Arch Capital (ACGL) 10-Q 5 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	May 01, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	ARCH CAPITAL GROUP LTD.
Entity Central Index Key	947,484
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		123,069,706

Unaudited Consolidated Balance

Unaudited Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investments:
Fixed maturities available for sale, at fair value (amortized cost: $13,767,375 and $13,522,671)	$ 13,745,932	$ 13,426,577
Short-term investments available for sale, at fair value (amortized cost: $803,624 and $611,878)	803,619	612,005
Collateral received under securities lending, at fair value (amortized cost: $538,353 and $762,554)	538,361	762,565
Equity securities available for sale, at fair value (cost: $369,189 and $475,085)	428,594	518,041
Other investments available for sale, at fair value (cost: $197,431 and $149,077)	228,437	167,970
Investments accounted for using the fair value option	3,648,120	3,421,220
Investments accounted for using the equity method	861,607	811,273
Total investments	20,254,670	19,719,651
Cash	703,754	842,942
Accrued investment income	104,168	124,483
Securities pledged under securities lending, at fair value (amortized cost: $524,758 and $746,409)	525,569	744,980
Premiums receivable	1,254,048	1,072,435
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	2,133,148	2,114,138
Contractholder receivables	1,766,340	1,717,436
Ceded unearned premiums	941,923	859,567
Deferred acquisition costs	487,925	447,560
Receivable for securities sold	239,678	58,284
Goodwill and intangible assets	750,315	781,553
Other assets	930,688	889,080
Total assets	30,092,226	29,372,109
Liabilities
Reserve for losses and loss adjustment expenses	10,296,821	10,200,960
Unearned premiums	3,631,259	3,406,870
Reinsurance balances payable	321,285	300,407
Contractholder payables	1,766,340	1,717,436
Collateral held for insured obligations	327,161	301,406
Senior notes	1,732,410	1,732,258
Revolving credit agreement borrowings	734,961	756,650
Securities lending payable	538,353	762,554
Payable for securities purchased	389,649	76,183
Other liabilities	674,313	806,260
Total liabilities	20,412,552	20,060,984
Commitments and Contingencies
Redeemable noncontrolling interests	205,644	205,553
Shareholders' Equity
Non-cumulative preferred shares	772,555	772,555
Convertible non-voting common equivalent preferred shares	1,101,304	1,101,304
Common shares ($0.0033 par, shares issued: 174,935,104 and 174,644,101)	583	582
Additional paid-in capital	548,053	531,687
Retained earnings	8,238,296	7,996,701
Accumulated other comprehensive income (loss), net of deferred income tax	(15,677)	(114,541)
Common shares held in treasury, at cost (shares: 51,907,618 and 51,856,584)	(2,039,270)	(2,034,570)
Total shareholders' equity available to Arch	8,605,844	8,253,718
Non-redeemable noncontrolling interests	868,186	851,854
Total shareholders' equity	9,474,030	9,105,572
Total liabilities, noncontrolling interests and shareholders' equity	$ 30,092,226	$ 29,372,109

Unaudited Consolidated Balance3

Unaudited Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fixed maturities available for sale, at amortized cost	$ 13,767,375	$ 13,522,671
Short-term investments available for sale, at amortized cost	803,624	611,878
Collateral received under securities lending, at amortized cost	538,353	762,554
Equity securities available for sale, at cost	369,189	475,085
Other investments available for sale, at cost	197,431	149,077
Securities pledged under securities lending, at amortized cost	$ 524,758	$ 746,409
Common shares, par value per share	$ 0.0033	$ 0.0033
Common shares issued (shares)	174,935,104	174,644,101
Common shares held in treasury (shares)	51,907,618	51,856,584

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues
Net premiums written	$ 1,276,260	$ 1,121,235
Change in unearned premiums	(159,243)	(169,656)
Net premiums earned	1,117,017	951,579
Net investment income	117,874	93,735
Net realized gains (losses)	34,153	37,324
Other-than-temporary impairment losses	(1,807)	(7,737)
Less investment impairments recognized in other comprehensive income, before taxes	0	98
Net impairment losses recognized in earnings	(1,807)	(7,639)
Other underwriting income	4,633	5,047
Equity in net income (loss) of investment funds accounted for using the equity method	48,088	6,655
Other income (loss)	(782)	(25)
Total revenues	1,319,176	1,086,676
Expenses
Losses and loss adjustment expenses	552,570	522,949
Acquisition expenses	182,289	167,838
Other operating expenses	174,719	150,148
Corporate expenses	27,792	9,383
Amortization of intangible assets	31,294	4,748
Interest expense	28,676	16,107
Net foreign exchange losses (gains)	19,404	23,566
Total expenses	1,016,744	894,739
Income before income taxes	302,432	191,937
Income tax expense	(28,397)	(16,310)
Net income	274,035	175,627
Net (income) loss attributable to noncontrolling interests	(20,908)	(20,829)
Net income available to Arch	253,127	154,798
Preferred dividends	(11,218)	(5,484)
Net income available to Arch common shareholders	$ 241,909	$ 149,314
Net income per common share
Basic (per share)	$ 1.80	$ 1.24
Diluted (per share)	$ 1.74	$ 1.20
Weighted average common shares and common share equivalents outstanding
Basic (shares)	134,034,927	120,428,179
Diluted (shares)	139,047,672	124,496,496

Unaudited Consolidated Stateme5

Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Comprehensive Income
Net income	$ 274,035	$ 175,627
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during period	100,792	132,981
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0	(98)
Reclassification of net realized (gains) losses, net of income taxes, included in net income	(5,044)	(32,223)
Foreign currency translation adjustments	3,124	17,313
Comprehensive income	372,907	293,600
Net (income) loss attributable to noncontrolling interests	(20,908)	(20,829)
Foreign currency translation adjustments attributable to noncontrolling interests	(8)	158
Comprehensive income available to Arch	$ 351,991	$ 272,929

Unaudited Consolidated Stateme6

Unaudited Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Non-cumulative preferred shares	Common shares	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss), net of deferred income tax	Unrealized appreciation (decline) in value of available-for-sale securities, net of deferred income tax	Foreign currency translation adjustments	Common shares held in treasury, at cost	Convertible non-voting common equivalent preferred shares
Cumulative effect of an accounting change					$ 0
Balance at beginning of year, as adjusted					7,332,032
Balance at beginning of year at Dec. 31, 2015		$ 325,000	$ 577	$ 467,339	7,332,032	$ (16,502)	$ 50,085	$ (66,587)	$ (1,941,904)	$ 0
Common shares issued, net			2	0
Exercise of stock options				4,222
Amortization of share-based compensation				14,265
Other				117
Net income	$ 175,627				175,627
Net (income) loss attributable to noncontrolling interests	(20,829)				(20,829)
Preferred share dividends	(5,484)				(5,484)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							100,758
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(98)						(98)
Foreign currency translation adjustments	17,313							17,313
Foreign currency translation adjustments attributable to noncontrolling interests								158
Shares repurchased for treasury									(77,345)
Balance at end of period at Mar. 31, 2016	6,375,248	325,000	579	485,943	7,481,346	101,629	150,745	(49,116)	(2,019,249)	0
Non-redeemable noncontrolling interests, end of period at Mar. 31, 2016	754,915
Total shareholders’ equity at Mar. 31, 2016	7,130,163
Cumulative effect of an accounting change					(314)
Balance at beginning of year, as adjusted					7,996,387
Balance at beginning of year at Dec. 31, 2016	8,253,718	772,555	582	531,687	7,996,701	(114,541)	(27,641)	(86,900)	(2,034,570)	1,101,304
Common shares issued, net			1	(1)
Exercise of stock options				710
Amortization of share-based compensation				15,657
Other				0
Net income	274,035				274,035
Net (income) loss attributable to noncontrolling interests	(20,908)				(20,908)
Preferred share dividends	(11,218)				(11,218)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							95,748
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0						0
Foreign currency translation adjustments	3,124							3,124
Foreign currency translation adjustments attributable to noncontrolling interests								(8)
Shares repurchased for treasury									(4,700)
Balance at end of period at Mar. 31, 2017	8,605,844	$ 772,555	$ 583	$ 548,053	$ 8,238,296	$ (15,677)	$ 68,107	$ (83,784)	$ (2,039,270)	$ 1,101,304
Non-redeemable noncontrolling interests, end of period at Mar. 31, 2017	868,186
Total shareholders’ equity at Mar. 31, 2017	$ 9,474,030

Unaudited Consolidated Stateme7

Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Activities
Net income	$ 274,035	$ 175,627
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized (gains) losses	(40,855)	(43,034)
Net impairment losses recognized in earnings	1,807	7,639
Equity in net income or loss of investment funds accounted for using the equity method and other income or loss	(36,141)	3,243
Amortization of intangible assets	31,294	4,748
Share-based compensation	15,657	14,265
Changes in:
Reserve for losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable	53,027	111,255
Unearned premiums, net of ceded unearned premiums	159,243	169,656
Premiums receivable	(176,350)	(217,348)
Deferred acquisition costs	(41,728)	(30,050)
Reinsurance balances payable	20,114	51,929
Other items, net	(51,985)	74,613
Net Cash Provided By Operating Activities	208,118	322,543
Investing Activities
Purchases of fixed maturity investments	(10,476,918)	(8,133,537)
Purchases of equity securities	(143,833)	(128,263)
Purchases of other investments	(427,039)	(305,198)
Proceeds from sales of fixed maturity investments	10,386,746	7,827,536
Proceeds from sales of equity securities	253,347	216,012
Proceeds from sales, redemptions and maturities of other investments	317,518	211,125
Proceeds from redemptions and maturities of fixed maturity investments	174,718	163,894
Net settlements of derivative instruments	(3,921)	21,091
Net (purchases) sales of short-term investments	(397,851)	(65,594)
Change in cash collateral related to securities lending	180,946	(43,118)
Purchases of fixed assets	(5,194)	(3,952)
Change in other assets	19,603	6,737
Net Cash Provided By (Used For) Investing Activities	(121,878)	(233,267)
Financing Activities
Purchases of common shares under share repurchase program	0	(75,256)
Proceeds from common shares issued, net	(3,990)	202
Proceeds from borrowings	0
Repayments of borrowings	(22,000)	(74,171)
Change in cash collateral related to securities lending	(180,946)	43,118
Dividends paid to redeemable noncontrolling interests	(4,497)	(4,497)
Other	(5,018)	29,115
Preferred dividends paid	(11,218)	(5,484)
Net Cash Provided By (Used For) Financing Activities	(227,669)	(86,973)
Effects of exchange rate changes on foreign currency cash	2,241	2,332
Increase (decrease) in cash	(139,188)	4,635
Cash beginning of year	842,942	553,326
Cash end of period	703,754	557,961
Income taxes paid	711	2,504
Interest paid	$ 5,829	$ 3,813

General

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

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Issued Accounting Standards Adopted The Company adopted Financial Accounting Standards Board (“FASB”) Accounting Standard Update (“ASU”) 2016-09, “Compensation - Stock Compensation (Topic 718) - Improvements to Employee Share-Based Payment Accounting,” effective January 1, 2017 . This ASU was issued in the 2016 first quarter to improve and simplify the accounting for employee share-based payment transactions. This ASU provides simplifications with respect to income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows for these types of transactions. With respect to the forfeiture accounting policy election, the Company has elected to account for forfeitures as they occur, which did not result in a material cumulative effect adjustment. With respect to the change in presentation in the statement of cash flows related to excess tax benefits, the Company has applied the guidance prospectively and prior periods have not been adjusted. Recently Issued Accounting Standards Not Yet Adopted ASU 2016-18, "Statement of Cash Flows (Topic 230) - Restricted Cash " was issued in the 2016 fourth quarter. The ASU requires that restricted cash and restricted cash equivalents be included with cash and cash equivalents in the reconciliation of beginning and ending cash on the statements of cash flows. As a result, transfers between cash and cash equivalents and restricted cash and restricted cash equivalents will no longer be presented on the statement of cash flows. The ASU also requires a reconciliation of the statement of the cash flows to the balance sheet if the balance sheet includes more than one line item of cash, cash equivalents, and restricted cash. The ASU is effective, with retrospective adoption, for interim and annual periods beginning after December 15, 2017, with early adoption permitted. The Company is currently assessing the impact the implementation of this ASU will have on its consolidated financial statements. ASU 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities,” was issued in the 2017 first quarter. The ASU amends the amortization period for certain purchased callable debt securities held at a premium by shortening the amortization period for the premium to the earliest call date. The ASU will be effective for the Company on January 1, 2019 and is required to be applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The Company is currently assessing the impact the implementation of this ASU will have on its consolidated financial statements.

Variable Interest Entities and

Variable Interest Entities and Noncontrolling Interests	3 Months Ended
	Mar. 31, 2017
Noncontrolling Interest [Abstract]
Variable Interest Entity and Noncontrolling Interests	Variable Interest Entities and Noncontrolling Interests A variable interest entity (“VIE”) refers to an entity that has characteristics such as (i) insufficient equity at risk to allow the entity to finance its activities without additional financial support or (ii) instances where the equity investors, as a group, do not have characteristics of a controlling financial interest. The primary beneficiary of a VIE is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (i) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (ii) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. If a company is determined to be the primary beneficiary, it is required to consolidate the VIE in its financial statements. Watford Holdings Ltd. In March 2014, the Company invested $100.0 million and acquired approximately 11% of Watford Holdings Ltd.’s common equity and a warrant to purchase additional common equity. Watford Holdings Ltd. is the parent of Watford Re Ltd., a multi-line Bermuda reinsurance company (together with Watford Holdings Ltd., “Watford Re”). Watford Re is considered a VIE and the Company concluded that it is the primary beneficiary of Watford Re. As such, the results of Watford Re are included in the Company’s consolidated financial statements. The Company does not guarantee or provide credit support for Watford Re, and the Company’s financial exposure to Watford Re is limited to its investment in Watford Re’s common and preferred shares and counterparty credit risk (mitigated by collateral) arising from reinsurance transactions. The following table provides the carrying amount and balance sheet caption in which the assets and liabilities of Watford Re are reported: March 31, December 31, 2017 2016 Assets Investments accounted for using the fair value option $ 1,976,466 $ 1,857,623 Cash 47,566 74,893 Accrued investment income 14,066 17,017 Premiums receivable 196,866 189,911 Reinsurance recoverable on unpaid and paid losses and LAE 25,673 24,420 Ceded unearned premiums 16,383 12,145 Deferred acquisition costs 93,227 86,379 Receivable for securities sold 19,235 1,326 Goodwill and intangible assets 7,650 7,650 Other assets 116,336 111,386 Total assets of consolidated VIE $ 2,513,468 $ 2,382,750 Liabilities Reserves for losses and loss adjustment expenses $ 566,175 $ 510,809 Unearned premiums 319,677 293,480 Reinsurance balances payable 15,171 12,289 Revolving credit agreement borrowings 234,961 256,650 Payable for securities purchased 81,216 42,922 Other liabilities 100,198 88,976 Total liabilities of consolidated VIE $ 1,317,398 $ 1,205,126 Redeemable noncontrolling interests $ 220,344 $ 220,253 For the three months ended March 31, 2017 , Watford Re generated $62.2 million of cash provided by operating activities, $60.5 million of cash used for investing activities and $29.0 million of cash used for financing activities, compared to $65.3 million of cash provided by operating activities, $43.7 million of cash used for investing activities and $51.3 million of cash used for financing activities for the three months ended March 31, 2016 . Non-redeemable noncontrolling interests The Company accounts for the portion of Watford Re’s common equity attributable to third party investors in the shareholders’ equity section of its consolidated balance sheets. The noncontrolling ownership in Watford Re’s common shares was approximately 89% at March 31, 2017 . The portion of Watford Re’s income or loss attributable to third party investors is recorded in the consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests.’ The following table sets forth activity in the non-redeemable noncontrolling interests: March 31, 2017 2016 Three Months Ended Balance, beginning of period $ 851,854 $ 738,831 Amounts attributable to noncontrolling interests 16,324 16,242 Foreign currency translation adjustments attributable to noncontrolling interests 8 (158 ) Balance, end of period $ 868,186 $ 754,915 Redeemable noncontrolling interests The Company accounts for redeemable noncontrolling interests in the mezzanine section of its consolidated balance sheets in accordance with applicable accounting guidance. Such redeemable noncontrolling interests relate to the 9,065,200 cumulative redeemable preference shares (“Watford Preference Shares”) issued in March 2014 with a par value of $0.01 per share and a liquidation preference of $25.00 per share. Preferred dividends, including the accretion of the discount and issuance costs, are included in ‘net (income) loss attributable to noncontrolling interests’ in the Company’s consolidated statements of income. The following table sets forth activity in the redeemable non-controlling interests: March 31, 2017 2016 Three Months Ended Balance, beginning of period $ 205,553 $ 205,182 Accretion of preference share issuance costs 91 92 Balance, end of period $ 205,644 $ 205,274 The portion of Watford Re’s income or loss attributable to third party investors, recorded in the Company’s consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests,’ are summarized in the table below: March 31, 2017 2016 Three Months Ended Amounts attributable to non-redeemable noncontrolling interests $ (16,324 ) $ (16,242 ) Dividends attributable to redeemable noncontrolling interests (4,584 ) (4,587 ) Net (income) loss attributable to noncontrolling interests $ (20,908 ) $ (20,829 ) Bellemeade Re I and II Upon closing of the UGC acquisition, the Company acquired the rights and obligations related to aggregate excess of loss reinsurance agreements with Bellemeade Re I Ltd. (“Bellemeade I”), entered into in July 2015, and with Bellemeade Re II Ltd. (“Bellemeade II”), entered into in May 2016 (the “Bellemeade Agreements”). Bellemeade I and Bellemeade II are special purpose reinsurance companies domiciled in Bermuda, each of which provided for up to approximately $300 million of aggregate excess of loss reinsurance coverage at inception for new delinquencies on portfolios of in-force policies issued. As a result of the evaluation of the Bellemeade Agreements, the Company concluded that both Bellemeade I and Bellemeade II are VIEs. However, given that the ceding insurers do not have the unilateral power to direct those activities that are significant to the economic performance of Bellemeade I and Bellemeade II, the Company does not consolidate Bellemeade I and Bellemeade II in its consolidated financial statements. The following table presents total assets of Bellemeade I and Bellemeade II as well as the Company’s maximum exposure to loss associated with these VIEs: Maximum Exposure to Loss Total VIE Assets On-Balance Sheet Off-Balance Sheet Total Bellemeade I $ 146,200 $ 351 $ 1,310 $ 1,661 Bellemeade II 283,777 54 1,103 1,157 Total $ 429,977 $ 405 $ 2,413 $ 2,818 Irving Partners Limited Partnership Upon closing of the UGC acquisition, the Company acquired a limited partnership interest in Irving Partners Limited Partnership (“Irving Partners”), which owns and operates an office building in Greensboro, North Carolina in which the Company is the main tenant. The Company concluded that Irving Partners is a VIE but that it is not the primary beneficiary. The Company’s maximum exposure to loss is approximately $14.5 million at March 31, 2017 .

Earnings Per Common Share

Earnings Per Common Share	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share The following table sets forth the computation of basic and diluted earnings per common share: Three Months Ended March 31, 2017 2016 Numerator: Net income $ 274,035 $ 175,627 Amounts attributable to noncontrolling interests (20,908 ) (20,829 ) Net income available to Arch 253,127 154,798 Preferred dividends (11,218 ) (5,484 ) Net income available to Arch common shareholders $ 241,909 $ 149,314 Denominator: Weighted average common shares outstanding 121,272,107 120,428,179 Series D preferred shares (1) 12,762,820 — Weighted average common shares and common share equivalents outstanding — basic 134,034,927 120,428,179 Effect of dilutive common share equivalents: Nonvested restricted shares 1,646,555 1,460,654 Stock options (2) 3,366,190 2,607,663 Weighted average common shares and common share equivalents outstanding — diluted 139,047,672 124,496,496 Earnings per common share: Basic $ 1.80 $ 1.24 Diluted $ 1.74 $ 1.20 (1) Such shares are convertible non-voting common equivalent preferred shares issued in connection with the UGC acquisition. (2) Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2017 first quarter and 2016 first quarter , the number of stock options excluded were 263,475 and 607,208 , respectively.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
Segment Information	Segment Information The Company classifies its businesses into three underwriting segments — insurance, reinsurance and mortgage — and two other operating segments — ‘other’ and corporate (non-underwriting). The Company determined its reportable segments using the management approach described in accounting guidance regarding disclosures about segments of an enterprise and related information. The accounting policies of the segments are the same as those used for the preparation of the Company’s consolidated financial statements. Intersegment business is allocated to the segment accountable for the underwriting results. The Company’s insurance, reinsurance and mortgage segments each have managers who are responsible for the overall profitability of their respective segments and who are directly accountable to the Company’s chief operating decision makers, the Chairman and Chief Executive Officer, the President and Chief Operating Officer, and the Chief Financial Officer of ACGL. The chief operating decision makers do not assess performance, measure return on equity or make resource allocation decisions on a line of business basis. Management measures segment performance for its three underwriting segments based on underwriting income or loss. The Company does not manage its assets by underwriting segment, with the exception of goodwill and intangible assets, and, accordingly, investment income is not allocated to each underwriting segment. The insurance segment consists of the Company’s insurance underwriting units which offer specialty product lines on a worldwide basis. Product lines include: construction and national accounts; excess and surplus casualty; lenders products; professional lines; programs; property, energy, marine and aviation; travel, accident and health; and other (consisting of alternative markets, excess workers' compensation and surety business). The reinsurance segment consists of the Company’s reinsurance underwriting units which offer specialty product lines on a worldwide basis. Product lines include: casualty; marine and aviation; other specialty; property catastrophe; property excluding property catastrophe (losses on a single risk, both excess of loss and pro rata); and other (consisting of life reinsurance, casualty clash and other). The mortgage segment includes the Company’s U.S. and international mortgage insurance and reinsurance operations as well as government sponsored enterprise (“GSE”) credit-risk sharing transactions. Arch Mortgage Insurance Company, United Guaranty Residential Insurance Company and United Guaranty Mortgage Indemnity Company (combined “Arch MI U.S.”) are approved as eligible mortgage insurers by Federal National Mortgage Association (“Fannie Mae”) and Federal Home Loan Mortgage Corporation (“Freddie Mac”), each a GSE. The corporate (non-underwriting) segment results include net investment income, other income (loss), corporate expenses, UGC transaction costs and other, interest expense, dividends related to the Company’s non-cumulative preferred shares, net realized gains or losses, net impairment losses included in earnings, equity in net income or loss of investment funds accounted for using the equity method, net foreign exchange gains or losses and income taxes. Such amounts exclude the results of the ‘other’ segment. The ‘other’ segment includes the results of Watford Re (see Note 3 ). Watford Re has its own management and board of directors that is responsible for the overall profitability of the ‘other’ segment. For the ‘other’ segment, performance is measured based on net income or loss. The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income or loss to net income available to common shareholders: Three Months Ended March 31, 2017 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 782,281 $ 475,782 $ 348,623 $ 1,606,686 $ 154,120 $ 1,657,990 Premiums ceded (234,095 ) (166,092 ) (73,925 ) (474,112 ) (10,434 ) (381,730 ) Net premiums written 548,186 309,690 274,698 1,132,574 143,686 1,276,260 Change in unearned premiums (42,540 ) (64,839 ) (30,175 ) (137,554 ) (21,689 ) (159,243 ) Net premiums earned 505,646 244,851 244,523 995,020 121,997 1,117,017 Other underwriting income — (306 ) 4,123 3,817 816 4,633 Losses and loss adjustment expenses (332,641 ) (105,454 ) (29,065 ) (467,160 ) (85,410 ) (552,570 ) Acquisition expenses, net (74,868 ) (46,147 ) (28,766 ) (149,781 ) (32,508 ) (182,289 ) Other operating expenses (88,126 ) (37,533 ) (41,870 ) (167,529 ) (7,190 ) (174,719 ) Underwriting income (loss) $ 10,011 $ 55,411 $ 148,945 214,367 (2,295 ) 212,072 Net investment income 95,812 22,062 117,874 Net realized gains (losses) 28,512 5,641 34,153 Net impairment losses recognized in earnings (1,807 ) — (1,807 ) Equity in net income (loss) of investment funds accounted for using the equity method 48,088 — 48,088 Other income (loss) (782 ) — (782 ) Corporate expenses (2) (12,208 ) — (12,208 ) UGC transaction costs and other (2) (15,584 ) — (15,584 ) Amortization of intangible assets (31,294 ) — (31,294 ) Interest expense (25,756 ) (2,920 ) (28,676 ) Net foreign exchange gains (losses) (19,845 ) 441 (19,404 ) Income (loss) before income taxes 279,503 22,929 302,432 Income tax expense (28,397 ) — (28,397 ) Net income (loss) 251,106 22,929 274,035 Dividends attributable to redeemable noncontrolling interests — (4,584 ) (4,584 ) Amounts attributable to noncontrolling interests — (16,324 ) (16,324 ) Net income (loss) available to Arch 251,106 2,021 253,127 Preferred dividends (11,218 ) — (11,218 ) Net income (loss) available to Arch common shareholders $ 239,888 $ 2,021 $ 241,909 Underwriting Ratios Loss ratio 65.8 % 43.1 % 11.9 % 46.9 % 70.0 % 49.5 % Acquisition expense ratio 14.8 % 18.8 % 11.8 % 15.1 % 26.6 % 16.3 % Other operating expense ratio 17.4 % 15.3 % 17.1 % 16.8 % 5.9 % 15.6 % Combined ratio 98.0 % 77.2 % 40.8 % 78.8 % 102.5 % 81.4 % Goodwill and intangible assets $ 24,371 $ 773 $ 717,521 $ 742,665 $ 7,650 $ 750,315 (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’ Three Months Ended March 31, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 798,553 $ 481,390 $ 111,280 $ 1,391,061 $ 148,606 $ 1,437,966 Premiums ceded (248,789 ) (160,566 ) (4,767 ) (413,960 ) (4,472 ) (316,731 ) Net premiums written 549,764 320,824 106,513 977,101 144,134 1,121,235 Change in unearned premiums (36,675 ) (59,616 ) (44,748 ) (141,039 ) (28,617 ) (169,656 ) Net premiums earned 513,089 261,208 61,765 836,062 115,517 951,579 Other underwriting income — 325 3,793 4,118 929 5,047 Losses and loss adjustment expenses (323,609 ) (111,598 ) (8,629 ) (443,836 ) (79,113 ) (522,949 ) Acquisition expenses, net (74,348 ) (54,758 ) (5,793 ) (134,899 ) (32,939 ) (167,838 ) Other operating expenses (85,058 ) (36,258 ) (23,494 ) (144,810 ) (5,338 ) (150,148 ) Underwriting income (loss) $ 30,074 $ 58,919 $ 27,642 116,635 (944 ) 115,691 Net investment income 70,409 23,326 93,735 Net realized gains (losses) 31,862 5,462 37,324 Net impairment losses recognized in earnings (7,639 ) — (7,639 ) Equity in net income (loss) of investment funds accounted for using the equity method 6,655 — 6,655 Other income (loss) (25 ) — (25 ) Corporate expenses (9,383 ) — (9,383 ) Amortization of intangible assets (4,748 ) — (4,748 ) Interest expense (12,627 ) (3,480 ) (16,107 ) Net foreign exchange gains (losses) (22,041 ) (1,525 ) (23,566 ) Income (loss) before income taxes 169,098 22,839 191,937 Income tax expense (16,310 ) — (16,310 ) Net income (loss) 152,788 22,839 175,627 Dividends attributable to redeemable noncontrolling interests — (4,587 ) (4,587 ) Amounts attributable to noncontrolling interests — (16,242 ) (16,242 ) Net income (loss) available to Arch 152,788 2,010 154,798 Preferred dividends (5,484 ) — (5,484 ) Net income (loss) available to Arch common shareholders $ 147,304 $ 2,010 $ 149,314 Underwriting Ratios Loss ratio 63.1 % 42.7 % 14.0 % 53.1 % 68.5 % 55.0 % Acquisition expense ratio 14.5 % 21.0 % 9.4 % 16.1 % 28.5 % 17.6 % Other operating expense ratio 16.6 % 13.9 % 38.0 % 17.3 % 4.6 % 15.8 % Combined ratio 94.2 % 77.6 % 61.4 % 86.5 % 101.6 % 88.4 % Goodwill and intangible assets $ 27,825 $ 1,713 $ 63,132 $ 92,670 $ — $ 92,670 (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.

Reserve for Losses and Loss Adj

Reserve for Losses and Loss Adjustment Expenses	3 Months Ended
	Mar. 31, 2017
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Reserve for Losses and Loss Adjustment Expenses	Reserve for Losses and Loss Adjustment Expenses The following table represents an analysis of losses and loss adjustment expenses and a reconciliation of the beginning and ending reserve for losses and loss adjustment expenses: Three Months Ended March 31, 2017 2016 Reserve for losses and loss adjustment expenses at beginning of year $ 10,200,960 $ 9,125,250 Unpaid losses and loss adjustment expenses recoverable 2,083,575 1,828,837 Net reserve for losses and loss adjustment expenses at beginning of year 8,117,385 7,296,413 Net incurred losses and loss adjustment expenses relating to losses occurring in: Current year 635,775 578,978 Prior years (83,205 ) (56,029 ) Total net incurred losses and loss adjustment expenses 552,570 522,949 Net foreign exchange losses (gains) 31,278 33,575 Net paid losses and loss adjustment expenses relating to losses occurring in: Current year (34,957 ) (49,079 ) Prior years (464,585 ) (362,595 ) Total net paid losses and loss adjustment expenses (499,542 ) (411,674 ) Net reserve for losses and loss adjustment expenses at end of year 8,201,691 7,441,263 Unpaid losses and loss adjustment expenses recoverable 2,095,130 1,937,724 Reserve for losses and loss adjustment expenses at end of period $ 10,296,821 $ 9,378,987 2017 Prior Year Development During the 2017 first quarter , the Company recorded net favorable development on prior year loss reserves of $83.2 million , which consisted of $57.2 million from the reinsurance segment, $2.1 million from the insurance segment, $23.6 million from the mortgage segment and $0.3 million from the ‘other’ segment. The reinsurance segment’s net favorable development of $57.2 million , or 23.4 points, for the 2017 first quarter consisted of $40.8 million from short-tailed lines and $16.4 million from long-tailed and medium-tailed lines. Favorable development in short-tailed lines included $34.0 million from property catastrophe and property other than property catastrophe reserves, across most underwriting years ( i.e. , all premiums and losses attributable to contracts having an inception or renewal date within the given twelve-month period), reflecting lower levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during the period. Favorable development in long-tailed and medium-tailed lines reflected reductions in casualty reserves of $5.5 million based on varying levels of reported and paid claims activity, primarily from the 2003 to 2013 underwriting years, and favorable development in marine reserves of $9.9 million across most underwriting years. The insurance segment’s net favorable development of $2.1 million , or 0.4 points, for the 2017 first quarter consisted of $7.0 million of net favorable development in long-tailed lines and $1.9 million of net favorable development in short-tailed lines, partially offset by $6.8 million of net adverse development in medium-tailed lines. Net favorable development in long-tailed lines reflected net reductions in executive assurance reserves from the 2008 to 2014 accident years ( i.e. , the year in which a loss occurred). Net favorable development in short-tailed lines primarily resulted from property (including special risk other than marine) reserves from the 2011 to 2016 accident years. Net adverse development in medium-tailed lines primarily resulted from an increase in programs of $14.2 million stemming in part from development on a small number of programs in the 2013 and 2014 accident years, partially offset by net favorable development of $7.5 million in other medium-tailed lines, primarily in professional liability and surety. The mortgage segment’s net favorable development was $23.6 million , or 9.6 points, for the 2017 first quarter . The 2017 first quarter development was primarily driven by continued lower than expected claim emergence across most origination years and also reflected $8.2 million related to subrogation recoveries on second lien and other portfolios. 2016 Prior Year Reserve Development During the 2016 first quarter , the Company recorded net favorable development on prior year loss reserves of $56.0 million , which consisted of $47.4 million from the reinsurance segment, $6.2 million from the insurance segment, $2.7 million from the mortgage segment less adverse development of $0.2 million from the ‘other’ segment. The reinsurance segment’s net favorable development of $47.4 million , or 18.1 points, for the 2016 first quarter consisted of $36.5 million from short-tailed lines and $10.9 million from long-tailed and medium-tailed lines. Favorable development in short-tailed lines included $29.8 million from property catastrophe and property other than property catastrophe reserves, primarily from the 2013 to 2015 underwriting years, reflecting lower levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during the period. Favorable development in long-tailed lines reflected reductions in casualty reserves of $14.2 million based on varying levels of reported and paid claims activity, primarily from the 2002 to 2005 underwriting years and 2009 to 2011 underwriting years. Such amounts were partially offset by net adverse development on marine reserves of $2.0 million , partially offset by favorable development from most other underwriting years. The insurance segment’s net favorable development of $6.2 million , or 1.2 points, for the 2016 first quarter consisted of $9.9 million of net favorable development in long-tailed lines and $3.7 million of net favorable development in short-tailed lines, partially offset by $7.4 million of net adverse development in medium-tailed lines. Net favorable development in long-tailed lines reflected favorable development in casualty reserves of $6.9 million , primarily from the 2008 and 2012 accident years. Net favorable development in short-tailed lines primarily resulted from reductions in property (including special risk other than marine) reserves from the 2012 to 2014 accident years, primarily due to varying levels of reported claims activity. Net adverse development in medium tailed lines primarily resulted from an increase in programs of $6.1 million with approximately 30% stemming from terminated programs. The mortgage segment’s net favorable development was $2.7 million , or 4.4 points, for the 2016 first quarter . The 2016 first quarter development was primarily driven by lower than expected claim rates across most origination years.

Investment Information

Investment Information	3 Months Ended
	Mar. 31, 2017
Disclosure Investment Information [Abstract]
Investment Information	Investment Information At March 31, 2017 , total investable assets of $20.74 billion included $18.83 billion managed by the Company and $1.90 billion attributable to Watford Re. Available For Sale Investments The following table summarizes the fair value and cost or amortized cost of the Company’s investments classified as available for sale: Estimated Fair Value Gross Unrealized Gains Gross Unrealized Losses Cost or Amortized Cost OTTI Unrealized Losses (2) March 31, 2017 Fixed maturities (1): Corporate bonds $ 4,546,756 $ 31,033 $ (36,615 ) $ 4,552,338 $ (1,876 ) Mortgage backed securities 412,023 5,210 (2,712 ) 409,525 (3,323 ) Municipal bonds 2,519,112 14,332 (17,411 ) 2,522,191 (201 ) Commercial mortgage backed securities 590,521 3,485 (6,040 ) 593,076 — U.S. government and government agencies 3,266,908 7,940 (11,152 ) 3,270,120 — Non-U.S. government securities 1,295,366 26,017 (39,356 ) 1,308,705 — Asset backed securities 1,638,347 8,984 (4,910 ) 1,634,273 (22 ) Total 14,269,033 97,001 (118,196 ) 14,290,228 (5,422 ) Equity securities 431,062 66,628 (6,660 ) 371,094 — Other investments 228,437 31,844 (838 ) 197,431 — Short-term investments 803,619 120 (125 ) 803,624 — Total $ 15,732,151 $ 195,593 $ (125,819 ) $ 15,662,377 $ (5,422 ) December 31, 2016 Fixed maturities (1): Corporate bonds $ 4,392,373 $ 27,606 $ (46,905 ) $ 4,411,672 $ (2,285 ) Mortgage backed securities 490,093 4,794 (8,357 ) 493,656 (3,323 ) Municipal bonds 3,713,434 8,554 (29,154 ) 3,734,034 (201 ) Commercial mortgage backed securities 536,051 2,876 (6,508 ) 539,683 — U.S. government and government agencies 2,804,540 9,319 (24,437 ) 2,819,658 — Non-U.S. government securities 1,096,440 19,036 (56,872 ) 1,134,276 — Asset backed securities 1,123,987 6,897 (6,526 ) 1,123,616 (22 ) Total 14,156,918 79,082 (178,759 ) 14,256,595 (5,831 ) Equity securities 532,680 62,627 (17,517 ) 487,570 — Other investments 167,970 21,358 (2,465 ) 149,077 — Short-term investments 612,005 272 (145 ) 611,878 — Total $ 15,469,573 $ 163,339 $ (198,886 ) $ 15,505,120 $ (5,831 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” (2) Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At March 31, 2017 , the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $2.0 million , compared to a net unrealized gain of $2.8 million at December 31, 2016 . The following table summarizes, for all available for sale securities in an unrealized loss position, the fair value and gross unrealized loss by length of time the security has been in a continual unrealized loss position: Less than 12 Months 12 Months or More Total Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses March 31, 2017 Fixed maturities (1): Corporate bonds $ 1,832,009 $ (34,331 ) $ 26,288 $ (2,284 ) $ 1,858,297 $ (36,615 ) Mortgage backed securities 137,291 (2,652 ) 4,150 (60 ) 141,441 (2,712 ) Municipal bonds 1,043,998 (16,890 ) 25,004 (521 ) 1,069,002 (17,411 ) Commercial mortgage backed securities 304,022 (5,890 ) 3,928 (150 ) 307,950 (6,040 ) U.S. government and government agencies 1,803,247 (11,152 ) — — 1,803,247 (11,152 ) Non-U.S. government securities 914,310 (39,153 ) 13,924 (203 ) 928,234 (39,356 ) Asset backed securities 662,917 (4,257 ) 40,477 (653 ) 703,394 (4,910 ) Total 6,697,794 (114,325 ) 113,771 (3,871 ) 6,811,565 (118,196 ) Equity securities 134,646 (6,660 ) — — 134,646 (6,660 ) Other investments 25,189 (838 ) — — 25,189 (838 ) Short-term investments 43,717 (125 ) — — 43,717 (125 ) Total $ 6,901,346 $ (121,948 ) $ 113,771 $ (3,871 ) $ 7,015,117 $ (125,819 ) December 31, 2016 Fixed maturities (1): Corporate bonds $ 1,700,813 $ (43,011 ) $ 46,902 $ (3,894 ) $ 1,747,715 $ (46,905 ) Mortgage backed securities 402,699 (8,134 ) 6,105 (223 ) 408,804 (8,357 ) Municipal bonds 1,513,308 (28,504 ) 29,636 (650 ) 1,542,944 (29,154 ) Commercial mortgage backed securities 231,374 (6,331 ) 5,635 (177 ) 237,009 (6,508 ) U.S. government and government agencies 1,888,018 (24,437 ) — — 1,888,018 (24,437 ) Non-U.S. government securities 807,598 (56,872 ) — — 807,598 (56,872 ) Asset backed securities 627,557 (5,465 ) 65,723 (1,061 ) 693,280 (6,526 ) Total 7,171,367 (172,754 ) 154,001 (6,005 ) 7,325,368 (178,759 ) Equity securities 269,381 (17,517 ) — — 269,381 (17,517 ) Other investments 39,299 (2,465 ) — — 39,299 (2,465 ) Short-term investments 29,146 (145 ) — — 29,146 (145 ) Total $ 7,509,193 $ (192,881 ) $ 154,001 $ (6,005 ) $ 7,663,194 $ (198,886 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” At March 31, 2017 , on a lot level basis, approximately 3,350 security lots out of a total of approximately 7,720 security lots were in an unrealized loss position and the largest single unrealized loss from a single lot in the Company’s fixed maturity portfolio was $4.4 million . At December 31, 2016 , on a lot level basis, approximately 3,540 security lots out of a total of approximately 7,240 security lots were in an unrealized loss position and the largest single unrealized loss from a single lot in the Company’s fixed maturity portfolio was $4.6 million . The contractual maturities of the Company’s fixed maturities are shown in the following table. Expected maturities, which are management’s best estimates, will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. March 31, 2017 December 31, 2016 Maturity Estimated Fair Value Amortized Cost Estimated Amortized Cost Due in one year or less $ 633,926 $ 632,468 $ 560,830 $ 557,675 Due after one year through five years 7,197,090 7,217,033 6,158,148 6,211,099 Due after five years through 10 years 3,337,574 3,339,974 4,676,847 4,710,017 Due after 10 years 459,552 463,879 610,962 620,849 11,628,142 11,653,354 12,006,787 12,099,640 Mortgage backed securities 412,023 409,525 490,093 493,656 Commercial mortgage backed securities 590,521 593,076 536,051 539,683 Asset backed securities 1,638,347 1,634,273 1,123,987 1,123,616 Total (1) $ 14,269,033 $ 14,290,228 $ 14,156,918 $ 14,256,595 (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” Securities Lending Agreements The Company enters into securities lending agreements with financial institutions to enhance investment income whereby it loans certain of its securities to third parties, primarily major brokerage firms, for short periods of time through a lending agent. The Company maintains legal control over the securities it lends, retains the earnings and cash flows associated with the loaned securities and receives a fee from the borrower for the temporary use of the securities. An indemnification agreement with the lending agent protects the Company in the event a borrower becomes insolvent or fails to return any of the securities on loan from the Company. The Company receives collateral in the form of cash or securities. Cash collateral primarily consists of short-term investments. At March 31, 2017 , the fair value of the cash collateral received on securities lending was $31.5 million and the fair value of security collateral received was $506.9 million . At December 31, 2016 , the fair value of the cash collateral received on securities lending was $212.5 million , and the fair value of security collateral received was $550.1 million . The Company’s securities lending transactions were accounted for as secured borrowings with significant investment categories as follows: Remaining Contractual Maturity of the Agreements Overnight and Continuous Less than 30 Days 30-90 Days 90 Days or More Total March 31, 2017 U.S. government and government agencies $ 358,293 $ — $ 139,416 $ 8,501 $ 506,210 Corporate bonds 29,624 — — — 29,624 Equity securities 2,519 — — — 2,519 Total $ 390,436 $ — $ 139,416 $ 8,501 $ 538,353 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9 $ — Amounts related to securities lending not included in offsetting disclosure in Note 9 $ 538,353 December 31, 2016 U.S. government and government agencies $ 556,015 $ 31,244 $ 126,093 $ 5,140 $ 718,492 Corporate bonds 29,078 — — — 29,078 Equity securities 14,984 — — — 14,984 Total $ 600,077 $ 31,244 $ 126,093 $ 5,140 $ 762,554 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9 $ — Amounts related to securities lending not included in offsetting disclosure in Note 9 $ 762,554 Other Investments The following table summarizes the Company’s other investments, including available for sale and fair value option components: March 31, December 31, Available for sale: Asian and emerging markets $ 109,084 $ 84,778 Investment grade fixed income 52,016 33,923 Credit related funds 11,003 7,469 Other 56,334 41,800 Total available for sale 228,437 167,970 Fair value option: Term loan investments (par value: $1,145,832 and $1,208,537) 1,123,568 1,190,799 Mezzanine debt funds 109,334 127,943 Credit related funds 208,707 218,298 Investment grade fixed income 82,718 75,468 Asian and emerging markets 205,150 178,568 Other (1) 165,837 129,717 Total fair value option 1,895,314 1,920,793 Total $ 2,123,751 $ 2,088,763 (1) Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other. Certain of the Company’s other investments are in investment funds for which the Company has the option to redeem at agreed upon values as described in each investment fund’s subscription agreement. Depending on the terms of the various subscription agreements, investments in investment funds may be redeemed daily, monthly, quarterly or on other terms. Two common redemption restrictions which may impact the Company’s ability to redeem these investment funds are gates and lockups. A gate is a suspension of redemptions which may be implemented by the general partner or investment manager of the fund in order to defer, in whole or in part, the redemption request in the event the aggregate amount of redemption requests exceeds a predetermined percentage of the investment fund’s net assets which may otherwise hinder the general partner or investment manager’s ability to liquidate holdings in an orderly fashion in order to generate the cash necessary to fund extraordinarily large redemption payouts. A lockup period is the initial amount of time an investor is contractually required to hold the security before having the ability to redeem. If the investment funds are eligible to be redeemed, the time to redeem such fund can take weeks or months following the notification. Fair Value Option The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option: March 31, December 31, Fixed maturities $ 1,112,945 $ 1,099,116 Other investments 1,895,314 1,920,793 Short-term investments 581,508 373,669 Equity securities 58,353 27,642 Investments accounted for using the fair value option $ 3,648,120 $ 3,421,220 Limited partnership interests In the normal course of its activities, the Company invests in limited partnerships as part of its overall investment strategy. Such amounts are included in ‘investments accounted for using the equity method’ and ‘investments accounted for using the fair value option.’ The Company has determined that it is not required to consolidate these investments because it is not the primary beneficiary of the funds. The Company’s maximum exposure to loss with respect to these investments is limited to the investment carrying amounts reported in the Company’s consolidated balance sheet and any unfunded commitment. The following table summarizes investments in limited partnership interests where the Company has a variable interest by balance sheet line item: March 31, December 31, Investments accounted for using the equity method (1) $ 861,607 $ 800,970 Investments accounted for using the fair value option (2) 89,726 90,804 Total $ 951,333 $ 891,774 (1) Aggregate unfunded commitments were $797.6 million at March 31, 2017 , compared to $776.6 million at December 31, 2016 . (2) Aggregate unfunded commitments were $66.7 million at March 31, 2017 , compared to $16.7 million at December 31, 2016 . Net Investment Income The components of net investment income were derived from the following sources: March 31, 2017 2016 Three Months Ended Fixed maturities $ 94,393 $ 73,673 Term loan investments 21,170 20,012 Equity securities (dividends) 2,643 3,435 Short-term investments 1,759 496 Other (1) 18,410 13,743 Gross investment income 138,375 111,359 Investment expenses (20,501 ) (17,624 ) Net investment income $ 117,874 $ 93,735 (1) Includes income distributions from investment funds and other items. Net Realized Gains (Losses) Net realized gains (losses) were as follows, excluding other than-temporary impairment provision. March 31, 2017 2016 Three Months Ended Available for sale securities: Gross gains on investment sales $ 69,175 $ 107,819 Gross losses on investment sales (61,362 ) (63,131 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 20,541 (333 ) Other investments 17,248 (21,548 ) Equity securities 3,545 36 Short-term investments 4 (422 ) Derivative instruments (1) (9,181 ) 20,732 Other (2) (5,817 ) (5,829 ) Net realized gains (losses) $ 34,153 $ 37,324 (1) See Note 9 for information on the Company’s derivative instruments. (2) Includes the re-measurement of contingent consideration liability amounts. Equity in Net Income (Loss) of Investment Funds Accounted for Using the Equity Method The Company recorded $48.1 million of equity in net income related to investment funds accounted for using the equity method in the 2017 first quarter , compared to $6.7 million of loss for the 2016 first quarter . In applying the equity method, investments are initially recorded at cost and are subsequently adjusted based on the Company’s proportionate share of the net income or loss of the funds (which include changes in the market value of the underlying securities in the funds). Such investments are generally recorded on a one to three month lag based on the availability of reports from the investment funds. Other-Than-Temporary Impairments The Company performs quarterly reviews of its available for sale investments in order to determine whether declines in fair value below the amortized cost basis were considered other-than-temporary in accordance with applicable guidance. The following table details the net impairment losses recognized in earnings by asset class: March 31, 2017 2016 Three Months Ended Fixed maturities: Mortgage backed securities $ (1,319 ) $ (473 ) Corporate bonds (1 ) (4,880 ) Non-U.S. government securities (198 ) (181 ) Asset backed securities — (6 ) Total (1,518 ) (5,540 ) Equity securities (186 ) (1,102 ) Other investments (103 ) (997 ) Net impairment losses recognized in earnings $ (1,807 ) $ (7,639 ) Net impairment losses recognized in earnings in the 2017 first quarter were primarily on mortgage backed securities and reflected the Company’s decision to liquidate a portfolio of mortgage backed securities in April 2017. The Company recorded impairment losses on securities in such portfolio that were in an unrealized loss position at March 31, 2017 . The Company believes that the $5.4 million of OTTI included in accumulated other comprehensive income at March 31, 2017 on the securities which were considered by the Company to be impaired was due to market and sector-related factors ( i.e. , not credit losses). At March 31, 2017 , the Company did not intend to sell these securities, or any other securities which were in an unrealized loss position, and determined that it is more likely than not that the Company will not be required to sell such securities before recovery of their cost basis. The following table provides a roll forward of the amount related to credit losses recognized in earnings for which a portion of an OTTI was recognized in accumulated other comprehensive income: March 31, 2017 2016 Three Months Ended Balance at start of period $ 13,138 $ 26,875 Credit loss impairments recognized on securities not previously impaired — 1,063 Credit loss impairments recognized on securities previously impaired 23 522 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 (624 ) (10,169 ) Balance at end of period $ 12,537 $ 18,291 Restricted Assets The Company is required to maintain assets on deposit, which primarily consist of fixed maturities, with various regulatory authorities to support its insurance and reinsurance operations. The Company’s insurance and reinsurance subsidiaries maintain assets in trust accounts as collateral for insurance and reinsurance transactions with affiliated companies and also have investments in segregated portfolios primarily to provide collateral or guarantees for letters of credit to third parties. See Note 10 for further details. The following table details the value of the Company’s restricted assets: March 31, December 31, Assets used for collateral or guarantees: Affiliated transactions $ 3,991,217 $ 3,871,971 Third party agreements 1,545,255 1,513,079 Deposits with U.S. regulatory authorities 528,594 472,890 Deposits with non-U.S. regulatory authorities 45,332 44,399 Total restricted assets $ 6,110,398 $ 5,902,339

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value	Fair Value Accounting guidance regarding fair value measurements addresses how companies should measure fair value when they are required to use a fair value measure for recognition or disclosure purposes under GAAP and provides a common definition of fair value to be used throughout GAAP. It defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly fashion between market participants at the measurement date. In addition, it establishes a three-level valuation hierarchy for the disclosure of fair value measurements. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. The level in the hierarchy within which a given fair value measurement falls is determined based on the lowest level input that is significant to the measurement (Level 1 being the highest priority and Level 3 being the lowest priority). The levels in the hierarchy are defined as follows: Level 1: Inputs to the valuation methodology are observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets Level 2: Inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets, and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument Level 3: Inputs to the valuation methodology are unobservable and significant to the fair value measurement Following is a description of the valuation methodologies used for securities measured at fair value, as well as the general classification of such securities pursuant to the valuation hierarchy. The Company reviews its securities measured at fair value and discusses the proper classification of such investments with investment advisers and others. The Company determines the existence of an active market based on its judgment as to whether transactions for the financial instrument occur in such market with sufficient frequency and volume to provide reliable pricing information. The independent pricing sources obtain market quotations and actual transaction prices for securities that have quoted prices in active markets. The Company uses quoted values and other data provided by nationally recognized independent pricing sources as inputs into its process for determining fair values of its fixed maturity investments. To validate the techniques or models used by pricing sources, the Company's review process includes, but is not limited to: (i) quantitative analysis (e.g., comparing the quarterly return for each managed portfolio to its target benchmark, with significant differences identified and investigated); (ii) a review of the average number of prices obtained in the pricing process and the range of resulting fair values; (iii) initial and ongoing evaluation of methodologies used by outside parties to calculate fair value; (iv) a comparison of the fair value estimates to the Company’s knowledge of the current market; (v) a comparison of the pricing services' fair values to other pricing services' fair values for the same investments; and (vi) periodic back-testing, which includes randomly selecting purchased or sold securities and comparing the executed prices to the fair value estimates from the pricing service. A price source hierarchy was maintained in order to determine which price source would be used (i.e. , a price obtained from a pricing service with more seniority in the hierarchy will be used over a less senior one in all cases). The hierarchy prioritizes pricing services based on availability and reliability and assigns the highest priority to index providers. Based on the above review, the Company will challenge any prices for a security or portfolio which are considered not to be representative of fair value. The Company did not adjust any of the prices obtained from the independent pricing sources at March 31, 2017 . In certain circumstances, when fair values are unavailable from these independent pricing sources, quotes are obtained directly from broker-dealers who are active in the corresponding markets. Such quotes are subject to the validation procedures noted above. Of the $19.62 billion of financial assets and liabilities measured at fair value at March 31, 2017 , approximately $177.9 million , or 0.9% , were priced using non-binding broker-dealer quotes. Of the $19.10 billion of financial assets and liabilities measured at fair value at December 31, 2016 , approximately $234.0 million , or 1.2% , were priced using non-binding broker-dealer quotes. Fixed maturities The Company uses the market approach valuation technique to estimate the fair value of its fixed maturity securities, when possible. The market approach includes obtaining prices from independent pricing services, such as index providers and pricing vendors, as well as to a lesser extent quotes from broker-dealers. The independent pricing sources obtain market quotations and actual transaction prices for securities that have quoted prices in active markets. Each source has its own proprietary method for determining the fair value of securities that are not actively traded. In general, these methods involve the use of “matrix pricing” in which the independent pricing source uses observable market inputs including, but not limited to, investment yields, credit risks and spreads, benchmarking of like securities, broker-dealer quotes, reported trades and sector groupings to determine a reasonable fair value. The following describes the significant inputs generally used to determine the fair value of the Company’s fixed maturity securities by asset class: • U.S. government and government agencies — valuations provided by independent pricing services, with all prices provided through index providers and pricing vendors. The Company determined that all U.S. Treasuries would be classified as Level 1 securities due to observed levels of trading activity, the high number of strongly correlated pricing quotes received on U.S. Treasuries and other factors. The fair values of U.S. government agency securities are generally determined using the spread above the risk-free yield curve. As the yields for the risk-free yield curve and the spreads for these securities are observable market inputs, the fair values of U.S. government agency securities are classified within Level 2. • Corporate bonds — valuations provided by independent pricing services, substantially all through index providers and pricing vendors with a small amount through broker-dealers. The fair values of these securities are generally determined using the spread above the risk-free yield curve. These spreads are generally obtained from the new issue market, secondary trading and from broker-dealers who trade in the relevant security market. As the significant inputs used in the pricing process for corporate bonds are observable market inputs, the fair value of these securities are classified within Level 2. One security is included in Level 3 due to a low level of transparency on the inputs used in the pricing process. • Mortgage-backed securities — valuations provided by independent pricing services, substantially all through pricing vendors and index providers with a small amount through broker-dealers. The fair values of these securities are generally determined through the use of pricing models (including Option Adjusted Spread) which use spreads to determine the expected average life of the securities. These spreads are generally obtained from the new issue market, secondary trading and from broker-dealers who trade in the relevant security market. The pricing services also review prepayment speeds and other indicators, when applicable. As the significant inputs used in the pricing process for mortgage-backed securities are observable market inputs, the fair value of these securities are classified within Level 2. • 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 are generally determined through the use of pricing models (including Option Adjusted Spread) which use spreads to determine the appropriate average life of the securities. These spreads are generally obtained from the new issue market, secondary trading and from broker-dealers who trade in the relevant security market. The pricing services also review prepayment speeds and other indicators, when applicable. As the significant inputs used in the pricing process for asset-backed securities are observable market inputs, the fair value of these securities are classified within Level 2. A small number of securities are included in Level 3 due to a low level of transparency on the inputs used in the pricing process. 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. Derivative instruments The Company’s futures contracts, foreign currency forward contracts, interest rate swaps and other derivatives trade in the over-the-counter derivative market. The Company uses the market approach valuation technique to estimate the fair value for these derivatives based on significant observable market inputs from third party pricing vendors, non-binding broker-dealer quotes and/or recent trading activity. As the significant inputs used in the pricing process for these derivative instruments are observable market inputs, the fair value of these securities are classified within Level 2. Short-term investments The Company determined that certain of its short-term investments held in highly liquid money market-type funds, Treasury bills and commercial paper would be included in Level 1 as their fair values are based on quoted market prices in active markets. The fair values of other short-term investments are generally determined using the spread above the risk-free yield curve and are classified within Level 2. Contingent consideration liabilities Contingent consideration liabilities (included in ‘other liabilities’ in the consolidated balance sheets) include amounts related to the acquisition of CMG Mortgage Insurance Company and its affiliated mortgage insurance companies and other acquisitions. Such amounts are remeasured at fair value at each balance sheet date with changes in fair value recognized in ‘net realized gains (losses).’ To determine the fair value of contingent consideration liabilities, the Company estimates future payments using an income approach based on modeled inputs which include a weighted average cost of capital. The Company determined that contingent consideration liabilities would be included within Level 3. The following table presents the Company’s financial assets and liabilities measured at fair value by level at March 31, 2017 : Estimated Fair Value Measurements Using: Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets measured at fair value (1): Available for sale securities: Fixed maturities: Corporate bonds $ 4,546,756 $ — $ 4,528,155 $ 18,601 Mortgage backed securities 412,023 — 412,023 — Municipal bonds 2,519,112 — 2,519,112 — Commercial mortgage backed securities 590,521 — 590,521 — U.S. government and government agencies 3,266,908 3,192,592 74,316 — Non-U.S. government securities 1,295,366 — 1,295,366 — Asset backed securities 1,638,347 — 1,627,710 10,637 Total 14,269,033 3,192,592 11,047,203 29,238 Equity securities 431,062 427,762 3,300 — Short-term investments 803,619 796,075 7,544 — Other investments 126,112 122,773 3,339 — Other investments measured at net asset value (2) 102,325 Total other investments 228,437 122,773 3,339 — Derivative instruments (4) 29,059 — 29,059 — Fair value option: Corporate bonds 817,690 — 817,690 — Non-U.S. government bonds 55,504 — 55,504 — Mortgage backed securities 16,489 — 16,489 — Asset backed securities 16,198 — 16,198 — U.S. government and government agencies 207,064 207,064 — — Short-term investments 581,508 580,315 1,193 — Equity securities 58,353 55,311 3,042 — Other investments 1,338,661 90,475 1,223,186 25,000 Other investments measured at net asset value (2) 556,653 Total 3,648,120 933,165 2,133,302 25,000 Total assets measured at fair value $ 19,409,330 $ 5,472,367 $ 13,223,747 $ 54,238 Liabilities measured at fair value: Contingent consideration liabilities $ (125,544 ) $ — $ — $ (125,544 ) Securities sold but not yet purchased (3) (59,430 ) — (59,430 ) — Derivative instruments (4) (22,227 ) — (22,227 ) — Total liabilities measured at fair value $ (207,201 ) $ — $ (81,657 ) $ (125,544 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7 , “Investment Information—Securities Lending Agreements.” (2) In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. (3) Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets. (4) See Note 9 , “Derivative Instruments.” The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2016 : Estimated Fair Value Measurements Using: Estimated Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets measured at fair value (1): Available for sale securities: Fixed maturities: Corporate bonds $ 4,392,373 $ — $ 4,374,029 $ 18,344 Mortgage backed securities 490,093 — 490,093 — Municipal bonds 3,713,434 — 3,713,434 — Commercial mortgage backed securities 536,051 — 536,051 — U.S. government and government agencies 2,804,540 2,691,575 112,965 — Non-U.S. government securities 1,096,440 — 1,096,440 — Asset backed securities 1,123,987 — 1,112,698 11,289 Total 14,156,918 2,691,575 11,435,710 29,633 Equity securities 532,680 529,695 2,985 — Short-term investments 612,005 608,862 3,143 — Other investments 112,313 112,313 — — Other investments measured at net asset value (2) 55,657 Total other investments 167,970 112,313 — — Derivative instruments (4) 28,410 — 28,410 — Fair value option: Corporate bonds 790,935 — 790,935 — Non-U.S. government bonds 61,747 — 61,747 — Mortgage backed securities 18,624 — 18,624 — Asset backed securities 30,324 — 30,324 — U.S. government and government agencies 197,486 197,486 — — Short-term investments 373,669 309,127 64,542 — Equity securities 27,642 25,328 2,314 — Other investments 1,226,242 80,706 1,120,536 25,000 Other investments measured at net asset value (2) 694,551 Total 3,421,220 612,647 2,089,022 25,000 Total assets measured at fair value $ 18,919,203 $ 4,555,092 $ 13,559,270 $ 54,633 Liabilities measured at fair value: Contingent consideration liabilities $ (122,350 ) $ — $ — $ (122,350 ) Securities sold but not yet purchased (3) (33,157 ) — (33,157 ) — Derivative instruments (4) (26,049 ) — (26,049 ) — Total liabilities measured at fair value $ (181,556 ) $ — $ (59,206 ) $ (122,350 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7 , “Investment Information—Securities Lending Agreements.” (2) In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. (3) Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets. (4) See Note 9 , “Derivative Instruments.” The following table presents a reconciliation of the beginning and ending balances for all financial assets and liabilities measured at fair value on a recurring basis using Level 3 inputs: Assets Liabilities s Available For Sale Fair Value Option Asset Backed Securities Corporate Bonds Other Investments Total Contingent Consideration Liabilities Three Months Ended March 31, 2017 Balance at beginning of period $ 11,289 $ 18,344 $ 25,000 $ 54,633 $ (122,350 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) 707 257 — 964 (3,646 ) Included in other comprehensive income — — — — — Purchases, issuances, sales and settlements Purchases — — — — — Issuances — — — — — Sales — — — — — Settlements (1,359 ) — — (1,359 ) 452 Transfers in and/or out of Level 3 — — — — — Balance at end of period $ 10,637 $ 18,601 $ 25,000 $ 54,238 $ (125,544 ) Three Months Ended March 31, 2016 Balance at beginning of period $ 57,500 $ 16,368 $ — $ 73,868 $ (96,048 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — (1,202 ) — (1,202 ) (5,198 ) Included in other comprehensive income — — — — — Purchases, issuances, sales and settlements Purchases — — — — — Issuances — — — — — Sales — — — — — Settlements — — — — 536 Transfers in and/or out of Level 3 — — — — — Balance at end of period $ 57,500 $ 15,166 $ — $ 72,666 $ (100,710 ) (1) Gains or losses on asset backed securities were included in net impairment losses recognized in earnings while gains or losses on corporate bonds and contingent consideration liabilities were included in net realized gains (losses). Financial Instruments Disclosed, But Not Carried, At Fair Value The Company uses various financial instruments in the normal course of its business. The carrying values of cash, accrued investment income, receivable for securities sold, certain other assets, payable for securities purchased and certain other liabilities approximated their fair values at March 31, 2017 , due to their respective short maturities. As these financial instruments are not actively traded, their respective fair values are classified within Level 2. At March 31, 2017 , the senior notes of ACGL were carried at their cost, net of debt issuance costs, of $297.0 million and had a fair value of $394.7 million , while the senior notes of Arch Capital Group (U.S.) Inc. (“Arch-U.S.”) were carried at their cost, net of debt issuance costs, of $494.5 million and had a fair value of $535.6 million . The senior notes of Arch Capital Finance LLC due in 2026 were carried at their cost, net of debt issuance costs, of $495.8 million and had a fair value of $515.2 million , while the senior notes due in 2046 were carried at their cost, net of debt issuance costs, of $445.1 million and had a fair value of $488.0 million . The fair values of the senior notes were obtained from a third party pricing service and are based on observable market inputs. As such, the fair values of the senior notes are classified within Level 2.

Derivative Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments The Company’s investment strategy allows for the use of derivative instruments. The Company’s derivative instruments are recorded on its consolidated balance sheets at fair value. The Company utilizes exchange traded U.S. Treasury note, Eurodollar and other futures contracts and commodity futures to manage portfolio duration or replicate investment positions in its portfolios and the Company routinely utilizes foreign currency forward contracts, currency options, index futures contracts and other derivatives as part of its total return objective. In addition, certain of the Company’s investments are managed in portfolios which incorporate the use of foreign currency forward contracts which are intended to provide an economic hedge against foreign currency movements. In addition, the Company purchases to-be-announced mortgage backed securities (“TBAs”) as part of its investment strategy. TBAs represent commitments to purchase a future issuance of agency mortgage backed securities. For the period between purchase of a TBA and issuance of the underlying security, the Company’s position is accounted for as a derivative. The Company purchases TBAs in both long and short positions to enhance investment performance and as part of its overall investment strategy. The following table summarizes information on the fair values and notional values of the Company’s derivative instruments: Estimated Fair Value Asset Derivatives Liability Derivatives Notional Value (1) March 31, 2017 Futures contracts (2) $ 3,550 $ (4,489 ) $ 2,276,070 Foreign currency forward contracts (2) 7,363 (11,435 ) 1,264,235 TBAs (3) 32,011 (32,791 ) 63,966 Other (2) 18,146 (6,303 ) 1,552,009 Total $ 61,070 $ (55,018 ) December 31, 2016 Futures contracts (2) $ 360 $ (9,398 ) $ 1,655,530 Foreign currency forward contracts (2) 9,354 (12,941 ) 1,186,386 TBAs (3) — — — Other (2) 20,287 (3,710 ) 1,014,863 Total $ 30,001 $ (26,049 ) (1) Represents the absolute notional value of all outstanding contracts, consisting of long and short positions. (2) The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’ (3) The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’ The Company did not hold any derivatives which were designated as hedging instruments at March 31, 2017 or December 31, 2016 . The Company’s derivative instruments can be traded under master netting agreements, which establish terms that apply to all derivative transactions with a counterparty. In the event of a bankruptcy or other stipulated event of default, such agreements provide that the non-defaulting party may elect to terminate all outstanding derivative transactions, in which case all individual derivative positions (loss or gain) with a counterparty are closed out and netted and replaced with a single amount, usually referred to as the termination amount, which is expressed in a single currency. The resulting single net amount, where positive, is payable to the party “in-the-money” regardless of whether or not it is the defaulting party, unless the parties have agreed that only the non-defaulting party is entitled to receive a termination payment where the net amount is positive and is in its favor. Contractual close-out netting reduces derivatives credit exposure from gross to net exposure. At March 31, 2017 , asset derivatives and liability derivatives of $59.3 million and $54.6 million , respectively, were subject to a master netting agreement, compared to $28.4 million and $26.0 million , respectively, at December 31, 2016 . The remaining derivatives included in the preceding table were not subject to a master netting agreement. All realized and unrealized contract gains and losses on the Company’s derivative instruments are reflected in net realized gains (losses) in the consolidated statements of income, as summarized in the following table: Derivatives not designated as March 31, hedging instruments: 2017 2016 Three Months Ended Net realized gains (losses): Futures contracts $ 7,720 $ 26,451 Foreign currency forward contracts (11,766 ) (4,752 ) TBAs (65 ) 297 Other (5,070 ) (1,264 ) Total $ (9,181 ) $ 20,732

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies 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 $1.45 billion at March 31, 2017 .

Share Transactions

Share Transactions	3 Months Ended
	Mar. 31, 2017
Stockholders' Equity Note [Abstract]
Share Transactions	Share Transactions Share Repurchases The board of directors of ACGL has authorized the investment in ACGL’s common shares through a share repurchase program. Since the inception of the share repurchase program, ACGL has repurchased approximately 125.2 million common shares for an aggregate purchase price of $3.68 billion . During the 2017 first quarter , the Company did not repurchase any shares under the share repurchase program. During the 2016 first quarter , ACGL repurchased 1.1 million common shares for an aggregate purchase price of $75.3 million . At March 31, 2017 , $446.5 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 through December 31, 2019. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2017
Comprehensive Income Note Disclosure [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The following tables present details about amounts reclassified from accumulated other comprehensive income and the tax effects allocated to each component of other comprehensive income (loss): Amounts Reclassified from AOCI Consolidated Statement of Income Three Months Ended Details About Line Item That Includes March 31, AOCI Components Reclassification 2017 2016 Unrealized appreciation on available-for-sale investments Net realized gains (losses) $ 7,813 $ 44,687 Other-than-temporary impairment losses (1,807 ) (7,737 ) Total before tax 6,006 36,950 Income tax (expense) benefit (962 ) (4,727 ) Net of tax $ 5,044 $ 32,223 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Three Months Ended March 31, 2017 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 111,472 $ 10,680 $ 100,792 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 6,006 962 5,044 Foreign currency translation adjustments 3,165 41 3,124 Other comprehensive income (loss) $ 108,631 $ 9,759 $ 98,872 Three Months Ended March 31, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 152,174 $ 19,193 $ 132,981 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (98 ) — (98 ) Less reclassification of net realized gains (losses) included in net income 36,950 4,727 32,223 Foreign currency translation adjustments 17,860 547 17,313 Other comprehensive income (loss) $ 132,986 $ 15,013 $ 117,973

Guarantor Financial Information

Guarantor Financial Information	3 Months Ended
	Mar. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Guarantor Financial Information	Guarantor Financial Information The following tables present condensed financial information for ACGL, Arch-U.S., a 100% owned subsidiary of ACGL, and ACGL’s other subsidiaries. March 31, 2017 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 256 $ 41,715 $ 20,227,399 $ (14,700 ) $ 20,254,670 Cash 10,177 42,745 650,832 — 703,754 Investments in subsidiaries 8,992,903 3,843,774 — (12,836,677 ) — Due from subsidiaries and affiliates 1,626 52,032 1,868,171 (1,921,829 ) — Premiums receivable — — 1,891,983 (637,935 ) 1,254,048 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 6,209,021 (4,075,873 ) 2,133,148 Contractholder receivables — — 1,766,340 — 1,766,340 Ceded unearned premiums — — 2,201,994 (1,260,071 ) 941,923 Deferred acquisition costs — — 638,415 (150,490 ) 487,925 Goodwill and intangible assets — — 750,315 — 750,315 Other assets 14,730 55,658 1,893,742 (164,027 ) 1,800,103 Total assets $ 9,019,692 $ 4,035,924 $ 38,098,212 $ (21,061,602 ) $ 30,092,226 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 14,337,192 $ (4,040,371 ) $ 10,296,821 Unearned premiums — — 4,891,330 (1,260,071 ) 3,631,259 Reinsurance balances payable — — 959,221 (637,936 ) 321,285 Contractholder payables — — 1,766,340 — 1,766,340 Collateral held for insured obligations — — 327,161 327,161 Senior notes 296,979 494,548 940,883 — 1,732,410 Revolving credit agreement borrowings 100,000 — 634,961 — 734,961 Due to subsidiaries and affiliates 2,044 541,400 1,378,384 (1,921,828 ) — Other liabilities 14,825 61,055 1,876,454 (350,019 ) 1,602,315 Total liabilities 413,848 1,097,003 27,111,926 (8,210,225 ) 20,412,552 Redeemable noncontrolling interests — — 220,344 (14,700 ) 205,644 Shareholders’ Equity Total shareholders’ equity available to Arch 8,605,844 2,938,921 9,897,756 (12,836,677 ) 8,605,844 Non-redeemable noncontrolling interests — — 868,186 — 868,186 Total shareholders’ equity 8,605,844 2,938,921 10,765,942 (12,836,677 ) 9,474,030 Total liabilities, noncontrolling interests and shareholders’ equity $ 9,019,692 $ 4,035,924 $ 38,098,212 $ (21,061,602 ) $ 30,092,226 December 31, 2016 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 2,612 $ 41,672 $ 19,690,067 $ (14,700 ) $ 19,719,651 Cash 1,687 71,955 769,300 — 842,942 Investments in subsidiaries 8,660,586 3,716,681 — (12,377,267 ) — Due from subsidiaries and affiliates 14,297 51,298 1,866,681 (1,932,276 ) — Premiums receivable — — 1,579,865 (507,430 ) 1,072,435 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 6,114,518 (4,000,380 ) 2,114,138 Contractholder receivables — — 1,717,436 — 1,717,436 Ceded unearned premiums — — 1,985,311 (1,125,744 ) 859,567 Deferred acquisition costs — — 577,461 (129,901 ) 447,560 Goodwill and intangible assets — — 781,553 — 781,553 Other assets 15,725 49,244 1,901,786 (149,928 ) 1,816,827 Total assets $ 8,694,907 $ 3,930,850 $ 36,983,978 $ (20,237,626 ) $ 29,372,109 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 14,164,191 $ (3,963,231 ) $ 10,200,960 Unearned premiums — — 4,532,614 (1,125,744 ) 3,406,870 Reinsurance balances payable — — 807,837 (507,430 ) 300,407 Contractholder payables — — 1,717,436 — 1,717,436 Collateral held for insured obligations — — 301,406 — 301,406 Deposit accounting liabilities — — 22,150 — 22,150 Senior notes 296,957 494,525 940,776 — 1,732,258 Revolving credit agreement borrowings 100,000 — 656,650 — 756,650 Due to subsidiaries and affiliates 26,270 535,584 1,370,422 (1,932,276 ) — Other liabilities 17,962 54,823 1,867,040 (316,978 ) 1,622,847 Total liabilities 441,189 1,084,932 26,380,522 (7,845,659 ) 20,060,984 Redeemable noncontrolling interests — — 220,253 (14,700 ) 205,553 Shareholders’ Equity Total shareholders’ equity available to Arch 8,253,718 2,845,918 9,531,349 (12,377,267 ) 8,253,718 Non-redeemable noncontrolling interests — — 851,854 — 851,854 Total shareholders’ equity 8,253,718 2,845,918 10,383,203 (12,377,267 ) 9,105,572 Total liabilities, noncontrolling interests and shareholders’ equity $ 8,694,907 $ 3,930,850 $ 36,983,978 $ (20,237,626 ) $ 29,372,109 Three Months Ended March 31, 2017 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 1,117,017 $ — $ 1,117,017 Net investment income 5 816 137,981 (20,928 ) 117,874 Net realized gains (losses) — — 34,153 — 34,153 Net impairment losses recognized in earnings — — (1,807 ) — (1,807 ) Other underwriting income — — 4,633 — 4,633 Equity in net income (loss) of investment funds accounted for using the equity method — — 48,088 — 48,088 Other income (loss) 171 — (953 ) — (782 ) Total revenues 176 816 1,339,112 (20,928 ) 1,319,176 Expenses Losses and loss adjustment expenses — — 552,570 — 552,570 Acquisition expenses — — 182,289 — 182,289 Other operating expenses — — 174,719 — 174,719 Corporate expenses 17,247 2,008 8,537 — 27,792 Amortization of intangible assets — — 31,294 — 31,294 Interest expense 6,015 11,930 31,336 (20,605 ) 28,676 Net foreign exchange (gains) losses — — 15,348 4,056 19,404 Total expenses 23,262 13,938 996,093 (16,549 ) 1,016,744 Income (loss) before income taxes (23,086 ) (13,122 ) 343,019 (4,379 ) 302,432 Income tax (expense) benefit — 4,873 (33,270 ) — (28,397 ) Income (loss) before equity in net income of subsidiaries (23,086 ) (8,249 ) 309,749 (4,379 ) 274,035 Equity in net income of subsidiaries 276,213 77,373 — (353,586 ) — Net income 253,127 69,124 309,749 (357,965 ) 274,035 Net (income) loss attributable to noncontrolling interests — — (21,231 ) 323 (20,908 ) Net income available to Arch 253,127 69,124 288,518 (357,642 ) 253,127 Preferred dividends (11,218 ) — — — (11,218 ) Net income available to Arch common shareholders $ 241,909 $ 69,124 $ 288,518 $ (357,642 ) $ 241,909 Comprehensive income (loss) available to Arch $ 351,991 $ 87,781 $ 224,173 $ (311,954 ) $ 351,991 Three Months Ended March 31, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 951,579 $ — $ 951,579 Net investment income 1 773 100,261 (7,300 ) 93,735 Net realized gains (losses) — — 37,324 — 37,324 Net impairment losses recognized in earnings — — (7,639 ) — (7,639 ) Other underwriting income — — 5,319 (272 ) 5,047 Equity in net income (loss) of investment funds accounted for using the equity method — — 6,655 — 6,655 Other income (loss) 206 — (231 ) — (25 ) Total revenues 207 773 1,093,268 (7,572 ) 1,086,676 Expenses Losses and loss adjustment expenses — — 522,949 — 522,949 Acquisition expenses — — 167,838 — 167,838 Other operating expenses — — 150,148 — 150,148 Corporate expenses 9,355 582 (554 ) — 9,383 Amortization of intangible assets — — 4,748 — 4,748 Interest expense 5,934 6,672 10,752 (7,251 ) 16,107 Net foreign exchange (gains) losses — — 16,495 7,071 23,566 Total expenses 15,289 7,254 872,376 (180 ) 894,739 Income (loss) before income taxes (15,082 ) (6,481 ) 220,892 (7,392 ) 191,937 Income tax (expense) benefit — 2,244 (18,554 ) — (16,310 ) Income (loss) before equity in net income of subsidiaries (15,082 ) (4,237 ) 202,338 (7,392 ) 175,627 Equity in net income of subsidiaries 169,880 22,866 — (192,746 ) — Net income 154,798 18,629 202,338 (200,138 ) 175,627 Net (income) loss attributable to noncontrolling interests — — (21,150 ) 321 (20,829 ) Net income available to Arch 154,798 18,629 181,188 (199,817 ) 154,798 Preferred dividends (5,484 ) — — — (5,484 ) Net income available to Arch common shareholders $ 149,314 $ 18,629 $ 181,188 $ (199,817 ) $ 149,314 Comprehensive income (loss) available to Arch $ 272,929 $ 58,649 $ 292,251 $ (350,900 ) $ 272,929 Three Months Ended March 31, 2017 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 701 $ (3,257 ) $ 264,088 $ (53,414 ) $ 208,118 Investing Activities Purchases of fixed maturity investments — — (10,476,918 ) — (10,476,918 ) Purchases of equity securities — — (143,833 ) — (143,833 ) Purchases of other investments — — (427,039 ) — (427,039 ) Proceeds from the sales of fixed maturity investments — — 10,386,746 — 10,386,746 Proceeds from the sales of equity securities — — 253,347 — 253,347 Proceeds from the sales, redemptions and maturities of other investments — — 317,518 — 317,518 Proceeds from redemptions and maturities of fixed maturity investments — — 174,718 — 174,718 Net settlements of derivative instruments — — (3,921 ) — (3,921 ) Net (purchases) sales of short-term investments 2,356 (43 ) (400,164 ) — (397,851 ) Change in cash collateral related to securities lending — — 180,946 — 180,946 Contributions to subsidiaries — (25,900 ) (60,050 ) 85,950 — Purchases of fixed assets — (10 ) (5,184 ) — (5,194 ) Other 20,641 — 19,603 (20,641 ) 19,603 Net Cash Provided By (Used For) Investing Activities 22,997 (25,953 ) (184,231 ) 65,309 (121,878 ) Financing Activities Proceeds from common shares issued, net (3,990 ) — 85,950 (85,950 ) (3,990 ) Proceeds from borrowings — — — — — Repayments of borrowings — — (22,000 ) — (22,000 ) Change in cash collateral related to securities lending — — (180,946 ) — (180,946 ) Dividends paid to redeemable noncontrolling interests — — (4,816 ) 319 (4,497 ) Dividends paid to parent (1) — — (53,095 ) 53,095 — Other — — (25,659 ) 20,641 (5,018 ) Preferred dividends paid (11,218 ) — — — (11,218 ) Net Cash Provided By (Used For) Financing Activities (15,208 ) — (200,566 ) (11,895 ) (227,669 ) Effects of exchange rates changes on foreign currency cash — — 2,241 — 2,241 Increase (decrease) in cash 8,490 (29,210 ) (118,468 ) — (139,188 ) Cash beginning of year 1,687 71,955 769,300 — 842,942 Cash end of period $ 10,177 $ 42,745 $ 650,832 $ — $ 703,754 (1) Dividends paid are included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) and/or Arch-U.S. (Subsidiary Issuer) columns. Three Months Ended March 31, 2016 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 83,892 $ (4,740 ) $ 340,558 $ (97,167 ) $ 322,543 Investing Activities Purchases of fixed maturity investments — — (8,133,537 ) — (8,133,537 ) Purchases of equity securities — — (128,263 ) — (128,263 ) Purchases of other investments — — (305,198 ) — (305,198 ) Proceeds from the sales of fixed maturity investments — — 7,827,536 — 7,827,536 Proceeds from the sales of equity securities — — 216,012 — 216,012 Proceeds from the sales, redemptions and maturities of other investments — — 211,125 — 211,125 Proceeds from redemptions and maturities of fixed maturity investments — — 163,894 — 163,894 Net settlements of derivative instruments — — 21,091 — 21,091 Net (purchases) sales of short-term investments (60 ) (30 ) (65,504 ) — (65,594 ) Change in cash collateral related to securities lending — — (43,118 ) — (43,118 ) Contributions to subsidiaries (3,300 ) — (2,779 ) 6,079 — Purchases of fixed assets (8 ) — (3,944 ) — (3,952 ) Other — — 6,737 — 6,737 Net Cash Provided By (Used For) Investing Activities (3,368 ) (30 ) (235,948 ) 6,079 (233,267 ) Financing Activities Purchases of common shares under share repurchase program (75,256 ) — — — (75,256 ) Proceeds from common shares issued, net 202 — 6,079 (6,079 ) 202 Repayments of borrowings — — (74,171 ) — (74,171 ) Change in cash collateral related to securities lending — — 43,118 — 43,118 Dividends paid to redeemable noncontrolling interests — — (4,816 ) 319 (4,497 ) Dividends paid to parent (1) — — (96,848 ) 96,848 — Other — 184 28,931 — 29,115 Preferred dividends paid (5,484 ) — — — (5,484 ) Net Cash Provided By (Used For) Financing Activities (80,538 ) 184 (97,707 ) 91,088 (86,973 ) Effects of exchange rates changes on foreign currency cash — — 2,332 — 2,332 Increase (decrease) in cash (14 ) (4,586 ) 9,235 — 4,635 Cash beginning of year 6,809 17,023 529,494 — 553,326 Cash end of period $ 6,795 $ 12,437 $ 538,729 $ — $ 557,961 (1) Dividends paid are included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) and/or Arch-U.S. (Subsidiary Issuer) columns.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company’s income tax provision on income before income taxes resulted in an expense of 9.4% for the three months ended March 31, 2017 , compared to an expense of 8.5% for the 2016 period. The Company’s effective tax rate, which is based upon the expected annual effective tax rate, may fluctuate from period to period based on the relative mix of income or loss reported by jurisdiction and the varying tax rates in each jurisdiction. For interim reporting purposes, the Company has calculated its effective tax rate for the full year of 2017 by treating any excess tax benefits that arise from the accounting for stock based compensation as a discrete item. As such, this amount is not included when projecting the Company’s full year effective tax rate but rather is accounted for at the U.S. Federal statutory rate of 35% after applying the projected full year effective tax rate to actual three-month results before the discrete item. The impact of the discrete item resulted in a benefit of 0.8% for the three months ended March 31, 2017. The Company had a net deferred tax asset of $227.5 million at March 31, 2017 , compared to $221.2 million at December 31, 2016 . In addition, the Company paid $0.7 million and $2.5 million of income taxes for the three months ended March 31, 2017 and 2016 , respectively.

Legal Proceedings

Legal Proceedings	3 Months Ended
	Mar. 31, 2017
Disclosure Legal Proceedings [Abstract]
Legal Proceedings	Legal Proceedings The Company, in common with the insurance industry in general, is subject to litigation and arbitration in the normal course of its business. As of March 31, 2017 , the Company was not a party to any litigation or arbitration which is expected by management to have a material adverse effect on the Company’s results of operations and financial condition and liquidity.

Transactions with Related Parti

Transactions with Related Parties	3 Months Ended
	Mar. 31, 2017
Related Party Transactions [Abstract]
Transactions with Related Parties	Transactions with Related Parties Kewsong Lee, a director of ACGL, is a Managing Director and Deputy Chief Investment Officer for Corporate Private Equity of 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 March 31, 2017 , the total value of the Company’s investments in funds or other investments managed by Carlyle was approximately $200.5 million , and the Company had aggregate unfunded commitments to funds managed by Carlyle of $510.0 million . The Company may make additional commitments to funds managed by Carlyle from time to time. During the three months ended March 31, 2017 and 2016 , the Company made aggregate capital contributions to funds managed by Carlyle of $7.9 million and $40.1 million , respectively, and received aggregate cash distributions from funds managed by Carlyle of $23.3 million and $8.8 million , respectively.

General (Policies)

General (Policies)	3 Months Ended
	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	The interim consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). All significant intercompany transactions and balances have been eliminated in consolidation.
Use of estimates	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates and assumptions. In the opinion of management, the accompanying unaudited interim consolidated financial statements reflect all adjustments (consisting of normally recurring accruals) necessary for a fair statement of results on an interim basis. The results of any interim period are not necessarily indicative of the results for a full year or any future periods.

Variable Interest Entities an25

Variable Interest Entities and Noncontrolling Interests (Tables)	3 Months Ended
	Mar. 31, 2017
Noncontrolling Interest [Abstract]
Carrying value of assets and liabilities of variable interest entity	The following table provides the carrying amount and balance sheet caption in which the assets and liabilities of Watford Re are reported: March 31, December 31, 2017 2016 Assets Investments accounted for using the fair value option $ 1,976,466 $ 1,857,623 Cash 47,566 74,893 Accrued investment income 14,066 17,017 Premiums receivable 196,866 189,911 Reinsurance recoverable on unpaid and paid losses and LAE 25,673 24,420 Ceded unearned premiums 16,383 12,145 Deferred acquisition costs 93,227 86,379 Receivable for securities sold 19,235 1,326 Goodwill and intangible assets 7,650 7,650 Other assets 116,336 111,386 Total assets of consolidated VIE $ 2,513,468 $ 2,382,750 Liabilities Reserves for losses and loss adjustment expenses $ 566,175 $ 510,809 Unearned premiums 319,677 293,480 Reinsurance balances payable 15,171 12,289 Revolving credit agreement borrowings 234,961 256,650 Payable for securities purchased 81,216 42,922 Other liabilities 100,198 88,976 Total liabilities of consolidated VIE $ 1,317,398 $ 1,205,126 Redeemable noncontrolling interests $ 220,344 $ 220,253
Activity in non-redeemable noncontrolling interests	The following table sets forth activity in the non-redeemable noncontrolling interests: March 31, 2017 2016 Three Months Ended Balance, beginning of period $ 851,854 $ 738,831 Amounts attributable to noncontrolling interests 16,324 16,242 Foreign currency translation adjustments attributable to noncontrolling interests 8 (158 ) Balance, end of period $ 868,186 $ 754,915
Activity in redeemable noncontrolling interests	The following table sets forth activity in the redeemable non-controlling interests: March 31, 2017 2016 Three Months Ended Balance, beginning of period $ 205,553 $ 205,182 Accretion of preference share issuance costs 91 92 Balance, end of period $ 205,644 $ 205,274
Portion of income or loss attributable to third party investors	The portion of Watford Re’s income or loss attributable to third party investors, recorded in the Company’s consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests,’ are summarized in the table below: March 31, 2017 2016 Three Months Ended Amounts attributable to non-redeemable noncontrolling interests $ (16,324 ) $ (16,242 ) Dividends attributable to redeemable noncontrolling interests (4,584 ) (4,587 ) Net (income) loss attributable to noncontrolling interests $ (20,908 ) $ (20,829 )
Total assets and maximum exposure to loss associated with VIEs	The following table presents total assets of Bellemeade I and Bellemeade II as well as the Company’s maximum exposure to loss associated with these VIEs: Maximum Exposure to Loss Total VIE Assets On-Balance Sheet Off-Balance Sheet Total Bellemeade I $ 146,200 $ 351 $ 1,310 $ 1,661 Bellemeade II 283,777 54 1,103 1,157 Total $ 429,977 $ 405 $ 2,413 $ 2,818

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Schedule of computation of basic and diluted earnings per common share	The following table sets forth the computation of basic and diluted earnings per common share: Three Months Ended March 31, 2017 2016 Numerator: Net income $ 274,035 $ 175,627 Amounts attributable to noncontrolling interests (20,908 ) (20,829 ) Net income available to Arch 253,127 154,798 Preferred dividends (11,218 ) (5,484 ) Net income available to Arch common shareholders $ 241,909 $ 149,314 Denominator: Weighted average common shares outstanding 121,272,107 120,428,179 Series D preferred shares (1) 12,762,820 — Weighted average common shares and common share equivalents outstanding — basic 134,034,927 120,428,179 Effect of dilutive common share equivalents: Nonvested restricted shares 1,646,555 1,460,654 Stock options (2) 3,366,190 2,607,663 Weighted average common shares and common share equivalents outstanding — diluted 139,047,672 124,496,496 Earnings per common share: Basic $ 1.80 $ 1.24 Diluted $ 1.74 $ 1.20 (1) Such shares are convertible non-voting common equivalent preferred shares issued in connection with the UGC acquisition. (2) Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2017 first quarter and 2016 first quarter , the number of stock options excluded were 263,475 and 607,208 , respectively.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
Analysis of underwriting income or loss by segment and reconciliation to net income available to common shareholders	The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income or loss to net income available to common shareholders: Three Months Ended March 31, 2017 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 782,281 $ 475,782 $ 348,623 $ 1,606,686 $ 154,120 $ 1,657,990 Premiums ceded (234,095 ) (166,092 ) (73,925 ) (474,112 ) (10,434 ) (381,730 ) Net premiums written 548,186 309,690 274,698 1,132,574 143,686 1,276,260 Change in unearned premiums (42,540 ) (64,839 ) (30,175 ) (137,554 ) (21,689 ) (159,243 ) Net premiums earned 505,646 244,851 244,523 995,020 121,997 1,117,017 Other underwriting income — (306 ) 4,123 3,817 816 4,633 Losses and loss adjustment expenses (332,641 ) (105,454 ) (29,065 ) (467,160 ) (85,410 ) (552,570 ) Acquisition expenses, net (74,868 ) (46,147 ) (28,766 ) (149,781 ) (32,508 ) (182,289 ) Other operating expenses (88,126 ) (37,533 ) (41,870 ) (167,529 ) (7,190 ) (174,719 ) Underwriting income (loss) $ 10,011 $ 55,411 $ 148,945 214,367 (2,295 ) 212,072 Net investment income 95,812 22,062 117,874 Net realized gains (losses) 28,512 5,641 34,153 Net impairment losses recognized in earnings (1,807 ) — (1,807 ) Equity in net income (loss) of investment funds accounted for using the equity method 48,088 — 48,088 Other income (loss) (782 ) — (782 ) Corporate expenses (2) (12,208 ) — (12,208 ) UGC transaction costs and other (2) (15,584 ) — (15,584 ) Amortization of intangible assets (31,294 ) — (31,294 ) Interest expense (25,756 ) (2,920 ) (28,676 ) Net foreign exchange gains (losses) (19,845 ) 441 (19,404 ) Income (loss) before income taxes 279,503 22,929 302,432 Income tax expense (28,397 ) — (28,397 ) Net income (loss) 251,106 22,929 274,035 Dividends attributable to redeemable noncontrolling interests — (4,584 ) (4,584 ) Amounts attributable to noncontrolling interests — (16,324 ) (16,324 ) Net income (loss) available to Arch 251,106 2,021 253,127 Preferred dividends (11,218 ) — (11,218 ) Net income (loss) available to Arch common shareholders $ 239,888 $ 2,021 $ 241,909 Underwriting Ratios Loss ratio 65.8 % 43.1 % 11.9 % 46.9 % 70.0 % 49.5 % Acquisition expense ratio 14.8 % 18.8 % 11.8 % 15.1 % 26.6 % 16.3 % Other operating expense ratio 17.4 % 15.3 % 17.1 % 16.8 % 5.9 % 15.6 % Combined ratio 98.0 % 77.2 % 40.8 % 78.8 % 102.5 % 81.4 % Goodwill and intangible assets $ 24,371 $ 773 $ 717,521 $ 742,665 $ 7,650 $ 750,315 (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. (2) Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’ Three Months Ended March 31, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 798,553 $ 481,390 $ 111,280 $ 1,391,061 $ 148,606 $ 1,437,966 Premiums ceded (248,789 ) (160,566 ) (4,767 ) (413,960 ) (4,472 ) (316,731 ) Net premiums written 549,764 320,824 106,513 977,101 144,134 1,121,235 Change in unearned premiums (36,675 ) (59,616 ) (44,748 ) (141,039 ) (28,617 ) (169,656 ) Net premiums earned 513,089 261,208 61,765 836,062 115,517 951,579 Other underwriting income — 325 3,793 4,118 929 5,047 Losses and loss adjustment expenses (323,609 ) (111,598 ) (8,629 ) (443,836 ) (79,113 ) (522,949 ) Acquisition expenses, net (74,348 ) (54,758 ) (5,793 ) (134,899 ) (32,939 ) (167,838 ) Other operating expenses (85,058 ) (36,258 ) (23,494 ) (144,810 ) (5,338 ) (150,148 ) Underwriting income (loss) $ 30,074 $ 58,919 $ 27,642 116,635 (944 ) 115,691 Net investment income 70,409 23,326 93,735 Net realized gains (losses) 31,862 5,462 37,324 Net impairment losses recognized in earnings (7,639 ) — (7,639 ) Equity in net income (loss) of investment funds accounted for using the equity method 6,655 — 6,655 Other income (loss) (25 ) — (25 ) Corporate expenses (9,383 ) — (9,383 ) Amortization of intangible assets (4,748 ) — (4,748 ) Interest expense (12,627 ) (3,480 ) (16,107 ) Net foreign exchange gains (losses) (22,041 ) (1,525 ) (23,566 ) Income (loss) before income taxes 169,098 22,839 191,937 Income tax expense (16,310 ) — (16,310 ) Net income (loss) 152,788 22,839 175,627 Dividends attributable to redeemable noncontrolling interests — (4,587 ) (4,587 ) Amounts attributable to noncontrolling interests — (16,242 ) (16,242 ) Net income (loss) available to Arch 152,788 2,010 154,798 Preferred dividends (5,484 ) — (5,484 ) Net income (loss) available to Arch common shareholders $ 147,304 $ 2,010 $ 149,314 Underwriting Ratios Loss ratio 63.1 % 42.7 % 14.0 % 53.1 % 68.5 % 55.0 % Acquisition expense ratio 14.5 % 21.0 % 9.4 % 16.1 % 28.5 % 17.6 % Other operating expense ratio 16.6 % 13.9 % 38.0 % 17.3 % 4.6 % 15.8 % Combined ratio 94.2 % 77.6 % 61.4 % 86.5 % 101.6 % 88.4 % Goodwill and intangible assets $ 27,825 $ 1,713 $ 63,132 $ 92,670 $ — $ 92,670 (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.

Reserve for Losses and Loss A28

Reserve for Losses and Loss Adjustment Expenses (Tables)	3 Months Ended
	Mar. 31, 2017
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Analysis of losses and loss adjustment expenses and reconciliation of beginning and ending reserve balances	The following table represents an analysis of losses and loss adjustment expenses and a reconciliation of the beginning and ending reserve for losses and loss adjustment expenses: Three Months Ended March 31, 2017 2016 Reserve for losses and loss adjustment expenses at beginning of year $ 10,200,960 $ 9,125,250 Unpaid losses and loss adjustment expenses recoverable 2,083,575 1,828,837 Net reserve for losses and loss adjustment expenses at beginning of year 8,117,385 7,296,413 Net incurred losses and loss adjustment expenses relating to losses occurring in: Current year 635,775 578,978 Prior years (83,205 ) (56,029 ) Total net incurred losses and loss adjustment expenses 552,570 522,949 Net foreign exchange losses (gains) 31,278 33,575 Net paid losses and loss adjustment expenses relating to losses occurring in: Current year (34,957 ) (49,079 ) Prior years (464,585 ) (362,595 ) Total net paid losses and loss adjustment expenses (499,542 ) (411,674 ) Net reserve for losses and loss adjustment expenses at end of year 8,201,691 7,441,263 Unpaid losses and loss adjustment expenses recoverable 2,095,130 1,937,724 Reserve for losses and loss adjustment expenses at end of period $ 10,296,821 $ 9,378,987

Investment Information (Tables)

Investment Information (Tables)	3 Months Ended
	Mar. 31, 2017
Disclosure Investment Information [Abstract]
Summary of fair value and cost or amortized cost of available for sale securities	The following table summarizes the fair value and cost or amortized cost of the Company’s investments classified as available for sale: Estimated Fair Value Gross Unrealized Gains Gross Unrealized Losses Cost or Amortized Cost OTTI Unrealized Losses (2) March 31, 2017 Fixed maturities (1): Corporate bonds $ 4,546,756 $ 31,033 $ (36,615 ) $ 4,552,338 $ (1,876 ) Mortgage backed securities 412,023 5,210 (2,712 ) 409,525 (3,323 ) Municipal bonds 2,519,112 14,332 (17,411 ) 2,522,191 (201 ) Commercial mortgage backed securities 590,521 3,485 (6,040 ) 593,076 — U.S. government and government agencies 3,266,908 7,940 (11,152 ) 3,270,120 — Non-U.S. government securities 1,295,366 26,017 (39,356 ) 1,308,705 — Asset backed securities 1,638,347 8,984 (4,910 ) 1,634,273 (22 ) Total 14,269,033 97,001 (118,196 ) 14,290,228 (5,422 ) Equity securities 431,062 66,628 (6,660 ) 371,094 — Other investments 228,437 31,844 (838 ) 197,431 — Short-term investments 803,619 120 (125 ) 803,624 — Total $ 15,732,151 $ 195,593 $ (125,819 ) $ 15,662,377 $ (5,422 ) December 31, 2016 Fixed maturities (1): Corporate bonds $ 4,392,373 $ 27,606 $ (46,905 ) $ 4,411,672 $ (2,285 ) Mortgage backed securities 490,093 4,794 (8,357 ) 493,656 (3,323 ) Municipal bonds 3,713,434 8,554 (29,154 ) 3,734,034 (201 ) Commercial mortgage backed securities 536,051 2,876 (6,508 ) 539,683 — U.S. government and government agencies 2,804,540 9,319 (24,437 ) 2,819,658 — Non-U.S. government securities 1,096,440 19,036 (56,872 ) 1,134,276 — Asset backed securities 1,123,987 6,897 (6,526 ) 1,123,616 (22 ) Total 14,156,918 79,082 (178,759 ) 14,256,595 (5,831 ) Equity securities 532,680 62,627 (17,517 ) 487,570 — Other investments 167,970 21,358 (2,465 ) 149,077 — Short-term investments 612,005 272 (145 ) 611,878 — Total $ 15,469,573 $ 163,339 $ (198,886 ) $ 15,505,120 $ (5,831 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” (2) Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At March 31, 2017 , the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $2.0 million , compared to a net unrealized gain of $2.8 million at December 31, 2016 .
Summary of available for sale securities in a continual unrealized loss position	The following table summarizes, for all available for sale securities in an unrealized loss position, the fair value and gross unrealized loss by length of time the security has been in a continual unrealized loss position: Less than 12 Months 12 Months or More Total Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses March 31, 2017 Fixed maturities (1): Corporate bonds $ 1,832,009 $ (34,331 ) $ 26,288 $ (2,284 ) $ 1,858,297 $ (36,615 ) Mortgage backed securities 137,291 (2,652 ) 4,150 (60 ) 141,441 (2,712 ) Municipal bonds 1,043,998 (16,890 ) 25,004 (521 ) 1,069,002 (17,411 ) Commercial mortgage backed securities 304,022 (5,890 ) 3,928 (150 ) 307,950 (6,040 ) U.S. government and government agencies 1,803,247 (11,152 ) — — 1,803,247 (11,152 ) Non-U.S. government securities 914,310 (39,153 ) 13,924 (203 ) 928,234 (39,356 ) Asset backed securities 662,917 (4,257 ) 40,477 (653 ) 703,394 (4,910 ) Total 6,697,794 (114,325 ) 113,771 (3,871 ) 6,811,565 (118,196 ) Equity securities 134,646 (6,660 ) — — 134,646 (6,660 ) Other investments 25,189 (838 ) — — 25,189 (838 ) Short-term investments 43,717 (125 ) — — 43,717 (125 ) Total $ 6,901,346 $ (121,948 ) $ 113,771 $ (3,871 ) $ 7,015,117 $ (125,819 ) December 31, 2016 Fixed maturities (1): Corporate bonds $ 1,700,813 $ (43,011 ) $ 46,902 $ (3,894 ) $ 1,747,715 $ (46,905 ) Mortgage backed securities 402,699 (8,134 ) 6,105 (223 ) 408,804 (8,357 ) Municipal bonds 1,513,308 (28,504 ) 29,636 (650 ) 1,542,944 (29,154 ) Commercial mortgage backed securities 231,374 (6,331 ) 5,635 (177 ) 237,009 (6,508 ) U.S. government and government agencies 1,888,018 (24,437 ) — — 1,888,018 (24,437 ) Non-U.S. government securities 807,598 (56,872 ) — — 807,598 (56,872 ) Asset backed securities 627,557 (5,465 ) 65,723 (1,061 ) 693,280 (6,526 ) Total 7,171,367 (172,754 ) 154,001 (6,005 ) 7,325,368 (178,759 ) Equity securities 269,381 (17,517 ) — — 269,381 (17,517 ) Other investments 39,299 (2,465 ) — — 39,299 (2,465 ) Short-term investments 29,146 (145 ) — — 29,146 (145 ) Total $ 7,509,193 $ (192,881 ) $ 154,001 $ (6,005 ) $ 7,663,194 $ (198,886 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”
Contractual maturities of the Company's fixed maturities and fixed maturities pledged under securities lending arrangements	The contractual maturities of the Company’s fixed maturities are shown in the following table. Expected maturities, which are management’s best estimates, will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. March 31, 2017 December 31, 2016 Maturity Estimated Fair Value Amortized Cost Estimated Amortized Cost Due in one year or less $ 633,926 $ 632,468 $ 560,830 $ 557,675 Due after one year through five years 7,197,090 7,217,033 6,158,148 6,211,099 Due after five years through 10 years 3,337,574 3,339,974 4,676,847 4,710,017 Due after 10 years 459,552 463,879 610,962 620,849 11,628,142 11,653,354 12,006,787 12,099,640 Mortgage backed securities 412,023 409,525 490,093 493,656 Commercial mortgage backed securities 590,521 593,076 536,051 539,683 Asset backed securities 1,638,347 1,634,273 1,123,987 1,123,616 Total (1) $ 14,269,033 $ 14,290,228 $ 14,156,918 $ 14,256,595 (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”
Securities lending transactions accounted for as secured borrowings, by significant investment category	The Company’s securities lending transactions were accounted for as secured borrowings with significant investment categories as follows: Remaining Contractual Maturity of the Agreements Overnight and Continuous Less than 30 Days 30-90 Days 90 Days or More Total March 31, 2017 U.S. government and government agencies $ 358,293 $ — $ 139,416 $ 8,501 $ 506,210 Corporate bonds 29,624 — — — 29,624 Equity securities 2,519 — — — 2,519 Total $ 390,436 $ — $ 139,416 $ 8,501 $ 538,353 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9 $ — Amounts related to securities lending not included in offsetting disclosure in Note 9 $ 538,353 December 31, 2016 U.S. government and government agencies $ 556,015 $ 31,244 $ 126,093 $ 5,140 $ 718,492 Corporate bonds 29,078 — — — 29,078 Equity securities 14,984 — — — 14,984 Total $ 600,077 $ 31,244 $ 126,093 $ 5,140 $ 762,554 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9 $ — Amounts related to securities lending not included in offsetting disclosure in Note 9 $ 762,554
Summary of other investments, including available for sale and fair value option components	The following table summarizes the Company’s other investments, including available for sale and fair value option components: March 31, December 31, Available for sale: Asian and emerging markets $ 109,084 $ 84,778 Investment grade fixed income 52,016 33,923 Credit related funds 11,003 7,469 Other 56,334 41,800 Total available for sale 228,437 167,970 Fair value option: Term loan investments (par value: $1,145,832 and $1,208,537) 1,123,568 1,190,799 Mezzanine debt funds 109,334 127,943 Credit related funds 208,707 218,298 Investment grade fixed income 82,718 75,468 Asian and emerging markets 205,150 178,568 Other (1) 165,837 129,717 Total fair value option 1,895,314 1,920,793 Total $ 2,123,751 $ 2,088,763 (1) Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other.
Summary of assets and liabilities accounted for using the fair value option	The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option: March 31, December 31, Fixed maturities $ 1,112,945 $ 1,099,116 Other investments 1,895,314 1,920,793 Short-term investments 581,508 373,669 Equity securities 58,353 27,642 Investments accounted for using the fair value option $ 3,648,120 $ 3,421,220
Summary of investments in limited partnership interests where the Company has a variable interest	The following table summarizes investments in limited partnership interests where the Company has a variable interest by balance sheet line item: March 31, December 31, Investments accounted for using the equity method (1) $ 861,607 $ 800,970 Investments accounted for using the fair value option (2) 89,726 90,804 Total $ 951,333 $ 891,774 (1) Aggregate unfunded commitments were $797.6 million at March 31, 2017 , compared to $776.6 million at December 31, 2016 . (2) Aggregate unfunded commitments were $66.7 million at March 31, 2017 , compared to $16.7 million at December 31, 2016 .
Components of net investment income	The components of net investment income were derived from the following sources: March 31, 2017 2016 Three Months Ended Fixed maturities $ 94,393 $ 73,673 Term loan investments 21,170 20,012 Equity securities (dividends) 2,643 3,435 Short-term investments 1,759 496 Other (1) 18,410 13,743 Gross investment income 138,375 111,359 Investment expenses (20,501 ) (17,624 ) Net investment income $ 117,874 $ 93,735 (1) Includes income distributions from investment funds and other items.
Summary of net realized gains (losses), excluding other-than-temporary impairment provisions	Net realized gains (losses) were as follows, excluding other than-temporary impairment provision. March 31, 2017 2016 Three Months Ended Available for sale securities: Gross gains on investment sales $ 69,175 $ 107,819 Gross losses on investment sales (61,362 ) (63,131 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 20,541 (333 ) Other investments 17,248 (21,548 ) Equity securities 3,545 36 Short-term investments 4 (422 ) Derivative instruments (1) (9,181 ) 20,732 Other (2) (5,817 ) (5,829 ) Net realized gains (losses) $ 34,153 $ 37,324 (1) See Note 9 for information on the Company’s derivative instruments. (2) Includes the re-measurement of contingent consideration liability amounts.
Summary of OTTI recognized in earnings by asset class	The following table details the net impairment losses recognized in earnings by asset class: March 31, 2017 2016 Three Months Ended Fixed maturities: Mortgage backed securities $ (1,319 ) $ (473 ) Corporate bonds (1 ) (4,880 ) Non-U.S. government securities (198 ) (181 ) Asset backed securities — (6 ) Total (1,518 ) (5,540 ) Equity securities (186 ) (1,102 ) Other investments (103 ) (997 ) Net impairment losses recognized in earnings $ (1,807 ) $ (7,639 )
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: March 31, 2017 2016 Three Months Ended Balance at start of period $ 13,138 $ 26,875 Credit loss impairments recognized on securities not previously impaired — 1,063 Credit loss impairments recognized on securities previously impaired 23 522 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 (624 ) (10,169 ) Balance at end of period $ 12,537 $ 18,291
Summary of restricted assets	The following table details the value of the Company’s restricted assets: March 31, December 31, Assets used for collateral or guarantees: Affiliated transactions $ 3,991,217 $ 3,871,971 Third party agreements 1,545,255 1,513,079 Deposits with U.S. regulatory authorities 528,594 472,890 Deposits with non-U.S. regulatory authorities 45,332 44,399 Total restricted assets $ 6,110,398 $ 5,902,339

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair value hierarchy	The following table presents the Company’s financial assets and liabilities measured at fair value by level at March 31, 2017 : Estimated Fair Value Measurements Using: Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets measured at fair value (1): Available for sale securities: Fixed maturities: Corporate bonds $ 4,546,756 $ — $ 4,528,155 $ 18,601 Mortgage backed securities 412,023 — 412,023 — Municipal bonds 2,519,112 — 2,519,112 — Commercial mortgage backed securities 590,521 — 590,521 — U.S. government and government agencies 3,266,908 3,192,592 74,316 — Non-U.S. government securities 1,295,366 — 1,295,366 — Asset backed securities 1,638,347 — 1,627,710 10,637 Total 14,269,033 3,192,592 11,047,203 29,238 Equity securities 431,062 427,762 3,300 — Short-term investments 803,619 796,075 7,544 — Other investments 126,112 122,773 3,339 — Other investments measured at net asset value (2) 102,325 Total other investments 228,437 122,773 3,339 — Derivative instruments (4) 29,059 — 29,059 — Fair value option: Corporate bonds 817,690 — 817,690 — Non-U.S. government bonds 55,504 — 55,504 — Mortgage backed securities 16,489 — 16,489 — Asset backed securities 16,198 — 16,198 — U.S. government and government agencies 207,064 207,064 — — Short-term investments 581,508 580,315 1,193 — Equity securities 58,353 55,311 3,042 — Other investments 1,338,661 90,475 1,223,186 25,000 Other investments measured at net asset value (2) 556,653 Total 3,648,120 933,165 2,133,302 25,000 Total assets measured at fair value $ 19,409,330 $ 5,472,367 $ 13,223,747 $ 54,238 Liabilities measured at fair value: Contingent consideration liabilities $ (125,544 ) $ — $ — $ (125,544 ) Securities sold but not yet purchased (3) (59,430 ) — (59,430 ) — Derivative instruments (4) (22,227 ) — (22,227 ) — Total liabilities measured at fair value $ (207,201 ) $ — $ (81,657 ) $ (125,544 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7 , “Investment Information—Securities Lending Agreements.” (2) In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. (3) Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets. (4) See Note 9 , “Derivative Instruments.” The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2016 : Estimated Fair Value Measurements Using: Estimated Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets measured at fair value (1): Available for sale securities: Fixed maturities: Corporate bonds $ 4,392,373 $ — $ 4,374,029 $ 18,344 Mortgage backed securities 490,093 — 490,093 — Municipal bonds 3,713,434 — 3,713,434 — Commercial mortgage backed securities 536,051 — 536,051 — U.S. government and government agencies 2,804,540 2,691,575 112,965 — Non-U.S. government securities 1,096,440 — 1,096,440 — Asset backed securities 1,123,987 — 1,112,698 11,289 Total 14,156,918 2,691,575 11,435,710 29,633 Equity securities 532,680 529,695 2,985 — Short-term investments 612,005 608,862 3,143 — Other investments 112,313 112,313 — — Other investments measured at net asset value (2) 55,657 Total other investments 167,970 112,313 — — Derivative instruments (4) 28,410 — 28,410 — Fair value option: Corporate bonds 790,935 — 790,935 — Non-U.S. government bonds 61,747 — 61,747 — Mortgage backed securities 18,624 — 18,624 — Asset backed securities 30,324 — 30,324 — U.S. government and government agencies 197,486 197,486 — — Short-term investments 373,669 309,127 64,542 — Equity securities 27,642 25,328 2,314 — Other investments 1,226,242 80,706 1,120,536 25,000 Other investments measured at net asset value (2) 694,551 Total 3,421,220 612,647 2,089,022 25,000 Total assets measured at fair value $ 18,919,203 $ 4,555,092 $ 13,559,270 $ 54,633 Liabilities measured at fair value: Contingent consideration liabilities $ (122,350 ) $ — $ — $ (122,350 ) Securities sold but not yet purchased (3) (33,157 ) — (33,157 ) — Derivative instruments (4) (26,049 ) — (26,049 ) — Total liabilities measured at fair value $ (181,556 ) $ — $ (59,206 ) $ (122,350 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 7 , “Investment Information—Securities Lending Agreements.” (2) In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. (3) Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets. (4) See Note 9 , “Derivative Instruments.”
Rollforward of Level 3 investments	The following table presents a reconciliation of the beginning and ending balances for all financial assets and liabilities measured at fair value on a recurring basis using Level 3 inputs: Assets Liabilities s Available For Sale Fair Value Option Asset Backed Securities Corporate Bonds Other Investments Total Contingent Consideration Liabilities Three Months Ended March 31, 2017 Balance at beginning of period $ 11,289 $ 18,344 $ 25,000 $ 54,633 $ (122,350 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) 707 257 — 964 (3,646 ) Included in other comprehensive income — — — — — Purchases, issuances, sales and settlements Purchases — — — — — Issuances — — — — — Sales — — — — — Settlements (1,359 ) — — (1,359 ) 452 Transfers in and/or out of Level 3 — — — — — Balance at end of period $ 10,637 $ 18,601 $ 25,000 $ 54,238 $ (125,544 ) Three Months Ended March 31, 2016 Balance at beginning of period $ 57,500 $ 16,368 $ — $ 73,868 $ (96,048 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — (1,202 ) — (1,202 ) (5,198 ) Included in other comprehensive income — — — — — Purchases, issuances, sales and settlements Purchases — — — — — Issuances — — — — — Sales — — — — — Settlements — — — — 536 Transfers in and/or out of Level 3 — — — — — Balance at end of period $ 57,500 $ 15,166 $ — $ 72,666 $ (100,710 ) (1) Gains or losses on asset backed securities were included in net impairment losses recognized in earnings while gains or losses on corporate bonds and contingent consideration liabilities were included in net realized gains (losses).

Derivative Instruments (Tables)

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair value and notional amount of derivatives	The following table summarizes information on the fair values and notional values of the Company’s derivative instruments: Estimated Fair Value Asset Derivatives Liability Derivatives Notional Value (1) March 31, 2017 Futures contracts (2) $ 3,550 $ (4,489 ) $ 2,276,070 Foreign currency forward contracts (2) 7,363 (11,435 ) 1,264,235 TBAs (3) 32,011 (32,791 ) 63,966 Other (2) 18,146 (6,303 ) 1,552,009 Total $ 61,070 $ (55,018 ) December 31, 2016 Futures contracts (2) $ 360 $ (9,398 ) $ 1,655,530 Foreign currency forward contracts (2) 9,354 (12,941 ) 1,186,386 TBAs (3) — — — Other (2) 20,287 (3,710 ) 1,014,863 Total $ 30,001 $ (26,049 ) (1) Represents the absolute notional value of all outstanding contracts, consisting of long and short positions. (2) The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’ (3) The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’
Summary of net realized gains (losses) recorded in the consolidated statements of income	All realized and unrealized contract gains and losses on the Company’s derivative instruments are reflected in net realized gains (losses) in the consolidated statements of income, as summarized in the following table: Derivatives not designated as March 31, hedging instruments: 2017 2016 Three Months Ended Net realized gains (losses): Futures contracts $ 7,720 $ 26,451 Foreign currency forward contracts (11,766 ) (4,752 ) TBAs (65 ) 297 Other (5,070 ) (1,264 ) Total $ (9,181 ) $ 20,732

Other Comprehensive Income (L32

Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2017
Comprehensive Income Note Disclosure [Abstract]
Details about amounts reclassified from AOCI	The following tables present details about amounts reclassified from accumulated other comprehensive income and the tax effects allocated to each component of other comprehensive income (loss): Amounts Reclassified from AOCI Consolidated Statement of Income Three Months Ended Details About Line Item That Includes March 31, AOCI Components Reclassification 2017 2016 Unrealized appreciation on available-for-sale investments Net realized gains (losses) $ 7,813 $ 44,687 Other-than-temporary impairment losses (1,807 ) (7,737 ) Total before tax 6,006 36,950 Income tax (expense) benefit (962 ) (4,727 ) Net of tax $ 5,044 $ 32,223
Schedule of comprehensive income (loss)	Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Three Months Ended March 31, 2017 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 111,472 $ 10,680 $ 100,792 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 6,006 962 5,044 Foreign currency translation adjustments 3,165 41 3,124 Other comprehensive income (loss) $ 108,631 $ 9,759 $ 98,872 Three Months Ended March 31, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 152,174 $ 19,193 $ 132,981 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (98 ) — (98 ) Less reclassification of net realized gains (losses) included in net income 36,950 4,727 32,223 Foreign currency translation adjustments 17,860 547 17,313 Other comprehensive income (loss) $ 132,986 $ 15,013 $ 117,973

Guarantor Financial Informati33

Guarantor Financial Information (Tables)	3 Months Ended
	Mar. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed consolidating balance sheet	March 31, 2017 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 256 $ 41,715 $ 20,227,399 $ (14,700 ) $ 20,254,670 Cash 10,177 42,745 650,832 — 703,754 Investments in subsidiaries 8,992,903 3,843,774 — (12,836,677 ) — Due from subsidiaries and affiliates 1,626 52,032 1,868,171 (1,921,829 ) — Premiums receivable — — 1,891,983 (637,935 ) 1,254,048 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 6,209,021 (4,075,873 ) 2,133,148 Contractholder receivables — — 1,766,340 — 1,766,340 Ceded unearned premiums — — 2,201,994 (1,260,071 ) 941,923 Deferred acquisition costs — — 638,415 (150,490 ) 487,925 Goodwill and intangible assets — — 750,315 — 750,315 Other assets 14,730 55,658 1,893,742 (164,027 ) 1,800,103 Total assets $ 9,019,692 $ 4,035,924 $ 38,098,212 $ (21,061,602 ) $ 30,092,226 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 14,337,192 $ (4,040,371 ) $ 10,296,821 Unearned premiums — — 4,891,330 (1,260,071 ) 3,631,259 Reinsurance balances payable — — 959,221 (637,936 ) 321,285 Contractholder payables — — 1,766,340 — 1,766,340 Collateral held for insured obligations — — 327,161 327,161 Senior notes 296,979 494,548 940,883 — 1,732,410 Revolving credit agreement borrowings 100,000 — 634,961 — 734,961 Due to subsidiaries and affiliates 2,044 541,400 1,378,384 (1,921,828 ) — Other liabilities 14,825 61,055 1,876,454 (350,019 ) 1,602,315 Total liabilities 413,848 1,097,003 27,111,926 (8,210,225 ) 20,412,552 Redeemable noncontrolling interests — — 220,344 (14,700 ) 205,644 Shareholders’ Equity Total shareholders’ equity available to Arch 8,605,844 2,938,921 9,897,756 (12,836,677 ) 8,605,844 Non-redeemable noncontrolling interests — — 868,186 — 868,186 Total shareholders’ equity 8,605,844 2,938,921 10,765,942 (12,836,677 ) 9,474,030 Total liabilities, noncontrolling interests and shareholders’ equity $ 9,019,692 $ 4,035,924 $ 38,098,212 $ (21,061,602 ) $ 30,092,226 December 31, 2016 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 2,612 $ 41,672 $ 19,690,067 $ (14,700 ) $ 19,719,651 Cash 1,687 71,955 769,300 — 842,942 Investments in subsidiaries 8,660,586 3,716,681 — (12,377,267 ) — Due from subsidiaries and affiliates 14,297 51,298 1,866,681 (1,932,276 ) — Premiums receivable — — 1,579,865 (507,430 ) 1,072,435 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 6,114,518 (4,000,380 ) 2,114,138 Contractholder receivables — — 1,717,436 — 1,717,436 Ceded unearned premiums — — 1,985,311 (1,125,744 ) 859,567 Deferred acquisition costs — — 577,461 (129,901 ) 447,560 Goodwill and intangible assets — — 781,553 — 781,553 Other assets 15,725 49,244 1,901,786 (149,928 ) 1,816,827 Total assets $ 8,694,907 $ 3,930,850 $ 36,983,978 $ (20,237,626 ) $ 29,372,109 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 14,164,191 $ (3,963,231 ) $ 10,200,960 Unearned premiums — — 4,532,614 (1,125,744 ) 3,406,870 Reinsurance balances payable — — 807,837 (507,430 ) 300,407 Contractholder payables — — 1,717,436 — 1,717,436 Collateral held for insured obligations — — 301,406 — 301,406 Deposit accounting liabilities — — 22,150 — 22,150 Senior notes 296,957 494,525 940,776 — 1,732,258 Revolving credit agreement borrowings 100,000 — 656,650 — 756,650 Due to subsidiaries and affiliates 26,270 535,584 1,370,422 (1,932,276 ) — Other liabilities 17,962 54,823 1,867,040 (316,978 ) 1,622,847 Total liabilities 441,189 1,084,932 26,380,522 (7,845,659 ) 20,060,984 Redeemable noncontrolling interests — — 220,253 (14,700 ) 205,553 Shareholders’ Equity Total shareholders’ equity available to Arch 8,253,718 2,845,918 9,531,349 (12,377,267 ) 8,253,718 Non-redeemable noncontrolling interests — — 851,854 — 851,854 Total shareholders’ equity 8,253,718 2,845,918 10,383,203 (12,377,267 ) 9,105,572 Total liabilities, noncontrolling interests and shareholders’ equity $ 8,694,907 $ 3,930,850 $ 36,983,978 $ (20,237,626 ) $ 29,372,109
Condensed consolidating statement of income and comprehensive income	Three Months Ended March 31, 2017 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 1,117,017 $ — $ 1,117,017 Net investment income 5 816 137,981 (20,928 ) 117,874 Net realized gains (losses) — — 34,153 — 34,153 Net impairment losses recognized in earnings — — (1,807 ) — (1,807 ) Other underwriting income — — 4,633 — 4,633 Equity in net income (loss) of investment funds accounted for using the equity method — — 48,088 — 48,088 Other income (loss) 171 — (953 ) — (782 ) Total revenues 176 816 1,339,112 (20,928 ) 1,319,176 Expenses Losses and loss adjustment expenses — — 552,570 — 552,570 Acquisition expenses — — 182,289 — 182,289 Other operating expenses — — 174,719 — 174,719 Corporate expenses 17,247 2,008 8,537 — 27,792 Amortization of intangible assets — — 31,294 — 31,294 Interest expense 6,015 11,930 31,336 (20,605 ) 28,676 Net foreign exchange (gains) losses — — 15,348 4,056 19,404 Total expenses 23,262 13,938 996,093 (16,549 ) 1,016,744 Income (loss) before income taxes (23,086 ) (13,122 ) 343,019 (4,379 ) 302,432 Income tax (expense) benefit — 4,873 (33,270 ) — (28,397 ) Income (loss) before equity in net income of subsidiaries (23,086 ) (8,249 ) 309,749 (4,379 ) 274,035 Equity in net income of subsidiaries 276,213 77,373 — (353,586 ) — Net income 253,127 69,124 309,749 (357,965 ) 274,035 Net (income) loss attributable to noncontrolling interests — — (21,231 ) 323 (20,908 ) Net income available to Arch 253,127 69,124 288,518 (357,642 ) 253,127 Preferred dividends (11,218 ) — — — (11,218 ) Net income available to Arch common shareholders $ 241,909 $ 69,124 $ 288,518 $ (357,642 ) $ 241,909 Comprehensive income (loss) available to Arch $ 351,991 $ 87,781 $ 224,173 $ (311,954 ) $ 351,991 Three Months Ended March 31, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 951,579 $ — $ 951,579 Net investment income 1 773 100,261 (7,300 ) 93,735 Net realized gains (losses) — — 37,324 — 37,324 Net impairment losses recognized in earnings — — (7,639 ) — (7,639 ) Other underwriting income — — 5,319 (272 ) 5,047 Equity in net income (loss) of investment funds accounted for using the equity method — — 6,655 — 6,655 Other income (loss) 206 — (231 ) — (25 ) Total revenues 207 773 1,093,268 (7,572 ) 1,086,676 Expenses Losses and loss adjustment expenses — — 522,949 — 522,949 Acquisition expenses — — 167,838 — 167,838 Other operating expenses — — 150,148 — 150,148 Corporate expenses 9,355 582 (554 ) — 9,383 Amortization of intangible assets — — 4,748 — 4,748 Interest expense 5,934 6,672 10,752 (7,251 ) 16,107 Net foreign exchange (gains) losses — — 16,495 7,071 23,566 Total expenses 15,289 7,254 872,376 (180 ) 894,739 Income (loss) before income taxes (15,082 ) (6,481 ) 220,892 (7,392 ) 191,937 Income tax (expense) benefit — 2,244 (18,554 ) — (16,310 ) Income (loss) before equity in net income of subsidiaries (15,082 ) (4,237 ) 202,338 (7,392 ) 175,627 Equity in net income of subsidiaries 169,880 22,866 — (192,746 ) — Net income 154,798 18,629 202,338 (200,138 ) 175,627 Net (income) loss attributable to noncontrolling interests — — (21,150 ) 321 (20,829 ) Net income available to Arch 154,798 18,629 181,188 (199,817 ) 154,798 Preferred dividends (5,484 ) — — — (5,484 ) Net income available to Arch common shareholders $ 149,314 $ 18,629 $ 181,188 $ (199,817 ) $ 149,314 Comprehensive income (loss) available to Arch $ 272,929 $ 58,649 $ 292,251 $ (350,900 ) $ 272,929
Condensed consolidating statement of cash flows	Three Months Ended March 31, 2017 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 701 $ (3,257 ) $ 264,088 $ (53,414 ) $ 208,118 Investing Activities Purchases of fixed maturity investments — — (10,476,918 ) — (10,476,918 ) Purchases of equity securities — — (143,833 ) — (143,833 ) Purchases of other investments — — (427,039 ) — (427,039 ) Proceeds from the sales of fixed maturity investments — — 10,386,746 — 10,386,746 Proceeds from the sales of equity securities — — 253,347 — 253,347 Proceeds from the sales, redemptions and maturities of other investments — — 317,518 — 317,518 Proceeds from redemptions and maturities of fixed maturity investments — — 174,718 — 174,718 Net settlements of derivative instruments — — (3,921 ) — (3,921 ) Net (purchases) sales of short-term investments 2,356 (43 ) (400,164 ) — (397,851 ) Change in cash collateral related to securities lending — — 180,946 — 180,946 Contributions to subsidiaries — (25,900 ) (60,050 ) 85,950 — Purchases of fixed assets — (10 ) (5,184 ) — (5,194 ) Other 20,641 — 19,603 (20,641 ) 19,603 Net Cash Provided By (Used For) Investing Activities 22,997 (25,953 ) (184,231 ) 65,309 (121,878 ) Financing Activities Proceeds from common shares issued, net (3,990 ) — 85,950 (85,950 ) (3,990 ) Proceeds from borrowings — — — — — Repayments of borrowings — — (22,000 ) — (22,000 ) Change in cash collateral related to securities lending — — (180,946 ) — (180,946 ) Dividends paid to redeemable noncontrolling interests — — (4,816 ) 319 (4,497 ) Dividends paid to parent (1) — — (53,095 ) 53,095 — Other — — (25,659 ) 20,641 (5,018 ) Preferred dividends paid (11,218 ) — — — (11,218 ) Net Cash Provided By (Used For) Financing Activities (15,208 ) — (200,566 ) (11,895 ) (227,669 ) Effects of exchange rates changes on foreign currency cash — — 2,241 — 2,241 Increase (decrease) in cash 8,490 (29,210 ) (118,468 ) — (139,188 ) Cash beginning of year 1,687 71,955 769,300 — 842,942 Cash end of period $ 10,177 $ 42,745 $ 650,832 $ — $ 703,754 (1) Dividends paid are included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) and/or Arch-U.S. (Subsidiary Issuer) columns. Three Months Ended March 31, 2016 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 83,892 $ (4,740 ) $ 340,558 $ (97,167 ) $ 322,543 Investing Activities Purchases of fixed maturity investments — — (8,133,537 ) — (8,133,537 ) Purchases of equity securities — — (128,263 ) — (128,263 ) Purchases of other investments — — (305,198 ) — (305,198 ) Proceeds from the sales of fixed maturity investments — — 7,827,536 — 7,827,536 Proceeds from the sales of equity securities — — 216,012 — 216,012 Proceeds from the sales, redemptions and maturities of other investments — — 211,125 — 211,125 Proceeds from redemptions and maturities of fixed maturity investments — — 163,894 — 163,894 Net settlements of derivative instruments — — 21,091 — 21,091 Net (purchases) sales of short-term investments (60 ) (30 ) (65,504 ) — (65,594 ) Change in cash collateral related to securities lending — — (43,118 ) — (43,118 ) Contributions to subsidiaries (3,300 ) — (2,779 ) 6,079 — Purchases of fixed assets (8 ) — (3,944 ) — (3,952 ) Other — — 6,737 — 6,737 Net Cash Provided By (Used For) Investing Activities (3,368 ) (30 ) (235,948 ) 6,079 (233,267 ) Financing Activities Purchases of common shares under share repurchase program (75,256 ) — — — (75,256 ) Proceeds from common shares issued, net 202 — 6,079 (6,079 ) 202 Repayments of borrowings — — (74,171 ) — (74,171 ) Change in cash collateral related to securities lending — — 43,118 — 43,118 Dividends paid to redeemable noncontrolling interests — — (4,816 ) 319 (4,497 ) Dividends paid to parent (1) — — (96,848 ) 96,848 — Other — 184 28,931 — 29,115 Preferred dividends paid (5,484 ) — — — (5,484 ) Net Cash Provided By (Used For) Financing Activities (80,538 ) 184 (97,707 ) 91,088 (86,973 ) Effects of exchange rates changes on foreign currency cash — — 2,332 — 2,332 Increase (decrease) in cash (14 ) (4,586 ) 9,235 — 4,635 Cash beginning of year 6,809 17,023 529,494 — 553,326 Cash end of period $ 6,795 $ 12,437 $ 538,729 $ — $ 557,961 (1) Dividends paid are included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) and/or Arch-U.S. (Subsidiary Issuer) columns.

Variable Interest Entities an34

Variable Interest Entities and Noncontrolling Interests - Carrying amount of assets and liabilities of variable interest entity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Investments accounted for using the fair value option	$ 3,648,120	$ 3,421,220
Cash	703,754	842,942	$ 557,961	$ 553,326
Accrued investment income	104,168	124,483
Premiums receivable	1,254,048	1,072,435
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	2,133,148	2,114,138
Ceded unearned premiums	941,923	859,567
Deferred acquisition costs	487,925	447,560
Receivable for securities sold	239,678	58,284
Goodwill and intangible assets	750,315	781,553	92,670
Other assets	930,688	889,080
Total assets of consolidated VIE	30,092,226	29,372,109
Reserve for losses and loss adjustment expenses	10,296,821	10,200,960	9,378,987	9,125,250
Unearned premiums	3,631,259	3,406,870
Reinsurance balances payable	321,285	300,407
Revolving credit agreement borrowings	734,961	756,650
Payable for securities purchased	389,649	76,183
Other liabilities	674,313	806,260
Total liabilities of consolidated VIE	20,412,552	20,060,984
Redeemable noncontrolling interests	205,644	205,553
Watford Re
Variable Interest Entity [Line Items]
Redeemable noncontrolling interests	205,644	205,553	$ 205,274	$ 205,182
Variable Interest Entity, Primary Beneficiary | Watford Re
Variable Interest Entity [Line Items]
Investments accounted for using the fair value option	1,976,466	1,857,623
Cash	47,566	74,893
Accrued investment income	14,066	17,017
Premiums receivable	196,866	189,911
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	25,673	24,420
Ceded unearned premiums	16,383	12,145
Deferred acquisition costs	93,227	86,379
Receivable for securities sold	19,235	1,326
Goodwill and intangible assets	7,650	7,650
Other assets	116,336	111,386
Total assets of consolidated VIE	2,513,468	2,382,750
Reserve for losses and loss adjustment expenses	566,175	510,809
Unearned premiums	319,677	293,480
Reinsurance balances payable	15,171	12,289
Revolving credit agreement borrowings	234,961	256,650
Payable for securities purchased	81,216	42,922
Other liabilities	100,198	88,976
Total liabilities of consolidated VIE	1,317,398	1,205,126
Redeemable noncontrolling interests	$ 220,344	$ 220,253

Variable Interest Entities an35

Variable Interest Entities and Noncontrolling Interests - Variable interest entity (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2017	Mar. 31, 2016
Variable Interest Entity [Line Items]
Net cash provided by operating activities		$ 208,118	$ 322,543
Net cash used for investing activities		(121,878)	(233,267)
Net cash used for financing activities		(227,669)	(86,973)
Variable Interest Entity, Primary Beneficiary | Watford Holdings Ltd
Variable Interest Entity [Line Items]
Initial investment contribution amount	$ 100,000
Ownership percentage	11.00%
Variable Interest Entity, Primary Beneficiary | Watford Re
Variable Interest Entity [Line Items]
Net cash provided by operating activities		62,200	65,300
Net cash used for investing activities		(60,500)	(43,700)
Net cash used for financing activities		$ (29,000)	$ (51,300)

Variable Interest Entities an36

Variable Interest Entities and Noncontrolling Interests - Non-redeemable noncontrolling interests (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interests, beginning of period	$ 851,854
Amounts attributable to noncontrolling interests	16,324	$ 16,242
Non-redeemable noncontrolling interests, end of period	868,186	754,915
Watford Re
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interests, beginning of period	851,854	738,831
Amounts attributable to noncontrolling interests	16,324	16,242
Foreign currency translation adjustments attributable to noncontrolling interests	8	(158)
Non-redeemable noncontrolling interests, end of period	$ 868,186	$ 754,915
Common shares | Watford Re
Noncontrolling Interest [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	89.00%

Variable Interest Entities an37

Variable Interest Entities and Noncontrolling Interests - Redeemable noncontrolling interests (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests, beginning of period	$ 205,553
Redeemable noncontrolling interests, end of period	205,644
Watford Re
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests, beginning of period	205,553	$ 205,182
Shares acquired by the Company	0	0
Accretion of preference share issuance costs	91	92
Redeemable noncontrolling interests, end of period	$ 205,644	$ 205,274
Cumulative redeemable preference shares | Watford Re
Redeemable Noncontrolling Interest [Line Items]
Preference shares, number of shares issued	9,065,200
Par value per share	$ 0.01
Liquidation preference per share	$ 25

Variable Interest Entities an38

Variable Interest Entities and Noncontrolling Interests - Income or loss attributable to third party investors (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Noncontrolling Interest [Abstract]
Amounts attributable to non-redeemable noncontrolling interests	$ (16,324)	$ (16,242)
Dividends attributable to redeemable noncontrolling interests	(4,584)	(4,587)
Net (income) loss attributable to noncontrolling interests	$ (20,908)	$ (20,829)

Variable Interest Entities an39

Variable Interest Entities and Noncontrolling Interests - Other variable interest entity disclosures (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 951,333	$ 891,774
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Total VIE Assets	429,977
Maximum Exposure to Loss	2,818
Variable Interest Entity, Not Primary Beneficiary | On-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	405
Variable Interest Entity, Not Primary Beneficiary | Off-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	2,413
Variable Interest Entity, Not Primary Beneficiary | Bellemeade I
Variable Interest Entity [Line Items]
Total VIE Assets	146,200
Maximum Exposure to Loss	1,661
Aggregate Excess Of Loss Reinsurance Agreement	300,000
Variable Interest Entity, Not Primary Beneficiary | Bellemeade I | On-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	351
Variable Interest Entity, Not Primary Beneficiary | Bellemeade I | Off-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,310
Variable Interest Entity, Not Primary Beneficiary | Bellemeade II
Variable Interest Entity [Line Items]
Total VIE Assets	283,777
Maximum Exposure to Loss	1,157
Aggregate Excess Of Loss Reinsurance Agreement	300,000
Variable Interest Entity, Not Primary Beneficiary | Bellemeade II | On-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	54
Variable Interest Entity, Not Primary Beneficiary | Bellemeade II | Off-Balance Sheet
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,103
Variable Interest Entity, Not Primary Beneficiary | Irving Partners
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 14,500

Earnings Per Common Share (Deta

Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income		$ 274,035	$ 175,627
Net (income) loss attributable to noncontrolling interests		(20,908)	(20,829)
Net income available to Arch		253,127	154,798
Preferred dividends		(11,218)	(5,484)
Net income (loss) available to Arch common shareholders		$ 241,909	$ 149,314
Denominator:
Weighted average common shares outstanding		121,272,107	120,428,179
Series D preferred shares	[1]	12,762,820	0
Weighted average common shares outstanding — basic		134,034,927	120,428,179
Effect of dilutive common share equivalents:
Nonvested restricted shares		1,646,555	1,460,654
Stock options	[2]	3,366,190	2,607,663
Weighted average common shares and common share equivalents outstanding — diluted		139,047,672	124,496,496
Earnings per common share:
Basic (per share)		$ 1.80	$ 1.24
Diluted (per share)		$ 1.74	$ 1.20
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per common share (shares)		263,475	607,208
[1]	non-voting common equivalent preferred shares issued in connection with the UGC acquisition.
[2]	Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2017 first quarter and 2016 first quarter, the number of stock options excluded were 263,475 and 607,208, respectively.

Segment Information - Summary o

Segment Information - Summary of underwriting income or loss by segment (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017		Mar. 31, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Gross premiums written		$ 1,657,990		$ 1,437,966
Premiums ceded		(381,730)		(316,731)
Net premiums written		1,276,260		1,121,235
Change in unearned premiums		(159,243)		(169,656)
Net premiums earned		1,117,017		951,579
Other underwriting income		4,633		5,047
Losses and loss adjustment expenses		(552,570)		(522,949)
Acquisition expenses, net		(182,289)		(167,838)
Other operating expenses		(174,719)		(150,148)
Underwriting income (loss)		212,072		115,691
Net investment income		117,874		93,735
Net realized gains (losses)		34,153		37,324
Net impairment losses recognized in earnings		(1,807)		(7,639)
Equity in net income (loss) of investment funds accounted for using the equity method		48,088		6,655
Other income (loss)		(782)		(25)
Corporate expenses		(12,208)	[1]	(9,383)
UGC transaction costs and other	[1]	(15,584)
Amortization of intangible assets		(31,294)		(4,748)
Corporate expenses		(27,792)		(9,383)
Interest expense		(28,676)		(16,107)
Net foreign exchange gains (losses)		(19,404)		(23,566)
Income before income taxes		302,432		191,937
Income tax expense		(28,397)		(16,310)
Net income (loss)		274,035		175,627
Dividends attributable to redeemable noncontrolling interests		(4,584)		(4,587)
Amounts attributable to non-redeemable noncontrolling interests		(16,324)		(16,242)
Net income available to Arch		253,127		154,798
Preferred dividends		(11,218)		(5,484)
Net income (loss) available to Arch common shareholders		$ 241,909		$ 149,314
Underwriting Ratios
Loss ratio		49.50%		55.00%
Acquisition expense ratio		16.30%		17.60%
Other operating expense ratio		15.60%		15.80%
Combined ratio		81.40%		88.40%
Goodwill and intangible assets		$ 750,315		$ 92,670	$ 781,553
Other
Segment Reporting Information [Line Items]
Gross premiums written	[2]	154,120		148,606
Premiums ceded		(10,434)		(4,472)
Net premiums written		143,686		144,134
Change in unearned premiums		(21,689)		(28,617)
Net premiums earned		121,997		115,517
Other underwriting income		816		929
Losses and loss adjustment expenses		(85,410)		(79,113)
Acquisition expenses, net		(32,508)		(32,939)
Other operating expenses		(7,190)		(5,338)
Underwriting income (loss)		(2,295)		(944)
Net investment income		22,062		23,326
Net realized gains (losses)		5,641		5,462
Net impairment losses recognized in earnings		0		0
Equity in net income (loss) of investment funds accounted for using the equity method		0		0
Other income (loss)		0		0
Corporate expenses		0	[1]	0
UGC transaction costs and other	[1]	0
Amortization of intangible assets		0		0
Interest expense		(2,920)		(3,480)
Net foreign exchange gains (losses)		441		(1,525)
Income before income taxes		22,929		22,839
Income tax expense		0		0
Net income (loss)		22,929		22,839
Dividends attributable to redeemable noncontrolling interests		(4,584)		(4,587)
Amounts attributable to non-redeemable noncontrolling interests		(16,324)		(16,242)
Net income available to Arch		2,021		2,010
Preferred dividends		0		0
Net income (loss) available to Arch common shareholders		$ 2,021		$ 2,010
Underwriting Ratios
Loss ratio		70.00%		68.50%
Acquisition expense ratio		26.60%		28.50%
Other operating expense ratio		5.90%		4.60%
Combined ratio		102.50%		101.60%
Goodwill and intangible assets		$ 7,650		$ 0
Sub-Total
Segment Reporting Information [Line Items]
Gross premiums written	[2]	1,606,686		1,391,061
Premiums ceded		(474,112)		(413,960)
Net premiums written		1,132,574		977,101
Change in unearned premiums		(137,554)		(141,039)
Net premiums earned		995,020		836,062
Other underwriting income		3,817		4,118
Losses and loss adjustment expenses		(467,160)		(443,836)
Acquisition expenses, net		(149,781)		(134,899)
Other operating expenses		(167,529)		(144,810)
Underwriting income (loss)		214,367		116,635
Net investment income		95,812		70,409
Net realized gains (losses)		28,512		31,862
Net impairment losses recognized in earnings		(1,807)		(7,639)
Equity in net income (loss) of investment funds accounted for using the equity method		48,088		6,655
Other income (loss)		(782)		(25)
Corporate expenses		(12,208)	[1]	(9,383)
UGC transaction costs and other	[1]	(15,584)
Amortization of intangible assets		(31,294)		(4,748)
Interest expense		(25,756)		(12,627)
Net foreign exchange gains (losses)		(19,845)		(22,041)
Income before income taxes		279,503		169,098
Income tax expense		(28,397)		(16,310)
Net income (loss)		251,106		152,788
Dividends attributable to redeemable noncontrolling interests		0		0
Amounts attributable to non-redeemable noncontrolling interests		0		0
Net income available to Arch		251,106		152,788
Preferred dividends		(11,218)		(5,484)
Net income (loss) available to Arch common shareholders		$ 239,888		$ 147,304
Underwriting Ratios
Loss ratio		46.90%		53.10%
Acquisition expense ratio		15.10%		16.10%
Other operating expense ratio		16.80%		17.30%
Combined ratio		78.80%		86.50%
Goodwill and intangible assets		$ 742,665		$ 92,670
Sub-Total | Insurance
Segment Reporting Information [Line Items]
Gross premiums written	[2]	782,281		798,553
Premiums ceded		(234,095)		(248,789)
Net premiums written		548,186		549,764
Change in unearned premiums		(42,540)		(36,675)
Net premiums earned		505,646		513,089
Other underwriting income		0		0
Losses and loss adjustment expenses		(332,641)		(323,609)
Acquisition expenses, net		(74,868)		(74,348)
Other operating expenses		(88,126)		(85,058)
Underwriting income (loss)		$ 10,011		$ 30,074
Underwriting Ratios
Loss ratio		65.80%		63.10%
Acquisition expense ratio		14.80%		14.50%
Other operating expense ratio		17.40%		16.60%
Combined ratio		98.00%		94.20%
Goodwill and intangible assets		$ 24,371		$ 27,825
Sub-Total | Reinsurance
Segment Reporting Information [Line Items]
Gross premiums written	[2]	475,782		481,390
Premiums ceded		(166,092)		(160,566)
Net premiums written		309,690		320,824
Change in unearned premiums		(64,839)		(59,616)
Net premiums earned		244,851		261,208
Other underwriting income		(306)		325
Losses and loss adjustment expenses		(105,454)		(111,598)
Acquisition expenses, net		(46,147)		(54,758)
Other operating expenses		(37,533)		(36,258)
Underwriting income (loss)		$ 55,411		$ 58,919
Underwriting Ratios
Loss ratio		43.10%		42.70%
Acquisition expense ratio		18.80%		21.00%
Other operating expense ratio		15.30%		13.90%
Combined ratio		77.20%		77.60%
Goodwill and intangible assets		$ 773		$ 1,713
Sub-Total | Mortgage
Segment Reporting Information [Line Items]
Gross premiums written	[2]	348,623		111,280
Premiums ceded		(73,925)		(4,767)
Net premiums written		274,698		106,513
Change in unearned premiums		(30,175)		(44,748)
Net premiums earned		244,523		61,765
Other underwriting income		4,123		3,793
Losses and loss adjustment expenses		(29,065)		(8,629)
Acquisition expenses, net		(28,766)		(5,793)
Other operating expenses		(41,870)		(23,494)
Underwriting income (loss)		$ 148,945		$ 27,642
Underwriting Ratios
Loss ratio		11.90%		14.00%
Acquisition expense ratio		11.80%		9.40%
Other operating expense ratio		17.10%		38.00%
Combined ratio		40.80%		61.40%
Goodwill and intangible assets		$ 717,521		$ 63,132
[1]	Certain expenses have been excluded from ‘corporate expenses’ and reflected in ‘UGC transaction costs and other.’
[2]	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

Segment Information - Narrative

Segment Information - Narrative (Details)	3 Months Ended
	Mar. 31, 2017segment
Underwriting segments
Segment Reporting Information [Line Items]
Number of segments	3
Other
Segment Reporting Information [Line Items]
Number of segments	2

Reserve for Losses and Loss A43

Reserve for Losses and Loss Adjustment Expenses - Reconciliation of beginning and ending balances of losses and loss adjustment reserves(Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Reserve for losses and loss adjustment expenses at beginning of year	$ 10,200,960	$ 9,125,250
Unpaid losses and loss adjustment expenses recoverable	2,083,575	1,828,837
Net reserve for losses and loss adjustment expenses at beginning of year	8,117,385	7,296,413
Net incurred losses and loss adjustment expenses relating to losses occurring in:
Current year	635,775	578,978
Prior years	(83,205)	(56,029)
Total net incurred losses and loss adjustment expenses	552,570	522,949
Net foreign exchange losses (gains)	31,278	33,575
Net paid losses and loss adjustment expenses relating to losses occurring in:
Current year	(34,957)	(49,079)
Prior years	(464,585)	(362,595)
Total net paid losses and loss adjustment expenses	(499,542)	(411,674)
Net reserve for losses and loss adjustment expenses at end of year	8,201,691	7,441,263
Unpaid losses and loss adjustment expenses recoverable	2,095,130	1,937,724
Reserve for losses and loss adjustment expenses at end of period	$ 10,296,821	$ 9,378,987

Reserve for Losses and Loss A44

Reserve for Losses and Loss Adjustment Expenses - Prior year development (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (83,205)	$ (56,029)
Underwriting segments | Reinsurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (57,200)	$ (47,400)
Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims Prior Years Percentage	(23.40%)	(18.10%)
Underwriting segments | Reinsurance | Short Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (40,800)	$ (36,500)
Underwriting segments | Reinsurance | Short Tailed Lines | Property Catastrophe And Property Other Than Property Catastrophe
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(34,000)	(29,800)
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(16,400)	(10,900)
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines | Casualty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years		(14,200)
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines | Casualty | 2003-2013
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(5,500)
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines | Marine And Aviation
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years		2,000
Underwriting segments | Reinsurance | Medium Tailed And Long Tailed Lines | Marine And Aviation | 2014-2016
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(9,900)
Underwriting segments | Insurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (2,100)	$ (6,200)
Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims Prior Years Percentage	(0.40%)	(1.20%)
Underwriting segments | Insurance | Programs
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years		$ 6,100
Percentage of Prior Year Development		30.00%
Underwriting segments | Insurance | Short Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (1,900)	$ (3,700)
Underwriting segments | Insurance | Medium Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	6,800	7,400
Underwriting segments | Insurance | Medium Tailed Lines | 2013 and 2014
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	14,200
Underwriting segments | Insurance | Medium Tailed Lines | Professional Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(7,500)
Underwriting segments | Insurance | Long Tailed Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	(7,000)	(9,900)
Underwriting segments | Insurance | Long Tailed Lines | 2008 and 2012
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years		(6,900)
Underwriting segments | Mortgage
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (23,600)	$ (2,700)
Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims Prior Years Percentage	(9.60%)	(4.40%)
Underwriting segments | Mortgage | Most origination years
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (8,200)
Underwriting segments | Other
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years	$ (300)	$ 200

Investment Information - Summar

Investment Information - Summary of available for sale securities (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2017	Dec. 31, 2016
Available for sale securities:
Estimated Fair Value		$ 15,732,151	$ 15,469,573
Gross Unrealized Gains		195,593	163,339
Gross Unrealized Losses		(125,819)	(198,886)
Cost or Amortized Cost		15,662,377	15,505,120
OTTI Unrealized Losses	[1]	(5,422)	(5,831)
Fixed maturities
Available for sale securities:
Estimated Fair Value		14,269,033	14,156,918
Gross Unrealized Gains	[2]	97,001	79,082
Gross Unrealized Losses	[2]	(118,196)	(178,759)
Cost or Amortized Cost	[2]	14,290,228	14,256,595
OTTI Unrealized Losses	[1],[2]	(5,422)	(5,831)
Fixed maturities | Corporate bonds
Available for sale securities:
Estimated Fair Value		4,546,756	4,392,373
Gross Unrealized Gains	[2]	31,033	27,606
Gross Unrealized Losses	[2]	(36,615)	(46,905)
Cost or Amortized Cost	[2]	4,552,338	4,411,672
OTTI Unrealized Losses	[1],[2]	(1,876)	(2,285)
Fixed maturities | Mortgage backed securities
Available for sale securities:
Estimated Fair Value		412,023	490,093
Gross Unrealized Gains	[2]	5,210	4,794
Gross Unrealized Losses	[2]	(2,712)	(8,357)
Cost or Amortized Cost	[2]	409,525	493,656
OTTI Unrealized Losses	[1],[2]	(3,323)	(3,323)
Fixed maturities | Municipal bonds
Available for sale securities:
Estimated Fair Value		2,519,112	3,713,434
Gross Unrealized Gains	[2]	14,332	8,554
Gross Unrealized Losses	[2]	(17,411)	(29,154)
Cost or Amortized Cost	[2]	2,522,191	3,734,034
OTTI Unrealized Losses	[1],[2]	(201)	(201)
Fixed maturities | Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value		590,521	536,051
Gross Unrealized Gains	[2]	3,485	2,876
Gross Unrealized Losses	[2]	(6,040)	(6,508)
Cost or Amortized Cost	[2]	593,076	539,683
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | US government and government agencies
Available for sale securities:
Estimated Fair Value		3,266,908	2,804,540
Gross Unrealized Gains	[2]	7,940	9,319
Gross Unrealized Losses	[2]	(11,152)	(24,437)
Cost or Amortized Cost	[2]	3,270,120	2,819,658
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | Non-US government securities
Available for sale securities:
Estimated Fair Value		1,295,366	1,096,440
Gross Unrealized Gains	[2]	26,017	19,036
Gross Unrealized Losses	[2]	(39,356)	(56,872)
Cost or Amortized Cost	[2]	1,308,705	1,134,276
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | Asset backed securities
Available for sale securities:
Estimated Fair Value		1,638,347	1,123,987
Gross Unrealized Gains	[2]	8,984	6,897
Gross Unrealized Losses	[2]	(4,910)	(6,526)
Cost or Amortized Cost	[2]	1,634,273	1,123,616
OTTI Unrealized Losses	[1],[2]	(22)	(22)
Equity securities
Available for sale securities:
Estimated Fair Value		431,062	532,680
Gross Unrealized Gains		66,628	62,627
Gross Unrealized Losses		(6,660)	(17,517)
Cost or Amortized Cost		371,094	487,570
OTTI Unrealized Losses	[1]	0	0
Other investments
Available for sale securities:
Estimated Fair Value		228,437	167,970
Gross Unrealized Gains		31,844	21,358
Gross Unrealized Losses		(838)	(2,465)
Cost or Amortized Cost		197,431	149,077
OTTI Unrealized Losses	[1]	0	0
Short-term investments
Available for sale securities:
Estimated Fair Value		803,619	612,005
Gross Unrealized Gains		120	272
Gross Unrealized Losses		(125)	(145)
Cost or Amortized Cost		803,624	611,878
OTTI Unrealized Losses	[1]	$ 0	$ 0
[1]	Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At March 31, 2017, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $2.0 million, compared to a net unrealized gain of $2.8 million at December 31, 2016.
[2]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Aging

Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Available for sale securities:
Estimated Fair Value - Less than 12 Months		$ 6,901,346	$ 7,509,193
Gross Unrealized Losses - Less than 12 Months		(121,948)	(192,881)
Estimated Fair Value - 12 Months or More		113,771	154,001
Gross Unrealized Losses - 12 Months or More		(3,871)	(6,005)
Estimated Fair Value - Total		7,015,117	7,663,194
Gross Unrealized Losses - Total		(125,819)	(198,886)
Fixed maturities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	6,697,794	7,171,367
Gross Unrealized Losses - Less than 12 Months	[1]	(114,325)	(172,754)
Estimated Fair Value - 12 Months or More	[1]	113,771	154,001
Gross Unrealized Losses - 12 Months or More	[1]	(3,871)	(6,005)
Estimated Fair Value - Total	[1]	6,811,565	7,325,368
Gross Unrealized Losses - Total	[1]	(118,196)	(178,759)
Fixed maturities | Corporate bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,832,009	1,700,813
Gross Unrealized Losses - Less than 12 Months	[1]	(34,331)	(43,011)
Estimated Fair Value - 12 Months or More	[1]	26,288	46,902
Gross Unrealized Losses - 12 Months or More	[1]	(2,284)	(3,894)
Estimated Fair Value - Total	[1]	1,858,297	1,747,715
Gross Unrealized Losses - Total	[1]	(36,615)	(46,905)
Fixed maturities | Mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	137,291	402,699
Gross Unrealized Losses - Less than 12 Months	[1]	(2,652)	(8,134)
Estimated Fair Value - 12 Months or More	[1]	4,150	6,105
Gross Unrealized Losses - 12 Months or More	[1]	(60)	(223)
Estimated Fair Value - Total	[1]	141,441	408,804
Gross Unrealized Losses - Total	[1]	(2,712)	(8,357)
Fixed maturities | Municipal bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,043,998	1,513,308
Gross Unrealized Losses - Less than 12 Months	[1]	(16,890)	(28,504)
Estimated Fair Value - 12 Months or More	[1]	25,004	29,636
Gross Unrealized Losses - 12 Months or More	[1]	(521)	(650)
Estimated Fair Value - Total	[1]	1,069,002	1,542,944
Gross Unrealized Losses - Total	[1]	(17,411)	(29,154)
Fixed maturities | Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	304,022	231,374
Gross Unrealized Losses - Less than 12 Months	[1]	(5,890)	(6,331)
Estimated Fair Value - 12 Months or More	[1]	3,928	5,635
Gross Unrealized Losses - 12 Months or More	[1]	(150)	(177)
Estimated Fair Value - Total	[1]	307,950	237,009
Gross Unrealized Losses - Total	[1]	(6,040)	(6,508)
Fixed maturities | US government and government agencies
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,803,247	1,888,018
Gross Unrealized Losses - Less than 12 Months	[1]	(11,152)	(24,437)
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]	1,803,247	1,888,018
Gross Unrealized Losses - Total	[1]	(11,152)	(24,437)
Fixed maturities | Non-US government securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	914,310	807,598
Gross Unrealized Losses - Less than 12 Months	[1]	(39,153)	(56,872)
Estimated Fair Value - 12 Months or More	[1]	13,924	0
Gross Unrealized Losses - 12 Months or More	[1]	(203)	0
Estimated Fair Value - Total	[1]	928,234	807,598
Gross Unrealized Losses - Total	[1]	(39,356)	(56,872)
Fixed maturities | Asset backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	662,917	627,557
Gross Unrealized Losses - Less than 12 Months	[1]	(4,257)	(5,465)
Estimated Fair Value - 12 Months or More	[1]	40,477	65,723
Gross Unrealized Losses - 12 Months or More	[1]	(653)	(1,061)
Estimated Fair Value - Total	[1]	703,394	693,280
Gross Unrealized Losses - Total	[1]	(4,910)	(6,526)
Equity securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months		134,646	269,381
Gross Unrealized Losses - Less than 12 Months		(6,660)	(17,517)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		134,646	269,381
Gross Unrealized Losses - Total		(6,660)	(17,517)
Other investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months		25,189	39,299
Gross Unrealized Losses - Less than 12 Months		(838)	(2,465)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		25,189	39,299
Gross Unrealized Losses - Total		(838)	(2,465)
Short-term investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months		43,717	29,146
Gross Unrealized Losses - Less than 12 Months		(125)	(145)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		43,717	29,146
Gross Unrealized Losses - Total		$ (125)	$ (145)
[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Maturi

Investment Information - Maturity profile of available for sale securities) (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Estimated Fair Value:
Estimated fair value		$ 13,745,932	$ 13,426,577
Amortized Cost:
Amortized cost		13,767,375	13,522,671
Fixed maturities
Estimated Fair Value:
Due in one year or less		633,926	560,830
Due after one year through five years		7,197,090	6,158,148
Due after five years through 10 years		3,337,574	4,676,847
Due after 10 years		459,552	610,962
Single maturity date		11,628,142	12,006,787
Estimated fair value	[1]	14,269,033	14,156,918
Amortized Cost:
Due in one year or less		632,468	557,675
Due after one year through five years		7,217,033	6,211,099
Due after five years through 10 years		3,339,974	4,710,017
Due after 10 years		463,879	620,849
Single maturity date		11,653,354	12,099,640
Amortized cost	[1]	14,290,228	14,256,595
Fixed maturities | Mortgage backed securities
Estimated Fair Value:
Securities without single maturity date		412,023	490,093
Amortized Cost:
Securities without single maturity date		409,525	493,656
Fixed maturities | Commercial mortgage backed securities
Estimated Fair Value:
Securities without single maturity date		590,521	536,051
Amortized Cost:
Securities without single maturity date		593,076	539,683
Fixed maturities | Asset backed securities
Estimated Fair Value:
Securities without single maturity date		1,638,347	1,123,987
Amortized Cost:
Securities without single maturity date		$ 1,634,273	$ 1,123,616
[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Securi

Investment Information - Securities lending agreements (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Disclosure Investment Information [Abstract]
Fair value of cash collateral received on securities lending	$ 31,500	$ 212,500
Fair value of non-cash collateral received on securities lending	506,900	550,100
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	538,353	762,554
Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 9	0	0
Amounts related to securities lending not included in offsetting disclosure in Note 9	538,353	762,554
US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	506,210	718,492
Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	29,624	29,078
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	2,519	14,984
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	390,436	600,077
Overnight and continuous | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	358,293	556,015
Overnight and continuous | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	29,624	29,078
Overnight and continuous | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	2,519	14,984
Less than 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	31,244
Less than 30 days | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	31,244
Less than 30 days | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
Less than 30 days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
30 - 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	139,416	126,093
30 - 90 days | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	139,416	126,093
30 - 90 days | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
30 - 90 days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
90 days or more
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	8,501	5,140
90 days or more | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	8,501	5,140
90 days or more | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
90 days or more | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	$ 0	$ 0

Investment Information - Other

Investment Information - Other investments (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		$ 2,123,751	$ 2,088,763
Available for sale
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		228,437	167,970
Available for sale | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		109,084	84,778
Available for sale | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		52,016	33,923
Available for sale | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		11,003	7,469
Available for sale | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		56,334	41,800
Fair value option
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		1,895,314	1,920,793
Fair value option | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		1,123,568	1,190,799
Other investments par		1,145,832	1,208,537
Fair value option | Mezzanine debt funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		109,334	127,943
Fair value option | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		205,150	178,568
Fair value option | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		82,718	75,468
Fair value option | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		208,707	218,298
Fair value option | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	[1]	$ 165,837	$ 129,717
[1]	Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other.

Investment Information - Fair v

Investment Information - Fair value option (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 3,648,120	$ 3,421,220
Fixed maturities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	1,112,945	1,099,116
Other investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	1,895,314	1,920,793
Short-term investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	581,508	373,669
Equity securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 58,353	$ 27,642

Investment Information - Limite

Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss		$ 951,333	$ 891,774
Aggregate unfunded commitments		1,450,000
Equity method investments
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[1]	861,607	800,970
Aggregate unfunded commitments		797,600	776,600
Fair value option
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[2]	89,726	90,804
Aggregate unfunded commitments		$ 66,700	$ 16,700
[1]	Aggregate unfunded commitments were $797.6 million at March 31, 2017, compared to $776.6 million at December 31, 2016.
[2]	Aggregate unfunded commitments were $66.7 million at March 31, 2017, compared to $16.7 million at December 31, 2016.

Investment Information - Net in

Investment Information - Net investment income (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Net investment income:
Gross investment income		$ 138,375	$ 111,359
Investment expenses		(20,501)	(17,624)
Net investment income		117,874	93,735
Fixed maturities
Net investment income:
Gross investment income		94,393	73,673
Term loan investments
Net investment income:
Gross investment income		21,170	20,012
Equity securities (dividends)
Net investment income:
Gross investment income		2,643	3,435
Short-term investments
Net investment income:
Gross investment income		1,759	496
Other
Net investment income:
Gross investment income	[1]	$ 18,410	$ 13,743
[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
		Mar. 31, 2017	Mar. 31, 2016
Net realized gains and losses:
Available for sale securities, gross gains on investment sales		$ 69,175	$ 107,819
Available for sale securities, gross losses on investment sales		(61,362)	(63,131)
Derivative instruments	[1]	(9,181)	20,732
Other	[2]	(5,817)	(5,829)
Net realized gains (losses)		34,153	37,324
Fixed maturities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		20,541	(333)
Other investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		17,248	(21,548)
Equity securities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		3,545	36
Short-term investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		$ 4	$ (422)
[1]	See Note 9 for information on the Company’s derivative instruments.
[2]	Includes the re-measurement of contingent consideration liability amounts.

Investment Information - Othe54

Investment Information - Other than temporary impairments recognized in earnings (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ (1,807)	$ (7,639)
Fixed maturities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(1,518)	(5,540)
Fixed maturities | Mortgage backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(1,319)	(473)
Fixed maturities | Corporate bonds
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(1)	(4,880)
Fixed maturities | Non-US government securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(198)	(181)
Fixed maturities | Asset backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	0	(6)
Equity securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(186)	(1,102)
Other investments
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ (103)	$ (997)

Investment Information - Othe55

Investment Information - Other than temporary impairments rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Rollforward:
Balance at start of period	$ 13,138	$ 26,875
Credit loss impairments recognized on securities not previously impaired	0	1,063
Credit loss impairments recognized on securities previously impaired	23	522
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	0	0
Reductions for securities sold during the period	(624)	(10,169)
Balance at end of period	$ 12,537	$ 18,291

Investment Information - Restri

Investment Information - Restricted assets (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Restricted Assets [Line Items]
Restricted assets	$ 6,110,398	$ 5,902,339
Collateral or guarantees - affiliated transactions
Restricted Assets [Line Items]
Restricted assets	3,991,217	3,871,971
Collateral or guarantees - third party agreements
Restricted Assets [Line Items]
Restricted assets	1,545,255	1,513,079
Deposits with US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	528,594	472,890
Deposits with non-US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	$ 45,332	$ 44,399

Investment Information - Narrat

Investment Information - Narrative (Details) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2017USD ($)lots	Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)lots
Narrative items:
Investable assets		$ 20,740,000
Income (Loss) from Equity Method Investments		48,088	$ 6,655
OTTI unrealized (losses) gains at current fair value		$ 2,000		$ 2,800
Continuous unrealized loss, qualitative disclosures:
Number of positions in an unrealized loss position (lots) | lots		3,350		3,540
Total number of positions (lots) | lots		7,720		7,240
Largest single loss		$ 4,400		$ 4,600
OTTI unrealized losses (gains)	[1]	5,422		$ 5,831
Underwriting segments
Narrative items:
Investable assets		18,830,000
Income (Loss) from Equity Method Investments		48,088	6,655
Other
Narrative items:
Investable assets		1,900,000
Income (Loss) from Equity Method Investments		$ 0	$ 0
[1]	Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At March 31, 2017, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $2.0 million, compared to a net unrealized gain of $2.8 million at December 31, 2016.

Fair Value - Fair Value Hierarc

Fair Value - Fair Value Hierarchy (Details) - Recurring - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		$ 5,472,367	$ 4,555,092
Liabilities measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Securities sold but not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[1]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	3,192,592	2,691,575
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	3,192,592	2,691,575
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed maturities | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		427,762	529,695
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		796,075	608,862
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		122,773	112,313
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		122,773	112,313
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		933,165	612,647
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		207,064	197,486
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		580,315	309,127
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		55,311	25,328
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		90,475	80,706
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		13,223,747	13,559,270
Liabilities measured at fair value		(81,657)	(59,206)
Significant Other Observable Inputs (Level 2) | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		0	0
Significant Other Observable Inputs (Level 2) | Securities sold but not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[1]	(59,430)	(33,157)
Significant Other Observable Inputs (Level 2) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(22,227)	(26,049)
Significant Other Observable Inputs (Level 2) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	11,047,203	11,435,710
Significant Other Observable Inputs (Level 2) | Fixed maturities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	4,528,155	4,374,029
Significant Other Observable Inputs (Level 2) | Fixed maturities | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	412,023	490,093
Significant Other Observable Inputs (Level 2) | Fixed maturities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	2,519,112	3,713,434
Significant Other Observable Inputs (Level 2) | Fixed maturities | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	590,521	536,051
Significant Other Observable Inputs (Level 2) | Fixed maturities | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	74,316	112,965
Significant Other Observable Inputs (Level 2) | Fixed maturities | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	1,295,366	1,096,440
Significant Other Observable Inputs (Level 2) | Fixed maturities | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	1,627,710	1,112,698
Significant Other Observable Inputs (Level 2) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		3,300	2,985
Significant Other Observable Inputs (Level 2) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		7,544	3,143
Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		3,339	0
Significant Other Observable Inputs (Level 2) | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		3,339	0
Significant Other Observable Inputs (Level 2) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		29,059	28,410
Significant Other Observable Inputs (Level 2) | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		2,133,302	2,089,022
Significant Other Observable Inputs (Level 2) | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		817,690	790,935
Significant Other Observable Inputs (Level 2) | Fair value option | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		16,489	18,624
Significant Other Observable Inputs (Level 2) | Fair value option | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Other Observable Inputs (Level 2) | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		55,504	61,747
Significant Other Observable Inputs (Level 2) | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		16,198	30,324
Significant Other Observable Inputs (Level 2) | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,193	64,542
Significant Other Observable Inputs (Level 2) | Fair value option | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		3,042	2,314
Significant Other Observable Inputs (Level 2) | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,223,186	1,120,536
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		54,238	54,633
Liabilities measured at fair value		(125,544)	(122,350)
Significant Unobservable Inputs (Level 3) | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(125,544)	(122,350)
Significant Unobservable Inputs (Level 3) | Securities sold but not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[1]	0	0
Significant Unobservable Inputs (Level 3) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	29,238	29,633
Significant Unobservable Inputs (Level 3) | Fixed maturities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	18,601	18,344
Significant Unobservable Inputs (Level 3) | Fixed maturities | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	0	0
Significant Unobservable Inputs (Level 3) | Fixed maturities | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[2]	10,637	11,289
Significant Unobservable Inputs (Level 3) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		25,000	25,000
Significant Unobservable Inputs (Level 3) | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		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	0
Significant Unobservable Inputs (Level 3) | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		25,000	25,000
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		19,409,330	18,919,203
Liabilities measured at fair value		(207,201)	(181,556)
Estimated Fair Value | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(125,544)	(122,350)
Estimated Fair Value | Securities sold but not yet purchased
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	[1]	(59,430)	(33,157)
Estimated Fair Value | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(22,227)	(26,049)
Estimated Fair Value | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		14,269,033	14,156,918
Estimated Fair Value | Fixed maturities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		4,546,756	4,392,373
Estimated Fair Value | Fixed maturities | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		412,023	490,093
Estimated Fair Value | Fixed maturities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		2,519,112	3,713,434
Estimated Fair Value | Fixed maturities | Commercial mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		590,521	536,051
Estimated Fair Value | Fixed maturities | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		3,266,908	2,804,540
Estimated Fair Value | Fixed maturities | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,295,366	1,096,440
Estimated Fair Value | Fixed maturities | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,638,347	1,123,987
Estimated Fair Value | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		431,062	532,680
Estimated Fair Value | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		803,619	612,005
Estimated Fair Value | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		228,437	167,970
Estimated Fair Value | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		126,112	112,313
Estimated Fair Value | Other investments measured at net asset value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	102,325	55,657
Estimated Fair Value | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		29,059	28,410
Estimated Fair Value | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		3,648,120	3,421,220
Estimated Fair Value | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		817,690	790,935
Estimated Fair Value | Fair value option | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		16,489	18,624
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		207,064	197,486
Estimated Fair Value | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		55,504	61,747
Estimated Fair Value | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		16,198	30,324
Estimated Fair Value | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		581,508	373,669
Estimated Fair Value | Fair value option | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		58,353	27,642
Estimated Fair Value | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,338,661	1,226,242
Estimated Fair Value | Fair value option | Other investments measured at net asset value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	[3]	$ 556,653	$ 694,551
[1]	Represents the Company’s obligations to deliver securities that it did not own at the time of sale. Such amounts are included in “other liabilities” on the Company’s consolidated balance sheets.
[2]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value.
[3]	In accordance with applicable accounting guidance, certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets.

Fair Value - Rollforward of Lev

Fair Value - Rollforward of Level 3 assets and liabilities (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ 54,633	$ 73,868
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	964	(1,202)
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		(1,359)	0
Transfers in and/or out of Level 3		0	0
Balance at end of period		54,238	72,666
Contingent consideration liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		(122,350)	(96,048)
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(3,646)	(5,198)
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		452	536
Transfers in and/or out of Level 3		0	0
Balance at end of period		(125,544)	(100,710)
Available for sale | Asset backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		11,289	57,500
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	707	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		(1,359)	0
Transfers in and/or out of Level 3		0	0
Balance at end of period		10,637	57,500
Fair value option | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		18,344	16,368
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	257	(1,202)
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	0
Balance at end of period		18,601	15,166
Fair value option | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		25,000	0
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	0
Balance at end of period		$ 25,000	$ 0
[1]	Gains or losses on asset backed securities were included in net impairment losses recognized in earnings while gains or losses on corporate bonds and contingent consideration liabilities were included in net realized gains (losses).

Fair Value - Narrative (Details

Fair Value - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Total assets and liabilities measured at fair value	$ 19,620,000	$ 19,100,000
Total assets and liabilities measured at fair value priced using non-binding broker quotes	$ 177,900	$ 234,000
Total assets and liabilities measured at fair value priced using non-binding broker quotes (percentage)	0.90%	1.20%
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 1,732,410	$ 1,732,258
Reportable Legal Entities | ACGL (Parent Guarantor)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	296,979	296,957
Estimated fair value of senior notes	394,700
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	494,548	$ 494,525
Estimated fair value of senior notes	535,600
Unsecured debt | Notes due 2026
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	495,800
Estimated fair value of senior notes	515,200
Unsecured debt | Notes due 2046
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	445,100
Estimated fair value of senior notes	$ 488,000

Derivative Instruments (Details

Derivative Instruments (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017		Mar. 31, 2016	Dec. 31, 2016
Derivative offsetting [Abstract]
Derivative assets subject to master netting agreements		$ 59,300			$ 28,400
Derivative liabilities subject to master netting agreements		(54,600)			(26,000)
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	[1]	(9,181)		$ 20,732
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives - fair value		61,070			30,001
Liability derivatives - fair value		(55,018)			(26,049)
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(9,181)		20,732
Not Designated as Hedging Instrument [Member] | Futures contracts
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	2,276,070			1,655,530
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		7,720		26,451
Not Designated as Hedging Instrument [Member] | Futures contracts | Other assets
Derivative [Line Items]
Asset derivatives - fair value		3,550	[3]		360
Not Designated as Hedging Instrument [Member] | Futures contracts | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	(4,489)			(9,398)
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	1,264,235			1,186,386
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(11,766)		(4,752)
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts | Other assets
Derivative [Line Items]
Asset derivatives - fair value	[3]	7,363			9,354
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	(11,435)			(12,941)
Not Designated as Hedging Instrument [Member] | TBAs
Derivative [Line Items]
Net derivatives - notional value	[2],[4]	63,966			0
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(65)		297
Not Designated as Hedging Instrument [Member] | TBAs | Fixed maturities available for sale
Derivative [Line Items]
Asset derivatives - fair value		32,011	[4]		0
Liability derivatives - fair value	[4]	(32,791)			0
Not Designated as Hedging Instrument [Member] | Other
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	1,552,009			1,014,863
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(5,070)		$ (1,264)
Not Designated as Hedging Instrument [Member] | Other | Other assets
Derivative [Line Items]
Asset derivatives - fair value	[3]	18,146			20,287
Not Designated as Hedging Instrument [Member] | Other | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	$ (6,303)			$ (3,710)
[1]	See Note 9 for information on the Company’s derivative instruments.
[2]	Represents the absolute notional value of all outstanding contracts, consisting of long and short positions.
[3]	The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’
[4]	The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Mar. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
Investment commitments	$ 1,450

Share Transactions - Share repu

Share Transactions - Share repurchases (Details) - Common shares - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Class of Stock [Line Items]
Cumulative number of shares acquired since inception of share repurchase program	125.2
Aggregate purchase price of shares acquired since inception of share repurchase program	$ 3,680
Treasury stock, shares acquired (shares)		1.1
Treasury stock, value of shares acquired		$ 75.3
Remaining authorized repurchase amount	$ 446.5

Other Comprehensive Income (L64

Other Comprehensive Income (Loss) - Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses	$ (1,807)	$ (7,737)
Income before income taxes	302,432	191,937
Income tax expense	(28,397)	(16,310)
Net of tax	253,127	154,798
Reclassification out of accumulated other comprehensive income | Unrealized appreciation on available-for-sale investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses)	7,813	44,687
Other-than-temporary impairment losses	(1,807)	(7,737)
Income before income taxes	6,006	36,950
Income tax expense	(962)	(4,727)
Net of tax	$ 5,044	$ 32,223

Other Comprehensive Income (L65

Other Comprehensive Income (Loss) - Components of other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Before tax amount:
Unrealized holding gains (losses) arising during period, before tax	$ 111,472	$ 152,174
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), before tax	0	(98)
Less reclassification of net realized gains included in net income, before tax	6,006	36,950
Foreign currency translation adjustments, before tax	3,165	17,860
Other comprehensive income (loss), before tax	108,631	132,986
Tax expense (benefit):
Unrealized holding gains (losses) arising during period, tax	10,680	19,193
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), tax	0	0
Less reclassification of net realized gains included in net income, tax	962	4,727
Foreign currency translation adjustments, tax	41	547
Other comprehensive income (loss), tax	9,759	15,013
Net of tax amount:
Unrealized holding gains (losses) arising during period, net of tax	100,792	132,981
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), net of tax	0	(98)
Less reclassification of net realized gains included in net income, net of tax	5,044	32,223
Foreign currency translation adjustments, net of tax	3,124	17,313
Net current period other comprehensive income (loss)	$ 98,872	$ 117,973

Guarantor Financial Informati66

Guarantor Financial Information - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Assets
Total investments	$ 20,254,670	$ 19,719,651
Cash	703,754	842,942	$ 557,961	$ 553,326
Investments in subsidiaries	0	0
Due from subsidiaries and affiliates	0	0
Premiums receivable	1,254,048	1,072,435
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	2,133,148	2,114,138
Contractholder receivables	1,766,340	1,717,436
Ceded unearned premiums	941,923	859,567
Deferred acquisition costs	487,925	447,560
Goodwill and intangible assets	750,315	781,553	92,670
Other assets	1,800,103	1,816,827
Total assets	30,092,226	29,372,109
Liabilities
Reserve for losses and loss adjustment expenses	10,296,821	10,200,960	9,378,987	9,125,250
Unearned premiums	3,631,259	3,406,870
Reinsurance balances payable	321,285	300,407
Contractholder payables	1,766,340	1,717,436
Collateral held for insured obligations	327,161	301,406
Deposit accounting liabilities		22,150
Senior notes	1,732,410	1,732,258
Revolving credit agreement borrowings	734,961	756,650
Due to subsidiaries and affiliates	0	0
Other liabilities	1,602,315	1,622,847
Total liabilities	20,412,552	20,060,984
Redeemable noncontrolling interests	205,644	205,553
Shareholders' Equity
Total shareholders’ equity available to Arch	8,605,844	8,253,718	6,375,248
Non-redeemable noncontrolling interests	868,186	851,854	754,915
Total shareholders’ equity	9,474,030	9,105,572	7,130,163
Total liabilities, noncontrolling interests and shareholders’ equity	30,092,226	29,372,109
Reportable Legal Entities | ACGL (Parent Guarantor)
Assets
Total investments	256	2,612
Cash	10,177	1,687	6,795	6,809
Investments in subsidiaries	8,992,903	8,660,586
Due from subsidiaries and affiliates	1,626	14,297
Premiums receivable	0	0
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	0	0
Contractholder receivables	0	0
Ceded unearned premiums	0	0
Deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Other assets	14,730	15,725
Total assets	9,019,692	8,694,907
Liabilities
Reserve for losses and loss adjustment expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Contractholder payables	0	0
Collateral held for insured obligations	0	0
Deposit accounting liabilities		0
Senior notes	296,979	296,957
Revolving credit agreement borrowings	100,000	100,000
Due to subsidiaries and affiliates	2,044	26,270
Other liabilities	14,825	17,962
Total liabilities	413,848	441,189
Redeemable noncontrolling interests	0	0
Shareholders' Equity
Total shareholders’ equity available to Arch	8,605,844	8,253,718
Non-redeemable noncontrolling interests	0	0
Total shareholders’ equity	8,605,844	8,253,718
Total liabilities, noncontrolling interests and shareholders’ equity	9,019,692	8,694,907
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Assets
Total investments	41,715	41,672
Cash	42,745	71,955	12,437	17,023
Investments in subsidiaries	3,843,774	3,716,681
Due from subsidiaries and affiliates	52,032	51,298
Premiums receivable	0	0
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	0	0
Contractholder receivables	0	0
Ceded unearned premiums	0	0
Deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Other assets	55,658	49,244
Total assets	4,035,924	3,930,850
Liabilities
Reserve for losses and loss adjustment expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Contractholder payables	0	0
Collateral held for insured obligations	0	0
Deposit accounting liabilities		0
Senior notes	494,548	494,525
Revolving credit agreement borrowings	0	0
Due to subsidiaries and affiliates	541,400	535,584
Other liabilities	61,055	54,823
Total liabilities	1,097,003	1,084,932
Redeemable noncontrolling interests	0	0
Shareholders' Equity
Total shareholders’ equity available to Arch	2,938,921	2,845,918
Non-redeemable noncontrolling interests	0	0
Total shareholders’ equity	2,938,921	2,845,918
Total liabilities, noncontrolling interests and shareholders’ equity	$ 4,035,924	3,930,850
Percentage Ownership of Subsidiary	100.00%
Reportable Legal Entities | Other ACGL Subsidiaries
Assets
Total investments	$ 20,227,399	19,690,067
Cash	650,832	769,300	538,729	529,494
Investments in subsidiaries	0	0
Due from subsidiaries and affiliates	1,868,171	1,866,681
Premiums receivable	1,891,983	1,579,865
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	6,209,021	6,114,518
Contractholder receivables	1,766,340	1,717,436
Ceded unearned premiums	2,201,994	1,985,311
Deferred acquisition costs	638,415	577,461
Goodwill and intangible assets	750,315	781,553
Other assets	1,893,742	1,901,786
Total assets	38,098,212	36,983,978
Liabilities
Reserve for losses and loss adjustment expenses	14,337,192	14,164,191
Unearned premiums	4,891,330	4,532,614
Reinsurance balances payable	959,221	807,837
Contractholder payables	1,766,340	1,717,436
Collateral held for insured obligations	327,161	301,406
Deposit accounting liabilities		22,150
Senior notes	940,883	940,776
Revolving credit agreement borrowings	634,961	656,650
Due to subsidiaries and affiliates	1,378,384	1,370,422
Other liabilities	1,876,454	1,867,040
Total liabilities	27,111,926	26,380,522
Redeemable noncontrolling interests	220,344	220,253
Shareholders' Equity
Total shareholders’ equity available to Arch	9,897,756	9,531,349
Non-redeemable noncontrolling interests	868,186	851,854
Total shareholders’ equity	10,765,942	10,383,203
Total liabilities, noncontrolling interests and shareholders’ equity	38,098,212	36,983,978
Consolidating Adjustments and Eliminations
Assets
Total investments	(14,700)	(14,700)
Cash	0	0	$ 0	$ 0
Investments in subsidiaries	(12,836,677)	(12,377,267)
Due from subsidiaries and affiliates	(1,921,829)	(1,932,276)
Premiums receivable	(637,935)	(507,430)
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	(4,075,873)	(4,000,380)
Contractholder receivables	0	0
Ceded unearned premiums	(1,260,071)	(1,125,744)
Deferred acquisition costs	(150,490)	(129,901)
Goodwill and intangible assets	0	0
Other assets	(164,027)	(149,928)
Total assets	(21,061,602)	(20,237,626)
Liabilities
Reserve for losses and loss adjustment expenses	(4,040,371)	(3,963,231)
Unearned premiums	(1,260,071)	(1,125,744)
Reinsurance balances payable	(637,936)	(507,430)
Contractholder payables	0	0
Collateral held for insured obligations		0
Deposit accounting liabilities		0
Senior notes	0	0
Revolving credit agreement borrowings	0	0
Due to subsidiaries and affiliates	(1,921,828)	(1,932,276)
Other liabilities	(350,019)	(316,978)
Total liabilities	(8,210,225)	(7,845,659)
Redeemable noncontrolling interests	(14,700)	(14,700)
Shareholders' Equity
Total shareholders’ equity available to Arch	(12,836,677)	(12,377,267)
Non-redeemable noncontrolling interests	0	0
Total shareholders’ equity	(12,836,677)	(12,377,267)
Total liabilities, noncontrolling interests and shareholders’ equity	$ (21,061,602)	$ (20,237,626)

Guarantor Financial Informati67

Guarantor Financial Information - Condensed consolidating statement of income and comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues
Net premiums earned	$ 1,117,017	$ 951,579
Net investment income	117,874	93,735
Net realized gains (losses)	34,153	37,324
Net impairment losses recognized in earnings	(1,807)	(7,639)
Other underwriting income	4,633	5,047
Equity in net income (loss) of investment funds accounted for using the equity method	48,088	6,655
Other income (loss)	(782)	(25)
Total revenues	1,319,176	1,086,676
Expenses
Losses and loss adjustment expenses	552,570	522,949
Acquisition expenses	182,289	167,838
Other operating expenses	174,719	150,148
Corporate expenses	27,792	9,383
Amortization of intangible assets	31,294	4,748
Interest expense	28,676	16,107
Net foreign exchange (gains) losses	19,404	23,566
Total expenses	1,016,744	894,739
Income (loss) before income taxes	302,432	191,937
Income tax (expense) benefit	(28,397)	(16,310)
Income (loss) before equity in net income of subsidiaries	274,035	175,627
Equity in net income of subsidiaries	0	0
Net income	274,035	175,627
Net (income) loss attributable to noncontrolling interests	(20,908)	(20,829)
Net income available to Arch	253,127	154,798
Preferred dividends	(11,218)	(5,484)
Net income (loss) available to Arch common shareholders	241,909	149,314
Comprehensive income (loss) available to Arch	351,991	272,929
Reportable Legal Entities | ACGL (Parent Guarantor)
Revenues
Net premiums earned	0	0
Net investment income	5	1
Net realized gains (losses)	0	0
Net impairment losses recognized in earnings	0	0
Other underwriting income	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	0	0
Other income (loss)	171	206
Total revenues	176	207
Expenses
Losses and loss adjustment expenses	0	0
Acquisition expenses	0	0
Other operating expenses	0	0
Corporate expenses	17,247	9,355
Amortization of intangible assets	0	0
Interest expense	6,015	5,934
Net foreign exchange (gains) losses	0	0
Total expenses	23,262	15,289
Income (loss) before income taxes	(23,086)	(15,082)
Income tax (expense) benefit	0	0
Income (loss) before equity in net income of subsidiaries	(23,086)	(15,082)
Equity in net income of subsidiaries	276,213	169,880
Net income	253,127	154,798
Net (income) loss attributable to noncontrolling interests	0	0
Net income available to Arch	253,127	154,798
Preferred dividends	(11,218)	(5,484)
Net income (loss) available to Arch common shareholders	241,909	149,314
Comprehensive income (loss) available to Arch	351,991	272,929
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Revenues
Net premiums earned	0	0
Net investment income	816	773
Net realized gains (losses)	0	0
Net impairment losses recognized in earnings	0	0
Other underwriting income	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	0	0
Other income (loss)	0	0
Total revenues	816	773
Expenses
Losses and loss adjustment expenses	0	0
Acquisition expenses	0	0
Other operating expenses	0	0
Corporate expenses	2,008	582
Amortization of intangible assets	0	0
Interest expense	11,930	6,672
Net foreign exchange (gains) losses	0	0
Total expenses	13,938	7,254
Income (loss) before income taxes	(13,122)	(6,481)
Income tax (expense) benefit	4,873	2,244
Income (loss) before equity in net income of subsidiaries	(8,249)	(4,237)
Equity in net income of subsidiaries	77,373	22,866
Net income	69,124	18,629
Net (income) loss attributable to noncontrolling interests	0	0
Net income available to Arch	69,124	18,629
Preferred dividends	0	0
Net income (loss) available to Arch common shareholders	69,124	18,629
Comprehensive income (loss) available to Arch	87,781	58,649
Reportable Legal Entities | Other ACGL Subsidiaries
Revenues
Net premiums earned	1,117,017	951,579
Net investment income	137,981	100,261
Net realized gains (losses)	34,153	37,324
Net impairment losses recognized in earnings	(1,807)	(7,639)
Other underwriting income	4,633	5,319
Equity in net income (loss) of investment funds accounted for using the equity method	48,088	6,655
Other income (loss)	(953)	(231)
Total revenues	1,339,112	1,093,268
Expenses
Losses and loss adjustment expenses	552,570	522,949
Acquisition expenses	182,289	167,838
Other operating expenses	174,719	150,148
Corporate expenses	8,537	(554)
Amortization of intangible assets	31,294	4,748
Interest expense	31,336	10,752
Net foreign exchange (gains) losses	15,348	16,495
Total expenses	996,093	872,376
Income (loss) before income taxes	343,019	220,892
Income tax (expense) benefit	(33,270)	(18,554)
Income (loss) before equity in net income of subsidiaries	309,749	202,338
Equity in net income of subsidiaries	0	0
Net income	309,749	202,338
Net (income) loss attributable to noncontrolling interests	(21,231)	(21,150)
Net income available to Arch	288,518	181,188
Preferred dividends	0	0
Net income (loss) available to Arch common shareholders	288,518	181,188
Comprehensive income (loss) available to Arch	224,173	292,251
Consolidating Adjustments and Eliminations
Revenues
Net premiums earned	0	0
Net investment income	(20,928)	(7,300)
Net realized gains (losses)	0	0
Net impairment losses recognized in earnings	0	0
Other underwriting income	0	(272)
Equity in net income (loss) of investment funds accounted for using the equity method	0	0
Other income (loss)	0	0
Total revenues	(20,928)	(7,572)
Expenses
Losses and loss adjustment expenses	0	0
Acquisition expenses	0	0
Other operating expenses	0	0
Corporate expenses	0	0
Amortization of intangible assets	0	0
Interest expense	(20,605)	(7,251)
Net foreign exchange (gains) losses	4,056	7,071
Total expenses	(16,549)	(180)
Income (loss) before income taxes	(4,379)	(7,392)
Income tax (expense) benefit	0	0
Income (loss) before equity in net income of subsidiaries	(4,379)	(7,392)
Equity in net income of subsidiaries	(353,586)	(192,746)
Net income	(357,965)	(200,138)
Net (income) loss attributable to noncontrolling interests	323	321
Net income available to Arch	(357,642)	(199,817)
Preferred dividends	0	0
Net income (loss) available to Arch common shareholders	(357,642)	(199,817)
Comprehensive income (loss) available to Arch	$ (311,954)	$ (350,900)

Guarantor Financial Informati68

Guarantor Financial Information - Condensed consolidating statement of cash flows (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Operating Activities
Net Cash Provided by (Used in) Operating Activities		$ 208,118	$ 322,543
Investing Activities
Purchases of fixed maturity investments		(10,476,918)	(8,133,537)
Purchases of equity securities		(143,833)	(128,263)
Purchases of other investments		(427,039)	(305,198)
Proceeds from sales of fixed maturity investments		10,386,746	7,827,536
Proceeds from sales of equity securities		253,347	216,012
Proceeds from sales, redemptions and maturities of other investments		317,518	211,125
Proceeds from redemptions and maturities of fixed maturity investments		174,718	163,894
Net settlements of derivative instruments		(3,921)	21,091
Net (purchases) sales of short-term investments		(397,851)	(65,594)
Change in cash collateral related to securities lending		180,946	(43,118)
Contributions to subsidiaries		0	0
Purchases of fixed assets		(5,194)	(3,952)
Change in other assets		19,603	6,737
Net Cash Provided By (Used For) Investing Activities		(121,878)	(233,267)
Financing Activities
Purchases of common shares under share repurchase program		0	(75,256)
Proceeds from common shares issued, net		(3,990)	202
Proceeds from borrowings		0
Repayments of borrowings		(22,000)	(74,171)
Change in cash collateral related to securities lending		(180,946)	43,118
Dividends paid to redeemable noncontrolling interests		(4,497)	(4,497)
Dividends paid to parent	[1]	0	0
Other		(5,018)	29,115
Preferred dividends paid		(11,218)	(5,484)
Net Cash Provided By (Used For) Financing Activities		(227,669)	(86,973)
Effects of exchange rate changes on foreign currency cash		2,241	2,332
Increase (decrease) in cash		(139,188)	4,635
Cash beginning of year		842,942	553,326
Cash end of period		703,754	557,961
Reportable Legal Entities | ACGL (Parent Guarantor)
Operating Activities
Net Cash Provided by (Used in) Operating Activities		701	83,892
Investing Activities
Purchases of fixed maturity investments		0	0
Purchases of equity securities		0	0
Purchases of other investments		0	0
Proceeds from sales of fixed maturity investments		0	0
Proceeds from sales of equity securities		0	0
Proceeds from sales, redemptions and maturities of other investments		0	0
Proceeds from redemptions and maturities of fixed maturity investments		0	0
Net settlements of derivative instruments		0	0
Net (purchases) sales of short-term investments		2,356	(60)
Change in cash collateral related to securities lending		0	0
Contributions to subsidiaries		0	(3,300)
Purchases of fixed assets		0	(8)
Change in other assets		20,641	0
Net Cash Provided By (Used For) Investing Activities		22,997	(3,368)
Financing Activities
Purchases of common shares under share repurchase program			(75,256)
Proceeds from common shares issued, net		(3,990)	202
Proceeds from borrowings		0
Repayments of borrowings		0	0
Change in cash collateral related to securities lending		0	0
Dividends paid to redeemable noncontrolling interests		0	0
Dividends paid to parent	[1]	0	0
Other		0	0
Preferred dividends paid		(11,218)	(5,484)
Net Cash Provided By (Used For) Financing Activities		(15,208)	(80,538)
Effects of exchange rate changes on foreign currency cash		0	0
Increase (decrease) in cash		8,490	(14)
Cash beginning of year		1,687	6,809
Cash end of period		10,177	6,795
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Operating Activities
Net Cash Provided by (Used in) Operating Activities		(3,257)	(4,740)
Investing Activities
Purchases of fixed maturity investments		0	0
Purchases of equity securities		0	0
Purchases of other investments		0	0
Proceeds from sales of fixed maturity investments		0	0
Proceeds from sales of equity securities		0	0
Proceeds from sales, redemptions and maturities of other investments		0	0
Proceeds from redemptions and maturities of fixed maturity investments		0	0
Net settlements of derivative instruments		0	0
Net (purchases) sales of short-term investments		(43)	(30)
Change in cash collateral related to securities lending		0	0
Contributions to subsidiaries		(25,900)	0
Purchases of fixed assets		(10)	0
Change in other assets		0	0
Net Cash Provided By (Used For) Investing Activities		(25,953)	(30)
Financing Activities
Purchases of common shares under share repurchase program			0
Proceeds from common shares issued, net		0	0
Proceeds from borrowings		0
Repayments of borrowings		0	0
Change in cash collateral related to securities lending		0	0
Dividends paid to redeemable noncontrolling interests		0	0
Dividends paid to parent	[1]	0	0
Other		0	184
Preferred dividends paid		0	0
Net Cash Provided By (Used For) Financing Activities		0	184
Effects of exchange rate changes on foreign currency cash		0	0
Increase (decrease) in cash		(29,210)	(4,586)
Cash beginning of year		71,955	17,023
Cash end of period		42,745	12,437
Reportable Legal Entities | Other ACGL Subsidiaries
Operating Activities
Net Cash Provided by (Used in) Operating Activities		264,088	340,558
Investing Activities
Purchases of fixed maturity investments		(10,476,918)	(8,133,537)
Purchases of equity securities		(143,833)	(128,263)
Purchases of other investments		(427,039)	(305,198)
Proceeds from sales of fixed maturity investments		10,386,746	7,827,536
Proceeds from sales of equity securities		253,347	216,012
Proceeds from sales, redemptions and maturities of other investments		317,518	211,125
Proceeds from redemptions and maturities of fixed maturity investments		174,718	163,894
Net settlements of derivative instruments		(3,921)	21,091
Net (purchases) sales of short-term investments		(400,164)	(65,504)
Change in cash collateral related to securities lending		180,946	(43,118)
Contributions to subsidiaries		(60,050)	(2,779)
Purchases of fixed assets		(5,184)	(3,944)
Change in other assets		19,603	6,737
Net Cash Provided By (Used For) Investing Activities		(184,231)	(235,948)
Financing Activities
Purchases of common shares under share repurchase program			0
Proceeds from common shares issued, net		85,950	6,079
Proceeds from borrowings		0
Repayments of borrowings		(22,000)	(74,171)
Change in cash collateral related to securities lending		(180,946)	43,118
Dividends paid to redeemable noncontrolling interests		(4,816)	(4,816)
Dividends paid to parent	[1]	(53,095)	(96,848)
Other		(25,659)	28,931
Preferred dividends paid		0	0
Net Cash Provided By (Used For) Financing Activities		(200,566)	(97,707)
Effects of exchange rate changes on foreign currency cash		2,241	2,332
Increase (decrease) in cash		(118,468)	9,235
Cash beginning of year		769,300	529,494
Cash end of period		650,832	538,729
Consolidating Adjustments and Eliminations
Operating Activities
Net Cash Provided by (Used in) Operating Activities		(53,414)	(97,167)
Investing Activities
Purchases of fixed maturity investments		0	0
Purchases of equity securities		0	0
Purchases of other investments		0	0
Proceeds from sales of fixed maturity investments		0	0
Proceeds from sales of equity securities		0	0
Proceeds from sales, redemptions and maturities of other investments		0	0
Proceeds from redemptions and maturities of fixed maturity investments		0	0
Net settlements of derivative instruments		0	0
Net (purchases) sales of short-term investments		0	0
Change in cash collateral related to securities lending		0	0
Contributions to subsidiaries		85,950	6,079
Purchases of fixed assets		0	0
Change in other assets		(20,641)	0
Net Cash Provided By (Used For) Investing Activities		65,309	6,079
Financing Activities
Purchases of common shares under share repurchase program			0
Proceeds from common shares issued, net		(85,950)	(6,079)
Proceeds from borrowings		0
Repayments of borrowings		0	0
Change in cash collateral related to securities lending		0	0
Dividends paid to redeemable noncontrolling interests		319	319
Dividends paid to parent	[1]	53,095	96,848
Other		20,641	0
Preferred dividends paid		0	0
Net Cash Provided By (Used For) Financing Activities		(11,895)	91,088
Effects of exchange rate changes on foreign currency cash		0	0
Increase (decrease) in cash		0	0
Cash beginning of year		0	0
Cash end of period		$ 0	$ 0
[1]	Dividends paid are included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) and/or Arch-U.S. (Subsidiary Issuer) columns.

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective tax rate on income before income taxes (percentage)	9.40%	8.50%
Statutory federal tax rate	35.00%
Tax benefit on share-based compensation	0.80%
Net deferred tax assets	$ 227.5		$ 221.2
Income taxes paid	$ 0.7	$ 2.5

Transactions with Related Par70

Transactions with Related Parties (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Related Party Transaction [Line Items]
Investment commitments	$ 1,450,000
Purchases of other investments	427,039	$ 305,198
Common director | The Carlyle Group
Related Party Transaction [Line Items]
Investments, value	200,500
Unfunded commitments	510,000
Purchases of other investments	7,900	40,100
Aggregate cash distributions received	$ 23,300	$ 8,800