Arch Capital (ACGL) 10-Q 4 Nov 16 2016 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 31, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	ARCH CAPITAL GROUP LTD.
Entity Central Index Key	947,484
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		122,694,041

Unaudited Consolidated Balance

Unaudited Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Investments:
Fixed maturities available for sale, at fair value (amortized cost: $10,897,965 and $10,515,440)	$ 11,026,929	$ 10,459,353
Short-term investments available for sale, at fair value (amortized cost: $1,185,811 and $591,141)	1,184,408	587,904
Collateral received under securities lending, at fair value (amortized cost: $466,047 and $385,984)	466,055	389,336
Equity securities available for sale, at fair value (cost: $454,319 and $543,767)	521,587	618,405
Other investments available for sale, at fair value (cost: $151,430 and $261,343)	168,243	300,476
Investments accounted for using the fair value option	3,389,573	2,894,494
Investments accounted for using the equity method	797,542	592,973
Total investments	17,554,337	15,842,941
Cash	578,816	553,326
Accrued investment income	81,907	87,206
Securities pledged under securities lending, at fair value (amortized cost: $449,026 and $386,411)	453,757	384,081
Premiums receivable	1,182,708	983,443
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	2,076,248	1,867,373
Contractholder receivables	1,649,441	1,486,296
Prepaid reinsurance premiums	541,238	427,609
Deferred acquisition costs, net	469,466	433,477
Receivable for securities sold	285,112	45,505
Goodwill and intangible assets	90,941	97,531
Other assets	679,260	968,482
Total assets	25,643,231	23,177,270
Liabilities
Reserve for losses and loss adjustment expenses	9,610,189	9,125,250
Unearned premiums	2,671,121	2,333,932
Reinsurance balances payable	271,688	224,120
Contractholder payables	1,649,441	1,486,296
Collateral held for insured obligations	277,463	248,982
Deposit accounting liabilities	22,281	260,364
Senior notes	791,437	791,306
Revolving credit agreement borrowings	398,100	530,434
Securities lending payable	466,047	393,844
Payable for securities purchased	474,041	64,996
Other liabilities	618,834	568,852
Total liabilities	17,250,642	16,028,376
Commitments and Contingencies
Redeemable noncontrolling interests	205,459	205,182
Shareholders' Equity
Non-cumulative preferred shares	775,000	325,000
Common shares ($0.0033 par, shares issued: 174,499,023 and 173,107,849)	582	577
Additional paid-in capital	516,204	467,339
Retained earnings	7,972,643	7,370,371
Accumulated other comprehensive income (loss), net of deferred income tax	119,752	(16,502)
Common shares held in treasury, at cost (shares: 51,823,826 and 50,480,066)	(2,031,859)	(1,941,904)
Total shareholders' equity available to Arch	7,352,322	6,204,881
Non-redeemable noncontrolling interests	834,808	738,831
Total shareholders' equity	8,187,130	6,943,712
Total liabilities, noncontrolling interests and shareholders' equity	$ 25,643,231	$ 23,177,270

Unaudited Consolidated Balance3

Unaudited Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fixed maturities available for sale, at amortized cost	$ 10,897,965	$ 10,515,440
Short-term investments available for sale, at amortized cost	1,185,811	591,141
Collateral received under securities lending, at amortized cost	466,047	385,984
Equity securities available for sale, at cost	454,319	543,767
Other investments available for sale, at cost	151,430	261,343
Securities pledged under securities lending, at amortized cost	$ 449,026	$ 386,411
Common shares, par value per share	$ 0.0033	$ 0.0033
Common shares issued (shares)	174,499,023	173,107,849
Common shares held in treasury (shares)	51,823,826	50,480,066

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues
Net premiums written	$ 1,014,278	$ 971,972	$ 3,159,076	$ 2,982,547
Change in unearned premiums	(55,875)	(35,289)	(243,109)	(192,162)
Net premiums earned	958,403	936,683	2,915,967	2,790,385
Net investment income	93,618	86,233	275,691	252,190
Net realized gains (losses)	125,105	(89,698)	230,647	(42,075)
Other-than-temporary impairment losses	(3,867)	(8,901)	(16,999)	(17,274)
Less investment impairments recognized in other comprehensive income, before taxes	0	3,033	150	4,494
Net impairment losses recognized in earnings	(3,867)	(5,868)	(16,849)	(12,780)
Other underwriting income	7,980	7,623	38,251	26,876
Equity in net income (loss) of investment funds accounted for using the equity method	16,662	(2,118)	32,054	19,938
Other income (loss)	(400)	(265)	(432)	52
Total revenues	1,197,501	932,590	3,475,329	3,034,586
Expenses
Losses and loss adjustment expenses	524,183	531,741	1,631,724	1,544,883
Acquisition expenses	163,861	171,566	509,607	510,067
Other operating expenses	155,557	146,220	467,416	445,947
Corporate expenses	18,485	10,739	45,068	37,502
Interest expense	15,943	13,300	47,713	30,047
Net foreign exchange (gains) losses	2,621	(14,680)	1,525	(61,598)
Total expenses	880,650	858,886	2,703,053	2,506,848
Income before income taxes	316,851	73,704	772,276	527,738
Income tax expense	(13,231)	(9,704)	(43,672)	(29,162)
Net income	303,620	64,000	728,604	498,576
Net (income) loss attributable to noncontrolling interests	(50,748)	16,033	(109,879)	(19,417)
Net income available to Arch	252,872	80,033	618,725	479,159
Preferred dividends	(5,484)	(5,484)	(16,453)	(16,453)
Net income available to Arch common shareholders	$ 247,388	$ 74,549	$ 602,272	$ 462,706
Net income per common share
Basic (per share)	$ 2.05	$ 0.62	$ 4.99	$ 3.79
Diluted (per share)	$ 1.98	$ 0.60	$ 4.84	$ 3.66
Weighted average common shares and common share equivalents outstanding
Basic (shares)	120,938,916	120,567,410	120,656,420	122,151,971
Diluted (shares)	124,931,653	125,011,773	124,528,174	126,354,759

Unaudited Consolidated Stateme5

Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Comprehensive Income
Net income	$ 303,620	$ 64,000	$ 728,604	$ 498,576
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during period	16,281	(53,891)	251,722	(51,522)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0	(3,033)	(150)	(4,494)
Reclassification of net realized (gains) losses, net of income taxes, included in net income	(54,992)	12,278	(109,309)	(39,868)
Foreign currency translation adjustments	(5,312)	(12,083)	(6,150)	(23,260)
Comprehensive income	259,597	7,271	864,717	379,432
Net (income) loss attributable to noncontrolling interests	(50,748)	16,033	(109,879)	(19,417)
Foreign currency translation adjustments attributable to noncontrolling interests	(59)	96	141	96
Comprehensive income available to Arch	$ 208,790	$ 23,400	$ 754,979	$ 360,111

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
Balance at beginning of year at Dec. 31, 2014		$ 325,000	$ 572	$ 383,073	$ 6,854,571	$ 128,856	$ 161,598	$ (32,742)	$ (1,562,019)
Series E Preferred shares issued		0
Common shares issued, net			4	7,440
Exercise of stock options				12,363
Amortization of share-based compensation				46,575
Issue costs on Series E preferred shares				0
Other				1,497
Net income	$ 498,576				498,576
Net (income) loss attributable to noncontrolling interests	(19,417)				(19,417)
Preferred share dividends	(16,453)				(16,453)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							(91,390)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(4,494)						(4,494)
Foreign currency translation adjustments	(23,260)							(23,260)
Foreign currency translation adjustments attributable to noncontrolling interests								97
Shares repurchased for treasury									(378,776)
Balance at end of period at Sep. 30, 2015	6,162,815	325,000	576	450,948	7,317,277	9,809	65,714	(55,905)	(1,940,795)
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2015	774,162
Total shareholders’ equity at Sep. 30, 2015	6,936,977
Net income	64,000
Net (income) loss attributable to noncontrolling interests	16,033
Preferred share dividends	(5,484)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(3,033)
Foreign currency translation adjustments	(12,083)
Balance at end of period at Sep. 30, 2015	6,162,815	325,000	576	450,948	7,317,277	9,809	65,714	(55,905)	(1,940,795)
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2015	774,162
Total shareholders’ equity at Sep. 30, 2015	6,936,977
Balance at beginning of year at Dec. 31, 2015	6,204,881	325,000	577	467,339	7,370,371	(16,502)	50,085	(66,587)	(1,941,904)
Series E Preferred shares issued		450,000
Common shares issued, net			5	8,406
Exercise of stock options				7,738
Amortization of share-based compensation				46,311
Issue costs on Series E preferred shares				(15,101)
Other				1,511
Net income	728,604				728,604
Net (income) loss attributable to noncontrolling interests	(109,879)				(109,879)
Preferred share dividends	(16,453)				(16,453)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							142,413
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(150)						(150)
Foreign currency translation adjustments	(6,150)							(6,150)
Foreign currency translation adjustments attributable to noncontrolling interests								141
Shares repurchased for treasury									(89,955)
Balance at end of period at Sep. 30, 2016	7,352,322	775,000	582	516,204	7,972,643	119,752	192,348	(72,596)	(2,031,859)
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2016	834,808
Total shareholders’ equity at Sep. 30, 2016	8,187,130
Net income	303,620
Net (income) loss attributable to noncontrolling interests	(50,748)
Preferred share dividends	(5,484)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0
Foreign currency translation adjustments	(5,312)
Balance at end of period at Sep. 30, 2016	7,352,322	$ 775,000	$ 582	$ 516,204	$ 7,972,643	$ 119,752	$ 192,348	$ (72,596)	$ (2,031,859)
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2016	834,808
Total shareholders’ equity at Sep. 30, 2016	$ 8,187,130

Unaudited Consolidated Stateme7

Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating Activities
Net income	$ 728,604	$ 498,576
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized (gains) losses	(262,112)	21,980
Net impairment losses recognized in earnings	16,849	12,780
Equity in net income or loss of investment funds accounted for using the equity method and other income or loss	8,157	3,983
Share-based compensation	46,311	46,575
Changes in:
Reserve for losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable	277,277	139,577
Unearned premiums, net of prepaid reinsurance premiums	243,109	192,162
Premiums receivable	(198,909)	(108,741)
Deferred acquisition costs, net	(40,906)	(41,722)
Reinsurance balances payable	49,198	4,242
Other liabilities	139,596	6,638
Other items	29,965	31,529
Net Cash Provided By Operating Activities	1,037,139	807,579
Investing Activities
Purchases of fixed maturity investments	(27,840,555)	(22,382,104)
Purchases of equity securities	(377,767)	(485,526)
Purchases of other investments	(1,008,774)	(1,320,250)
Proceeds from sales of fixed maturity investments	26,731,924	21,411,554
Proceeds from sales of equity securities	464,904	509,008
Proceeds from sales, redemptions and maturities of other investments	879,330	858,368
Proceeds from redemptions and maturities of fixed maturity investments	540,823	630,397
Net settlements of derivative instruments	23,396	81,114
Proceeds from investment in joint venture	0	40,000
Net (purchases) sales of short-term investments	(604,162)	181,741
Change in cash collateral related to securities lending	(27,935)	28,685
Acquisitions, net of cash	(20,911)	818
Purchases of fixed assets	(11,565)	(10,901)
Change in other assets	(3,816)	(43,654)
Net Cash Provided By (Used For) Investing Activities	(1,255,108)	(500,750)
Financing Activities
Proceeds from issuance of preferred shares, net	434,899	0
Purchases of common shares under share repurchase program	(75,256)	(365,383)
Proceeds from common shares issued, net	(3,785)	697
Proceeds from borrowings	46,000	239,077
Repayments of borrowings	(179,171)	0
Change in cash collateral related to securities lending	27,935	(28,685)
Dividends paid to redeemable noncontrolling interests	(13,491)	(13,810)
Other	33,113	50,463
Preferred dividends paid	(16,453)	(16,453)
Net Cash Provided By (Used For) Financing Activities	253,791	(134,094)
Effects of exchange rate changes on foreign currency cash	(10,332)	(8,658)
Increase (decrease) in cash	25,490	164,077
Cash beginning of year	553,326	485,702
Cash end of period	578,816	649,779
Income taxes paid	40,742	35,460
Interest paid	$ 35,234	$ 25,195

General

General	9 Months Ended
	Sep. 30, 2016
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 . 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, 2015 (“2015 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. Such reclassifications had no effect on the Company’s net income, comprehensive income, shareholders’ equity or cash flows. Tabular amounts are in U.S. Dollars in thousands, except share amounts, unless otherwise noted.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Issued Accounting Standards Adopted The Company adopted a new accounting standard in the 2016 first quarter that provided targeted improvements to consolidation guidance for limited partnerships and other similarly structured entities. The adoption of this standard resulted in the Company concluding that it no longer had a variable interest in Alternative Re Ltd. and, as a result, no longer is required to consolidate Alternative Re Ltd. in its financial statements. Alternative Re Ltd. is a Bermuda-domiciled company that provides collateralized segregated accounts to its clients. The Company applied this new standard on a modified retrospective basis as of January 1, 2016. Such adoption did not impact the Company’s shareholders’ equity or net income. The adoption of the new standard also resulted in a review of certain funds within the Company’s investment portfolio where the Company has a limited partnership interest. See Note 6 for disclosures on limited partnership interests. The Company also adopted new accounting guidance pertaining to hybrid instruments. The new guidance clarified the evaluation of whether the nature of a host contract within a hybrid instrument issued in the form of a share is more akin to debt or equity. The Company has adopted this new guidance on a modified retrospective basis as of January 1, 2016. Based on a review of hybrid instruments issued in the form of a share (both held in its investment portfolio and issued as part of capital raising), the Company determined the new accounting guidance had no impact on the classification or accounting for its existing hybrid instruments. Recently Issued Accounting Standards Not Yet Adopted An accounting standard was issued in the 2015 second quarter requiring new disclosures about the reserve for losses and loss adjustment expenses for short-duration insurance contracts. These disclosures will provide additional insight into an insurance entity’s ability to underwrite and anticipate costs associated with claims. This accounting guidance is effective for the 2016 annual reporting period and interim periods thereafter and should be applied retrospectively. The Company is assessing the impact the implementation of this standard will have on the disclosures included in its consolidated financial statements. An accounting standard was issued in the 2016 first quarter to improve and simplify the accounting for employee share-based payment transactions. The new standard 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. The standard is effective in the 2017 first quarter and early adoption is permitted. The application of the new standard is dependent on the specific area that is amended. The Company is assessing the impact the implementation of this standard will have on its consolidated financial statements. New accounting guidance was issued in the 2016 first quarter pertaining to the accounting for leases by a lessee. The new accounting guidance requires that the lessee recognize an asset and a liability for leases with a lease term greater than 12 months regardless of whether the lease is classified as operating or financing. Under current accounting, operating leases are not reflected in the balance sheet. This accounting guidance is effective for the 2019 first quarter, though early application is permitted, and should be applied on a modified retrospective basis. The Company is assessing the impact the implementation of this standard will have on its consolidated financial statements. An accounting standard was issued in the 2016 second quarter that changes how entities will measure credit losses for most financial assets and certain other instruments that aren’t measured at fair value through net income. The standard requires an entity to estimate its lifetime “expected credit loss” and record an allowance that, when deducted from the amortized cost basis of the financial asset, presents the net amount expected to be collected on the financial asset. This accounting guidance is effective for the 2020 first quarter, though early application is permitted in the 2019 first quarter, and should be applied on a modified retrospective basis for the majority of the provisions. The Company is assessing the impact the implementation of this standard will have on its consolidated financial statements. An accounting standard was issued in the 2016 third quarter addressing several clarifications on the presentation and classification of certain cash receipts and cash payments in the statement of cash flows. Among several other cash flow issues, the new guidance specifically addresses the classification of debt prepayment or debt issuance costs, contingent consideration payments made after a business combination and distributions received from equity method investees. The new guidance also provides a broader principle on identifying the type of activity of the cash flow item by focusing on the cash flow item’s nature and the predominant source or use of that item. This accounting guidance is effective in the 2018 first quarter and should be applied retrospectively. Early adoption is permitted. The Company is assessing the impact the implementation of this standard will have on the classification and presentation of its statement of cash flows.

Variable Interest Entities and

Variable Interest Entities and Noncontrolling Interests	9 Months Ended
	Sep. 30, 2016
Noncontrolling Interest [Abstract]
Variable Interest Entity and Noncontrolling Interests	Variable Interest Entities and Noncontrolling Interests A variable interest entity (“VIE”) refers to an entity that has characteristics such as (i) insufficient equity at risk to allow the entity to finance its activities without additional financial support or (ii) instances where the equity investors, as a group, do not have characteristics of a controlling financial interest. The primary beneficiary of a VIE is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (i) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (ii) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. If a company is determined to be the primary beneficiary, it is required to consolidate the VIE in its financial statements. Watford Holdings Ltd. In March 2014, the Company invested $100.0 million and acquired approximately 11% of Watford Holdings Ltd.’s common equity and a warrant to purchase additional common equity. Watford Holdings Ltd. is the parent of Watford Re Ltd., a multi-line Bermuda reinsurance company (together with Watford Holdings Ltd., “Watford Re”). Watford Re is considered a VIE and the Company concluded that it is the primary beneficiary of Watford Re. As such, the results of Watford Re are included in the Company’s consolidated financial statements. The Company does not guarantee or provide credit support for Watford Re, and the Company’s financial exposure to Watford Re is limited to its investment in Watford Re’s common and preferred shares and counterparty credit risk (mitigated by collateral) arising from reinsurance transactions. The following table provides the carrying amount and balance sheet caption in which the assets and liabilities of Watford Re are reported: September 30, December 31, 2016 2015 Assets Investments accounted for using the fair value option $ 1,872,342 $ 1,617,107 Cash 67,032 108,550 Accrued investment income 16,891 19,249 Premiums receivable 211,444 162,263 Reinsurance recoverable on unpaid and paid losses and LAE 25,822 14,135 Prepaid reinsurance premiums 11,556 11,129 Deferred acquisition costs, net 87,490 75,443 Receivable for securities sold 94,965 34,095 Goodwill and intangible assets 7,650 — Other assets 122,641 80,361 Total assets of consolidated VIE $ 2,517,833 $ 2,122,332 Liabilities Reserves for losses and loss adjustment expenses $ 460,600 $ 290,997 Unearned premiums 308,063 249,980 Reinsurance balances payable 12,315 14,005 Revolving credit agreement borrowings 298,100 430,434 Payable for securities purchased 145,135 33,062 Other liabilities 135,248 53,624 Total liabilities of consolidated VIE $ 1,359,461 $ 1,072,102 Redeemable noncontrolling interests $ 220,159 $ 219,882 For the nine months ended September 30, 2016 , Watford Re generated $207.0 million of cash provided by operating activities, $124.0 million of cash used for investing activities and $119.6 million of cash used for financing activities, compared to $204.3 million of cash provided by operating activities, $354.5 million of cash used for investing activities and $268.3 million of cash provided by financing activities for the nine months ended September 30, 2015 . Non-redeemable noncontrolling interests The Company accounts for the portion of Watford Re’s common equity attributable to third party investors in the shareholders’ equity section of its consolidated balance sheets. The noncontrolling ownership in Watford Re’s common shares was approximately 89% at September 30, 2016 . The portion of Watford Re’s income or loss attributable to third party investors is recorded in the consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests.’ The following table sets forth activity in the non-redeemable noncontrolling interests: September 30, 2016 2015 Three Months Ended Balance, beginning of period $ 788,589 $ 794,880 Amounts attributable to noncontrolling interests 46,160 (20,621 ) Foreign currency translation adjustments attributable to noncontrolling interests 59 (97 ) Balance, end of period $ 834,808 $ 774,162 Nine Months Ended Balance, beginning of year $ 738,831 $ 769,081 Amounts attributable to noncontrolling interests 96,118 5,178 Foreign currency translation adjustments attributable to noncontrolling interests (141 ) (97 ) Balance, end of period $ 834,808 $ 774,162 Redeemable noncontrolling interests The Company accounts for redeemable noncontrolling interests in the mezzanine section of its consolidated balance sheets in accordance with applicable accounting guidance. Such redeemable noncontrolling interests relate to the 9,065,200 cumulative redeemable preference shares (“Watford Preference Shares”) issued in March 2014 with a par value of $0.01 per share and a liquidation preference of $25.00 per share. Preferred dividends, including the accretion of the discount and issuance costs, are included in ‘net (income) loss attributable to noncontrolling interests’ in the Company’s consolidated statements of income. The following table sets forth activity in the redeemable non-controlling interests: September 30, 2016 2015 Three Months Ended Balance, beginning of period $ 205,366 $ 204,996 Shares acquired by the Company — — Accretion of preference share issuance costs 93 93 Balance, end of period $ 205,459 $ 205,089 Nine Months Ended Balance, beginning of year $ 205,182 $ 219,512 Shares acquired by the Company — (14,700 ) Accretion of preference share issuance costs 277 277 Balance, end of period $ 205,459 $ 205,089 The portion of Watford Re’s income or loss attributable to third party investors, recorded in the Company’s consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests,’ are summarized in the table below: September 30, 2016 2015 Three Months Ended Amounts attributable to non-redeemable noncontrolling interests $ (46,160 ) $ 20,621 Dividends attributable to redeemable noncontrolling interests (4,588 ) (4,588 ) Net (income) loss attributable to noncontrolling interests $ (50,748 ) $ 16,033 Nine Months Ended Amounts attributable to non-redeemable noncontrolling interests $ (96,118 ) $ (5,178 ) Dividends attributable to redeemable noncontrolling interests (13,761 ) (14,239 ) Net (income) loss attributable to noncontrolling interests $ (109,879 ) $ (19,417 )

Earnings Per Common Share

Earnings Per Common Share	9 Months Ended
	Sep. 30, 2016
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 Nine Months Ended September 30, September 30, 2016 2015 2016 2015 Numerator: Net income $ 303,620 $ 64,000 $ 728,604 $ 498,576 Net (income) loss attributable to noncontrolling interests (50,748 ) 16,033 (109,879 ) (19,417 ) Net income available to Arch 252,872 80,033 618,725 479,159 Preferred dividends (5,484 ) (5,484 ) (16,453 ) (16,453 ) Net income available to Arch common shareholders $ 247,388 $ 74,549 $ 602,272 $ 462,706 Denominator: Weighted average common shares outstanding — basic 120,938,916 120,567,410 120,656,420 122,151,971 Effect of dilutive common share equivalents: Nonvested restricted shares 1,313,025 1,322,053 1,295,825 1,260,247 Stock options (1) 2,679,712 3,122,310 2,575,929 2,942,541 Weighted average common shares and common share equivalents outstanding — diluted 124,931,653 125,011,773 124,528,174 126,354,759 Earnings per common share: Basic $ 2.05 $ 0.62 $ 4.99 $ 3.79 Diluted $ 1.98 $ 0.60 $ 4.84 $ 3.66 (1) Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2016 third quarter and 2015 third quarter , the number of stock options excluded were 334,203 and 390,406 , respectively. For the nine months ended September 30, 2016 and 2015 , the number of stock options excluded were 842,105 and 957,838 , respectively.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2016
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 results of Arch Mortgage Insurance Company (“Arch MI U.S.”) and Arch Mortgage Insurance Designated Activity Company, leading providers of mortgage insurance products and services to the U.S. and European markets, respectively. Arch MI U.S. is approved as an eligible mortgage insurer by Federal National Mortgage Association (“Fannie Mae”) and Federal Home Loan Mortgage Corporation (“Freddie Mac”), each a government sponsored enterprise, or “GSE.” The mortgage segment also includes GSE credit risk-sharing transactions and mortgage reinsurance for the U.S. and Australian markets. The corporate (non-underwriting) segment results include net investment income, other income (loss), corporate expenses, interest expense, net realized gains or losses, net impairment losses included in earnings, equity in net income or loss of investment funds accounted for using the equity method, net foreign exchange gains or losses, income taxes and items related to the Company’s non-cumulative preferred shares. Such amounts exclude the results of the ‘other’ segment. The ‘other’ segment includes the results of Watford Re (see Note 3 ). Watford Re has its own management and board of directors that is responsible for the overall profitability of the ‘other’ segment. For the ‘other’ segment, performance is measured based on net income or loss. The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income or loss to net income available to common shareholders: Three Months Ended September 30, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 758,934 $ 324,361 $ 131,726 $ 1,214,765 $ 163,736 $ 1,278,765 Premiums ceded (217,446 ) (89,551 ) (51,182 ) (357,923 ) (6,300 ) (264,487 ) Net premiums written 541,488 234,810 80,544 856,842 157,436 1,014,278 Change in unearned premiums (22,410 ) 17,117 (3,582 ) (8,875 ) (47,000 ) (55,875 ) Net premiums earned 519,078 251,927 76,962 847,967 110,436 958,403 Other underwriting income — 2,216 4,740 6,956 1,024 7,980 Losses and loss adjustment expenses (332,845 ) (105,924 ) (11,107 ) (449,876 ) (74,307 ) (524,183 ) Acquisition expenses, net (77,148 ) (50,217 ) (7,757 ) (135,122 ) (28,739 ) (163,861 ) Other operating expenses (87,517 ) (35,589 ) (25,416 ) (148,522 ) (7,035 ) (155,557 ) Underwriting income (loss) $ 21,568 $ 62,413 $ 37,422 121,403 1,379 122,782 Net investment income 66,282 27,336 93,618 Net realized gains (losses) 95,946 29,159 125,105 Net impairment losses recognized in earnings (3,867 ) — (3,867 ) Equity in net income (loss) of investment funds accounted for using the equity method 16,662 — 16,662 Other income (loss) (400 ) — (400 ) Corporate expenses (18,485 ) — (18,485 ) Interest expense (12,924 ) (3,019 ) (15,943 ) Net foreign exchange gains (losses) (4,232 ) 1,611 (2,621 ) Income (loss) before income taxes 260,385 56,466 316,851 Income tax expense (13,232 ) 1 (13,231 ) Net income (loss) 247,153 56,467 303,620 Dividends attributable to redeemable noncontrolling interests — (4,588 ) (4,588 ) Amounts attributable to noncontrolling interests — (46,160 ) (46,160 ) Net income (loss) available to Arch 247,153 5,719 252,872 Preferred dividends (5,484 ) — (5,484 ) Net income (loss) available to Arch common shareholders $ 241,669 $ 5,719 $ 247,388 Underwriting Ratios Loss ratio 64.1 % 42.0 % 14.4 % 53.1 % 67.3 % 54.7 % Acquisition expense ratio 14.9 % 19.9 % 10.1 % 15.9 % 26.0 % 17.1 % Other operating expense ratio 16.9 % 14.1 % 33.0 % 17.5 % 6.4 % 16.2 % Combined ratio 95.9 % 76.0 % 57.5 % 86.5 % 99.7 % 88.0 % Goodwill and intangible assets $ 26,367 $ 1,228 $ 55,696 $ 83,291 $ 7,650 $ 90,941 (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. Three Months Ended September 30, 2015 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 752,438 $ 329,327 $ 74,657 $ 1,158,451 $ 131,165 $ 1,189,192 Premiums ceded (209,443 ) (92,182 ) (7,832 ) (311,486 ) (6,158 ) (217,220 ) Net premiums written 542,995 237,145 66,825 846,965 125,007 971,972 Change in unearned premiums (20,451 ) 23,286 (12,277 ) (9,442 ) (25,847 ) (35,289 ) Net premiums earned 522,544 260,431 54,548 837,523 99,160 936,683 Other underwriting income 519 2,783 3,565 6,867 756 7,623 Losses and loss adjustment expenses (339,859 ) (115,780 ) (9,562 ) (465,201 ) (66,540 ) (531,741 ) Acquisition expenses, net (77,076 ) (55,416 ) (10,428 ) (142,920 ) (28,646 ) (171,566 ) Other operating expenses (84,620 ) (37,131 ) (21,048 ) (142,799 ) (3,421 ) (146,220 ) Underwriting income (loss) $ 21,508 $ 54,887 $ 17,075 93,470 1,309 94,779 Net investment income 67,251 18,982 86,233 Net realized gains (losses) (53,480 ) (36,218 ) (89,698 ) Net impairment losses recognized in earnings (5,868 ) — (5,868 ) Equity in net income (loss) of investment funds accounted for using the equity method (2,118 ) — (2,118 ) Other income (loss) (265 ) — (265 ) Corporate expenses (10,739 ) — (10,739 ) Interest expense (12,014 ) (1,286 ) (13,300 ) Net foreign exchange gains (losses) 16,056 (1,376 ) 14,680 Income (loss) before income taxes 92,293 (18,589 ) 73,704 Income tax expense (9,704 ) — (9,704 ) Net income (loss) 82,589 (18,589 ) 64,000 Dividends attributable to redeemable noncontrolling interests — (4,588 ) (4,588 ) Amounts attributable to noncontrolling interests — 20,621 20,621 Net income (loss) available to Arch 82,589 (2,556 ) 80,033 Preferred dividends (5,484 ) — (5,484 ) Net income (loss) available to Arch common shareholders $ 77,105 $ (2,556 ) $ 74,549 Underwriting Ratios Loss ratio 65.0 % 44.5 % 17.5 % 55.5 % 67.1 % 56.8 % Acquisition expense ratio 14.8 % 21.3 % 19.1 % 17.1 % 28.9 % 18.3 % Other operating expense ratio 16.2 % 14.3 % 38.6 % 17.1 % 3.4 % 15.6 % Combined ratio 96.0 % 80.1 % 75.2 % 89.7 % 99.4 % 90.7 % Goodwill and intangible assets $ 29,834 $ 2,149 $ 71,637 $ 103,620 $ — $ 103,620 (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. Nine Months Ended September 30, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,319,530 $ 1,217,804 $ 361,440 $ 3,898,025 $ 421,627 $ 4,046,667 Premiums ceded (713,110 ) (370,068 ) (62,918 ) (1,145,347 ) (15,229 ) (887,591 ) Net premiums written 1,606,420 847,736 298,522 2,752,678 406,398 3,159,076 Change in unearned premiums (46,603 ) (43,345 ) (93,283 ) (183,231 ) (59,878 ) (243,109 ) Net premiums earned 1,559,817 804,391 205,239 2,569,447 346,520 2,915,967 Other underwriting income — 22,659 12,670 35,329 2,922 38,251 Losses and loss adjustment expenses (1,011,087 ) (363,613 ) (20,102 ) (1,394,802 ) (236,922 ) (1,631,724 ) Acquisition expenses, net (228,819 ) (160,800 ) (24,665 ) (414,284 ) (95,323 ) (509,607 ) Other operating expenses (265,749 ) (109,159 ) (74,022 ) (448,930 ) (18,486 ) (467,416 ) Underwriting income (loss) $ 54,162 $ 193,478 $ 99,120 346,760 (1,289 ) 345,471 Net investment income 207,088 68,603 275,691 Net realized gains (losses) 168,735 61,912 230,647 Net impairment losses recognized in earnings (16,849 ) — (16,849 ) Equity in net income (loss) of investment funds accounted for using the equity method 32,054 — 32,054 Other income (loss) (432 ) — (432 ) Corporate expenses (45,068 ) — (45,068 ) Interest expense (37,983 ) (9,730 ) (47,713 ) Net foreign exchange gains (losses) (3,812 ) 2,287 (1,525 ) Income (loss) before income taxes 650,493 121,783 772,276 Income tax expense (43,673 ) 1 (43,672 ) Net income (loss) 606,820 121,784 728,604 Dividends attributable to redeemable noncontrolling interests — (13,761 ) (13,761 ) Amounts attributable to noncontrolling interests — (96,118 ) (96,118 ) Net income (loss) available to Arch 606,820 11,905 618,725 Preferred dividends (16,453 ) — (16,453 ) Net income (loss) available to Arch common shareholders $ 590,367 $ 11,905 $ 602,272 Underwriting Ratios Loss ratio 64.8 % 45.2 % 9.8 % 54.3 % 68.4 % 56.0 % Acquisition expense ratio 14.7 % 20.0 % 12.0 % 16.1 % 27.5 % 17.5 % Other operating expense ratio 17.0 % 13.6 % 36.1 % 17.5 % 5.3 % 16.0 % Combined ratio 96.5 % 78.8 % 57.9 % 87.9 % 101.2 % 89.5 % (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. Nine Months Ended September 30, 2015 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,263,401 $ 1,156,540 $ 203,770 $ 3,625,382 $ 387,752 $ 3,730,423 Premiums ceded (669,336 ) (318,197 ) (23,404 ) (1,012,608 ) (17,979 ) (747,876 ) Net premiums written 1,594,065 838,343 180,366 2,612,774 369,773 2,982,547 Change in unearned premiums (53,782 ) (24,230 ) (22,992 ) (101,004 ) (91,158 ) (192,162 ) Net premiums earned 1,540,283 814,113 157,374 2,511,770 278,615 2,790,385 Other underwriting income 1,467 6,870 14,969 23,306 3,570 26,876 Losses and loss adjustment expenses (978,681 ) (339,495 ) (33,010 ) (1,351,186 ) (193,697 ) (1,544,883 ) Acquisition expenses, net (228,877 ) (170,380 ) (31,046 ) (430,303 ) (79,764 ) (510,067 ) Other operating expenses (261,793 ) (114,182 ) (61,096 ) (437,071 ) (8,876 ) (445,947 ) Underwriting income (loss) $ 72,399 $ 196,926 $ 47,191 316,516 (152 ) 316,364 Net investment income 204,710 47,480 252,190 Net realized gains (losses) (14,831 ) (27,244 ) (42,075 ) Net impairment losses recognized in earnings (12,780 ) — (12,780 ) Equity in net income (loss) of investment funds accounted for using the equity method 19,938 — 19,938 Other income (loss) 52 — 52 Corporate expenses (37,502 ) — (37,502 ) Interest expense (28,761 ) (1,286 ) (30,047 ) Net foreign exchange gains (losses) 60,338 1,260 61,598 Income (loss) before income taxes 507,680 20,058 527,738 Income tax expense (29,162 ) — (29,162 ) Net income (loss) 478,518 20,058 498,576 Dividends attributable to redeemable noncontrolling interests — (14,239 ) (14,239 ) Amounts attributable to noncontrolling interests — (5,178 ) (5,178 ) Net income (loss) available to Arch 478,518 641 479,159 Preferred dividends (16,453 ) — (16,453 ) Net income (loss) available to Arch common shareholders $ 462,065 $ 641 $ 462,706 Underwriting Ratios Loss ratio 63.5 % 41.7 % 21.0 % 53.8 % 69.5 % 55.4 % Acquisition expense ratio 14.9 % 20.9 % 19.7 % 17.1 % 28.6 % 18.3 % Other operating expense ratio 17.0 % 14.0 % 38.8 % 17.4 % 3.2 % 16.0 % Combined ratio 95.4 % 76.6 % 79.5 % 88.3 % 101.3 % 89.7 % (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.

Investment Information

Investment Information	9 Months Ended
	Sep. 30, 2016
Disclosure Investment Information [Abstract]
Investment Information	Investment Information At September 30, 2016 , total investable assets of $17.88 billion included $16.04 billion managed by the Company and $1.84 billion attributable to Watford Re. Available For Sale Investments The following table summarizes the fair value and cost or amortized cost of the Company’s investments classified as available for sale: Estimated Fair Value Gross Unrealized Gains Gross Unrealized Losses Cost or Amortized Cost OTTI Unrealized Losses (2) September 30, 2016 Fixed maturities (1): Corporate bonds $ 2,956,514 $ 54,901 $ (14,297 ) $ 2,915,910 $ (2,286 ) Mortgage backed securities 557,913 11,716 (1,518 ) 547,715 (3,327 ) Municipal bonds 1,893,728 36,567 (1,743 ) 1,858,904 — Commercial mortgage backed securities 618,235 9,217 (1,015 ) 610,033 — U.S. government and government agencies 3,014,830 17,195 (1,745 ) 2,999,380 — Non-U.S. government securities 1,186,639 45,372 (33,218 ) 1,174,485 — Asset backed securities 1,241,169 11,463 (2,068 ) 1,231,774 (69 ) Total 11,469,028 186,431 (55,604 ) 11,338,201 (5,682 ) Equity securities 533,245 76,733 (6,597 ) 463,109 — Other investments 168,243 17,871 (1,058 ) 151,430 — Short-term investments 1,184,408 553 (1,956 ) 1,185,811 — Total $ 13,354,924 $ 281,588 $ (65,215 ) $ 13,138,551 $ (5,682 ) December 31, 2015 Fixed maturities (1): Corporate bonds $ 2,725,729 $ 15,978 $ (60,508 ) $ 2,770,259 $ (3,553 ) Mortgage backed securities 754,870 9,872 (5,334 ) 750,332 (3,350 ) Municipal bonds 1,626,281 27,014 (1,534 ) 1,600,801 — Commercial mortgage backed securities 764,152 3,269 (6,978 ) 767,861 — U.S. government and government agencies 2,423,455 6,228 (9,978 ) 2,427,205 — Non-U.S. government securities 917,664 10,414 (39,122 ) 946,372 — Asset backed securities 1,620,506 3,307 (12,951 ) 1,630,150 (22 ) Total 10,832,657 76,082 (136,405 ) 10,892,980 (6,925 ) Equity securities 629,182 94,341 (17,796 ) 552,637 — Other investments 300,476 43,798 (4,665 ) 261,343 — Short-term investments 587,904 187 (3,425 ) 591,142 — Total $ 12,350,219 $ 214,408 $ (162,291 ) $ 12,298,102 $ (6,925 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” (2) Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At September 30, 2016 , 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 loss of $1.4 million at December 31, 2015 . The following table summarizes, for all available for sale securities in an unrealized loss position, the fair value and gross unrealized loss by length of time the security has been in a continual unrealized loss position: Less than 12 Months 12 Months or More Total Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses September 30, 2016 Fixed maturities (1): Corporate bonds $ 566,387 $ (4,281 ) $ 111,303 $ (10,016 ) $ 677,690 $ (14,297 ) Mortgage backed securities 104,159 (1,249 ) 13,230 (269 ) 117,389 (1,518 ) Municipal bonds 415,130 (1,274 ) 8,348 (469 ) 423,478 (1,743 ) Commercial mortgage backed securities 89,999 (778 ) 26,710 (237 ) 116,709 (1,015 ) U.S. government and government agencies 1,233,737 (1,745 ) — — 1,233,737 (1,745 ) Non-U.S. government securities 336,149 (13,113 ) 133,652 (20,105 ) 469,801 (33,218 ) Asset backed securities 178,769 (781 ) 104,273 (1,287 ) 283,042 (2,068 ) Total 2,924,330 (23,221 ) 397,516 (32,383 ) 3,321,846 (55,604 ) Equity securities 167,172 (6,597 ) — — 167,172 (6,597 ) Other investments 24,740 (1,058 ) — — 24,740 (1,058 ) Short-term investments 28,506 (1,956 ) — — 28,506 (1,956 ) Total $ 3,144,748 $ (32,832 ) $ 397,516 $ (32,383 ) $ 3,542,264 $ (65,215 ) December 31, 2015 Fixed maturities (1): Corporate bonds $ 1,810,988 $ (37,445 ) $ 129,896 $ (23,063 ) $ 1,940,884 $ (60,508 ) Mortgage backed securities 487,018 (4,508 ) 48,991 (826 ) 536,009 (5,334 ) Municipal bonds 269,015 (1,303 ) 9,692 (231 ) 278,707 (1,534 ) Commercial mortgage backed securities 511,261 (6,639 ) 20,596 (339 ) 531,857 (6,978 ) U.S. government and government agencies 1,991,163 (9,978 ) — — 1,991,163 (9,978 ) Non-U.S. government securities 458,414 (13,494 ) 138,792 (25,628 ) 597,206 (39,122 ) Asset backed securities 1,217,163 (9,328 ) 134,841 (3,623 ) 1,352,004 (12,951 ) Total 6,745,022 (82,695 ) 482,808 (53,710 ) 7,227,830 (136,405 ) Equity securities 232,275 (17,796 ) — — 232,275 (17,796 ) Other investments 93,614 (4,665 ) — — 93,614 (4,665 ) Short-term investments 30,625 (3,425 ) — — 30,625 (3,425 ) Total $ 7,101,536 $ (108,581 ) $ 482,808 $ (53,710 ) $ 7,584,344 $ (162,291 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” At September 30, 2016 , on a lot level basis, approximately 1,660 security lots out of a total of approximately 6,440 security lots were in an unrealized loss position and the largest single unrealized loss from a single lot in the Company’s fixed maturity portfolio was $3.8 million . At December 31, 2015 , on a lot level basis, approximately 3,560 security lots out of a total of approximately 5,550 security lots were in an unrealized loss position and the largest single unrealized loss from a single lot in the Company’s fixed maturity portfolio was $3.1 million . The contractual maturities of the Company’s fixed maturities are shown in the following table. Expected maturities, which are management’s best estimates, will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. September 30, 2016 December 31, 2015 Maturity Estimated Fair Value Amortized Cost Estimated Amortized Cost Due in one year or less $ 287,716 $ 285,210 $ 337,898 $ 341,595 Due after one year through five years 5,305,049 5,278,946 4,644,516 4,677,230 Due after five years through 10 years 2,732,834 2,677,238 2,214,413 2,228,638 Due after 10 years 726,112 707,285 496,302 497,174 9,051,711 8,948,679 7,693,129 7,744,637 Mortgage backed securities 557,913 547,715 754,870 750,332 Commercial mortgage backed securities 618,235 610,033 764,152 767,861 Asset backed securities 1,241,169 1,231,774 1,620,506 1,630,150 Total (1) $ 11,469,028 $ 11,338,201 $ 10,832,657 $ 10,892,980 (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 by the Company. The Company receives collateral in the form of cash or securities. Cash collateral primarily consists of short-term investments. At September 30, 2016 , the fair value of the cash collateral received on securities lending was $85.1 million and the fair value of security collateral received was $380.9 million . At December 31, 2015 , the fair value of the cash collateral received on securities lending was $52.7 million , which included $3.0 million that was reinvested in sub-prime mortgage backed securities, and the fair value of security collateral received was $336.7 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 September 30, 2016 U.S. government and government agencies $ 324,936 $ — $ 71,130 $ 12,538 $ 408,604 Corporate bonds 45,770 — — — 45,770 Equity securities 11,673 — — — 11,673 Total $ 382,379 $ — $ 71,130 $ 12,538 $ 466,047 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 8 $ — Amounts related to securities lending not included in offsetting disclosure in Note 8 $ 466,047 December 31, 2015 U.S. government and government agencies $ 235,728 $ — $ 82,286 $ 9,598 $ 327,612 Corporate bonds 55,086 — — — 55,086 Equity securities 6,722 4,424 — — 11,146 Total $ 297,536 $ 4,424 $ 82,286 $ 9,598 $ 393,844 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 8 $ — Amounts related to securities lending not included in offsetting disclosure in Note 8 $ 393,844 Other Investments The following table summarizes the Company’s other investments, including available for sale and fair value option components: September 30, December 31, Available for sale: Asian and emerging markets $ 88,731 $ 206,861 Investment grade fixed income 34,536 31,370 Credit related funds 6,478 22,512 Other 38,498 39,733 Total available for sale 168,243 300,476 Fair value option: Term loan investments (par value: $1,152,530 and $1,197,143) 1,106,707 1,108,017 Mezzanine debt funds 122,528 121,589 Credit related funds 219,161 219,049 Investment grade fixed income 73,264 63,053 Asian and emerging markets 142,298 34,761 Other (1) 126,405 124,502 Total fair value option 1,790,363 1,670,971 Total $ 1,958,606 $ 1,971,447 (1) Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other. Certain of the Company’s other investments are in investment funds for which the Company has the option to redeem at agreed upon values as described in each investment fund’s subscription agreement. Depending on the terms of the various subscription agreements, investments in investment funds may be redeemed daily, monthly, quarterly or on other terms. Two common redemption restrictions which may impact the Company’s ability to redeem these investment funds are gates and lockups. A gate is a suspension of redemptions which may be implemented by the general partner or investment manager of the fund in order to defer, in whole or in part, the redemption request in the event the aggregate amount of redemption requests exceeds a predetermined percentage of the investment fund’s net assets which may otherwise hinder the general partner or investment manager’s ability to liquidate holdings in an orderly fashion in order to generate the cash necessary to fund extraordinarily large redemption payouts. A lockup period is the initial amount of time an investor is contractually required to hold the security before having the ability to redeem. If the investment funds are eligible to be redeemed, the time to redeem such fund can take weeks or months following the notification. Fair Value Option The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option: September 30, December 31, Fixed maturities $ 1,182,909 $ 936,802 Other investments 1,790,363 1,670,971 Short-term investments 388,125 285,923 Equity securities 28,176 798 Investments accounted for using the fair value option $ 3,389,573 $ 2,894,494 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.’ Based on the new accounting guidance for consolidation, the Company determined that these limited partnership interests represented variable interests in the funds because the general partner did not have a significant interest in the fund. The Company has determined that it is not required to consolidate these investments because it is not the primary beneficiary of the funds. The Company’s maximum exposure to loss with respect to these investments is limited to the investment carrying amounts reported in the Company’s consolidated balance sheet and any unfunded commitment. The following table summarizes investments in limited partnership interests where the Company has a variable interest by balance sheet line item: September 30, December 31, Investments accounted for using the equity method (1) $ 787,456 $ 584,158 Investments accounted for using the fair value option (2) 81,341 90,969 Total $ 868,797 $ 675,127 (1) Aggregate unfunded commitments were $798.8 million at September 30, 2016 , compared to $535.4 million at December 31, 2015 . (2) Aggregate unfunded commitments were $27.7 million at September 30, 2016 , compared to $22.7 million at December 31, 2015 . Net Investment Income The components of net investment income were derived from the following sources: September 30, 2016 2015 Three Months Ended Fixed maturities $ 71,366 $ 70,626 Term loan investments 28,630 16,922 Equity securities (dividends) 3,311 3,486 Short-term investments 1,703 127 Other (1) 8,836 10,277 Gross investment income 113,846 101,438 Investment expenses (20,228 ) (15,205 ) Net investment income $ 93,618 $ 86,233 Nine Months Ended Fixed maturities $ 223,033 $ 210,497 Term loan investments 67,250 49,699 Equity securities (dividends) 10,409 8,743 Short-term investments 3,015 548 Other (1) 30,839 33,513 Gross investment income 334,546 303,000 Investment expenses (58,855 ) (50,810 ) Net investment income $ 275,691 $ 252,190 (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. September 30, 2016 2015 Three Months Ended Available for sale securities: Gross gains on investment sales $ 84,451 $ 51,933 Gross losses on investment sales (22,985 ) (53,953 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 43,935 (41,236 ) Other investments 46,428 (75,251 ) Equity securities (52 ) 71 Short-term investments 1,150 (9 ) Derivative instruments (1) (16,964 ) 35,889 Other (2) (10,858 ) (7,142 ) Net realized gains (losses) $ 125,105 $ (89,698 ) Nine Months Ended Available for sale securities: Gross gains on investment sales $ 266,965 $ 231,757 Gross losses on investment sales (129,409 ) (168,087 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 62,234 (49,729 ) Other investments 38,016 (68,179 ) Equity securities 385 — Short-term investments 107 1,462 Derivative instruments (1) 24,102 31,069 Other (2) (31,753 ) (20,368 ) Net realized gains (losses) $ 230,647 $ (42,075 ) (1) See Note 8 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 $16.7 million of equity in net income related to investment funds accounted for using the equity method in the 2016 third quarter , compared to $2.1 million of loss for the 2015 third quarter , and $32.1 million of equity in net income related to investment funds accounted for using the equity method for the nine months ended September 30, 2016 , compared to $19.9 million of equity in net income for the 2015 period. In applying the equity method, investments are initially recorded at cost and are subsequently adjusted based on the Company’s proportionate share of the net income or loss of the funds (which include changes in the market value of the underlying securities in the funds). Such investments are generally recorded on a one to three month lag based on the availability of reports from the investment funds. Other-Than-Temporary Impairments The Company performs quarterly reviews of its available for sale investments in order to determine whether declines in fair value below the amortized cost basis were considered other-than-temporary in accordance with applicable guidance. The following table details the net impairment losses recognized in earnings by asset class: September 30, 2016 2015 Three Months Ended Fixed maturities: Mortgage backed securities $ (233 ) $ (85 ) Corporate bonds — (4,282 ) Non-U.S. government securities (545 ) — Asset backed securities — — Total (778 ) (4,367 ) Short-term investments — — Equity securities (557 ) (1,501 ) Other investments (2,532 ) — Net impairment losses recognized in earnings $ (3,867 ) $ (5,868 ) Nine Months Ended Fixed maturities: Mortgage backed securities $ (788 ) $ (1,483 ) Corporate bonds (5,655 ) (6,268 ) Non-U.S. government securities (777 ) — Asset backed securities (2,506 ) — Total (9,726 ) (7,751 ) Short-term investments — (2,341 ) Equity securities (3,594 ) (1,754 ) Other investments (3,529 ) (934 ) Net impairment losses recognized in earnings $ (16,849 ) $ (12,780 ) A description of the methodology and significant inputs used to measure the amount of net impairment losses recognized in earnings in the 2016 periods is as follows: • Corporate bonds — the Company reviewed the business prospects, credit ratings, estimated loss given default factors, foreign currency impacts and information received from asset managers and rating agencies for certain corporate bonds. Impairment losses primarily resulted from reductions on non-investment grade corporate bonds in the energy sector, reflecting current market conditions; • Equity securities — the Company utilized information received from asset managers on common stocks, including the business prospects, recent events, industry and market data and other factors. Impairment losses were primarily on equities which were in an unrealized loss position for a significant length of time; • Asset backed securities — the Company utilized underlying data provided by asset managers, cash flow projections and additional information from credit agencies in order to determine an expected recovery value for each security. Impairment losses primarily reflected a reduction on one security following an analysis of expected cash flows. • Other investments — the Company utilized information received from asset managers on investment funds, including the business prospects, recent events, industry and market data and other factors. Impairment losses reflected a reduction on certain funds which were in an unrealized loss position for a significant length of time; • Mortgage backed securities — the Company utilized underlying data provided by asset managers, cash flow projections and additional information from credit agencies in order to determine an expected recovery value for each security. The analysis includes a review of cash flow projections under base case and stress case scenarios which modify the expected default expectations and loss severities and slow down prepayment assumptions. The significant inputs in the models include the expected default rates, delinquency rates and foreclosure costs. Impairment losses resulted from relatively small adjustments on a number of mortgage backed securities; • Non-U.S. government securities — impairment losses related to foreign currency impacts on securities which were in an unrealized loss position for a significant length of time. The Company believes that the $5.7 million of OTTI included in accumulated other comprehensive income at September 30, 2016 on the securities which were considered by the Company to be impaired was due to market and sector-related factors ( i.e. , not credit losses). At September 30, 2016 , the Company did not intend to sell these securities, or any other securities which were in an unrealized loss position, and determined that it is more likely than not that the Company will not be required to sell such securities before recovery of their cost basis. The following table provides a roll forward of the amount related to credit losses recognized in earnings for which a portion of an OTTI was recognized in accumulated other comprehensive income: September 30, 2016 2015 Three Months Ended Balance at start of period $ 14,847 $ 20,906 Credit loss impairments recognized on securities not previously impaired 38 4,024 Credit loss impairments recognized on securities previously impaired 60 41 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 (1,166 ) — Balance at end of period $ 13,779 $ 24,971 Nine Months Ended Balance at start of year $ 26,875 $ 20,196 Credit loss impairments recognized on securities not previously impaired 1,388 8,794 Credit loss impairments recognized on securities previously impaired 582 175 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 (15,066 ) (4,194 ) Balance at end of period $ 13,779 $ 24,971 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 9 for further details. The following table details the value of the Company’s restricted assets: September 30, December 31, Assets used for collateral or guarantees: Affiliated transactions $ 3,908,206 $ 3,810,104 Third party agreements 1,524,785 1,286,257 Deposits with U.S. regulatory authorities 473,094 391,458 Deposits with non-U.S. regulatory authorities 42,354 38,230 Total restricted assets $ 5,948,439 $ 5,526,049

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value	Fair Value Accounting guidance regarding fair value measurements addresses how companies should measure fair value when they are required to use a fair value measure for recognition or disclosure purposes under GAAP and provides a common definition of fair value to be used throughout GAAP. It defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly fashion between market participants at the measurement date. In addition, it establishes a three-level valuation hierarchy for the disclosure of fair value measurements. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. The level in the hierarchy within which a given fair value measurement falls is determined based on the lowest level input that is significant to the measurement (Level 1 being the highest priority and Level 3 being the lowest priority). The levels in the hierarchy are defined as follows: Level 1: Inputs to the valuation methodology are observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets Level 2: Inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets, and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument Level 3: Inputs to the valuation methodology are unobservable and significant to the fair value measurement Following is a description of the valuation methodologies used for securities measured at fair value, as well as the general classification of such securities pursuant to the valuation hierarchy. The Company reviews its securities measured at fair value and discusses the proper classification of such investments with investment advisers and others. The Company determines the existence of an active market based on its judgment as to whether transactions for the financial instrument occur in such market with sufficient frequency and volume to provide reliable pricing information. The independent pricing sources obtain market quotations and actual transaction prices for securities that have quoted prices in active markets. The Company uses quoted values and other data provided by nationally recognized independent pricing sources as inputs into its process for determining fair values of its fixed maturity investments. To validate the techniques or models used by pricing sources, the Company's review process includes, but is not limited to: (i) quantitative analysis (e.g., comparing the quarterly return for each managed portfolio to its target benchmark, with significant differences identified and investigated); (ii) a review of the average number of prices obtained in the pricing process and the range of resulting fair values; (iii) initial and ongoing evaluation of methodologies used by outside parties to calculate fair value; (iv) a comparison of the fair value estimates to the Company’s knowledge of the current market; (v) a comparison of the pricing services' fair values to other pricing services' fair values for the same investments; and (vi) periodic back-testing, which includes randomly selecting purchased or sold securities and comparing the executed prices to the fair value estimates from the pricing service. A price source hierarchy was maintained in order to determine which price source would be used (i.e., a price obtained from a pricing service with more seniority in the hierarchy will be used over a less senior one in all cases). The hierarchy prioritizes pricing services based on availability and reliability and assigns the highest priority to index providers. Based on the above review, the Company will challenge any prices for a security or portfolio which are considered not to be representative of fair value. The Company did not adjust any of the prices obtained from the independent pricing sources at September 30, 2016 . 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 $16.94 billion of financial assets and liabilities measured at fair value at September 30, 2016 , approximately $511.6 million , or 3.1% , were priced using non-binding broker-dealer quotes. Of the $15.40 billion of financial assets and liabilities measured at fair value at December 31, 2015 , approximately $317.8 million , or 2.1% , were priced using non-binding broker-dealer quotes. 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 September 30, 2016 : 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 $ 2,956,514 $ — $ 2,937,542 $ 18,972 Mortgage backed securities 557,913 — 557,913 — Municipal bonds 1,893,728 — 1,893,728 — Commercial mortgage backed securities 618,235 — 618,235 — U.S. government and government agencies 3,014,830 2,891,078 123,752 — Non-U.S. government securities 1,186,639 — 1,186,639 — Asset backed securities 1,241,169 — 1,214,393 26,776 Total 11,469,028 2,891,078 8,532,202 45,748 Equity securities 533,245 532,118 1,127 — Short-term investments 1,184,408 1,162,900 21,508 — Other investments 87,189 87,189 — — Other investments measured at net asset value (2) 81,054 Total other investments 168,243 87,189 — — Derivative instruments (4) 20,054 — 20,054 — Fair value option: Corporate bonds 830,484 — 830,484 — Non-U.S. government bonds 110,642 — 110,642 — Mortgage backed securities 19,184 — 19,184 — Asset backed securities 29,258 — 29,258 — U.S. government and government agencies 193,341 193,341 — — Short-term investments 388,125 388,125 — — Equity securities 28,176 27,644 532 — Other investments 1,182,619 75,912 1,106,707 — Other investments measured at net asset value (2) 607,744 Total 3,389,573 685,022 2,096,807 — Total assets measured at fair value $ 16,764,551 $ 5,358,307 $ 10,671,698 $ 45,748 Liabilities measured at fair value: Contingent consideration liabilities $ (116,377 ) $ — $ — $ (116,377 ) Securities sold but not yet purchased (3) (52,195 ) — (52,195 ) — Derivative instruments (4) (10,311 ) — (10,311 ) — Total liabilities measured at fair value $ (178,883 ) $ — $ (62,506 ) $ (116,377 ) (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 6 , “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 8 , “Derivative Instruments.” The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2015 : 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 $ 2,725,729 $ — $ 2,709,361 $ 16,368 Mortgage backed securities 754,870 — 754,870 — Municipal bonds 1,626,281 — 1,626,281 — Commercial mortgage backed securities 764,152 — 764,152 — U.S. government and government agencies 2,423,455 2,378,662 44,793 — Non-U.S. government securities 917,664 — 917,664 — Asset backed securities 1,620,506 — 1,563,006 57,500 Total 10,832,657 2,378,662 8,380,127 73,868 Equity securities 629,182 627,441 1,741 — Short-term investments 587,904 572,604 15,300 — Other investments 99,159 99,159 — — Other investments measured at net asset value (2) 201,317 Total other investments 300,476 99,159 — — Derivative instruments (4) 20,022 — 20,022 — Fair value option: Corporate bonds 771,733 — 771,733 — Non-U.S. government bonds 81,824 — 81,824 — Mortgage backed securities 57,687 — 57,687 — Asset backed securities 25,444 — 25,444 — U.S. government and government agencies 114 114 — — Short-term investments 285,923 285,923 — — Equity securities 798 798 — — Other investments 1,176,312 68,295 1,108,017 — Other investments measured at net asset value (2) 494,659 Total 2,894,494 355,130 2,044,705 — Total assets measured at fair value $ 15,264,735 $ 4,032,996 $ 10,461,895 $ 73,868 Liabilities measured at fair value: Contingent consideration liabilities $ (96,048 ) $ — $ — $ (96,048 ) Securities sold but not yet purchased (3) (30,583 ) — (30,583 ) — Derivative instruments (4) (11,863 ) — (11,863 ) — Total liabilities measured at fair value $ (138,494 ) $ — $ (42,446 ) $ (96,048 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 6 , “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 8 , “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 Total Contingent Consideration Liabilities Three Months Ended September 30, 2016 Balance at beginning of period $ 49,211 $ 17,305 $ 66,516 $ (111,670 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — 1,667 1,667 (4,795 ) Included in other comprehensive income — — — 88 Purchases, issuances, sales and settlements Purchases — — — — Issuances — — — — Sales — — — — Settlements (22,435 ) — (22,435 ) — Transfers in and/or out of Level 3 — — — — Balance at end of period $ 26,776 $ 18,972 $ 45,748 $ (116,377 ) Three Months Ended September 30, 2015 Balance at beginning of period $ 57,500 $ — $ 57,500 $ (71,256 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — — — (9,596 ) Included in other comprehensive income — — — — Purchases, issuances, sales and settlements Purchases — — — — Issuances — — — — Sales — — — — Settlements — — — — Transfers in and/or out of Level 3 — — — — Balance at end of period $ 57,500 $ — $ 57,500 $ (80,852 ) Nine Months Ended September 30, 2016 Balance at beginning of year $ 57,500 $ 16,368 $ 73,868 $ (96,048 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) (2,500 ) 1,828 (672 ) (20,916 ) Included in other comprehensive income — — — 51 Purchases, issuances, sales and settlements Purchases — 776 776 — Issuances — — — — Sales — — — — Settlements (28,224 ) — (28,224 ) 536 Transfers in and/or out of Level 3 — — — — Balance at end of period $ 26,776 $ 18,972 $ 45,748 $ (116,377 ) Nine Months Ended September 30, 2015 Balance at beginning of year $ 57,500 $ — $ 57,500 $ (61,845 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — — — (17,939 ) Included in other comprehensive income — — — — Purchases, issuances, sales and settlements Purchases — — — — Issuances — — — (1,068 ) Sales — — — — Settlements — — — — Transfers in and/or out of Level 3 — — — — Balance at end of period $ 57,500 $ — $ 57,500 $ (80,852 ) (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 September 30, 2016 , due to their respective short maturities. As these financial instruments are not actively traded, their respective fair values are classified within Level 2. At September 30, 2016 , the senior notes of ACGL were carried at their cost, net of debt issuance costs, of $296.9 million and had a fair value of $407.3 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 $552.4 million . The fair values of the senior notes were obtained from a third party pricing service and are based on observable market inputs. As such, the fair value of the senior notes is classified within Level 2.

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2016
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 Liability Derivatives Notional Value (1) September 30, 2016 Futures contracts (2) $ 1,297 $ (2,710 ) $ 1,549,238 Foreign currency forward contracts (2) 5,430 (4,539 ) 1,019,946 TBAs (3) 92,301 (102,861 ) 183,559 Other (2) 13,327 (3,062 ) 1,328,628 Total $ 112,355 $ (113,172 ) December 31, 2015 Futures contracts (2) $ 2,816 $ (1,202 ) $ 1,797,115 Foreign currency forward contracts (2) 9,336 (6,344 ) 773,619 TBAs (3) 6,525 — 6,316 Other (2) 7,870 (4,317 ) 1,694,935 Total $ 26,547 $ (11,863 ) (1) Represents the absolute notional value of all outstanding contracts, consisting of long and short positions. (2) The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’ (3) The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’ The Company did not hold any derivatives which were designated as hedging instruments at September 30, 2016 or December 31, 2015 . The Company’s derivative instruments can be traded under master netting agreements, which establish terms that apply to all derivative transactions with a counterparty. In the event of a bankruptcy or other stipulated event of default, such agreements provide that the non-defaulting party may elect to terminate all outstanding derivative transactions, in which case all individual derivative positions (loss or gain) with a counterparty are closed out and netted and replaced with a single amount, usually referred to as the termination amount, which is expressed in a single currency. The resulting single net amount, where positive, is payable to the party “in-the-money” regardless of whether or not it is the defaulting party, unless the parties have agreed that only the non-defaulting party is entitled to receive a termination payment where the net amount is positive and is in its favor. Contractual close-out netting reduces derivatives credit exposure from gross to net exposure. At September 30, 2016 , asset derivatives and liability derivatives of $111.2 million and $113.2 million , respectively, were subject to a master netting agreement, compared to $26.5 million and $11.9 million , respectively, at December 31, 2015 . The remaining derivatives included in the preceding table were not subject to a master netting agreement. All realized and unrealized contract gains and losses on the Company’s derivative instruments are reflected in net realized gains (losses) in the consolidated statements of income, as summarized in the following table: Derivatives not designated as September 30, hedging instruments: 2016 2015 Three Months Ended Net realized gains (losses): Futures contracts $ (15,368 ) $ 28,562 Foreign currency forward contracts 4,583 5,395 TBAs (23 ) 1,064 Other (6,156 ) 868 Total $ (16,964 ) $ 35,889 Nine Months Ended Net realized gains (losses): Futures contracts $ 45,954 $ 16,442 Foreign currency forward contracts (13,951 ) 13,490 TBAs 311 1,368 Other (8,212 ) (231 ) Total $ 24,102 $ 31,069

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Letter of Credit and Revolving Credit Facilities As of September 30, 2016 , ACGL and its wholly-owned subsidiaries had a $300.0 million unsecured revolving loan and letter of credit facility and a $500.0 million secured letter of credit facility (the “Credit Agreement”). Under the terms of the Credit Agreement, Arch Reinsurance Company and Arch Reinsurance Ltd. are limited to issuing an aggregate of $100.0 million of unsecured letters of credit as part of the unsecured revolving loan. The Credit Agreement expires on June 30, 2019 . In addition, certain of ACGL’s subsidiaries had outstanding letters of credit of $175.6 million as of September 30, 2016 , which were issued on a limited basis and for limited purposes (together with the secured portion of the Credit Agreement and these letter of credit facilities, the “LOC Facilities”). ACGL and its’ subsidiaries which are party to the LOC Facilities were in compliance with all covenants contained in the LOC Facilities at September 30, 2016 . At such date, $334.2 million in letters of credit under the LOC Facilities were outstanding, which were secured by investments with a fair value of $386.2 million , and had $100.0 million of borrowings outstanding under the Credit Agreement. Under the $500.0 million secured letter of credit facility, ACGL’s subsidiaries had remaining capacity of $341.4 million (outstanding letters of credit of $158.6 million ) at September 30, 2016 . See Note 16 , “Subsequent Events.” As of September 30, 2016 , Watford Re had a $100.0 million letter of credit facility expiring on May 19, 2017 and an $800.0 million secured credit facility expiring on June 4, 2018 , that provides for borrowings and the issuance of letters of credit not to exceed $400.0 million . Borrowings of revolving loans may be made by Watford Re at a variable rate based on LIBOR or an alternative base rate at the option of Watford Re. At September 30, 2016 , Watford Re had $207.8 million in outstanding letters of credit under the two facilities and $298.1 million of borrowings outstanding under the secured credit facility, backed by Watford Re’s investment portfolio. Watford Re was in compliance with all covenants contained in both of its credit facilities at September 30, 2016 . The Company does not guarantee or provide credit support for Watford Re, and the Company’s financial exposure to Watford Re is limited to its investment in Watford Re’s common and preferred shares and counterparty credit risk (mitigated by collateral) arising from the reinsurance transactions. 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 $1.34 billion at September 30, 2016 , compared to $1.11 billion at December 31, 2015 . Acquisition of United Guaranty Corporation On August 15, 2016, ACGL entered into a Stock Purchase Agreement (the “Stock Purchase Agreement”) with American International Group, Inc. (“AIG”) pursuant to which, upon the terms and subject to the conditions thereof, ACGL agreed to purchase from AIG all of the issued and outstanding shares of capital stock of United Guaranty Corporation, a North Carolina corporation (“UG Corp”), and AIG United Guaranty (Asia) Limited (“AIG UG Asia” and, together with UG Corp, “UGC”). The acquisition under the Stock Purchase Agreement is referred to herein as the “UGC Acquisition.” As consideration in the UGC Acquisition, ACGL will pay to AIG aggregate consideration of approximately $3.43 billion (using the ACGL closing share price as of October 27, 2016 ), consisting of the following: (i) cash consideration of approximately $2.20 billion (the “Base Cash Consideration”); (ii) a number of shares of ACGL’s convertible non-voting common-equivalent preference shares (the “Series D Preferred Shares”) which are subject to a formula and a collar and an estimated fair value (using the ACGL closing share price as of October 27, 2016 of $77.03 per share) of approximately $983.1 million , subject to adjustment and subject to certain restrictions on transfer within the first 18 months ; and (iii) an additional amount (or if such amount is negative $0 ) in cash equal to $250.0 million less the Company Dividend Amount (as defined below), if any, less the value of Perpetual Preferred Shares (as defined below) issued to AIG, if any. The Stock Purchase Agreement entitles AIG to take dividends or other distributions from UGC in an amount not to exceed $250.0 million between the signing of the Stock Purchase Agreement and the closing date of the UGC Acquisition (the amount of any such dividends or distributions, the “Company Dividend Amount”). As an additional component of the consideration for the transaction, ACGL can require AIG to accept up to $250.0 million of Perpetual Preferred Shares (which will have the same terms as ACGL’s 5.25% Non-Cumulative Preferred Shares, Series E (the “Perpetual Preferred Shares”) less the Company Dividend Amount. In connection with the UGC Acquisition, the 50% quota share reinsurance agreement between United Guaranty Residential Insurance Company and three subsidiaries of AIG relating to policy years 2014, 2015 and 2016 will be amended to terminate on a run-off basis as of 12:01 a.m. on January 1, 2017. The Stock Purchase Agreement may be terminated under certain circumstances, including: (i) the parties’ mutual agreement; (ii) by either ACGL or AIG, if the closing has not occurred on or before March 31, 2017, subject to an extension at the request of either party of up to three months for the receipt of certain approvals (such date, as may be extended, the “Outside Date”); (iii) by either ACGL or AIG, in the event of the issuance of a final, non-appealable governmental order restraining or prohibiting the consummation of the transaction contemplated by the Stock Purchase Agreement or in the event that any law has been enacted, promulgated or issued by any governmental authority that restrains, enjoins or prohibits the transaction contemplated by the Stock Purchase Agreement or that would render the consummation of such transaction illegal; or (iv) the non-terminating party’s material uncured breach of the Stock Purchase Agreement. In the event that either ACGL or AIG terminates the Stock Purchase Agreement due to a failure to obtain the necessary regulatory approvals on or before the Outside Date and specified ACGL conditions to closing are otherwise satisfied, ACGL will pay a termination fee of $150.0 million to AIG. Bridge Credit Agreement In connection with the UGC Acquisition, the Company entered into a bridge credit agreement with Credit Suisse AG, Cayman Islands Branch (“CS”), as administrative agent and initial lender (the ‘‘Bridge Credit Agreement’’). The Bridge Credit Agreement provides for commitments by the lenders thereunder to provide up to $1.375 billion of term loans (the “Bridge Loans”) to fund a portion of the cash consideration portion required in the UGC Acquisition and to pay related fees and expenses. Commitments under the Bridge Credit Agreement (or, to the extent funded, the Bridge Loans) may be voluntarily reduced (or prepaid) by ACGL without premium or penalty, other than payment of customary breakage costs. Commitments under the Bridge Credit Agreement (or, to the extent funded, Bridge Loans) will be subject to mandatory reduction (or, in the case of Bridge Loans, mandatory prepayment), by an amount equal to the net cash proceeds of certain debt incurrences, equity issuances and asset sales. The commitments under the Bridge Credit Agreement will expire five business days after the Outside Date if the closing of the acquisition has not occurred on or prior to such date. Conditions to borrowing under the Bridge Credit Agreement include the absence of a Material Adverse Effect (as defined in the Stock Purchase Agreement) in United Guaranty after December 31, 2015, the concurrent consummation of the acquisition in accordance with the Stock Purchase Agreement, and other conditions customary for bridge financings of this type. The Bridge Loans, if funded, will mature on the date that is 364 days after funding. Bridge Loans will bear interest at a rate based on LIBOR or the base rate plus, in each case, an applicable margin. The applicable margin for LIBOR loans would range from 0.875% to 1.625% per annum and for base rate loans would range from 0.0% to 0.625% per annum, in each case, depending on the public debt rating of ACGL then in effect, increasing by 0.25% (with respect to each level of public debt rating) every 90 days after funding. In addition, customary fees will be payable under the Bridge Credit Agreement and related documents. The Bridge Credit Agreement contains financial covenants that require ACGL to maintain a minimum consolidated tangible net worth and a maximum ratio of total consolidated debt to the sum of total consolidated debt plus consolidated net worth. The Bridge Credit Agreement also includes customary affirmative covenants, negative covenants and events of default. These provisions are generally consistent with those in ACGL’s existing revolving credit agreement. Arch-U.S. will provide a guaranty of the obligations under the Bridge Credit Agreement. ACGL has the ability under the Bridge Loan Agreement to designate one of its subsidiaries to be the borrower pursuant to the terms thereof. In such case, ACGL would guarantee the obligations of the subsidiary borrower. As a result of the preferred share offering in September 2016 (see note 10), the outstanding commitments under the Bridge Credit Agreement were reduced to $938.5 million at September 30, 2016.

Share Transactions

Share Transactions	9 Months Ended
	Sep. 30, 2016
Stockholders' Equity Note [Abstract]
Share Transactions	Share Transactions Preferred Share Offering On September 29, 2016, ACGL completed a $450 million underwritten public offering of 18.0 million depositary shares (the “Depositary Shares”), each of which represents a 1/1,000th interest in a share of its 5.25% Non-Cumulative Preferred Shares, Series E, have a $0.01 par value and $25,000 liquidation preference per share (equivalent to $25 liquidation preference per Depositary Share) (the “Series E Preferred Shares”). Each Depositary Share, evidenced by a depositary receipt, entitles the holder, through the depositary, to a proportional fractional interest in all rights and preferences of the Series E Preferred Shares represented thereby (including any dividend, liquidation, redemption and voting rights). In April 2012, the Company issued $325 million of Series C Non-Cumulative Preferred Shares that are on parity with the Series E Preferred Shares with respect to payment of dividends and the distribution of assets upon a liquidation, dissolution or winding-up of ACGL. Holders of Series E Preferred Shares will be entitled to receive dividend payments only when, as and if declared by our board of directors or a duly authorized committee of the board. Any such dividends will be payable from, and including, the date of original issue on a non-cumulative basis, quarterly in arrears on the last day of March, June, September and December of each year, at an annual rate of 5.25% . If declared, the first dividend payment date will be January 3, 2017. Dividends on the Series E Preferred Shares are not cumulative. The Company will be restricted from paying dividends on or repurchasing its common shares unless certain dividend payments are made on the Series E Preferred Shares. Except in specified circumstances relating to certain tax or corporate events, the Series E Preferred Shares are not redeemable prior to September 29, 2021 (the fifth anniversary of the issue date). On and after that date, the Series E Preferred Shares will be redeemable at the Company’s option, in whole or in part, at a redemption price of $25,000 per share of the Series E Preferred Shares (equivalent to $25 per depositary share), plus any declared and unpaid dividends, without accumulation of any undeclared dividends to, but excluding, the redemption date. The Depositary Shares will be redeemed if and to the extent the related Series E Preferred Shares are redeemed by the Company. Neither the Depositary Shares nor the Series E Preferred Shares have a stated maturity, nor will they be subject to any sinking fund or mandatory redemption. The Series E Preferred Shares are not convertible into any other securities. The Series E Preferred Shares will not have voting rights, except under limited circumstances. The Company intends to use the net proceeds from the offering of $434.9 million to fund a portion of the UGC Acquisition, to pay related costs and expenses and for general corporate purposes. See Note 9 for further detail on the UGC Acquisition. Share Repurchases The board of directors of ACGL has authorized the investment in ACGL’s common shares through a share repurchase program. Since the inception of the share repurchase program, ACGL has repurchased approximately 125.2 million common shares for an aggregate purchase price of $3.68 billion . For the nine months ended September 30, 2016 , ACGL repurchased 1.1 million common shares (no repurchases in the 2016 third quarter ) for an aggregate purchase price of $75.3 million . During the 2015 third quarter and nine months ended September 30, 2015 , ACGL repurchased 0.1 million and 5.9 million common shares, respectively, for an aggregate purchase price of $3.5 million and $365.4 million , respectively. At September 30, 2016 , $446.5 million of share repurchases were available under the program. 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)	9 Months Ended
	Sep. 30, 2016
Comprehensive Income Note Disclosure [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The following tables present details about amounts reclassified from accumulated other comprehensive income and the tax effects allocated to each component of other comprehensive income (loss): Amounts Reclassified from AOCI Consolidated Statement of Income Three Months Ended Nine Months Ended Details About Line Item That Includes September 30, September 30, AOCI Components Reclassification 2016 2015 2016 2015 Unrealized appreciation on available-for-sale investments Net realized gains (losses) $ 61,464 $ (2,019 ) $ 137,555 $ 63,671 Other-than-temporary impairment losses (3,867 ) (8,901 ) (16,999 ) (17,274 ) Total before tax 57,597 (10,920 ) 120,556 46,397 Income tax (expense) benefit (2,605 ) (1,358 ) (11,247 ) (6,529 ) Net of tax $ 54,992 $ (12,278 ) $ 109,309 $ 39,868 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Three Months Ended September 30, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 11,692 $ (4,589 ) $ 16,281 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 57,597 2,605 54,992 Foreign currency translation adjustments (5,407 ) (95 ) (5,312 ) Other comprehensive income (loss) $ (51,312 ) $ (7,289 ) $ (44,023 ) Three Months Ended September 30, 2015 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ (44,687 ) $ 9,204 $ (53,891 ) Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (3,033 ) — (3,033 ) Less reclassification of net realized gains (losses) included in net income (10,920 ) 1,358 (12,278 ) Foreign currency translation adjustments (12,639 ) (556 ) (12,083 ) Other comprehensive income (loss) $ (49,439 ) $ 7,290 $ (56,729 ) Nine Months Ended September 30, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 281,770 $ 30,048 $ 251,722 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (150 ) — (150 ) Less reclassification of net realized gains (losses) included in net income 120,556 11,247 109,309 Foreign currency translation adjustments (5,733 ) 417 (6,150 ) Other comprehensive income (loss) $ 155,331 $ 19,218 $ 136,113 Nine Months Ended September 30, 2015 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ (46,930 ) $ 4,592 $ (51,522 ) Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (4,494 ) — (4,494 ) Less reclassification of net realized gains (losses) included in net income 46,397 6,529 39,868 Foreign currency translation adjustments (24,568 ) (1,308 ) (23,260 ) Other comprehensive income (loss) $ (122,389 ) $ (3,245 ) $ (119,144 )

Guarantor Financial Information

Guarantor Financial Information	9 Months Ended
	Sep. 30, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Guarantor Financial Information	Guarantor Financial Information The following tables present condensed financial information for ACGL, Arch-U.S., a 100% owned subsidiary of ACGL, and ACGL’s other subsidiaries. September 30, 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 $ 538,713 $ 54,483 $ 16,975,841 $ (14,700 ) $ 17,554,337 Cash 2,041 19,392 557,383 — 578,816 Investments in subsidiaries 7,316,435 1,815,833 — (9,132,268 ) — Due from subsidiaries and affiliates 4 51,036 391,026 (442,066 ) — Premiums receivable — — 1,726,846 (544,138 ) 1,182,708 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 6,074,812 (3,998,564 ) 2,076,248 Contractholder receivables — — 1,649,441 — 1,649,441 Prepaid reinsurance premiums — — 1,723,344 (1,182,106 ) 541,238 Deferred acquisition costs, net — — 469,466 — 469,466 Other assets 17,348 48,285 1,695,117 (169,773 ) 1,590,977 Total assets $ 7,874,541 $ 1,989,029 $ 31,263,276 $ (15,483,615 ) $ 25,643,231 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 13,582,475 $ (3,972,286 ) $ 9,610,189 Unearned premiums — — 3,853,227 (1,182,106 ) 2,671,121 Reinsurance balances payable — — 815,826 (544,138 ) 271,688 Contractholder payables — — 1,649,441 — 1,649,441 Collateral held for insured obligations — — 277,463 277,463 Deposit accounting liabilities — — 22,281 — 22,281 Senior notes 296,936 494,501 — — 791,437 Revolving credit agreement borrowings 100,000 — 298,100 — 398,100 Due to subsidiaries and affiliates 270 35,003 406,793 (442,066 ) — Other liabilities (1) 125,013 57,753 1,572,207 (196,051 ) 1,558,922 Total liabilities 522,219 587,257 22,477,813 (6,336,647 ) 17,250,642 Redeemable noncontrolling interests — — 220,159 (14,700 ) 205,459 Shareholders’ Equity Total shareholders’ equity available to Arch 7,352,322 1,401,772 7,730,496 (9,132,268 ) 7,352,322 Non-redeemable noncontrolling interests — — 834,808 — 834,808 Total shareholders’ equity 7,352,322 1,401,772 8,565,304 (9,132,268 ) 8,187,130 Total liabilities, noncontrolling interests and shareholders’ equity $ 7,874,541 $ 1,989,029 $ 31,263,276 $ (15,483,615 ) $ 25,643,231 (1) Includes payable for securities purchased. December 31, 2015 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 50 $ 42,210 $ 15,815,381 $ (14,700 ) $ 15,842,941 Cash 6,809 17,023 529,494 — 553,326 Investments in subsidiaries 6,609,174 1,712,757 — (8,321,931 ) — Due from subsidiaries and affiliates 23 48,811 384,469 (433,303 ) — Premiums receivable — — 1,376,310 (392,867 ) 983,443 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 5,783,452 (3,916,079 ) 1,867,373 Contractholder receivables — — 1,486,296 — 1,486,296 Prepaid reinsurance premiums — — 1,511,795 (1,084,186 ) 427,609 Deferred acquisition costs, net — — 433,477 — 433,477 Other assets 4,138 45,522 2,119,279 (586,134 ) 1,582,805 Total assets $ 6,620,194 $ 1,866,323 $ 29,439,953 $ (14,749,200 ) $ 23,177,270 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 13,010,608 $ (3,885,358 ) $ 9,125,250 Unearned premiums — — 3,418,118 (1,084,186 ) 2,333,932 Reinsurance balances payable — — 603,586 (379,466 ) 224,120 Contractholder payables — — 1,486,296 — 1,486,296 Collateral held for insured obligations — — 248,982 — 248,982 Deposit accounting liabilities — — 463,507 (203,143 ) 260,364 Senior notes 296,874 494,432 — — 791,306 Revolving credit agreement borrowings 100,000 — 430,434 — 530,434 Due to subsidiaries and affiliates 26 35,000 398,277 (433,303 ) — Other liabilities (1) 18,413 50,890 1,385,500 (427,111 ) 1,027,692 Total liabilities 415,313 580,322 21,445,308 (6,412,567 ) 16,028,376 Redeemable noncontrolling interests — — 219,882 (14,700 ) 205,182 Shareholders’ Equity Total shareholders’ equity available to Arch 6,204,881 1,286,001 7,035,932 (8,321,933 ) 6,204,881 Non-redeemable noncontrolling interests — — 738,831 — 738,831 Total shareholders’ equity 6,204,881 1,286,001 7,774,763 (8,321,933 ) 6,943,712 Total liabilities, noncontrolling interests and shareholders’ equity $ 6,620,194 $ 1,866,323 $ 29,439,953 $ (14,749,200 ) $ 23,177,270 (1) Includes payable for securities purchased. Three Months Ended September 30, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 958,403 $ — $ 958,403 Net investment income 6 803 99,654 (6,845 ) 93,618 Net realized gains (losses) — — 125,105 — 125,105 Net impairment losses recognized in earnings — — (3,867 ) — (3,867 ) Other underwriting income — — 7,980 — 7,980 Equity in net income (loss) of investment funds accounted for using the equity method — — 16,662 — 16,662 Other income (loss) 71 — (471 ) — (400 ) Total revenues 77 803 1,203,466 (6,845 ) 1,197,501 Expenses Losses and loss adjustment expenses — — 524,183 — 524,183 Acquisition expenses — — 163,861 — 163,861 Other operating expenses — — 155,557 — 155,557 Corporate expenses 18,488 608 (611 ) — 18,485 Interest expense 5,948 6,627 9,890 (6,522 ) 15,943 Net foreign exchange (gains) losses — — 2,723 (102 ) 2,621 Total expenses 24,436 7,235 855,603 (6,624 ) 880,650 Income (loss) before income taxes (24,359 ) (6,432 ) 347,863 (221 ) 316,851 Income tax (expense) benefit — 2,116 (15,347 ) — (13,231 ) Income (loss) before equity in net income of subsidiaries (24,359 ) (4,316 ) 332,516 (221 ) 303,620 Equity in net income of subsidiaries 277,231 21,945 — (299,176 ) — Net income 252,872 17,629 332,516 (299,397 ) 303,620 Net (income) loss attributable to noncontrolling interests — — (51,071 ) 323 (50,748 ) Net income available to Arch 252,872 17,629 281,445 (299,074 ) 252,872 Preferred dividends (5,484 ) — — — (5,484 ) Net income available to Arch common shareholders $ 247,388 $ 17,629 $ 281,445 $ (299,074 ) $ 247,388 Comprehensive income (loss) available to Arch $ 208,790 $ 2,019 $ 237,555 $ (239,574 ) $ 208,790 Three Months Ended September 30, 2015 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 936,683 $ — $ 936,683 Net investment income — 764 92,773 (7,304 ) 86,233 Net realized gains (losses) — — (89,698 ) — (89,698 ) Net impairment losses recognized in earnings — — (5,868 ) — (5,868 ) Other underwriting income — — 7,623 — 7,623 Equity in net income (loss) of investment funds accounted for using the equity method — — (2,118 ) — (2,118 ) Other income (loss) — — (265 ) — (265 ) Total revenues — 764 939,130 (7,304 ) 932,590 Expenses Losses and loss adjustment expenses — — 531,741 — 531,741 Acquisition expenses — — 171,566 — 171,566 Other operating expenses — — 146,220 — 146,220 Corporate expenses 10,536 720 (517 ) — 10,739 Interest expense 5,863 6,689 7,734 (6,986 ) 13,300 Net foreign exchange (gains) losses — — (11,762 ) (2,918 ) (14,680 ) Total expenses 16,399 7,409 844,982 (9,904 ) 858,886 Income (loss) before income taxes (16,399 ) (6,645 ) 94,148 2,600 73,704 Income tax (expense) benefit — 2,324 (12,028 ) — (9,704 ) Income (loss) before equity in net income of subsidiaries (16,399 ) (4,321 ) 82,120 2,600 64,000 Equity in net income of subsidiaries 96,432 13,620 — (110,052 ) — Net income 80,033 9,299 82,120 (107,452 ) 64,000 Net (income) loss attributable to noncontrolling interests — — 15,712 321 16,033 Net income available to Arch 80,033 9,299 97,832 (107,131 ) 80,033 Preferred dividends (5,484 ) — — — (5,484 ) Net income available to Arch common shareholders $ 74,549 $ 9,299 $ 97,832 $ (107,131 ) $ 74,549 Comprehensive income (loss) available to Arch $ 23,400 $ 15,705 $ 44,127 $ (59,832 ) $ 23,400 Nine Months Ended September 30, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 2,915,967 $ — $ 2,915,967 Net investment income 7 2,351 294,012 (20,679 ) 275,691 Net realized gains (losses) — — 230,647 — 230,647 Net impairment losses recognized in earnings — — (16,849 ) — (16,849 ) Other underwriting income — — 54,749 (16,498 ) 38,251 Equity in net income (loss) of investment funds accounted for using the equity method — — 32,054 — 32,054 Other income (loss) 270 — (702 ) — (432 ) Total revenues 277 2,351 3,509,878 (37,177 ) 3,475,329 Expenses Losses and loss adjustment expenses — — 1,631,724 — 1,631,724 Acquisition expenses — — 509,607 — 509,607 Other operating expenses — — 467,416 — 467,416 Corporate expenses 45,284 1,549 (1,765 ) — 45,068 Interest expense 17,811 19,946 46,169 (36,213 ) 47,713 Net foreign exchange (gains) losses — — 5,093 (3,568 ) 1,525 Total expenses 63,095 21,495 2,658,244 (39,781 ) 2,703,053 Income (loss) before income taxes (62,818 ) (19,144 ) 851,634 2,604 772,276 Income tax (expense) benefit — 6,446 (50,118 ) — (43,672 ) Income (loss) before equity in net income of subsidiaries (62,818 ) (12,698 ) 801,516 2,604 728,604 Equity in net income of subsidiaries 681,543 64,684 — (746,227 ) — Net income 618,725 51,986 801,516 (743,623 ) 728,604 Net (income) loss attributable to noncontrolling interests — — (110,844 ) 965 (109,879 ) Net income available to Arch 618,725 51,986 690,672 (742,658 ) 618,725 Preferred dividends (16,453 ) — — — (16,453 ) Net income available to Arch common shareholders $ 602,272 $ 51,986 $ 690,672 $ (742,658 ) $ 602,272 Comprehensive income (loss) available to Arch $ 754,979 $ 89,204 $ 830,348 $ (919,552 ) $ 754,979 Nine Months Ended September 30, 2015 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 2,790,385 $ — $ 2,790,385 Net investment income — 1,569 265,937 (15,316 ) 252,190 Net realized gains (losses) — 1 (42,076 ) — (42,075 ) Net impairment losses recognized in earnings — — (12,780 ) — (12,780 ) Other underwriting income — — 26,876 — 26,876 Equity in net income (loss) of investment funds accounted for using the equity method — — 19,938 — 19,938 Other income (loss) — — 52 — 52 Total revenues — 1,570 3,048,332 (15,316 ) 3,034,586 Expenses Losses and loss adjustment expenses — — 1,544,883 — 1,544,883 Acquisition expenses — — 510,067 — 510,067 Other operating expenses — — 445,947 — 445,947 Corporate expenses 36,068 2,991 (1,557 ) — 37,502 Interest expense 17,581 19,824 7,476 (14,834 ) 30,047 Net foreign exchange (gains) losses — — (44,450 ) (17,148 ) (61,598 ) Total expenses 53,649 22,815 2,462,366 (31,982 ) 2,506,848 Income (loss) before income taxes (53,649 ) (21,245 ) 585,966 16,666 527,738 Income tax (expense) benefit — 7,434 (36,596 ) — (29,162 ) Income (loss) before equity in net income of subsidiaries (53,649 ) (13,811 ) 549,370 16,666 498,576 Equity in net income of subsidiaries 532,808 42,192 — (575,000 ) — Net income 479,159 28,381 549,370 (558,334 ) 498,576 Net (income) loss attributable to noncontrolling interests — — (19,902 ) 485 (19,417 ) Net income available to Arch 479,159 28,381 529,468 (557,849 ) 479,159 Preferred dividends (16,453 ) — — — (16,453 ) Net income available to Arch common shareholders $ 462,706 $ 28,381 $ 529,468 $ (557,849 ) $ 462,706 Comprehensive income (loss) available to Arch $ 360,111 $ 13,950 $ 427,569 $ (441,519 ) $ 360,111 Nine Months Ended September 30, 2016 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 94,250 $ 14,448 $ 1,096,443 $ (168,002 ) $ 1,037,139 Investing Activities Purchases of fixed maturity investments — — (27,840,555 ) — (27,840,555 ) Purchases of equity securities — — (377,767 ) — (377,767 ) Purchases of other investments — — (1,008,774 ) — (1,008,774 ) Proceeds from the sales of fixed maturity investments — — 26,731,924 — 26,731,924 Proceeds from the sales of equity securities — — 464,904 — 464,904 Proceeds from the sales, redemptions and maturities of other investments — — 879,330 — 879,330 Proceeds from redemptions and maturities of fixed maturity investments — 41,500 499,323 — 540,823 Net settlements of derivative instruments — — 23,396 — 23,396 Net (purchases) sales of short-term investments (436,830 ) (53,779 ) (113,553 ) — (604,162 ) Change in cash collateral related to securities lending — — (27,935 ) — (27,935 ) Contributions to subsidiaries (3,585 ) — (9,247 ) 12,832 — Intercompany loans issued — — — — — Acquisitions, net of cash — — (20,911 ) — (20,911 ) Purchases of fixed assets (8 ) — (11,557 ) — (11,565 ) Change in other assets 2,000 — (5,816 ) — (3,816 ) Net Cash Provided By (Used For) Investing Activities (438,423 ) (12,279 ) (817,238 ) 12,832 (1,255,108 ) Financing Activities Proceeds from issuance of preferred shares, net 434,899 — — — 434,899 Purchases of common shares under share repurchase program (75,256 ) — — — (75,256 ) Proceeds from common shares issued, net (3,785 ) — 12,832 (12,832 ) (3,785 ) Proceeds from borrowings — — 46,000 — 46,000 Repayments of borrowings — — (179,171 ) — (179,171 ) Change in cash collateral related to securities lending — — 27,935 — 27,935 Dividends paid to redeemable noncontrolling interests — — (14,448 ) 957 (13,491 ) Dividends paid to parent (1) — — (167,045 ) 167,045 — Other — 200 32,913 — 33,113 Preferred dividends paid (16,453 ) — — — (16,453 ) Net Cash Provided By (Used For) Financing Activities 339,405 200 (240,984 ) 155,170 253,791 Effects of exchange rates changes on foreign currency cash — — (10,332 ) — (10,332 ) Increase (decrease) in cash (4,768 ) 2,369 27,889 — 25,490 Cash beginning of year 6,809 17,023 529,494 — 553,326 Cash end of period $ 2,041 $ 19,392 $ 557,383 $ — $ 578,816 (1) Dividends 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. Nine Months Ended September 30, 2015 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 382,329 $ 10,622 $ 859,525 $ (444,897 ) $ 807,579 Investing Activities Purchases of fixed maturity investments — (3,505 ) (22,378,599 ) — (22,382,104 ) Purchases of equity securities (8,070 ) — (477,456 ) — (485,526 ) Purchases of other investments — — (1,320,250 ) — (1,320,250 ) Proceeds from the sales of fixed maturity investments — 23,507 21,388,047 — 21,411,554 Proceeds from the sales of equity securities — — 509,008 — 509,008 Proceeds from the sales, redemptions and maturities of other investments — — 858,368 — 858,368 Proceeds from redemptions and maturities of fixed maturity investments — — 630,397 — 630,397 Net settlements of derivative instruments — — 81,114 — 81,114 Proceeds from investment in joint venture — — 40,000 — 40,000 Net (purchases) sales of short-term investments 73 (12,183 ) 193,851 — 181,741 Change in cash collateral related to securities lending — — 28,685 — 28,685 Contributions to subsidiaries — — (9,290 ) 9,290 — Intercompany loans issued — (39,500 ) (41,523 ) 81,023 — Acquisitions, net of cash — — 818 — 818 Purchases of fixed assets (53 ) — (10,848 ) — (10,901 ) Change in other assets — — (43,654 ) — (43,654 ) Net Cash Provided By (Used For) Investing Activities (8,050 ) (31,681 ) (551,332 ) 90,313 (500,750 ) Financing Activities Purchases of common shares under share repurchase program (365,383 ) — — — (365,383 ) Proceeds from common shares issued, net 697 — 9,290 (9,290 ) 697 Proceeds from intercompany borrowings 14,023 27,500 39,500 (81,023 ) — Proceeds from borrowings — — 239,077 — 239,077 Change in cash collateral related to securities lending — — (28,685 ) — (28,685 ) Dividends paid to redeemable noncontrolling interests — — (14,447 ) 637 (13,810 ) Dividends paid to parent (1) — — (444,260 ) 444,260 — Other — 28 50,435 — 50,463 Preferred dividends paid (16,453 ) — — — (16,453 ) Net Cash Provided By (Used For) Financing Activities (367,116 ) 27,528 (149,090 ) 354,584 (134,094 ) Effects of exchange rates changes on foreign currency cash — — (8,658 ) — (8,658 ) Increase (decrease) in cash 7,163 6,469 150,445 — 164,077 Cash beginning of year 3,218 2,787 479,697 — 485,702 Cash end of period $ 10,381 $ 9,256 $ 630,142 $ — $ 649,779 (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	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company’s income tax provision on income before income taxes resulted in an expense of 5.7% for the nine months ended September 30, 2016 , compared to an expense of 5.5% for the 2015 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. The Company had a net deferred tax asset of $124.1 million at September 30, 2016 , compared to $135.7 million at December 31, 2015 . In addition, the Company paid $40.7 million and $35.5 million of income taxes for the nine months ended September 30, 2016 and 2015 , respectively.

Legal Proceedings

Legal Proceedings	9 Months Ended
	Sep. 30, 2016
Disclosure Legal Proceedings [Abstract]
Legal Proceedings	Legal Proceedings The Company, in common with the insurance industry in general, is subject to litigation and arbitration in the normal course of its business. As of September 30, 2016 , the Company was not a party to any litigation or arbitration which is expected by management to have a material adverse effect on the Company’s results of operations and financial condition and liquidity.

Transactions with Related Parti

Transactions with Related Parties	9 Months Ended
	Sep. 30, 2016
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 September 30, 2016 , the Company had aggregate commitments of $770.9 million to funds managed by Carlyle, of which $524.5 million was unfunded. The Company may make additional commitments to funds managed by Carlyle from time to time. During the nine months ended September 30, 2016 and 2015 , the Company made aggregate capital contributions to funds managed by Carlyle of $50.1 million and $97.7 million , respectively, and received aggregate cash distributions from funds managed by Carlyle of $17.9 million and $30.3 million , respectively.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2016
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events On October 26, 2016, ACGL and certain of its subsidiaries amended the existing Credit Agreement (the “Amended Credit Agreement”) (see Note 9). The Amended Credit Agreement provides for a $350.0 million secured facility for letters of credit and $500.0 million unsecured facility for revolving loans and letters of credit. Obligations of each borrower under the secured facility for letters of credit are secured by cash and eligible securities of such borrower held in collateral accounts. ACGL has a one-time option to convert any or all outstanding revolving loans of ACGL and/or Arch-U.S. to term loans with the same terms as the revolving loans except that any prepayments may not be reborrowed. Arch-U.S. guarantees the obligations of ACGL, and ACGL guarantees the obligations of Arch-U.S. Commitments under the Amended Credit Agreement will expire on October 26, 2021, and all loans then outstanding under the Amended Credit Agreement must be repaid. Letters of credit issued under the Amended Credit Agreement will not have an expiration date later than October 26, 2022. The Amended Credit Agreement contains customary representations and warranties, conditions to credit extensions, affirmative and negative covenants, and events of default.

General (Policies)

General (Policies)	9 Months Ended
	Sep. 30, 2016
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)	9 Months Ended
	Sep. 30, 2016
Noncontrolling Interest [Abstract]
Carrying value of assets and liabilities of variable interest entity	The following table provides the carrying amount and balance sheet caption in which the assets and liabilities of Watford Re are reported: September 30, December 31, 2016 2015 Assets Investments accounted for using the fair value option $ 1,872,342 $ 1,617,107 Cash 67,032 108,550 Accrued investment income 16,891 19,249 Premiums receivable 211,444 162,263 Reinsurance recoverable on unpaid and paid losses and LAE 25,822 14,135 Prepaid reinsurance premiums 11,556 11,129 Deferred acquisition costs, net 87,490 75,443 Receivable for securities sold 94,965 34,095 Goodwill and intangible assets 7,650 — Other assets 122,641 80,361 Total assets of consolidated VIE $ 2,517,833 $ 2,122,332 Liabilities Reserves for losses and loss adjustment expenses $ 460,600 $ 290,997 Unearned premiums 308,063 249,980 Reinsurance balances payable 12,315 14,005 Revolving credit agreement borrowings 298,100 430,434 Payable for securities purchased 145,135 33,062 Other liabilities 135,248 53,624 Total liabilities of consolidated VIE $ 1,359,461 $ 1,072,102 Redeemable noncontrolling interests $ 220,159 $ 219,882
Activity in non-redeemable noncontrolling interests	The following table sets forth activity in the non-redeemable noncontrolling interests: September 30, 2016 2015 Three Months Ended Balance, beginning of period $ 788,589 $ 794,880 Amounts attributable to noncontrolling interests 46,160 (20,621 ) Foreign currency translation adjustments attributable to noncontrolling interests 59 (97 ) Balance, end of period $ 834,808 $ 774,162 Nine Months Ended Balance, beginning of year $ 738,831 $ 769,081 Amounts attributable to noncontrolling interests 96,118 5,178 Foreign currency translation adjustments attributable to noncontrolling interests (141 ) (97 ) Balance, end of period $ 834,808 $ 774,162
Activity in redeemable noncontrolling interests	The following table sets forth activity in the redeemable non-controlling interests: September 30, 2016 2015 Three Months Ended Balance, beginning of period $ 205,366 $ 204,996 Shares acquired by the Company — — Accretion of preference share issuance costs 93 93 Balance, end of period $ 205,459 $ 205,089 Nine Months Ended Balance, beginning of year $ 205,182 $ 219,512 Shares acquired by the Company — (14,700 ) Accretion of preference share issuance costs 277 277 Balance, end of period $ 205,459 $ 205,089
Portion of income or loss attributable to third party investors	The portion of Watford Re’s income or loss attributable to third party investors, recorded in the Company’s consolidated statements of income in ‘net (income) loss attributable to noncontrolling interests,’ are summarized in the table below: September 30, 2016 2015 Three Months Ended Amounts attributable to non-redeemable noncontrolling interests $ (46,160 ) $ 20,621 Dividends attributable to redeemable noncontrolling interests (4,588 ) (4,588 ) Net (income) loss attributable to noncontrolling interests $ (50,748 ) $ 16,033 Nine Months Ended Amounts attributable to non-redeemable noncontrolling interests $ (96,118 ) $ (5,178 ) Dividends attributable to redeemable noncontrolling interests (13,761 ) (14,239 ) Net (income) loss attributable to noncontrolling interests $ (109,879 ) $ (19,417 )

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2016
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 Nine Months Ended September 30, September 30, 2016 2015 2016 2015 Numerator: Net income $ 303,620 $ 64,000 $ 728,604 $ 498,576 Net (income) loss attributable to noncontrolling interests (50,748 ) 16,033 (109,879 ) (19,417 ) Net income available to Arch 252,872 80,033 618,725 479,159 Preferred dividends (5,484 ) (5,484 ) (16,453 ) (16,453 ) Net income available to Arch common shareholders $ 247,388 $ 74,549 $ 602,272 $ 462,706 Denominator: Weighted average common shares outstanding — basic 120,938,916 120,567,410 120,656,420 122,151,971 Effect of dilutive common share equivalents: Nonvested restricted shares 1,313,025 1,322,053 1,295,825 1,260,247 Stock options (1) 2,679,712 3,122,310 2,575,929 2,942,541 Weighted average common shares and common share equivalents outstanding — diluted 124,931,653 125,011,773 124,528,174 126,354,759 Earnings per common share: Basic $ 2.05 $ 0.62 $ 4.99 $ 3.79 Diluted $ 1.98 $ 0.60 $ 4.84 $ 3.66 (1) Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2016 third quarter and 2015 third quarter , the number of stock options excluded were 334,203 and 390,406 , respectively. For the nine months ended September 30, 2016 and 2015 , the number of stock options excluded were 842,105 and 957,838 , respectively.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Analysis of underwriting income or loss by segment and reconciliation to net income available to common shareholders	The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income or loss to net income available to common shareholders: Three Months Ended September 30, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 758,934 $ 324,361 $ 131,726 $ 1,214,765 $ 163,736 $ 1,278,765 Premiums ceded (217,446 ) (89,551 ) (51,182 ) (357,923 ) (6,300 ) (264,487 ) Net premiums written 541,488 234,810 80,544 856,842 157,436 1,014,278 Change in unearned premiums (22,410 ) 17,117 (3,582 ) (8,875 ) (47,000 ) (55,875 ) Net premiums earned 519,078 251,927 76,962 847,967 110,436 958,403 Other underwriting income — 2,216 4,740 6,956 1,024 7,980 Losses and loss adjustment expenses (332,845 ) (105,924 ) (11,107 ) (449,876 ) (74,307 ) (524,183 ) Acquisition expenses, net (77,148 ) (50,217 ) (7,757 ) (135,122 ) (28,739 ) (163,861 ) Other operating expenses (87,517 ) (35,589 ) (25,416 ) (148,522 ) (7,035 ) (155,557 ) Underwriting income (loss) $ 21,568 $ 62,413 $ 37,422 121,403 1,379 122,782 Net investment income 66,282 27,336 93,618 Net realized gains (losses) 95,946 29,159 125,105 Net impairment losses recognized in earnings (3,867 ) — (3,867 ) Equity in net income (loss) of investment funds accounted for using the equity method 16,662 — 16,662 Other income (loss) (400 ) — (400 ) Corporate expenses (18,485 ) — (18,485 ) Interest expense (12,924 ) (3,019 ) (15,943 ) Net foreign exchange gains (losses) (4,232 ) 1,611 (2,621 ) Income (loss) before income taxes 260,385 56,466 316,851 Income tax expense (13,232 ) 1 (13,231 ) Net income (loss) 247,153 56,467 303,620 Dividends attributable to redeemable noncontrolling interests — (4,588 ) (4,588 ) Amounts attributable to noncontrolling interests — (46,160 ) (46,160 ) Net income (loss) available to Arch 247,153 5,719 252,872 Preferred dividends (5,484 ) — (5,484 ) Net income (loss) available to Arch common shareholders $ 241,669 $ 5,719 $ 247,388 Underwriting Ratios Loss ratio 64.1 % 42.0 % 14.4 % 53.1 % 67.3 % 54.7 % Acquisition expense ratio 14.9 % 19.9 % 10.1 % 15.9 % 26.0 % 17.1 % Other operating expense ratio 16.9 % 14.1 % 33.0 % 17.5 % 6.4 % 16.2 % Combined ratio 95.9 % 76.0 % 57.5 % 86.5 % 99.7 % 88.0 % Goodwill and intangible assets $ 26,367 $ 1,228 $ 55,696 $ 83,291 $ 7,650 $ 90,941 (1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. Three Months Ended September 30, 2015 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 752,438 $ 329,327 $ 74,657 $ 1,158,451 $ 131,165 $ 1,189,192 Premiums ceded (209,443 ) (92,182 ) (7,832 ) (311,486 ) (6,158 ) (217,220 ) Net premiums written 542,995 237,145 66,825 846,965 125,007 971,972 Change in unearned premiums (20,451 ) 23,286 (12,277 ) (9,442 ) (25,847 ) (35,289 ) Net premiums earned 522,544 260,431 54,548 837,523 99,160 936,683 Other underwriting income 519 2,783 3,565 6,867 756 7,623 Losses and loss adjustment expenses (339,859 ) (115,780 ) (9,562 ) (465,201 ) (66,540 ) (531,741 ) Acquisition expenses, net (77,076 ) (55,416 ) (10,428 ) (142,920 ) (28,646 ) (171,566 ) Other operating expenses (84,620 ) (37,131 ) (21,048 ) (142,799 ) (3,421 ) (146,220 ) Underwriting income (loss) $ 21,508 $ 54,887 $ 17,075 93,470 1,309 94,779 Net investment income 67,251 18,982 86,233 Net realized gains (losses) (53,480 ) (36,218 ) (89,698 ) Net impairment losses recognized in earnings (5,868 ) — (5,868 ) Equity in net income (loss) of investment funds accounted for using the equity method (2,118 ) — (2,118 ) Other income (loss) (265 ) — (265 ) Corporate expenses (10,739 ) — (10,739 ) Interest expense (12,014 ) (1,286 ) (13,300 ) Net foreign exchange gains (losses) 16,056 (1,376 ) 14,680 Income (loss) before income taxes 92,293 (18,589 ) 73,704 Income tax expense (9,704 ) — (9,704 ) Net income (loss) 82,589 (18,589 ) 64,000 Dividends attributable to redeemable noncontrolling interests — (4,588 ) (4,588 ) Amounts attributable to noncontrolling interests — 20,621 20,621 Net income (loss) available to Arch 82,589 (2,556 ) 80,033 Preferred dividends (5,484 ) — (5,484 ) Net income (loss) available to Arch common shareholders $ 77,105 $ (2,556 ) $ 74,549 Underwriting Ratios Loss ratio 65.0 % 44.5 % 17.5 % 55.5 % 67.1 % 56.8 % Acquisition expense ratio 14.8 % 21.3 % 19.1 % 17.1 % 28.9 % 18.3 % Other operating expense ratio 16.2 % 14.3 % 38.6 % 17.1 % 3.4 % 15.6 % Combined ratio 96.0 % 80.1 % 75.2 % 89.7 % 99.4 % 90.7 % Goodwill and intangible assets $ 29,834 $ 2,149 $ 71,637 $ 103,620 $ — $ 103,620 (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. Nine Months Ended September 30, 2016 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,319,530 $ 1,217,804 $ 361,440 $ 3,898,025 $ 421,627 $ 4,046,667 Premiums ceded (713,110 ) (370,068 ) (62,918 ) (1,145,347 ) (15,229 ) (887,591 ) Net premiums written 1,606,420 847,736 298,522 2,752,678 406,398 3,159,076 Change in unearned premiums (46,603 ) (43,345 ) (93,283 ) (183,231 ) (59,878 ) (243,109 ) Net premiums earned 1,559,817 804,391 205,239 2,569,447 346,520 2,915,967 Other underwriting income — 22,659 12,670 35,329 2,922 38,251 Losses and loss adjustment expenses (1,011,087 ) (363,613 ) (20,102 ) (1,394,802 ) (236,922 ) (1,631,724 ) Acquisition expenses, net (228,819 ) (160,800 ) (24,665 ) (414,284 ) (95,323 ) (509,607 ) Other operating expenses (265,749 ) (109,159 ) (74,022 ) (448,930 ) (18,486 ) (467,416 ) Underwriting income (loss) $ 54,162 $ 193,478 $ 99,120 346,760 (1,289 ) 345,471 Net investment income 207,088 68,603 275,691 Net realized gains (losses) 168,735 61,912 230,647 Net impairment losses recognized in earnings (16,849 ) — (16,849 ) Equity in net income (loss) of investment funds accounted for using the equity method 32,054 — 32,054 Other income (loss) (432 ) — (432 ) Corporate expenses (45,068 ) — (45,068 ) Interest expense (37,983 ) (9,730 ) (47,713 ) Net foreign exchange gains (losses) (3,812 ) 2,287 (1,525 ) Income (loss) before income taxes 650,493 121,783 772,276 Income tax expense (43,673 ) 1 (43,672 ) Net income (loss) 606,820 121,784 728,604 Dividends attributable to redeemable noncontrolling interests — (13,761 ) (13,761 ) Amounts attributable to noncontrolling interests — (96,118 ) (96,118 ) Net income (loss) available to Arch 606,820 11,905 618,725 Preferred dividends (16,453 ) — (16,453 ) Net income (loss) available to Arch common shareholders $ 590,367 $ 11,905 $ 602,272 Underwriting Ratios Loss ratio 64.8 % 45.2 % 9.8 % 54.3 % 68.4 % 56.0 % Acquisition expense ratio 14.7 % 20.0 % 12.0 % 16.1 % 27.5 % 17.5 % Other operating expense ratio 17.0 % 13.6 % 36.1 % 17.5 % 5.3 % 16.0 % Combined ratio 96.5 % 78.8 % 57.9 % 87.9 % 101.2 % 89.5 % (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. Nine Months Ended September 30, 2015 Insurance Reinsurance Mortgage Sub-Total Other Total Gross premiums written (1) $ 2,263,401 $ 1,156,540 $ 203,770 $ 3,625,382 $ 387,752 $ 3,730,423 Premiums ceded (669,336 ) (318,197 ) (23,404 ) (1,012,608 ) (17,979 ) (747,876 ) Net premiums written 1,594,065 838,343 180,366 2,612,774 369,773 2,982,547 Change in unearned premiums (53,782 ) (24,230 ) (22,992 ) (101,004 ) (91,158 ) (192,162 ) Net premiums earned 1,540,283 814,113 157,374 2,511,770 278,615 2,790,385 Other underwriting income 1,467 6,870 14,969 23,306 3,570 26,876 Losses and loss adjustment expenses (978,681 ) (339,495 ) (33,010 ) (1,351,186 ) (193,697 ) (1,544,883 ) Acquisition expenses, net (228,877 ) (170,380 ) (31,046 ) (430,303 ) (79,764 ) (510,067 ) Other operating expenses (261,793 ) (114,182 ) (61,096 ) (437,071 ) (8,876 ) (445,947 ) Underwriting income (loss) $ 72,399 $ 196,926 $ 47,191 316,516 (152 ) 316,364 Net investment income 204,710 47,480 252,190 Net realized gains (losses) (14,831 ) (27,244 ) (42,075 ) Net impairment losses recognized in earnings (12,780 ) — (12,780 ) Equity in net income (loss) of investment funds accounted for using the equity method 19,938 — 19,938 Other income (loss) 52 — 52 Corporate expenses (37,502 ) — (37,502 ) Interest expense (28,761 ) (1,286 ) (30,047 ) Net foreign exchange gains (losses) 60,338 1,260 61,598 Income (loss) before income taxes 507,680 20,058 527,738 Income tax expense (29,162 ) — (29,162 ) Net income (loss) 478,518 20,058 498,576 Dividends attributable to redeemable noncontrolling interests — (14,239 ) (14,239 ) Amounts attributable to noncontrolling interests — (5,178 ) (5,178 ) Net income (loss) available to Arch 478,518 641 479,159 Preferred dividends (16,453 ) — (16,453 ) Net income (loss) available to Arch common shareholders $ 462,065 $ 641 $ 462,706 Underwriting Ratios Loss ratio 63.5 % 41.7 % 21.0 % 53.8 % 69.5 % 55.4 % Acquisition expense ratio 14.9 % 20.9 % 19.7 % 17.1 % 28.6 % 18.3 % Other operating expense ratio 17.0 % 14.0 % 38.8 % 17.4 % 3.2 % 16.0 % Combined ratio 95.4 % 76.6 % 79.5 % 88.3 % 101.3 % 89.7 % (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.

Investment Information (Tables)

Investment Information (Tables)	9 Months Ended
	Sep. 30, 2016
Disclosure Investment Information [Abstract]
Summary of fair value and cost or amortized cost of available for sale securities	The following table summarizes the fair value and cost or amortized cost of the Company’s investments classified as available for sale: Estimated Fair Value Gross Unrealized Gains Gross Unrealized Losses Cost or Amortized Cost OTTI Unrealized Losses (2) September 30, 2016 Fixed maturities (1): Corporate bonds $ 2,956,514 $ 54,901 $ (14,297 ) $ 2,915,910 $ (2,286 ) Mortgage backed securities 557,913 11,716 (1,518 ) 547,715 (3,327 ) Municipal bonds 1,893,728 36,567 (1,743 ) 1,858,904 — Commercial mortgage backed securities 618,235 9,217 (1,015 ) 610,033 — U.S. government and government agencies 3,014,830 17,195 (1,745 ) 2,999,380 — Non-U.S. government securities 1,186,639 45,372 (33,218 ) 1,174,485 — Asset backed securities 1,241,169 11,463 (2,068 ) 1,231,774 (69 ) Total 11,469,028 186,431 (55,604 ) 11,338,201 (5,682 ) Equity securities 533,245 76,733 (6,597 ) 463,109 — Other investments 168,243 17,871 (1,058 ) 151,430 — Short-term investments 1,184,408 553 (1,956 ) 1,185,811 — Total $ 13,354,924 $ 281,588 $ (65,215 ) $ 13,138,551 $ (5,682 ) December 31, 2015 Fixed maturities (1): Corporate bonds $ 2,725,729 $ 15,978 $ (60,508 ) $ 2,770,259 $ (3,553 ) Mortgage backed securities 754,870 9,872 (5,334 ) 750,332 (3,350 ) Municipal bonds 1,626,281 27,014 (1,534 ) 1,600,801 — Commercial mortgage backed securities 764,152 3,269 (6,978 ) 767,861 — U.S. government and government agencies 2,423,455 6,228 (9,978 ) 2,427,205 — Non-U.S. government securities 917,664 10,414 (39,122 ) 946,372 — Asset backed securities 1,620,506 3,307 (12,951 ) 1,630,150 (22 ) Total 10,832,657 76,082 (136,405 ) 10,892,980 (6,925 ) Equity securities 629,182 94,341 (17,796 ) 552,637 — Other investments 300,476 43,798 (4,665 ) 261,343 — Short-term investments 587,904 187 (3,425 ) 591,142 — Total $ 12,350,219 $ 214,408 $ (162,291 ) $ 12,298,102 $ (6,925 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.” (2) Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At September 30, 2016 , 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 loss of $1.4 million at December 31, 2015 .
Summary of available for sale securities in a continual unrealized loss position	The following table summarizes, for all available for sale securities in an unrealized loss position, the fair value and gross unrealized loss by length of time the security has been in a continual unrealized loss position: Less than 12 Months 12 Months or More Total Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses Estimated Gross Unrealized Losses September 30, 2016 Fixed maturities (1): Corporate bonds $ 566,387 $ (4,281 ) $ 111,303 $ (10,016 ) $ 677,690 $ (14,297 ) Mortgage backed securities 104,159 (1,249 ) 13,230 (269 ) 117,389 (1,518 ) Municipal bonds 415,130 (1,274 ) 8,348 (469 ) 423,478 (1,743 ) Commercial mortgage backed securities 89,999 (778 ) 26,710 (237 ) 116,709 (1,015 ) U.S. government and government agencies 1,233,737 (1,745 ) — — 1,233,737 (1,745 ) Non-U.S. government securities 336,149 (13,113 ) 133,652 (20,105 ) 469,801 (33,218 ) Asset backed securities 178,769 (781 ) 104,273 (1,287 ) 283,042 (2,068 ) Total 2,924,330 (23,221 ) 397,516 (32,383 ) 3,321,846 (55,604 ) Equity securities 167,172 (6,597 ) — — 167,172 (6,597 ) Other investments 24,740 (1,058 ) — — 24,740 (1,058 ) Short-term investments 28,506 (1,956 ) — — 28,506 (1,956 ) Total $ 3,144,748 $ (32,832 ) $ 397,516 $ (32,383 ) $ 3,542,264 $ (65,215 ) December 31, 2015 Fixed maturities (1): Corporate bonds $ 1,810,988 $ (37,445 ) $ 129,896 $ (23,063 ) $ 1,940,884 $ (60,508 ) Mortgage backed securities 487,018 (4,508 ) 48,991 (826 ) 536,009 (5,334 ) Municipal bonds 269,015 (1,303 ) 9,692 (231 ) 278,707 (1,534 ) Commercial mortgage backed securities 511,261 (6,639 ) 20,596 (339 ) 531,857 (6,978 ) U.S. government and government agencies 1,991,163 (9,978 ) — — 1,991,163 (9,978 ) Non-U.S. government securities 458,414 (13,494 ) 138,792 (25,628 ) 597,206 (39,122 ) Asset backed securities 1,217,163 (9,328 ) 134,841 (3,623 ) 1,352,004 (12,951 ) Total 6,745,022 (82,695 ) 482,808 (53,710 ) 7,227,830 (136,405 ) Equity securities 232,275 (17,796 ) — — 232,275 (17,796 ) Other investments 93,614 (4,665 ) — — 93,614 (4,665 ) Short-term investments 30,625 (3,425 ) — — 30,625 (3,425 ) Total $ 7,101,536 $ (108,581 ) $ 482,808 $ (53,710 ) $ 7,584,344 $ (162,291 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”
Contractual maturities of the Company's fixed maturities and fixed maturities pledged under securities lending arrangements	The contractual maturities of the Company’s fixed maturities are shown in the following table. Expected maturities, which are management’s best estimates, will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. September 30, 2016 December 31, 2015 Maturity Estimated Fair Value Amortized Cost Estimated Amortized Cost Due in one year or less $ 287,716 $ 285,210 $ 337,898 $ 341,595 Due after one year through five years 5,305,049 5,278,946 4,644,516 4,677,230 Due after five years through 10 years 2,732,834 2,677,238 2,214,413 2,228,638 Due after 10 years 726,112 707,285 496,302 497,174 9,051,711 8,948,679 7,693,129 7,744,637 Mortgage backed securities 557,913 547,715 754,870 750,332 Commercial mortgage backed securities 618,235 610,033 764,152 767,861 Asset backed securities 1,241,169 1,231,774 1,620,506 1,630,150 Total (1) $ 11,469,028 $ 11,338,201 $ 10,832,657 $ 10,892,980 (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”
Securities lending transactions accounted for as secured borrowings, by significant investment category	The Company’s securities lending transactions were accounted for as secured borrowings with significant investment categories as follows: Remaining Contractual Maturity of the Agreements Overnight and Continuous Less than 30 Days 30-90 Days 90 Days or More Total September 30, 2016 U.S. government and government agencies $ 324,936 $ — $ 71,130 $ 12,538 $ 408,604 Corporate bonds 45,770 — — — 45,770 Equity securities 11,673 — — — 11,673 Total $ 382,379 $ — $ 71,130 $ 12,538 $ 466,047 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 8 $ — Amounts related to securities lending not included in offsetting disclosure in Note 8 $ 466,047 December 31, 2015 U.S. government and government agencies $ 235,728 $ — $ 82,286 $ 9,598 $ 327,612 Corporate bonds 55,086 — — — 55,086 Equity securities 6,722 4,424 — — 11,146 Total $ 297,536 $ 4,424 $ 82,286 $ 9,598 $ 393,844 Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 8 $ — Amounts related to securities lending not included in offsetting disclosure in Note 8 $ 393,844
Summary of other investments, including available for sale and fair value option components	The following table summarizes the Company’s other investments, including available for sale and fair value option components: September 30, December 31, Available for sale: Asian and emerging markets $ 88,731 $ 206,861 Investment grade fixed income 34,536 31,370 Credit related funds 6,478 22,512 Other 38,498 39,733 Total available for sale 168,243 300,476 Fair value option: Term loan investments (par value: $1,152,530 and $1,197,143) 1,106,707 1,108,017 Mezzanine debt funds 122,528 121,589 Credit related funds 219,161 219,049 Investment grade fixed income 73,264 63,053 Asian and emerging markets 142,298 34,761 Other (1) 126,405 124,502 Total fair value option 1,790,363 1,670,971 Total $ 1,958,606 $ 1,971,447 (1) Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other.
Summary of assets and liabilities accounted for using the fair value option	The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option: September 30, December 31, Fixed maturities $ 1,182,909 $ 936,802 Other investments 1,790,363 1,670,971 Short-term investments 388,125 285,923 Equity securities 28,176 798 Investments accounted for using the fair value option $ 3,389,573 $ 2,894,494
Summary of investments in limited partnership interests where the Company has a variable interest	The following table summarizes investments in limited partnership interests where the Company has a variable interest by balance sheet line item: September 30, December 31, Investments accounted for using the equity method (1) $ 787,456 $ 584,158 Investments accounted for using the fair value option (2) 81,341 90,969 Total $ 868,797 $ 675,127 (1) Aggregate unfunded commitments were $798.8 million at September 30, 2016 , compared to $535.4 million at December 31, 2015 . (2) Aggregate unfunded commitments were $27.7 million at September 30, 2016 , compared to $22.7 million at December 31, 2015 .
Components of net investment income	The components of net investment income were derived from the following sources: September 30, 2016 2015 Three Months Ended Fixed maturities $ 71,366 $ 70,626 Term loan investments 28,630 16,922 Equity securities (dividends) 3,311 3,486 Short-term investments 1,703 127 Other (1) 8,836 10,277 Gross investment income 113,846 101,438 Investment expenses (20,228 ) (15,205 ) Net investment income $ 93,618 $ 86,233 Nine Months Ended Fixed maturities $ 223,033 $ 210,497 Term loan investments 67,250 49,699 Equity securities (dividends) 10,409 8,743 Short-term investments 3,015 548 Other (1) 30,839 33,513 Gross investment income 334,546 303,000 Investment expenses (58,855 ) (50,810 ) Net investment income $ 275,691 $ 252,190 (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. September 30, 2016 2015 Three Months Ended Available for sale securities: Gross gains on investment sales $ 84,451 $ 51,933 Gross losses on investment sales (22,985 ) (53,953 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 43,935 (41,236 ) Other investments 46,428 (75,251 ) Equity securities (52 ) 71 Short-term investments 1,150 (9 ) Derivative instruments (1) (16,964 ) 35,889 Other (2) (10,858 ) (7,142 ) Net realized gains (losses) $ 125,105 $ (89,698 ) Nine Months Ended Available for sale securities: Gross gains on investment sales $ 266,965 $ 231,757 Gross losses on investment sales (129,409 ) (168,087 ) Change in fair value of assets and liabilities accounted for using the fair value option: Fixed maturities 62,234 (49,729 ) Other investments 38,016 (68,179 ) Equity securities 385 — Short-term investments 107 1,462 Derivative instruments (1) 24,102 31,069 Other (2) (31,753 ) (20,368 ) Net realized gains (losses) $ 230,647 $ (42,075 ) (1) See Note 8 for information on the Company’s derivative instruments. (2) Includes the re-measurement of contingent consideration liability amounts.
Summary of OTTI recognized in earnings by asset class	The following table details the net impairment losses recognized in earnings by asset class: September 30, 2016 2015 Three Months Ended Fixed maturities: Mortgage backed securities $ (233 ) $ (85 ) Corporate bonds — (4,282 ) Non-U.S. government securities (545 ) — Asset backed securities — — Total (778 ) (4,367 ) Short-term investments — — Equity securities (557 ) (1,501 ) Other investments (2,532 ) — Net impairment losses recognized in earnings $ (3,867 ) $ (5,868 ) Nine Months Ended Fixed maturities: Mortgage backed securities $ (788 ) $ (1,483 ) Corporate bonds (5,655 ) (6,268 ) Non-U.S. government securities (777 ) — Asset backed securities (2,506 ) — Total (9,726 ) (7,751 ) Short-term investments — (2,341 ) Equity securities (3,594 ) (1,754 ) Other investments (3,529 ) (934 ) Net impairment losses recognized in earnings $ (16,849 ) $ (12,780 )
Rollforward of the amount related to credit losses recognized in earnings for which a portion was recognized in AOCI	The following table provides a roll forward of the amount related to credit losses recognized in earnings for which a portion of an OTTI was recognized in accumulated other comprehensive income: September 30, 2016 2015 Three Months Ended Balance at start of period $ 14,847 $ 20,906 Credit loss impairments recognized on securities not previously impaired 38 4,024 Credit loss impairments recognized on securities previously impaired 60 41 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 (1,166 ) — Balance at end of period $ 13,779 $ 24,971 Nine Months Ended Balance at start of year $ 26,875 $ 20,196 Credit loss impairments recognized on securities not previously impaired 1,388 8,794 Credit loss impairments recognized on securities previously impaired 582 175 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 (15,066 ) (4,194 ) Balance at end of period $ 13,779 $ 24,971
Summary of restricted assets	The following table details the value of the Company’s restricted assets: September 30, December 31, Assets used for collateral or guarantees: Affiliated transactions $ 3,908,206 $ 3,810,104 Third party agreements 1,524,785 1,286,257 Deposits with U.S. regulatory authorities 473,094 391,458 Deposits with non-U.S. regulatory authorities 42,354 38,230 Total restricted assets $ 5,948,439 $ 5,526,049

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair value hierarchy	The following table presents the Company’s financial assets and liabilities measured at fair value by level at September 30, 2016 : 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 $ 2,956,514 $ — $ 2,937,542 $ 18,972 Mortgage backed securities 557,913 — 557,913 — Municipal bonds 1,893,728 — 1,893,728 — Commercial mortgage backed securities 618,235 — 618,235 — U.S. government and government agencies 3,014,830 2,891,078 123,752 — Non-U.S. government securities 1,186,639 — 1,186,639 — Asset backed securities 1,241,169 — 1,214,393 26,776 Total 11,469,028 2,891,078 8,532,202 45,748 Equity securities 533,245 532,118 1,127 — Short-term investments 1,184,408 1,162,900 21,508 — Other investments 87,189 87,189 — — Other investments measured at net asset value (2) 81,054 Total other investments 168,243 87,189 — — Derivative instruments (4) 20,054 — 20,054 — Fair value option: Corporate bonds 830,484 — 830,484 — Non-U.S. government bonds 110,642 — 110,642 — Mortgage backed securities 19,184 — 19,184 — Asset backed securities 29,258 — 29,258 — U.S. government and government agencies 193,341 193,341 — — Short-term investments 388,125 388,125 — — Equity securities 28,176 27,644 532 — Other investments 1,182,619 75,912 1,106,707 — Other investments measured at net asset value (2) 607,744 Total 3,389,573 685,022 2,096,807 — Total assets measured at fair value $ 16,764,551 $ 5,358,307 $ 10,671,698 $ 45,748 Liabilities measured at fair value: Contingent consideration liabilities $ (116,377 ) $ — $ — $ (116,377 ) Securities sold but not yet purchased (3) (52,195 ) — (52,195 ) — Derivative instruments (4) (10,311 ) — (10,311 ) — Total liabilities measured at fair value $ (178,883 ) $ — $ (62,506 ) $ (116,377 ) (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 6 , “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 8 , “Derivative Instruments.” The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2015 : 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 $ 2,725,729 $ — $ 2,709,361 $ 16,368 Mortgage backed securities 754,870 — 754,870 — Municipal bonds 1,626,281 — 1,626,281 — Commercial mortgage backed securities 764,152 — 764,152 — U.S. government and government agencies 2,423,455 2,378,662 44,793 — Non-U.S. government securities 917,664 — 917,664 — Asset backed securities 1,620,506 — 1,563,006 57,500 Total 10,832,657 2,378,662 8,380,127 73,868 Equity securities 629,182 627,441 1,741 — Short-term investments 587,904 572,604 15,300 — Other investments 99,159 99,159 — — Other investments measured at net asset value (2) 201,317 Total other investments 300,476 99,159 — — Derivative instruments (4) 20,022 — 20,022 — Fair value option: Corporate bonds 771,733 — 771,733 — Non-U.S. government bonds 81,824 — 81,824 — Mortgage backed securities 57,687 — 57,687 — Asset backed securities 25,444 — 25,444 — U.S. government and government agencies 114 114 — — Short-term investments 285,923 285,923 — — Equity securities 798 798 — — Other investments 1,176,312 68,295 1,108,017 — Other investments measured at net asset value (2) 494,659 Total 2,894,494 355,130 2,044,705 — Total assets measured at fair value $ 15,264,735 $ 4,032,996 $ 10,461,895 $ 73,868 Liabilities measured at fair value: Contingent consideration liabilities $ (96,048 ) $ — $ — $ (96,048 ) Securities sold but not yet purchased (3) (30,583 ) — (30,583 ) — Derivative instruments (4) (11,863 ) — (11,863 ) — Total liabilities measured at fair value $ (138,494 ) $ — $ (42,446 ) $ (96,048 ) (1) In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See Note 6 , “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 8 , “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 Total Contingent Consideration Liabilities Three Months Ended September 30, 2016 Balance at beginning of period $ 49,211 $ 17,305 $ 66,516 $ (111,670 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — 1,667 1,667 (4,795 ) Included in other comprehensive income — — — 88 Purchases, issuances, sales and settlements Purchases — — — — Issuances — — — — Sales — — — — Settlements (22,435 ) — (22,435 ) — Transfers in and/or out of Level 3 — — — — Balance at end of period $ 26,776 $ 18,972 $ 45,748 $ (116,377 ) Three Months Ended September 30, 2015 Balance at beginning of period $ 57,500 $ — $ 57,500 $ (71,256 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — — — (9,596 ) Included in other comprehensive income — — — — Purchases, issuances, sales and settlements Purchases — — — — Issuances — — — — Sales — — — — Settlements — — — — Transfers in and/or out of Level 3 — — — — Balance at end of period $ 57,500 $ — $ 57,500 $ (80,852 ) Nine Months Ended September 30, 2016 Balance at beginning of year $ 57,500 $ 16,368 $ 73,868 $ (96,048 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) (2,500 ) 1,828 (672 ) (20,916 ) Included in other comprehensive income — — — 51 Purchases, issuances, sales and settlements Purchases — 776 776 — Issuances — — — — Sales — — — — Settlements (28,224 ) — (28,224 ) 536 Transfers in and/or out of Level 3 — — — — Balance at end of period $ 26,776 $ 18,972 $ 45,748 $ (116,377 ) Nine Months Ended September 30, 2015 Balance at beginning of year $ 57,500 $ — $ 57,500 $ (61,845 ) Total gains or (losses) (realized/unrealized) Included in earnings (1) — — — (17,939 ) Included in other comprehensive income — — — — Purchases, issuances, sales and settlements Purchases — — — — Issuances — — — (1,068 ) Sales — — — — Settlements — — — — Transfers in and/or out of Level 3 — — — — Balance at end of period $ 57,500 $ — $ 57,500 $ (80,852 ) (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)	9 Months Ended
	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair value and notional amount of derivatives	The following table summarizes information on the fair values and notional values of the Company’s derivative instruments: Estimated Fair Value Asset Liability Derivatives Notional Value (1) September 30, 2016 Futures contracts (2) $ 1,297 $ (2,710 ) $ 1,549,238 Foreign currency forward contracts (2) 5,430 (4,539 ) 1,019,946 TBAs (3) 92,301 (102,861 ) 183,559 Other (2) 13,327 (3,062 ) 1,328,628 Total $ 112,355 $ (113,172 ) December 31, 2015 Futures contracts (2) $ 2,816 $ (1,202 ) $ 1,797,115 Foreign currency forward contracts (2) 9,336 (6,344 ) 773,619 TBAs (3) 6,525 — 6,316 Other (2) 7,870 (4,317 ) 1,694,935 Total $ 26,547 $ (11,863 ) (1) Represents the absolute notional value of all outstanding contracts, consisting of long and short positions. (2) The fair value of asset derivatives are included in ‘other assets’ and the fair value of liability derivatives are included in ‘other liabilities.’ (3) The fair value of TBAs are included in ‘fixed maturities available for sale, at fair value.’
Summary of net realized gains (losses) recorded in the consolidated statements of income	All realized and unrealized contract gains and losses on the Company’s derivative instruments are reflected in net realized gains (losses) in the consolidated statements of income, as summarized in the following table: Derivatives not designated as September 30, hedging instruments: 2016 2015 Three Months Ended Net realized gains (losses): Futures contracts $ (15,368 ) $ 28,562 Foreign currency forward contracts 4,583 5,395 TBAs (23 ) 1,064 Other (6,156 ) 868 Total $ (16,964 ) $ 35,889 Nine Months Ended Net realized gains (losses): Futures contracts $ 45,954 $ 16,442 Foreign currency forward contracts (13,951 ) 13,490 TBAs 311 1,368 Other (8,212 ) (231 ) Total $ 24,102 $ 31,069

Other Comprehensive Income (L31

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2016
Comprehensive Income Note Disclosure [Abstract]
Details about amounts reclassified from AOCI	The following tables present details about amounts reclassified from accumulated other comprehensive income and the tax effects allocated to each component of other comprehensive income (loss): Amounts Reclassified from AOCI Consolidated Statement of Income Three Months Ended Nine Months Ended Details About Line Item That Includes September 30, September 30, AOCI Components Reclassification 2016 2015 2016 2015 Unrealized appreciation on available-for-sale investments Net realized gains (losses) $ 61,464 $ (2,019 ) $ 137,555 $ 63,671 Other-than-temporary impairment losses (3,867 ) (8,901 ) (16,999 ) (17,274 ) Total before tax 57,597 (10,920 ) 120,556 46,397 Income tax (expense) benefit (2,605 ) (1,358 ) (11,247 ) (6,529 ) Net of tax $ 54,992 $ (12,278 ) $ 109,309 $ 39,868
Schedule of comprehensive income (loss)	Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Three Months Ended September 30, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 11,692 $ (4,589 ) $ 16,281 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) — — — Less reclassification of net realized gains (losses) included in net income 57,597 2,605 54,992 Foreign currency translation adjustments (5,407 ) (95 ) (5,312 ) Other comprehensive income (loss) $ (51,312 ) $ (7,289 ) $ (44,023 ) Three Months Ended September 30, 2015 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ (44,687 ) $ 9,204 $ (53,891 ) Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (3,033 ) — (3,033 ) Less reclassification of net realized gains (losses) included in net income (10,920 ) 1,358 (12,278 ) Foreign currency translation adjustments (12,639 ) (556 ) (12,083 ) Other comprehensive income (loss) $ (49,439 ) $ 7,290 $ (56,729 ) Nine Months Ended September 30, 2016 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ 281,770 $ 30,048 $ 251,722 Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (150 ) — (150 ) Less reclassification of net realized gains (losses) included in net income 120,556 11,247 109,309 Foreign currency translation adjustments (5,733 ) 417 (6,150 ) Other comprehensive income (loss) $ 155,331 $ 19,218 $ 136,113 Nine Months Ended September 30, 2015 Unrealized appreciation (decline) in value of investments: Unrealized holding gains (losses) arising during period $ (46,930 ) $ 4,592 $ (51,522 ) Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss) (4,494 ) — (4,494 ) Less reclassification of net realized gains (losses) included in net income 46,397 6,529 39,868 Foreign currency translation adjustments (24,568 ) (1,308 ) (23,260 ) Other comprehensive income (loss) $ (122,389 ) $ (3,245 ) $ (119,144 )

Guarantor Financial Informati32

Guarantor Financial Information (Tables)	9 Months Ended
	Sep. 30, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed consolidating balance sheet	September 30, 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 $ 538,713 $ 54,483 $ 16,975,841 $ (14,700 ) $ 17,554,337 Cash 2,041 19,392 557,383 — 578,816 Investments in subsidiaries 7,316,435 1,815,833 — (9,132,268 ) — Due from subsidiaries and affiliates 4 51,036 391,026 (442,066 ) — Premiums receivable — — 1,726,846 (544,138 ) 1,182,708 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 6,074,812 (3,998,564 ) 2,076,248 Contractholder receivables — — 1,649,441 — 1,649,441 Prepaid reinsurance premiums — — 1,723,344 (1,182,106 ) 541,238 Deferred acquisition costs, net — — 469,466 — 469,466 Other assets 17,348 48,285 1,695,117 (169,773 ) 1,590,977 Total assets $ 7,874,541 $ 1,989,029 $ 31,263,276 $ (15,483,615 ) $ 25,643,231 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 13,582,475 $ (3,972,286 ) $ 9,610,189 Unearned premiums — — 3,853,227 (1,182,106 ) 2,671,121 Reinsurance balances payable — — 815,826 (544,138 ) 271,688 Contractholder payables — — 1,649,441 — 1,649,441 Collateral held for insured obligations — — 277,463 277,463 Deposit accounting liabilities — — 22,281 — 22,281 Senior notes 296,936 494,501 — — 791,437 Revolving credit agreement borrowings 100,000 — 298,100 — 398,100 Due to subsidiaries and affiliates 270 35,003 406,793 (442,066 ) — Other liabilities (1) 125,013 57,753 1,572,207 (196,051 ) 1,558,922 Total liabilities 522,219 587,257 22,477,813 (6,336,647 ) 17,250,642 Redeemable noncontrolling interests — — 220,159 (14,700 ) 205,459 Shareholders’ Equity Total shareholders’ equity available to Arch 7,352,322 1,401,772 7,730,496 (9,132,268 ) 7,352,322 Non-redeemable noncontrolling interests — — 834,808 — 834,808 Total shareholders’ equity 7,352,322 1,401,772 8,565,304 (9,132,268 ) 8,187,130 Total liabilities, noncontrolling interests and shareholders’ equity $ 7,874,541 $ 1,989,029 $ 31,263,276 $ (15,483,615 ) $ 25,643,231 (1) Includes payable for securities purchased. December 31, 2015 Condensed Consolidating Balance Sheet ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Assets Total investments $ 50 $ 42,210 $ 15,815,381 $ (14,700 ) $ 15,842,941 Cash 6,809 17,023 529,494 — 553,326 Investments in subsidiaries 6,609,174 1,712,757 — (8,321,931 ) — Due from subsidiaries and affiliates 23 48,811 384,469 (433,303 ) — Premiums receivable — — 1,376,310 (392,867 ) 983,443 Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses — — 5,783,452 (3,916,079 ) 1,867,373 Contractholder receivables — — 1,486,296 — 1,486,296 Prepaid reinsurance premiums — — 1,511,795 (1,084,186 ) 427,609 Deferred acquisition costs, net — — 433,477 — 433,477 Other assets 4,138 45,522 2,119,279 (586,134 ) 1,582,805 Total assets $ 6,620,194 $ 1,866,323 $ 29,439,953 $ (14,749,200 ) $ 23,177,270 Liabilities Reserve for losses and loss adjustment expenses $ — $ — $ 13,010,608 $ (3,885,358 ) $ 9,125,250 Unearned premiums — — 3,418,118 (1,084,186 ) 2,333,932 Reinsurance balances payable — — 603,586 (379,466 ) 224,120 Contractholder payables — — 1,486,296 — 1,486,296 Collateral held for insured obligations — — 248,982 — 248,982 Deposit accounting liabilities — — 463,507 (203,143 ) 260,364 Senior notes 296,874 494,432 — — 791,306 Revolving credit agreement borrowings 100,000 — 430,434 — 530,434 Due to subsidiaries and affiliates 26 35,000 398,277 (433,303 ) — Other liabilities (1) 18,413 50,890 1,385,500 (427,111 ) 1,027,692 Total liabilities 415,313 580,322 21,445,308 (6,412,567 ) 16,028,376 Redeemable noncontrolling interests — — 219,882 (14,700 ) 205,182 Shareholders’ Equity Total shareholders’ equity available to Arch 6,204,881 1,286,001 7,035,932 (8,321,933 ) 6,204,881 Non-redeemable noncontrolling interests — — 738,831 — 738,831 Total shareholders’ equity 6,204,881 1,286,001 7,774,763 (8,321,933 ) 6,943,712 Total liabilities, noncontrolling interests and shareholders’ equity $ 6,620,194 $ 1,866,323 $ 29,439,953 $ (14,749,200 ) $ 23,177,270 (1) Includes payable for securities purchased.
Condensed consolidating statement of income and comprehensive income	Three Months Ended September 30, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 958,403 $ — $ 958,403 Net investment income 6 803 99,654 (6,845 ) 93,618 Net realized gains (losses) — — 125,105 — 125,105 Net impairment losses recognized in earnings — — (3,867 ) — (3,867 ) Other underwriting income — — 7,980 — 7,980 Equity in net income (loss) of investment funds accounted for using the equity method — — 16,662 — 16,662 Other income (loss) 71 — (471 ) — (400 ) Total revenues 77 803 1,203,466 (6,845 ) 1,197,501 Expenses Losses and loss adjustment expenses — — 524,183 — 524,183 Acquisition expenses — — 163,861 — 163,861 Other operating expenses — — 155,557 — 155,557 Corporate expenses 18,488 608 (611 ) — 18,485 Interest expense 5,948 6,627 9,890 (6,522 ) 15,943 Net foreign exchange (gains) losses — — 2,723 (102 ) 2,621 Total expenses 24,436 7,235 855,603 (6,624 ) 880,650 Income (loss) before income taxes (24,359 ) (6,432 ) 347,863 (221 ) 316,851 Income tax (expense) benefit — 2,116 (15,347 ) — (13,231 ) Income (loss) before equity in net income of subsidiaries (24,359 ) (4,316 ) 332,516 (221 ) 303,620 Equity in net income of subsidiaries 277,231 21,945 — (299,176 ) — Net income 252,872 17,629 332,516 (299,397 ) 303,620 Net (income) loss attributable to noncontrolling interests — — (51,071 ) 323 (50,748 ) Net income available to Arch 252,872 17,629 281,445 (299,074 ) 252,872 Preferred dividends (5,484 ) — — — (5,484 ) Net income available to Arch common shareholders $ 247,388 $ 17,629 $ 281,445 $ (299,074 ) $ 247,388 Comprehensive income (loss) available to Arch $ 208,790 $ 2,019 $ 237,555 $ (239,574 ) $ 208,790 Three Months Ended September 30, 2015 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 936,683 $ — $ 936,683 Net investment income — 764 92,773 (7,304 ) 86,233 Net realized gains (losses) — — (89,698 ) — (89,698 ) Net impairment losses recognized in earnings — — (5,868 ) — (5,868 ) Other underwriting income — — 7,623 — 7,623 Equity in net income (loss) of investment funds accounted for using the equity method — — (2,118 ) — (2,118 ) Other income (loss) — — (265 ) — (265 ) Total revenues — 764 939,130 (7,304 ) 932,590 Expenses Losses and loss adjustment expenses — — 531,741 — 531,741 Acquisition expenses — — 171,566 — 171,566 Other operating expenses — — 146,220 — 146,220 Corporate expenses 10,536 720 (517 ) — 10,739 Interest expense 5,863 6,689 7,734 (6,986 ) 13,300 Net foreign exchange (gains) losses — — (11,762 ) (2,918 ) (14,680 ) Total expenses 16,399 7,409 844,982 (9,904 ) 858,886 Income (loss) before income taxes (16,399 ) (6,645 ) 94,148 2,600 73,704 Income tax (expense) benefit — 2,324 (12,028 ) — (9,704 ) Income (loss) before equity in net income of subsidiaries (16,399 ) (4,321 ) 82,120 2,600 64,000 Equity in net income of subsidiaries 96,432 13,620 — (110,052 ) — Net income 80,033 9,299 82,120 (107,452 ) 64,000 Net (income) loss attributable to noncontrolling interests — — 15,712 321 16,033 Net income available to Arch 80,033 9,299 97,832 (107,131 ) 80,033 Preferred dividends (5,484 ) — — — (5,484 ) Net income available to Arch common shareholders $ 74,549 $ 9,299 $ 97,832 $ (107,131 ) $ 74,549 Comprehensive income (loss) available to Arch $ 23,400 $ 15,705 $ 44,127 $ (59,832 ) $ 23,400 Nine Months Ended September 30, 2016 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 2,915,967 $ — $ 2,915,967 Net investment income 7 2,351 294,012 (20,679 ) 275,691 Net realized gains (losses) — — 230,647 — 230,647 Net impairment losses recognized in earnings — — (16,849 ) — (16,849 ) Other underwriting income — — 54,749 (16,498 ) 38,251 Equity in net income (loss) of investment funds accounted for using the equity method — — 32,054 — 32,054 Other income (loss) 270 — (702 ) — (432 ) Total revenues 277 2,351 3,509,878 (37,177 ) 3,475,329 Expenses Losses and loss adjustment expenses — — 1,631,724 — 1,631,724 Acquisition expenses — — 509,607 — 509,607 Other operating expenses — — 467,416 — 467,416 Corporate expenses 45,284 1,549 (1,765 ) — 45,068 Interest expense 17,811 19,946 46,169 (36,213 ) 47,713 Net foreign exchange (gains) losses — — 5,093 (3,568 ) 1,525 Total expenses 63,095 21,495 2,658,244 (39,781 ) 2,703,053 Income (loss) before income taxes (62,818 ) (19,144 ) 851,634 2,604 772,276 Income tax (expense) benefit — 6,446 (50,118 ) — (43,672 ) Income (loss) before equity in net income of subsidiaries (62,818 ) (12,698 ) 801,516 2,604 728,604 Equity in net income of subsidiaries 681,543 64,684 — (746,227 ) — Net income 618,725 51,986 801,516 (743,623 ) 728,604 Net (income) loss attributable to noncontrolling interests — — (110,844 ) 965 (109,879 ) Net income available to Arch 618,725 51,986 690,672 (742,658 ) 618,725 Preferred dividends (16,453 ) — — — (16,453 ) Net income available to Arch common shareholders $ 602,272 $ 51,986 $ 690,672 $ (742,658 ) $ 602,272 Comprehensive income (loss) available to Arch $ 754,979 $ 89,204 $ 830,348 $ (919,552 ) $ 754,979 Nine Months Ended September 30, 2015 Condensed Consolidating Statement of Income and Comprehensive Income ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Revenues Net premiums earned $ — $ — $ 2,790,385 $ — $ 2,790,385 Net investment income — 1,569 265,937 (15,316 ) 252,190 Net realized gains (losses) — 1 (42,076 ) — (42,075 ) Net impairment losses recognized in earnings — — (12,780 ) — (12,780 ) Other underwriting income — — 26,876 — 26,876 Equity in net income (loss) of investment funds accounted for using the equity method — — 19,938 — 19,938 Other income (loss) — — 52 — 52 Total revenues — 1,570 3,048,332 (15,316 ) 3,034,586 Expenses Losses and loss adjustment expenses — — 1,544,883 — 1,544,883 Acquisition expenses — — 510,067 — 510,067 Other operating expenses — — 445,947 — 445,947 Corporate expenses 36,068 2,991 (1,557 ) — 37,502 Interest expense 17,581 19,824 7,476 (14,834 ) 30,047 Net foreign exchange (gains) losses — — (44,450 ) (17,148 ) (61,598 ) Total expenses 53,649 22,815 2,462,366 (31,982 ) 2,506,848 Income (loss) before income taxes (53,649 ) (21,245 ) 585,966 16,666 527,738 Income tax (expense) benefit — 7,434 (36,596 ) — (29,162 ) Income (loss) before equity in net income of subsidiaries (53,649 ) (13,811 ) 549,370 16,666 498,576 Equity in net income of subsidiaries 532,808 42,192 — (575,000 ) — Net income 479,159 28,381 549,370 (558,334 ) 498,576 Net (income) loss attributable to noncontrolling interests — — (19,902 ) 485 (19,417 ) Net income available to Arch 479,159 28,381 529,468 (557,849 ) 479,159 Preferred dividends (16,453 ) — — — (16,453 ) Net income available to Arch common shareholders $ 462,706 $ 28,381 $ 529,468 $ (557,849 ) $ 462,706 Comprehensive income (loss) available to Arch $ 360,111 $ 13,950 $ 427,569 $ (441,519 ) $ 360,111
Condensed consolidating statement of cash flows	Nine Months Ended September 30, 2016 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 94,250 $ 14,448 $ 1,096,443 $ (168,002 ) $ 1,037,139 Investing Activities Purchases of fixed maturity investments — — (27,840,555 ) — (27,840,555 ) Purchases of equity securities — — (377,767 ) — (377,767 ) Purchases of other investments — — (1,008,774 ) — (1,008,774 ) Proceeds from the sales of fixed maturity investments — — 26,731,924 — 26,731,924 Proceeds from the sales of equity securities — — 464,904 — 464,904 Proceeds from the sales, redemptions and maturities of other investments — — 879,330 — 879,330 Proceeds from redemptions and maturities of fixed maturity investments — 41,500 499,323 — 540,823 Net settlements of derivative instruments — — 23,396 — 23,396 Net (purchases) sales of short-term investments (436,830 ) (53,779 ) (113,553 ) — (604,162 ) Change in cash collateral related to securities lending — — (27,935 ) — (27,935 ) Contributions to subsidiaries (3,585 ) — (9,247 ) 12,832 — Intercompany loans issued — — — — — Acquisitions, net of cash — — (20,911 ) — (20,911 ) Purchases of fixed assets (8 ) — (11,557 ) — (11,565 ) Change in other assets 2,000 — (5,816 ) — (3,816 ) Net Cash Provided By (Used For) Investing Activities (438,423 ) (12,279 ) (817,238 ) 12,832 (1,255,108 ) Financing Activities Proceeds from issuance of preferred shares, net 434,899 — — — 434,899 Purchases of common shares under share repurchase program (75,256 ) — — — (75,256 ) Proceeds from common shares issued, net (3,785 ) — 12,832 (12,832 ) (3,785 ) Proceeds from borrowings — — 46,000 — 46,000 Repayments of borrowings — — (179,171 ) — (179,171 ) Change in cash collateral related to securities lending — — 27,935 — 27,935 Dividends paid to redeemable noncontrolling interests — — (14,448 ) 957 (13,491 ) Dividends paid to parent (1) — — (167,045 ) 167,045 — Other — 200 32,913 — 33,113 Preferred dividends paid (16,453 ) — — — (16,453 ) Net Cash Provided By (Used For) Financing Activities 339,405 200 (240,984 ) 155,170 253,791 Effects of exchange rates changes on foreign currency cash — — (10,332 ) — (10,332 ) Increase (decrease) in cash (4,768 ) 2,369 27,889 — 25,490 Cash beginning of year 6,809 17,023 529,494 — 553,326 Cash end of period $ 2,041 $ 19,392 $ 557,383 $ — $ 578,816 (1) Dividends 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. Nine Months Ended September 30, 2015 Condensed Consolidating Statement of Cash Flows ACGL (Parent Guarantor) Arch-U.S. (Subsidiary Issuer) Other ACGL Subsidiaries Consolidating Adjustments and Eliminations ACGL Consolidated Operating Activities Net Cash Provided By (Used For) Operating Activities $ 382,329 $ 10,622 $ 859,525 $ (444,897 ) $ 807,579 Investing Activities Purchases of fixed maturity investments — (3,505 ) (22,378,599 ) — (22,382,104 ) Purchases of equity securities (8,070 ) — (477,456 ) — (485,526 ) Purchases of other investments — — (1,320,250 ) — (1,320,250 ) Proceeds from the sales of fixed maturity investments — 23,507 21,388,047 — 21,411,554 Proceeds from the sales of equity securities — — 509,008 — 509,008 Proceeds from the sales, redemptions and maturities of other investments — — 858,368 — 858,368 Proceeds from redemptions and maturities of fixed maturity investments — — 630,397 — 630,397 Net settlements of derivative instruments — — 81,114 — 81,114 Proceeds from investment in joint venture — — 40,000 — 40,000 Net (purchases) sales of short-term investments 73 (12,183 ) 193,851 — 181,741 Change in cash collateral related to securities lending — — 28,685 — 28,685 Contributions to subsidiaries — — (9,290 ) 9,290 — Intercompany loans issued — (39,500 ) (41,523 ) 81,023 — Acquisitions, net of cash — — 818 — 818 Purchases of fixed assets (53 ) — (10,848 ) — (10,901 ) Change in other assets — — (43,654 ) — (43,654 ) Net Cash Provided By (Used For) Investing Activities (8,050 ) (31,681 ) (551,332 ) 90,313 (500,750 ) Financing Activities Purchases of common shares under share repurchase program (365,383 ) — — — (365,383 ) Proceeds from common shares issued, net 697 — 9,290 (9,290 ) 697 Proceeds from intercompany borrowings 14,023 27,500 39,500 (81,023 ) — Proceeds from borrowings — — 239,077 — 239,077 Change in cash collateral related to securities lending — — (28,685 ) — (28,685 ) Dividends paid to redeemable noncontrolling interests — — (14,447 ) 637 (13,810 ) Dividends paid to parent (1) — — (444,260 ) 444,260 — Other — 28 50,435 — 50,463 Preferred dividends paid (16,453 ) — — — (16,453 ) Net Cash Provided By (Used For) Financing Activities (367,116 ) 27,528 (149,090 ) 354,584 (134,094 ) Effects of exchange rates changes on foreign currency cash — — (8,658 ) — (8,658 ) Increase (decrease) in cash 7,163 6,469 150,445 — 164,077 Cash beginning of year 3,218 2,787 479,697 — 485,702 Cash end of period $ 10,381 $ 9,256 $ 630,142 $ — $ 649,779 (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 an33

Variable Interest Entities and Noncontrolling Interests - Carrying amount of assets and liabilities of variable interest entity (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Investments accounted for using the fair value option	$ 3,389,573		$ 2,894,494
Cash	578,816		553,326	$ 649,779		$ 485,702
Accrued investment income	81,907		87,206
Premiums receivable	1,182,708		983,443
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	2,076,248		1,867,373
Prepaid reinsurance premiums	541,238		427,609
Deferred acquisition costs, net	469,466		433,477
Receivable for securities sold	285,112		45,505
Goodwill and intangible assets	90,941		97,531	103,620
Other assets	679,260		968,482
Total assets of consolidated VIE	25,643,231		23,177,270
Reserve for losses and loss adjustment expenses	9,610,189		9,125,250
Unearned premiums	2,671,121		2,333,932
Reinsurance balances payable	271,688		224,120
Revolving credit agreement borrowings	398,100		530,434
Payable for securities purchased	474,041		64,996
Other liabilities	618,834		568,852
Total liabilities of consolidated VIE	17,250,642		16,028,376
Redeemable noncontrolling interests	205,459		205,182
Watford Re
Variable Interest Entity [Line Items]
Redeemable noncontrolling interests	205,459	$ 205,366	205,182	$ 205,089	$ 204,996	$ 219,512
Variable Interest Entity, Primary Beneficiary | Watford Re
Variable Interest Entity [Line Items]
Investments accounted for using the fair value option	1,872,342		1,617,107
Cash	67,032		108,550
Accrued investment income	16,891		19,249
Premiums receivable	211,444		162,263
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	25,822		14,135
Prepaid reinsurance premiums	11,556		11,129
Deferred acquisition costs, net	87,490		75,443
Receivable for securities sold	94,965		34,095
Goodwill and intangible assets	7,650		0
Other assets	122,641		80,361
Total assets of consolidated VIE	2,517,833		2,122,332
Reserve for losses and loss adjustment expenses	460,600		290,997
Unearned premiums	308,063		249,980
Reinsurance balances payable	12,315		14,005
Revolving credit agreement borrowings	298,100		430,434
Payable for securities purchased	145,135		33,062
Other liabilities	135,248		53,624
Total liabilities of consolidated VIE	1,359,461		1,072,102
Redeemable noncontrolling interests	$ 220,159		$ 219,882

Variable Interest Entities an34

Variable Interest Entities and Noncontrolling Interests - Variable interest entity (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Mar. 31, 2014	Sep. 30, 2016	Sep. 30, 2015
Variable Interest Entity [Line Items]
Net cash provided by operating activities		$ 1,037,139	$ 807,579
Net cash used for investing activities		(1,255,108)	(500,750)
Net cash used for financing activities		253,791	(134,094)
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		207,000	204,300
Net cash used for investing activities		(124,000)	(354,500)
Net cash used for financing activities		$ (119,600)	$ 268,300

Variable Interest Entities an35

Variable Interest Entities and Noncontrolling Interests - Non-redeemable noncontrolling interests (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interests, beginning of period			$ 738,831
Amounts attributable to noncontrolling interests	$ 46,160	$ (20,621)	96,118	$ 5,178
Non-redeemable noncontrolling interests, end of period	834,808	774,162	834,808	774,162
Watford Re
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interests, beginning of period	788,589	794,880	738,831	769,081
Amounts attributable to noncontrolling interests	46,160	(20,621)	96,118	5,178
Foreign currency translation adjustments attributable to noncontrolling interests	59	(97)	(141)	(97)
Non-redeemable noncontrolling interests, end of period	$ 834,808	$ 774,162	$ 834,808	$ 774,162
Common shares | Watford Re
Noncontrolling Interest [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	89.00%		89.00%

Variable Interest Entities an36

Variable Interest Entities and Noncontrolling Interests - Redeemable noncontrolling interests (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests, beginning of period			$ 205,182
Redeemable noncontrolling interests, end of period	$ 205,459		205,459
Watford Re
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests, beginning of period	205,366	$ 204,996	205,182	$ 219,512
Shares acquired by the Company	0	0	0	(14,700)
Accretion of preference share issuance costs	93	93	277	277
Redeemable noncontrolling interests, end of period	$ 205,459	$ 205,089	$ 205,459	$ 205,089
Cumulative redeemable preference shares | Watford Re
Redeemable Noncontrolling Interest [Line Items]
Preference shares, number of shares issued	9,065,200		9,065,200
Par value per share	$ 0.01		$ 0.01
Liquidation preference per share	$ 25		$ 25

Variable Interest Entities an37

Variable Interest Entities and Noncontrolling Interests - Income or loss attributable to third party investors (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Noncontrolling Interest [Abstract]
Amounts attributable to non-redeemable noncontrolling interests	$ (46,160)	$ 20,621	$ (96,118)	$ (5,178)
Dividends attributable to redeemable noncontrolling interests	(4,588)	(4,588)	(13,761)	(14,239)
Net (income) loss attributable to noncontrolling interests	$ (50,748)	$ 16,033	$ (109,879)	$ (19,417)

Earnings Per Common Share (Deta

Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income		$ 303,620	$ 64,000	$ 728,604	$ 498,576
Net (income) loss attributable to noncontrolling interests		(50,748)	16,033	(109,879)	(19,417)
Net income available to Arch		252,872	80,033	618,725	479,159
Preferred dividends		(5,484)	(5,484)	(16,453)	(16,453)
Net income (loss) available to Arch common shareholders		$ 247,388	$ 74,549	$ 602,272	$ 462,706
Denominator:
Weighted average common shares outstanding — basic		120,938,916	120,567,410	120,656,420	122,151,971
Effect of dilutive common share equivalents:
Nonvested restricted shares		1,313,025	1,322,053	1,295,825	1,260,247
Stock options	[1]	2,679,712	3,122,310	2,575,929	2,942,541
Weighted average common shares and common share equivalents outstanding — diluted		124,931,653	125,011,773	124,528,174	126,354,759
Earnings per common share:
Basic (per share)		$ 2.05	$ 0.62	$ 4.99	$ 3.79
Diluted (per share)		$ 1.98	$ 0.60	$ 4.84	$ 3.66
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per common share (shares)		334,203	390,406	842,105	957,838
[1]	Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2016 third quarter and 2015 third quarter, the number of stock options excluded were 334,203 and 390,406, respectively. For the nine months ended September 30, 2016 and 2015, the number of stock options excluded were 842,105 and 957,838, respectively.

Segment Information - Summary o

Segment Information - Summary of underwriting income or loss by segment (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Gross premiums written		$ 1,278,765	$ 1,189,192	$ 4,046,667	$ 3,730,423
Premiums ceded		(264,487)	(217,220)	(887,591)	(747,876)
Net premiums written		1,014,278	971,972	3,159,076	2,982,547
Change in unearned premiums		(55,875)	(35,289)	(243,109)	(192,162)
Net premiums earned		958,403	936,683	2,915,967	2,790,385
Other underwriting income		7,980	7,623	38,251	26,876
Losses and loss adjustment expenses		(524,183)	(531,741)	(1,631,724)	(1,544,883)
Acquisition expenses, net		(163,861)	(171,566)	(509,607)	(510,067)
Other operating expenses		(155,557)	(146,220)	(467,416)	(445,947)
Underwriting income (loss)		122,782	94,779	345,471	316,364
Net investment income		93,618	86,233	275,691	252,190
Net realized gains (losses)		125,105	(89,698)	230,647	(42,075)
Net impairment losses recognized in earnings		(3,867)	(5,868)	(16,849)	(12,780)
Equity in net income (loss) of investment funds accounted for using the equity method		16,662	(2,118)	32,054	19,938
Other income (loss)		(400)	(265)	(432)	52
Corporate expenses		(18,485)	(10,739)	(45,068)	(37,502)
Interest expense		(15,943)	(13,300)	(47,713)	(30,047)
Net foreign exchange gains (losses)		(2,621)	14,680	(1,525)	61,598
Income before income taxes		316,851	73,704	772,276	527,738
Income tax expense		(13,231)	(9,704)	(43,672)	(29,162)
Net income (loss)		303,620	64,000	728,604	498,576
Dividends attributable to redeemable noncontrolling interests		(4,588)	(4,588)	(13,761)	(14,239)
Amounts attributable to non-redeemable noncontrolling interests		(46,160)	20,621	(96,118)	(5,178)
Net income available to Arch		252,872	80,033	618,725	479,159
Preferred dividends		(5,484)	(5,484)	(16,453)	(16,453)
Net income (loss) available to Arch common shareholders		$ 247,388	$ 74,549	$ 602,272	$ 462,706
Underwriting Ratios
Loss ratio		54.70%	56.80%	56.00%	55.40%
Acquisition expense ratio		17.10%	18.30%	17.50%	18.30%
Other operating expense ratio		16.20%	15.60%	16.00%	16.00%
Combined ratio		88.00%	90.70%	89.50%	89.70%
Goodwill and intangible assets		$ 90,941	$ 103,620	$ 90,941	$ 103,620	$ 97,531
Other
Segment Reporting Information [Line Items]
Gross premiums written	[1]	163,736	131,165	421,627	387,752
Premiums ceded		(6,300)	(6,158)	(15,229)	(17,979)
Net premiums written		157,436	125,007	406,398	369,773
Change in unearned premiums		(47,000)	(25,847)	(59,878)	(91,158)
Net premiums earned		110,436	99,160	346,520	278,615
Other underwriting income		1,024	756	2,922	3,570
Losses and loss adjustment expenses		(74,307)	(66,540)	(236,922)	(193,697)
Acquisition expenses, net		(28,739)	(28,646)	(95,323)	(79,764)
Other operating expenses		(7,035)	(3,421)	(18,486)	(8,876)
Underwriting income (loss)		1,379	1,309	(1,289)	(152)
Net investment income		27,336	18,982	68,603	47,480
Net realized gains (losses)		29,159	(36,218)	61,912	(27,244)
Net impairment losses recognized in earnings		0	0	0	0
Equity in net income (loss) of investment funds accounted for using the equity method		0	0	0	0
Other income (loss)		0	0	0	0
Corporate expenses		0	0	0	0
Interest expense		(3,019)	(1,286)	(9,730)	(1,286)
Net foreign exchange gains (losses)		1,611	(1,376)	2,287	1,260
Income before income taxes		56,466	(18,589)	121,783	20,058
Income tax expense		1	0	1	0
Net income (loss)		56,467	(18,589)	121,784	20,058
Dividends attributable to redeemable noncontrolling interests		(4,588)	(4,588)	(13,761)	(14,239)
Amounts attributable to non-redeemable noncontrolling interests		(46,160)	20,621	(96,118)	(5,178)
Net income available to Arch		5,719	(2,556)	11,905	641
Preferred dividends		0	0	0	0
Net income (loss) available to Arch common shareholders		$ 5,719	$ (2,556)	$ 11,905	$ 641
Underwriting Ratios
Loss ratio		67.30%	67.10%	68.40%	69.50%
Acquisition expense ratio		26.00%	28.90%	27.50%	28.60%
Other operating expense ratio		6.40%	3.40%	5.30%	3.20%
Combined ratio		99.70%	99.40%	101.20%	101.30%
Goodwill and intangible assets		$ 7,650	$ 0	$ 7,650	$ 0
Sub-Total
Segment Reporting Information [Line Items]
Gross premiums written	[1]	1,214,765	1,158,451	3,898,025	3,625,382
Premiums ceded		(357,923)	(311,486)	(1,145,347)	(1,012,608)
Net premiums written		856,842	846,965	2,752,678	2,612,774
Change in unearned premiums		(8,875)	(9,442)	(183,231)	(101,004)
Net premiums earned		847,967	837,523	2,569,447	2,511,770
Other underwriting income		6,956	6,867	35,329	23,306
Losses and loss adjustment expenses		(449,876)	(465,201)	(1,394,802)	(1,351,186)
Acquisition expenses, net		(135,122)	(142,920)	(414,284)	(430,303)
Other operating expenses		(148,522)	(142,799)	(448,930)	(437,071)
Underwriting income (loss)		121,403	93,470	346,760	316,516
Net investment income		66,282	67,251	207,088	204,710
Net realized gains (losses)		95,946	(53,480)	168,735	(14,831)
Net impairment losses recognized in earnings		(3,867)	(5,868)	(16,849)	(12,780)
Equity in net income (loss) of investment funds accounted for using the equity method		16,662	(2,118)	32,054	19,938
Other income (loss)		(400)	(265)	(432)	52
Corporate expenses		(18,485)	(10,739)	(45,068)	(37,502)
Interest expense		(12,924)	(12,014)	(37,983)	(28,761)
Net foreign exchange gains (losses)		(4,232)	16,056	(3,812)	60,338
Income before income taxes		260,385	92,293	650,493	507,680
Income tax expense		(13,232)	(9,704)	(43,673)	(29,162)
Net income (loss)		247,153	82,589	606,820	478,518
Dividends attributable to redeemable noncontrolling interests		0	0	0	0
Amounts attributable to non-redeemable noncontrolling interests		0	0	0	0
Net income available to Arch		247,153	82,589	606,820	478,518
Preferred dividends		(5,484)	(5,484)	(16,453)	(16,453)
Net income (loss) available to Arch common shareholders		$ 241,669	$ 77,105	$ 590,367	$ 462,065
Underwriting Ratios
Loss ratio		53.10%	55.50%	54.30%	53.80%
Acquisition expense ratio		15.90%	17.10%	16.10%	17.10%
Other operating expense ratio		17.50%	17.10%	17.50%	17.40%
Combined ratio		86.50%	89.70%	87.90%	88.30%
Goodwill and intangible assets		$ 83,291	$ 103,620	$ 83,291	$ 103,620
Sub-Total | Insurance
Segment Reporting Information [Line Items]
Gross premiums written	[1]	758,934	752,438	2,319,530	2,263,401
Premiums ceded		(217,446)	(209,443)	(713,110)	(669,336)
Net premiums written		541,488	542,995	1,606,420	1,594,065
Change in unearned premiums		(22,410)	(20,451)	(46,603)	(53,782)
Net premiums earned		519,078	522,544	1,559,817	1,540,283
Other underwriting income		0	519	0	1,467
Losses and loss adjustment expenses		(332,845)	(339,859)	(1,011,087)	(978,681)
Acquisition expenses, net		(77,148)	(77,076)	(228,819)	(228,877)
Other operating expenses		(87,517)	(84,620)	(265,749)	(261,793)
Underwriting income (loss)		$ 21,568	$ 21,508	$ 54,162	$ 72,399
Underwriting Ratios
Loss ratio		64.10%	65.00%	64.80%	63.50%
Acquisition expense ratio		14.90%	14.80%	14.70%	14.90%
Other operating expense ratio		16.90%	16.20%	17.00%	17.00%
Combined ratio		95.90%	96.00%	96.50%	95.40%
Goodwill and intangible assets		$ 26,367	$ 29,834	$ 26,367	$ 29,834
Sub-Total | Reinsurance
Segment Reporting Information [Line Items]
Gross premiums written	[1]	324,361	329,327	1,217,804	1,156,540
Premiums ceded		(89,551)	(92,182)	(370,068)	(318,197)
Net premiums written		234,810	237,145	847,736	838,343
Change in unearned premiums		17,117	23,286	(43,345)	(24,230)
Net premiums earned		251,927	260,431	804,391	814,113
Other underwriting income		2,216	2,783	22,659	6,870
Losses and loss adjustment expenses		(105,924)	(115,780)	(363,613)	(339,495)
Acquisition expenses, net		(50,217)	(55,416)	(160,800)	(170,380)
Other operating expenses		(35,589)	(37,131)	(109,159)	(114,182)
Underwriting income (loss)		$ 62,413	$ 54,887	$ 193,478	$ 196,926
Underwriting Ratios
Loss ratio		42.00%	44.50%	45.20%	41.70%
Acquisition expense ratio		19.90%	21.30%	20.00%	20.90%
Other operating expense ratio		14.10%	14.30%	13.60%	14.00%
Combined ratio		76.00%	80.10%	78.80%	76.60%
Goodwill and intangible assets		$ 1,228	$ 2,149	$ 1,228	$ 2,149
Sub-Total | Mortgage
Segment Reporting Information [Line Items]
Gross premiums written	[1]	131,726	74,657	361,440	203,770
Premiums ceded		(51,182)	(7,832)	(62,918)	(23,404)
Net premiums written		80,544	66,825	298,522	180,366
Change in unearned premiums		(3,582)	(12,277)	(93,283)	(22,992)
Net premiums earned		76,962	54,548	205,239	157,374
Other underwriting income		4,740	3,565	12,670	14,969
Losses and loss adjustment expenses		(11,107)	(9,562)	(20,102)	(33,010)
Acquisition expenses, net		(7,757)	(10,428)	(24,665)	(31,046)
Other operating expenses		(25,416)	(21,048)	(74,022)	(61,096)
Underwriting income (loss)		$ 37,422	$ 17,075	$ 99,120	$ 47,191
Underwriting Ratios
Loss ratio		14.40%	17.50%	9.80%	21.00%
Acquisition expense ratio		10.10%	19.10%	12.00%	19.70%
Other operating expense ratio		33.00%	38.60%	36.10%	38.80%
Combined ratio		57.50%	75.20%	57.90%	79.50%
Goodwill and intangible assets		$ 55,696	$ 71,637	$ 55,696	$ 71,637
[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.

Segment Information - Narrative

Segment Information - Narrative (Details)	9 Months Ended
	Sep. 30, 2016segment
Underwriting segments
Segment Reporting Information [Line Items]
Number of segments	3
Other operating segments
Segment Reporting Information [Line Items]
Number of segments	2

Investment Information - Summar

Investment Information - Summary of available for sale securities (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2016	Dec. 31, 2015
Available for sale securities:
Estimated Fair Value		$ 13,354,924	$ 12,350,219
Gross Unrealized Gains		281,588	214,408
Gross Unrealized Losses		(65,215)	(162,291)
Cost or Amortized Cost		13,138,551	12,298,102
OTTI Unrealized Losses	[1]	(5,682)	(6,925)
Fixed maturities
Available for sale securities:
Estimated Fair Value		11,469,028	10,832,657
Gross Unrealized Gains	[2]	186,431	76,082
Gross Unrealized Losses	[2]	(55,604)	(136,405)
Cost or Amortized Cost	[2]	11,338,201	10,892,980
OTTI Unrealized Losses	[1],[2]	(5,682)	(6,925)
Fixed maturities | Corporate bonds
Available for sale securities:
Estimated Fair Value		2,956,514	2,725,729
Gross Unrealized Gains	[2]	54,901	15,978
Gross Unrealized Losses	[2]	(14,297)	(60,508)
Cost or Amortized Cost	[2]	2,915,910	2,770,259
OTTI Unrealized Losses	[1],[2]	(2,286)	(3,553)
Fixed maturities | Mortgage backed securities
Available for sale securities:
Estimated Fair Value		557,913	754,870
Gross Unrealized Gains	[2]	11,716	9,872
Gross Unrealized Losses	[2]	(1,518)	(5,334)
Cost or Amortized Cost	[2]	547,715	750,332
OTTI Unrealized Losses	[1],[2]	(3,327)	(3,350)
Fixed maturities | Municipal bonds
Available for sale securities:
Estimated Fair Value		1,893,728	1,626,281
Gross Unrealized Gains	[2]	36,567	27,014
Gross Unrealized Losses	[2]	(1,743)	(1,534)
Cost or Amortized Cost	[2]	1,858,904	1,600,801
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value		618,235	764,152
Gross Unrealized Gains	[2]	9,217	3,269
Gross Unrealized Losses	[2]	(1,015)	(6,978)
Cost or Amortized Cost	[2]	610,033	767,861
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | US government and government agencies
Available for sale securities:
Estimated Fair Value		3,014,830	2,423,455
Gross Unrealized Gains	[2]	17,195	6,228
Gross Unrealized Losses	[2]	(1,745)	(9,978)
Cost or Amortized Cost	[2]	2,999,380	2,427,205
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | Non-US government securities
Available for sale securities:
Estimated Fair Value		1,186,639	917,664
Gross Unrealized Gains	[2]	45,372	10,414
Gross Unrealized Losses	[2]	(33,218)	(39,122)
Cost or Amortized Cost	[2]	1,174,485	946,372
OTTI Unrealized Losses	[1],[2]	0	0
Fixed maturities | Asset backed securities
Available for sale securities:
Estimated Fair Value		1,241,169	1,620,506
Gross Unrealized Gains	[2]	11,463	3,307
Gross Unrealized Losses	[2]	(2,068)	(12,951)
Cost or Amortized Cost	[2]	1,231,774	1,630,150
OTTI Unrealized Losses	[1],[2]	(69)	(22)
Equity securities
Available for sale securities:
Estimated Fair Value		533,245	629,182
Gross Unrealized Gains		76,733	94,341
Gross Unrealized Losses		(6,597)	(17,796)
Cost or Amortized Cost		463,109	552,637
OTTI Unrealized Losses	[1]	0	0
Other investments
Available for sale securities:
Estimated Fair Value		168,243	300,476
Gross Unrealized Gains		17,871	43,798
Gross Unrealized Losses		(1,058)	(4,665)
Cost or Amortized Cost		151,430	261,343
OTTI Unrealized Losses	[1]	0	0
Short-term investments
Available for sale securities:
Estimated Fair Value		1,184,408	587,904
Gross Unrealized Gains		553	187
Gross Unrealized Losses		(1,956)	(3,425)
Cost or Amortized Cost		1,185,811	591,142
OTTI Unrealized Losses	[1]	$ 0	$ 0
[1]	Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At September 30, 2016, 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 loss of $1.4 million at December 31, 2015.
[2]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Aging

Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Available for sale securities:
Estimated Fair Value - Less than 12 Months		$ 3,144,748	$ 7,101,536
Gross Unrealized Losses - Less than 12 Months		(32,832)	(108,581)
Estimated Fair Value - 12 Months or More		397,516	482,808
Gross Unrealized Losses - 12 Months or More		(32,383)	(53,710)
Estimated Fair Value - Total		3,542,264	7,584,344
Gross Unrealized Losses - Total		(65,215)	(162,291)
Fixed maturities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	2,924,330	6,745,022
Gross Unrealized Losses - Less than 12 Months	[1]	(23,221)	(82,695)
Estimated Fair Value - 12 Months or More	[1]	397,516	482,808
Gross Unrealized Losses - 12 Months or More	[1]	(32,383)	(53,710)
Estimated Fair Value - Total	[1]	3,321,846	7,227,830
Gross Unrealized Losses - Total	[1]	(55,604)	(136,405)
Fixed maturities | Corporate bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	566,387	1,810,988
Gross Unrealized Losses - Less than 12 Months	[1]	(4,281)	(37,445)
Estimated Fair Value - 12 Months or More	[1]	111,303	129,896
Gross Unrealized Losses - 12 Months or More	[1]	(10,016)	(23,063)
Estimated Fair Value - Total	[1]	677,690	1,940,884
Gross Unrealized Losses - Total	[1]	(14,297)	(60,508)
Fixed maturities | Mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	104,159	487,018
Gross Unrealized Losses - Less than 12 Months	[1]	(1,249)	(4,508)
Estimated Fair Value - 12 Months or More	[1]	13,230	48,991
Gross Unrealized Losses - 12 Months or More	[1]	(269)	(826)
Estimated Fair Value - Total	[1]	117,389	536,009
Gross Unrealized Losses - Total	[1]	(1,518)	(5,334)
Fixed maturities | Municipal bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	415,130	269,015
Gross Unrealized Losses - Less than 12 Months	[1]	(1,274)	(1,303)
Estimated Fair Value - 12 Months or More	[1]	8,348	9,692
Gross Unrealized Losses - 12 Months or More	[1]	(469)	(231)
Estimated Fair Value - Total	[1]	423,478	278,707
Gross Unrealized Losses - Total	[1]	(1,743)	(1,534)
Fixed maturities | Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	89,999	511,261
Gross Unrealized Losses - Less than 12 Months	[1]	(778)	(6,639)
Estimated Fair Value - 12 Months or More	[1]	26,710	20,596
Gross Unrealized Losses - 12 Months or More	[1]	(237)	(339)
Estimated Fair Value - Total	[1]	116,709	531,857
Gross Unrealized Losses - Total	[1]	(1,015)	(6,978)
Fixed maturities | US government and government agencies
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	1,233,737	1,991,163
Gross Unrealized Losses - Less than 12 Months	[1]	(1,745)	(9,978)
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]	1,233,737	1,991,163
Gross Unrealized Losses - Total	[1]	(1,745)	(9,978)
Fixed maturities | Non-US government securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	336,149	458,414
Gross Unrealized Losses - Less than 12 Months	[1]	(13,113)	(13,494)
Estimated Fair Value - 12 Months or More	[1]	133,652	138,792
Gross Unrealized Losses - 12 Months or More	[1]	(20,105)	(25,628)
Estimated Fair Value - Total	[1]	469,801	597,206
Gross Unrealized Losses - Total	[1]	(33,218)	(39,122)
Fixed maturities | Asset backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	[1]	178,769	1,217,163
Gross Unrealized Losses - Less than 12 Months	[1]	(781)	(9,328)
Estimated Fair Value - 12 Months or More	[1]	104,273	134,841
Gross Unrealized Losses - 12 Months or More	[1]	(1,287)	(3,623)
Estimated Fair Value - Total	[1]	283,042	1,352,004
Gross Unrealized Losses - Total	[1]	(2,068)	(12,951)
Equity securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months		167,172	232,275
Gross Unrealized Losses - Less than 12 Months		(6,597)	(17,796)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		167,172	232,275
Gross Unrealized Losses - Total		(6,597)	(17,796)
Other investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months		24,740	93,614
Gross Unrealized Losses - Less than 12 Months		(1,058)	(4,665)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		24,740	93,614
Gross Unrealized Losses - Total		(1,058)	(4,665)
Short-term investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months		28,506	30,625
Gross Unrealized Losses - Less than 12 Months		(1,956)	(3,425)
Estimated Fair Value - 12 Months or More		0	0
Gross Unrealized Losses - 12 Months or More		0	0
Estimated Fair Value - Total		28,506	30,625
Gross Unrealized Losses - Total		$ (1,956)	$ (3,425)
[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Maturi

Investment Information - Maturity profile of available for sale securities) (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Estimated Fair Value:
Estimated fair value		$ 11,026,929	$ 10,459,353
Amortized Cost:
Amortized cost		10,897,965	10,515,440
Fixed maturities
Estimated Fair Value:
Due in one year or less		287,716	337,898
Due after one year through five years		5,305,049	4,644,516
Due after five years through 10 years		2,732,834	2,214,413
Due after 10 years		726,112	496,302
Single maturity date		9,051,711	7,693,129
Estimated fair value	[1]	11,469,028	10,832,657
Amortized Cost:
Due in one year or less		285,210	341,595
Due after one year through five years		5,278,946	4,677,230
Due after five years through 10 years		2,677,238	2,228,638
Due after 10 years		707,285	497,174
Single maturity date		8,948,679	7,744,637
Amortized cost	[1]	11,338,201	10,892,980
Fixed maturities | Mortgage backed securities
Estimated Fair Value:
Securities without single maturity date		557,913	754,870
Amortized Cost:
Securities without single maturity date		547,715	750,332
Fixed maturities | Commercial mortgage backed securities
Estimated Fair Value:
Securities without single maturity date		618,235	764,152
Amortized Cost:
Securities without single maturity date		610,033	767,861
Fixed maturities | Asset backed securities
Estimated Fair Value:
Securities without single maturity date		1,241,169	1,620,506
Amortized Cost:
Securities without single maturity date		$ 1,231,774	$ 1,630,150
[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the securities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

Investment Information - Securi

Investment Information - Securities lending agreements (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Disclosure Investment Information [Abstract]
Fair value of cash collateral received on securities lending	$ 85,100	$ 52,700
Approximate fair value of sub-prime securities backing the securities lending program		3,000
Fair value of non-cash collateral received on securities lending	380,900	336,700
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	466,047	393,844
Gross amount of recognized liabilities for securities lending in offsetting disclosure in Note 8	0	0
Amounts related to securities lending not included in offsetting disclosure in Note 8	466,047	393,844
US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	408,604	327,612
Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	45,770	55,086
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	11,673	11,146
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	382,379	297,536
Overnight and continuous | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	324,936	235,728
Overnight and continuous | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	45,770	55,086
Overnight and continuous | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	11,673	6,722
Less than 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	4,424
Less than 30 days | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
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	4,424
30 - 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	71,130	82,286
30 - 90 days | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	71,130	82,286
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	12,538	9,598
90 days or more | US government and government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	12,538	9,598
90 days or more | Corporate bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	0	0
90 days or more | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending payable	$ 0	$ 0

Investment Information - Other

Investment Information - Other investments (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		$ 1,958,606	$ 1,971,447
Available for sale
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		168,243	300,476
Available for sale | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		88,731	206,861
Available for sale | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		34,536	31,370
Available for sale | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		6,478	22,512
Available for sale | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		38,498	39,733
Fair value option
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		1,790,363	1,670,971
Fair value option | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		1,106,707	1,108,017
Other investments par		1,152,530	1,197,143
Fair value option | Mezzanine debt funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		122,528	121,589
Fair value option | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		142,298	34,761
Fair value option | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		73,264	63,053
Fair value option | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		219,161	219,049
Fair value option | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	[1]	$ 126,405	$ 124,502
[1]	Includes fund investments with strategies in mortgage servicing rights, transportation, infrastructure and other.

Investment Information - Fair v

Investment Information - Fair value option (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 3,389,573	$ 2,894,494
Fixed Maturities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	1,182,909	936,802
Other investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	1,790,363	1,670,971
Short-term investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	388,125	285,923
Equity securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments accounted for using the fair value option	$ 28,176	$ 798

Investment Information - Limite

Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Maximum loss exposure, amount		$ 868,797	$ 675,127
Aggregate unfunded commitments		1,340,000	1,110,000
Equity method investments
Schedule of Equity Method Investments [Line Items]
Maximum loss exposure, amount	[1]	787,456	584,158
Aggregate unfunded commitments		798,800	535,400
Fair value option
Schedule of Equity Method Investments [Line Items]
Maximum loss exposure, amount	[2]	81,341	90,969
Aggregate unfunded commitments		$ 27,700	$ 22,700
[1]	Aggregate unfunded commitments were $798.8 million at September 30, 2016, compared to $535.4 million at December 31, 2015.
[2]	Aggregate unfunded commitments were $27.7 million at September 30, 2016, compared to $22.7 million at December 31, 2015.

Investment Information - Net in

Investment Information - Net investment income (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net investment income:
Gross investment income		$ 113,846	$ 101,438	$ 334,546	$ 303,000
Investment expenses		(20,228)	(15,205)	(58,855)	(50,810)
Net investment income		93,618	86,233	275,691	252,190
Fixed Maturities
Net investment income:
Gross investment income		71,366	70,626	223,033	210,497
Term loan investments
Net investment income:
Gross investment income		28,630	16,922	67,250	49,699
Equity securities (dividends)
Net investment income:
Gross investment income		3,311	3,486	10,409	8,743
Short-term investments
Net investment income:
Gross investment income		1,703	127	3,015	548
Other
Net investment income:
Gross investment income	[1]	$ 8,836	$ 10,277	$ 30,839	$ 33,513
[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		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net realized gains and losses:
Available for sale securities, gross gains on investment sales		$ 84,451	$ 51,933	$ 266,965	$ 231,757
Available for sale securities, gross losses on investment sales		(22,985)	(53,953)	(129,409)	(168,087)
Derivative instruments	[1]	(16,964)	35,889	24,102	31,069
Other	[2]	(10,858)	(7,142)	(31,753)	(20,368)
Net realized gains (losses)		125,105	(89,698)	230,647	(42,075)
Fixed Maturities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		43,935	(41,236)	62,234	(49,729)
Other investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		46,428	(75,251)	38,016	(68,179)
Equity securities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		(52)	71	385	0
Short-term investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		$ 1,150	$ (9)	$ 107	$ 1,462
[1]	See Note 8 for information on the Company’s derivative instruments.
[2]	Includes the re-measurement of contingent consideration liability amounts.

Investment Information - Othe50

Investment Information - Other than temporary impairments recognized in earnings (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ (3,867)	$ (5,868)	$ (16,849)	$ (12,780)
Fixed Maturities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(778)	(4,367)	(9,726)	(7,751)
Fixed Maturities | Mortgage backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(233)	(85)	(788)	(1,483)
Fixed Maturities | Corporate bonds
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	0	(4,282)	(5,655)	(6,268)
Fixed Maturities | Non-US government securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(545)	0	(777)	0
Fixed Maturities | Asset backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	0	0	(2,506)	0
Short-term investments
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	0	0	0	(2,341)
Equity securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(557)	(1,501)	(3,594)	(1,754)
Other investments
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ (2,532)	$ 0	$ (3,529)	$ (934)

Investment Information - Othe51

Investment Information - Other than temporary impairments rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Rollforward:
Balance at start of period	$ 14,847	$ 20,906	$ 26,875	$ 20,196
Credit loss impairments recognized on securities not previously impaired	38	4,024	1,388	8,794
Credit loss impairments recognized on securities previously impaired	60	41	582	175
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	0	0	0	0
Reductions for securities sold during the period	(1,166)	0	(15,066)	(4,194)
Balance at end of period	$ 13,779	$ 24,971	$ 13,779	$ 24,971

Investment Information - Restri

Investment Information - Restricted assets (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Restricted Assets [Line Items]
Restricted assets	$ 5,948,439	$ 5,526,049
Collateral or guarantees - affiliated transactions
Restricted Assets [Line Items]
Restricted assets	3,908,206	3,810,104
Collateral or guarantees - third party agreements
Restricted Assets [Line Items]
Restricted assets	1,524,785	1,286,257
Deposits with US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	473,094	391,458
Deposits with non-US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	$ 42,354	$ 38,230

Investment Information - Narrat

Investment Information - Narrative (Details) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2016USD ($)lots	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)lots	Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)lots
Narrative items:
Investable assets		$ 17,880,000		$ 17,880,000
Income (Loss) from Equity Method Investments		16,662	$ (2,118)	32,054	$ 19,938
OTTI unrealized (losses) gains at current fair value		$ 2,000		$ 2,000		$ (1,400)
Continuous unrealized loss, qualitative disclosures:
Number of positions in an unrealized loss position (lots) | lots		1,660		1,660		3,560
Total number of positions (lots) | lots		6,440		6,440		5,550
Largest single loss		$ 3,800		$ 3,800		$ 3,100
OTTI unrealized losses (gains)	[1]			5,682		$ 6,925
Underwriting segments
Narrative items:
Investable assets		16,040,000		16,040,000
Income (Loss) from Equity Method Investments		16,662	(2,118)	32,054	19,938
Other
Narrative items:
Investable assets		1,840,000		1,840,000
Income (Loss) from Equity Method Investments		$ 0	$ 0	$ 0	$ 0
[1]	Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At September 30, 2016, 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 loss of $1.4 million at December 31, 2015.

Fair Value - Fair Value Hierarc

Fair Value - Fair Value Hierarchy (Details) - Recurring - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
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		$ 5,358,307	$ 4,032,996
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]	2,891,078	2,378,662
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]	2,891,078	2,378,662
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		532,118	627,441
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,162,900	572,604
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		87,189	99,159
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		87,189	99,159
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		685,022	355,130
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		193,341	114
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		388,125	285,923
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		27,644	798
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		75,912	68,295
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		10,671,698	10,461,895
Liabilities measured at fair value		(62,506)	(42,446)
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]	(52,195)	(30,583)
Significant Other Observable Inputs (Level 2) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(10,311)	(11,863)
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]	8,532,202	8,380,127
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]	2,937,542	2,709,361
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]	557,913	754,870
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]	1,893,728	1,626,281
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]	618,235	764,152
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]	123,752	44,793
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]	1,186,639	917,664
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]	1,214,393	1,563,006
Significant Other Observable Inputs (Level 2) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,127	1,741
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		21,508	15,300
Significant Other Observable Inputs (Level 2) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	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		0	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		20,054	20,022
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		2,096,807	2,044,705
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		830,484	771,733
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		19,184	57,687
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		110,642	81,824
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		29,258	25,444
Significant Other Observable Inputs (Level 2) | Fair value option | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
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		532	0
Significant Other Observable Inputs (Level 2) | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,106,707	1,108,017
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		45,748	73,868
Liabilities measured at fair value		(116,377)	(96,048)
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		(116,377)	(96,048)
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]	45,748	73,868
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]	18,972	16,368
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]	26,776	57,500
Significant Unobservable Inputs (Level 3) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Other investments at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | Mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	0
Significant Unobservable Inputs (Level 3) | Fair value option | US government and government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		0	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		0	0
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		16,764,551	15,264,735
Liabilities measured at fair value		(178,883)	(138,494)
Estimated Fair Value | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(116,377)	(96,048)
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]	(52,195)	(30,583)
Estimated Fair Value | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value		(10,311)	(11,863)
Estimated Fair Value | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		11,469,028	10,832,657
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		2,956,514	2,725,729
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		557,913	754,870
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		1,893,728	1,626,281
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		618,235	764,152
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		3,014,830	2,423,455
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		1,186,639	917,664
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		1,241,169	1,620,506
Estimated Fair Value | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		533,245	629,182
Estimated Fair Value | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,184,408	587,904
Estimated Fair Value | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		168,243	300,476
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		87,189	99,159
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]	81,054	201,317
Estimated Fair Value | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		20,054	20,022
Estimated Fair Value | Fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		3,389,573	2,894,494
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		830,484	771,733
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		19,184	57,687
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		193,341	114
Estimated Fair Value | Fair value option | Non-US government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		110,642	81,824
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		29,258	25,444
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		388,125	285,923
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		28,176	798
Estimated Fair Value | Fair value option | Other investments fair value option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value		1,182,619	1,176,312
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]	$ 607,744	$ 494,659
[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		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ 66,516	$ 57,500	$ 73,868	$ 57,500
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	1,667	0	(672)	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	776	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		(22,435)	0	(28,224)	0
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		45,748	57,500	45,748	57,500
Contingent consideration liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		(111,670)	(71,256)	(96,048)	(61,845)
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(4,795)	(9,596)	(20,916)	(17,939)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		88	0	51	0
Purchases, issuances, sales and settlements
Purchases		0	0	0	0
Issuances		0	0	0	(1,068)
Sales		0	0	0	0
Settlements		0	0	536	0
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		(116,377)	(80,852)	(116,377)	(80,852)
Available for sale | Asset backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		49,211	57,500	57,500	57,500
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	(2,500)	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	0	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		(22,435)	0	(28,224)	0
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		26,776	57,500	26,776	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		17,305	0	16,368	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	1,667	0	1,828	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	776	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		$ 18,972	$ 0	$ 18,972	$ 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	Sep. 30, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Total assets and liabilities measured at fair value	$ 16,940,000	$ 15,400,000
Total assets and liabilities measured at fair value priced using non-binding broker quotes	$ 511,600	$ 317,800
Total assets and liabilities measured at fair value priced using non-binding broker quotes (percentage)	3.10%	2.10%
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 791,437	$ 791,306
Reportable Legal Entities | ACGL (Parent Guarantor)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	296,936	296,874
Estimated fair value of senior notes	407,300
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	494,501	$ 494,432
Estimated fair value of senior notes	$ 552,400

Derivative Instruments (Details

Derivative Instruments (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2016		Sep. 30, 2015	Sep. 30, 2016		Sep. 30, 2015	Dec. 31, 2015
Derivative offsetting [Abstract]
Derivative assets subject to master netting agreements		$ 111,200			$ 111,200			$ 26,500
Derivative liabilities subject to master netting agreements		113,200			113,200			11,900
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	[1]	(16,964)		$ 35,889	24,102		$ 31,069
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives - fair value		112,355			112,355			26,547
Liability derivatives - fair value		(113,172)			(113,172)			(11,863)
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(16,964)		35,889	24,102		31,069
Not Designated as Hedging Instrument [Member] | Futures contracts
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	1,549,238			1,549,238			1,797,115
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(15,368)		28,562	45,954		16,442
Not Designated as Hedging Instrument [Member] | Futures contracts | Other assets
Derivative [Line Items]
Asset derivatives - fair value		1,297	[3]		1,297	[3]		2,816
Not Designated as Hedging Instrument [Member] | Futures contracts | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	(2,710)			(2,710)			(1,202)
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	1,019,946			1,019,946			773,619
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		4,583		5,395	(13,951)		13,490
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts | Other assets
Derivative [Line Items]
Asset derivatives - fair value	[3]	5,430			5,430			9,336
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	(4,539)			(4,539)			(6,344)
Not Designated as Hedging Instrument [Member] | TBAs
Derivative [Line Items]
Net derivatives - notional value	[2],[4]	183,559			183,559			6,316
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(23)		1,064	311		1,368
Not Designated as Hedging Instrument [Member] | TBAs | Fixed maturities available for sale
Derivative [Line Items]
Asset derivatives - fair value		92,301	[4]		92,301	[4]		6,525
Liability derivatives - fair value	[4]	(102,861)			(102,861)			0
Not Designated as Hedging Instrument [Member] | Other
Derivative [Line Items]
Net derivatives - notional value	[2],[3]	1,328,628			1,328,628			1,694,935
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments		(6,156)		$ 868	(8,212)		$ (231)
Not Designated as Hedging Instrument [Member] | Other | Other assets
Derivative [Line Items]
Asset derivatives - fair value	[3]	13,327			13,327			7,870
Not Designated as Hedging Instrument [Member] | Other | Other liabilities
Derivative [Line Items]
Liability derivatives - fair value	[3]	$ (3,062)			$ (3,062)			$ (4,317)
[1]	See Note 8 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 - Letter of credit and revolving credit facilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Line of Credit Facility [Abstract]
Revolving credit agreement borrowings	$ 398,100	$ 530,434
Unfunded Investment Commitments [Abstract]
Investment commitments	1,340,000	1,110,000
LOC Facilities [Member]
Line of Credit Facility [Abstract]
Letters of credit outstanding, amount	334,200
Investments pledged as collateral	386,200
Other secured letter of credit facilities
Line of Credit Facility [Abstract]
Letters of credit outstanding, amount	$ 175,600
Credit Agreement
Line of Credit Facility [Abstract]
Credit facility expiration date	Jun. 30, 2019
Revolving credit agreement borrowings	$ 100,000
Unsecured revolving loan and letter of credit facility
Line of Credit Facility [Abstract]
Maximum borrowing capacity	300,000
Secured letter of credit facility
Line of Credit Facility [Abstract]
Maximum borrowing capacity	500,000
Letters of credit outstanding, amount	158,600
Remaining borrowing capacity	341,400
Unsecured letter of credit
Line of Credit Facility [Abstract]
Maximum borrowing capacity	100,000
Watford Re | Line of credit
Line of Credit Facility [Abstract]
Maximum borrowing capacity	$ 100,000
Credit facility expiration date	May 19, 2017
Letters of credit outstanding, amount	$ 207,800
Watford Re | Letter of credit
Line of Credit Facility [Abstract]
Maximum borrowing capacity	400,000
Watford Re | Other secured letter of credit facilities
Line of Credit Facility [Abstract]
Maximum borrowing capacity	$ 800,000
Credit facility expiration date	Jun. 4, 2018
Variable Interest Entity, Primary Beneficiary | Watford Re
Line of Credit Facility [Abstract]
Revolving credit agreement borrowings	$ 298,100	$ 430,434

Commitments and Contingencies59

Commitments and Contingencies - Acquisition of United Guaranty Corporation (Details) - USD ($)	Sep. 29, 2016	Aug. 15, 2016	Oct. 27, 2016
Series E Preferred Shares
Business Acquisition [Line Items]
Preferred stock value outstanding	$ 450,000,000
Dividend rate percentage	5.25%
United Guaranty Corporation
Business Acquisition [Line Items]
Aggregate consideration		$ 3,430,000,000
Cash consideration		2,200,000,000
Fair value of equity interests transferred		$ 983,100,000
Measurement Period		18 months
Contingent payment, minimum		$ 0
Contingent payment, maximum		$ 250,000,000
Quota share percentage		50.00%
Termination fee in event of unsuccessful acquisition		$ 150,000,000
United Guaranty Corporation | Perpetual preferred shares
Business Acquisition [Line Items]
Preferred stock value outstanding		$ 250,000,000
Subsequent event | United Guaranty Corporation
Business Acquisition [Line Items]
ACGL closing share price			$ 77.03

Commitments and Contingencies60

Commitments and Contingencies - Bridge credit agreement (Details) - USD ($) $ in Millions	Aug. 15, 2016	Sep. 30, 2016
LIBOR | Minimum
Short-term Debt [Line Items]
Spread on variable rate	0.875%
LIBOR | Maximum
Short-term Debt [Line Items]
Spread on variable rate	1.625%
Base rate | Minimum
Short-term Debt [Line Items]
Spread on variable rate	0.00%
Base rate | Maximum
Short-term Debt [Line Items]
Spread on variable rate	0.625%
Bridge loan
Short-term Debt [Line Items]
Borrowing capacity	$ 1,375	$ 938.5
Term of facility	364 days
Increase due to ratings change	0.25%
Measurement period	90 days

Share Transactions - Preferred

Share Transactions - Preferred share offering (Details) - USD ($) $ / shares in Units, shares in Millions	Sep. 29, 2016	Sep. 30, 2016	Sep. 30, 2015	Apr. 30, 2012
Class of Stock [Line Items]
Proceeds from issuance of preferred shares, net		$ 434,899,000	$ 0
Series E Preferred Shares
Class of Stock [Line Items]
Preferred stock value outstanding	$ 450,000,000
Proportionate interest per depositary share	0.10%
Dividend rate percentage	5.25%
Par value per share	$ 0.01
Liquidation preference per share	$ 25,000
Redemption price per share	$ 25,000
Proceeds from issuance of preferred shares, net	$ 434,900,000
Depositary Share Equivalent
Class of Stock [Line Items]
Number of shares outstanding	18
Liquidation preference per share	$ 25
Redemption price per share	$ 25
Series C Preferred Shares
Class of Stock [Line Items]
Preferred stock value outstanding				$ 325,000,000

Share Transactions - Share repu

Share Transactions - Share repurchases (Details) - Common shares - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
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)	0	0.1	1.1	5.9
Treasury stock, value of shares acquired	$ 0	$ 3.5	$ 75.3	$ 365.4
Remaining authorized repurchase amount	$ 446.5		$ 446.5

Other Comprehensive Income (L63

Other Comprehensive Income (Loss) - Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses	$ (3,867)	$ (8,901)	$ (16,999)	$ (17,274)
Income before income taxes	316,851	73,704	772,276	527,738
Income tax expense	(13,231)	(9,704)	(43,672)	(29,162)
Net of tax	252,872	80,033	618,725	479,159
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)	61,464	(2,019)	137,555	63,671
Other-than-temporary impairment losses	(3,867)	(8,901)	(16,999)	(17,274)
Income before income taxes	57,597	(10,920)	120,556	46,397
Income tax expense	(2,605)	(1,358)	(11,247)	(6,529)
Net of tax	$ 54,992	$ (12,278)	$ 109,309	$ 39,868

Other Comprehensive Income (L64

Other Comprehensive Income (Loss) - Components of other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Before tax amount:
Unrealized holding gains (losses) arising during period, before tax	$ 11,692	$ (44,687)	$ 281,770	$ (46,930)
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), before tax	0	(3,033)	(150)	(4,494)
Less reclassification of net realized gains included in net income, before tax	57,597	(10,920)	120,556	46,397
Foreign currency translation adjustments, before tax	(5,407)	(12,639)	(5,733)	(24,568)
Other comprehensive income (loss), before tax	(51,312)	(49,439)	155,331	(122,389)
Tax expense (benefit):
Unrealized holding gains (losses) arising during period, tax	(4,589)	9,204	30,048	4,592
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), tax	0	0	0	0
Less reclassification of net realized gains included in net income, tax	2,605	1,358	11,247	6,529
Foreign currency translation adjustments, tax	(95)	(556)	417	(1,308)
Other comprehensive income (loss), tax	(7,289)	7,290	19,218	(3,245)
Net of tax amount:
Unrealized holding gains (losses) arising during period, net of tax	16,281	(53,891)	251,722	(51,522)
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), net of tax	0	(3,033)	(150)	(4,494)
Less reclassification of net realized gains included in net income, net of tax	54,992	(12,278)	109,309	39,868
Foreign currency translation adjustments, net of tax	(5,312)	(12,083)	(6,150)	(23,260)
Net current period other comprehensive income (loss)	$ (44,023)	$ (56,729)	$ 136,113	$ (119,144)

Guarantor Financial Informati65

Guarantor Financial Information - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Assets
Total investments		$ 17,554,337	$ 15,842,941
Cash		578,816	553,326	$ 649,779	$ 485,702
Investments in subsidiaries		0	0
Due from subsidiaries and affiliates		0	0
Premiums receivable		1,182,708	983,443
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses		2,076,248	1,867,373
Contractholder receivables		1,649,441	1,486,296
Prepaid reinsurance premiums		541,238	427,609
Deferred acquisition costs, net		469,466	433,477
Other assets		1,590,977	1,582,805
Total assets		25,643,231	23,177,270
Liabilities
Reserve for losses and loss adjustment expenses		9,610,189	9,125,250
Unearned premiums		2,671,121	2,333,932
Reinsurance balances payable		271,688	224,120
Contractholder payables		1,649,441	1,486,296
Collateral held for insured obligations		277,463	248,982
Deposit accounting liabilities		22,281	260,364
Senior notes		791,437	791,306
Revolving credit agreement borrowings		398,100	530,434
Due to subsidiaries and affiliates		0	0
Other liabilities (1)		1,558,922	1,027,692
Total liabilities		17,250,642	16,028,376
Redeemable noncontrolling interests		205,459	205,182
Shareholders' Equity
Total shareholders’ equity available to Arch		7,352,322	6,204,881	6,162,815
Non-redeemable noncontrolling interests		834,808	738,831	774,162
Total shareholders’ equity		8,187,130	6,943,712	6,936,977
Total liabilities, noncontrolling interests and shareholders’ equity		25,643,231	23,177,270
Reportable Legal Entities | ACGL (Parent Guarantor)
Assets
Total investments		538,713	50
Cash		2,041	6,809	10,381	3,218
Investments in subsidiaries		7,316,435	6,609,174
Due from subsidiaries and affiliates		4	23
Premiums receivable		0	0
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses		0	0
Contractholder receivables		0	0
Prepaid reinsurance premiums		0	0
Deferred acquisition costs, net		0	0
Other assets		17,348	4,138
Total assets		7,874,541	6,620,194
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	0
Senior notes		296,936	296,874
Revolving credit agreement borrowings		100,000	100,000
Due to subsidiaries and affiliates		270	26
Other liabilities (1)	[1]	125,013	18,413
Total liabilities		522,219	415,313
Redeemable noncontrolling interests		0	0
Shareholders' Equity
Total shareholders’ equity available to Arch		7,352,322	6,204,881
Non-redeemable noncontrolling interests		0	0
Total shareholders’ equity		7,352,322	6,204,881
Total liabilities, noncontrolling interests and shareholders’ equity		7,874,541	6,620,194
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Assets
Total investments		54,483	42,210
Cash		19,392	17,023	9,256	2,787
Investments in subsidiaries		1,815,833	1,712,757
Due from subsidiaries and affiliates		51,036	48,811
Premiums receivable		0	0
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses		0	0
Contractholder receivables		0	0
Prepaid reinsurance premiums		0	0
Deferred acquisition costs, net		0	0
Other assets		48,285	45,522
Total assets		1,989,029	1,866,323
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	0
Senior notes		494,501	494,432
Revolving credit agreement borrowings		0	0
Due to subsidiaries and affiliates		35,003	35,000
Other liabilities (1)	[1]	57,753	50,890
Total liabilities		587,257	580,322
Redeemable noncontrolling interests		0	0
Shareholders' Equity
Total shareholders’ equity available to Arch		1,401,772	1,286,001
Non-redeemable noncontrolling interests		0	0
Total shareholders’ equity		1,401,772	1,286,001
Total liabilities, noncontrolling interests and shareholders’ equity		$ 1,989,029	1,866,323
Percentage Ownership of Subsidiary		100.00%
Reportable Legal Entities | Other ACGL Subsidiaries
Assets
Total investments		$ 16,975,841	15,815,381
Cash		557,383	529,494	630,142	479,697
Investments in subsidiaries		0	0
Due from subsidiaries and affiliates		391,026	384,469
Premiums receivable		1,726,846	1,376,310
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses		6,074,812	5,783,452
Contractholder receivables		1,649,441	1,486,296
Prepaid reinsurance premiums		1,723,344	1,511,795
Deferred acquisition costs, net		469,466	433,477
Other assets		1,695,117	2,119,279
Total assets		31,263,276	29,439,953
Liabilities
Reserve for losses and loss adjustment expenses		13,582,475	13,010,608
Unearned premiums		3,853,227	3,418,118
Reinsurance balances payable		815,826	603,586
Contractholder payables		1,649,441	1,486,296
Collateral held for insured obligations		277,463	248,982
Deposit accounting liabilities		22,281	463,507
Senior notes		0	0
Revolving credit agreement borrowings		298,100	430,434
Due to subsidiaries and affiliates		406,793	398,277
Other liabilities (1)	[1]	1,572,207	1,385,500
Total liabilities		22,477,813	21,445,308
Redeemable noncontrolling interests		220,159	219,882
Shareholders' Equity
Total shareholders’ equity available to Arch		7,730,496	7,035,932
Non-redeemable noncontrolling interests		834,808	738,831
Total shareholders’ equity		8,565,304	7,774,763
Total liabilities, noncontrolling interests and shareholders’ equity		31,263,276	29,439,953
Consolidating Adjustments and Eliminations
Assets
Total investments		(14,700)	(14,700)
Cash		0	0	$ 0	$ 0
Investments in subsidiaries		(9,132,268)	(8,321,931)
Due from subsidiaries and affiliates		(442,066)	(433,303)
Premiums receivable		(544,138)	(392,867)
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses		(3,998,564)	(3,916,079)
Contractholder receivables		0	0
Prepaid reinsurance premiums		(1,182,106)	(1,084,186)
Deferred acquisition costs, net		0	0
Other assets		(169,773)	(586,134)
Total assets		(15,483,615)	(14,749,200)
Liabilities
Reserve for losses and loss adjustment expenses		(3,972,286)	(3,885,358)
Unearned premiums		(1,182,106)	(1,084,186)
Reinsurance balances payable		(544,138)	(379,466)
Contractholder payables		0	0
Collateral held for insured obligations			0
Deposit accounting liabilities		0	(203,143)
Senior notes		0	0
Revolving credit agreement borrowings		0	0
Due to subsidiaries and affiliates		(442,066)	(433,303)
Other liabilities (1)	[1]	(196,051)	(427,111)
Total liabilities		(6,336,647)	(6,412,567)
Redeemable noncontrolling interests		(14,700)	(14,700)
Shareholders' Equity
Total shareholders’ equity available to Arch		(9,132,268)	(8,321,933)
Non-redeemable noncontrolling interests		0	0
Total shareholders’ equity		(9,132,268)	(8,321,933)
Total liabilities, noncontrolling interests and shareholders’ equity		$ (15,483,615)	$ (14,749,200)
[1]	Includes payable for securities purchased.

Guarantor Financial Informati66

Guarantor Financial Information - Condensed consolidating statement of income and comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues
Net premiums earned	$ 958,403	$ 936,683	$ 2,915,967	$ 2,790,385
Net investment income	93,618	86,233	275,691	252,190
Net realized gains (losses)	125,105	(89,698)	230,647	(42,075)
Net impairment losses recognized in earnings	(3,867)	(5,868)	(16,849)	(12,780)
Other underwriting income	7,980	7,623	38,251	26,876
Equity in net income (loss) of investment funds accounted for using the equity method	16,662	(2,118)	32,054	19,938
Other income (loss)	(400)	(265)	(432)	52
Total revenues	1,197,501	932,590	3,475,329	3,034,586
Expenses
Losses and loss adjustment expenses	524,183	531,741	1,631,724	1,544,883
Acquisition expenses	163,861	171,566	509,607	510,067
Other operating expenses	155,557	146,220	467,416	445,947
Corporate expenses	18,485	10,739	45,068	37,502
Interest expense	15,943	13,300	47,713	30,047
Net foreign exchange (gains) losses	2,621	(14,680)	1,525	(61,598)
Total expenses	880,650	858,886	2,703,053	2,506,848
Income (loss) before income taxes	316,851	73,704	772,276	527,738
Income tax (expense) benefit	(13,231)	(9,704)	(43,672)	(29,162)
Income (loss) before equity in net income of subsidiaries	303,620	64,000	728,604	498,576
Equity in net income of subsidiaries	0	0	0	0
Net income	303,620	64,000	728,604	498,576
Net (income) loss attributable to noncontrolling interests	(50,748)	16,033	(109,879)	(19,417)
Net income available to Arch	252,872	80,033	618,725	479,159
Preferred dividends	(5,484)	(5,484)	(16,453)	(16,453)
Net income (loss) available to Arch common shareholders	247,388	74,549	602,272	462,706
Comprehensive income (loss) available to Arch	208,790	23,400	754,979	360,111
Reportable Legal Entities | ACGL (Parent Guarantor)
Revenues
Net premiums earned	0	0	0	0
Net investment income	6	0	7	0
Net realized gains (losses)	0	0	0	0
Net impairment losses recognized in earnings	0	0	0	0
Other underwriting income	0	0	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	0	0	0	0
Other income (loss)	71	0	270	0
Total revenues	77	0	277	0
Expenses
Losses and loss adjustment expenses	0	0	0	0
Acquisition expenses	0	0	0	0
Other operating expenses	0	0	0	0
Corporate expenses	18,488	10,536	45,284	36,068
Interest expense	5,948	5,863	17,811	17,581
Net foreign exchange (gains) losses	0	0	0	0
Total expenses	24,436	16,399	63,095	53,649
Income (loss) before income taxes	(24,359)	(16,399)	(62,818)	(53,649)
Income tax (expense) benefit	0	0	0	0
Income (loss) before equity in net income of subsidiaries	(24,359)	(16,399)	(62,818)	(53,649)
Equity in net income of subsidiaries	277,231	96,432	681,543	532,808
Net income	252,872	80,033	618,725	479,159
Net (income) loss attributable to noncontrolling interests	0	0	0	0
Net income available to Arch	252,872	80,033	618,725	479,159
Preferred dividends	(5,484)	(5,484)	(16,453)	(16,453)
Net income (loss) available to Arch common shareholders	247,388	74,549	602,272	462,706
Comprehensive income (loss) available to Arch	208,790	23,400	754,979	360,111
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Revenues
Net premiums earned	0	0	0	0
Net investment income	803	764	2,351	1,569
Net realized gains (losses)	0	0	0	1
Net impairment losses recognized in earnings	0	0	0	0
Other underwriting income	0	0	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	0	0	0	0
Other income (loss)	0	0	0	0
Total revenues	803	764	2,351	1,570
Expenses
Losses and loss adjustment expenses	0	0	0	0
Acquisition expenses	0	0	0	0
Other operating expenses	0	0	0	0
Corporate expenses	608	720	1,549	2,991
Interest expense	6,627	6,689	19,946	19,824
Net foreign exchange (gains) losses	0	0	0	0
Total expenses	7,235	7,409	21,495	22,815
Income (loss) before income taxes	(6,432)	(6,645)	(19,144)	(21,245)
Income tax (expense) benefit	2,116	2,324	6,446	7,434
Income (loss) before equity in net income of subsidiaries	(4,316)	(4,321)	(12,698)	(13,811)
Equity in net income of subsidiaries	21,945	13,620	64,684	42,192
Net income	17,629	9,299	51,986	28,381
Net (income) loss attributable to noncontrolling interests	0	0	0	0
Net income available to Arch	17,629	9,299	51,986	28,381
Preferred dividends	0	0	0	0
Net income (loss) available to Arch common shareholders	17,629	9,299	51,986	28,381
Comprehensive income (loss) available to Arch	2,019	15,705	89,204	13,950
Reportable Legal Entities | Other ACGL Subsidiaries
Revenues
Net premiums earned	958,403	936,683	2,915,967	2,790,385
Net investment income	99,654	92,773	294,012	265,937
Net realized gains (losses)	125,105	(89,698)	230,647	(42,076)
Net impairment losses recognized in earnings	(3,867)	(5,868)	(16,849)	(12,780)
Other underwriting income	7,980	7,623	54,749	26,876
Equity in net income (loss) of investment funds accounted for using the equity method	16,662	(2,118)	32,054	19,938
Other income (loss)	(471)	(265)	(702)	52
Total revenues	1,203,466	939,130	3,509,878	3,048,332
Expenses
Losses and loss adjustment expenses	524,183	531,741	1,631,724	1,544,883
Acquisition expenses	163,861	171,566	509,607	510,067
Other operating expenses	155,557	146,220	467,416	445,947
Corporate expenses	(611)	(517)	(1,765)	(1,557)
Interest expense	9,890	7,734	46,169	7,476
Net foreign exchange (gains) losses	2,723	(11,762)	5,093	(44,450)
Total expenses	855,603	844,982	2,658,244	2,462,366
Income (loss) before income taxes	347,863	94,148	851,634	585,966
Income tax (expense) benefit	(15,347)	(12,028)	(50,118)	(36,596)
Income (loss) before equity in net income of subsidiaries	332,516	82,120	801,516	549,370
Equity in net income of subsidiaries	0	0	0	0
Net income	332,516	82,120	801,516	549,370
Net (income) loss attributable to noncontrolling interests	(51,071)	15,712	(110,844)	(19,902)
Net income available to Arch	281,445	97,832	690,672	529,468
Preferred dividends	0	0	0	0
Net income (loss) available to Arch common shareholders	281,445	97,832	690,672	529,468
Comprehensive income (loss) available to Arch	237,555	44,127	830,348	427,569
Consolidating Adjustments and Eliminations
Revenues
Net premiums earned	0	0	0	0
Net investment income	(6,845)	(7,304)	(20,679)	(15,316)
Net realized gains (losses)	0	0	0	0
Net impairment losses recognized in earnings	0	0	0	0
Other underwriting income	0	0	(16,498)	0
Equity in net income (loss) of investment funds accounted for using the equity method	0	0	0	0
Other income (loss)	0	0	0	0
Total revenues	(6,845)	(7,304)	(37,177)	(15,316)
Expenses
Losses and loss adjustment expenses	0	0	0	0
Acquisition expenses	0	0	0	0
Other operating expenses	0	0	0	0
Corporate expenses	0	0	0	0
Interest expense	(6,522)	(6,986)	(36,213)	(14,834)
Net foreign exchange (gains) losses	(102)	(2,918)	(3,568)	(17,148)
Total expenses	(6,624)	(9,904)	(39,781)	(31,982)
Income (loss) before income taxes	(221)	2,600	2,604	16,666
Income tax (expense) benefit	0	0	0	0
Income (loss) before equity in net income of subsidiaries	(221)	2,600	2,604	16,666
Equity in net income of subsidiaries	(299,176)	(110,052)	(746,227)	(575,000)
Net income	(299,397)	(107,452)	(743,623)	(558,334)
Net (income) loss attributable to noncontrolling interests	323	321	965	485
Net income available to Arch	(299,074)	(107,131)	(742,658)	(557,849)
Preferred dividends	0	0	0	0
Net income (loss) available to Arch common shareholders	(299,074)	(107,131)	(742,658)	(557,849)
Comprehensive income (loss) available to Arch	$ (239,574)	$ (59,832)	$ (919,552)	$ (441,519)

Guarantor Financial Informati67

Guarantor Financial Information - Condensed consolidating statement of cash flows (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015
Operating Activities
Net Cash Provided by (Used in) Operating Activities		$ 1,037,139	$ 807,579
Investing Activities
Purchases of fixed maturity investments		(27,840,555)	(22,382,104)
Purchases of equity securities		(377,767)	(485,526)
Purchases of other investments		(1,008,774)	(1,320,250)
Proceeds from sales of fixed maturity investments		26,731,924	21,411,554
Proceeds from sales of equity securities		464,904	509,008
Proceeds from sales, redemptions and maturities of other investments		879,330	858,368
Proceeds from redemptions and maturities of fixed maturity investments		540,823	630,397
Net settlements of derivative instruments		23,396	81,114
Proceeds from investment in joint venture		0	40,000
Net (purchases) sales of short-term investments		(604,162)	181,741
Change in cash collateral related to securities lending		(27,935)	28,685
Contributions to subsidiaries		0	0
Intercompany loans issued		0	0
Acquisitions, net of cash		(20,911)	818
Purchases of fixed assets		(11,565)	(10,901)
Change in other assets		(3,816)	(43,654)
Net Cash Provided By (Used For) Investing Activities		(1,255,108)	(500,750)
Financing Activities
Proceeds from issuance of preferred shares, net		434,899	0
Purchases of common shares under share repurchase program		(75,256)	(365,383)
Proceeds from common shares issued, net		(3,785)	697
Proceeds from borrowings		46,000	239,077
Proceeds from intercompany borrowings			0
Repayments of borrowings		(179,171)	0
Change in cash collateral related to securities lending		27,935	(28,685)
Dividends paid to redeemable noncontrolling interests		(13,491)	(13,810)
Dividends paid to parent	[1]	0	0
Other		33,113	50,463
Preferred dividends paid		(16,453)	(16,453)
Net Cash Provided By (Used For) Financing Activities		253,791	(134,094)
Effects of exchange rate changes on foreign currency cash		(10,332)	(8,658)
Increase (decrease) in cash		25,490	164,077
Cash beginning of year		553,326	485,702
Cash end of period		578,816	649,779
Reportable Legal Entities | ACGL (Parent Guarantor)
Operating Activities
Net Cash Provided by (Used in) Operating Activities		94,250	382,329
Investing Activities
Purchases of fixed maturity investments		0	0
Purchases of equity securities		0	(8,070)
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
Proceeds from investment in joint venture			0
Net (purchases) sales of short-term investments		(436,830)	73
Change in cash collateral related to securities lending		0	0
Contributions to subsidiaries		(3,585)	0
Intercompany loans issued		0	0
Acquisitions, net of cash		0	0
Purchases of fixed assets		(8)	(53)
Change in other assets		2,000	0
Net Cash Provided By (Used For) Investing Activities		(438,423)	(8,050)
Financing Activities
Proceeds from issuance of preferred shares, net		434,899
Purchases of common shares under share repurchase program		(75,256)	(365,383)
Proceeds from common shares issued, net		(3,785)	697
Proceeds from borrowings		0	0
Proceeds from intercompany borrowings			14,023
Repayments of borrowings		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		(16,453)	(16,453)
Net Cash Provided By (Used For) Financing Activities		339,405	(367,116)
Effects of exchange rate changes on foreign currency cash		0	0
Increase (decrease) in cash		(4,768)	7,163
Cash beginning of year		6,809	3,218
Cash end of period		2,041	10,381
Reportable Legal Entities | Arch-U.S. (Subsidiary Issuer)
Operating Activities
Net Cash Provided by (Used in) Operating Activities		14,448	10,622
Investing Activities
Purchases of fixed maturity investments		0	(3,505)
Purchases of equity securities		0	0
Purchases of other investments		0	0
Proceeds from sales of fixed maturity investments		0	23,507
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		41,500	0
Net settlements of derivative instruments		0	0
Proceeds from investment in joint venture			0
Net (purchases) sales of short-term investments		(53,779)	(12,183)
Change in cash collateral related to securities lending		0	0
Contributions to subsidiaries		0	0
Intercompany loans issued		0	(39,500)
Acquisitions, net of cash		0	0
Purchases of fixed assets		0	0
Change in other assets		0	0
Net Cash Provided By (Used For) Investing Activities		(12,279)	(31,681)
Financing Activities
Proceeds from issuance of preferred shares, net		0
Purchases of common shares under share repurchase program		0	0
Proceeds from common shares issued, net		0	0
Proceeds from borrowings		0	0
Proceeds from intercompany borrowings			27,500
Repayments of borrowings		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		200	28
Preferred dividends paid		0	0
Net Cash Provided By (Used For) Financing Activities		200	27,528
Effects of exchange rate changes on foreign currency cash		0	0
Increase (decrease) in cash		2,369	6,469
Cash beginning of year		17,023	2,787
Cash end of period		19,392	9,256
Reportable Legal Entities | Other ACGL Subsidiaries
Operating Activities
Net Cash Provided by (Used in) Operating Activities		1,096,443	859,525
Investing Activities
Purchases of fixed maturity investments		(27,840,555)	(22,378,599)
Purchases of equity securities		(377,767)	(477,456)
Purchases of other investments		(1,008,774)	(1,320,250)
Proceeds from sales of fixed maturity investments		26,731,924	21,388,047
Proceeds from sales of equity securities		464,904	509,008
Proceeds from sales, redemptions and maturities of other investments		879,330	858,368
Proceeds from redemptions and maturities of fixed maturity investments		499,323	630,397
Net settlements of derivative instruments		23,396	81,114
Proceeds from investment in joint venture			40,000
Net (purchases) sales of short-term investments		(113,553)	193,851
Change in cash collateral related to securities lending		(27,935)	28,685
Contributions to subsidiaries		(9,247)	(9,290)
Intercompany loans issued		0	(41,523)
Acquisitions, net of cash		(20,911)	818
Purchases of fixed assets		(11,557)	(10,848)
Change in other assets		(5,816)	(43,654)
Net Cash Provided By (Used For) Investing Activities		(817,238)	(551,332)
Financing Activities
Proceeds from issuance of preferred shares, net		0
Purchases of common shares under share repurchase program		0	0
Proceeds from common shares issued, net		12,832	9,290
Proceeds from borrowings		46,000	239,077
Proceeds from intercompany borrowings			39,500
Repayments of borrowings		(179,171)
Change in cash collateral related to securities lending		27,935	(28,685)
Dividends paid to redeemable noncontrolling interests		(14,448)	(14,447)
Dividends paid to parent	[1]	(167,045)	(444,260)
Other		32,913	50,435
Preferred dividends paid		0	0
Net Cash Provided By (Used For) Financing Activities		(240,984)	(149,090)
Effects of exchange rate changes on foreign currency cash		(10,332)	(8,658)
Increase (decrease) in cash		27,889	150,445
Cash beginning of year		529,494	479,697
Cash end of period		557,383	630,142
Consolidating Adjustments and Eliminations
Operating Activities
Net Cash Provided by (Used in) Operating Activities		(168,002)	(444,897)
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
Proceeds from investment in joint venture			0
Net (purchases) sales of short-term investments		0	0
Change in cash collateral related to securities lending		0	0
Contributions to subsidiaries		12,832	9,290
Intercompany loans issued		0	81,023
Acquisitions, net of cash		0	0
Purchases of fixed assets		0	0
Change in other assets		0	0
Net Cash Provided By (Used For) Investing Activities		12,832	90,313
Financing Activities
Proceeds from issuance of preferred shares, net		0
Purchases of common shares under share repurchase program		0	0
Proceeds from common shares issued, net		(12,832)	(9,290)
Proceeds from borrowings		0	0
Proceeds from intercompany borrowings			(81,023)
Repayments of borrowings		0
Change in cash collateral related to securities lending		0	0
Dividends paid to redeemable noncontrolling interests		957	637
Dividends paid to parent	[1]	167,045	444,260
Other		0	0
Preferred dividends paid		0	0
Net Cash Provided By (Used For) Financing Activities		155,170	354,584
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	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Effective tax rate on income before income taxes (percentage)	5.70%	5.50%
Net deferred tax assets	$ 124.1		$ 135.7
Income taxes paid	$ 40.7	$ 35.5

Transactions with Related Par69

Transactions with Related Parties (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Investment commitments	$ 1,340,000		$ 1,110,000
Purchases of other investments	1,008,774	$ 1,320,250
Common director | The Carlyle Group
Related Party Transaction [Line Items]
Investment commitments	770,900
Unfunded commitments	524,500
Purchases of other investments	50,100	97,700
Aggregate cash distributions received	$ 17,900	$ 30,300

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent event $ in Millions	Oct. 26, 2016USD ($)
Secured letter of credit facility
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 350
Unsecured revolving loan and letter of credit facility
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 500