481	$ 959,539	$ 971,928	$ 1,064,990	3,817,531		3,891,938		3,351,367
Change in unearned premiums										(83,626)		(298,190)		(205,415)
Net premiums earned		943,520	936,683	943,438	910,264	923,165	903,651	907,152	859,780	3,733,905		3,593,748		3,145,952
Other underwriting income										35,497		10,142		7,639
Losses and loss adjustment expenses										(2,050,903)		(1,919,250)		(1,679,424)
Acquisition expenses, net										(681,476)		(657,262)		(564,103)
Other operating expenses										(607,516)		(556,280)		(458,327)
Underwriting income (loss)		113,143	94,779	105,114	116,471	113,464	101,087	124,091	132,456	429,507		471,098		451,737
Net investment income		95,900	86,233	86,963	78,994	82,496	80,105	72,990	66,994	348,090		302,585		267,219
Net realized gains (losses)		(143,767)	(89,698)	(35,725)	83,348	10,561	18,515	54,144	19,697	(185,842)		102,917		74,018
Net impairment losses recognized in earnings		(7,336)	(5,868)	(1,113)	(5,799)	(3,837)	(8,593)	(14,749)	(2,971)	(20,116)		(30,150)		(3,786)
Equity in net income (loss) of investment funds accounted for using the equity method										25,455		19,883		35,701
Other income (loss)										(399)		(10,252)		(586)
Other expenses										(49,745)		(49,944)		(42,403)
Interest expense										(45,874)		(45,634)		(27,060)
Net foreign exchange gains (losses)										66,118		83,744		(12,335)
Income (loss) before income taxes										567,194		844,247		742,505
Income tax expense										(40,612)		(22,987)		(32,774)
Net income (loss)		58,579	80,033	115,790	283,336	215,164	228,675	208,016	182,500	526,582		821,260		709,731
Dividends attributable to redeemable noncontrolling interests										(18,828)		(14,728)		0
Amounts attributable to noncontrolling interests										29,984		27,823		0
Net income available to Arch										537,738		834,355		709,731
Preferred dividends		(5,485)	(5,484)	(5,485)	(5,484)	(5,485)	(5,484)	(5,485)	(5,484)	(21,938)		(21,938)		(21,938)
Net income (loss) available to Arch common shareholders		53,094	$ 74,549	$ 110,305	$ 277,852	209,679	$ 223,191	$ 202,531	$ 177,016	$ 515,800		$ 812,417		$ 687,793
Underwriting Ratios
Loss ratio										54.90%		53.40%		53.40%
Acquisition expense ratio										18.30%		18.30%		17.90%
Other operating expense ratio										16.30%		15.50%		14.60%
Combined ratio										89.50%		87.20%		85.90%
Goodwill and intangible assets		97,531				109,539				$ 97,531		$ 109,539		$ 27,319
Total investable assets		16,340,938				15,762,730				16,340,938		15,762,730		14,049,525
Total assets		23,177,270				22,006,081				23,177,270		22,006,081		19,557,054
Total liabilities		16,028,376				14,887,435				16,028,376		14,887,435		13,909,558
Insurance
Segment Reporting Information [Line Items]
Premiums ceded	[1]									(898,347)		(862,015)		(763,713)
Net premiums written										2,045,671		2,146,654		1,948,796
Reinsurance
Segment Reporting Information [Line Items]
Premiums ceded	[1]									(380,614)		(261,255)		(86,620)
Net premiums written										1,038,408		1,265,991		1,313,001
Mortgage
Segment Reporting Information [Line Items]
Premiums ceded	[1]									(28,064)		(22,519)		0
Net premiums written										$ 267,493		204,837		89,570
Other
Segment Reporting Information [Line Items]
Number of segments | segment										2
Gross premiums written	[2]									$ 488,899		288,627		0
Premiums ceded										(22,940)	[1]	(14,171)	[1]	0
Net premiums written										465,959		274,456		0
Change in unearned premiums										(68,107)		(170,979)		0
Net premiums earned										397,852		103,477		0
Other underwriting income										4,468		0		0
Losses and loss adjustment expenses										(277,659)		(70,173)		0
Acquisition expenses, net										(113,451)		(30,116)		0
Other operating expenses										(14,919)		(6,268)		0
Underwriting income (loss)										(3,709)		(3,080)		0
Net investment income										76,410		18,249		0
Net realized gains (losses)										(86,709)		(30,467)		0
Net impairment losses recognized in earnings										0		0		0
Equity in net income (loss) of investment funds accounted for using the equity method										0		0		0
Other income (loss)										0		0		0
Other expenses										0		(2,329)		0
Interest expense										(4,356)		0		0
Net foreign exchange gains (losses)										3,494		1,086		0
Income (loss) before income taxes										(14,870)		(16,541)		0
Income tax expense										0		0		0
Net income (loss)										(14,870)		(16,541)		0
Dividends attributable to redeemable noncontrolling interests										(18,828)		(14,728)		0
Amounts attributable to noncontrolling interests										29,984		27,823		0
Net income available to Arch										(3,714)		(3,446)		0
Preferred dividends										0		0		0
Net income (loss) available to Arch common shareholders										$ (3,714)		$ (3,446)		$ 0
Underwriting Ratios
Loss ratio										69.80%		67.80%		0.00%
Acquisition expense ratio										28.50%		29.10%		0.00%
Other operating expense ratio										3.70%		6.10%		0.00%
Combined ratio										102.00%		103.00%		0.00%
Goodwill and intangible assets		0				0				$ 0		$ 0		$ 0
Total investable assets		1,696,107				1,163,240				1,696,107		1,163,240		0
Total assets		2,122,332				1,482,516				2,122,332		1,482,516		0
Total liabilities		1,072,102				398,660				$ 1,072,102		398,660		0
Underwriting segments
Segment Reporting Information [Line Items]
Number of segments | segment										3
Gross premiums written	[2]									$ 4,656,723		4,760,394		4,196,623
Premiums ceded										(1,305,151)		(1,142,912)		(845,256)
Net premiums written										3,351,572		3,617,482		3,351,367
Change in unearned premiums										(15,519)		(127,211)		(205,415)
Net premiums earned										3,336,053		3,490,271		3,145,952
Other underwriting income										31,029		10,142		7,639
Losses and loss adjustment expenses										(1,773,244)		(1,849,077)		(1,679,424)
Acquisition expenses, net										(568,025)		(627,146)		(564,103)
Other operating expenses										(592,597)		(550,012)		(458,327)
Underwriting income (loss)										433,216		474,178		451,737
Net investment income										271,680		284,336		267,219
Net realized gains (losses)										(99,133)		133,384		74,018
Net impairment losses recognized in earnings										(20,116)		(30,150)		(3,786)
Equity in net income (loss) of investment funds accounted for using the equity method										25,455		19,883		35,701
Other income (loss)										(399)		(10,252)		(586)
Other expenses										(49,745)		(47,615)		(42,403)
Interest expense										(41,518)		(45,634)		(27,060)
Net foreign exchange gains (losses)										62,624		82,658		(12,335)
Income (loss) before income taxes										582,064		860,788		742,505
Income tax expense										(40,612)		(22,987)		(32,774)
Net income (loss)										541,452		837,801		709,731
Dividends attributable to redeemable noncontrolling interests										0		0		0
Amounts attributable to noncontrolling interests										0		0		0
Net income available to Arch										541,452		837,801		709,731
Preferred dividends										(21,938)		(21,938)		(21,938)
Net income (loss) available to Arch common shareholders										$ 519,514		$ 815,863		$ 687,793
Underwriting Ratios
Loss ratio										53.20%		53.00%		53.40%
Acquisition expense ratio										17.00%		18.00%		17.90%
Other operating expense ratio										17.80%		15.80%		14.60%
Combined ratio										88.00%		86.80%		85.90%
Goodwill and intangible assets		97,531				109,539				$ 97,531		$ 109,539		$ 27,319
Total investable assets		14,644,831				14,599,490				14,644,831		14,599,490		14,049,525
Total assets		21,054,938				20,523,565				21,054,938		20,523,565		19,557,054
Total liabilities		14,956,274				14,488,775				14,956,274		14,488,775		13,909,558
Underwriting segments | Insurance
Segment Reporting Information [Line Items]
Gross premiums written	[2]									2,944,018		3,008,669		2,712,509
Premiums ceded										(898,347)		(862,015)		(763,713)
Net premiums written										2,045,671		2,146,654		1,948,796
Change in unearned premiums										(863)		(129,284)		(72,782)
Net premiums earned										2,044,808		2,017,370		1,876,014
Other underwriting income										1,993		2,135		2,122
Losses and loss adjustment expenses										(1,292,647)		(1,260,953)		(1,188,445)
Acquisition expenses, net										(299,317)		(316,308)		(311,904)
Other operating expenses										(354,416)		(335,157)		(315,387)
Underwriting income (loss)										$ 100,421		$ 107,087		$ 62,400
Underwriting Ratios
Loss ratio										63.20%		62.50%		63.30%
Acquisition expense ratio										14.60%		15.70%		16.60%
Other operating expense ratio										17.30%		16.60%		16.80%
Combined ratio										95.10%		94.80%		96.70%
Goodwill and intangible assets		28,810				28,331				$ 28,810		$ 28,331		$ 20,419
Underwriting segments | Reinsurance
Segment Reporting Information [Line Items]
Gross premiums written	[2]									1,419,022		1,527,245		1,399,621
Premiums ceded										(380,614)		(261,254)		(86,620)
Net premiums written										1,038,408		1,265,991		1,313,001
Change in unearned premiums										38,727		13,337		(94,329)
Net premiums earned										1,077,135		1,279,328		1,218,672
Other underwriting income										10,606		3,167		5,258
Losses and loss adjustment expenses										(440,350)		(532,450)		(486,236)
Acquisition expenses, net										(223,632)		(261,438)		(234,373)
Other operating expenses										(155,811)		(147,964)		(134,563)
Underwriting income (loss)										$ 267,948		$ 340,643		$ 368,758
Underwriting Ratios
Loss ratio										40.90%		41.60%		39.90%
Acquisition expense ratio										20.80%		20.40%		19.20%
Other operating expense ratio										14.50%		11.60%		11.00%
Combined ratio										76.20%		73.60%		70.10%
Goodwill and intangible assets		1,875				3,333				$ 1,875		$ 3,333		$ 6,900
Underwriting segments | Mortgage
Segment Reporting Information [Line Items]
Gross premiums written	[2]									295,557		227,356		89,570
Premiums ceded										(28,064)		(22,519)		0
Net premiums written										267,493		204,837		89,570
Change in unearned premiums										(53,383)		(11,264)		(38,304)
Net premiums earned										214,110		193,573		51,266
Other underwriting income										18,430		4,840		259
Losses and loss adjustment expenses										(40,247)		(55,674)		(4,743)
Acquisition expenses, net										(45,076)		(49,400)		(17,826)
Other operating expenses										(82,370)		(66,891)		(8,377)
Underwriting income (loss)										$ 64,847		$ 26,448		$ 20,579
Underwriting Ratios
Loss ratio										18.80%		28.80%		9.30%
Acquisition expense ratio										21.10%		25.50%		34.80%
Other operating expense ratio										38.50%		34.60%		16.30%
Combined ratio										78.40%		88.90%		60.40%
Goodwill and intangible assets		$ 66,846				$ 77,875				$ 66,846		$ 77,875		$ 0
[1]	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions and are included in the gross premiums written of each segment. 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 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 - Summary o

Segment Information - Summary of net premiums written and earned by major line of business and net premiums written by location (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net premiums written		$ 834,984	$ 971,972	$ 943,580	$ 1,066,995	$ 895,481	$ 959,539	$ 971,928	$ 1,064,990	$ 3,817,531	$ 3,891,938	$ 3,351,367
Net premiums earned		$ 943,520	$ 936,683	$ 943,438	$ 910,264	$ 923,165	$ 903,651	$ 907,152	$ 859,780	3,733,905	3,593,748	3,145,952
Insurance
Segment Reporting Information [Line Items]
Net premiums written										2,045,671	2,146,654	1,948,796
Reinsurance
Segment Reporting Information [Line Items]
Net premiums written										1,038,408	1,265,991	1,313,001
Mortgage
Segment Reporting Information [Line Items]
Net premiums written										267,493	204,837	89,570
Other
Segment Reporting Information [Line Items]
Net premiums written										465,959	274,456	0
Net premiums earned										397,852	103,477	0
Other | Client Location [Member] | United States
Segment Reporting Information [Line Items]
Net premiums written	[1]									350,228	186,795	0
Other | Client Location [Member] | Europe
Segment Reporting Information [Line Items]
Net premiums written	[1]									67,279	54,131	0
Other | Client Location [Member] | Bermuda
Segment Reporting Information [Line Items]
Net premiums written	[1]									39,414	27,977	0
Other | Client Location [Member] | Other geographic location
Segment Reporting Information [Line Items]
Net premiums written	[1]									9,038	5,553	0
Other | Casualty [Member]
Segment Reporting Information [Line Items]
Net premiums written	[1],[2]									320,619	179,054	0
Net premiums earned	[1],[2]									275,708	72,395	0
Other | Other specialty [Member]
Segment Reporting Information [Line Items]
Net premiums written	[1],[3]									112,666	66,524	0
Net premiums earned	[1],[3]									101,588	24,157	0
Other | Property excluding property catastrophe [Member]
Segment Reporting Information [Line Items]
Net premiums written	[1]									2,892	564	0
Net premiums earned	[1]									1,340	182	0
Other | Property catastrophe [Member]
Segment Reporting Information [Line Items]
Net premiums written	[1]									12,441	9,280	0
Net premiums earned	[1]									12,540	5,115	0
Other | Marine and aviation [Member]
Segment Reporting Information [Line Items]
Net premiums written	[1]									1,256	1,251	0
Net premiums earned	[1]									1,585	789	0
Other | Other [Member]
Segment Reporting Information [Line Items]
Net premiums written	[1],[4]									16,085	17,783	0
Net premiums earned	[1],[4]									5,091	839	0
Underwriting segments
Segment Reporting Information [Line Items]
Net premiums written										3,351,572	3,617,482	3,351,367
Net premiums earned										3,336,053	3,490,271	3,145,952
Underwriting segments | Insurance
Segment Reporting Information [Line Items]
Net premiums written										2,045,671	2,146,654	1,948,796
Net premiums earned										2,044,808	2,017,370	1,876,014
Underwriting segments | Insurance | Client Location [Member] | United States
Segment Reporting Information [Line Items]
Net premiums written	[5]									1,710,918	1,726,181	1,526,156
Underwriting segments | Insurance | Client Location [Member] | Europe
Segment Reporting Information [Line Items]
Net premiums written	[5]									187,020	240,136	226,254
Underwriting segments | Insurance | Client Location [Member] | Asia and Pacific
Segment Reporting Information [Line Items]
Net premiums written	[5]									64,638	79,564	95,970
Underwriting segments | Insurance | Client Location [Member] | Other geographic location
Segment Reporting Information [Line Items]
Net premiums written	[5]									83,095	100,773	100,416
Underwriting segments | Insurance | Underwriting Location [Member] | United States
Segment Reporting Information [Line Items]
Net premiums written	[5]									1,673,867	1,688,887	1,478,930
Underwriting segments | Insurance | Underwriting Location [Member] | Europe
Segment Reporting Information [Line Items]
Net premiums written	[5]									317,998	394,430	389,763
Underwriting segments | Insurance | Underwriting Location [Member] | Other geographic location
Segment Reporting Information [Line Items]
Net premiums written	[5]									53,806	63,337	80,103
Underwriting segments | Insurance | Professional lines [Member]
Segment Reporting Information [Line Items]
Net premiums written	[6]									434,024	476,604	476,193
Net premiums earned	[6]									424,968	456,508	491,791
Underwriting segments | Insurance | Programs [Member]
Segment Reporting Information [Line Items]
Net premiums written	[5]									423,157	480,580	419,673
Net premiums earned	[5]									446,512	460,392	386,840
Underwriting segments | Insurance | Construction and national accounts [Member]
Segment Reporting Information [Line Items]
Net premiums written	[5]									299,463	286,994	271,110
Net premiums earned	[5]									296,828	277,811	250,729
Underwriting segments | Insurance | Excess and surplus casualty [Member]
Segment Reporting Information [Line Items]
Net premiums written	[5],[7]									204,856	212,519	149,286
Net premiums earned	[5],[7]									208,091	182,024	118,395
Underwriting segments | Insurance | Property, energy, marine and aviation [Member]
Segment Reporting Information [Line Items]
Net premiums written	[5]									203,186	244,640	280,551
Net premiums earned	[5]									216,127	244,974	304,294
Underwriting segments | Insurance | Travel, accident and health [Member]
Segment Reporting Information [Line Items]
Net premiums written	[5]									160,132	145,732	104,903
Net premiums earned	[5]									153,578	127,691	97,135
Underwriting segments | Insurance | Lenders products [Member]
Segment Reporting Information [Line Items]
Net premiums written	[5]									106,916	100,407	101,576
Net premiums earned	[5]									90,906	94,438	99,847
Underwriting segments | Insurance | Other [Member]
Segment Reporting Information [Line Items]
Net premiums written	[5],[8]									213,937	199,178	145,504
Net premiums earned	[5],[8]									207,798	173,532	126,983
Underwriting segments | Reinsurance
Segment Reporting Information [Line Items]
Net premiums written										1,038,408	1,265,991	1,313,001
Net premiums earned										1,077,135	1,279,328	1,218,672
Underwriting segments | Reinsurance | Pro Rata [Member]
Segment Reporting Information [Line Items]
Net premiums written	[9]									537,556	663,135	692,024
Net premiums earned	[9]									563,585	686,201	608,586
Underwriting segments | Reinsurance | Excess Of Loss [Member]
Segment Reporting Information [Line Items]
Net premiums written	[9]									500,852	602,856	620,977
Net premiums earned	[9]									513,550	593,127	610,086
Underwriting segments | Reinsurance | Client Location [Member] | United States
Segment Reporting Information [Line Items]
Net premiums written	[9]									470,484	589,255	706,388
Underwriting segments | Reinsurance | Client Location [Member] | Europe
Segment Reporting Information [Line Items]
Net premiums written	[9]									307,165	355,735	327,059
Underwriting segments | Reinsurance | Client Location [Member] | Asia and Pacific
Segment Reporting Information [Line Items]
Net premiums written	[9]									94,609	142,626	94,252
Underwriting segments | Reinsurance | Client Location [Member] | Bermuda
Segment Reporting Information [Line Items]
Net premiums written	[9]									80,888	77,620	87,047
Underwriting segments | Reinsurance | Client Location [Member] | Other geographic location
Segment Reporting Information [Line Items]
Net premiums written	[9]									85,262	100,755	98,255
Underwriting segments | Reinsurance | Underwriting Location [Member] | United States
Segment Reporting Information [Line Items]
Net premiums written	[9]									439,190	492,891	507,183
Underwriting segments | Reinsurance | Underwriting Location [Member] | Europe
Segment Reporting Information [Line Items]
Net premiums written	[9]									298,790	343,823	309,129
Underwriting segments | Reinsurance | Underwriting Location [Member] | Bermuda
Segment Reporting Information [Line Items]
Net premiums written	[9]									281,985	394,351	459,467
Underwriting segments | Reinsurance | Underwriting Location [Member] | Other geographic location
Segment Reporting Information [Line Items]
Net premiums written	[9]									18,443	34,926	37,222
Underwriting segments | Reinsurance | Casualty [Member]
Segment Reporting Information [Line Items]
Net premiums written	[9],[10]									303,093	317,996	306,304
Net premiums earned	[9],[10]									310,249	327,518	241,774
Underwriting segments | Reinsurance | Other specialty [Member]
Segment Reporting Information [Line Items]
Net premiums written	[9],[11]									298,794	405,126	417,865
Net premiums earned	[9],[11]									311,307	424,725	387,630
Underwriting segments | Reinsurance | Property excluding property catastrophe [Member]
Segment Reporting Information [Line Items]
Net premiums written	[9],[12]									280,511	343,043	292,536
Net premiums earned	[9],[12]									295,487	303,496	274,719
Underwriting segments | Reinsurance | Property catastrophe [Member]
Segment Reporting Information [Line Items]
Net premiums written	[9]									91,620	137,471	220,749
Net premiums earned	[9]									96,865	150,761	232,423
Underwriting segments | Reinsurance | Marine and aviation [Member]
Segment Reporting Information [Line Items]
Net premiums written	[9]									50,834	50,444	64,380
Net premiums earned	[9]									50,808	61,118	70,105
Underwriting segments | Reinsurance | Other [Member]
Segment Reporting Information [Line Items]
Net premiums written	[9],[13]									13,556	11,911	11,167
Net premiums earned	[9],[13]									12,419	11,710	12,021
Underwriting segments | Mortgage
Segment Reporting Information [Line Items]
Net premiums written										267,493	204,837	89,570
Net premiums earned										214,110	193,573	51,266
Underwriting segments | Mortgage | Client Location [Member] | United States
Segment Reporting Information [Line Items]
Net premiums written										193,617	184,333	63,692
Net premiums earned										202,930	187,194	49,045
Underwriting segments | Mortgage | Client Location [Member] | Other geographic location
Segment Reporting Information [Line Items]
Net premiums written										73,876	20,504	25,878
Net premiums earned										11,180	6,379	2,221
Underwriting segments | Mortgage | Underwriting Location [Member] | United States
Segment Reporting Information [Line Items]
Net premiums written										125,317	98,809	0
Net premiums earned										113,062	92,236	0
Underwriting segments | Mortgage | Underwriting Location [Member] | Other geographic location
Segment Reporting Information [Line Items]
Net premiums written										142,176	106,028	89,570
Net premiums earned										$ 101,048	$ 101,337	$ 51,266
[1]	Other segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.
[2]	Includes professional liability, excess motor, programs and other.
[3]	Includes proportional motor and other.
[4]	Includes mortgage and other.
[5]	Insurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.
[6]	Includes professional liability, executive assurance and healthcare business.
[7]	Includes casualty and contract binding business.
[8]	Includes alternative markets, excess workers' compensation and surety business.
[9]	Reinsurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.
[10]	Includes executive assurance, professional liability, workers’ compensation, excess motor, healthcare and other.
[11]	Includes proportional motor, surety, accident and health, workers’ compensation catastrophe, agriculture, trade credit and other.
[12]	Includes facultative business.
[13]	Includes life, casualty clash and other.

Reserve for Losses and Loss A64

Reserve for Losses and Loss Adjustment Expenses - Reconciliation of beginning and ending balances of losses and loss adjustment reserves (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Reserve for losses and loss adjustment expenses at beginning of year		$ 9,036,448	$ 8,824,696	$ 8,933,292
Unpaid losses and loss adjustment expenses recoverable		1,778,303	1,748,250	1,829,070
Net reserve for losses and loss adjustment expenses at beginning of year		7,258,145	7,076,446	7,104,222
Net incurred losses and loss adjustment expenses relating to losses occurring in:
Current year		2,336,026	2,246,152	1,943,466
Prior years		(285,123)	(326,902)	(264,042)
Total net incurred losses and loss adjustment expenses		2,050,903	1,919,250	1,679,424
Net losses and loss adjustment expense reserves of acquired business (1)	[1]	262	120,671	0
Foreign exchange (gains) losses		(143,653)	(160,486)	1,617
Net paid losses and loss adjustment expenses relating to losses occurring in:
Current year		(454,179)	(347,270)	(288,114)
Prior years		(1,415,065)	(1,350,466)	(1,420,703)
Total net paid losses and loss adjustment expenses		(1,869,244)	(1,697,736)	(1,708,817)
Net reserve for losses and loss adjustment expenses at end of year		7,296,413	7,258,145	7,076,446
Unpaid losses and loss adjustment expenses recoverable		1,828,837	1,778,303	1,748,250
Reserve for losses and loss adjustment expenses at end of year		$ 9,125,250	$ 9,036,448	$ 8,824,696
[1]	2014 amount relates to the Company’s acquisition of Arch MI U.S.

Reserve for Losses and Loss A65

Reserve for Losses and Loss Adjustment Expenses - Prior years reserve development (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	$ 285,123	$ 326,902	$ 264,042
Other
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	800
Underwriting segments | Reinsurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	$ 224,800	$ 267,300	$ 217,900
Prior year reserve development (points)	20.90%	20.90%	17.90%
Underwriting segments | Reinsurance | Short tailed lines [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	$ 107,600	$ 146,700	$ 111,100
Underwriting segments | Reinsurance | Short tailed lines [Member] | Property catastrophe and property other than property catastrophe [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	80,900
Underwriting segments | Reinsurance | Short tailed lines [Member] | 2005-2014 | Property catastrophe and property other than property catastrophe [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	11,800
Underwriting segments | Reinsurance | Short tailed lines [Member] | 2011-2013 | Property catastrophe and property other than property catastrophe [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development		107,600
Underwriting segments | Reinsurance | Short tailed lines [Member] | 2005-2013 | Property catastrophe and property other than property catastrophe [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development		23,300
Underwriting segments | Reinsurance | Short tailed lines [Member] | 2009-2012 | Property catastrophe and property other than property catastrophe [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development			110,100
Underwriting segments | Reinsurance | Short tailed lines [Member] | 2005-2012 | Property catastrophe and property other than property catastrophe [Member] | Named catastrophic events [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development			28,600
Underwriting segments | Reinsurance | Medium tailed and long tailed lines [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	117,200	120,600	106,800
Underwriting segments | Reinsurance | Medium tailed and long tailed lines [Member] | Casualty [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	99,700	101,600
Underwriting segments | Reinsurance | Medium tailed and long tailed lines [Member] | Marine and aviation [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	11,700
Underwriting segments | Reinsurance | Medium tailed and long tailed lines [Member] | 2008-2012 | Marine and aviation [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development		14,700
Underwriting segments | Reinsurance | Medium tailed and long tailed lines [Member] | 2003-2009 | Casualty [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development			98,800
Underwriting segments | Reinsurance | Medium tailed and long tailed lines [Member] | 2007 and 2009 | Marine and aviation [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development			8,100
Underwriting segments | Insurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	$ 47,200	$ 58,700	$ 45,100
Prior year reserve development (points)	2.30%	2.90%	2.40%
Underwriting segments | Insurance | Programs [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development			$ (26,200)
Underwriting segments | Insurance | 2011 | Programs [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development, percentage attributable to a single cause			0.90
Underwriting segments | Insurance | Short tailed lines [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	$ 27,300	$ 73,500	$ 67,000
Underwriting segments | Insurance | Short tailed lines [Member] | Property [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	32,400	60,500
Underwriting segments | Insurance | Short tailed lines [Member] | Property [Member] | Named catastrophic events [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development		7,900
Underwriting segments | Insurance | Short tailed lines [Member] | 2005-2014 | Property [Member] | Named catastrophic events [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	5,700
Underwriting segments | Insurance | Short tailed lines [Member] | 2005-2012 | Property [Member] | Named catastrophic events [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development			15,900
Underwriting segments | Insurance | Short tailed lines [Member] | 2008-2011 | Property [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development			62,400
Underwriting segments | Insurance | Medium tailed and long tailed lines [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	19,900	(14,800)	(21,900)
Underwriting segments | Insurance | Medium tailed and long tailed lines [Member] | Specialty Casualty [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development			(28,000)
Underwriting segments | Insurance | Medium tailed and long tailed lines [Member] | Programs [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	(15,000)
Underwriting segments | Insurance | Medium tailed and long tailed lines [Member] | Professional liability [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	29,700
Underwriting segments | Insurance | Medium tailed and long tailed lines [Member] | 2011-2013 | Surety [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development		7,800
Underwriting segments | Insurance | Medium tailed and long tailed lines [Member] | 2009-2013 | Construction [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development		(41,300)
Underwriting segments | Insurance | Medium tailed and long tailed lines [Member] | 2011 and 2012 | Programs [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development		(26,200)
Underwriting segments | Insurance | Medium tailed and long tailed lines [Member] | 2003-2011 | Professional liability [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development		39,000
Underwriting segments | Mortgage
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	$ 12,300	$ 900	$ 1,000
Prior year reserve development (points)	5.70%
Underwriting segments | Mortgage | Arch MI US
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	$ 11,100
Underwriting segments | Mortgage | US Mortgage Reinsurance [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year reserve development	$ 1,200

Reinsurance - Effects of reinsu

Reinsurance - Effects of reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Premiums Written
Direct									$ 3,086,919	$ 3,100,946	$ 2,754,582
Assumed									1,710,244	1,739,670	1,442,041
Ceded									(979,632)	(948,678)	(845,256)
Net	$ 834,984	$ 971,972	$ 943,580	$ 1,066,995	$ 895,481	$ 959,539	$ 971,928	$ 1,064,990	3,817,531	3,891,938	3,351,367
Premiums Earned
Direct									3,002,508	2,914,755	2,666,104
Assumed									1,659,456	1,574,049	1,296,048
Ceded									(928,059)	(895,056)	(816,200)
Net premiums earned	$ 943,520	$ 936,683	$ 943,438	$ 910,264	$ 923,165	$ 903,651	$ 907,152	$ 859,780	3,733,905	3,593,748	3,145,952
Losses and Loss Adjustment Expenses
Direct									1,830,785	1,763,492	1,603,369
Assumed									752,304	621,346	450,618
Ceded									(532,186)	(465,588)	(374,563)
Net									$ 2,050,903	$ 1,919,250	$ 1,679,424

Reinsurance - Ceded credit risk

Reinsurance - Ceded credit risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	$ 1,867,373	$ 1,812,845
Reinsurer concentration risk | Stockholders' equity
Concentration Risk [Line Items]
Concentration risk percentage	3.40%	3.70%
AM Best A minus Or Better Rating | Credit concentration risk | Reinsurance recoverable
Concentration Risk [Line Items]
Concentration risk percentage	77.90%	83.00%
Not Rated | Credit concentration risk | Reinsurance recoverable
Concentration Risk [Line Items]
Concentration risk percentage	22.00%	17.00%

Investment Information - Summar

Investment Information - Summary of Available for Sale Securities (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Available for sale securities:
Estimated Fair Value		$ 12,350,219	$ 12,553,204
Gross Unrealized Gains		214,408	282,262
Gross Unrealized Losses		(162,291)	(111,730)
Cost or Amortized Cost		12,298,102	12,382,672
OTTI Unrealized Losses		(6,925)	(3,646)
Fixed maturities and fixed maturities pledged under securities lending agreements
Available for sale securities:
Estimated Fair Value		10,832,657	10,801,572
Gross Unrealized Gains	[1]	76,082	140,673
Gross Unrealized Losses	[1]	(136,405)	(92,734)
Cost or Amortized Cost		10,892,980	10,753,633
OTTI Unrealized Losses	[2]	(6,925)	(3,646)
Fixed maturities and fixed maturities pledged under securities lending agreements | Corporate bonds
Available for sale securities:
Estimated Fair Value		2,725,729	3,108,513
Gross Unrealized Gains	[1]	15,978	37,928
Gross Unrealized Losses	[1]	(60,508)	(38,974)
Cost or Amortized Cost		2,770,259	3,109,559
OTTI Unrealized Losses	[2]	(3,553)	(317)
Fixed maturities and fixed maturities pledged under securities lending agreements | Mortgage backed securities
Available for sale securities:
Estimated Fair Value		754,870	943,343
Gross Unrealized Gains	[1]	9,872	18,843
Gross Unrealized Losses	[1]	(5,334)	(3,842)
Cost or Amortized Cost		750,332	928,342
OTTI Unrealized Losses	[2]	(3,350)	(3,307)
Fixed maturities and fixed maturities pledged under securities lending agreements | Municipal bonds
Available for sale securities:
Estimated Fair Value		1,626,281	1,494,122
Gross Unrealized Gains	[1]	27,014	31,227
Gross Unrealized Losses	[1]	(1,534)	(1,044)
Cost or Amortized Cost		1,600,801	1,463,939
OTTI Unrealized Losses	[2]	0	0
Fixed maturities and fixed maturities pledged under securities lending agreements | Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value		764,152	1,114,528
Gross Unrealized Gains	[1]	3,269	14,594
Gross Unrealized Losses	[1]	(6,978)	(3,822)
Cost or Amortized Cost		767,861	1,103,756
OTTI Unrealized Losses	[2]	0	0
Fixed maturities and fixed maturities pledged under securities lending agreements | US government and government agencies
Available for sale securities:
Estimated Fair Value		2,423,455	1,447,972
Gross Unrealized Gains	[1]	6,228	8,345
Gross Unrealized Losses	[1]	(9,978)	(1,760)
Cost or Amortized Cost		2,427,205	1,441,387
OTTI Unrealized Losses	[2]	0	0
Fixed maturities and fixed maturities pledged under securities lending agreements | Non-US government securities
Available for sale securities:
Estimated Fair Value		917,664	1,015,153
Gross Unrealized Gains	[1]	10,414	21,311
Gross Unrealized Losses	[1]	(39,122)	(37,203)
Cost or Amortized Cost		946,372	1,031,045
OTTI Unrealized Losses	[2]	0	0
Fixed maturities and fixed maturities pledged under securities lending agreements | Asset backed securities
Available for sale securities:
Estimated Fair Value		1,620,506	1,677,941
Gross Unrealized Gains	[1]	3,307	8,425
Gross Unrealized Losses	[1]	(12,951)	(6,089)
Cost or Amortized Cost		1,630,150	1,675,605
OTTI Unrealized Losses	[2]	(22)	(22)
Equity securities
Available for sale securities:
Estimated Fair Value		629,182	658,182
Gross Unrealized Gains	[1]	94,341	109,012
Gross Unrealized Losses	[1]	(17,796)	(13,364)
Cost or Amortized Cost		552,637	562,534
OTTI Unrealized Losses		0	0
Other investments
Available for sale securities:
Estimated Fair Value		300,476	296,224
Gross Unrealized Gains	[1]	43,798	31,839
Gross Unrealized Losses	[1]	(4,665)	(362)
Cost or Amortized Cost		261,343	264,747
OTTI Unrealized Losses		0	0
Short-term investments
Available for sale securities:
Estimated Fair Value		587,904	797,226
Gross Unrealized Gains	[1]	187	738
Gross Unrealized Losses	[1]	(3,425)	(5,270)
Cost or Amortized Cost		591,142	801,758
OTTI Unrealized Losses		$ 0	$ 0
[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments 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 December 31, 2015, the net unrealized loss related to securities for which a non-credit OTTI was recognized in AOCI was $1.4 million, compared to a net unrealized gain of $0.9 million at December 31, 2014.

Investment Information - Aging

Investment Information - Aging of Available For Sale Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	$ 7,101,536	$ 4,108,030
Gross Unrealized Losses - Less than 12 Months	[1]	(108,581)	(90,017)
Estimated Fair Value - 12 Months or More	[1]	482,808	641,407
Gross Unrealized Losses - 12 Months or More	[1]	(53,710)	(21,713)
Estimated Fair Value - Total	[1]	7,584,344	4,749,437
Gross Unrealized Losses - Total	[1]	(162,291)	(111,730)
Fixed maturities and fixed maturities pledged under securities lending agreements
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	6,745,022	3,788,119
Gross Unrealized Losses - Less than 12 Months	[1]	(82,695)	(71,021)
Estimated Fair Value - 12 Months or More	[1]	482,808	641,407
Gross Unrealized Losses - 12 Months or More	[1]	(53,710)	(21,713)
Estimated Fair Value - Total	[1]	7,227,830	4,429,526
Gross Unrealized Losses - Total	[1]	(136,405)	(92,734)
Fixed maturities and fixed maturities pledged under securities lending agreements | Corporate bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,810,988	1,309,637
Gross Unrealized Losses - Less than 12 Months	[1]	(37,445)	(32,903)
Estimated Fair Value - 12 Months or More	[1]	129,896	148,963
Gross Unrealized Losses - 12 Months or More	[1]	(23,063)	(6,071)
Estimated Fair Value - Total	[1]	1,940,884	1,458,600
Gross Unrealized Losses - Total	[1]	(60,508)	(38,974)
Fixed maturities and fixed maturities pledged under securities lending agreements | Mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	487,018	293,624
Gross Unrealized Losses - Less than 12 Months	[1]	(4,508)	(1,476)
Estimated Fair Value - 12 Months or More	[1]	48,991	59,107
Gross Unrealized Losses - 12 Months or More	[1]	(826)	(2,366)
Estimated Fair Value - Total	[1]	536,009	352,731
Gross Unrealized Losses - Total	[1]	(5,334)	(3,842)
Fixed maturities and fixed maturities pledged under securities lending agreements | Municipal bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	269,015	210,614
Gross Unrealized Losses - Less than 12 Months	[1]	(1,303)	(588)
Estimated Fair Value - 12 Months or More	[1]	9,692	13,643
Gross Unrealized Losses - 12 Months or More	[1]	(231)	(456)
Estimated Fair Value - Total	[1]	278,707	224,257
Gross Unrealized Losses - Total	[1]	(1,534)	(1,044)
Fixed maturities and fixed maturities pledged under securities lending agreements | Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	511,261	232,147
Gross Unrealized Losses - Less than 12 Months	[1]	(6,639)	(770)
Estimated Fair Value - 12 Months or More	[1]	20,596	125,894
Gross Unrealized Losses - 12 Months or More	[1]	(339)	(3,052)
Estimated Fair Value - Total	[1]	531,857	358,041
Gross Unrealized Losses - Total	[1]	(6,978)	(3,822)
Fixed maturities and fixed maturities pledged under securities lending agreements | US government and government agencies
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,991,163	618,381
Gross Unrealized Losses - Less than 12 Months	[1]	(9,978)	(1,626)
Estimated Fair Value - 12 Months or More	[1]	0	3,438
Gross Unrealized Losses - 12 Months or More	[1]	0	(134)
Estimated Fair Value - Total	[1]	1,991,163	621,819
Gross Unrealized Losses - Total	[1]	(9,978)	(1,760)
Fixed maturities and fixed maturities pledged under securities lending agreements | Non-US government securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	458,414	510,766
Gross Unrealized Losses - Less than 12 Months	[1]	(13,494)	(31,172)
Estimated Fair Value - 12 Months or More	[1]	138,792	46,910
Gross Unrealized Losses - 12 Months or More	[1]	(25,628)	(6,031)
Estimated Fair Value - Total	[1]	597,206	557,676
Gross Unrealized Losses - Total	[1]	(39,122)	(37,203)
Fixed maturities and fixed maturities pledged under securities lending agreements | Asset backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,217,163	612,950
Gross Unrealized Losses - Less than 12 Months	[1]	(9,328)	(2,486)
Estimated Fair Value - 12 Months or More	[1]	134,841	243,452
Gross Unrealized Losses - 12 Months or More	[1]	(3,623)	(3,603)
Estimated Fair Value - Total	[1]	1,352,004	856,402
Gross Unrealized Losses - Total	[1]	(12,951)	(6,089)
Equity securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	232,275	181,002
Gross Unrealized Losses - Less than 12 Months	[1]	(17,796)	(13,364)
Estimated Fair Value - 12 Months or More	[1]	0	0
Gross Unrealized Losses - 12 Months or More	[1]	0	0
Estimated Fair Value - Total	[1]	232,275	181,002
Gross Unrealized Losses - Total	[1]	(17,796)	(13,364)
Other investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	93,614	59,638
Gross Unrealized Losses - Less than 12 Months	[1]	(4,665)	(362)
Estimated Fair Value - 12 Months or More	[1]	0	0
Gross Unrealized Losses - 12 Months or More	[1]	0	0
Estimated Fair Value - Total	[1]	93,614	59,638
Gross Unrealized Losses - Total	[1]	(4,665)	(362)
Short-term investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	30,625	79,271
Gross Unrealized Losses - Less than 12 Months	[1]	(3,425)	(5,270)
Estimated Fair Value - 12 Months or More	[1]	0	0
Gross Unrealized Losses - 12 Months or More	[1]	0	0
Estimated Fair Value - Total	[1]	30,625	79,271
Gross Unrealized Losses - Total	[1]	$ (3,425)	$ (5,270)
[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments 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	Dec. 31, 2015	Dec. 31, 2014
Estimated Fair Value:
Estimated fair value	$ 10,459,353	$ 10,750,770
Amortized Cost:
Amortized cost	10,515,440	10,701,557
Fixed maturities and fixed maturities pledged under securities lending agreements
Estimated Fair Value:
Due in one year or less	337,898	235,930
Due after one year through five years	4,644,516	4,074,562
Due after five years through 10 years	2,214,413	2,475,726
Due after 10 years	496,302	279,542
Single maturity date	7,693,129	7,065,760
Estimated fair value	10,832,657	10,801,572
Amortized Cost:
Due in one year or less	341,595	233,794
Due after one year through five years	4,677,230	4,077,408
Due after five years through 10 years	2,228,638	2,461,356
Due after 10 years	497,174	273,372
Single maturity date	7,744,637	7,045,930
Amortized cost	10,892,980	10,753,633
Fixed maturities and fixed maturities pledged under securities lending agreements | Mortgage backed securities
Estimated Fair Value:
Securities without single maturity date	754,870	943,343
Amortized Cost:
Securities without single maturity date	750,332	928,342
Fixed maturities and fixed maturities pledged under securities lending agreements | Commercial mortgage backed securities
Estimated Fair Value:
Securities without single maturity date	764,152	1,114,528
Amortized Cost:
Securities without single maturity date	767,861	1,103,756
Fixed maturities and fixed maturities pledged under securities lending agreements | Asset backed securities
Estimated Fair Value:
Securities without single maturity date	1,620,506	1,677,941
Amortized Cost:
Securities without single maturity date	$ 1,630,150	$ 1,675,605

Investment Information - Securi

Investment Information - Securities lending arrangements (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	$ 393,844	$ 50,529
Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 10	0
Amounts related to securities lending not included in offsetting disclosure in Note 10	393,844
US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	327,612
Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	55,086
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	11,146
Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	297,536
Overnight and Continuous | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	235,728
Overnight and Continuous | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	55,086
Overnight and Continuous | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	6,722
Less than 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	4,424
Less than 30 Days | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0
Less than 30 Days | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0
Less than 30 Days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	4,424
30-90 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	82,286
30-90 Days | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	82,286
30-90 Days | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0
30-90 Days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0
90 Days or More
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	9,598
90 Days or More | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	9,598
90 Days or More | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0
90 Days or More | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	$ 0

Investment Information - Other

Investment Information - Other Investments (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		$ 1,971,447	$ 1,837,652
Available for sale
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		300,476	296,224
Available for sale | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		206,861	236,586
Available for sale | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		31,370	59,638
Available for sale | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		39,733	0
Available for sale | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		22,512	0
Fair value option
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		1,670,971	1,541,428
Fair value option | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		34,761	25,800
Fair value option | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		63,053	69,108
Fair value option | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	[1]	124,502	137,094
Fair value option | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		1,108,017	1,073,649
Other investments par		1,197,143	1,094,337
Fair value option | Mezzanine debt funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		121,589	121,341
Fair value option | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		$ 219,049	$ 114,436
[1]	Includes fund investments with strategies in mortgage servicing rights, transportation and infrastructure assets and other.

Investment Information - Fair V

Investment Information - Fair Value Option (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 2,894,494	$ 2,425,053
Fixed Maturities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	936,802	632,024
Other investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	1,670,971	1,541,428
Short-term investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	285,923	251,601
Equity securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 798	$ 0

Investment Information - Net In

Investment Information - Net Investment Income (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net investment income:
Gross investment income										$ 411,128	$ 348,921	$ 300,329
Investment expenses										(63,038)	(46,336)	(33,110)
Net investment income		$ 95,900	$ 86,233	$ 86,963	$ 78,994	$ 82,496	$ 80,105	$ 72,990	$ 66,994	348,090	302,585	267,219
Fixed Maturities
Net investment income:
Gross investment income										283,998	265,219	249,833
Term loan investments
Net investment income:
Gross investment income										71,120	39,940	20,608
Short-term investments
Net investment income:
Gross investment income										669	1,888	1,259
Equity securities
Net investment income:
Gross investment income										13,534	13,005	8,919
Other
Net investment income:
Gross investment income	[1]									$ 41,807	$ 28,869	$ 19,710
[1]	Includes income distributions from investment funds and other items.

Investment Information - Net Re

Investment Information - Net Realized Gains and Losses (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net realized gains and losses:
Available for sale securities, gross gains on investment sales										$ 281,786	$ 248,031	$ 239,421
Available for sale securities, gross losses on investment sales										(218,970)	(145,808)	(203,077)
Change in fair value of assets and liabilities accounted for using the fair value option - derivatives	[1]									(7,114)	43,934	20,912
Change in fair value of assets and liabilities accounted for using the fair value option - other investments	[2]									(36,130)	(24,774)	(1,499)
Net realized gains (losses)		$ (143,767)	$ (89,698)	$ (35,725)	$ 83,348	$ 10,561	$ 18,515	$ 54,144	$ 19,697	(185,842)	102,917	74,018
Fixed Maturities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option										(84,620)	(20,743)	54
Equity securities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option										(85)	0	704
Other investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option										(122,171)	2,672	17,503
Short-term investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option										$ 1,462	$ (395)	$ 0
[1]	See Note 10 for information on the Company’s derivative instruments.
[2]	Includes the re-measurement of contingent consideration liability amounts.

Investment Information - Othe76

Investment Information - Other Than Temporary Impairments Recognized in Earnings (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ (7,336)	$ (5,868)	$ (1,113)	$ (5,799)	$ (3,837)	$ (8,593)	$ (14,749)	$ (2,971)	$ (20,116)	$ (30,150)	$ (3,786)
Fixed Maturities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings									(12,635)	(3,634)	(511)
Fixed Maturities | Mortgage backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings									(1,794)	(1,525)	(295)
Fixed Maturities | Corporate bonds
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings									(10,841)	(2,062)	(88)
Fixed Maturities | Commercial mortgage backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings									0	(7)	0
Fixed Maturities | Asset backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings									0	(40)	(128)
Short-term investments
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings									(2,341)	0	0
Equity securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings									(4,206)	(1,106)	(3,275)
Other investments
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings									$ (934)	$ (25,410)	$ 0

Investment Information - Othe77

Investment Information - Other Than Temporary Impairments Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Rollforward:
Balance at start of year	$ 20,196	$ 60,062	$ 62,001
Credit loss impairments recognized on securities not previously impaired	12,777	691	423
Credit loss impairments recognized on securities previously impaired	1,673	162	88
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	0	0	0
Reductions for securities sold during the period	(7,771)	(40,719)	(2,450)
Balance at end of year	$ 26,875	$ 20,196	$ 60,062

Investment Information - Restri

Investment Information - Restricted Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Restricted Assets [Line Items]
Restricted assets	$ 5,526,049	$ 5,519,089
Collateral or guarantees - affiliated transactions
Restricted Assets [Line Items]
Restricted assets	3,810,104	4,138,527
Collateral or guarantees - third party agreements
Restricted Assets [Line Items]
Restricted assets	1,181,087	970,120
Deposits with US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	391,458	337,981
Deposits with non-US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	38,230	0
Trust funds
Restricted Assets [Line Items]
Restricted assets	$ 105,170	$ 72,461

Investment Information - Narrat

Investment Information - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)lots	Dec. 31, 2014USD ($)lots	Dec. 31, 2013USD ($)
Segment Reporting Information [Line Items]
Investable assets	$ 16,340,938	$ 15,762,730	$ 14,049,525
OTTI unrealized losses at current fair value	$ (1,400)	$ 900
Continuous unrealized loss, qualitative disclosures:
Number of positions in an unrealized loss position (lots) | lots	3,560	1,900
Total number of positions (lots) | lots	5,550	4,790
Largest single loss	$ 3,100	$ 2,900
OTTI Unrealized Losses	6,925	3,646
Securities lending, qualitative disclosures:
Fair value of fixed maturities and short-term investments pledged under securities lending agreements	384,100	50,800
Amortized cost of fixed maturities and short-term investments pledged under securities lending agreements	386,411	52,076
Approximate fair value of sub-prime securities backing the securities lending program	3,000	5,800
Collateral received under securities lending, at fair value (amortized cost: $385,984 and $40,473)	389,336	44,301
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Equity in net income (loss) of investment funds accounted for using the equity method	$ 25,455	19,883	$ 35,701
Equity method investments, time lag for reporting - low end of range	1 month
Equity method investments, time lag for reporting - high end of range	3 months
Investments accounted for using the equity method	$ 592,973	349,014
ACGL
Segment Reporting Information [Line Items]
Investable assets	14,640,000
Watford Re
Segment Reporting Information [Line Items]
Investable assets	1,700,000
Cash and Cash Equivalents [Member]
Securities lending, qualitative disclosures:
Collateral received under securities lending, at fair value (amortized cost: $385,984 and $40,473)	52,700	44,300
Securities Pledged as Collateral [Member]
Securities lending, qualitative disclosures:
Collateral received under securities lending, at fair value (amortized cost: $385,984 and $40,473)	$ 336,600	$ 0
Corporate bonds
Segment Reporting Information [Line Items]
Impairment Losses, Percentage	43.00%
Non investment grade | Corporate bonds
Segment Reporting Information [Line Items]
Impairment Losses, Percentage	57.00%

Fair Value - Fair Value Hierarc

Fair Value - Fair Value Hierarchy (Details) - Recurring - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
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		$ 4,032,996	$ 3,116,355
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
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	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities and fixed maturities pledged under securities lending agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		2,378,662	1,447,972
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities and fixed maturities pledged under securities lending agreements | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities and fixed maturities pledged under securities lending agreements | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities and fixed maturities pledged under securities lending agreements | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities and fixed maturities pledged under securities lending agreements | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities and fixed maturities pledged under securities lending agreements | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	2,378,662	1,447,972
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities and fixed maturities pledged under securities lending agreements | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities and fixed maturities pledged under securities lending agreements | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	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		627,441	658,182
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		572,604	759,621
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		99,159	0
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		99,159	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]
Assets measured at fair value	[2]	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		355,130	250,580
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 | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		114
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		285,923	250,580
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		798
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		68,295	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		10,461,895	11,220,264
Liabilities measured at fair value		(42,446)	(5,397)
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]	(30,583)
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	[2]	(11,863)	(5,397)
Significant Other Observable Inputs (Level 2) | Fixed maturities and fixed maturities pledged under securities lending agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		8,380,127	9,296,100
Significant Other Observable Inputs (Level 2) | Fixed maturities and fixed maturities pledged under securities lending agreements | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	2,709,361	3,108,513
Significant Other Observable Inputs (Level 2) | Fixed maturities and fixed maturities pledged under securities lending agreements | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	754,870	943,343
Significant Other Observable Inputs (Level 2) | Fixed maturities and fixed maturities pledged under securities lending agreements | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	1,626,281	1,494,122
Significant Other Observable Inputs (Level 2) | Fixed maturities and fixed maturities pledged under securities lending agreements | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	764,152	1,114,528
Significant Other Observable Inputs (Level 2) | Fixed maturities and fixed maturities pledged under securities lending agreements | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	44,793	0
Significant Other Observable Inputs (Level 2) | Fixed maturities and fixed maturities pledged under securities lending agreements | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	917,664	1,015,153
Significant Other Observable Inputs (Level 2) | Fixed maturities and fixed maturities pledged under securities lending agreements | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	1,563,006	1,620,441
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		1,741	0
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		15,300	37,605
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		0	97,372
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		0	97,372
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	[2]	20,022	15,876
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		2,044,705	1,773,311
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		771,733	497,101
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		57,687	22,190
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
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		81,824	88,411
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		25,444	24,322
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		0	1,021
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		0
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		1,108,017	1,140,266
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		73,868	57,500
Liabilities measured at fair value		(96,048)	(61,845)
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		(96,048)	(61,845)
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
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	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities and fixed maturities pledged under securities lending agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		73,868	57,500
Significant Unobservable Inputs (Level 3) | Fixed maturities and fixed maturities pledged under securities lending agreements | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	16,368	0
Significant Unobservable Inputs (Level 3) | Fixed maturities and fixed maturities pledged under securities lending agreements | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities and fixed maturities pledged under securities lending agreements | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities and fixed maturities pledged under securities lending agreements | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities and fixed maturities pledged under securities lending agreements | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities and fixed maturities pledged under securities lending agreements | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities and fixed maturities pledged under securities lending agreements | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	57,500	57,500
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	[2]	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		0	0
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		0	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 | US government and government agencies
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 | 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
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		0	0
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		15,264,735	14,994,133
Liabilities measured at fair value		(138,494)	(67,242)
Estimated Fair Value | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(96,048)	(61,845)
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]	(30,583)
Estimated Fair Value | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[2]	(11,863)	(5,397)
Estimated Fair Value | Fixed maturities and fixed maturities pledged under securities lending agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		10,832,657	10,801,572
Estimated Fair Value | Fixed maturities and fixed maturities pledged under securities lending agreements | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	2,725,729	3,108,513
Estimated Fair Value | Fixed maturities and fixed maturities pledged under securities lending agreements | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	754,870	943,343
Estimated Fair Value | Fixed maturities and fixed maturities pledged under securities lending agreements | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	1,626,281	1,494,122
Estimated Fair Value | Fixed maturities and fixed maturities pledged under securities lending agreements | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	764,152	1,114,528
Estimated Fair Value | Fixed maturities and fixed maturities pledged under securities lending agreements | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	2,423,455	1,447,972
Estimated Fair Value | Fixed maturities and fixed maturities pledged under securities lending agreements | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	917,664	1,015,153
Estimated Fair Value | Fixed maturities and fixed maturities pledged under securities lending agreements | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	1,620,506	1,677,941
Estimated Fair Value | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		629,182	658,182
Estimated Fair Value | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		587,904	797,226
Estimated Fair Value | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		300,476	296,224
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		99,159	97,372
Estimated Fair Value | Other investments at net asset value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[4]	201,317	198,852
Estimated Fair Value | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	20,022	15,876
Estimated Fair Value | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		2,894,494	2,425,053
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		771,733	497,101
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		57,687	22,190
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		114
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		81,824	88,411
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		25,444	24,322
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		285,923	251,601
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		798
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		1,176,312	1,140,266
Estimated Fair Value | Fair value option | Other investments at net asset value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[4]	$ 494,659	$ 401,162
[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]	See Note 10, “Derivative Instruments.”
[3]	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 8, “Investment Information—Securities Lending Agreements.”
[4]	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		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Level 3 assets rollforward
Balance at beginning of year		$ 57,500	$ 549,990
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		0	(2,045)
Settlements		0	0
Transfers in and/or out of Level 3		16,368	(490,445)
Balance at end of year		73,868	57,500
Contingent consideration liability
Level 3 liabilities rollforward
Balance at beginning of year		(61,845)	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(33,135)	(20,083)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		(1,068)	(41,762)
Sales		0	0
Settlements		0	0
Transfers in and/or out of Level 3		0	0
Balance at end of year		(96,048)	(61,845)
Available for sale | Asset backed securities
Level 3 assets rollforward
Balance at beginning of year		57,500	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		0	0
Settlements		0	0
Transfers in and/or out of Level 3		0	57,500
Balance at end of year		57,500	57,500
Available for sale | Corporate bonds
Level 3 assets rollforward
Balance at beginning of year		0	2,045
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		0	(2,045)
Settlements		0	0
Transfers in and/or out of Level 3		16,368	0
Balance at end of year		16,368	0
Available for sale | Other investments
Level 3 assets rollforward
Balance at beginning of year		0	170,420
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		0	0
Settlements		0	0
Transfers in and/or out of Level 3		0	(170,420)
Balance at end of year		0	0
Fair value option | Other investments
Level 3 assets rollforward
Balance at beginning of year		0	377,525
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		0	0
Settlements		0	0
Transfers in and/or out of Level 3		0	(377,525)
Balance at end of year		$ 0	$ 0
[1]	Gains or losses on fixed maturities available for sale were included in net realized gains (losses) while gains or losses on other investments were included in net realized gains (losses) or net investment income. Gains or losses on contingent consideration liabilities were included in net realized gains (losses).

Fair Value - Narrative (Details

Fair Value - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	$ 791,306	$ 791,141
Transfers from Level 1 to Level 2	44,600
Transfers from Level 2 to Level 1	99,700
Total assets and liabilities measured at fair value	15,400,000	15,060,000
Total assets and liabilities measured at fair value priced using non-binding broker quotes	$ 317,800	$ 260,800
Total assets and liabilities measured at fair value priced using non-binding broker quotes (percentage)	2.10%	1.70%
Transfers in and/or out of Level 3	$ 16,368	$ (490,445)
Unsecured debt | 7.35% senior notes due 2034
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of senior notes	390,100	462,400
Unsecured debt | 5.144% senior notes due 2043
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of senior notes	513,900	609,900
Available for sale | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers in and/or out of Level 3	16,368	0
Reportable legal entities | ACGL (Parent Guarantor)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	296,874	296,796
Reportable legal entities | Arch-U.S. (Subsidiary Issuer)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	$ 494,432	$ 494,345

Derivative Instruments (Details

Derivative Instruments (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative offsetting [Abstract]
Derivative assets subject to master netting agreements		$ (26,500)	$ (25,300)
Derivative liabilities subject to master netting agreements		11,900	5,400
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	[1]	(7,114)	43,934	$ 20,912
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives - fair value		26,547	26,468
Liability derivatives - fair value		(11,863)	(5,397)
Net derivatives - fair value		14,684	21,071
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(7,114)	43,934	20,912
Not Designated as Hedging Instrument [Member] | Futures contracts
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(21,533)	30,444	10,742
Not Designated as Hedging Instrument [Member] | Futures contracts | Other investments available for sale, at fair value
Derivative [Line Items]
Asset derivatives - fair value	[2]	2,816	2,156
Liability derivatives - fair value	[2]	(1,202)	(1,907)
Net derivatives - fair value	[2]	1,614	249
Net derivatives - notional value	[2],[3]	1,797,115	2,549,027
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		16,045	13,430	9,762
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts | Other investments available for sale, at fair value
Derivative [Line Items]
Asset derivatives - fair value	[2]	9,336	10,511
Liability derivatives - fair value	[2]	(6,344)	(1,145)
Net derivatives - fair value	[2]	2,992	9,366
Net derivatives - notional value	[2],[3]	773,619	397,106
Not Designated as Hedging Instrument [Member] | TBAs
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		1,452	(342)	(1,623)
Not Designated as Hedging Instrument [Member] | TBAs | Fixed maturities available for sale, at fair value
Derivative [Line Items]
Asset derivatives - fair value	[4]	6,525	10,592
Liability derivatives - fair value	[4]	0	0
Net derivatives - fair value	[4]	6,525	10,592
Net derivatives - notional value	[3],[4]	6,316	10,056
Not Designated as Hedging Instrument [Member] | Other
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(3,078)	402	$ 2,031
Not Designated as Hedging Instrument [Member] | Other | Other investments available for sale, at fair value
Derivative [Line Items]
Asset derivatives - fair value	[2]	7,870	3,209
Liability derivatives - fair value	[2]	(4,317)	(2,345)
Net derivatives - fair value	[2]	3,553	864
Net derivatives - notional value	[2],[3]	$ 1,694,935	$ 735,684
[1]	See Note 10 for information on the Company’s derivative instruments.
[2]	The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’ Such amounts include risk in force on GSE credit-risk sharing transactions that are accounted for as derivatives.
[3]	Represents the absolute notional value of all outstanding contracts, consisting of long and short positions.
[4]	The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’

Other Comprehensive Income - C

Other Comprehensive Income - Components of accumulated other comprehensive income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 128,856	$ 74,964	$ 287,017
Other comprehensive income (loss) before reclassifications	(117,125)	118,996	(179,367)
Amounts reclassified from accumulated other comprehensive income	(28,233)	(65,104)	(32,686)
Net current period other comprehensive income (loss)	(145,358)	53,892	(212,053)
Ending balance	(16,502)	128,856	74,964
Unrealized Appreciation on Available-For-Sale Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	161,598	80,692	289,956
Other comprehensive income (loss) before reclassifications	(83,280)	146,010	(176,578)
Amounts reclassified from accumulated other comprehensive income	(28,233)	(65,104)	(32,686)
Net current period other comprehensive income (loss)	(111,513)	80,906	(209,264)
Ending balance	50,085	161,598	80,692
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(32,742)	(5,728)	(2,939)
Other comprehensive income (loss) before reclassifications	(33,845)	(27,014)	(2,789)
Amounts reclassified from accumulated other comprehensive income	0	0	0
Net current period other comprehensive income (loss)	(33,845)	(27,014)	(2,789)
Ending balance	$ (66,587)	$ (32,742)	$ (5,728)

Other Comprehensive Income - A

Other Comprehensive Income - Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses	$ (7,336)	$ (5,868)	$ (1,113)	$ (5,799)	$ (3,837)	$ (8,593)	$ (14,749)	$ (2,971)	$ (20,116)	$ (30,150)	$ (3,786)
Income (loss) before income taxes									567,194	844,247	742,505
Income tax (expense) benefit									(40,612)	(22,987)	(32,774)
Net of tax									537,738	834,355	709,731
Reclassification out of accumulated other comprehensive income | Unrealized Appreciation on Available-For-Sale Investments
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains									62,817	102,223	39,308
Other-than-temporary impairment losses									(26,152)	(30,470)	(3,961)
Income (loss) before income taxes									36,665	71,753	35,347
Income tax (expense) benefit									(8,432)	(6,649)	(2,661)
Net of tax									$ 28,233	$ 65,104	$ 32,686

Other Comprehensive Income -86

Other Comprehensive Income - Components of other comprehensive income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Before tax amount:
Unrealized holding gains (losses) arising during period, before tax	$ (77,311)	$ 161,685	$ (201,386)
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), before tax	(6,036)	(320)	(175)
Less reclassification of net realized gains (losses) included in net income, before tax	36,665	71,753	35,347
Foreign currency translation adjustments, before tax	(35,678)	(27,014)	(2,789)
Other comprehensive income (loss), before tax	(155,690)	62,598	(239,697)
Tax expense (benefit):
Unrealized holding gains (losses) arising during period, tax	(67)	15,355	(24,983)
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), tax	0	0	0
Less reclassification of net realized gains (losses) included in net income, tax	8,432	6,649	2,661
Foreign currency translation adjustments, tax	(1,568)	0	0
Other comprehensive income (loss), tax	(10,067)	8,706	(27,644)
Net of tax amount:
Unrealized holding gains (losses) arising during period, net of tax	(77,244)	146,330	(176,403)
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), net of tax	(6,036)	(320)	(175)
Less reclassification of net realized gains (losses) included in net income, net of tax	28,233	65,104	32,686
Foreign currency translation adjustments, net of tax	(34,110)	(27,014)	(2,789)
Net current period other comprehensive income (loss)	$ (145,623)	$ 53,892	$ (212,053)

Earnings Per Common Share (Deta

Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net income (loss)		$ 58,579	$ 80,033	$ 115,790	$ 283,336	$ 215,164	$ 228,675	$ 208,016	$ 182,500	$ 526,582	$ 821,260	$ 709,731
Net (income) loss attributable to noncontrolling interests										11,156	13,095	0
Net income available to Arch										537,738	834,355	709,731
Preferred dividends		(5,485)	(5,484)	(5,485)	(5,484)	(5,485)	(5,484)	(5,485)	(5,484)	(21,938)	(21,938)	(21,938)
Net income available to Arch common shareholders		$ 53,094	$ 74,549	$ 110,305	$ 277,852	$ 209,679	$ 223,191	$ 202,531	$ 177,016	$ 515,800	$ 812,417	$ 687,793
Denominator:
Weighted average common shares outstanding — basic										121,786,127	130,817,610	131,355,392
Effect of dilutive common share equivalents:
Nonvested restricted shares										1,253,938	1,128,540	1,090,100
Stock options	[1]									2,998,678	2,976,172	3,331,691
Weighted average common shares and common share equivalents outstanding — diluted										126,038,743	134,922,322	135,777,183
Earnings per common share:
Basic (per share)		$ 0.44	$ 0.62	$ 0.91	$ 2.24	$ 1.65	$ 1.69	$ 1.53	$ 1.34	$ 4.24	$ 6.21	$ 5.24
Diluted (per share)		$ 0.42	$ 0.60	$ 0.88	$ 2.16	$ 1.60	$ 1.64	$ 1.48	$ 1.30	$ 4.09	$ 6.02	$ 5.07
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per common share (shares)										799,535	1,435,955	892,439
[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 2015, 2014 and 2013, the number of stock options excluded were 799,535, 1,435,955 and 892,439, respectively.

Income Taxes - Components of i

Income Taxes - Components of income tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current expense (benefit):
United States	$ 37,186	$ 29,749	$ 27,537
Non-U.S.	7,008	801	5,159
Current Income Tax Expense (Benefit)	44,194	30,550	32,696
Deferred expense (benefit):
United States	(4,893)	(8,168)	1,937
Non-U.S.	1,311	605	(1,859)
Deferred Income Tax Expense (Benefit)	(3,582)	(7,563)	78
Income tax expense (benefit)	$ 40,612	$ 22,987	$ 32,774

Income Taxes - Income before t

Income Taxes - Income before taxes by jurisdiction (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Line Items]
Income (loss) before income taxes	$ 567,194	$ 844,247	$ 742,505
Bermuda
Income Tax Disclosure [Line Items]
Income (loss) before income taxes	508,561	794,926	717,661
United States
Income Tax Disclosure [Line Items]
Income (loss) before income taxes	57,527	53,055	87,032
Other
Income Tax Disclosure [Line Items]
Income (loss) before income taxes	$ 1,106	$ (3,734)	$ (62,188)

Income Taxes - Statutory tax r

Income Taxes - Statutory tax rate by jurisdiction (Details)	12 Months Ended
	Dec. 31, 2015
Bermuda
Income Tax Disclosure [Line Items]
Statutory tax rate (percentage)	0.00%
United States
Income Tax Disclosure [Line Items]
Statutory tax rate (percentage)	35.00%
United Kingdom
Income Tax Disclosure [Line Items]
Statutory tax rate (percentage)	20.25%
Ireland
Income Tax Disclosure [Line Items]
Statutory tax rate (percentage)	12.50%
Denmark
Income Tax Disclosure [Line Items]
Statutory tax rate (percentage)	23.50%
Canada
Income Tax Disclosure [Line Items]
Statutory tax rate (percentage)	26.50%
Gibraltar
Income Tax Disclosure [Line Items]
Statutory tax rate (percentage)	10.00%
Netherlands
Income Tax Disclosure [Line Items]
Statutory tax rate (percentage)	25.00%

Income Taxes - Reconciliation

Income Taxes - Reconciliation of effective tax rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Expected income tax expense (benefit) computed on pre-tax income at weighted average income tax rate	$ 20,058	$ 18,178	$ 17,506
Addition (reduction) in income tax expense (benefit) resulting from:
Tax-exempt investment income	(9,588)	(8,048)	(8,255)
Meals and entertainment	897	711	599
State taxes, net of U.S. federal tax benefit	858	1,281	431
Foreign branch taxes	1,456	464	703
Prior year adjustment	2,510	320	2,810
Foreign exchange gains & losses	670	746	(1,254)
Changes in applicable tax rate	40	(51)	2,007
Dividend withholding taxes	6,323	3,276	4,619
Change in valuation allowance	2,917	(736)	11,795
Contingent consideration	11,548	6,763	0
Uncertain tax position	2,008	0	0
Other	915	83	1,813
Income tax expense	$ 40,612	$ 22,987	$ 32,774

Income Taxes - Components of de

Income Taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred income tax assets:
Net operating loss	$ 11,436	$ 12,017
AMT credit carryforward	5,304	5,309
Discounting of net loss reserves	54,373	63,880
Net unearned premium reserve	33,579	34,087
Compensation liabilities	29,069	27,765
Foreign tax credit carryforward	6,215	4,628
Interest expense	1,972	5,208
Goodwill and intangible assets	2,683	885
Tax and loss bonds	14,150	21,247
Net unrealized foreign exchange gains	1,573	0
Other, net	21,273	13,408
Deferred tax assets before valuation allowance	181,627	188,434
Valuation allowance	(13,816)	(12,624)
Deferred tax assets net of valuation allowance	167,811	175,810
Deferred income tax liabilities:
Depreciation and amortization	(7,368)	(7,579)
Deferred acquisition costs, net	(164)	(2,744)
Deposit accounting liability	(4,151)	(4,170)
Contingency reserve	(15,289)	(18,480)
Net unrealized appreciation of investments	(4,103)	(11,695)
Other, net	(1,042)	(150)
Total deferred tax liabilities	(32,117)	(44,818)
Net deferred income tax assets	$ 135,694	$ 130,992

Income Taxes - Unrecognized tax

Income Taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of beginning and ending amount of unrecognized tax benefits
Balance at beginning of year	$ 0	$ 0
Additions based on tax positions related to the current year	517	0
Additions for tax positions of prior years	1,491	0
Reductions for tax positions of prior years	0	0
Settlements	0	0
Balance at end of year	$ 2,008	$ 0

Income Taxes - Summary of open

Income Taxes - Summary of open tax years by major jurisdiction (Details)	12 Months Ended
	Dec. 31, 2015
United States | Minimum
Income Tax Contingency [Line Items]
Open tax year	2,012
United States | Maximum
Income Tax Contingency [Line Items]
Open tax year	2,015
United Kingdom | Minimum
Income Tax Contingency [Line Items]
Open tax year	2,010
United Kingdom | Maximum
Income Tax Contingency [Line Items]
Open tax year	2,015
Ireland | Minimum
Income Tax Contingency [Line Items]
Open tax year	2,011
Ireland | Maximum
Income Tax Contingency [Line Items]
Open tax year	2,015
Canada | Minimum
Income Tax Contingency [Line Items]
Open tax year	2,011
Canada | Maximum
Income Tax Contingency [Line Items]
Open tax year	2,015
Switzerland | Minimum
Income Tax Contingency [Line Items]
Open tax year	2,012
Switzerland | Maximum
Income Tax Contingency [Line Items]
Open tax year	2,015
Denmark | Minimum
Income Tax Contingency [Line Items]
Open tax year	2,012
Denmark | Maximum
Income Tax Contingency [Line Items]
Open tax year	2,015

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Net operating loss	$ 11,436	$ 12,017
Valuation allowance	13,816	12,624
Foreign tax credit carryforward	6,215	4,628
AMT credit carryforward	5,304	5,309
Tax and loss bonds	14,150	21,247
Unrecognized tax benefits	2,008	$ 0	$ 0
Current income tax recoverable	900
United Kingdom
Operating Loss Carryforwards [Line Items]
Net operating loss	600
Net operating loss carryforwards	16,100
Foreign tax credit carryforward	6,200
Net operating loss carryforward, valuation allowance	100
Foreign tax credit carryforward, valuation allowance	6,200
Ireland
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	5,300
Net operating loss carryforward, valuation allowance	600
United States
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	18,800
Operating loss carryforward, portion subject to utilization limits	11,500
Operating loss carryforward, annual utilization limit	600
AMT credit carryforward	$ 5,300

Transactions with Related Par96

Transactions with Related Parties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Investment commitments	$ 1,110,000
Purchases of other investments	1,749,525	$ 1,590,648	$ 994,185
The Carlyle Group | Common director
Related Party Transaction [Line Items]
Investment commitments	695,900
Unfunded commitments	482,500
Purchases of other investments	116,500	63,500	60,800
Aggregate cash distributions received	44,600	45,800	15,000
Return of Capital From Other Investments	$ 38,800	$ 34,400	$ 12,900

Commitments and Contingencies -

Commitments and Contingencies - Concentrations of credit risk (Details) - Customer Concentration Risk [Member] - Gross Written Premiums [Member]	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Aon Corporation [Member]
Concentration Risk [Line Items]
Concentration risk percentage	13.10%	13.40%	16.00%
Marsh And McLennan Companies [Member]
Concentration Risk [Line Items]
Concentration risk percentage	15.30%	15.00%	17.00%

Commitments and Contingencies98

Commitments and Contingencies - Future minimum rental payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Rent expense
Rental expense net of income from subleases	$ 23,800	$ 23,100	$ 18,700
Office Space [Member]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Due next twelve months	25,494
Due in two years	24,660
Due in three years	24,337
Due in four years	21,024
Due in five years	18,250
Thereafter	40,361
Total	$ 154,126

Commitments and Contingencies99

Commitments and Contingencies - Credit facilities and other commitments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Line of Credit Facility [Line Items]
Investment commitments	$ 1,110,000
Estimated purchase commitments, primarily related to software and computerized systems	20,700	$ 22,200
Line of Credit Facility [Abstract]
Amount outstanding	530,434	$ 100,000
LOC Facilities
Line of Credit Facility [Abstract]
Amount outstanding	464,800
Investments pledged as collateral	529,300
Outstanding borrowings	100,000
Aggregate limit on unsecured letters of credit
Line of Credit Facility [Abstract]
Maximum borrowing capacity	$ 100,000
Credit Agreement
Line of Credit Facility [Abstract]
Debt to total capital ratio (expressed as a percent)	0.35
Minimum tangible net worth	$ 3,950,000
Percentage of aggregate future net income for each quarterly period	25.00%
Percentage of future aggregate proceeds from issuance of common or preferred equity	25.00%
Unsecured revolving loan and letter of credit facility
Line of Credit Facility [Abstract]
Maximum borrowing capacity	$ 300,000
Secured letter of credit facility
Line of Credit Facility [Abstract]
Maximum borrowing capacity	500,000
Line of Credit Facility, Remaining Borrowing Capacity	277,500
Other secured letter of credit facilities
Line of Credit Facility [Abstract]
Maximum borrowing capacity	242,300
Watford Re
Line of Credit Facility [Abstract]
Amount outstanding	125,600
Watford Re | Credit facility expiring May 2016
Line of Credit Facility [Abstract]
Maximum borrowing capacity	100,000
Watford Re | Secured credit facility expiring June 2018
Line of Credit Facility [Abstract]
Maximum borrowing capacity	800,000
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases	400,000
Outstanding borrowings	$ 430,400

Senior Notes (Details)

Senior Notes (Details) - Unsecured debt - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 13, 2013	May. 04, 2004
7.35% senior notes due 2034
Debt Instrument [Line Items]
Face amount of issued debt				$ 300
Stated interest rate (percentage)				7.35%
Estimated fair value of senior notes	$ 390.1	$ 462.4
5.144% senior notes due 2043
Debt Instrument [Line Items]
Face amount of issued debt			$ 500
Stated interest rate (percentage)			5.144%
Estimated fair value of senior notes	$ 513.9	$ 609.9

Goodwill and Intangible Asse101

Goodwill and Intangible Assets - Analysis of goodwill and intangible assets (Details) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Schedule of Goodwill And Intangible Assets [Line Items]
Goodwill, beginning of year		$ 14,946	$ 0
Goodwill, acquisitions		663	14,965
Goodwill, foreign currency translation adjustment		(73)	(19)
Goodwill, end of year	$ 14,946	15,536	14,946
Intangible assets with an indefinite life, beginning of year		33,524	16,666
Intangible assets with an indefinite life, acquisitions		0	16,858
Intangible assets with an indefinite life, foreign currency translation adjustment		0	0
Intangible assets with an indefinite life, end of year	33,524	33,524	33,524
Intangible assets with a finite life, beginning of year		61,069	10,653
Intangible assets with a finite life, acquisitions		10,844	76,435
Intangible assets with a finite life, amortization	(20,100)	(22,968)	(25,520)
Intangible assets with a finite life, foreign currency translation adjustment		(474)	(499)
Intangible assets with a finite life, end of year	61,069	48,471	61,069
Goodwill and intangible assets, beginning of year		109,539	27,319
Goodwill and intangible assets, acquisitions		11,507	108,258
Goodwill and intangible assets, foreign currency translation adjustment		(547)	(518)
Goodwill and intangible assets, end of year	109,539	97,531	109,539
Goodwill and intangible assets, gross balance				$ 184,904
Intangible assets with a finite life, accumulated amortization				(86,407)	$ (63,439)
Goodwill and intangible assets, accumulated foreign currency translation adjustment				(966)	(419)
Goodwill and intangible assets, net balance	$ 109,539	109,539	$ 27,319	97,531	109,539
Goodwill
Schedule of Goodwill And Intangible Assets [Line Items]
Goodwill, end of year		15,536
Goodwill, gross balance				15,628
Goodwill and intangible assets, accumulated foreign currency translation adjustment				(92)	$ (19)
Intangible assets with an indefinite life
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with an indefinite life, end of year		33,524
Goodwill and intangible assets, accumulated foreign currency translation adjustment				0
Intangible assets with a finite life
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with a finite life, end of year		$ 48,471
Intangible assets with a finite life, gross balance				135,752
Intangible assets with a finite life, accumulated amortization				(86,407)
Goodwill and intangible assets, accumulated foreign currency translation adjustment				$ (874)

Goodwill and Intangible Asse102

Goodwill and Intangible Assets - Summary of intangible assets by major class (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with a finite life, accumulated amortization	$ (86,407)	$ (63,439)
Goodwill and intangible assets, accumulated foreign currency translation adjustment	(966)	(419)
Goodwill and intangible assets, net balance	97,531	109,539
Intangible Assets, Liabilities and Goodwill, Gross	184,904	173,397
Intangible liability - unfavorable service contract
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with a finite life, accumulated amortization	4,192	2,229
Goodwill and intangible assets, accumulated foreign currency translation adjustment	0	0
Goodwill and intangible assets, net balance	(5,341)	(7,304)
Intangible Assets, Liabilities and Goodwill, Gross	(9,533)	(9,533)
Intangible assets with a finite life
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with a finite life, accumulated amortization	(86,407)
Goodwill and intangible assets, accumulated foreign currency translation adjustment	(874)
Intangible assets with a finite life | Acquired insurance contracts
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with a finite life, accumulated amortization	(62,377)	(47,710)
Goodwill and intangible assets, accumulated foreign currency translation adjustment	(152)	(107)
Goodwill and intangible assets, net balance	22,503	29,757
Intangible Assets, Liabilities and Goodwill, Gross	85,032	77,574
Intangible assets with a finite life | Operating platform
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with a finite life, accumulated amortization	(11,462)	(5,482)
Goodwill and intangible assets, accumulated foreign currency translation adjustment	0	0
Goodwill and intangible assets, net balance	18,438	24,418
Intangible Assets, Liabilities and Goodwill, Gross	29,900	29,900
Intangible assets with a finite life | Customer relationships
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with a finite life, accumulated amortization	(16,355)	(12,283)
Goodwill and intangible assets, accumulated foreign currency translation adjustment	(722)	(293)
Goodwill and intangible assets, net balance	12,219	13,334
Intangible Assets, Liabilities and Goodwill, Gross	29,296	25,910
Intangible assets with a finite life | Other
Schedule of Goodwill And Intangible Assets [Line Items]
Intangible assets with a finite life, accumulated amortization	(405)	(193)
Goodwill and intangible assets, accumulated foreign currency translation adjustment	0	0
Goodwill and intangible assets, net balance	652	864
Intangible Assets, Liabilities and Goodwill, Gross	1,057	1,057
Intangible assets with an indefinite life
Schedule of Goodwill And Intangible Assets [Line Items]
Goodwill and intangible assets, accumulated foreign currency translation adjustment	0
Intangible assets with an indefinite life | Insurance licenses
Schedule of Goodwill And Intangible Assets [Line Items]
Goodwill and intangible assets, accumulated foreign currency translation adjustment	0	0
Goodwill and intangible assets, net balance	33,524	33,524
Intangible Assets, Liabilities and Goodwill, Gross	33,524	33,524
Goodwill
Schedule of Goodwill And Intangible Assets [Line Items]
Goodwill and intangible assets, accumulated foreign currency translation adjustment	(92)	(19)
Goodwill and intangible assets, net balance	15,536	14,946
Intangible Assets, Liabilities and Goodwill, Gross	$ 15,628	$ 14,965

Goodwill and Intangible Asse103

Goodwill and Intangible Assets - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Future amortization expense, next fiscal year	$ 19.3
Future amortization expense, year two	15.3
Future amortization expense, year three	11.9
Future amortization expense, year four	3.1
Future amortization expense, year five	$ 0.1
Minimum
Finite-Lived Intangible Assets [Line Items]
Remaining useful lives of intangible assets	2 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Remaining useful lives of intangible assets	7 years

Shareholders' Equity - Roll-for

Shareholders' Equity - Roll-forward of changes in issued and outstanding common shares (Details) - $ / shares		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Authorized and Issued:
Common shares authorized		600,000,000
Common shares, par value per share		$ 0.0033	$ 0.0033
Preferred shares authorized		50,000,000
Preferred shares, par value per share		$ 0.01
Common Shares:
Shares issued, beginning of year		171,672,408	169,560,591	168,255,572
Shares issued	[1]	1,001,667	1,493,524	811,732
Restricted shares issued, net of cancellations		433,774	618,293	493,287
Shares issued, end of year		173,107,849	171,672,408	169,560,591
Common shares held in treasury, end of year		(50,480,066)	(44,304,474)	(35,885,707)
Common shares outstanding, end of year		122,627,783	127,367,934	133,674,884
[1]	Includes shares issued from the exercise of stock options and stock appreciation rights, and shares issued from the employee share purchase plan.

Shareholders' Equity - Share re

Shareholders' Equity - Share repurchases and treasury shares (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Common shares held in treasury (shares)	50,480,066	44,304,474	35,885,707
Common shares held in treasury, at cost	$ 1,941,904	$ 1,562,019
Common shares
Class of Stock [Line Items]
Cumulative number of shares acquired since inception of share repurchase program	124,100,000
Aggregate purchase price of shares acquired since inception of share repurchase program	$ 3,610,000
Treasury stock, shares acquired (shares)	5,900,000	8,200,000	1,300,000
Treasury stock, value of shares acquired	$ 365,400	$ 454,100	$ 57,800
Remaining authorized repurchase amount	521,800
February 2007 | Common shares
Class of Stock [Line Items]
Share repurchase authorizations, amount	1,000,000
May 2008 | Common shares
Class of Stock [Line Items]
Share repurchase authorizations, amount	500,000
November 2009 | Common shares
Class of Stock [Line Items]
Share repurchase authorizations, amount	1,000,000
February 2011 | Common shares
Class of Stock [Line Items]
Share repurchase authorizations, amount	1,000,000
November 2014 | Common shares
Class of Stock [Line Items]
Share repurchase authorizations, amount	$ 629,200

Shareholders' Equity - Preferre

Shareholders' Equity - Preferred shares (Details) - USD ($) $ / shares in Units, $ in Thousands	May. 02, 2012	Apr. 02, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Shares issued - Series C					$ 315,800
Preferred dividends paid			$ 21,938	$ 21,938	$ 21,938
Series A and B Preferred Shares
Class of Stock [Line Items]
Preferred shares, redemption price per share	$ 25
Series A Preferred Stock
Class of Stock [Line Items]
Shares redeemed during period, value	$ 200,000
Preferred shares, dividend rate (as a percent)	8.00%
Series B Preferred Stock
Class of Stock [Line Items]
Shares redeemed during period, value	$ 125,000
Preferred shares, dividend rate (as a percent)	7.875%
Series C Preferred Stock
Class of Stock [Line Items]
Shares issued - Series C		$ 325,000
Preferred shares, dividend rate (as a percent)		6.75%	6.75%
Preferred shares, redemption price per share			$ 25

Share-Based Compensation - Long

Share-Based Compensation - Long Term Incentive Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
2015 Long Term Incentive And Share Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for issuance	4,300,000
Maximum number of incentive stock options	2,000,000
Shares available for issuance	3,242,692
2007 Long Term Incentive and Share Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance transferred	3,153,924
2007 Employee Share Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for issuance	2,250,000
Shares available for issuance	563,259
Length of offering period, in months	27 months
Maximum employee subscription rate	20.00%
Purchase price (percentage of market value)	85.00%
Maximum number of shares per employee	3,000
Maximum accumulation per calendar year	$ 25,000
Share based compensation expense	1,700,000	$ 1,600,000	$ 1,400,000
Tax benefit	$ 200,000	$ 100,000	$ 100,000
2012 Long Term Incentive and Share Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for issuance	4,280,000
Total number of shares reserved under plan	7,433,924
Maximum percentage of awards to be issued in connection with full value awarrds	50.00%
Maximum number of incentive stock options	2,000,000
Shares available for issuance	950,307

Share-Based Compensation - Valu

Share-Based Compensation - Valuation assumptions (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Dividend yield	0.00%	0.00%	0.00%
Expected volatility	22.10%	22.80%	23.60%
Risk free interest rate	1.80%	1.90%	1.00%
Expected option life	6 years	6 years	6 years

Share-Based Compensation - Stoc

Share-Based Compensation - Stock option activity (Details) - Stock Options	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Number of Options / SARs
Outstanding, beginning of year (in shares) | shares	7,804,033
Granted (in shares) | shares	693,107
Exercised (in shares) | shares	(926,958)
Forfeited or expired (in shares) | shares	(87,720)
Outstanding, end of year (in shares) | shares	7,482,462
Exercisable, end of year (in shares) | shares	5,429,047
Weighted Average Exercise Price
Outstanding, beginning of year, weighted average exercise price | $ / shares	$ 34.52
Granted, weighted average exercise price | $ / shares	61.93
Exercised, weighted average exercise price | $ / shares	24.91
Forfeited or expired, weighted average exercise price | $ / shares	50.09
Outstanding, end of year, weighted average exercise price | $ / shares	38.07
Exercisable, end of year, weighted average exercise price | $ / shares	$ 32.88

Share-Based Compensation - Rest

Share-Based Compensation - Restricted common shares and restricted stock units activity (Details)	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Restricted Common Shares
Unvested Shares:
Unvested balance, beginning of year (in shares) | shares	1,969,842
Granted (in shares) | shares	502,638
Vested (in shares) | shares	(603,023)
Forfeited (in shares) | shares	(68,864)
Unvested balance, end of year (in shares) | shares	1,800,593
Weighted Average Grant Date Fair Value:
Unvested balance, beginning of year, weighted average grant date fair value | $ / shares	$ 48.47
Granted, weighted average grant date fair value | $ / shares	62.70
Vested, weighted average grant date fair value | $ / shares	49.75
Forfeited, weighted average grant date fair value | $ / shares	50.45
Unvested balance, end of year, weighted average grant date fair value | $ / shares	$ 51.94
Restricted Unit Awards
Unvested Shares:
Unvested balance, beginning of year (in shares) | shares	305,133
Granted (in shares) | shares	69,340
Vested (in shares) | shares	(88,916)
Forfeited (in shares) | shares	(20,928)
Unvested balance, end of year (in shares) | shares	264,629
Weighted Average Grant Date Fair Value:
Unvested balance, beginning of year, weighted average grant date fair value | $ / shares	$ 48.49
Granted, weighted average grant date fair value | $ / shares	62.61
Vested, weighted average grant date fair value | $ / shares	50.94
Forfeited, weighted average grant date fair value | $ / shares	48.97
Unvested balance, end of year, weighted average grant date fair value | $ / shares	$ 51.33

Share-Based Compensation - Addi

Share-Based Compensation - Additional information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Life of award	10 years
Share based compensation expense	$ 10.5	$ 12.5	$ 10.6
Tax benefit	2.2	$ 2.1	$ 2
Unrecognized compensation cost related to unvested awards	$ 12
Expected period for recognition (years)	1 year 3 months 18 days
Weighted average grant date fair value	$ 15.90	$ 14.77	$ 12.96
Aggregate intrinsic value of options exercised	$ 38.6	$ 58.4	$ 21.7
Aggregate intrinsic value of options outstanding	237.1
Aggregate intrinsic value of options exercisable	$ 200.2
Options outstanding, weighted average remaining contractual term (in years)	5 years 4 months 24 days
Options exercisable, weighted average remaining contractual term (in years)	4 years 4 months 24 days
Proceeds from stock options exercised	$ 9.4
Tax benefit from stock options exercised	$ 8
Restricted Common Shares And Restricted Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Share based compensation expense	$ 32.9	30	27.4
Tax benefit	$ 8.6	$ 8.4	$ 7.8
Granted (in shares)	571,978	767,469	590,118
Granted, weighted average grant date fair value	$ 62.69	$ 56.97	$ 53.21
Aggregate fair value of awards that vested in the period	$ 43.8	$ 38.6	$ 41
Restricted Common Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 39.9
Expected period for recognition (years)	1 year 3 months 18 days
Granted (in shares)	502,638
Granted, weighted average grant date fair value	$ 62.70
Restricted Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested awards	$ 6.2
Expected period for recognition (years)	1 year 3 months 18 days
Granted (in shares)	69,340
Granted, weighted average grant date fair value	$ 62.61
Aggregate intrinsic value of awards outstanding	$ 28.8
Aggregate intrinsic value of awards exercisable	$ 10.4

Retirement Plans (Details)

Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Defined contribution plan, expense	$ 29.7	$ 26.8	$ 21.5

Statutory Information - Summar

Statutory Information - Summary of statutory capital, surplus and net income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Bermuda
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	$ 6,397,010	$ 6,447,803
Required statutory capital and surplus	[1]	2,129,064	2,209,757
Statutory net income (loss)		514,151	692,676	$ 719,267
Ireland
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	559,996	553,561
Required statutory capital and surplus	[1]	459,271	463,877
Statutory net income (loss)		29,041	43,197	(24,410)
United States
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	1,564,056	1,454,282
Required statutory capital and surplus	[1]	488,794	467,797
Statutory net income (loss)		76,604	46,110	62,605
United Kingdom
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	404,821	384,525
Required statutory capital and surplus	[1]	321,462	307,596
Statutory net income (loss)		3,285	13,016	(11,353)
Canada
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	67,436	79,123
Required statutory capital and surplus	[1]	36,360	58,837
Statutory net income (loss)		$ (1,098)	$ 1,517	$ (36,203)
[1]	Such amounts include ownership interests in affiliated insurance and reinsurance subsidiaries.

Statutory Information - Narrat

Statutory Information - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Bermuda
Statutory Accounting Practices [Line Items]
Required statutory capital and surplus	[1]	$ 2,129,064	$ 2,209,757
United States
Statutory Accounting Practices [Line Items]
Required statutory capital and surplus	[1]	$ 488,794	$ 467,797
Arch Re Bermuda | Bermuda
Statutory Accounting Practices [Line Items]
Dividends, percentage permitted		25.00%
Dividend required notice period		7 days
Capital reduction, percentage permitted		15.00%
Dividends available for payment in 2016 without prior regulatory approval		$ 1,360,000
Arch Re US | United States
Statutory Accounting Practices [Line Items]
Dividends available for payment in 2016, total		$ 120,000
Dividend restriction period		30 days
[1]	Such amounts include ownership interests in affiliated insurance and reinsurance subsidiaries.

Unaudited Condensed Quarterl115

Unaudited Condensed Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Net premiums written	$ 834,984	$ 971,972	$ 943,580	$ 1,066,995	$ 895,481	$ 959,539	$ 971,928	$ 1,064,990	$ 3,817,531	$ 3,891,938	$ 3,351,367
Net premiums earned	943,520	936,683	943,438	910,264	923,165	903,651	907,152	859,780	3,733,905	3,593,748	3,145,952
Net investment income	95,900	86,233	86,963	78,994	82,496	80,105	72,990	66,994	348,090	302,585	267,219
Net realized gains (losses)	(143,767)	(89,698)	(35,725)	83,348	10,561	18,515	54,144	19,697	(185,842)	102,917	74,018
Net impairment losses recognized in earnings	(7,336)	(5,868)	(1,113)	(5,799)	(3,837)	(8,593)	(14,749)	(2,971)	(20,116)	(30,150)	(3,786)
Underwriting Income Loss Segment	113,143	94,779	105,114	116,471	113,464	101,087	124,091	132,456	429,507	471,098	451,737
Net income (loss)	58,579	80,033	115,790	283,336	215,164	228,675	208,016	182,500	526,582	821,260	709,731
Preferred dividends	(5,485)	(5,484)	(5,485)	(5,484)	(5,485)	(5,484)	(5,485)	(5,484)	(21,938)	(21,938)	(21,938)
Net income available to Arch common shareholders	$ 53,094	$ 74,549	$ 110,305	$ 277,852	$ 209,679	$ 223,191	$ 202,531	$ 177,016	$ 515,800	$ 812,417	$ 687,793
Basic (per share)	$ 0.44	$ 0.62	$ 0.91	$ 2.24	$ 1.65	$ 1.69	$ 1.53	$ 1.34	$ 4.24	$ 6.21	$ 5.24
Diluted (per share)	$ 0.42	$ 0.60	$ 0.88	$ 2.16	$ 1.60	$ 1.64	$ 1.48	$ 1.30	$ 4.09	$ 6.02	$ 5.07

Guarantor Financial Informat116

Guarantor Financial Information - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Total investments	$ 15,842,941	$ 15,320,770
Cash	553,326	485,702	$ 434,057	$ 371,041
Investment in subsidiaries	0	0
Due from subsidiaries and affiliates	0	0
Premiums receivable	983,443	948,695
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	1,867,373	1,812,845
Contractholder receivables	1,486,296	1,309,192
Prepaid reinsurance premiums	427,609	377,078
Deferred acquisition costs, net	433,477	414,525
Other assets	1,582,805	1,337,274
Total assets	23,177,270	22,006,081	19,557,054
Liabilities
Reserve for losses and loss adjustment expenses	9,125,250	9,036,448	8,824,696	8,933,292
Unearned premiums	2,333,932	2,231,578
Reinsurance balances payable	224,120	219,312
Contractholder payables	1,486,296	1,309,192
Collateral held for insured obligations	248,982	184,219
Deposit accounting liabilities	260,364	327,384
Senior notes	791,306	791,141
Revolving credit agreement borrowings	530,434	100,000
Due to subsidiaries and affiliates	0	0
Other liabilities	1,027,692	688,161
Total liabilities	16,028,376	14,887,435	13,909,558
Redeemable noncontrolling interests	205,182	219,512
Shareholders’ Equity
Total shareholders' equity available to Arch	6,204,881	6,130,053	5,647,496
Non-redeemable noncontrolling interests	738,831	769,081	0
Total shareholders' equity	6,943,712	6,899,134	5,647,496
Total liabilities, noncontrolling interests and shareholders' equity	23,177,270	22,006,081
Reportable legal entities | ACGL (Parent Guarantor)
Assets
Total investments	50	107
Cash	6,809	3,218	3,223	6,417
Investment in subsidiaries	6,609,174	6,536,644
Due from subsidiaries and affiliates	23	48
Premiums receivable	0	0
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	0	0
Contractholder receivables	0	0
Prepaid reinsurance premiums	0	0
Deferred acquisition costs, net	0	0
Other assets	4,138	4,386
Total assets	6,620,194	6,544,403
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
Deposit accounting liabilities	$ 0	$ 0
Senior notes	296,874	296,796
Revolving credit agreement borrowings	100,000	100,000
Due to subsidiaries and affiliates	26	417
Other liabilities	18,413	17,137
Total liabilities	415,313	414,350
Redeemable noncontrolling interests	0	0
Shareholders’ Equity
Total shareholders' equity available to Arch	6,204,881	6,130,053
Non-redeemable noncontrolling interests	0	0
Total shareholders' equity	6,204,881	6,130,053
Total liabilities, noncontrolling interests and shareholders' equity	6,620,194	6,544,403
Reportable legal entities | Arch-U.S. (Subsidiary Issuer)
Assets
Total investments	42,210	62,867
Cash	17,023	2,787	509	612
Investment in subsidiaries	1,712,757	1,685,185
Due from subsidiaries and affiliates	48,811	7,517
Premiums receivable	0	0
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	0	0
Contractholder receivables	0	0
Prepaid reinsurance premiums	0	0
Deferred acquisition costs, net	0	0
Other assets	45,522	43,921
Total assets	1,866,323	1,802,277
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
Deposit accounting liabilities	$ 0	$ 0
Senior notes	494,432	494,345
Revolving credit agreement borrowings	0	0
Due to subsidiaries and affiliates	35,000	7,505
Other liabilities	50,890	49,403
Total liabilities	580,322	551,253
Redeemable noncontrolling interests	0	0
Shareholders’ Equity
Total shareholders' equity available to Arch	1,286,001	1,251,024
Non-redeemable noncontrolling interests	0	0
Total shareholders' equity	1,286,001	1,251,024
Total liabilities, noncontrolling interests and shareholders' equity	1,866,323	1,802,277
Reportable legal entities | Other ACGL Subsidiaries
Assets
Total investments	15,815,381	15,257,796
Cash	529,494	479,697	430,325	364,012
Investment in subsidiaries	0	0
Due from subsidiaries and affiliates	384,469	370,429
Premiums receivable	1,376,310	1,331,511
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	5,783,452	5,584,973
Contractholder receivables	1,486,296	1,309,192
Prepaid reinsurance premiums	1,511,795	1,373,008
Deferred acquisition costs, net	433,477	414,525
Other assets	2,119,279	1,705,546
Total assets	29,439,953	27,826,677
Liabilities
Reserve for losses and loss adjustment expenses	13,010,608	12,784,030
Unearned premiums	3,418,118	3,227,508
Reinsurance balances payable	603,586	589,289
Contractholder payables	1,486,296	1,309,192
Collateral held for insured obligations	248,982	184,219
Deposit accounting liabilities	463,507	587,050
Senior notes	0	0
Revolving credit agreement borrowings	430,434	0
Due to subsidiaries and affiliates	398,277	370,072
Other liabilities	1,385,500	815,919
Total liabilities	21,445,308	19,867,279
Redeemable noncontrolling interests	219,882	219,512
Shareholders’ Equity
Total shareholders' equity available to Arch	7,035,932	6,970,805
Non-redeemable noncontrolling interests	738,831	769,081
Total shareholders' equity	7,774,763	7,739,886
Total liabilities, noncontrolling interests and shareholders' equity	29,439,953	27,826,677
Consolidating adjustments and eliminations
Assets
Total investments	(14,700)	0
Cash	0	0	$ 0	$ 0
Investment in subsidiaries	(8,321,931)	(8,221,829)
Due from subsidiaries and affiliates	(433,303)	(377,994)
Premiums receivable	(392,867)	(382,816)
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	(3,916,079)	(3,772,128)
Contractholder receivables	0	0
Prepaid reinsurance premiums	(1,084,186)	(995,930)
Deferred acquisition costs, net	0	0
Other assets	(586,134)	(416,579)
Total assets	(14,749,200)	(14,167,276)
Liabilities
Reserve for losses and loss adjustment expenses	(3,885,358)	(3,747,582)
Unearned premiums	(1,084,186)	(995,930)
Reinsurance balances payable	(379,466)	(369,977)
Contractholder payables	$ 0	$ 0
Collateral held for insured obligations
Deposit accounting liabilities	$ (203,143)	$ (259,666)
Senior notes	0	0
Revolving credit agreement borrowings	0	0
Due to subsidiaries and affiliates	(433,303)	(377,994)
Other liabilities	(427,111)	(194,298)
Total liabilities	(6,412,567)	(5,945,447)
Redeemable noncontrolling interests	(14,700)	0
Shareholders’ Equity
Total shareholders' equity available to Arch	(8,321,933)	(8,221,829)
Non-redeemable noncontrolling interests	0	0
Total shareholders' equity	(8,321,933)	(8,221,829)
Total liabilities, noncontrolling interests and shareholders' equity	$ (14,749,200)	$ (14,167,276)

Guarantor Financial Informat117

Guarantor Financial Information - Condensed consolidating statement of income and comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues
Net premiums earned	$ 943,520	$ 936,683	$ 943,438	$ 910,264	$ 923,165	$ 903,651	$ 907,152	$ 859,780	$ 3,733,905	$ 3,593,748	$ 3,145,952
Net investment income	95,900	86,233	86,963	78,994	82,496	80,105	72,990	66,994	348,090	302,585	267,219
Net realized gains (losses)	(143,767)	(89,698)	(35,725)	83,348	10,561	18,515	54,144	19,697	(185,842)	102,917	74,018
Net impairment losses recognized in earnings	(7,336)	(5,868)	(1,113)	(5,799)	(3,837)	(8,593)	(14,749)	(2,971)	(20,116)	(30,150)	(3,786)
Other underwriting income									35,497	10,142	7,639
Equity in net income of investment funds accounted for using the equity method									25,455	19,883	35,701
Other income (loss)									(399)	(10,252)	(586)
Total revenues									3,936,590	3,988,873	3,526,157
Expenses
Losses and loss adjustment expenses									2,050,903	1,919,250	1,679,424
Acquisition expenses									681,476	657,262	564,103
Other operating expenses									657,261	606,224	500,730
Interest expense									45,874	45,634	27,060
Net foreign exchange (gains) losses									(66,118)	(83,744)	12,335
Total expenses									3,369,396	3,144,626	2,783,652
Income (loss) before income taxes									567,194	844,247	742,505
Income tax expense									(40,612)	(22,987)	(32,774)
Income (loss) before equity in net income of subsidiaries									526,582	821,260	709,731
Equity in net income of subsidiaries									0	0	0
Net income	58,579	80,033	115,790	283,336	215,164	228,675	208,016	182,500	526,582	821,260	709,731
Net (income) loss attributable to noncontrolling interests									11,156	13,095	0
Net income available to Arch									537,738	834,355	709,731
Preferred dividends	(5,485)	(5,484)	(5,485)	(5,484)	(5,485)	(5,484)	(5,485)	(5,484)	(21,938)	(21,938)	(21,938)
Net income available to Arch common shareholders	$ 53,094	$ 74,549	$ 110,305	$ 277,852	$ 209,679	$ 223,191	$ 202,531	$ 177,016	515,800	812,417	687,793
Comprehensive Income									392,380	888,247	497,678
Reportable legal entities | ACGL (Parent Guarantor)
Revenues
Net premiums earned									0	0	0
Net investment income									1	0	0
Net realized gains (losses)									0	0	0
Net impairment losses recognized in earnings									0	0	0
Other underwriting income									0	0	0
Equity in net income of investment funds accounted for using the equity method									0	0	0
Other income (loss)									0	0	0
Total revenues									1	0	0
Expenses
Losses and loss adjustment expenses									0	0	0
Acquisition expenses									0	0	0
Other operating expenses									48,107	46,074	38,702
Interest expense									23,450	23,423	23,272
Net foreign exchange (gains) losses									0	0	0
Total expenses									71,557	69,497	61,974
Income (loss) before income taxes									(71,556)	(69,497)	(61,974)
Income tax expense									0	0	0
Income (loss) before equity in net income of subsidiaries									(71,556)	(69,497)	(61,974)
Equity in net income of subsidiaries									609,294	903,852	771,705
Net income									537,738	834,355	709,731
Net (income) loss attributable to noncontrolling interests									0	0	0
Net income available to Arch									537,738	834,355	709,731
Preferred dividends									(21,938)	(21,938)	(21,938)
Net income available to Arch common shareholders									515,800	812,417	687,793
Comprehensive Income									392,380	888,247	497,678
Reportable legal entities | Arch-U.S. (Subsidiary Issuer)
Revenues
Net premiums earned									0	0	0
Net investment income									2,342	0	31
Net realized gains (losses)									1	5	0
Net impairment losses recognized in earnings									0	0	0
Other underwriting income									0	0	0
Equity in net income of investment funds accounted for using the equity method									0	0	0
Other income (loss)									0	0	0
Total revenues									2,343	5	31
Expenses
Losses and loss adjustment expenses									0	0	0
Acquisition expenses									0	0	0
Other operating expenses									3,689	3,387	2,691
Interest expense									26,502	25,817	1,316
Net foreign exchange (gains) losses									0	0	0
Total expenses									30,191	29,204	4,007
Income (loss) before income taxes									(27,848)	(29,199)	(3,976)
Income tax expense									9,732	10,125	1,383
Income (loss) before equity in net income of subsidiaries									(18,116)	(19,074)	(2,593)
Equity in net income of subsidiaries									50,156	53,584	25,644
Net income									32,040	34,510	23,051
Net (income) loss attributable to noncontrolling interests									0	0	0
Net income available to Arch									32,040	34,510	23,051
Preferred dividends									0	0	0
Net income available to Arch common shareholders									32,040	34,510	23,051
Comprehensive Income									838	33,671	(28,330)
Reportable legal entities | Other ACGL Subsidiaries
Revenues
Net premiums earned									3,733,905	3,593,748	3,145,952
Net investment income									368,413	326,831	307,449
Net realized gains (losses)									(185,843)	102,912	74,018
Net impairment losses recognized in earnings									(20,116)	(30,150)	(3,786)
Other underwriting income									35,739	10,142	7,639
Equity in net income of investment funds accounted for using the equity method									25,455	19,883	35,701
Other income (loss)									(399)	(10,252)	(586)
Total revenues									3,957,154	4,013,114	3,566,387
Expenses
Losses and loss adjustment expenses									2,050,903	1,919,250	1,679,424
Acquisition expenses									681,476	657,262	564,103
Other operating expenses									605,465	556,763	459,337
Interest expense									18,024	20,640	42,733
Net foreign exchange (gains) losses									(41,622)	(53,222)	2,145
Total expenses									3,314,246	3,100,693	2,747,742
Income (loss) before income taxes									642,908	912,421	818,645
Income tax expense									(50,344)	(33,112)	(34,157)
Income (loss) before equity in net income of subsidiaries									592,564	879,309	784,488
Equity in net income of subsidiaries									0	0	0
Net income									592,564	879,309	784,488
Net (income) loss attributable to noncontrolling interests									10,351	13,095	0
Net income available to Arch									602,915	892,404	784,488
Preferred dividends									0	0	0
Net income available to Arch common shareholders									602,915	892,404	784,488
Comprehensive Income									482,047	976,821	562,245
Consolidating adjustments and eliminations
Revenues
Net premiums earned									0	0	0
Net investment income									(22,666)	(24,246)	(40,261)
Net realized gains (losses)									0	0	0
Net impairment losses recognized in earnings									0	0	0
Other underwriting income									(242)	0	0
Equity in net income of investment funds accounted for using the equity method									0	0	0
Other income (loss)									0	0	0
Total revenues									(22,908)	(24,246)	(40,261)
Expenses
Losses and loss adjustment expenses									0	0	0
Acquisition expenses									0	0	0
Other operating expenses									0	0	0
Interest expense									(22,102)	(24,246)	(40,261)
Net foreign exchange (gains) losses									(24,496)	(30,522)	10,190
Total expenses									(46,598)	(54,768)	(30,071)
Income (loss) before income taxes									23,690	30,522	(10,190)
Income tax expense									0	0	0
Income (loss) before equity in net income of subsidiaries									23,690	30,522	(10,190)
Equity in net income of subsidiaries									(659,450)	(957,436)	(797,349)
Net income									(635,760)	(926,914)	(807,539)
Net (income) loss attributable to noncontrolling interests									805	0	0
Net income available to Arch									(634,955)	(926,914)	(807,539)
Preferred dividends									0	0	0
Net income available to Arch common shareholders									(634,955)	(926,914)	(807,539)
Comprehensive Income									$ (482,885)	$ (1,010,492)	$ (533,915)

Guarantor Financial Informat118

Guarantor Financial Information - Condensed consolidating statement of cash flows (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net Cash Provided by (Used in) Operating Activities		$ 997,906	$ 1,037,130	$ 850,868
Investing Activities
Purchases of fixed maturity investments		(29,451,873)	(28,745,279)	(18,174,988)
Purchases of equity securities		(515,413)	(520,817)	(535,857)
Purchases of other investments		(1,749,525)	(1,590,648)	(994,185)
Proceeds from the sale of fixed maturity investments		28,094,047	26,823,189	17,194,635
Proceeds from the sale of equity securities		564,011	411,362	462,787
Proceeds from sales, redemptions and maturities of other investments		1,250,883	941,798	817,648
Proceeds from redemptions and maturities of fixed maturity investments		748,529	762,995	731,708
Net settlements of derivative instruments		(5,056)	34,372	14,494
Proceeds from investment in joint venture		40,000	0	0
Net (purchases) sales of short-term investments		169,095	577,126	(750,613)
Change in cash collateral related to securities lending		(6,662)	57,470	(55,643)
Contributions to subsidiaries		0	0	0
Intercompany loans issued		0	0	0
Purchase of business, net of cash acquired		818	(237,106)	0
Purchases of fixed assets		(15,736)	(19,883)	(17,499)
Change in other assets		(36,993)	0	0
Net Cash Used For Investing Activities		(913,875)	(1,505,421)	(1,307,513)
Financing Activities
Purchases of common shares under share repurchase program		(365,383)	(454,137)	(57,796)
Proceeds from common shares issued, net		4,861	6,827	3,051
Proceeds from intercompany loans		0	0	0
Repayments of intercompany loans			0
Proceeds from borrowings		431,362	0	494,228
Change in cash collateral related to securities lending		6,662	(57,470)	55,643
Third party investment in non-redeemable noncontrolling interests		0	796,903	0
Third party investment in redeemable noncontrolling interests		0	219,233	0
Dividends paid to redeemable noncontrolling interests		(18,307)	(14,448)	0
Dividends paid to parent	[1]	0	0	0
Other		(41,913)	64,973	50,830
Preferred dividends paid		(21,938)	(21,938)	(21,938)
Net Cash Provided By (Used For) Financing Activities		(4,656)	539,943	524,018
Effects of exchange rate changes on foreign currency cash		(11,751)	(20,007)	(4,357)
Increase (decrease) in cash		67,624	51,645	63,016
Cash beginning of year		485,702	434,057	371,041
Cash end of year		553,326	485,702	434,057
Reportable legal entities | ACGL (Parent Guarantor)
Operating Activities
Net Cash Provided by (Used in) Operating Activities		404,144	467,091	68,562
Investing Activities
Purchases of fixed maturity investments		0	0	0
Purchases of equity securities		(8,070)	0	0
Purchases of other investments		0	0	0
Proceeds from the sale of fixed maturity investments		0	0	0
Proceeds from the sale of equity securities		0	0	0
Proceeds from sales, redemptions and maturities of other investments		0	0	0
Proceeds from redemptions and maturities of fixed maturity investments		0	0	0
Net settlements of derivative instruments		0	0	0
Proceeds from investment in joint venture		0
Net (purchases) sales of short-term investments		57	2,423	5,799
Change in cash collateral related to securities lending		0	0	0
Contributions to subsidiaries		(10,000)	0	(160)
Intercompany loans issued		0	0	0
Purchase of business, net of cash acquired		0	0
Purchases of fixed assets		(80)	(271)	(712)
Change in other assets		0
Net Cash Used For Investing Activities		(18,093)	2,152	4,927
Financing Activities
Purchases of common shares under share repurchase program		(365,383)	(454,137)	(57,796)
Proceeds from common shares issued, net		4,861	6,827	3,051
Proceeds from intercompany loans		0	0	0
Repayments of intercompany loans			0
Proceeds from borrowings		0		0
Change in cash collateral related to securities lending		0	0	0
Third party investment in non-redeemable noncontrolling interests			0
Third party investment in redeemable noncontrolling interests			0
Dividends paid to redeemable noncontrolling interests		0	0
Dividends paid to parent	[1]	0	0	0
Other		0	0	0
Preferred dividends paid		(21,938)	(21,938)	(21,938)
Net Cash Provided By (Used For) Financing Activities		(382,460)	(469,248)	(76,683)
Effects of exchange rate changes on foreign currency cash		0	0	0
Increase (decrease) in cash		3,591	(5)	(3,194)
Cash beginning of year		3,218	3,223	6,417
Cash end of year		6,809	3,218	3,223
Reportable legal entities | Arch-U.S. (Subsidiary Issuer)
Operating Activities
Net Cash Provided by (Used in) Operating Activities		5,505	8,142	(6,569)
Investing Activities
Purchases of fixed maturity investments		(3,505)	(78,509)	0
Purchases of equity securities		0	0	0
Purchases of other investments		0	0	0
Proceeds from the sale of fixed maturity investments		24,507	16,011	0
Proceeds from the sale of equity securities		0	0	0
Proceeds from sales, redemptions and maturities of other investments		0	0	0
Proceeds from redemptions and maturities of fixed maturity investments		0	0	0
Net settlements of derivative instruments		0	0	0
Proceeds from investment in joint venture		0
Net (purchases) sales of short-term investments		(338)	408,591	(400,162)
Change in cash collateral related to securities lending		0	0	0
Contributions to subsidiaries		0	(341,707)	(97,850)
Intercompany loans issued		(39,500)	(7,500)	0
Purchase of business, net of cash acquired		0	0
Purchases of fixed assets		0	0	0
Change in other assets		0
Net Cash Used For Investing Activities		(18,836)	(3,114)	(498,012)
Financing Activities
Purchases of common shares under share repurchase program		0	0	0
Proceeds from common shares issued, net		0	0	0
Proceeds from intercompany loans		27,500	7,500	10,250
Repayments of intercompany loans			(10,250)
Proceeds from borrowings		0		494,228
Change in cash collateral related to securities lending		0	0	0
Third party investment in non-redeemable noncontrolling interests			0
Third party investment in redeemable noncontrolling interests			0
Dividends paid to redeemable noncontrolling interests		0	0
Dividends paid to parent	[1]	0	0	0
Other		67	0	0
Preferred dividends paid		0	0	0
Net Cash Provided By (Used For) Financing Activities		27,567	(2,750)	504,478
Effects of exchange rate changes on foreign currency cash		0	0	0
Increase (decrease) in cash		14,236	2,278	(103)
Cash beginning of year		2,787	509	612
Cash end of year		17,023	2,787	509
Reportable legal entities | Other ACGL Subsidiaries
Operating Activities
Net Cash Provided by (Used in) Operating Activities		1,074,021	1,077,597	908,375
Investing Activities
Purchases of fixed maturity investments		(29,448,368)	(28,666,770)	(18,174,988)
Purchases of equity securities		(507,343)	(520,817)	(535,857)
Purchases of other investments		(1,749,525)	(1,590,648)	(994,185)
Proceeds from the sale of fixed maturity investments		28,069,540	26,807,178	17,194,635
Proceeds from the sale of equity securities		564,011	411,362	462,787
Proceeds from sales, redemptions and maturities of other investments		1,250,883	941,798	817,648
Proceeds from redemptions and maturities of fixed maturity investments		748,529	762,995	731,708
Net settlements of derivative instruments		(5,056)	34,372	14,494
Proceeds from investment in joint venture		40,000
Net (purchases) sales of short-term investments		169,376	166,112	(356,250)
Change in cash collateral related to securities lending		(6,662)	57,470	(55,643)
Contributions to subsidiaries		(49,348)	(128,825)	(20,250)
Intercompany loans issued		(27,500)	31,464	(10,250)
Purchase of business, net of cash acquired		818	(237,106)
Purchases of fixed assets		(15,656)	(19,612)	(16,787)
Change in other assets		(36,993)
Net Cash Used For Investing Activities		(1,003,294)	(1,951,027)	(942,938)
Financing Activities
Purchases of common shares under share repurchase program		0	0	0
Proceeds from common shares issued, net		59,348	470,532	118,260
Proceeds from intercompany loans		39,500	7,500	0
Repayments of intercompany loans			(28,714)
Proceeds from borrowings		431,362		0
Change in cash collateral related to securities lending		6,662	(57,470)	55,643
Third party investment in non-redeemable noncontrolling interests			796,903
Third party investment in redeemable noncontrolling interests			219,233
Dividends paid to redeemable noncontrolling interests		(19,263)	(14,448)
Dividends paid to parent	[1]	(484,808)	(515,700)	(119,500)
Other		(41,980)	64,973	50,830
Preferred dividends paid		0	0	0
Net Cash Provided By (Used For) Financing Activities		(9,179)	942,809	105,233
Effects of exchange rate changes on foreign currency cash		(11,751)	(20,007)	(4,357)
Increase (decrease) in cash		49,797	49,372	66,313
Cash beginning of year		479,697	430,325	364,012
Cash end of year		529,494	479,697	430,325
Consolidating adjustments and eliminations
Operating Activities
Net Cash Provided by (Used in) Operating Activities		(485,764)	(515,700)	(119,500)
Investing Activities
Purchases of fixed maturity investments		0	0	0
Purchases of equity securities		0	0	0
Purchases of other investments		0	0	0
Proceeds from the sale of fixed maturity investments		0	0	0
Proceeds from the sale of equity securities		0	0	0
Proceeds from sales, redemptions and maturities of other investments		0	0	0
Proceeds from redemptions and maturities of fixed maturity investments		0	0	0
Net settlements of derivative instruments		0	0	0
Proceeds from investment in joint venture		0
Net (purchases) sales of short-term investments		0	0	0
Change in cash collateral related to securities lending		0	0	0
Contributions to subsidiaries		59,348	470,532	118,260
Intercompany loans issued		67,000	(23,964)	10,250
Purchase of business, net of cash acquired		0	0
Purchases of fixed assets		0	0	0
Change in other assets		0
Net Cash Used For Investing Activities		126,348	446,568	128,510
Financing Activities
Purchases of common shares under share repurchase program		0	0	0
Proceeds from common shares issued, net		(59,348)	(470,532)	(118,260)
Proceeds from intercompany loans		(67,000)	(15,000)	(10,250)
Repayments of intercompany loans			38,964
Proceeds from borrowings		0		0
Change in cash collateral related to securities lending		0	0	0
Third party investment in non-redeemable noncontrolling interests			0
Third party investment in redeemable noncontrolling interests			0
Dividends paid to redeemable noncontrolling interests		956	0
Dividends paid to parent	[1]	484,808	515,700	119,500
Other		0	0	0
Preferred dividends paid		0	0	0
Net Cash Provided By (Used For) Financing Activities		359,416	69,132	(9,010)
Effects of exchange rate changes on foreign currency cash		0	0	0
Increase (decrease) in cash		0	0	0
Cash beginning of year		0	0	0
Cash end of year		$ 0	$ 0	$ 0
[1]	Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.

Schedule III - Supplementary119

Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs, Net		$ 433,477	$ 414,525	$ 342,314
Reserves for Losses and Loss Adjustment Expenses		9,125,250	9,036,448	8,824,696
Unearned Premiums		2,333,932	2,231,578	1,896,365
Net Premiums Earned		3,733,905	3,593,748	3,145,952
Net Losses and Loss Adjustment Expenses Incurred		2,050,903	1,919,250	1,679,424
Amortization of Deferred Acquisition Costs		681,476	657,262	564,103
Other Operating Expenses	[1]	607,516	556,280	458,327
Net Premiums Written		3,817,531	3,891,938	3,351,367
Insurance
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs, Net		166,771	178,545	158,121
Reserves for Losses and Loss Adjustment Expenses		6,050,922	6,161,500	6,137,121
Unearned Premiums		1,217,490	1,237,099	1,192,188
Net Premiums Earned		2,044,808	2,017,370	1,876,014
Net Losses and Loss Adjustment Expenses Incurred		1,292,647	1,260,953	1,188,445
Amortization of Deferred Acquisition Costs		299,317	316,308	311,904
Other Operating Expenses	[1]	354,416	335,157	315,387
Net Premiums Written		2,045,671	2,146,654	1,948,796
Reinsurance
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs, Net		138,184	148,130	167,642
Reserves for Losses and Loss Adjustment Expenses		2,672,044	2,690,070	2,680,288
Unearned Premiums		650,138	666,233	612,725
Net Premiums Earned		1,077,135	1,279,328	1,218,672
Net Losses and Loss Adjustment Expenses Incurred		440,350	532,450	486,236
Amortization of Deferred Acquisition Costs		223,632	261,438	234,373
Other Operating Expenses	[1]	155,811	147,964	134,563
Net Premiums Written		1,038,408	1,265,991	1,313,001
Mortgage
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs, Net		53,079	38,321	16,551
Reserves for Losses and Loss Adjustment Expenses		111,287	118,550	7,287
Unearned Premiums		216,324	148,232	91,452
Net Premiums Earned		214,110	193,573	51,266
Net Losses and Loss Adjustment Expenses Incurred		40,247	55,674	4,743
Amortization of Deferred Acquisition Costs		45,076	49,400	17,826
Other Operating Expenses	[1]	82,370	66,891	8,377
Net Premiums Written		267,493	204,837	$ 89,570
Other
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs, Net		75,443	49,529
Reserves for Losses and Loss Adjustment Expenses		290,997	66,328
Unearned Premiums		249,980	180,014
Net Premiums Earned		397,852	103,477
Net Losses and Loss Adjustment Expenses Incurred		277,659	70,173
Amortization of Deferred Acquisition Costs		113,451	30,116
Other Operating Expenses	[1]	14,919	6,268
Net Premiums Written		$ 465,959	$ 274,456
[1]	Certain other operating expenses relate to the Company’s corporate segment (non-underwriting). Such amounts are not reflected in the table above. See Note 5.

Schedule IV - Reinsurance (Deta

Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount										$ 3,086,919		$ 3,100,946		$ 2,754,582
Ceded to other Companies										(979,632)		(948,678)		(845,256)
Assumed From Other Companies										1,710,244		1,739,670		1,442,041
Net Amount		$ 834,984	$ 971,972	$ 943,580	$ 1,066,995	$ 895,481	$ 959,539	$ 971,928	$ 1,064,990	$ 3,817,531		$ 3,891,938		$ 3,351,367
Percentage of Amount Assumed to Net										44.80%		44.70%		43.00%
Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount										$ 2,908,906		$ 2,974,996		$ 2,682,446
Ceded to other Companies	[1]									(898,347)		(862,015)		(763,713)
Assumed From Other Companies	[1]									35,112		33,673		30,063
Net Amount										$ 2,045,671		$ 2,146,654		$ 1,948,796
Percentage of Amount Assumed to Net										1.70%		1.60%		1.50%
Reinsurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount										$ 28,510		$ 22,405		$ 72,136
Ceded to other Companies	[1]									(380,614)		(261,255)		(86,620)
Assumed From Other Companies	[1]									1,390,512		1,504,841		1,327,485
Net Amount										$ 1,038,408		$ 1,265,991		$ 1,313,001
Percentage of Amount Assumed to Net										133.90%		118.90%		101.10%
Mortgage
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount										$ 137,338		$ 103,545		$ 0
Ceded to other Companies	[1]									(28,064)		(22,519)		0
Assumed From Other Companies	[1]									158,219		123,811		89,570
Net Amount										$ 267,493		$ 204,837		$ 89,570
Percentage of Amount Assumed to Net										59.10%		60.40%		100.00%
Other
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount										$ 12,165		$ 0
Ceded to other Companies										(22,940)	[1]	(14,171)	[1]	$ 0
Assumed From Other Companies	[1]									476,734		288,627
Net Amount										$ 465,959		$ 274,456		$ 0
Percentage of Amount Assumed to Net										102.30%		105.20%
[1]	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions and are included in the gross premiums written of each segment. 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.

Schedule VI - Supplementary 121

Schedule VI - Supplementary Information For Property and Casualty Insurance Underwriters (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Net investment income	$ 95,900	$ 86,233	$ 86,963	$ 78,994	$ 82,496	$ 80,105	$ 72,990	$ 66,994	$ 348,090	$ 302,585	$ 267,219
Net Losees and Loss Adjustment Expenses Incurred Related to Current Year									2,336,026	2,246,152	1,943,466
Net Losees and Loss Adjustment Expenses Incurred Related to Prior Years									(285,123)	(326,902)	(264,042)
Consolidated Subsidiaries
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Acquisition Costs, Net	433,477				414,525				433,477	414,525	342,314
Reserves for Losses and Loss Adjustment Expenses	9,125,250				9,036,448				9,125,250	9,036,448	8,824,696
Discount, if any, deducted in Column C	16,789				14,732				16,789	14,732	12,539
Unearned Premiums	$ 2,333,932				$ 2,231,578				2,333,932	2,231,578	1,896,365
Net Premiums Earned									3,733,905	3,593,748	3,145,952
Net investment income									348,090	302,585	267,219
Net Losees and Loss Adjustment Expenses Incurred Related to Current Year									2,336,026	2,246,152	1,943,466
Net Losees and Loss Adjustment Expenses Incurred Related to Prior Years									(285,123)	(326,902)	(264,042)
Amortization of Deferred Acquisition Costs									681,476	657,262	564,103
Net Paid Losses and Loss Adjustment Expenses									1,869,244	1,697,736	1,708,817
Net Premiums Written									$ 3,817,531	$ 3,891,938	$ 3,351,367