Arch Capital (ACGL) 10-K3 Mar 142013 FY Annual reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Billions, except Share data, unless otherwise specified	Dec. 31, 2013	Feb. 24, 2014	Jun. 30, 2013
Document and Entity Information [Abstract]	'	'	'
Entity Registrant Name	'ARCH CAPITAL GROUP LTD.	'	'
Entity Central Index Key	'0000947484	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Document Type	'10-K	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Amendment Flag	'false	'	'
Entity Common Stock, Shares Outstanding	'	133,805,667	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Public Float	'	'	$6.62

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investments:	'	'
Fixed maturities available for sale, at fair value (amortized cost: $9,564,634 and $9,567,290)	$9,571,776	$9,839,988
Short-term investments available for sale, at fair value (amortized cost: $1,477,584 and $719,848)	1,478,367	722,121
Investment of funds received under securities lending, at fair value (amortized cost: $97,943 and $42,302)	100,584	42,531
Equity securities available for sale, at fair value (cost: $433,275 and $298,414)	496,824	312,749
Other investments available for sale, at fair value (cost: $488,687 and $519,955)	498,310	549,280
Investments accounted for using the fair value option	1,221,534	917,466
Investments accounted for using the equity method	244,339	307,105
Total investments	13,611,734	12,691,240
Cash	434,057	371,041
Accrued investment income	66,848	71,748
Investment in joint venture (cost: $100,000)	104,856	107,284
Fixed maturities and short-term investments pledged under securities lending, at fair value	105,081	50,848
Premiums receivable	753,924	688,873
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	1,804,330	1,870,037
Contractholder receivables	1,064,246	865,728
Prepaid reinsurance premiums	328,343	298,484
Deferred acquisition costs, net	342,314	262,822
Receivable for securities sold	50,555	19,248
Other assets	899,806	519,409
Total Assets	19,566,094	17,816,762
Liabilities	'	'
Reserve for losses and loss adjustment expenses	8,824,696	8,933,292
Unearned premiums	1,896,365	1,647,978
Reinsurance balances payable	196,167	188,546
Contractholder payables	1,064,246	865,728
Deposit accounting liabilities	421,297	27,594
Senior notes	800,000	300,000
Revolving credit agreement borrowings	100,000	100,000
Securities lending payable	107,999	52,356
Payable for securities purchased	51,318	37,788
Other liabilities	456,510	494,602
Total Liabilities	13,918,598	12,647,884
Commitments and Contingencies	'	'
Shareholdersâ€™ Equity	'	'
Non-cumulative preferred shares	325,000	325,000
Common shares ($0.0033 par, shares issued: 169,560,591 and 168,255,572)	565	561
Additional paid-in capital	299,517	227,778
Retained earnings	6,042,154	5,354,361
Accumulated other comprehensive income, net of deferred income tax	74,964	287,017
Common shares held in treasury, at cost (shares: 35,885,707 and 34,412,959)	-1,094,704	-1,025,839
Total Shareholders' Equity	5,647,496	5,168,878
Total Liabilities and Shareholders' Equity	$19,566,094	$17,816,762

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parentheticals) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fixed maturities available for sale, at amortized cost	$9,564,634	$9,567,290
Short-term investments available for sale, at amortized cost	1,477,584	719,848
Investment of funds received under securities lending agreements, at cost	97,943	42,302
Equity securities, at cost	433,275	298,414
Other investments, at cost	488,687	519,955
Investment in joint venture, at cost	$100,000	$100,000
Common shares, par value per share	$0.00	$0.00
Common shares issued (shares)	169,560,591	168,255,572
Common shares held in treasury (shares)	35,885,707	34,412,959

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues	'	'	'
Net premiums written	$3,351,367	$3,052,235	$2,673,326
Change in unearned premiums	-205,415	-117,095	-41,511
Net premiums earned	3,145,952	2,935,140	2,631,815
Net investment income	267,219	294,895	338,198
Net realized gains	74,018	194,228	110,646
Other-than-temporary impairment losses	-3,961	-12,175	-13,850
Less investment impairments recognized in other comprehensive income, before taxes	175	787	4,788
Net impairment losses recognized in earnings	-3,786	-11,388	-9,062
Other underwriting income	7,639	8,090	3,429
Equity in net income (loss) of investment funds accounted for using the equity method	35,701	73,510	-9,605
Other income (loss)	-586	-12,094	-2,114
Total revenues	3,526,157	3,482,381	3,063,307
Expenses	'	'	'
Losses and loss adjustment expenses	1,679,424	1,861,277	1,727,553
Acquisition expenses	564,103	508,884	462,937
Other operating expenses	500,730	465,353	432,122
Interest expense	27,060	28,525	31,691
Net foreign exchange losses (gains)	12,335	28,955	-17,366
Total expenses	2,783,652	2,892,994	2,636,937
Income before income taxes	742,505	589,387	426,370
Current tax expense	32,696	9,004	7,831
Deferred tax expense (benefit)	78	-13,014	-17,624
Income tax expense (benefit)	32,774	-4,010	-9,793
Net income	709,731	593,397	436,163
Preferred dividends	21,938	25,079	25,844
Loss on repurchase of preferred shares	0	10,612	0
Net income available to common shareholders	$687,793	$557,706	$410,319
Net income per common share	'	'	'
Basic (per share)	$5.24	$4.15	$3.10
Diluted (per share)	$5.07	$4.03	$2.97
Weighted average common shares and common share equivalents outstanding	'	'	'
Basic (shares)	131,355,392	134,446,158	132,221,970
Diluted (shares)	135,777,183	138,258,847	138,289,702

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Comprehensive Income (Loss)	'	'	'
Net income	$709,731	$593,397	$436,163
Unrealized appreciation (decline) in value of available-for-sale investments:	'	'	'
Unrealized holding (losses) gains arising during period	-176,403	273,931	89,059
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	-175	-787	-4,788
Reclassification of net realized gains, net of income taxes, included in net income	-32,686	-157,824	-123,562
Foreign currency translation adjustments	-2,789	17,774	-11,289
Other comprehensive income (loss)	-212,053	133,094	-50,580
Comprehensive Income	$497,678	$726,491	$385,583

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Shareholders' Equity (USD $)	Total	Non-Cumulative Preferred Shares	Common Shares	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Common Shares Held in Treasury, at Cost
In Thousands	Total	Non-Cumulative Preferred Shares	Common Shares	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Common Shares Held in Treasury, at Cost
Balance at beginning of year at Dec. 31, 2010	'	$325,000	$534	$110,325	$4,386,336	$204,503	($549,912)
Shares issued - Series C	'	0	'	'	'	'	'
Common shares issued, net	'	'	15	5,767	'	'	'
Issue costs on Series C preferred shares	'	'	'	0	'	'	'
Shares repurchased - Series A and B	'	0	'	0	0	'	'
Exercise of stock options	'	'	'	12,305	'	'	'
Amortization of share-based compensation	'	'	'	30,986	'	'	'
Other	'	'	'	2,036	'	'	'
Net income	436,163	'	'	'	436,163	'	'
Dividends declared on preferred shares	-25,844	'	'	'	-25,844	'	'
Change in unrealized appreciation (decline) in value of investments, net of deferred income tax	'	'	'	'	'	-34,503	'
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	-4,788	'	'	'	'	-4,788	'
Foreign currency translation adjustments	-11,289	'	'	'	'	-11,289	'
Shares repurchased for treasury	'	'	'	'	'	'	-295,560
Balance at end of period at Dec. 31, 2011	4,592,074	325,000	549	161,419	4,796,655	153,923	-845,472
Shares issued - Series C	'	325,000	'	'	'	'	'
Common shares issued, net	'	'	12	6,823	'	'	'
Issue costs on Series C preferred shares	'	'	'	-9,398	'	'	'
Shares repurchased - Series A and B	'	-325,000	'	10,612	-10,612	'	'
Exercise of stock options	'	'	'	14,218	'	'	'
Amortization of share-based compensation	'	'	'	42,303	'	'	'
Other	'	'	'	1,801	'	'	'
Net income	593,397	'	'	'	593,397	'	'
Dividends declared on preferred shares	-25,079	'	'	'	-25,079	'	'
Change in unrealized appreciation (decline) in value of investments, net of deferred income tax	'	'	'	'	'	116,107	'
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	-787	'	'	'	'	-787	'
Foreign currency translation adjustments	17,774	'	'	'	'	17,774	'
Shares repurchased for treasury	'	'	'	'	'	'	-180,367
Balance at end of period at Dec. 31, 2012	5,168,878	325,000	561	227,778	5,354,361	287,017	-1,025,839
Shares issued - Series C	'	0	'	'	'	'	'
Common shares issued, net	'	'	4	8,237	'	'	'
Issue costs on Series C preferred shares	'	'	'	0	'	'	'
Shares repurchased - Series A and B	'	0	'	0	0	'	'
Exercise of stock options	'	'	'	10,561	'	'	'
Amortization of share-based compensation	'	'	'	49,237	'	'	'
Other	'	'	'	3,704	'	'	'
Net income	709,731	'	'	'	709,731	'	'
Dividends declared on preferred shares	-21,938	'	'	'	-21,938	'	'
Change in unrealized appreciation (decline) in value of investments, net of deferred income tax	'	'	'	'	'	-209,089	'
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	-175	'	'	'	'	-175	'
Foreign currency translation adjustments	-2,789	'	'	'	'	-2,789	'
Shares repurchased for treasury	'	'	'	'	'	'	-68,865
Balance at end of period at Dec. 31, 2013	$5,647,496	$325,000	$565	$299,517	$6,042,154	$74,964	($1,094,704)

Unaudited_Consolidated_Stateme

Unaudited Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities	'	'	'
Net income	$709,731	$593,397	$436,163
Adjustments to reconcile net income to net cash provided by operating activities:	'	'	'
Net realized losses	-78,084	-199,547	-113,922
Net impairment losses recognized in earnings	3,786	11,388	9,062
Equity in net income or loss of investment funds accounted for using the equity method and other income or loss	52,824	-43,633	71,100
Share-based compensation	49,237	42,303	30,986
Changes in:	'	'	'
Reserve for losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable	-29,393	395,901	274,622
Unearned premiums, net of prepaid reinsurance premiums	205,415	117,095	41,552
Premiums receivable	-60,224	-120,380	-7,226
Deferred acquisition costs, net	-75,948	-34,371	-1,259
Reinsurance balances payable	6,830	42,740	5,515
Other liabilities	-29,989	41,049	43,298
Other items, net	96,683	75,661	76,221
Net Cash Provided By Operating Activities	850,868	921,603	866,112
Investing Activities	'	'	'
Purchases of fixed maturity investments	-18,174,988	-17,568,592	-13,875,635
Purchases of equity securities	-535,857	-268,999	-413,024
Purchases of other investments	-1,326,729	-1,000,049	-593,862
Proceeds from the sale of fixed maturity investments	17,196,614	16,366,306	12,398,253
Proceeds from the sale of equity securities	462,787	313,617	369,503
Proceeds from the sale of other investments	1,162,707	443,630	543,757
Proceeds from redemptions and maturities of fixed maturity investments	731,708	1,115,594	1,034,489
Net purchases of short-term investments	-750,613	185,919	-2,389
Change in investment of securities lending collateral	-55,643	6,190	19,475
Purchase of business, net of cash acquired	0	28,948	0
Purchases of furniture, equipment and other assets	-17,499	-18,532	-18,987
Net Cash Used For Investing Activities	-1,307,513	-395,968	-538,420
Financing Activities	'	'	'
Proceeds from issuance of Series C preferred shares, net	0	315,763	0
Repurchase of Series A and B preferred shares	0	-325,000	0
Purchases of common shares under share repurchase program	-57,796	-172,056	-287,561
Proceeds from common shares issued, net	3,051	7,033	6,332
Proceeds from borrowings	494,228	0	0
Repayments of borrowings	0	-310,868	-15,352
Change in securities lending collateral	55,643	-6,190	-19,475
Other	50,830	6,664	4,765
Preferred dividends paid	-21,938	-28,381	-25,844
Net Cash Used For Financing Activities	524,018	-513,035	-337,135
Effects of exchange rate changes on foreign currency cash	-4,357	6,742	-1,598
Increase in cash	63,016	19,342	-11,041
Cash beginning of year	371,041	351,699	362,740
Cash end of period	$434,057	$371,041	$351,699

General

General	12 Months Ended
General	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
General	'
	General
	Arch Capital Group Ltd. (“ACGL”) is a Bermuda public limited liability company which provides insurance and reinsurance on a worldwide basis through its wholly owned subsidiaries. ACGL was formed in September 2000 and became the sole shareholder of Arch Capital Group (U.S.) Inc. (“Arch-U.S.”) pursuant to an internal reorganization transaction completed in November 2000. In October 2001, the Company launched an underwriting initiative to meet current and future demand in the global insurance and reinsurance markets that included the recruitment of new management teams and an equity capital infusion of $763.2 million.
	As used herein, the “Company” means ACGL and its subsidiaries. Similarly, “Common Shares” means the common shares, par value $0.0033, of ACGL. The Company has reclassified the presentation of certain prior year information to conform to the current presentation. Such reclassifications had no effect on the Company’s net income, shareholders’ equity or cash flows. Tabular amounts are in U.S. Dollars in thousands, except share amounts, unless otherwise noted.

Significant_Accounting_Policie

Significant Accounting Policies	12 Months Ended
Significant Accounting Policies	Dec. 31, 2013
Accounting Policies [Abstract]	'
Significant accounting policies	'
	Significant Accounting Policies
	(a) Basis of Presentation
	The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of ACGL and its subsidiaries, including Arch Reinsurance Ltd. (“Arch Re Bermuda”), Arch Re U.S., Arch-U.S., Arch Insurance Company, Arch Specialty Insurance Company, Arch Excess & Surplus Insurance Company, Arch Indemnity Insurance Company, Arch Insurance Canada Ltd. ("Arch Insurance Canada"), Arch Risk Transfer Services Ltd., Arch Reinsurance Europe Underwriting Limited (“Arch Re Europe”), Arch Mortgage Insurance Limited (“Arch MI Europe”), Arch Insurance Company (Europe) Limited (“Arch Insurance Company Europe”) and Lloyd’s of London syndicate 2012 and related companies (“Arch Syndicate 2012”). All significant intercompany transactions and balances have been eliminated in consolidation. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates and assumptions.
	(b) Premium Revenues and Related Expenses
	Insurance premiums written are generally recorded at the policy inception and are primarily earned on a pro rata basis over the terms of the policies for all products, usually 12 months. Premiums written include estimates in the Company’s programs, specialty lines, lenders products business and for participation in involuntary pools. Such premium estimates are derived from multiple sources which include the historical experience of the underlying business, similar business and available industry information. Unearned premium reserves represent the portion of premiums written that relates to the unexpired terms of in-force insurance policies.
	Reinsurance premiums written include amounts reported by brokers and ceding companies, supplemented by the Company’s own estimates of premiums where reports have not been received. The determination of premium estimates requires a review of the Company’s experience with the ceding companies, familiarity with each market, the timing of the reported information, an analysis and understanding of the characteristics of each line of business, and management’s judgment of the impact of various factors, including premium or loss trends, on the volume of business written and ceded to the Company. On an ongoing basis, the Company’s underwriters review the amounts reported by these third parties for reasonableness based on their experience and knowledge of the subject class of business, taking into account the Company’s historical experience with the brokers or ceding companies. In addition, reinsurance contracts under which the Company assumes business generally contain specific provisions which allow the Company to perform audits of the ceding company to ensure compliance with the terms and conditions of the contract, including accurate and timely reporting of information. Based on a review of all available information, management establishes premium estimates where reports have not been received. Premium estimates are updated when new information is received and differences between such estimates and actual amounts are recorded in the period in which estimates are changed or the actual amounts are determined.
	Reinsurance premiums written are recorded based on the type of contracts the Company writes. Premiums on the Company’s excess of loss and pro rata reinsurance contracts are estimated when the business is underwritten. For excess of loss contracts, premiums are recorded as written based on the terms of the contract. Estimates of premiums written under pro rata contracts are recorded in the period in which the underlying risks are expected to incept and are based on information provided by the brokers and the ceding companies. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term.
	Reinstatement premiums for the Company’s insurance and reinsurance operations are recognized at the time a loss event occurs, where coverage limits for the remaining life of the contract are reinstated under pre-defined contract terms. Reinstatement premiums, if obligatory, are fully earned when recognized. The accrual of reinstatement premiums is based on an estimate of losses and loss adjustment expenses, which reflects management’s judgment. Premium estimates are reviewed by management at least quarterly. Such review includes a comparison of actual reported premiums to expected ultimate premiums along with a review of the aging and collection of premium estimates. Based on management’s review, the appropriateness of the premium estimates is evaluated, and any adjustment to these estimates is recorded in the period in which it becomes known. Adjustments to premium estimates could be material and such adjustments could directly and significantly impact earnings favorably or unfavorably in the period they are determined because the estimated premium may be fully or substantially earned. A significant portion of amounts included as premiums receivable, which represent estimated premiums written, net of commissions, are not currently due based on the terms of the underlying contracts.
	Reinsurance premiums written, irrespective of the class of business, are generally earned on a pro rata basis over the terms of the underlying policies or reinsurance contracts. Contracts and policies written on a “losses occurring” basis cover claims that may occur during the term of the contract or policy, which is typically 12 months. Accordingly, the premium is earned evenly over the term. Contracts which are written on a “risks attaching” basis cover claims which attach to the underlying insurance policies written during the terms of such contracts. Premiums earned on such contracts usually extend beyond the original term of the reinsurance contract, typically resulting in recognition of premiums earned over a 24-month period. Certain of the Company’s reinsurance contracts include provisions that adjust premiums or acquisition expenses based upon the experience under the contracts. Premiums written and earned, as well as related acquisition expenses, are recorded based upon the projected experience under such contracts.
	The Company also writes certain reinsurance business that is intended to provide insurers with risk management solutions that complement traditional reinsurance. Under these contracts, the Company assumes a measured amount of insurance risk in exchange for an anticipated margin, which is typically lower than on traditional reinsurance contracts. The terms and conditions of these contracts may include additional or return premiums based on loss experience, loss corridors, sublimits and caps. Examples of such business include aggregate stop-loss coverages, financial quota share coverages and multi-year retrospectively rated excess of loss coverages. If these contracts are deemed to transfer risk, they are accounted for as reinsurance.
	Acquisition expenses and other expenses related to the Company’s underwriting operations that vary with, and are directly related to, the successful acquisition or renewal of business are deferred and amortized over the period in which the related premiums are earned. Acquisition expenses, net of ceding commissions received from reinsurers, consist principally of commissions and premium taxes paid to obtain the Company’s business. Other operating expenses also include expenses that vary with, and are directly related to, the acquisition of business. Deferred acquisition costs, which are based on the related unearned premiums, are carried at their estimated realizable value and take into account anticipated losses and loss adjustment expenses, based on historical and current experience, and anticipated investment income. A premium deficiency occurs if the sum of anticipated losses and loss adjustment expenses, unamortized acquisition costs and maintenance costs exceed unearned premiums and anticipated investment income. A premium deficiency is recorded by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. No significant premium deficiency charges were recorded by the Company during 2013, 2012 or 2011.
	(c) Deposit Accounting
	Certain assumed reinsurance contracts, which pursuant to Financial Accounting Standards Board (“FASB”) guidance regarding the accounting and reporting for reinsurance and short-duration and long-duration contracts, that are deemed not to transfer insurance risk, are accounted for using the deposit method of accounting as prescribed in the FASB guidance. However, it is possible that the Company could incur financial losses on such contracts. Management exercises significant judgment in the assumptions used in determining whether assumed contracts should be accounted for as reinsurance contracts or deposit contracts. Under the FASB guidance, for those contracts that contain only significant underwriting risk, the estimated profit margin is deferred and amortized over the contract period and such amount is included in the Company’s underwriting results. When the estimated profit margin is explicit, the margin is reflected as other underwriting income and any adverse financial results on such contracts are reflected as incurred losses. When the estimated profit margin is implicit, the margin is reflected as an offset to paid losses and any adverse financial results on such contracts are reflected as incurred losses. Additional judgments are required when applying the accounting guidance with respect to the revenue recognition criteria for contracts deemed to transfer only significant underwriting risk. For those contracts that contain only significant timing risk, an accretion rate is established at inception of the contract based on actuarial estimates whereby the deposit accounting liability is increased to the estimated amount payable over the contract term. The accretion on the deposit is based on the expected rate of return required to fund the expected future payment obligations. Periodically the Company reassesses the estimated ultimate liability and the related expected rate of return. The accretion of the deposit accounting liability as well as changes to the estimated ultimate liability and the accretion rate are reflected as part of interest expense in the Company’s results of operations.

	Deposit accounting liabilities totaled $421.3 million and $27.6 million, respectively, at December 31, 2013 and 2012. Under some of these contracts, the ceding company retains the related assets on a funds-held basis. In those instances, the Company records the asset as a deposit accounting asset. Deposit accounting assets of $370.5 million and $6.5 million, respectively, at December 31, 2013 and 2012 are included in “Other assets” on the Company’s balance sheet. Interest income produced by those assets are recorded as part of net investment income in the Company's results of operations.

	(d) Retroactive Accounting
	Retroactive reinsurance reimburses a ceding company for liabilities incurred as a result of past insurable events covered by the underlying policies reinsured. In certain instances, reinsurance contracts cover losses both on a prospective basis and on a retroactive basis and, accordingly, the Company bifurcates the prospective and retrospective elements of these reinsurance contracts and accounts for each element separately. Underwriting income generated in connection with retroactive reinsurance contracts is deferred and amortized into income over the settlement period while losses are charged to income immediately. Subsequent changes in estimated or actual cash flows under such retroactive reinsurance contracts are accounted for by adjusting the previously deferred amount to the balance that would have existed had the revised estimate been available at the inception of the reinsurance transaction, with a corresponding charge or credit to income.
	(e) Reinsurance Ceded
	In the normal course of business, the Company purchases reinsurance to increase capacity and to limit the impact of individual losses and events on its underwriting results by reinsuring certain levels of risk with other insurance enterprises or reinsurers. The Company uses pro rata, excess of loss and facultative reinsurance contracts. Reinsurance ceding commissions are recognized as a reduction to acquisition costs on a pro rata basis over the period of risk while the portion of such commissions that will be earned in the future is deferred. The accompanying consolidated statement of income reflects premiums and losses and loss adjustment expenses and acquisition costs, net of reinsurance ceded. See Note 4 for information on the Company's reinsurance usage. Ceded unearned premiums are reported as prepaid reinsurance premiums and estimated amounts of reinsurance recoverable on unpaid losses are reported as unpaid losses and loss adjustment expenses recoverable. Reinsurance premiums ceded and unpaid losses and loss adjustment expenses recoverable are estimated in a manner consistent with that of the original policies issued and the terms of the reinsurance contracts. If the reinsurers are unable to satisfy their obligations under the agreements, the Company’s insurance or reinsurance subsidiaries would be liable for such defaulted amounts.
	(f) Cash
	Cash includes cash equivalents, which are investments with original maturities of three months or less that are not managed by external or internal investment advisors.
	(g) Investments
	The Company currently classifies substantially all of its fixed maturity investments, equity securities and short-term investments as “available for sale” and, accordingly, they are carried at estimated fair value (also known as fair value) with the changes in fair value recorded as an unrealized gain or loss component of accumulated other comprehensive income in shareholders’ equity. The fair value of fixed maturity securities and equity securities is generally determined from quotations received from nationally recognized pricing services, or when such prices are not available, by reference to broker or underwriter bid indications. Short-term investments comprise securities due to mature within one year of the date of issue. Short-term investments include certain cash equivalents which are part of investment portfolios under the management of external and internal investment managers.
	The Company participates in a securities lending program as a mechanism for generating additional interest income on its fixed income portfolio. Under the security lending agreements, certain of its fixed income portfolio securities are loaned to third parties, primarily major brokerage firms, for short periods of time through a lending agent. Such securities have been reclassified as “Fixed maturities and short-term investments pledged under securities lending agreements, at fair value.” The Company maintains legal control over the securities it lends, retains the earnings and cash flows associated with the loaned securities and receives a fee from the borrower for the temporary use of the securities. Collateral received, primarily in the form of cash, is required at a rate of 102% of the fair value of the loaned securities including accrued investment income and is monitored and maintained by the lending agent. Such collateral is reinvested and is reflected as “Investment of funds received under securities lending agreements, at fair value.”
	The Company’s investment portfolio includes certain funds that, due to their ownership structure, are accounted for by the Company using the equity method. In applying the equity method, these investments are initially recorded at cost and are subsequently adjusted based on the Company’s proportionate share of the net income or loss of the funds (which include changes in the fair value of the underlying securities in the funds). Such investments are generally recorded on a one month lag with some investments reported for on a three month lag based on the availability of reports from the investment funds. Changes in the carrying value of such investments are recorded in net income as “Equity in net income (loss) of investment funds accounted for using the equity method.” As such, fluctuations in the carrying value of the investment funds accounted for using the equity method may increase the volatility of the Company’s reported results of operations.
	Other investments include funds and separately managed accounts with holdings in Asian and emerging markets, fixed maturities, term loans and other investment strategies. The fair value for certain of the Company’s other investments are determined using net asset values (“NAVs”) as advised by external fund managers. The NAV is based on the fund manager’s valuation of the underlying holdings in accordance with the fund’s governing documents. Certain of the funds are accounted for as available for sale equity securities, regardless of the nature of the investments held within the fund.
	The Company elected to carry certain fixed maturity securities, equity securities and other investments at fair value under the fair value option afforded by accounting guidance regarding the fair value option for financial assets and liabilities. Changes in fair value of investments accounted for using the fair value option are included in "Net realized gains (losses)." The primary reasons for electing the fair value option were to address simplification and cost-benefit considerations.
	The Company invests in limited partner equity interests issued by third party variable interest entities (“VIE”). Such amounts are included in investments accounted for using the equity method, other investments available for sale and investments accounted for using the fair value option. A VIE refers to entities that have characteristics such as (i) insufficient equity at risk to allow the entity to finance its activities without additional financial support or (ii) instances where the equity investors, as a group, do not have the characteristic of a controlling financial interest. If the Company is determined to be the primary beneficiary, it is required to consolidate the VIE. The primary beneficiary is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (i) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (ii) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. At inception of the VIE as well as on an ongoing basis, the Company determines whether it is the primary beneficiary based on an analysis of the Company’s level of involvement in the VIE, the contractual terms, and the overall structure of the VIE. The Company's maximum exposure to loss with respect to these investments is limited to the investment carrying amounts reported in the Company's consolidated balance sheet and any unfunded commitment.
	The Company performs quarterly reviews of its investments to determine whether declines in fair value below the cost basis are considered other-than-temporary in accordance with applicable accounting guidance regarding the recognition and presentation of other-than-temporary impairments (“OTTI”). The process of determining whether a security is other-than-temporarily impaired requires judgment and involves analyzing many factors. These factors include (i) an analysis of the liquidity, business prospects and overall financial condition of the issuer, (ii) the time period in which there was a significant decline in value, (iii) the significance of the decline and (iv) the analysis of specific credit events. The Company evaluates the unrealized losses of its equity securities by issuer and forecasts a reasonable period of time by which the fair value of the securities would increase and the Company would recover its cost. If the Company is unable to forecast a reasonable period of time in which to recover the cost of its equity securities, a net impairment loss in earnings equivalent to the entire unrealized loss is recognized.
	When there are credit-related losses associated with debt securities for which the Company does not have an intent to sell and it is more likely than not that it will not be required to sell the security before recovery of its cost basis, the amount of the OTTI related to a credit loss is recognized in earnings and the amount of the OTTI related to other factors (e.g., interest rates, market conditions, etc.) is recorded as a component of other comprehensive income (loss). The amount of the credit loss of an impaired debt security is the difference between the amortized cost and the greater of (i) the present value of expected future cash flows and (ii) the fair value of the security. In instances where no credit loss exists but it is more likely than not that the Company will have to sell the debt security prior to the anticipated recovery, the decline in fair value below amortized cost is recognized as an OTTI in earnings. In periods after the recognition of an OTTI on debt securities, the Company accounts for such securities as if they had been purchased on the measurement date of the OTTI at an amortized cost basis equal to the previous amortized cost basis less the OTTI recognized in earnings. For debt securities for which OTTI were recognized in earnings, the difference between the new amortized cost basis and the cash flows expected to be collected will be accreted or amortized into net investment income. See Note 6, “Investment Information—Other-Than-Temporary Impairments” for additional information.
	Net investment income includes interest and dividend income together with amortization of market premiums and discounts and is net of investment management and custody fees. Anticipated prepayments and expected maturities are used in applying the interest method for certain investments such as mortgage and other asset-backed securities. When actual prepayments differ significantly from anticipated prepayments, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The net investment in such securities is adjusted to the amount that would have existed had the new effective yield been applied since the acquisition of the security. Such adjustments, if any, are included in net investment income when determined. Equity in net income (loss) of investment funds accounted for using the equity method includes changes in the fair value of certain alternative investments accounted for under the equity method.
	Investment gains or losses realized on the sale of investments, except for certain fund investments, are determined on a first-in, first-out basis and are reflected in net income. Investments gains or losses realized on the sale of certain fund investments are determined on an average cost basis. Unrealized appreciation or decline in the value of securities, which are carried at fair value, is excluded from net income and recorded as a separate component of accumulated other comprehensive income, net of applicable deferred income tax.
	(h) Derivative Instruments
	The Company recognizes all derivative instruments, including embedded derivative instruments, at fair value in the Consolidated Balance Sheets. The Company employs the use of derivative instruments within its operations in two primary ways: (i) through its investment activities to mitigate risks arising from assets and liabilities held in foreign currencies as well as part of its overall investment strategy. For such instruments, changes in assets and liabilities measured at fair value are recorded as “Net realized gains” in the Consolidated Statements of Income; and (ii) through its underwriting activities where an insurance or reinsurance contract meets the accounting definition of a derivative instrument. For such contracts, changes in fair value are reflected in “Other underwriting income” in the Consolidated Statements of Income as the underlying contract originates from the Company’s underwriting operations. For the periods ended 2013, 2012, and 2011, the Company did not designate any derivative instruments as hedges under the relevant accounting guidance. See Note 9 for information on the Company’s derivative instruments.
	(i) Reserves for Losses and Loss Adjustment Expenses
	The reserve for losses and loss adjustment expenses consists of estimates of unpaid reported losses and loss adjustment expenses and estimates for losses incurred but not reported. The reserve for unpaid reported losses and loss adjustment expenses, established by management based on reports from ceding companies and claims from insureds, excludes estimates of amounts due from insureds related to losses under high deductible policies, and represents the estimated ultimate cost of events or conditions that have been reported to or specifically identified by the Company. Such reserves are supplemented by management’s estimates of reserves for losses incurred for which reports or claims have not been received. The Company’s reserves are based on a combination of reserving methods, incorporating both Company and industry loss development patterns. The Company selects the initial expected loss and loss adjustment expense ratios based on information derived by its underwriters and actuaries during the initial pricing of the business, supplemented by industry data where appropriate. Such ratios consider, among other things, rate changes and changes in terms and conditions that have been observed in the market. These estimates are reviewed regularly and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments, if any, are reflected in income in the period in which they are determined. As actual loss information has been reported, the Company has developed its own loss experience and its reserving methods include other actuarial techniques. Over time, such techniques have been given further weight in its reserving process based on the continuing maturation of the Company’s reserves. Inherent in the estimates of ultimate losses and loss adjustment expenses are expected trends in claims severity and frequency and other factors which may vary significantly as claims are settled. Accordingly, ultimate losses and loss adjustment expenses may differ materially from the amounts recorded in the accompanying consolidated financial statements. Losses and loss adjustment expenses are recorded on an undiscounted basis, except for excess workers’ compensation and employers’ liability business written by the Company’s insurance operations.
	(j) Contractholder Receivables and Payables
	Certain insurance policies written by the Company’s insurance operations feature large deductibles, primarily in its construction and national accounts lines of business. Under such contracts, the Company is obligated to pay the claimant for the full amount of the claim. The Company is subsequently reimbursed by the policyholder for the deductible amount. These amounts are included on a gross basis in the consolidated balance sheet in contractholder payables and contractholder receivables, respectively. In the event that the Company is unable to collect from the policyholder, the Company would record an increase to losses and loss adjustment expenses related to such policy.
	(k) Foreign Exchange
	Assets and liabilities of foreign operations whose functional currency is not the U.S. Dollar are translated at the prevailing exchange rates at each balance sheet date. Revenues and expenses of such foreign operations are translated at average exchange rates during the year. The net effect of the translation adjustments for foreign operations is included in accumulated other comprehensive income, net of applicable deferred income tax. Monetary assets and liabilities, such as premiums receivable and the reserve for losses and loss adjustment expenses, denominated in foreign currencies are revalued at the exchange rate in effect at the balance sheet date with the resulting foreign exchange gains and losses included in net income. Accounts that are classified as non-monetary, such as deferred acquisition costs and the unearned premium reserves, are not revalued. In the case of foreign currency denominated fixed maturity securities which are classified as “available for sale,” the change in exchange rates between the local currency in which the investments are denominated and the Company’s functional currency at each balance sheet date is included in unrealized appreciation or decline in value of securities, a component of accumulated other comprehensive income, net of applicable deferred income tax.
	(l) Income Taxes
	Deferred income taxes reflect the expected future tax consequences of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and amounts used for income tax purposes. A valuation allowance is recorded if it is more likely than not that some or all of a deferred tax asset may not be realized. The Company considers future taxable income and feasible tax planning strategies in assessing the need for a valuation allowance. In the event the Company determines that it will not be able to realize all or part of its deferred income tax assets in the future, an adjustment to the deferred income tax assets would be charged to income in the period in which such determination is made. In addition, if the Company subsequently assesses that the valuation allowance is no longer needed, a benefit would be recorded to income in the period in which such determination is made. See Note 12 for more information.
	The Company recognizes a tax benefit where it concludes that it is more likely than not that the tax benefit will be sustained on audit by the taxing authority based solely on the technical merits of the associated tax position. If the recognition threshold is met, the Company recognizes a tax benefit measured at the largest amount of the tax benefit that, in the Company’s judgment, is greater than 50% likely to be realized. The Company records interest and penalties related to unrecognized tax benefits in the provision for income taxes.
	(m) Share-Based Payment Arrangements
	The Company applies a fair value based measurement method in accounting for its share-based payment arrangements with eligible employees and directors. Compensation expense is estimated based on the fair value of the award at the grant date and is recognized in net income over the requisite service period with a corresponding increase in shareholders’ equity. No value is attributed to awards that employees forfeit because they fail to satisfy vesting conditions. As such, the number of shares granted is reduced by assumed forfeitures and adjusted based on actual forfeitures until vesting. The Company’s share-based payment arrangements generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. The share-based compensation expense associated with such awards that have graded vesting features and vest based on service conditions only is calculated on a straight-line basis over the requisite service period for the entire award. For awards granted to retirement-eligible employees where no service is required for the employee to retain the award, the grant date fair value is immediately recognized as compensation expense at the grant date because the employee is able to retain the award without continuing to provide service. For employees near retirement eligibility, attribution of compensation cost is over the period from the grant date to the retirement eligibility date. In November 2012, the Company issued off-cycle share-based awards, which will cliff vest on the fifth anniversary of the grant date. The expense for such grant will be amortized on a straight- line basis over the five-year requisite service period. The off-cycle awards have similar terms as the annual award agreements, however with respect to retirement eligible employees service is required for the employee to retain the award. Retirement-eligible employees retiring prior to the fifth anniversary of the grant date will vest in a pro-rated portion of the award commensurate with the service performed. Such employees will receive the vested portion at the end of the five-year cliff period. These charges had no impact on the Company’s cash flows or total shareholders’ equity. See Note 17 for information relating to the Company’s share-based payment awards.
	(n) Guaranty Fund and Other Related Assessments
	Liabilities for guaranty fund and other related assessments in the Company’s insurance and reinsurance operations are accrued when the Company receives notice that an amount is payable, or earlier if a reasonable estimate of the assessment can be made.
	(o) Treasury Shares
	Treasury shares are common shares purchased by the Company and not subsequently canceled. These shares are recorded at cost and result in a reduction of the Company’s shareholders’ equity in its Consolidated Balance Sheets.
	(p) Recent Accounting Pronouncements
	Effective January 1, 2013, the Company adopted FASB guidance requiring additional disclosures about reclassification adjustments from accumulated other comprehensive income. As this guidance is disclosure-related only, the adoption of this guidance did not impact the Company’s results of operations, financial condition or liquidity. The additional disclosures are provided in Note 10, "Other Comprehensive Income (Loss)."
	Effective January 1, 2013, the Company adopted FASB guidance requiring additional disclosures about financial instruments and derivative instruments that are either: (1) offset for balance sheet presentation purposes or (2) subject to an enforceable master netting arrangement or similar arrangement, regardless of whether they are offset for balance sheet presentation purposes. The disclosure requirements of this guidance are limited to derivatives, repurchase agreements and reverse repurchase agreements, and securities borrowing/lending transactions. As this guidance is disclosure-related only and did not amend existing balance sheet offsetting guidance, adoption did not impact the Company’s results of operations, financial condition or liquidity. The additional disclosures are provided in Note 6, "Investment Information," and Note 9, "Derivative Instruments."

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Segment Information	'
	Segment Information
	The Company classifies its businesses into two underwriting segments – insurance and reinsurance – and corporate and other (non-underwriting). The Company’s insurance and reinsurance operating segments each have segment 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, President and Chief Executive Officer of ACGL and the Chief Financial Officer of ACGL. The chief operating decision makers do not assess performance, measure return on equity or make resource allocation decisions on a line of business basis. The Company determined its reportable operating segments using the management approach described in accounting guidance regarding disclosures about segments of an enterprise and related information.
	Management measures segment performance based on underwriting income or loss. The Company does not manage its assets by segment and, accordingly, investment income is not allocated to each underwriting segment. In addition, other revenue and expense items are not evaluated by segment. 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 insurance segment consists of the Company’s insurance underwriting subsidiaries which primarily write on both an admitted and non-admitted basis. Specialty product lines include: casualty; construction; executive assurance; healthcare; lenders products; national accounts; professional liability; programs; property, energy, marine and aviation; surety; travel and accident; and other (consisting of alternative markets, contract binding, accident and health and excess workers' compensation business).
	The reinsurance segment consists of the Company’s reinsurance underwriting subsidiaries. The reinsurance segment generally seeks to write significant lines on specialty property and casualty reinsurance contracts. Classes of business 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 mortgage, life, casualty clash and other).
	Corporate and other (non-underwriting) includes net investment income, other income (loss), other expenses incurred by the Company, interest expense, net realized gains or losses, net impairment losses recognized in earnings, equity in net income (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.
	The following tables set forth an analysis of the Company’s underwriting income by segment, together with a reconciliation of underwriting income to net income available to common shareholders, summary information regarding net premiums written and earned by major line of business and net premiums written by location:


		Year Ended December 31, 2013
		Insurance				Reinsurance				Total
	Gross premiums written (1)	$	2,712,509			$	1,489,191			$	4,196,623

	Net premiums written	1,948,796				1,402,571				3,351,367


	Net premiums earned	$	1,876,014			$	1,269,938			$	3,145,952

	Other underwriting income	2,122				5,517				7,639

	Losses and loss adjustment expenses	(1,188,445		)		(490,979		)		(1,679,424		)
	Acquisition expenses, net	(311,904		)		(252,199		)		(564,103		)
	Other operating expenses	(315,387		)		(142,940		)		(458,327		)
	Underwriting income	$	62,400			$	389,337			451,737

	Net investment income									267,219

	Net realized gains									74,018

	Net impairment losses recognized in earnings									(3,786		)
	Equity in net income (loss) of investment funds									35,701
	accounted for using the equity method
	Other income (loss)									(586		)
	Other expenses									(42,403		)
	Interest expense									(27,060		)
	Net foreign exchange losses									(12,335		)
	Income before income taxes									742,505

	Income tax expense									(32,774		)
	Net income									709,731

	Preferred dividends									(21,938		)
	Net income available to common shareholders									$	687,793


	Underwriting Ratios
	Loss ratio	63.3		%		38.7		%		53.4		%
	Acquisition expense ratio (2)	16.5		%		19.9		%		17.9		%
	Other operating expense ratio	16.8		%		11.3		%		14.6		%
	Combined ratio	96.6		%		69.9		%		85.9		%

	-1	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

	-2	The acquisition expense ratio is adjusted to include certain other underwriting income.


		Year Ended December 31, 2012
		Insurance				Reinsurance				Total
	Gross premiums written (1)	$	2,593,959			$	1,282,000			$	3,869,161

	Net premiums written	1,825,334				1,226,901				3,052,235


Net premiums earned	$	1,800,343			$	1,134,797			$	2,935,140

Other underwriting income	2,335				5,755				8,090

Losses and loss adjustment expenses	(1,283,841		)		(577,436		)		(1,861,277		)
Acquisition expenses, net	(298,983		)		(209,901		)		(508,884		)
Other operating expenses	(307,489		)		(122,546		)		(430,035		)
Underwriting income (loss)	$	(87,635	)		$	230,669			143,034

Net investment income									294,895

Net realized gains									194,228

Net impairment losses recognized in earnings									(11,388		)
Equity in net income (loss) of investment funds									73,510
accounted for using the equity method
Other income (loss)									(12,094		)
Other expenses									(35,318		)
Interest expense									(28,525		)
Net foreign exchange losses									(28,955		)
Income before income taxes									589,387

Income tax benefit									4,010

Net income									593,397

Preferred dividends									(25,079		)
Loss on repurchase of preferred shares									$	(10,612	)
Net income available to common shareholders									$	557,706


Underwriting Ratios
Loss ratio	71.3		%		50.9		%		63.4		%
Acquisition expense ratio (2)	16.5		%		18.5		%		17.3		%
Other operating expense ratio	17.1		%		10.8		%		14.7		%
Combined ratio	104.9		%		80.2		%		95.4		%

-1	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

-2	The acquisition expense ratio is adjusted to include certain other underwriting income.


	Year Ended December 31, 2011
	Insurance				Reinsurance				Total
Gross premiums written (1)	$	2,444,485			$	998,520			$	3,436,456

Net premiums written	1,721,279				952,047				2,673,326


Net premiums earned	$	1,679,047			$	952,768			$	2,631,815

Other underwriting income	2,870				559				3,429

Losses and loss adjustment expenses	(1,172,742		)		(554,811		)		(1,727,553		)
Acquisition expenses, net	(278,696		)		(184,241		)		(462,937		)
Other operating expenses	(307,797		)		(92,945		)		(400,742		)
Underwriting income (loss)	$	(77,318	)		$	121,330			44,012

Net investment income									338,198

Net realized gains									110,646

Net impairment losses recognized in earnings									(9,062		)
Equity in net income (loss) of investment funds									(9,605		)
accounted for using the equity method
Other income									(2,114		)
Other expenses									(31,380		)
Interest expense									(31,691		)
Net foreign exchange gains									17,366

Income before income taxes									426,370

Income tax benefit									9,793

Net income									436,163

Preferred dividends									(25,844		)
Net income available to common shareholders									$	410,319


Underwriting Ratios
Loss ratio	69.8		%		58.2		%		65.6		%
Acquisition expense ratio (2)	16.4		%		19.3		%		17.5		%
Other operating expense ratio	18.3		%		9.8		%		15.2		%
Combined ratio	104.5		%		87.3		%		98.3		%

-1	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

-2	The acquisition expense ratio is adjusted to include certain other underwriting income.


INSURANCE SEGMENT	Year Ended December 31,
	2013				2012				2011
Net premiums written (1)
Programs	$	419,673			$	340,130			$	290,378

Property, energy, marine and aviation	280,551				294,690				335,589

Professional liability	222,351				260,705				237,860

Executive assurance	213,727				250,904				231,405

Construction	161,877				130,201				120,405

Casualty	112,094				112,307				114,235

National accounts	109,233				80,929				80,973

Lenders products	101,576				99,724				94,301

Surety	64,911				53,271				42,475

Travel and accident	63,209				80,489				71,940

Healthcare	40,115				36,814				35,652

Other (2)	159,479				85,170				66,066

Total	$	1,948,796			$	1,825,334			$	1,721,279


Net premiums earned (1)
Programs	$	386,840			$	318,740			$	283,367

Property, energy, marine and aviation	304,294				313,081				322,510

Professional liability	231,014				258,401				252,037

Executive assurance	221,925				241,791				228,623

Construction	149,864				129,446				112,764

Casualty	103,152				113,597				111,654

National accounts	100,865				79,771				79,542

Lenders products	99,847				103,478				79,522

Surety	57,719				47,302				41,119

Travel and accident	59,987				78,050				69,945

Healthcare	38,852				36,779				35,906

Other (2)	121,655				79,907				62,058

Total	$	1,876,014			$	1,800,343			$	1,679,047


Net premiums written by client location (1)
United States	$	1,526,156			$	1,314,577			$	1,208,007

Europe	226,254				271,278				273,578

Asia and Pacific	95,970				120,492				119,523

Other	100,416				118,987				120,171

Total	$	1,948,796			$	1,825,334			$	1,721,279


Net premiums written by underwriting location (1)
United States	$	1,478,930			$	1,254,623			$	1,153,834

Europe	389,763				472,132				463,855

Other	80,103				98,579				103,590

Total	$	1,948,796			$	1,825,334			$	1,721,279


-1	Insurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

-2	Includes alternative markets, contract binding, accident and health and excess workers' compensation business.


REINSURANCE SEGMENT	Year Ended December 31,
	2013				2012				2011
Net premiums written (1)
Other specialty (2)	$	417,865			$	308,104			$	219,632

Casualty (3)	306,304				205,925				173,344

Property excluding property catastrophe (4)	292,536				265,783				226,013

Property catastrophe	220,749				283,677				246,793

Marine and aviation	64,380				84,649				77,309

Other (5)	100,737				78,763				8,956

Total	$	1,402,571			$	1,226,901			$	952,047


Net premiums earned (1)
Other specialty (2)	$	387,630			$	309,101			$	195,855

Casualty (3)	241,774				188,963				189,608

Property excluding property catastrophe (4)	274,719				254,338				243,702

Property catastrophe	232,423				280,185				238,748

Marine and aviation	70,105				76,145				77,819

Other (5)	63,287				26,065				7,036

Total	$	1,269,938			$	1,134,797			$	952,768


Net premiums written (1)
Pro rata	$	781,594			$	598,874			$	416,321

Excess of loss	620,977				628,027				535,726

Total	$	1,402,571			$	1,226,901			$	952,047


Net premiums earned (1)
Pro rata	$	659,852			$	515,764			$	435,311

Excess of loss	610,086				619,033				517,457

Total	$	1,269,938			$	1,134,797			$	952,768


Net premiums written by client location (1)
United States	$	770,080			$	629,614			$	512,319

Europe	327,172				341,674				250,809

Asia and Pacific	120,017				104,398				75,590

Bermuda	87,047				72,864				60,246

Other	98,255				78,351				53,083

Total	$	1,402,571			$	1,226,901			$	952,047


Net premiums written by underwriting location (1)
Bermuda	$	548,924			$	595,999			$	531,254

United States	507,183				379,239				323,731

Europe	309,242				225,491				84,919

Other	37,222				26,172				12,143

Total	$	1,402,571			$	1,226,901			$	952,047


-1	Reinsurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

-2	Includes U.K. motor, trade credit, surety, workers’ compensation catastrophe, accident and health, private passenger auto and other.

-3	Includes professional liability, executive assurance and healthcare business.

-4	Includes facultative business.

-5	Includes mortgage, life, casualty clash and other.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2013
Reinsurance Disclosures [Abstract]	'
Reinsurance	'
	Reinsurance
	In the normal course of business, the Company’s insurance subsidiaries cede a portion of their premium through pro rata and excess of loss reinsurance agreements on a treaty or facultative basis. The Company’s reinsurance subsidiaries participate in “common account” retrocessional arrangements for certain pro rata treaties. Such arrangements reduce the effect of individual or aggregate losses to all companies participating on such treaties, including the reinsurers, such as the Company’s reinsurance subsidiaries, and the ceding company. In addition, the Company’s reinsurance subsidiaries may purchase retrocessional coverage as part of their risk management program. Reinsurance recoverables are recorded as assets, predicated on the reinsurers’ ability to meet their obligations under the reinsurance agreements. If the reinsurers are unable to satisfy their obligations under the agreements, the Company’s insurance or reinsurance subsidiaries would be liable for such defaulted amounts.
	The effects of reinsurance on the Company’s written and earned premiums and losses and loss adjustment expenses with unaffiliated reinsurers were as follows:


		Year Ended December 31,
		2013			2012			2011
	Premiums Written
	Direct	$	2,754,582		$	2,673,864		$	2,402,153

	Assumed	1,442,041			1,195,297			1,034,303

	Ceded	(845,256		)	(816,926		)	(763,130		)
	Net	$	3,351,367		$	3,052,235		$	2,673,326


	Premiums Earned
	Direct	$	2,666,104		$	2,572,078		$	2,357,656

	Assumed	1,296,048			1,165,371			1,034,939

	Ceded	(816,200		)	(802,309		)	(760,780		)
	Net	$	3,145,952		$	2,935,140		$	2,631,815


	Losses and Loss Adjustment Expenses
	Direct	$	1,603,369		$	1,725,707		$	1,584,815

	Assumed	450,618			578,081			630,466

	Ceded	(374,563		)	(442,511		)	(487,728		)
	Net	$	1,679,424		$	1,861,277		$	1,727,553

	The Company monitors the financial condition of its reinsurers and attempts to place coverages only with substantial, financially sound carriers. At December 31, 2013, approximately 86.5% of the Company’s reinsurance recoverables on paid and unpaid losses (not including prepaid reinsurance premiums) of $1.80 billion were due from carriers which had an A.M. Best rating of “A-” or better and the largest reinsurance recoverables from any one carrier was approximately 4.2% of the Company’s total shareholders’ equity. At December 31, 2012, approximately 87.5% of the Company’s reinsurance recoverables on paid and unpaid losses (not including prepaid reinsurance premiums) of $1.87 billion were due from carriers which had an A.M. Best rating of “A-” or better and the largest reinsurance recoverables from any one carrier was approximately 4.7% of the Company’s total shareholders’ equity. Although the Company has not experienced any material credit losses to date, an inability of its reinsurers or retrocessionaires to meet their obligations to it over the relevant exposure periods for any reason could have a material adverse effect on its financial condition and results of operations.

Reserve_for_Losses_and_Loss_Ad

Reserve for Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2013
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]	'
Reserve for losses and loss adjustment expenses	'
	Reserve for Losses and Loss Adjustment Expenses
	The following table represents an analysis of losses and loss adjustment expenses and a reconciliation of the beginning and ending reserve for losses and loss adjustment expenses:


		Year Ended December 31,
		2013			2012			2011
	Reserve for losses and loss adjustment expenses at beginning of year	$	8,933,292		$	8,456,210		$	8,098,454

	Unpaid losses and loss adjustment expenses recoverable	1,829,070			1,818,047			1,703,201

	Net reserve for losses and loss adjustment expenses at beginning of year	7,104,222			6,638,163			6,395,253


	Net incurred losses and loss adjustment expenses relating to losses
	occurring in:
	Current year	1,943,466			2,082,805			2,012,569

	Prior years	(264,042		)	(221,528		)	(285,016		)
	Total net incurred losses and loss adjustment expenses	1,679,424			1,861,277			1,727,553


	Net losses and loss adjustment expense reserves of acquired business	—			31,977			—


	Foreign exchange losses (gains)	1,617			38,184			(32,020		)


	Net paid losses and loss adjustment expenses relating to losses
	occurring in:
	Current year	(288,114		)	(295,984		)	(325,273		)
	Prior years	(1,420,703		)	(1,169,395		)	(1,127,350		)
	Total net paid losses and loss adjustment expenses	(1,708,817		)	(1,465,379		)	(1,452,623		)

	Net reserve for losses and loss adjustment expenses at end of year	7,076,446			7,104,222			6,638,163

	Unpaid losses and loss adjustment expenses recoverable	1,748,250			1,829,070			1,818,047

	Reserve for losses and loss adjustment expenses at end of year	$	8,824,696		$	8,933,292		$	8,456,210

	2013 Prior Year Reserve Development
	During 2013, the Company recorded estimated net favorable development on prior year loss reserves of $264.0 million, which consisted of $218.9 million from the reinsurance segment and $45.1 million from the insurance segment.
	The reinsurance segment’s net favorable development of $218.9 million, or 17.2 points of net earned premium, consisted of $112.1 million from short-tailed lines and $106.8 million of net favorable development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines included $110.1 million from property catastrophe and property other than property catastrophe reserves, primarily from the 2009 to 2012 underwriting years. Contained within this release was favorable development of $28.6 million from the 2005 to 2012 named catastrophic events. The net reduction of loss estimates for the reinsurance segment’s short-tailed lines primarily resulted from varying levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during 2013. Net favorable development of $106.8 million in medium-tailed and long-tailed lines included reductions in casualty reserves of $98.8 million, primarily from the 2003 to 2009 underwriting years, and marine and aviation reserves of $8.1 million, primarily from the 2007 and 2009 underwriting years. The balance of net favorable development was spread across various lines and underwriting years.
	The insurance segment’s net favorable development of $45.1 million, or 2.4 points of net earned premium, consisted of $67.0 million of net favorable development from short-tailed lines, partially offset by $21.9 million of net adverse development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines predominantly consisted of $62.4 million of net favorable development in property lines from the 2008 to 2011 accident years, primarily due to varying levels of reported claims activity, with the balance emanating from lenders products, primarily from the 2011 and 2012 accident years, and travel and accident, primarily from the 2009 and 2010 accident years. Contained within this short tail release was favorable development of $15.9 million from 2005 to 2012 named catastrophic events. Net adverse development in medium-tailed and long-tailed lines of $21.9 million included a net increase of $28.0 million in specialty casualty reserves. Such development primarily stemmed from losses in two captive programs written by the insurance segment's Canadian operation, which was partially offset by favorable development in non-captive business, and from three large excess casualty claims in the insurance segment's U.S. operation, all of the above in the more recent accident years. In addition, the insurance segment experienced $26.2 million of net adverse development in program business, with nearly 90% of this development emanating from a single canceled program whose last inception year was 2011. Such amounts were partially offset by net favorable development spread across various lines and accident years.
	2012 Prior Year Reserve Development
	During 2012, the Company recorded estimated net favorable development on prior year loss reserves of $221.5 million, which consisted of $190.3 million from the reinsurance segment and $31.2 million from the insurance segment.
	The reinsurance segment’s net favorable development of $190.3 million, or 16.8 points of net earned premium, consisted of $117.6 million from short-tailed lines and $72.7 million of net favorable development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines included $92.1 million from property catastrophe and property other than property catastrophe reserves, primarily from the 2008 to 2011 underwriting years. Contained within this release was favorable development of $16.8 million from the 2005 to 2011 named catastrophic events. The net reduction of loss estimates for the reinsurance segment’s short-tailed lines primarily resulted from varying levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during 2012. Net favorable development of $72.7 million in medium-tailed and long-tailed lines included reductions in casualty reserves of $55.9 million, primarily from the 2003 to 2009 underwriting years, and marine and aviation reserves of $16.8 million, primarily from the 2008 to 2010 underwriting years. The balance of net favorable development was spread across various lines and underwriting years.
	The insurance segment’s net favorable development of $31.2 million, or 1.7 points of net earned premium, consisted of $79.3 million of net favorable development from short-tailed lines, partially offset by $48.1 million of net adverse development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines predominantly consisted of $69.0 million of net favorable development in property lines from the 2007 to 2011 accident years, primarily due to varying levels of reported claims activity, with the balance emanating from travel and accident and lender’s products, both primarily from the 2009 to 2011 accident years. Contained within this short tail release was favorable development of $19.1 million from 2005 to 2011 named catastrophic events. Net adverse development in medium-tailed and long-tailed lines of $48.1 million included a net increase of $38.9 million from the insurance segment’s U.K. underwriting operations for the 2007 to 2010 accident years, primarily due to an increase in Australian executive assurance reserves. In addition, U.S. primary specialty casualty reserves reflected a net increase of $23.0 million, primarily from the 2003 to 2005 accident years, and $19.8 million from U.S. professional liability in the two most recent accident years. Such amounts were partially offset by net favorable development spread across various lines and accident years.
	2011 Prior Year Reserve Development
	During 2011, the Company recorded estimated net favorable development on prior year loss reserves of $285.0 million, which consisted of $232.9 million from the reinsurance segment and $52.1 million from the insurance segment.
	The reinsurance segment’s net favorable development of $232.9 million, or 24.4 points of net earned premium, consisted of $118.5 million from short-tailed lines and $114.4 million of net favorable development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines included $97.6 million from property catastrophe and property other than property catastrophe reserves, primarily from the 2007 to 2010 underwriting years. Contained within this release was favorable development of $19.4 million from the 2005 to 2010 named catastrophic events. The net reduction of loss estimates for the reinsurance segment’s short-tailed lines primarily resulted from varying levels of reported and paid claims activity than previously anticipated which led to decreases in certain loss ratio selections during 2011. Net favorable development of $114.4 million in medium-tailed and long-tailed lines included reductions in casualty reserves of $99.0 million, primarily from the 2002 to 2007 underwriting years, and marine and aviation reserves of $15.4 million, primarily from the 2006 to 2010 underwriting years. The balance of net favorable development was spread across various lines and underwriting years.
	The insurance segment’s net favorable development of $52.1 million, or 3.1 points of net earned premium, consisted of $75.7 million of net favorable development from short-tailed lines, partially offset by $23.6 million of net adverse development from medium-tailed and long-tailed lines. Favorable development in short-tailed lines predominantly consisted of $68.5 million of net favorable development in property lines from the 2008 to 2010 accident years, primarily due to varying levels of reported claims activity, with the balance emanating from surety and lender’s products, both primarily from the 2008 to 2010 accident years. Contained within this short tail release was favorable development of $23.0 million from 2005 to 2010 named catastrophic events. Net adverse development in medium-tailed and long-tailed lines of $23.6 million included a net increase of $32.3 million in casualty reserves which consisted of $14.3 million of adverse development, primarily from the 2005 and 2007 accident years, on New York residential contractors business, $8.5 million of adverse development on a 2010 accident year energy casualty claim, and $9.5 million from other commercial claims. In addition, there was a net increase of $9.8 million in program business, primarily from the 2003 and 2004 accident years. Such amounts were partially offset by net favorable development spread across various lines and accident years.

Investment_Information

Investment Information	12 Months Ended
	Dec. 31, 2013
Disclosure Investment Information [Abstract]	'
Investment Information	'
	Investment Information
	Available For Sale Securities
	The following table summarizes the fair value and cost or amortized cost of the Company’s securities classified as available for sale:


		Estimated			Gross			Gross				Cost or			OTTI
		Fair			Unrealized			Unrealized				Amortized			Unrealized
		Value			Gains			Losses				Cost			Losses (2)
	31-Dec-13
	Fixed maturities and fixed maturities pledged
	under securities lending agreements (1):
	Corporate bonds	$	2,267,263		$	35,289		$	(35,537	)		$	2,267,511		$	(16	)

	Mortgage backed securities	1,133,095			16,270			(22,209		)		1,139,034			(9,269		)

	Municipal bonds	1,481,738			29,378			(9,730		)		1,462,090			(17		)

	Commercial mortgage backed securities	1,074,497			13,972			(15,224		)		1,075,749			(199		)

	U.S. government and government agencies	1,301,809			3,779			(11,242		)		1,309,272			(19		)

	Non-U.S. government securities	1,085,861			14,729			(19,363		)		1,090,495			—

	Asset backed securities	1,332,594			20,033			(13,795		)		1,326,356			(3,422		)

	Total	9,676,857			133,450			(127,100		)		9,670,507			(12,942		)

	Equity securities	496,824			69,487			(5,938		)		433,275			—

	Other investments	498,310			28,082			(18,459		)		488,687			—

	Short-term investments	1,478,367			1,654			(871		)		1,477,584			—

	Total	$	12,150,358		$	232,673		$	(152,368	)		$	12,070,053		$	(12,942	)


	31-Dec-12
	Fixed maturities and fixed maturities pledged
	under securities lending agreements (1):
	Corporate bonds	$	2,857,513		$	105,798		$	(6,710	)		$	2,758,425		$	(62	)

	Mortgage backed securities	1,532,736			24,809			(7,484		)		1,515,411			(9,329		)

	Municipal bonds	1,463,586			62,322			(1,421		)		1,402,685			(17		)

	Commercial mortgage backed securities	824,165			37,514			(4,468		)		791,119			(270		)

	U.S. government and government agencies	1,131,688			20,178			(1,095		)		1,112,605			(19		)

	Non-U.S. government securities	998,901			33,701			(8,860		)		974,060			—

	Asset backed securities	1,073,999			25,528			(5,838		)		1,054,309			(3,346		)

	Total	9,882,588			309,850			(35,876		)		9,608,614			(13,043		)

	Equity securities	312,749			26,625			(12,290		)		298,414			—

	Other investments	549,280			32,582			(3,257		)		519,955			—

	Short-term investments	730,369			3,521			(1,248		)		728,096			—

	Total	$	11,474,986		$	372,578		$	(52,671	)		$	11,155,079		$	(13,043	)


-1	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged. See “—Securities Lending Agreements.”

-2	Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At December 31, 2013, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $6.0 million, compared to a net unrealized gain of $2.0 million at December 31, 2012.
The following table summarizes, for all available for sale securities in an unrealized loss position, the fair value and gross unrealized loss by length of time the security has been in a continual unrealized loss position:


	Less than 12 Months						12 Months or More							Total
	Estimated			Gross			Estimated				Gross			Estimated				Gross
	Fair			Unrealized			Fair				Unrealized			Fair				Unrealized
	Value			Losses			Value				Losses			Value				Losses
31-Dec-13
Fixed maturities and fixed maturities pledged under securities lending agreements (1):
Corporate bonds	$	1,183,625		$	(32,837	)	$	46,673			$	(2,700	)	$	1,230,298			$	(35,537	)

Mortgage backed securities	778,693			(20,253		)	43,634				(1,956		)	822,327				(22,209		)

Municipal bonds	589,009			(9,422		)	6,092				(308		)	595,101				(9,730		)

Commercial mortgage backed securities	677,617			(15,110		)	1,612				(114		)	679,229				(15,224		)

U.S. government and government agencies	1,144,809			(11,242		)	—				—			1,144,809				(11,242		)

Non-U.S. government securities	821,506			(15,776		)	24,334				(3,587		)	845,840				(19,363		)

Asset backed securities	692,362			(10,431		)	88,629				(3,364		)	780,991				(13,795		)

Total	5,887,621			(115,071		)	210,974				(12,029		)	6,098,595				(127,100		)

Equity securities	76,563			(5,938		)	0				0			76,563				(5,938		)

Other investments	165,891			(15,775		)	47,316				(2,684		)	213,207				(18,459		)

Short-term investments	28,170			(871		)	—				—			28,170				(871		)

Total	$	6,158,245		$	(137,655	)	$	258,290			$	(14,713	)	$	6,416,535			$	(152,368	)


31-Dec-12
Fixed maturities and fixed maturities pledged under securities lending agreements (1):
Corporate bonds	$	490,784		$	(3,692	)	$	52,334			$	(3,018	)	$	543,118			$	(6,710	)

Mortgage backed securities	537,883			(4,290		)	60,574				(3,194		)	598,457				(7,484		)

Municipal bonds	147,766			(1,120		)	7,052				(301		)	154,818				(1,421		)

Commercial mortgage backed securities	36,649			(2,261		)	8,878				(2,207		)	45,527				(4,468		)

U.S. government and government agencies	146,526			(1,095		)	—				—			146,526				(1,095		)

Non-U.S. government securities	244,827			(1,070		)	135,564				(7,790		)	380,391				(8,860		)

Asset backed securities	234,584			(1,508		)	57,371				(4,330		)	291,955				(5,838		)

Total	1,839,019			(15,036		)	321,773				(20,840		)	2,160,792				(35,876		)

Equity securities	130,385			(10,200		)	16,469				(2,090		)	146,854				(12,290		)

Other investments	23,849			(2,474		)	35,083				(783		)	58,932				(3,257		)

Short-term investments	57,415			(1,248		)	—				—			57,415				(1,248		)

Total	$	2,050,668		$	(28,958	)	$	373,325			$	(23,713	)	$	2,423,993			$	(52,671	)


-1	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged. See “—Securities Lending Agreements.”
At December 31, 2013, on a lot level basis, approximately 2,080 security lots out of a total of approximately 4,400 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 $3.5 million. At December 31, 2012, on a lot level basis, approximately 910 security lots out of a total of approximately 4,580 security lots were in an unrealized loss position and the largest single unrealized loss from a single lot in the Company’s fixed maturity portfolio was $2.5 million.
The contractual maturities of the Company’s fixed maturities and fixed maturities pledged under securities lending agreements are shown in the following table. Expected maturities, which are management’s best estimates, will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.


	December 31, 2013						December 31, 2012
Maturity	Estimated Fair Value			Amortized Cost			Estimated Fair Value				Amortized Cost
Due in one year or less	$	235,330		$	232,652		$	446,402			$	436,376

Due after one year through five years	3,738,500			3,718,920			3,876,062				3,769,426

Due after five years through 10 years	1,966,536			1,979,510			1,949,297				1,869,698

Due after 10 years	196,305			198,286			179,927				172,275

	6,136,671			6,129,368			6,451,688				6,247,775

Mortgage backed securities	1,133,095			1,139,034			1,532,736				1,515,411

Commercial mortgage backed securities	1,074,497			1,075,749			824,165				791,119

Asset backed securities	1,332,594			1,326,356			1,073,999				1,054,309

Total	$	9,676,857		$	9,670,507		$	9,882,588			$	9,608,614

Securities Lending Agreements
The Company operates a securities lending program under which certain of its fixed income portfolio securities are loaned to third parties, primarily major brokerage firms, for short periods of time through a lending agent. 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. At December 31, 2013, the fair value and amortized cost of fixed maturities and short-term investments pledged under securities lending agreements were $105.1 million and $105.9 million, respectively, compared to $50.8 million and $49.6 million at December 31, 2012, respectively. At December 31, 2013, the portfolio of collateral backing the Company’s securities lending program included sub-prime securities with a fair value of $6.3 million with an average credit quality of “CCC/Caa3” from Standard & Poor’s Rating Services (“S&P”)/ Moody’s Investors Service (“Moody’s”), compared to a fair value of $5.4 million with an average credit quality of “CCC/Caa2” from S&P/Moody’s at December 31, 2012.
Other Investments
The following table summarizes the Company’s other investments, including available for sale and fair value option components:


	December 31,
	2013			2012
Available for sale securities:
Asian and emerging markets	$	331,984		$	316,860

Investment grade fixed income	159,115			220,410

Other	7,211			12,010

Total available for sale	498,310			549,280

Fair value option:
Term loan investments (par value: $494,502 and $307,016)	512,076			308,596

Asian and emerging markets	14,054			24,035

Investment grade fixed income	75,062			67,624

Non-investment grade fixed income	—			11,093

Other	172,088			116,623

Total fair value option	773,280			527,971

Total	$	1,271,590		$	1,077,251

Certain of the Company’s other investments are in investment funds for which the Company has the option to redeem at agreed upon values as described in each investment fund’s subscription agreement. Depending on the terms of the various subscription agreements, investments in investment funds may be redeemed daily, monthly, quarterly or on other terms. Two common redemption restrictions which may impact the Company’s ability to redeem these investment funds are gates and lockups. A gate is a suspension of redemptions which may be implemented by the general partner or investment manager of the fund in order to defer, in whole or in part, the redemption request in the event the aggregate amount of redemption requests exceeds a predetermined percentage of the investment fund's net assets which may otherwise hinder the general partner or investment manager's ability to liquidate holdings in an orderly fashion in order to generate the cash necessary to fund extraordinarily large redemption payouts. A lockup period is the initial amount of time an investor is contractually required to hold the security before having the ability to redeem. If the investment funds are eligible to be redeemed, the time to redeem such fund can take weeks or months following the notification.
Fair Value Option
The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option:


	December 31,
	2013			2012
Fixed maturities	$	448,254		$	363,541

Other investments	773,280			527,971

Equity securities	—			25,954

Investments accounted for using the fair value option	1,221,534			917,466

Securities sold but not yet purchased (1)	—			(6,924		)

Net assets accounted for using the fair value option	$	1,221,534		$	910,542


-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.
Net Investment Income
The components of net investment income were derived from the following sources:


	Year Ended December 31,
	2013			2012			2011
Fixed maturities	$	249,833		$	281,140		$	331,469

Term loan investments	20,608			15,283			2,854

Equity securities	8,919			7,963			7,332

Short-term investments	1,259			1,980			2,174

Other (1)	19,710			14,196			19,152

Gross investment income	300,329			320,562			362,981

Investment expenses	(33,110		)	(25,667		)	(24,783		)
Net investment income	$	267,219		$	294,895		$	338,198


-1	Includes dividends on investment funds and other items.
Net Realized Gains (Losses)
Net realized gains (losses) were as follows, excluding the other-than-temporary impairment provisions discussed above:


	Year Ended December 31,
	2013			2012			2011
Available for sale securities:
Gross gains on investment sales	$	239,421		$	247,291		$	271,818

Gross losses on investment sales	(203,077		)	(71,722		)	(132,166		)
Change in fair value of assets and liabilities
accounted for using the fair value option:
Fixed maturities	54			13,195			(12,164		)

Equity securities	704			(73		)	(31,519		)

Other investments	17,503			7,383			(3,272		)

Derivative instruments (1)	20,912			(1,326		)	19,851

Other	(1,499		)	(520		)	(1,902		)
Net realized gains	$	74,018		$	194,228		$	110,646


-1	See Note 9 for information on the Company’s derivative instruments.

Other-Than-Temporary Impairments
The Company performs quarterly reviews of its available for sale investments in order to determine whether declines in fair value below the amortized cost basis were considered other-than-temporary in accordance with applicable guidance. The following table details the net impairment losses recognized in earnings by asset class:


	Year Ended December 31,
	2013			2012			2011
Fixed maturities:
Mortgage backed securities	$	(295	)	$	(2,491	)	$	(5,023	)
Corporate bonds	(88		)	(1,512		)	(931		)
Non-U.S. government securities	—			(261		)	—

Commercial mortgage backed securities	—			(211		)	—

Asset backed securities	(128		)	(127		)	(10		)
U.S. government and government agencies	—			(10		)	—

Total	(511		)	(4,612		)	(5,964		)
Investment of funds received under securities lending agreements	—			(87		)	(1,623		)

Equity securities	(3,275		)	(6,689		)	(1,475		)
Net impairment losses recognized in earnings	$	(3,786	)	$	(11,388	)	$	(9,062	)
A description of the methodology and significant inputs used to measure the amount of net impairment losses recognized in earnings in 2013 is as follows:

•	Equity securities – the Company utilized information received from asset managers on common stocks, including the business prospects, recent events, industry and market data and other factors. For certain equities which were in an unrealized loss position and where the Company determined that it did not have the intent or ability to hold such securities for a reasonable period of time by which the fair value of the securities would increase and the Company would recover its cost, the cost basis of such securities was adjusted down accordingly;

•	Mortgage backed securities – the Company utilized underlying data provided by asset managers, cash flow projections and additional information from credit agencies in order to determine an expected recovery value for each security. The analysis includes expected cash flow projections under base case and stress case scenarios which modify the expected default expectations and loss severities and slow down prepayment assumptions. The significant inputs in the models include the expected default rates, delinquency rates and foreclosure costs. The expected recovery values were reduced on a number of mortgage backed securities, primarily as a result of increases in expected default expectations and foreclosure costs. The amortized cost basis of the mortgage backed securities were adjusted down, if required, to the expected recovery value calculated in the OTTI review process;

•	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. The amortized cost basis of the corporate bonds was adjusted down, if required, to the expected recovery value calculated in the OTTI review process.
The Company believes that the $12.9 million of OTTI included in accumulated other comprehensive income at December 31, 2013 on the securities which were considered by the Company to be impaired was due to market and sector-related factors (i.e., not credit losses). At December 31, 2013, the Company did not intend to sell these securities, or any other securities which were in an unrealized loss position, and determined that it is more likely than not that the Company will not be required to sell such securities before recovery of their cost basis.
The following table provides a roll forward of the amount related to credit losses recognized in earnings for which a portion of an OTTI was recognized in accumulated other comprehensive income:


	Year Ended December 31,
	2013			2012			2011
Balance at start of year	$	62,001		$	66,545		$	86,040

Credit loss impairments recognized on securities not previously impaired	423			1,962			3,736

Credit loss impairments recognized on securities previously impaired	88			2,735			3,850

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	(2,450		)	(9,241		)	(27,081		)
Balance at end of year	$	60,062		$	62,001		$	66,545

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 14, “Commitments and Contingencies—Letter of Credit and Revolving Credit Facilities,” for further details. The following table details the value of the Company’s restricted assets:


	December 31,
	2013			2012
Assets used for collateral or guarantees:
Affiliated transactions	$	4,060,533		$	4,062,097

Third party agreements	856,890			771,631

Deposits with U.S. regulatory authorities	302,809			290,441

Deposits with non-U.S. regulatory authorities	6,546			247,321

Trust funds	75,264			96,342

Total restricted assets	$	5,302,042		$	5,467,832

Investment Funds Accounted For Using the Equity Method
The Company recorded equity in net income related to investment funds accounted for using the equity method of $35.7 million for 2013, compared to equity in net income of $73.5 million for 2012 and equity in net loss of $9.6 million for 2011, respectively. Due to the ownership structure of these investment funds (e.g., limited partnership), the Company uses the equity method where it does not have a controlling interest and is not the primary beneficiary. In applying the equity method, these investments are initially recorded at cost and are subsequently adjusted based on the Company’s proportionate share of the net income or loss of the funds (which include changes in the fair value of the underlying securities in the funds). Such investments are generally recorded on a one month lag with some investments reported on a three month lag based on the availability of reports from the investment funds. Changes in the carrying value of such investments are recorded in net income as “Equity in net income (loss) of investment funds accounted for using the equity method.” As such, fluctuations in the carrying value of the investment funds accounted for using the equity method may increase the volatility of the Company’s reported results of operations. Investment funds accounted for using the equity method (excluding the Company’s investment in Aeolus LP) totaled $242.3 million at December 31, 2013, compared to $302.5 million at December 31, 2012.

Investment_in_Joint_Venture

Investment in Joint Venture	12 Months Ended
Investment in Joint Venture	Dec. 31, 2013
Equity Method Investments and Joint Ventures [Abstract]	'
Equity Method Investments and Joint Ventures Disclosure [Text Block]	'
	Investment in Joint Venture
	In May 2008, the Company provided $100.0 million of funding to Gulf Reinsurance Limited (“Gulf Re”), a newly formed reinsurer based in the Dubai International Financial Centre, pursuant to the joint venture agreement with Gulf Investment Corporation GSC (“GIC”). Under the agreement, Arch Re Bermuda and GIC each own 50% of Gulf Re, which commenced underwriting activities in June 2008. Gulf Re provides property and casualty reinsurance primarily in the member states of the Gulf Cooperation Council, which include Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates. The initial capital of the joint venture consisted of $200.0 million with an additional $200.0 million commitment to be funded equally by the Company and GIC depending on the joint venture’s business needs. The Company accounts for its investment in Gulf Re, shown as “Investment in joint venture,” using the equity method and records its equity in the operating results of Gulf Re in “Other income” on a quarter lag basis.

Fair_Value

Fair Value	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value	'
	Fair Value
	Accounting guidance regarding fair value measurements addresses how companies should measure fair value when they are required to use a fair value measure for recognition or disclosure purposes under GAAP and provides a common definition of fair value to be used throughout GAAP. It defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly fashion between market participants at the measurement date. In addition, it establishes a three-level valuation hierarchy for the disclosure of fair value measurements. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. The level in the hierarchy within which a given fair value measurement falls is determined based on the lowest level input that is significant to the measurement (Level 1 being the highest priority and Level 3 being the lowest priority).
	The levels in the hierarchy are defined as follows:

	Level 1:	Inputs to the valuation methodology are observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets

	Level 2:	Inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets, and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument

	Level 3:	Inputs to the valuation methodology are unobservable and significant to the fair value measurement
	Fair Value Measurements on a Recurring Basis
	Following is a description of the valuation methodologies used for securities measured at fair value, as well as the general classification of such securities pursuant to the valuation hierarchy.
	The Company 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 including a review of deep dive reports on selected securities which indicate the use of observable inputs in the pricing process; (iv) comparing the fair value estimates to its 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. For a majority of investments, the Company obtained multiple quotes. 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. At December 31, 2013, the Company adjusted certain prices (primarily on structured securities) obtained from the pricing services and substituted alternate prices (primarily broker-dealer quotes) for such securities. Such adjustments did not have a material impact on the overall fair value of the Company’s investment portfolio at December 31, 2013.
	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. In addition, pricing vendors use model processes, such as an Option Adjusted Spread model, to develop prepayment and interest rate scenarios. The Option Adjusted Spread model is commonly used to estimate fair value for securities such as mortgage backed and asset backed securities. 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 $13.4 billion of financial assets and liabilities measured at fair value at December 31, 2013, approximately $1.33 billion, or 9.9%, were priced using non-binding broker-dealer quotes. Of the $12.4 billion of financial assets and liabilities measured at fair value at December 31, 2012, approximately $927.9 million, or 7.5%, were priced using non-binding broker-dealer quotes.
	The Company reviews its securities measured at fair value and discusses the proper classification of such investments with investment advisors and others. A discussion of the general classification of the Company’s financial instruments follows:
	Fixed maturities. The Company 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. Where the Company believes that quoted market prices are not available or that the market is not active, fair values are estimated by using quoted prices of securities with similar characteristics, pricing models or matrix pricing and are generally classified as Level 2 securities. The Company determined that Level 2 securities included corporate bonds, mortgage backed securities, municipal bonds, asset backed securities and non-U.S. government securities. The Company determined that certain Euro-denominated corporate bonds which invest in underlying portfolios of fixed income securities for which there is a low level of transparency around inputs to the valuation process should be classified within Level 3 of the valuation hierarchy and certain other corporate bonds.
	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 fair values for certain of the Company's other investments are determined using net asset values (“NAV”) as advised by external fund managers. The NAV is based on the fund manager's valuation of the underlying holdings in accordance with the fund's governing documents. Periodically, the Company performs a number of monitoring procedures in order to assess the quality of the NAVs, including regular review and discussion of each fund's performance, regular evaluation of fund performance against applicable benchmarks and the backtesting of the NAVs against audited and interim financial statements. Other investments with liquidity terms allowing the Company to substantially redeem its holdings in a short time frame at the applicable NAV are reflected in Level 2. Other investments with redemption restrictions that prevent the Company from redeeming in the near term are classified in Level 3 of the valuation hierarchy.

	Short-term investments. The Company determined that certain of its short-term investments held in highly liquid money market-type funds would be included in Level 1 as their fair values are based on quoted market prices in active markets. Other short-term investments are classified in Level 2 of the valuation hierarchy.

	The Company reviews the classification of its investments each quarter. No transfers were made between Level 1 and Level 2 in 2011, 2012 or 2013. In the 2012 fourth quarter, the Company determined that certain other investments priced using a NAV would be included in Level 3 due to a review of the redemption restrictions discussed above. This resulted in a transfer of $257.8 million from Level 2 into Level 3 in the 2012 fourth quarter. In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged under securities lending agreements. For purposes of the following tables, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged under securities lending agreements, at fair value.
	The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2013:


					Fair Value Measurement Using:
		Estimated			Quoted Prices in Active Markets for Identical Assets			Significant Other Observable Inputs			Significant Unobservable Inputs
		Fair Value			(Level 1)			(Level 2)			(Level 3)
	Assets measured at fair value:
	Available for sale securities:
	Fixed maturities and fixed maturities pledged under securities lending agreements (1):
	Corporate bonds	$	2,267,263		$	—		$	2,265,218		$	2,045

	Mortgage backed securities	1,133,095			—			1,133,095			—

	Municipal bonds	1,481,738			—			1,481,738			—

	Commercial mortgage backed securities	1,074,497			—			1,074,497			—

	U.S. government and government agencies	1,301,809			1,301,809			—			—

	Non-U.S. government securities	1,085,861			—			1,085,861			—

	Asset backed securities	1,332,594			—			1,332,594			—

	Total	9,676,857			1,301,809			8,373,003			2,045

	Equity securities	496,824			496,738			86			—

	Other investments	498,310			—			327,890			170,420

	Short-term investments	1,478,367			1,427,744			50,623			—

	Fair value option:
	Investments accounted for using the fair value option:
	Corporate bonds	334,065			—			334,065			—

	Non-U.S. government bonds	73,156			—			73,156			—

	Mortgage backed securities	41,033			—			41,033			—

	Other investments	773,280			—			395,755			377,525

	Total	1,221,534			—			844,009			377,525

Total assets measured at fair value	$	13,371,892		$	3,226,291		$	9,595,611		$	549,990


-1	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged.
The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2012:


				Fair Value Measurement Using:
	Estimated			Quoted Prices in Active Markets for Identical Assets			Significant Other Observable Inputs			Significant Unobservable Inputs
	Fair Value			(Level 1)			(Level 2)			(Level 3)
Assets measured at fair value:
Available for sale securities:
Fixed maturities and fixed maturities pledged under securities lending agreements (1):
Corporate bonds	$	2,857,513		$	—		$	2,759,109		$	98,404

Mortgage backed securities	1,532,736			—			1,532,736			—

Municipal bonds	1,463,586			—			1,463,586			—

Commercial mortgage backed securities	824,165			—			824,165			—

U.S. government and government agencies	1,131,688			1,131,688			—			—

Non-U.S. government securities	998,901			—			998,901			—

Asset backed securities	1,073,999			—			1,073,999			—

Total	9,882,588			1,131,688			8,652,496			98,404

Equity securities	312,749			312,666			83			—

Other investments	549,280			—			365,078			184,202

Short-term investments	730,369			678,441			51,928			—

Fair value option:
Investments accounted for using the fair value option:
Corporate bonds	275,132			—			275,132			—

Non-U.S. government bonds	88,409			—			88,409			—

Equity securities	25,954			25,954			—			—

Other investments	527,971			—			332,621			195,350

Total	917,466			25,954			696,162			195,350

Total assets measured at fair value	$	12,392,452		$	2,148,749		$	9,765,747		$	477,956


Liabilities measured at fair value:
Fair value option:
Securities sold but not yet purchased (2)	6,924			6,924			—			—

Total liabilities measured at fair value	$	6,924		$	6,924		$	—		$	—


-1	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged.

-2	Represents the Company’s obligation 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.
The following table presents a reconciliation of the beginning and ending balances for all investments measured at fair value on a recurring basis using Level 3 inputs for 2013, 2012 and 2011:


	Fair Value Measurements Using:
	Significant Unobservable Inputs (Level 3)
	Available for sale						Fair value option
	Corporate Bonds			Other Investments			Other Investments			Total
Year Ended December 31, 2013
Balance at beginning of year	$	98,404		$	184,202		$	195,350		$	477,956

Total gains or (losses) (realized/unrealized)
Included in earnings (1)	4,679			8,915			11,743			25,337

Included in other comprehensive income	(3,051		)	473			—			(2,578		)

Purchases, issuances and settlements
Purchases	—			25,000			275,067			300,067

Issuances	—			—			—			—

Sales	(96,655		)	0			(20,156		)	(116,811		)

Settlements	(1,332		)	(48,170		)	(84,479		)	(133,981		)
Transfers in and/or out of Level 3	—			—			—			—

Balance at end of year	$	2,045		$	170,420		$	377,525		$	549,990


Year Ended December 31, 2012
Balance at beginning of year	$	92,091		$	5,124		$	—		$	97,215

Total gains or (losses) (realized/unrealized)
Included in earnings (1)	4,419			1,829			(611		)	5,637

Included in other comprehensive income	2,049			1,026			—			3,075

Purchases, issuances and settlements
Purchases	—			25,000			91,232			116,232

Issuances	—			—			—			—

Sales	0			0			—			0

Settlements	(155		)	(1,830		)	—			(1,985		)

Transfers in and/or out of Level 3	—			153,053			104,729			257,782

Balance at end of year	$	98,404		$	184,202		$	195,350		$	477,956


Year Ended December 31, 2011
Balance at beginning of year	$	153,509		$	7,858		$	—		$	161,367

Total gains or (losses) (realized/unrealized)
Included in earnings (1)	2,276			1,709			—			3,985

Included in other comprehensive income	(4,515		)	(3,777		)	—			(8,292		)

Purchases, issuances and settlements
Purchases	—			—			—			—

Issuances	—			—			—			—

Sales	(49,947		)	(666		)	—			(50,613		)

Settlements	(9,232		)	—			—			(9,232		)

Transfers in and/or out of Level 3	—			—			—			—

Balance at end of year	$	92,091		$	5,124		$	—		$	97,215


-1	Gains or losses on corporate bonds and other investments were recorded in net realized gains (losses).
The amount of total gains for 2013 included in earnings attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2013 was $22.0 million. The amount of total gains for 2012 included in earnings attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2012 was $5.6 million. The amount of total gains for 2011 included in earnings attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2011 was $0.6 million.
Fair Value Measurements on a Non-Recurring Basis
The Company measures the fair value of certain assets on a non-recurring basis, generally quarterly, annually, or when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. These assets include investment funds accounted for using the equity method, investment in joint venture, certain other investments, goodwill and intangible assets, and long-lived assets. The Company uses a variety of techniques to measure the fair value of these assets when appropriate, as described below:
Investments accounted for using the equity method and Investment in joint venture. When the Company determines that the carrying value of these assets may not be recoverable, the Company records the assets at fair value with the loss recognized in income. In such cases, the Company measures the fair value of these assets using the techniques discussed above in “—Fair Value Measurements on a Recurring Basis.”
Goodwill and Intangible Assets. The goodwill and intangible assets of acquired businesses, which totaled $27.3 million and $38.3 million, respectively, at December 31, 2013 and 2012, is included in “Other assets” in the Company’s balance sheet and represents the difference between the purchase price and the fair value of the net tangible assets of the acquired businesses. The Company tests goodwill and intangible assets for impairment whenever events or changes in circumstances indicate the carrying amount may not be recoverable, but at least annually for goodwill. When the Company determines goodwill and intangible assets may be impaired, the Company uses techniques including discounted expected future cash flows, to measure fair value.
Long-Lived Assets. The Company tests its long-lived assets for impairment whenever events or changes in circumstances indicate the carrying amount of a long-lived asset may not be recoverable.

Derivative_Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments	'
	Derivative Instruments
	The Company’s investment strategy allows for the use of derivative securities. The fair values of those derivatives are based on quoted market prices. 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. Certain of the Company’s corporate bonds are managed in a global bond portfolio which incorporates the use of foreign currency forward contracts which are intended to provide an economic hedge against foreign currency movements on the portfolio’s non-U.S. Dollar denominated holdings. The Company routinely utilizes other foreign currency forward contracts, currency options, index futures contracts and other derivatives as part of its total return objective.

	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. The fair value of TBAs is included in “fixed maturities available for sale, at fair value.”



		Asset			Liability Derivatives			Net
		Derivatives						Derivatives
		Fair Value			Fair Value			Fair Value			Notional Value
	31-Dec-13

	Futures contracts	$	461		$	(110	)	$	351		$	475,967

	Foreign currency forward contracts	5,023			(3,090		)	1,933			330,746

	TBAs	33,455			(21,731		)	11,724			56,160

	Other	920			(1,541		)	(621		)	347,916

	Total	$	39,859		$	(26,472	)	$	13,387


	31-Dec-12

	Futures contracts	$	52		$	(52	)	$	—		$	340,400

	Foreign currency forward contracts	2,809			(2,678		)	131			396,468

	TBAs	23,599			(4,346		)	19,253			26,000

	Other	448			(676		)	(228		)	50,341

	Total	$	26,908		$	(7,752	)	$	19,156


	The Company's derivative instruments are generally traded under master netting agreements or similar arrangements, which establish terms that apply to all derivative transactions with a counterparty. In the event of a bankruptcy or other stipulated event of default, such agreements provide that the non-defaulting party may elect to terminate all outstanding derivative transactions, in which case all individual derivative positions (loss or gain) with a counterparty are closed out and netted and replaced with a single amount, usually referred to as the termination amount, which is expressed in a single currency. The resulting single net amount, where positive, is payable to the party "in-the-money" regardless of whether or not it is the defaulting party, unless the parties have agreed that only the non-defaulting party is entitled to receive a termination payment where the net amount is positive and is in its favor. Effectively, contractual close-out netting reduces derivatives credit exposure from gross to net exposure. At December 31, 2013, asset derivatives and liability derivatives of $28.0 million and $14.6 million, respectively, were subject to a master netting agreement or similar arrangement, compared to $26.9 million and $7.8 million, respectively, at December 31, 2012. The remaining derivatives included in the table above were not subject to a master netting agreement.

	The following table summarizes derivative instrument activity, which is reflected as net realized gains or losses in the consolidated statements of operations:


	Derivatives not designated	Year Ended December 31,
	as hedging instruments	2013			2012			2011
	Futures contracts	$	10,742		$	(3,307	)	$	2,293

	Foreign currency forward contracts	9,762			(214		)	895

	TBAs	(1,623		)	4,413			12,329

	Other	2,031			(2,218		)	4,334

	Total	$	20,912		$	(1,326	)	$	19,851

Other_Comprehensive_Income_Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2013
Comprehensive Income Note Disclosure [Abstract]	'
Other Comprehensive Income (Loss)	'
	Other Comprehensive Income (Loss)
	The following table presents the changes in each component of accumulated other comprehensive income ("AOCI"), net of tax:


		Unrealized Appreciation on Available-For-Sale Investments				Foreign Currency Translation Adjustments				Total
	Year Ended December 31, 2013
	Beginning balance	$	289,956			$	(2,939	)		$	287,017

	Other comprehensive income (loss) before reclassifications	(176,578		)		(2,789		)		(179,367		)
	Amounts reclassified from accumulated other comprehensive income	(32,686		)		—				(32,686		)

	Net current period other comprehensive income (loss)	(209,264		)		(2,789		)		(212,053		)
	Ending balance	$	80,692			$	(5,728	)		$	74,964


	Year Ended December 31, 2012
	Beginning balance	$	174,636			$	(20,713	)		$	153,923

	Other comprehensive income (loss) before reclassifications	273,144				17,774				290,918

	Amounts reclassified from accumulated other comprehensive income	(157,824		)		—				(157,824		)

	Net current period other comprehensive income (loss)	115,320				17,774				133,094

	Ending balance	$	289,956			$	(2,939	)		$	287,017


	Year Ended December 31, 2011
	Beginning balance	$	213,927			$	(9,424	)		$	204,503

	Other comprehensive income (loss) before reclassifications	84,271				(11,289		)		72,982

	Amounts reclassified from accumulated other comprehensive income	(123,562		)		—				(123,562		)

	Net current period other comprehensive income (loss)	(39,291		)		(11,289		)		(50,580		)
	Ending balance	$	174,636			$	(20,713	)		$	153,923


	The following table presents details about amounts reclassified from accumulated other comprehensive income:


			Consolidated Statement of Income		Amounts Reclassed from AOCI
			Line Item That Includes		Year Ended December 31,
	Details About AOCI Components		Reclassification		2013				2012				2011

	Unrealized appreciation on available-for-sale investments
			Net realized gains		$	39,308			$	180,144			$	139,752

			Other-than-temporary impairment losses		(3,961		)		(12,175		)		(13,850		)
			Total before tax		35,347				167,969				125,902

			Income tax expense		(2,661		)		(10,145		)		(2,340		)
			Net of tax		$	32,686			$	157,824			$	123,562


	Following are the related tax effects allocated to each component of other comprehensive income (loss):


		Before				Tax				Net
		Tax				Expense				of Tax
		Amount				(Benefit)				Amount
	Year Ended December 31, 2013
	Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding losses arising during period	$	(201,386	)		$	(24,983	)		$	(176,403	)
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss)	(175		)		—				(175		)

Less reclassification of net realized gains included in net income	35,347				2,661				32,686

Foreign currency translation adjustments	(2,789		)		—				(2,789		)

Other comprehensive income (loss)	$	(239,697	)		$	(27,644	)		$	(212,053	)
Year Ended December 31, 2012
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains arising during period	$	278,917			$	4,986			$	273,931

Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss)	(787		)		—				(787		)

Less reclassification of net realized gains included in net income	167,969				10,145				157,824

Foreign currency translation adjustments	18,748				974				17,774

Other comprehensive income (loss)	$	128,909			$	(4,185	)		$	133,094

Year Ended December 31, 2011
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains arising during period	$	108,046			$	18,987			$	89,059

Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss)	(4,788		)		—				(4,788		)

Less reclassification of net realized gains included in net income	125,902				2,340				123,562

Foreign currency translation adjustments	(12,461		)		(1,172		)		(11,289		)
Other comprehensive income	$	(35,105	)		$	15,475			$	(50,580	)

Earnings_Per_Common_Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Earnings Per Common Share	'
	Earnings Per Common Share
	The calculation of basic earnings per common share excludes dilutive securities and is computed by dividing income available to common shareholders by the weighted average number of Common Shares, including vested restricted shares, outstanding for the periods. The following table sets forth the computation of basic and diluted earnings per common share:


		Year Ended December 31,
		2013			2012			2011
	Numerator:
	Net income	$	709,731		$	593,397		$	436,163

	Preferred dividends	(21,938		)	(25,079		)	(25,844		)
	Loss on repurchase of preferred shares	—			(10,612		)	—

	Net income available to common shareholders	$	687,793		$	557,706		$	410,319


	Denominator:
	Weighted average common shares outstanding – basic	131,355,392			134,446,158			132,221,970

	Effect of dilutive common share equivalents:
	Nonvested restricted shares	1,090,100			857,174			940,612

	Stock options (1)	3,331,691			2,955,515			5,127,120

	Weighted average common shares and common share	135,777,183			138,258,847			138,289,702
	equivalents outstanding – diluted

	Earnings per common share:
	Basic	$	5.24		$	4.15		$	3.1

	Diluted	$	5.07		$	4.03		$	2.97


	-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 2013, 2012 and 2011, the number of stock options excluded were 892,439, 839,414 and 462,020, respectively.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes
	ACGL is incorporated under the laws of Bermuda and, under current Bermuda law, is not obligated to pay any taxes in Bermuda based upon income or capital gains. The Company has received a written undertaking from the Minister of Finance in Bermuda under the Exempted Undertakings Tax Protection Act 1966 that, in the event that any legislation is enacted in Bermuda imposing any tax computed on profits, income, gain or appreciation on any capital asset, or any tax in the nature of estate duty or inheritance tax, such tax will not be applicable to ACGL or any of its operations until March 31, 2035. This undertaking does not, however, prevent the imposition of taxes on any person ordinarily resident in Bermuda or any company in respect of its ownership of real property or leasehold interests in Bermuda.
	ACGL and its non-U.S. subsidiaries will be subject to U.S. federal income tax only to the extent that they derive U.S. source income that is subject to U.S. withholding tax or income that is effectively connected with the conduct of a trade or business within the U.S. and is not exempt from U.S. tax under an applicable income tax treaty with the U.S. ACGL and its non-U.S. subsidiaries will be subject to a withholding tax on dividends from U.S. investments and interest from certain U.S. payors (subject to reduction by any applicable income tax treaty). ACGL and its non-U.S. subsidiaries intend to conduct their operations in a manner that will not cause them to be treated as engaged in a trade or business in the United States and, therefore, will not be required to pay U.S. federal income taxes (other than U.S. excise taxes on insurance and reinsurance premium and withholding taxes on dividends and certain other U.S. source investment income). However, because there is uncertainty as to the activities which constitute being engaged in a trade or business within the United States, there can be no assurances that the U.S. Internal Revenue Service will not contend successfully that ACGL or its non-U.S. subsidiaries are engaged in a trade or business in the United States. If ACGL or any of its non-U.S. subsidiaries were subject to U.S. income tax, ACGL’s shareholders’ equity and earnings could be materially adversely affected. ACGL has subsidiaries and branches that operate in various jurisdictions around the world that are subject to tax in the jurisdictions in which they operate. The significant jurisdictions in which ACGL’s subsidiaries and branches are subject to tax include the United States, United Kingdom, Ireland, Canada, Switzerland and Denmark.
	The components of income taxes attributable to operations were as follows:


		Year Ended December 31,
		2013				2012				2011
	Current expense (benefit):
	United States	$	27,537			$	8,267			$	(214	)

	Non-U.S.	5,159				737				8,045

		32,696				9,004				7,831

	Deferred expense (benefit):
	United States	1,937				(9,779		)		(11,563		)

	Non-U.S.	(1,859		)		(3,235		)		(6,061		)
		78				(13,014		)		(17,624		)

	Income tax expense (benefit)	$	32,774			$	(4,010	)		$	(9,793	)

	The Company’s income or loss before income taxes was earned in the following jurisdictions:


		Year Ended December 31,
		2013				2012				2011
	Income (Loss) Before Income Taxes:
	Bermuda	$	717,661			$	609,710			$	454,673

	United States	87,032				9,600				(18,662		)

	Other	(62,188		)		(29,923		)		(9,641		)
	Total	$	742,505			$	589,387			$	426,370

	The expected tax provision computed on pre-tax income or loss at the weighted average tax rate has been calculated as the sum of the pre-tax income in each jurisdiction multiplied by that jurisdiction’s applicable statutory tax rate. The statutory tax rates by jurisdiction were as follows: Bermuda (0.0%), United States (35.0%), United Kingdom (23.25%), Ireland (12.5%), Denmark (25.0%), Canada (24.0%), Gibraltar (10.0%) and the Netherlands (22.6%).
	A reconciliation of the difference between the provision for income taxes and the expected tax provision at the weighted average tax rate follows:


		Year Ended December 31,
		2013				2012				2011
	Expected income tax (benefit) expense computed on pre-tax income	$	17,506			$	(3,426	)		$	(5,388	)
	at weighted average income tax rate
	Addition (reduction) in income tax expense (benefit) resulting from:
	Tax-exempt investment income	(8,255		)		(9,257		)		(8,885		)
	Meals and entertainment	599				688				633

	State taxes, net of U.S. federal tax benefit	431				270				309

	U.S. operations’ foreign taxes, net of U.S. federal tax benefit	703				544				(402		)

	Prior year adjustment	2,810				(1,581		)		(91		)

	Non deductible foreign exchange gains & losses	(1,254		)		(436		)		978

	Changes in applicable tax rate	2,007				1,193				217

	Dividend withholding taxes	4,619				2,511				2,237

	Change in valuation allowance	11,795				4,281				—

	Other	1,813				1,203				599

Income tax expense (benefit)	$	32,774			$	(4,010	)		$	(9,793	)

The Company has a foreign tax credit carryforward of $4.3 million, which relates to the Company’s U.K. operations and can be carried forward indefinitely. Additionally, the Company has an alternative minimum tax (“AMT”) credit carryforward in the amount of $14.5 million which can be carried forward indefinitely.
The Company has net operating loss carryforwards in its U.K. and Irish operating subsidiaries of $24.0 million and $15.5 million, respectively. These losses can be carried forward without expiration. Additionally, the Company has net operating loss carryforwards in its Canadian operating subsidiary of $32.2 million. These losses can be carried forward for a period of 20 years and will expire in 2033.
Deferred income tax assets and liabilities reflect temporary differences based on enacted tax rates between the carrying amounts of assets and liabilities for financial reporting and income tax purposes. Significant components of the Company’s deferred income tax assets and liabilities were as follows:


	December 31,
	2013				2012
Deferred income tax assets:
Net operating loss	$	15,294			$	4,925

AMT credit carryforward	14,456				14,423

Discounting of net loss reserves	53,293				54,860

Net unearned premium reserve	30,698				30,614

Compensation liabilities	26,481				22,713

Foreign tax credit carryforward	4,343				8,229

Interest expense	6,049				3,628

Other, net	13,347				15,237

Deferred tax assets before valuation allowance	163,961				154,629

Valuation allowance	(15,548		)		(4,309		)
Deferred tax assets net of valuation allowance	148,413				150,320

Deferred income tax liabilities:
Depreciation and amortization	(3,810		)		(4,896		)
Deferred acquisition costs, net	(3,369		)		(5,988		)
Deposit accounting liability	(4,581		)		(4,823		)
Net unrealized foreign exchange gains	0				(2,825		)

Net unrealized appreciation of investments	(6,354		)		(30,662		)
Other, net	(1,738		)		(2,544		)
Total deferred tax liabilities	(19,852		)		(51,738		)
Net deferred income tax assets	$	128,561			$	98,582

The Company provides a valuation allowance to reduce certain deferred tax assets to an amount which management expects to more likely than not be realized. As of December 31, 2013, the Company’s valuation allowance was $15.5 million, compared to $4.3 million at December 31, 2012. The increase in the valuation allowance during 2013 was primarily attributable to the Company’s Canadian operations.
Deferred income tax liabilities have not been accrued with respect to the undistributed earnings of the Company's U.S. and Canadian subsidiaries. If the earnings were to be distributed, as dividends or otherwise, such amounts may be subject to withholding tax in the jurisdiction of the paying entity. No withholding taxes have been accrued with respect to the earnings of the Company's U.S. and Canadian subsidiaries, as it is the intention that all such earnings will be permanently reinvested. Additionally, determining the amount of the deferred income tax liability is not practicable.
The Company recognizes interest and penalties relating to unrecognized tax benefits in the provision for income taxes. As of December 31, 2013, the Company’s total unrecognized tax benefits, including interest and penalties, were nil.
The Company or its subsidiaries or branches files income tax returns in the U.S. federal jurisdiction and various state, local and foreign jurisdictions. With few exceptions, the Company is no longer subject to U.S. federal, state, local, or non-U.S. income tax examination for years before 2009.
During 2013, the Company paid $15.3 million in income taxes, net of recoveries, compared to income taxes recovered of $1.8 million in 2012 and income taxes paid of $1.9 million in 2011. As of December 31, 2013, the Company’s current income tax payable (included in “Other liabilities”) was $4.2 million.
Federal Excise Taxes
The United States also imposes an excise tax on insurance and reinsurance premiums paid to non-U.S. insurers or reinsurers with respect to risks located in the United States. The rates of tax, unless reduced by an applicable U.S. tax treaty, are four percent for non-life insurance premiums and one percent for life insurance and all reinsurance premiums. The Company incurs federal excise taxes on certain of its reinsurance transactions, including amounts ceded through intercompany transactions. For 2013, 2012 and 2011, the Company incurred approximately $9.5 million, $8.6 million and $9.3 million, respectively, of federal excise taxes. Such amounts are reflected as acquisition expenses in the Company’s consolidated statements of income.

Transactions_with_Related_Part

Transactions with Related Parties	12 Months Ended
Transactions with Related Parties	Dec. 31, 2013
Related Party Transactions [Abstract]	'
Related Party Transactions Disclosure [Text Block]	'
	Transactions with Related Parties
	The Company made an investment of $50.0 million in Aeolus LP (“Aeolus”) in 2006. Aeolus operates as an unrated reinsurance platform that provides property catastrophe protection to insurers and reinsurers on both an ultimate net loss and industry loss warranty basis. The Company’s investment in Aeolus, included in “Investments accounted for using the equity method” on the balance sheet, represents an approximate 4% share in Aeolus and is accounted for using the equity method. The Company made its investment in Aeolus on the same economic terms as a fund affiliated with Warburg Pincus LLC. During 2010, all remaining shares of the Company owned by funds affiliated with Warburg Pincus LLC were distributed. In addition, one of the founders of Aeolus is Peter Appel, former President and CEO and a former director of the Company. During 2013, 2012 and 2011, the Company received distributions of $2.1 million, $19.8 million and $33.2 million, respectively, from Aeolus.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Commitments and Contingencies
	Concentrations of Credit Risk
	The creditworthiness of a counterparty is evaluated by the Company, taking into account credit ratings assigned by independent agencies. The credit approval process involves an assessment of factors, including, among others, the counterparty, country and industry credit exposure limits. Collateral may be required, at the discretion of the Company, on certain transactions based on the creditworthiness of the counterparty.
	The areas where significant concentrations of credit risk may exist include unpaid losses and loss adjustment expenses recoverable, prepaid reinsurance premiums and paid losses and loss adjustment expenses recoverable net of reinsurance balances payable (collectively, “reinsurance recoverables”), investments and cash and cash equivalent balances. The Company’s reinsurance recoverables at December 31, 2013 and 2012 amounted to $1.94 billion and $1.98 billion, respectively, and primarily resulted from reinsurance arrangements entered into in the course of its operations. A credit exposure exists with respect to reinsurance recoverables as they may become uncollectible. The Company manages its credit risk in its reinsurance relationships by transacting with reinsurers that it considers financially sound and, if necessary, the Company may hold collateral in the form of funds, trust accounts and/or irrevocable letters of credit. This collateral can be drawn on for amounts that remain unpaid beyond specified time periods on an individual reinsurer basis.
	In addition, the Company underwrites a significant amount of its business through brokers and a credit risk exists should any of these brokers be unable to fulfill their contractual obligations with respect to the payments of insurance and reinsurance balances owed to the Company. During 2013, approximately 16.0% and 17.0% of the Company’s consolidated gross written premiums were generated from or placed by Aon Corporation and its subsidiaries and Marsh & McLennan Companies and its subsidiaries, respectively, compared to approximately 20.3% and 14.1% for 2012, respectively, and 19.4% and 14.2% for 2011, respectively. No other broker and no one insured or reinsured accounted for more than 10% of gross premiums written for 2013, 2012 and 2011.
	The Company’s available for sale investment portfolio is managed in accordance with guidelines that have been tailored to meet specific investment strategies, including standards of diversification, which limit the allowable holdings of any single issue. There were no investments in any entity in excess of 10% of the Company’s shareholders’ equity at December 31, 2013 other than investments issued or guaranteed by the United States government or its agencies.
	Investment Commitments
	The Company’s investment commitments, which are primarily related to agreements entered into by the Company to invest in funds and separately managed accounts when called upon, were approximately $807.6 million at December 31, 2013.
	Letter of Credit and Revolving Credit Facilities
	As of December 31, 2013, the Company had a $300.0 million unsecured revolving loan and letter of credit facility and a $500.0 million secured letter of credit facility (the “Credit Agreement”). Under the terms of the Credit Agreement, Arch Re U.S. and Arch Re Bermuda are limited to issuing an aggregate of $100.0 million of unsecured letters of credit as part of the $300.0 million unsecured revolving loan. Borrowings of revolving loans may be made by ACGL at a variable rate based on LIBOR or an alternative base rate at the option of the Company. Secured letters of credit are available for issuance on behalf of the Company’s insurance and reinsurance subsidiaries. The Credit Agreement and related documents are structured such that each party that requests a letter of credit or borrowing does so only for itself and for only its own obligations. Issuance of letters of credit and borrowings under the Credit Agreement are subject to the Company’s compliance with certain covenants and conditions, including absence of a material adverse change. These covenants require, among other things, that the Company maintain a debt to total capital ratio of not greater than 0.35 to 1 and consolidated tangible net worth in excess of $3.09 billion plus 25% of future aggregate net income for each quarterly period (not including any future net losses) beginning after June 30, 2011 and 25% of future aggregate proceeds from the issuance of common or preferred equity and that the Company’s principal insurance and reinsurance subsidiaries maintain at least a “B++” rating from A.M. Best. In addition, certain of the Company’s subsidiaries which are party to the Credit Agreement are required to maintain minimum shareholders’ equity levels. The Company was in compliance with all covenants contained in the Credit Agreement at December 31, 2013. The Credit Agreement expires on August 18, 2014.
	In addition, the Company has access to secured letter of credit facilities for up to a total of $197.6 million, which are available on a limited basis and for limited purposes (together with the secured portion of the Credit Agreement and these letter of credit facilities, the “LOC Facilities”). The principal purpose of the LOC Facilities is to issue, as required, evergreen standby letters of credit in favor of primary insurance or reinsurance counterparties with which the Company has entered into reinsurance arrangements to ensure that such counterparties are permitted to take credit for reinsurance obtained from the Company’s reinsurance subsidiaries in United States jurisdictions where such subsidiaries are not licensed or otherwise admitted as an insurer, as required under insurance regulations in the United States, and to comply with requirements of Lloyd’s of London in connection with qualifying quota share and other arrangements. The amount of letters of credit issued is driven by, among other things, the timing and payment of catastrophe losses, loss development of existing reserves, the payment pattern of such reserves, the further expansion of the Company’s business and the loss experience of such business. When issued, certain letters of credit are secured by a portion of the Company’s investment portfolio. In addition, the LOC Facilities also require the maintenance of certain covenants, which the Company was in compliance with at December 31, 2013. At such date, the Company had approximately $459.7 million in outstanding letters of credit under the LOC Facilities, which were secured by investments with a fair value of $537.7 million, and had $100.0 million of borrowings outstanding under the Credit Agreement.
	Leases and Purchase Obligations
	At December 31, 2013, the future minimum rental commitments, exclusive of escalation clauses and maintenance costs and net of rental income, for all of the Company’s operating leases are as follows:


	2014	$	19,009

	2015	18,390

	2016	17,850

	2017	15,464

	2018	15,266

	Thereafter	54,406

	Total	$	140,385

	All of these leases are for the rental of office space, with expiration terms that range from 2014 to 2024. Rental expense, net of income from subleases, was approximately $18.7 million, $17.1 million and $16.4 million for 2013, 2012 and 2011, respectively.
	The Company has also entered into certain agreements which commit the Company to purchase goods or services, primarily related to software and computerized systems. Such purchase obligations were approximately $35.9 million and $21.5 million at December 31, 2013 and 2012, respectively.
	Employment and Other Arrangements
	At December 31, 2013, the Company has entered into employment agreements with certain of its executive officers for periods extending up to March 2018. Such employment arrangements provide for compensation in the form of base salary, annual bonus, share-based awards, participation in the Company’s employee benefit programs and the reimbursements of expenses.

Senior_Notes

Senior Notes	12 Months Ended
Senior Notes	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Long-term Debt [Text Block]	'
	Senior Notes
	On May 4, 2004, ACGL completed a public offering of $300.0 million principal amount of 7.35% senior notes due May 1, 2034 (“ACGL Senior Notes”). The ACGL Senior Notes are ACGL’s senior unsecured obligations and rank equally with all of its existing and future senior unsecured indebtedness. Interest payments on the ACGL Senior Notes are due on May 1st and November 1st of each year. ACGL may redeem the ACGL Senior Notes at any time and from time to time, in whole or in part, at a “make-whole” redemption price. The fair value of the ACGL Senior Notes at December 31, 2013 and 2012 was $381.0 million and $379.1 million, respectively.
	On December 13, 2013, Arch-U.S., a wholly-owned subsidiary of ACGL, completed a public offering of $500.0 million principal amount of 5.144% senior notes due November 1, 2043 (“Arch-U.S. Senior Notes”), fully and unconditionally guaranteed by ACGL (the “Guarantee”). The Arch-U.S. Senior Notes are unsecured and unsubordinated obligations of Arch-U.S. and ACGL, respectively, and rank equally and ratably with the other unsecured and unsubordinated indebtnedness of Arch-U.S. and ACGL, respectively. Interest payments on the Arch-U.S. Senior Notes are due on May 1st and November 1st of each year. Arch-U.S. may redeem the Arch-U.S. Senior Notes at any time and from time to time, in whole or in part, at a “make-whole” redemption price. The fair value of the Arch-U.S. Senior Notes at December 31, 2013 was $514.1 million.
	During 2013, 2012 and 2011, the Company made interest payments of $23.7 million, $29.1 million and $30.5 million, respectively, related to its senior notes and other financing arrangements discussed in Note 14.

Shareholders_Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2013
Stockholders' Equity Note [Abstract]	'
Shareholders' Equity	'
	Shareholders’ Equity
	Authorized and Issued
	The authorized share capital of the Company consists of 600 million Common Shares, par value of $0.0033 per share, and 50 million Preferred Shares, par value of $0.01 per share.
	Common Shares
	The following table presents a roll-forward of changes in the Company’s issued and outstanding Common Shares:


		Year Ended December 31,
		2013		2012		2011
	Common Shares:
	Shares issued and outstanding, beginning of year	168,255,572		164,636,338		160,073,616

	Shares issued (1)	811,732		2,066,065		3,592,713

	Restricted shares issued, net of cancellations	493,287		1,553,169		970,009

	Shares issued, end of year	169,560,591		168,255,572		164,636,338

	Common shares in treasury, end of year	(35,885,707	)	(34,412,959	)	(30,277,993	)
	Shares issued and outstanding, end of year	133,674,884		133,842,613		134,358,345


	-1	Includes shares issued from the exercise of stock options and stock appreciation rights, and shares issued from the employee share purchase plan.

	Share Repurchases
	The board of directors of ACGL has authorized the investment in ACGL’s common shares through a share repurchase program. Authorizations have consisted of a $1.0 billion authorization in February 2007, a $500.0 million authorization in May 2008, a $1.0 billion authorization in November 2009 and a $1.0 billion authorization in February 2011. Since the inception of the share repurchase program through December 31, 2013, ACGL has repurchased approximately 109.9 million common shares for an aggregate purchase price of $2.79 billion. During 2013, ACGL repurchased 1.3 million common shares for an aggregate purchase price of $57.8 million, compared to 3.9 million common shares for an aggregate purchase price of $172.1 million during 2012 and 9.6 million common shares for an aggregate purchase price of $287.6 million during 2011. Weighted average shares outstanding for 2013 were reduced by 109.6 million shares, compared to 105.0 million shares for 2012 and 103.2 million shares for 2011. At December 31, 2013, approximately $712.1 million of share repurchases were available under the program. Repurchases under the program may be effected from time to time in open market or privately negotiated transactions. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations.
	Treasury Shares
	In May 2010, ACGL’s shareholders approved amendments to the bye-laws to permit ACGL to hold its own acquired shares as treasury shares in lieu of cancellation, as determined by ACGL’s board of directors. From May 5, 2010 to December 31, 2013, all repurchases of ACGL’s common shares in connection with the share repurchase plan noted above and other share-based transactions were held in the treasury under the cost method, and the cost of the common shares acquired is included in ‘Common shares held in treasury, at cost.’ At December 31, 2013, the Company held 35.9 million shares for an aggregate cost of $1.09 billion in treasury, at cost.
	Preferred Shares
	On April 2, 2012, the Company completed the underwritten public offering of $325.0 million of its 6.75% Series C non-cumulative preferred shares (“Preferred Shares”). Except in specified circumstances relating to certain tax or corporate events, the Preferred Shares are not redeemable prior to April 2, 2017. The net proceeds from the offering of $315.8 million and other available funds were used to redeem all of the Company’s $200.0 million of 8.0% Series A preferred shares and $125.0 million of 7.875% Series B preferred shares on May 2, 2012. The Series A preferred shares and Series B preferred shares were redeemed at a redemption price equal to $25.00 per share, plus all declared and unpaid dividends to (but excluding) the redemption date.
	Dividends on the Preferred Shares are non-cumulative. Consequently, in the event dividends are not declared on the Preferred Shares for any dividend period, holders of Preferred Shares will not be entitled to receive a dividend for such period, and such undeclared dividend will not accrue and will not be payable. Holders of Preferred Shares will be entitled to receive dividend payments only when, as and if declared by ACGL’s board of directors or a duly authorized committee of the board of directors. Any such dividends will be payable from the date of original issue on a non-cumulative basis, quarterly in arrears. To the extent declared, these dividends will accumulate, with respect to each dividend period, in an amount per share equal to 6.75% of the $25.00 liquidation preference per annum. The Company paid dividends of $21.9 million in 2013, compared to $28.4 million in 2012 and $25.8 million in 2011 to holders of the Company’s preferred shares.

ShareBased_Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Share-Based Compensation	'
	Share-Based Compensation
	Long Term Incentive and Share Award Plans
	The 2012 Long Term Incentive and Share Award Plan (the “2012 Plan”) became effective as of May 9, 2012 (the “Effective Date”) following approval by shareholders of the Company. The 2012 Plan is intended to provide for competitive compensation opportunities, to encourage long-term service, to recognize individual contributions and reward achievement of performance goals and to promote the creation of long-term value for shareholders by aligning the interests of such persons with those of shareholders. The 2012 Plan provides for the grant to eligible employees and directors stock options, stock appreciation rights (“SARs”), restricted shares, restricted share units payable in common shares or cash, share awards in lieu of cash awards, dividend equivalents and other share-based awards. The 2012 Plan also provides the Company’s non-employee directors with the opportunity to receive the annual retainer fee for Board service in common shares. The 2012 Plan will terminate as to future awards on February 28, 2022.
	The 2007 Long Term Incentive and Share Award Plan (the “2007 Plan”) was merged with and into the 2012 Plan as of the Effective Date. As of the Effective Date, the 3,153,924 remaining shares available for issuance under the 2007 Plan were transferred into the 2012 Plan and as of such date no additional grants may be made under the 2007 Plan. Grants which were outstanding under the 2007 Plan as of the Effective Date will continue in accordance with their original terms (subject to such amendments as the compensation committee determines appropriate, consistent with the terms of the 2007 Plan) and will be issued or transferred under the 2012 Plan.
	The number of common shares reserved for grants of awards under the 2012 Plan, subject to anti-dilution adjustments in the event of certain changes in the Company’s capital structure is 7,433,924 which is the sum of (i) 4,280,000 and (ii) 3,153,924 shares remaining available for grants under the 2007 Plan. In addition, no more than 50% of such common shares may be issued in connection with full value awards (i.e., awards other than stock options or SARs) and no more than 2,000,000 common shares may be issued as incentive stock options under Section 422 of the Code. At December 31, 2013, 2,692,267 shares are available for grant under the 2012 Plan.
	On May 11, 2007, following shareholder approval, the Company adopted the 2007 Employee Share Purchase Plan (the "ESPP"). The purpose of the ESPP is to give employees of ACGL and its subsidiaries an opportunity to purchase common shares through payroll deductions, thereby encouraging employees to share in the economic growth and success of ACGL and its subsidiaries. The ESPP is designed to qualify as an “employee share purchase plan” under Section 423 of the Code. A total of 2,250,000 common shares are reserved for issuance under the ESPP. At December 31, 2013, approximately 944,766 shares remain available for issuance. The ESPP provides for consecutive six-month offering periods (or other periods of not more than 27 months as determined by the compensation committee) under which participating employees can elect to have up to 20% of their total compensation withheld and applied to the purchase of common shares of the Company at the end of the period. Unless otherwise determined by the compensation committee before an offering period commences, (1) the purchase price will be 85% of the fair market value of the common shares at the beginning of the offering period; and (2) the maximum number of common shares that may be purchased by an employee in any offering period is 3,000 shares. In addition, applicable Code limitations specify, in general, that a participant’s right to purchase stock under the ESPP cannot accumulate at a rate in excess of $25,000 (based on the value at the beginning of the applicable offering periods) per calendar year. The Company recorded $1.1 million of share-based compensation expense, net of a tax benefit of $0.4 million, related to the ESPP for 2013, compared to $0.9 million, net of a tax benefit of $0.3 million, for 2012 and $0.7 million, net of a tax benefit of $0.3 million, for 2011.
	In June 2002, following shareholder approval, the Company adopted the 2002 Long Term Incentive and Share Award Plan (the “2002 Plan”). An aggregate of 9,497,490 Common Shares has been reserved for issuance under the 2002 Plan. The 2002 Plan expired in January 2012.
	With respect to certain subsidiaries, the Company may withhold, or require a participant to remit to the Company, an amount sufficient to satisfy any federal, state or local withholding tax requirements associated with awards under the Company’s share award plans. This includes the authority to withhold or receive shares or other property and to make cash payments in respect thereof.
	Stock Options and Stock Appreciation Rights
	The Company generally issues stock options and SARs to eligible employees, with exercise prices equal to the fair market values of the Company’s Common Shares on the grant dates. Such grants generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. In addition, in November 2012 the Company issued off-cycle stock options and SARs to certain employees, which will cliff vest on the fifth anniversary of the grant date. Option awards and SARs have a 10 year contractual life. Refer to Note 2(m) for details related to the Company’s accounting for stock options and SARs.
	The Company recorded after-tax share-based compensation expense of $10.6 million related to stock options and SARs for 2013, net of a tax benefit of $2.0 million, compared to $8.5 million for 2012, net of a tax benefit of $1.8 million, and $5.3 million for 2011, net of a tax benefit of $1.5 million. As of December 31, 2013, there was approximately $14.1 million of unrecognized compensation cost related to nonvested stock options and SARs. Such cost is expected to be recognized over a weighted average period of 2.09 years.
	For purposes of determining estimated market value, the Company has computed the estimated market values of share-based compensation related to stock options and SARs using the Black-Scholes option valuation model and has applied the assumptions set forth in the following table. As described above, stock options and SARs generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. The expected life assumption (i.e., the estimated period of time between the date an option or SAR is granted and the date the option or SAR is exercised) was based on an expected term analysis which incorporated the Company’s historical exercise experience. The Company based its estimate of expected volatility for stock options and SARs granted during 2013 on daily historical trading data of its common shares from September 20, 2002, the date marking the completion of the Company’s transition as a worldwide insurance and reinsurance company. For stock options and SARs granted during 2012 and 2011, the Company based its volatility estimate under the same method used for 2013, using the period from September 20, 2002 through the last day of the applicable period.


		Year Ended December 31,
		2013			2012		2011
	Dividend yield	0	%		0	%	0	%
	Expected volatility	23.6	%		24.3	%	24.6	%
	Risk free interest rate	1	%		1	%	2.2	%
	Expected option life	6.0 years			6.25 years		6.0 years

	The Black-Scholes option pricing model requires the input of highly subjective assumptions. Because the Company’s employee stock options and SARs have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of its employee stock options and SARs. In addition, management will continue to assess the assumptions and methodologies used to calculate estimated fair value of share-based compensation. Circumstances may change and additional data may become available over time, which could result in changes to these assumptions and methodologies, and which could materially impact the Company’s fair value determination.
	A summary of stock option and SAR activity under the Company’s Long Term Incentive and Share Award Plans during 2013 is presented below:


		Year Ended December 31, 2013
		Number of			Weighted Average Exercise Price
		Options / SARs
	Outstanding, beginning of year	8,221,444			$	25.87

	Granted	860,881			$	51.76

	Exercised	(695,756	)		$	21.62

	Forfeited or expired	(48,089	)		$	40.54

	Outstanding, end of year	8,338,480			$	28.82

	Exercisable, end of year	6,119,335			$	23.51

	The weighted average grant-date fair value of stock options and SARs granted during 2013, 2012 and 2011 was $12.96, $10.61 and $9.73, respectively. The aggregate intrinsic value of stock options and SARs exercised during 2013, 2012 and 2011 was approximately $21.7 million, $64.0 million, and $106.0 million, respectively and represents the difference between the exercise price of the stock options and SARs and the closing market price of the Company’s common shares on the exercise dates. Shares issued upon exercise of stock options and SARs were from the Company’s authorized but unissued share capital pool.
	The aggregate intrinsic value of the Company’s outstanding and exercisable stock options and SARs at December 31, 2013 was $257.4 million and $221.4 million, respectively. The weighted average remaining contractual life of the Company’s outstanding and exercisable stock options and SARs at December 31, 2013 was 5.4 years and 4.3 years, respectively. During 2013, the Company received proceeds of $6.4 million from the exercise of stock options and recognized a tax benefit of $5.0 million from the exercise of stock options and SARs.
	Restricted Common Shares and Restricted Units
	The Company also issues restricted share and unit awards to eligible employees and directors, for which the fair value is equal to the fair market values of the Company’s Common Shares on the grant dates. Restricted share and unit awards generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. In addition, in November 2012 the Company issued off-cycle restricted share and unit awards to certain employees, which will cliff vest on the fifth anniversary of the grant date. Refer to Note 2(m) for details related to the Company’s accounting for restricted share and unit awards.
	The Company recorded $27.4 million of share-based compensation expense, net of a tax benefit of $7.8 million, related to restricted share and unit awards for 2013, compared to $24.6 million, net of a tax benefit of $6.3 million, for 2012 and $18.2 million, net of a tax benefit of $5.0 million, for 2011. As of December 31, 2013 , there were $46.3 million and $8.3 million, respectively, of unrecognized compensation costs related to unvested restricted share and unit awards which are expected to be recognized over a weighted average period of 2.1 years and 2.2 years, respectively.
	A summary of unvested restricted share and unit activity under the Company’s Long Term Incentive and Share Award Plans for 2013 is presented below:


		Year Ended December 31, 2013
		Restricted				Restricted
		Common				Unit
		Shares				Awards
	Unvested Shares:
	Unvested balance, beginning of year	2,114,640				357,250

	Granted	513,832				76,286

	Vested	(664,802		)		(97,943	)
	Forfeited	(20,545		)		(27,271	)
	Unvested balance, end of year	1,943,125				308,322


	Weighted Average Grant Date Fair Value:
Unvested balance, beginning of year	$	37.88			$	38.03

Granted	$	53.21			$	53.26

Vested	$	33.04			$	32.95

Forfeited	$	42.21			$	39.06

Unvested balance, end of year	$	43.55			$	43.32

During 2013, 2012 and 2011, the Company granted an aggregate of 590,118, 1,819,657 and 779,541 restricted share and restricted unit awards, respectively, with weighted average grant date fair values of $53.21, $40.75 and $33.82, respectively. During 2013, 2012 and 2011, the aggregate fair value of restricted shares and units that vested was $41.0 million, $33.2 million and $31.7 million, respectively. The aggregate intrinsic value of restricted units outstanding at December 31, 2013 was $26.5 million, and the aggregate intrinsic value of restricted units vested and deferred was $8.1 million.
The issuance of share-based awards and amortization thereon has no effect on the Company’s consolidated shareholders’ equity.

Retirement_Plans

Retirement Plans	12 Months Ended
Retirement Plans	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]	'
Pension and Other Postretirement Benefits Disclosure [Text Block]	'
	Retirement Plans
	For purposes of providing employees with retirement benefits, the Company maintains defined contribution retirement plans. Contributions are based on the participants’ eligible compensation. For 2013, 2012 and 2011, the Company expensed approximately $21.5 million, $19.3 million and $18.2 million, respectively, related to these retirement plans.

Legal_Proceedings

Legal Proceedings	12 Months Ended
Legal Proceedings	Dec. 31, 2013
Disclosure Legal Proceedings [Abstract]	'
Legal Proceedings	'
	Legal Proceedings
	The Company, in common with the insurance industry in general, is subject to litigation and arbitration in the normal course of its business. As of December 31, 2013, the Company was not a party to any litigation or arbitration which is expected by management to have a material adverse effect on the Company’s results of operations and financial condition and liquidity.

Statutory_Information

Statutory Information	12 Months Ended
	Dec. 31, 2013
Disclosure Statutory Information [Abstract]	'
Statutory Information	'
	Statutory Information
	The Company’s insurance and reinsurance subsidiaries are subject to insurance and/or reinsurance laws and regulations in the jurisdictions in which they operate. These regulations include certain restrictions on the amount of dividends or other distributions available to shareholders without prior approval of the insurance regulatory authorities.
	The actual and required statutory capital and surplus for the Company’s principal operating subsidiaries at December 31, 2013 and 2012 was as follows:


		December 31, 2013						December 31, 2012
		Actual (1)			Required (1)			Actual (1)			Required (1)
	Statutory capital and surplus (1):
	Bermuda	$	5,416,948		$	2,096,428		$	5,010,386		$	2,175,191

	Ireland	$	533,283		$	458,666		$	539,326		$	377,340

	United States	$	1,013,228		$	335,442		$	822,615		$	319,129

	United Kingdom	$	250,688		$	237,555		$	231,387		$	206,764

	Canada	$	77,877		$	74,951		—			—


	-1	Such amounts include ownership interests in affiliated insurance and reinsurance subsidiaries.
	The statutory net income (loss) for the Company’s principal operating subsidiaries for 2013, 2012 and 2011 was as follows:


		Year Ended December 31,
		2013			2012			2011
	Statutory net income (loss):
	Bermuda	$	719,267		$	631,483		$	447,447

	Ireland	$	24,410		$	(1,940	)	$	9,123

	United States	$	62,605		$	(21,517	)	$	(37,252	)

	United Kingdom	$	(11,353	)	$	(4,449	)	$	1,637

	Canada	$	(36,203	)	—			—

	Statutory accounting differs from U.S. GAAP in the reporting of certain items such as acquisition costs, deferred income taxes and investments.
	Bermuda
	Under The Insurance Act 1978, as amended, and related regulations of Bermuda (the “Insurance Act”), Arch Re Bermuda, the Company’s Bermuda reinsurance and insurance subsidiary, is registered as a Class 4 insurer and long-term insurer and is required to annually prepare and file statutory financial statements and a statutory financial return with the Bermuda Monetary Authority (“BMA”). The Insurance Act also requires Arch Re Bermuda to maintain minimum share capital and must ensure that the value of its general business assets exceeds the amount of its general business liabilities by an amount greater than the prescribed minimum solvency margins and enhanced capital requirement pertaining to its general business. At December 31, 2013, all such requirements were met.
	Arch Re Bermuda is also required to file a regulatory risk based capital model that measures risks and determines enhanced capital requirements and a target capital level. In addition, all Class 4 Bermuda insurers must prepare and file with the BMA audited GAAP basis annual financial statements, which must be made publicly available. Declarations of dividends from retained earnings and distributions from additional paid-in-capital are subject to these requirements being met. For all applicable periods presented herein, Arch Re Bermuda satisfied these requirements.
	The Bermuda Companies Act 1981 (the “Companies Act”) limits Arch Re Bermuda’s ability to pay dividends and distributions to shareholders if there are reasonable grounds for believing that: (a) Arch Re Bermuda is, or would after the payment be, unable to pay its liabilities as they become due; or (b) the realizable value of Arch Re Bermuda’s assets would thereby be less than the aggregate of its liabilities and its issued share capital and share premium accounts. Under the Insurance Act, Arch Re Bermuda is restricted with respect to the payment of dividends. Arch Re Bermuda is prohibited from declaring or paying in any financial year dividends of more than 25% of its total statutory capital and surplus (as shown on its previous financial year’s statutory balance sheet) unless it files, at least seven days before payment of such dividends, with the Bermuda Monetary Authority an affidavit stating that it will continue to meet the required margins. In addition, Arch Re Bermuda is prohibited, without prior approval of the Bermuda Monetary Authority, from reducing by 15% or more its total statutory capital, as set out in its previous year’s statutory financial statements. Accordingly, Arch Re Bermuda can pay approximately $1.35 billion to ACGL during 2014 without providing an affidavit to the BMA.
	Ireland
	Arch Re Europe was licensed and authorized by the Central Bank of Ireland (“CBOI”) as a non-life reinsurer in October 2008 and as a life reinsurer in November 2009 while Arch MI Europe was authorized as a non-life insurer in Ireland in December 2011. Irish authorized reinsurers and insurers, such as Arch Re Europe and Arch MI Europe, are also subject to the general body of Irish laws and regulations including the provisions of the Companies Acts 1963-2013. Arch Re Europe and Arch MI Europe must file and submit their annual audited financial statements in accordance with Irish generally accepted accounting principles and related reports to the Registrar of Companies (“Registrar”) under the Companies Acts 1963-2013 together with an annual return of certain core corporate information. Changes to core corporate information during the year must also be notified to the Registrar. These requirements are in addition to the regulatory returns required to be filed annually with the CBOI. Arch Re Europe and Arch MI Europe are required to maintain reserves, particularly in respect of underwriting liabilities and a solvency margin as provided for in the European Communities (Reinsurance) Regulations, 2006, related guidance and the European Communities Insurance Accounts Regulations, 1996. Assets constituting statutory reserves must comply with certain principles including obligations to secure sufficiency, liquidity, security, quality, profitability and currency matching of investments. Statutory reserves must be actuarially certified annually.
	Under Irish company law, Arch Re Europe and Arch MI Europe are permitted to make distributions only out of profits available for distribution. A company’s profits available for distribution are its accumulated, realized profits, so far as not previously utilized by distribution or capitalization, less its accumulated, realized losses, so far as not previously written off in a reduction or reorganization of capital duly made. Further, the CBOI has powers to intervene if a dividend payment were to lead to a breach of regulatory capital requirements.
	United States
	The Company’s U.S. insurance and reinsurance subsidiaries file financial statements prepared in accordance with statutory accounting practices prescribed or permitted by insurance regulators. Statutory net income and statutory surplus, as reported to the insurance regulatory authorities, differ in certain respects from the amounts prepared in accordance with GAAP. The main differences between statutory net income and GAAP net income relate to deferred acquisition costs and deferred income taxes. In addition to deferred acquisition costs and deferred income tax assets, other differences between statutory surplus and GAAP shareholder’s equity are unrealized appreciation or decline in value of investments and non-admitted assets.
	The Company’s U.S. insurance and reinsurance subsidiaries are subject to insurance laws and regulations in the jurisdictions in which they operate. The ability of the Company’s regulated insurance subsidiaries to pay dividends or make distributions is dependent on their ability to meet applicable regulatory standards. These regulations include restrictions that limit the amount of dividends or other distributions, such as loans or cash advances, available to shareholders without prior approval of the insurance regulatory authorities. Dividends or distributions, if any, made by Arch Re U.S. would result in an increase in available capital at Arch-U.S., the Company’s U.S. holding company. Arch Re U.S. can declare a maximum of approximately $101.3 million of dividends during 2014 subject to the authority of the Nebraska Director of Insurance to disapprove the payment of such dividend. Nebraska insurance laws also require that the statutory surplus of Arch Re U.S. following any dividend or distribution be reasonable in relation to its outstanding liabilities and adequate to its financial needs. In addition, Nebraska insurance laws require that each insurer give notice to the Nebraska Director of Insurance of all dividends and other distributions within five business days following declaration thereof and that any such dividend or other distribution may not be paid within ten business days of such notice, unless for good cause shown and the Nebraska Director of Insurance has approved such payment within the ten business days of such notice.
	United Kingdom
	The Company’s European insurance operations are conducted on two platforms: Arch Insurance Company Europe and Arch Syndicate 2012 (collectively, the insurance operations are referred to as “Arch Insurance Europe”). The Financial Services Authority (the “FSA”), which on April 1, 2013 was replaced by the Prudential Regulatory Authority (“PRA”) and the Financial Conduct Authority (“FCA”), regulated insurance and reinsurance companies and firms carrying on insurance mediation activities operating in the U.K. Arch Insurance Company Europe was licensed and authorized by the FSA to underwrite all classes of general insurance in the U.K. in May 2004. In 2009, AUAL was licensed and authorized by the FSA and the Lloyd’s Franchise Board. AUAL holds the relevant permissions for the classes of insurance business which are underwritten in the U.K. by Arch Syndicate 2012. Arch Syndicate 2012 has one member, Arch Syndicate Investments Ltd. Arch Risk Partners was licensed and authorized by the FSA in February 2012 to conduct insurance mediation activities. All U.K. companies are also subject to a range of statutory provisions, including the laws and regulations of the Companies Acts 2006 (as amended) (the “U.K. Companies Acts”).
	Like all U.K. companies, Arch Insurance Europe must file and submit their annual audited financial statements in accordance with International Financial Reporting Standards and related reports to the Registrar of Companies under the U.K. Companies Acts together with an annual return of certain core corporate information and changes from the prior year. This requirement is in addition to the regulatory returns required to be filed annually with the FSA (now the PRA or the FCA, as applicable) for Arch Insurance Company Europe, AUAL and Arch Risk Partners and, in the case of AUAL and ASIL, Lloyd’s.
	Arch Insurance Company Europe, AUAL (on behalf of itself, Arch Syndicate 2012 and ASIL) and Arch Risk Partners were each required to demonstrate to the FSA that each had adequate financial assets to meet the financial resources requirement for its category. However, since the FSA split into the PRA and FCA, Arch Insurance Company Europe and AUAL (on behalf of itself, Arch Syndicate 2012 and ASIL) are now each required to demonstrate the adequacy of its financial assets to the PRA, while Arch Risk Partners is required to demonstrate the adequacy of its financial assets to the FCA. On a periodic basis, Arch Insurance Europe was required to provide the FSA and Lloyd’s with its own risk-based assessment of its capital needs, taking into account comprehensive risk factors, including market, credit, operational, liquidity and group risks to generate a revised calculation of its expected liabilities which, in turn, enabled the FSA and Lloyd’s to provide individual capital guidance and requirements to Arch Insurance Europe. Following the split of the FSA into the PRA and FCA, similar requirements from the PRA have taken effect. Arch Insurance Europe’s surplus is above the risk-based capital threshold allowed by the FSA’s (now PRA's) individual capital assessment of Arch Insurance Europe. The FSA required, and now the PRA requires, that Arch Insurance Europe maintain a margin of solvency calculation based on the classes of business for which it is authorized and within its premium income projections applied to its worldwide general business.
	Under U.K. law, all U.K. companies are restricted from declaring a dividend to their shareholders unless they have “profits available for distribution.” The calculation as to whether a company has sufficient profits is based on its accumulated realized profits minus its accumulated realized losses. U.K. insurance regulatory laws do not prohibit the payment of dividends, but the FSA required, and now the PRA or FCA, as applicable, requires that insurance companies and insurance intermediaries maintain certain solvency margins and may restrict the payment of a dividend by Arch Insurance Company Europe, AUAL, ASIL or Arch Risk Partners. Dividends or distributions, if any, made by Arch Insurance Europe would result in an increase in available capital at Arch Re Europe, a subsidiary of Arch Re Bermuda.
	Canada
	Arch Insurance Canada, which commenced underwriting on January 1, 2013, is subject to federal, as well as provincial and territorial, regulation in Canada. The Office of the Superintendent of Financial Institutions (“OSFI”) is the federal regulatory body that, under the Insurance Companies Act (Canada), regulates federal Canadian and non-Canadian insurance companies operating in Canada. The primary goal of OSFI is to supervise the safety and soundness of insurance companies with the aim of securing the appropriate level of protection of insureds by imposing risk management, solvency and capital requirements on such companies. Arch Insurance Canada is subject to regulation in the provinces and territories in which it underwrites insurance, and the primary goal of insurance regulation at the provincial and territorial levels is to govern the market conduct of insurance companies. Arch Insurance Canada is licensed to carry on insurance business by OSFI and in each province and territory.
	Under the Insurance Companies Act (Canada), Arch Insurance Canada is required to maintain an adequate amount of capital in Canada, calculated in accordance with a test promulgated by OSFI called the Minimum Capital Test (“MCT”). Arch Insurance Canada is required to file financial information with OSFI on an ongoing basis, including annual audited financial statements in accordance with Canadian generally accepted accounting principles and other returns and quarterly unaudited financial statements. Dividends or distributions, if any, made by Arch Insurance Canada would result in an increase in available capital at Arch Insurance Company (see "—United States" section).

Unaudited_Condensed_Quarterly_

Unaudited Condensed Quarterly Financial Information	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Unaudited Condensed Quarterly Financial Information	'
	Unaudited Condensed Quarterly Financial Information
	The following table summarizes the Company’s 2013 and 2012 unaudited condensed quarterly financial information:


		Fourth			Third			Second			First
		Quarter			Quarter			Quarter			Quarter
	Year Ended December 31, 2013
	Net premiums written	$	748,921		$	839,135		$	810,535		$	952,776

	Net premiums earned	839,366			795,000			758,816			752,770

	Net investment income	67,095			66,083			68,369			65,672

	Net realized gains (losses)	9,048			(6,022		)	12,652			58,340

	Net impairment losses recognized in earnings	(88		)	(728		)	(724		)	(2,246		)
	Underwriting income	128,318			110,992			96,029			116,398

	Net income	161,490			114,825			176,940			256,476

	Preferred dividends	(5,485		)	(5,484		)	(5,485		)	(5,484		)
	Net income available to common shareholders	156,005			109,341			171,455			250,992

	Net income per common share -- basic	$	1.19		$	0.83		$	1.31		$	1.92

	Net income per common share -- diluted	$	1.14		$	0.8		$	1.26		$	1.85


	Year Ended December 31, 2012
	Net premiums written	$	613,142		$	755,249		$	820,233		$	863,611

	Net premiums earned	779,481			748,691			726,656			680,312

	Net investment income	73,769			73,221			73,608			74,297

	Net realized gains	54,849			60,391			34,867			44,121

	Net impairment losses recognized in earnings	(6,035		)	(2,379		)	(1,951		)	(1,023		)
	Underwriting income (loss)	(91,334		)	73,452			93,723			67,193

	Net income	19,217			189,656			220,268			164,256

	Preferred dividends	(5,485		)	(5,484		)	(7,649		)	(6,461		)
	Loss on repurchase of preferred shares	—			—			(10,612		)	—

	Net income available to common shareholders	13,732			184,172			202,007			157,795

	Net income per common share -- basic	$	0.1		$	1.36		$	1.5		$	1.18

	Net income per common share -- diluted	$	0.1		$	1.33		$	1.46		$	1.14

Guarantor_Financial_Informatio

Guarantor Financial Information	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Guarantor Financial Information	'
	Guarantor Financial Information
	The following tables present condensed consolidating balance sheets at December 31, 2013 and 2012 and condensed consolidating statements of income, comprehensive income and cash flows for the years ended December 31, 2013, 2012 and 2011 for ACGL, Arch-U.S., a 100% owned subsidiary of ACGL, and ACGL's other subsidiaries.


		31-Dec-13
	Condensed Consolidating Balance Sheet	ACGL (Parent Guarantor)			Arch-U.S. (Subsidiary Issuer)			Other ACGL Subsidiaries			Consolidating Adjustments and Eliminations				ACGL Consolidated
	Assets
	Total investments	$	2,530		$	408,957		$	13,200,247		$	—			$	13,611,734

	Cash	3,223			509			430,325			—				434,057

	Investments in subsidiaries	6,046,060			1,258,889			—			(7,304,949		)		—

	Due from subsidiaries and affiliates	2,251			—			405,110			(407,361		)		—

	Premiums receivable	—			—			1,085,369			(331,445		)		753,924

	Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	—			—			5,645,156			(3,840,826		)		1,804,330

	Contractholder receivables	—			—			1,064,246			—				1,064,246

	Prepaid reinsurance premiums	—			—			1,109,312			(780,969		)		328,343

	Deferred acquisition costs, net	—			—			342,314			—				342,314

	Other assets	6,598			60,342			1,714,651			(554,445		)		1,227,146

	Total Assets	$	6,060,662		$	1,728,697		$	24,996,730		$	(13,219,995	)		$	19,566,094


	Liabilities
	Reserve for losses and loss adjustment expenses	$	—		$	—		$	12,625,766		$	(3,801,070	)		$	8,824,696

	Unearned premiums	—			—			2,677,334			(780,969		)		1,896,365

	Reinsurance balances payable	—			—			662,394			(466,227		)		196,167

	Contractholder payables	—			—			1,064,246			—				1,064,246

	Deposit accounting liabilities	—			—			758,490			(337,193		)		421,297

	Senior notes	300,000			500,000			—			—				800,000

	Revolving credit agreement borrowings	100,000			—			—			—				100,000

	Due to subsidiaries and affiliates	18			10,250			397,093			(407,361		)		—

	Other liabilities	13,148			33,206			691,699			(122,226		)		615,827

	Total Liabilities	413,166			543,456			18,877,022			(5,915,046		)		13,918,598


	Shareholders' Equity
	Total Shareholders' Equity	5,647,496			1,185,241			6,119,708			(7,304,949		)		5,647,496


	Total Liabilities and Shareholders' Equity	$	6,060,662		$	1,728,697		$	24,996,730		$	(13,219,995	)		$	19,566,094



		31-Dec-12
	Condensed Consolidating Balance Sheet	ACGL (Parent Guarantor)			Arch-U.S. (Subsidiary Issuer)			Other ACGL Subsidiaries			Consolidating Adjustments and Eliminations				ACGL Consolidated
	Assets
Total investments	$	8,328		$	8,798		$	12,674,114		$	—			$	12,691,240

Cash	6,417			612			364,012			—				371,041

Investments in subsidiaries	5,560,655			1,155,839			—			(6,716,494		)		—

Due from subsidiaries and affiliates	254			—			352,063			(352,317		)		—

Premiums receivable	—			—			877,210			(188,337		)		688,873

Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	—			—			5,849,750			(3,979,713		)		1,870,037

Contractholder receivables	—			—			865,728			—				865,728

Prepaid reinsurance premiums	—			—			914,367			(615,883		)		298,484

Deferred acquisition costs, net	—			—			262,822			—				262,822

Other assets	6,430			48,571			662,186			51,350				768,537

Total Assets	$	5,582,084		$	1,213,820		$	22,822,252		$	(11,801,394	)		$	17,816,762


Liabilities
Reserve for losses and loss adjustment expenses	$	—		$	—		$	12,857,514		$	(3,924,222	)		$	8,933,292

Unearned premiums	—			—			2,263,861			(615,883		)		1,647,978

Reinsurance balances payable	—			—			529,562			(341,016		)		188,546

Contractholder payables	—			—			865,728			—				865,728

Deposit accounting liabilities	—			—			27,594			—				27,594

Senior notes	300,000			—			—			—				300,000

Revolving credit agreement borrowings	100,000			—			—			—				100,000

Due to subsidiaries and affiliates	2,397			—			349,920			(352,317		)		—

Other liabilities	10,809			31,193			394,206			148,538				584,746

Total Liabilities	413,206			31,193			17,288,385			(5,084,900		)		12,647,884


Shareholders' Equity
Total Shareholders' Equity	5,168,878			1,182,627			5,533,867			(6,716,494		)		5,168,878


Total Liabilities and Shareholders' Equity	$	5,582,084		$	1,213,820		$	22,822,252		$	(11,801,394	)		$	17,816,762



	Year Ended December 31, 2013
Condensed Consolidating Statement of Income and Comprehensive Income	ACGL (Parent Guarantor)			Arch-U.S. (Subsidiary Issuer)			Other ACGL Subsidiaries			Consolidating Adjustments and Eliminations				ACGL Consolidated
Revenues
Net premiums earned	$	—		$	—		$	3,145,952		$	—			$	3,145,952

Net investment income	(5		)	31			307,449			(40,256		)		267,219

Net realized gains	—			—			74,018			—				74,018

Net impairment losses recognized in earnings	—			—			(3,786		)	—				(3,786		)

Other underwriting income	—			—			7,639			—				7,639

Equity in net income (loss) of investment funds accounted for using the equity method	—			—			35,701			—				35,701

Other income (loss)	—			—			(586		)	—				(586		)

Total revenues	(5		)	31			3,566,387			(40,256		)		3,526,157


Expenses
Losses and loss adjustment expenses	—			—			1,679,424			—				1,679,424

Acquisition expenses	—			—			564,103			—				564,103

Other operating expenses	38,702			2,691			459,337			—				500,730

Interest expense	23,267			1,316			42,733			(40,256		)		27,060

Net foreign exchange losses	—			—			2,145			10,190				12,335

Total expenses	61,969			4,007			2,747,742			(30,066		)		2,783,652


Income (loss) before income taxes	(61,974		)	(3,976		)	818,645			(10,190		)		742,505

Income tax benefit (expense)	—			1,383			(34,157		)	—				(32,774		)


Income (loss) before equity in net income of subsidiaries	(61,974		)	(2,593		)	784,488			(10,190		)		709,731


Equity in net income (loss) of subsidiaries	771,705			25,644			—			(797,349		)		—


Net income	709,731			23,051			784,488			(807,539		)		709,731

Preferred dividends	(21,938		)	—			—			—				(21,938		)


Net income available to common shareholders	$	687,793		$	23,051		$	784,488		$	(807,539	)		$	687,793


Comprehensive income (loss)	$	497,678		$	(28,330	)	$	562,245		$	(533,915	)		$	497,678



	Year Ended December 31, 2012
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	$	—		$	—		$	2,935,140		$	—			$	2,935,140

Net investment income	4			8			321,805			(26,922		)		294,895

Net realized gains	—			—			194,228			—				194,228

Net impairment losses recognized in earnings	—			—			(11,388		)	—				(11,388		)

Other underwriting income	—			—			8,090			—				8,090

Equity in net income of investment funds accounted for using the equity method	—			—			73,510			—				73,510

Other income (loss)	—			—			(12,094		)	—				(12,094		)

Total revenues	4			8			3,509,291			(26,922		)		3,482,381


Expenses
Losses and loss adjustment expenses	—			—			1,861,277			—				1,861,277

Acquisition expenses	—			—			508,884			—				508,884

Other operating expenses	35,570			1,218			428,565			—				465,353

Interest expense	23,496			—			31,951			(26,922		)		28,525

Net foreign exchange losses	—			—			21,787			7,168				28,955

Total expenses	59,066			1,218			2,852,464			(19,754		)		2,892,994


Income before income taxes	(59,062		)	(1,210		)	656,827			(7,168		)		589,387

Income tax benefit	—			424			3,586			—				4,010


Income (loss) before equity in net income of subsidiaries	(59,062		)	(786		)	660,413			(7,168		)		593,397


Equity in net income (loss) of subsidiaries	652,459			9,738			—			(662,197		)		—


Net income	593,397			8,952			660,413			(669,365		)		593,397

Preferred dividends	(25,079		)	—			—			—				(25,079		)

Loss on repurchase of preferred shares	(10,612		)	—			—			—				(10,612		)


Net income available to common shareholders	$	557,706		$	8,952		$	660,413		$	(669,365	)		$	557,706


Comprehensive income (loss)	$	726,491		$	2,796		$	786,338		$	(789,134	)		$	726,491



	Year Ended December 31, 2011
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	$	—		$	—		$	2,631,815		$	—			$	2,631,815

Net investment income	—			3			350,412			(12,217		)		338,198

Net realized gains	63			—			107,021			3,562				110,646

Net impairment losses recognized in earnings	—			—			(9,062		)	—				(9,062		)

Other underwriting income	—			—			3,429			—				3,429

Equity in net income (loss) of investment funds accounted for using the equity method	—			—			(9,605		)	—				(9,605		)

Other income (loss)	—			—			(2,114		)	—				(2,114		)

Total revenues	63			3			3,071,896			(8,655		)		3,063,307


Expenses
Losses and loss adjustment expenses	—			—			1,727,553			—				1,727,553

Acquisition expenses	—			—			462,937			—				462,937

Other operating expenses	31,509			887			399,726			—				432,122

Interest expense	23,151			—			20,757			(12,217		)		31,691

Net foreign exchange gains	—			—			(9,024		)	(8,342		)		(17,366		)

Total expenses	54,660			887			2,601,949			(20,559		)		2,636,937


Income before income taxes	(54,597		)	(884		)	469,947			11,904				426,370

Income tax benefit	—			321			9,472			—				9,793


Income (loss) before equity in net income of subsidiaries	(54,597		)	(563		)	479,419			11,904				436,163


Equity in net income (loss) of subsidiaries	490,760			(134		)	—			(490,626		)		—


Net income	436,163			(697		)	479,419			(478,722		)		436,163

Preferred dividends	(25,844		)	—			—			—				(25,844		)


Net income available to common shareholders	$	410,319		$	(697	)	$	479,419		$	(478,722	)		$	410,319


Comprehensive income (loss)	$	385,583		$	23,155		$	440,745		$	(463,900	)		$	385,583



	Year Ended December 31, 2013
Condensed Consolidating Statement	ACGL (Parent Guarantor)			Arch-U.S. (Subsidiary Issuer)			Other ACGL Subsidiaries			Consolidating Adjustments and Eliminations				ACGL Consolidated
of Cash Flows
Operating Activities
Net Cash Provided By (Used For)	$	68,562		$	(6,569	)	$	908,375		$	(119,500	)		$	850,868
Operating Activities
Investing Activities
Purchases of fixed maturity investments	—			—			(18,174,988		)	—				(18,174,988		)

Purchases of equity securities	—			—			(535,857		)	—				(535,857		)

Purchases of other investments	—			—			(1,326,729		)	—				(1,326,729		)

Proceeds from the sales of fixed maturity investments	—			—			17,196,614			—				17,196,614

Proceeds from the sales of equity securities	—			—			462,787			—				462,787

Proceeds from the sales of other investments	—			—			1,162,707			—				1,162,707

Proceeds from redemptions and maturities of fixed maturity investments	—			—			731,708			—				731,708

Net (purchases) sales of short-term investments	5,799			(400,162		)	(356,250		)	—				(750,613		)

Change in investment of securities lending collateral	—			—			(55,643		)	—				(55,643		)

Contributions to subsidiaries	(160		)	(97,850		)	(20,250		)	118,260				—

Intercompany loans issued	—			—			(10,250		)	10,250				—

Purchase of business, net of cash acquired	—			—			—			—				—

Purchases of furniture, equipment and other assets	(712		)	—			(16,787		)	—				(17,499		)

Net Cash Provided By (Used For)	4,927			(498,012		)	(942,938		)	128,510				(1,307,513		)
Investing Activities
Financing Activities
Purchases of common shares under share repurchase program	(57,796		)	—			—			—				(57,796		)

Proceeds from common shares issued, net	3,051			—			118,260			(118,260		)		3,051

Proceeds from intercompany borrowings	—			10,250			—			(10,250		)		—

Proceeds from borrowings	—			494,228			—			—				494,228

Repayments of intercompany borrowings	—			—			—			—				—

Repayments of borrowings	—			—			—			—				—

Change in securities lending collateral	—			—			55,643			—				55,643

Dividends paid to parent (1)	—			—			(119,500		)	119,500				—

Other	—			—			50,830			—				50,830

Preferred dividends paid	(21,938		)	—			—			—				(21,938		)

Net Cash Provided By (Used For)	(76,683		)	504,478			105,233			(9,010		)		524,018
Financing Activities
Effects of exchange rates changes on foreign currency cash	—			—			(4,357		)	—				(4,357		)


Increase (decrease) in cash	(3,194		)	(103		)	66,313			—				63,016

Cash beginning of year	6,417			612			364,012			—				371,041

Cash end of year	$	3,223		$	509		$	430,325		$	—			$	434,057


-1	Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.


	Year Ended December 31, 2012
Condensed Consolidating Statement	ACGL (Parent Guarantor)			Arch-U.S. (Subsidiary Issuer)			Other ACGL Subsidiaries			Consolidating Adjustments and Eliminations				ACGL Consolidated
of Cash Flows
Operating Activities
Net Cash Provided By (Used For)	$	209,500		$	(8,086	)	$	978,679		$	(258,490	)		$	921,603
Operating Activities
Investing Activities
Purchases of fixed maturity investments	—			—			(17,568,592		)	—				(17,568,592		)

Purchases of equity securities	—			—			(268,999		)	—				(268,999		)

Purchases of other investments	—			—			(1,000,049		)	—				(1,000,049		)

Proceeds from the sales of fixed maturity investments	—			—			16,366,306			—				16,366,306

Proceeds from the sales of equity securities	—			—			313,617			—				313,617

Proceeds from the sales of other investments	—			—			443,630			—				443,630

Proceeds from redemptions and maturities of fixed maturity investments	—			—			1,115,594			—				1,115,594

Net (purchases) sales of short-term investments	(5,094		)	1,986			189,027			—				185,919

Change in investment of securities lending collateral	—			—			6,190			—				6,190

Contributions to subsidiaries	—			—			(38,576		)	38,576				—

Purchase of business, net of cash acquired	—			—			28,948			—				28,948

Purchases of furniture, equipment and other assets	(65		)	—			(18,467		)	—				(18,532		)

Net Cash Provided By (Used For)	(5,159		)	1,986			(431,371		)	38,576				(395,968		)
Investing Activities
Financing Activities
Proceeds from issuance of Series C preferred shares, net	315,763			—			—			—				315,763

Repurchase of Series A and B preferred shares	(325,000		)	—			—			—				(325,000		)

Purchases of common shares under share repurchase program	(172,056		)	—			—			—				(172,056		)

Proceeds from common shares issued, net	7,033			—			38,576			(38,576		)		7,033

Repayments of borrowings	—			—			(310,868		)	—				(310,868		)

Change in securities lending collateral	—			—			(6,190		)	—				(6,190		)

Dividends paid to parent (1)	—			—			(258,490		)	258,490				—

Other	—			—			6,664			—				6,664

Preferred dividends paid	(28,381		)	—			—			—				(28,381		)

Net Cash Provided By (Used For)	(202,641		)	—			(530,308		)	219,914				(513,035		)
Financing Activities
Effects of exchange rates changes on foreign currency cash	—			—			6,742			—				6,742


Increase (decrease) in cash	1,700			(6,100		)	23,742			—				19,342

Cash beginning of year	4,717			6,712			340,270			—				351,699

Cash end of year	$	6,417		$	612		$	364,012		$	—			$	371,041


-1	Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.


	Year Ended December 31, 2011
Condensed Consolidating Statement	ACGL (Parent Guarantor)			Arch-U.S. (Subsidiary Issuer)			Other ACGL Subsidiaries			Consolidating Adjustments and Eliminations				ACGL Consolidated
of Cash Flows
Operating Activities
Net Cash Provided By (Used For)	$	300,764		$	5,606		$	901,252		$	(341,510	)		$	866,112
Operating Activities
Investing Activities
Purchases of fixed maturity investments	—			—			(13,875,635		)	—				(13,875,635		)

Purchases of equity securities	—			—			(413,024		)	—				(413,024		)

Purchases of other investments	—			—			(593,862		)	—				(593,862		)

Proceeds from the sales of fixed maturity investments	—			—			12,398,253			—				12,398,253

Proceeds from the sales of equity securities	—			—			369,503			—				369,503

Proceeds from the sales of other investments	—			—			543,757			—				543,757

Proceeds from redemptions and maturities of fixed maturity investments	—			—			1,034,489			—				1,034,489

Net (purchases) sales of short-term investments	4,441			487			(7,317		)	—				(2,389		)

Change in investment of securities lending collateral	—			—			19,475			—				19,475

Contributions to subsidiaries	—			—			(59,844		)	59,844				—

Intercompany loans issued	—			—			(185,289		)	185,289				—

Purchases of furniture, equipment and other assets	(196		)	—			(18,791		)	—				(18,987		)

Net Cash Provided By (Used For)	4,245			487			(788,285		)	245,133				(538,420		)
Investing Activities
Financing Activities
Purchases of common shares under share repurchase program	(287,561		)	—			—			—				(287,561		)

Proceeds from common shares issued, net	6,332			—			59,844			(59,844		)		6,332

Proceeds from intercompany borrowings	—			—			185,289			(185,289		)		—

Repayments of borrowings	—			—			(15,352		)	—				(15,352		)

Change in securities lending collateral	—			—			(19,475		)	—				(19,475		)

Dividends paid to parent (1)	—			—			(341,510		)	341,510				—

Other	—			—			4,765			—				4,765

Preferred dividends paid	(25,844		)	—			—			—				(25,844		)

Net Cash Provided By (Used For)	(307,073		)	—			(126,439		)	96,377				(337,135		)
Financing Activities
Effects of exchange rates changes on foreign currency cash	—			—			(1,598		)	—				(1,598		)


Increase (decrease) in cash	(2,064		)	6,093			(15,070		)	—				(11,041		)

Cash beginning of year	6,781			619			355,340			—				362,740

Cash end of year	$	4,717		$	6,712		$	340,270		$	—			$	351,699


-1	Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.

Subsequent_Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2013
Subsequent Events [Abstract]	'
Schedule of Subsequent Events [Table Text Block]	'
	Subsequent Events
	On January 30, 2014, the Company’s U.S.-based subsidiaries completed the acquisition of CMG Mortgage Insurance Company and the mortgage insurance operating platform of PMI Mortgage Insurance Co. (“PMI”). CMG Mortgage Insurance Company has been renamed “Arch Mortgage Insurance Company” (“Arch MI U.S.”) subject to receipt of applicable state approvals. As part of the transaction, Arch MI U.S. has obtained approval as an eligible mortgage insurer from Fannie Mae and Freddie Mac, subject to maintaining certain ongoing requirements. In addition, the Company entered into a distribution agreement with CMFG Life Insurance Company (“CUNA Mutual”) and a reinsurance agreement with an affiliate of CUNA Mutual. At closing, the Company paid aggregate consideration of $253.0 million. Additional amounts may be paid based on the actual results of CMG Mortgage Insurance Company’s pre-closing portfolio over an agreed upon period.

Schedule_III_Supplementary_Ins

Schedule III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2013
Supplementary Insurance Information [Abstract]	'
Supplementary Insurance Information, for Insurance Companies Disclosure [Text Block]	'
	SCHEDULE III
	ARCH CAPITAL GROUP LTD. AND SUBSIDIARIES
	SUPPLEMENTARY INSURANCE INFORMATION
	(U.S. dollars in thousands)


		Deferred Acquisition Costs,		Reserves for Losses and Loss Adjustment Expenses		Unearned Premiums		Net Premiums Earned		Net Investment Income (1)	Net Losses and Loss Adjustment Expenses Incurred		Amortization of Deferred Acquisition Costs		Other Operating Expenses (2)		Net Premiums Written
		Net
	December 31, 2013
	Insurance		$158,121		$6,137,121		$1,192,188		$1,876,014	NM		$1,188,445		$311,904		$315,387		$1,948,796

	Reinsurance	184,193		2,687,575		704,177		1,269,938		NM	490,979		252,199		142,940		1,402,571

	Total		$342,314		$8,824,696		$1,896,365		$3,145,952	NM		$1,679,424		$564,103		$458,327		$3,351,367

	December 31, 2012
	Insurance		$141,962		$6,149,247		$1,077,211		$1,800,343	NM		$1,283,841		$298,983		$307,489		$1,825,334

	Reinsurance	120,860		2,784,045		570,767		1,134,797		NM	577,436		209,901		122,546		1,226,901

	Total		$262,822		$8,933,292		$1,647,978		$2,935,140	NM		$1,861,277		$508,884		$430,035		$3,052,235

	31-Dec-11
	Insurance		$161,907		$5,762,533		$1,039,081		$1,679,047	NM		$1,172,742		$278,696		$307,797		$1,721,279

	Reinsurance	65,977		2,693,677		372,791		952,768		NM	554,811		184,241		92,945		952,047

	Total		$227,884		$8,456,210		$1,411,872		$2,631,815	NM		$1,727,553		$462,937		$400,742		$2,673,326


	-1	The Company does not manage its assets by segment and, accordingly, net investment income is not allocated to each underwriting segment. See Note 3.

	-2	Certain other operating expenses relate to the Company’s corporate and other segment (non-underwriting). Such amounts are not reflected in the table above. See Note 3.

Schedule_IV_Reinsurance

Schedule IV - Reinsurance	12 Months Ended
	Dec. 31, 2013
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]	'
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Text Block]	'
	SCHEDULE IV
	ARCH CAPITAL GROUP LTD. AND SUBSIDIARIES
	REINSURANCE
	(U.S. dollars in thousands)


		Gross Amount		Ceded to Other Companies (1)			Assumed From Other Companies (1)		Net		Percentage of Amount Assumed to Net
									Amount
	Year Ended December 31, 2013
	Premiums Written:
	Insurance	$	2,682,446	$	(763,713	)	$	30,063	$	1,948,796	1.5	%

	Reinsurance	72,136		(86,620		)	1,417,055		1,402,571		101	%

	Total	$	2,754,582	$	(845,256	)	$	1,442,041	$	3,351,367	43	%

	Year Ended December 31, 2012
	Premiums Written:
	Insurance	$	2,562,788	$	(768,625	)	$	31,171	$	1,825,334	1.7	%

	Reinsurance	111,076		(55,099		)	1,170,924		1,226,901		95.4	%

	Total	$	2,673,864	$	(816,926	)	$	1,195,297	$	3,052,235	39.2	%

	Year Ended December 31, 2011
	Premiums Written:
	Insurance	$	2,402,153	$	(723,206	)	$	42,332	$	1,721,279	2.5	%

	Reinsurance	—		(46,473		)	998,520		952,047		104.9	%

	Total	$	2,402,153	$	(763,130	)	$	1,034,303	$	2,673,326	38.7	%


	-1	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions and are included in the gross premiums written of each segment. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

Schedule_VI_Supplementary_Info

Schedule VI - Supplementary Information For Property and Casualty Insurance Underwriters	12 Months Ended
	Dec. 31, 2013
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]	'
Schedule of Supplemental Information for Property, Casualty Insurance Underwriters [Text Block]	'
	SCHEDULE VI
	ARCH CAPITAL GROUP LTD. AND SUBSIDIARIES
	SUPPLEMENTARY INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS
	(U.S. dollars in thousands)


	Column A	Column B		Column C		Column D		Column E		Column F		Column G	Column H					Column I		Column J		Column K
	Affiliation with Registrant	Deferred Acquisition Costs,		Reserves for Losses and Loss Adjustment Expenses		Discount, if any, deducted in Column C		Unearned Premiums		Net		Net Investment Income (1)	Net Losses and Loss Adjustment Expenses Incurred Related to					Amortization		Net Paid Losses and Loss Adjustment Expenses		Net
		Net								Premiums Earned			(a) Current Year		(b)			of Deferred Acquisition Costs				Premiums Written
															Prior Years
	Insurance
	2013	$	158,121	$	6,137,121	$	12,539	$	1,192,188	$	1,876,014	NM	$	1,233,593	$	(45,148	)	$	311,904	$	1,068,699	$	1,948,796

	2012	141,962		6,191,705		10,485		1,077,211		1,800,343		NM	1,315,088		(31,247		)	298,983		981,790		1,825,334

	2011	161,907		5,762,533		9,834		1,039,081		1,679,047		NM	1,224,861		(52,119		)	278,696		900,398		1,721,279


	Reinsurance
	2013	$	184,193	$	2,687,575	$	—	$	704,177	$	1,269,938	NM	$	709,873	$	(218,894	)	$	252,199	$	640,118	$	1,402,571

	2012	120,860		2,741,587		—		570,767		1,134,797		NM	767,717		(190,281		)	209,901		483,589		1,226,901

	2011	65,977		2,693,677		—		372,791		952,768		NM	787,707		(232,896		)	184,241		552,225		952,047


	-1	The Company does not manage its assets by segment and, accordingly, net investment income is not allocated to each underwriting segment. See Note 3.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2013
Accounting Policies [Abstract]	'
Basis of presentation	'
Basis of presentation	The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of ACGL and its subsidiaries, including Arch Reinsurance Ltd. (“Arch Re Bermuda”), Arch Re U.S., Arch-U.S., Arch Insurance Company, Arch Specialty Insurance Company, Arch Excess & Surplus Insurance Company, Arch Indemnity Insurance Company, Arch Insurance Canada Ltd. ("Arch Insurance Canada"), Arch Risk Transfer Services Ltd., Arch Reinsurance Europe Underwriting Limited (“Arch Re Europe”), Arch Mortgage Insurance Limited (“Arch MI Europe”), Arch Insurance Company (Europe) Limited (“Arch Insurance Company Europe”) and Lloyd’s of London syndicate 2012 and related companies (“Arch Syndicate 2012”). 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.
Use of estimates	'
Use of estimates	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates and assumptions.
Premium revenues	'
	Insurance premiums written are generally recorded at the policy inception and are primarily earned on a pro rata basis over the terms of the policies for all products, usually 12 months. Premiums written include estimates in the Company’s programs, specialty lines, lenders products business and for participation in involuntary pools. Such premium estimates are derived from multiple sources which include the historical experience of the underlying business, similar business and available industry information. Unearned premium reserves represent the portion of premiums written that relates to the unexpired terms of in-force insurance policies.
	Reinsurance premiums written include amounts reported by brokers and ceding companies, supplemented by the Company’s own estimates of premiums where reports have not been received. The determination of premium estimates requires a review of the Company’s experience with the ceding companies, familiarity with each market, the timing of the reported information, an analysis and understanding of the characteristics of each line of business, and management’s judgment of the impact of various factors, including premium or loss trends, on the volume of business written and ceded to the Company. On an ongoing basis, the Company’s underwriters review the amounts reported by these third parties for reasonableness based on their experience and knowledge of the subject class of business, taking into account the Company’s historical experience with the brokers or ceding companies. In addition, reinsurance contracts under which the Company assumes business generally contain specific provisions which allow the Company to perform audits of the ceding company to ensure compliance with the terms and conditions of the contract, including accurate and timely reporting of information. Based on a review of all available information, management establishes premium estimates where reports have not been received. Premium estimates are updated when new information is received and differences between such estimates and actual amounts are recorded in the period in which estimates are changed or the actual amounts are determined.
	Reinsurance premiums written are recorded based on the type of contracts the Company writes. Premiums on the Company’s excess of loss and pro rata reinsurance contracts are estimated when the business is underwritten. For excess of loss contracts, premiums are recorded as written based on the terms of the contract. Estimates of premiums written under pro rata contracts are recorded in the period in which the underlying risks are expected to incept and are based on information provided by the brokers and the ceding companies. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term.
	Reinstatement premiums for the Company’s insurance and reinsurance operations are recognized at the time a loss event occurs, where coverage limits for the remaining life of the contract are reinstated under pre-defined contract terms. Reinstatement premiums, if obligatory, are fully earned when recognized. The accrual of reinstatement premiums is based on an estimate of losses and loss adjustment expenses, which reflects management’s judgment. Premium estimates are reviewed by management at least quarterly. Such review includes a comparison of actual reported premiums to expected ultimate premiums along with a review of the aging and collection of premium estimates. Based on management’s review, the appropriateness of the premium estimates is evaluated, and any adjustment to these estimates is recorded in the period in which it becomes known. Adjustments to premium estimates could be material and such adjustments could directly and significantly impact earnings favorably or unfavorably in the period they are determined because the estimated premium may be fully or substantially earned. A significant portion of amounts included as premiums receivable, which represent estimated premiums written, net of commissions, are not currently due based on the terms of the underlying contracts.
	Reinsurance premiums written, irrespective of the class of business, are generally earned on a pro rata basis over the terms of the underlying policies or reinsurance contracts. Contracts and policies written on a “losses occurring” basis cover claims that may occur during the term of the contract or policy, which is typically 12 months. Accordingly, the premium is earned evenly over the term. Contracts which are written on a “risks attaching” basis cover claims which attach to the underlying insurance policies written during the terms of such contracts. Premiums earned on such contracts usually extend beyond the original term of the reinsurance contract, typically resulting in recognition of premiums earned over a 24-month period. Certain of the Company’s reinsurance contracts include provisions that adjust premiums or acquisition expenses based upon the experience under the contracts. Premiums written and earned, as well as related acquisition expenses, are recorded based upon the projected experience under such contracts.
	The Company also writes certain reinsurance business that is intended to provide insurers with risk management solutions that complement traditional reinsurance. Under these contracts, the Company assumes a measured amount of insurance risk in exchange for an anticipated margin, which is typically lower than on traditional reinsurance contracts. The terms and conditions of these contracts may include additional or return premiums based on loss experience, loss corridors, sublimits and caps. Examples of such business include aggregate stop-loss coverages, financial quota share coverages and multi-year retrospectively rated excess of loss coverages. If these contracts are deemed to transfer risk, they are accounted for as reinsurance.
Deferred acquisition costs	'
Deferred acquisition costs	Acquisition expenses and other expenses related to the Company’s underwriting operations that vary with, and are directly related to, the successful acquisition or renewal of business are deferred and amortized over the period in which the related premiums are earned. Acquisition expenses, net of ceding commissions received from reinsurers, consist principally of commissions and premium taxes paid to obtain the Company’s business. Other operating expenses also include expenses that vary with, and are directly related to, the acquisition of business. Deferred acquisition costs, which are based on the related unearned premiums, are carried at their estimated realizable value and take into account anticipated losses and loss adjustment expenses, based on historical and current experience, and anticipated investment income. A premium deficiency occurs if the sum of anticipated losses and loss adjustment expenses, unamortized acquisition costs and maintenance costs exceed unearned premiums and anticipated investment income. A premium deficiency is recorded by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. No significant premium deficiency charges were recorded by the Company during 2013, 2012 or 2011.
Deposit accounting	'
	Certain assumed reinsurance contracts, which pursuant to Financial Accounting Standards Board (“FASB”) guidance regarding the accounting and reporting for reinsurance and short-duration and long-duration contracts, that are deemed not to transfer insurance risk, are accounted for using the deposit method of accounting as prescribed in the FASB guidance. However, it is possible that the Company could incur financial losses on such contracts. Management exercises significant judgment in the assumptions used in determining whether assumed contracts should be accounted for as reinsurance contracts or deposit contracts. Under the FASB guidance, for those contracts that contain only significant underwriting risk, the estimated profit margin is deferred and amortized over the contract period and such amount is included in the Company’s underwriting results. When the estimated profit margin is explicit, the margin is reflected as other underwriting income and any adverse financial results on such contracts are reflected as incurred losses. When the estimated profit margin is implicit, the margin is reflected as an offset to paid losses and any adverse financial results on such contracts are reflected as incurred losses. Additional judgments are required when applying the accounting guidance with respect to the revenue recognition criteria for contracts deemed to transfer only significant underwriting risk. For those contracts that contain only significant timing risk, an accretion rate is established at inception of the contract based on actuarial estimates whereby the deposit accounting liability is increased to the estimated amount payable over the contract term. The accretion on the deposit is based on the expected rate of return required to fund the expected future payment obligations. Periodically the Company reassesses the estimated ultimate liability and the related expected rate of return. The accretion of the deposit accounting liability as well as changes to the estimated ultimate liability and the accretion rate are reflected as part of interest expense in the Company’s results of operations.

	Deposit accounting liabilities totaled $421.3 million and $27.6 million, respectively, at December 31, 2013 and 2012. Under some of these contracts, the ceding company retains the related assets on a funds-held basis. In those instances, the Company records the asset as a deposit accounting asset. Deposit accounting assets of $370.5 million and $6.5 million, respectively, at December 31, 2013 and 2012 are included in “Other assets” on the Company’s balance sheet. Interest income produced by those assets are recorded as part of net investment income in the Company's results of operations.
Retroactive accounting	'
Retroactive accounting	Retroactive reinsurance reimburses a ceding company for liabilities incurred as a result of past insurable events covered by the underlying policies reinsured. In certain instances, reinsurance contracts cover losses both on a prospective basis and on a retroactive basis and, accordingly, the Company bifurcates the prospective and retrospective elements of these reinsurance contracts and accounts for each element separately. Underwriting income generated in connection with retroactive reinsurance contracts is deferred and amortized into income over the settlement period while losses are charged to income immediately. Subsequent changes in estimated or actual cash flows under such retroactive reinsurance contracts are accounted for by adjusting the previously deferred amount to the balance that would have existed had the revised estimate been available at the inception of the reinsurance transaction, with a corresponding charge or credit to income.
Reinsurance ceded	'
Reinsurance ceded	In the normal course of business, the Company purchases reinsurance to increase capacity and to limit the impact of individual losses and events on its underwriting results by reinsuring certain levels of risk with other insurance enterprises or reinsurers. The Company uses pro rata, excess of loss and facultative reinsurance contracts. Reinsurance ceding commissions are recognized as a reduction to acquisition costs on a pro rata basis over the period of risk while the portion of such commissions that will be earned in the future is deferred. The accompanying consolidated statement of income reflects premiums and losses and loss adjustment expenses and acquisition costs, net of reinsurance ceded. See Note 4 for information on the Company's reinsurance usage. Ceded unearned premiums are reported as prepaid reinsurance premiums and estimated amounts of reinsurance recoverable on unpaid losses are reported as unpaid losses and loss adjustment expenses recoverable. Reinsurance premiums ceded and unpaid losses and loss adjustment expenses recoverable are estimated in a manner consistent with that of the original policies issued and the terms of the reinsurance contracts. If the reinsurers are unable to satisfy their obligations under the agreements, the Company’s insurance or reinsurance subsidiaries would be liable for such defaulted amounts.
Cash	'
Cash	Cash includes cash equivalents, which are investments with original maturities of three months or less that are not managed by external or internal investment advisors.
Investments	'
	The Company currently classifies substantially all of its fixed maturity investments, equity securities and short-term investments as “available for sale” and, accordingly, they are carried at estimated fair value (also known as fair value) with the changes in fair value recorded as an unrealized gain or loss component of accumulated other comprehensive income in shareholders’ equity. The fair value of fixed maturity securities and equity securities is generally determined from quotations received from nationally recognized pricing services, or when such prices are not available, by reference to broker or underwriter bid indications. Short-term investments comprise securities due to mature within one year of the date of issue. Short-term investments include certain cash equivalents which are part of investment portfolios under the management of external and internal investment managers.
	The Company participates in a securities lending program as a mechanism for generating additional interest income on its fixed income portfolio. Under the security lending agreements, certain of its fixed income portfolio securities are loaned to third parties, primarily major brokerage firms, for short periods of time through a lending agent. Such securities have been reclassified as “Fixed maturities and short-term investments pledged under securities lending agreements, at fair value.” The Company maintains legal control over the securities it lends, retains the earnings and cash flows associated with the loaned securities and receives a fee from the borrower for the temporary use of the securities. Collateral received, primarily in the form of cash, is required at a rate of 102% of the fair value of the loaned securities including accrued investment income and is monitored and maintained by the lending agent. Such collateral is reinvested and is reflected as “Investment of funds received under securities lending agreements, at fair value.”
	The Company’s investment portfolio includes certain funds that, due to their ownership structure, are accounted for by the Company using the equity method. In applying the equity method, these investments are initially recorded at cost and are subsequently adjusted based on the Company’s proportionate share of the net income or loss of the funds (which include changes in the fair value of the underlying securities in the funds). Such investments are generally recorded on a one month lag with some investments reported for on a three month lag based on the availability of reports from the investment funds. Changes in the carrying value of such investments are recorded in net income as “Equity in net income (loss) of investment funds accounted for using the equity method.” As such, fluctuations in the carrying value of the investment funds accounted for using the equity method may increase the volatility of the Company’s reported results of operations.
	Other investments include funds and separately managed accounts with holdings in Asian and emerging markets, fixed maturities, term loans and other investment strategies. The fair value for certain of the Company’s other investments are determined using net asset values (“NAVs”) as advised by external fund managers. The NAV is based on the fund manager’s valuation of the underlying holdings in accordance with the fund’s governing documents. Certain of the funds are accounted for as available for sale equity securities, regardless of the nature of the investments held within the fund.
	The Company elected to carry certain fixed maturity securities, equity securities and other investments at fair value under the fair value option afforded by accounting guidance regarding the fair value option for financial assets and liabilities. Changes in fair value of investments accounted for using the fair value option are included in "Net realized gains (losses)." The primary reasons for electing the fair value option were to address simplification and cost-benefit considerations.
	The Company invests in limited partner equity interests issued by third party variable interest entities (“VIE”). Such amounts are included in investments accounted for using the equity method, other investments available for sale and investments accounted for using the fair value option. A VIE refers to entities that have characteristics such as (i) insufficient equity at risk to allow the entity to finance its activities without additional financial support or (ii) instances where the equity investors, as a group, do not have the characteristic of a controlling financial interest. If the Company is determined to be the primary beneficiary, it is required to consolidate the VIE. The primary beneficiary is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (i) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (ii) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. At inception of the VIE as well as on an ongoing basis, the Company determines whether it is the primary beneficiary based on an analysis of the Company’s level of involvement in the VIE, the contractual terms, and the overall structure of the VIE. The Company's maximum exposure to loss with respect to these investments is limited to the investment carrying amounts reported in the Company's consolidated balance sheet and any unfunded commitment.
	The Company performs quarterly reviews of its investments to determine whether declines in fair value below the cost basis are considered other-than-temporary in accordance with applicable accounting guidance regarding the recognition and presentation of other-than-temporary impairments (“OTTI”). The process of determining whether a security is other-than-temporarily impaired requires judgment and involves analyzing many factors. These factors include (i) an analysis of the liquidity, business prospects and overall financial condition of the issuer, (ii) the time period in which there was a significant decline in value, (iii) the significance of the decline and (iv) the analysis of specific credit events. The Company evaluates the unrealized losses of its equity securities by issuer and forecasts a reasonable period of time by which the fair value of the securities would increase and the Company would recover its cost. If the Company is unable to forecast a reasonable period of time in which to recover the cost of its equity securities, a net impairment loss in earnings equivalent to the entire unrealized loss is recognized.
	When there are credit-related losses associated with debt securities for which the Company does not have an intent to sell and it is more likely than not that it will not be required to sell the security before recovery of its cost basis, the amount of the OTTI related to a credit loss is recognized in earnings and the amount of the OTTI related to other factors (e.g., interest rates, market conditions, etc.) is recorded as a component of other comprehensive income (loss). The amount of the credit loss of an impaired debt security is the difference between the amortized cost and the greater of (i) the present value of expected future cash flows and (ii) the fair value of the security. In instances where no credit loss exists but it is more likely than not that the Company will have to sell the debt security prior to the anticipated recovery, the decline in fair value below amortized cost is recognized as an OTTI in earnings. In periods after the recognition of an OTTI on debt securities, the Company accounts for such securities as if they had been purchased on the measurement date of the OTTI at an amortized cost basis equal to the previous amortized cost basis less the OTTI recognized in earnings. For debt securities for which OTTI were recognized in earnings, the difference between the new amortized cost basis and the cash flows expected to be collected will be accreted or amortized into net investment income. See Note 6, “Investment Information—Other-Than-Temporary Impairments” for additional information.
	Net investment income includes interest and dividend income together with amortization of market premiums and discounts and is net of investment management and custody fees. Anticipated prepayments and expected maturities are used in applying the interest method for certain investments such as mortgage and other asset-backed securities. When actual prepayments differ significantly from anticipated prepayments, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The net investment in such securities is adjusted to the amount that would have existed had the new effective yield been applied since the acquisition of the security. Such adjustments, if any, are included in net investment income when determined. Equity in net income (loss) of investment funds accounted for using the equity method includes changes in the fair value of certain alternative investments accounted for under the equity method.
	Investment gains or losses realized on the sale of investments, except for certain fund investments, are determined on a first-in, first-out basis and are reflected in net income. Investments gains or losses realized on the sale of certain fund investments are determined on an average cost basis. Unrealized appreciation or decline in the value of securities, which are carried at fair value, is excluded from net income and recorded as a separate component of accumulated other comprehensive income, net of applicable deferred income tax.
Reserve for losses and loss adjustment expenses	'
Reserve for losses and loss adjustment expenses	The reserve for losses and loss adjustment expenses consists of estimates of unpaid reported losses and loss adjustment expenses and estimates for losses incurred but not reported. The reserve for unpaid reported losses and loss adjustment expenses, established by management based on reports from ceding companies and claims from insureds, excludes estimates of amounts due from insureds related to losses under high deductible policies, and represents the estimated ultimate cost of events or conditions that have been reported to or specifically identified by the Company. Such reserves are supplemented by management’s estimates of reserves for losses incurred for which reports or claims have not been received. The Company’s reserves are based on a combination of reserving methods, incorporating both Company and industry loss development patterns. The Company selects the initial expected loss and loss adjustment expense ratios based on information derived by its underwriters and actuaries during the initial pricing of the business, supplemented by industry data where appropriate. Such ratios consider, among other things, rate changes and changes in terms and conditions that have been observed in the market. These estimates are reviewed regularly and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments, if any, are reflected in income in the period in which they are determined. As actual loss information has been reported, the Company has developed its own loss experience and its reserving methods include other actuarial techniques. Over time, such techniques have been given further weight in its reserving process based on the continuing maturation of the Company’s reserves. Inherent in the estimates of ultimate losses and loss adjustment expenses are expected trends in claims severity and frequency and other factors which may vary significantly as claims are settled. Accordingly, ultimate losses and loss adjustment expenses may differ materially from the amounts recorded in the accompanying consolidated financial statements. Losses and loss adjustment expenses are recorded on an undiscounted basis, except for excess workers’ compensation and employers’ liability business written by the Company’s insurance operations.
Contractholder receivables and payables	'
Contractholder receivables and payables	Certain insurance policies written by the Company’s insurance operations feature large deductibles, primarily in its construction and national accounts lines of business. Under such contracts, the Company is obligated to pay the claimant for the full amount of the claim. The Company is subsequently reimbursed by the policyholder for the deductible amount. These amounts are included on a gross basis in the consolidated balance sheet in contractholder payables and contractholder receivables, respectively. In the event that the Company is unable to collect from the policyholder, the Company would record an increase to losses and loss adjustment expenses related to such policy.
Foreign exchange	'
Foreign exchange	Assets and liabilities of foreign operations whose functional currency is not the U.S. Dollar are translated at the prevailing exchange rates at each balance sheet date. Revenues and expenses of such foreign operations are translated at average exchange rates during the year. The net effect of the translation adjustments for foreign operations is included in accumulated other comprehensive income, net of applicable deferred income tax. Monetary assets and liabilities, such as premiums receivable and the reserve for losses and loss adjustment expenses, denominated in foreign currencies are revalued at the exchange rate in effect at the balance sheet date with the resulting foreign exchange gains and losses included in net income. Accounts that are classified as non-monetary, such as deferred acquisition costs and the unearned premium reserves, are not revalued. In the case of foreign currency denominated fixed maturity securities which are classified as “available for sale,” the change in exchange rates between the local currency in which the investments are denominated and the Company’s functional currency at each balance sheet date is included in unrealized appreciation or decline in value of securities, a component of accumulated other comprehensive income, net of applicable deferred income tax.
Income taxes	'
	Deferred income taxes reflect the expected future tax consequences of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and amounts used for income tax purposes. A valuation allowance is recorded if it is more likely than not that some or all of a deferred tax asset may not be realized. The Company considers future taxable income and feasible tax planning strategies in assessing the need for a valuation allowance. In the event the Company determines that it will not be able to realize all or part of its deferred income tax assets in the future, an adjustment to the deferred income tax assets would be charged to income in the period in which such determination is made. In addition, if the Company subsequently assesses that the valuation allowance is no longer needed, a benefit would be recorded to income in the period in which such determination is made. See Note 12 for more information.
	The Company recognizes a tax benefit where it concludes that it is more likely than not that the tax benefit will be sustained on audit by the taxing authority based solely on the technical merits of the associated tax position. If the recognition threshold is met, the Company recognizes a tax benefit measured at the largest amount of the tax benefit that, in the Company’s judgment, is greater than 50% likely to be realized. The Company records interest and penalties related to unrecognized tax benefits in the provision for income taxes.
Share-based payment arrangements	'
Share-based payment arrangements	The Company applies a fair value based measurement method in accounting for its share-based payment arrangements with eligible employees and directors. Compensation expense is estimated based on the fair value of the award at the grant date and is recognized in net income over the requisite service period with a corresponding increase in shareholders’ equity. No value is attributed to awards that employees forfeit because they fail to satisfy vesting conditions. As such, the number of shares granted is reduced by assumed forfeitures and adjusted based on actual forfeitures until vesting. The Company’s share-based payment arrangements generally vest over a three year period with one-third vesting on the first, second and third anniversaries of the grant date. The share-based compensation expense associated with such awards that have graded vesting features and vest based on service conditions only is calculated on a straight-line basis over the requisite service period for the entire award. For awards granted to retirement-eligible employees where no service is required for the employee to retain the award, the grant date fair value is immediately recognized as compensation expense at the grant date because the employee is able to retain the award without continuing to provide service. For employees near retirement eligibility, attribution of compensation cost is over the period from the grant date to the retirement eligibility date. In November 2012, the Company issued off-cycle share-based awards, which will cliff vest on the fifth anniversary of the grant date. The expense for such grant will be amortized on a straight- line basis over the five-year requisite service period. The off-cycle awards have similar terms as the annual award agreements, however with respect to retirement eligible employees service is required for the employee to retain the award. Retirement-eligible employees retiring prior to the fifth anniversary of the grant date will vest in a pro-rated portion of the award commensurate with the service performed. Such employees will receive the vested portion at the end of the five-year cliff period. These charges had no impact on the Company’s cash flows or total shareholders’ equity. See Note 17 for information relating to the Company’s share-based payment awards.
Guaranty fund and other related assessments	'
Guaranty fund and other related assessments	Liabilities for guaranty fund and other related assessments in the Company’s insurance and reinsurance operations are accrued when the Company receives notice that an amount is payable, or earlier if a reasonable estimate of the assessment can be made.
Treasury shares	'
Treasury shares	Treasury shares are common shares purchased by the Company and not subsequently canceled. These shares are recorded at cost and result in a reduction of the Company’s shareholders’ equity in its Consolidated Balance Sheets.
Recent accounting pronouncements	'
	Effective January 1, 2013, the Company adopted FASB guidance requiring additional disclosures about reclassification adjustments from accumulated other comprehensive income. As this guidance is disclosure-related only, the adoption of this guidance did not impact the Company’s results of operations, financial condition or liquidity. The additional disclosures are provided in Note 10, "Other Comprehensive Income (Loss)."
	Effective January 1, 2013, the Company adopted FASB guidance requiring additional disclosures about financial instruments and derivative instruments that are either: (1) offset for balance sheet presentation purposes or (2) subject to an enforceable master netting arrangement or similar arrangement, regardless of whether they are offset for balance sheet presentation purposes. The disclosure requirements of this guidance are limited to derivatives, repurchase agreements and reverse repurchase agreements, and securities borrowing/lending transactions. As this guidance is disclosure-related only and did not amend existing balance sheet offsetting guidance, adoption did not impact the Company’s results of operations, financial condition or liquidity. The additional disclosures are provided in Note 6, "Investment Information," and Note 9, "Derivative Instruments."

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Analysis of underwriting income by segment and reconciliation to net income available to common shareholders	'
	The following tables set forth an analysis of the Company’s underwriting income by segment, together with a reconciliation of underwriting income to net income available to common shareholders, summary information regarding net premiums written and earned by major line of business and net premiums written by location:


		Year Ended December 31, 2013
		Insurance				Reinsurance				Total
	Gross premiums written (1)	$	2,712,509			$	1,489,191			$	4,196,623

	Net premiums written	1,948,796				1,402,571				3,351,367


	Net premiums earned	$	1,876,014			$	1,269,938			$	3,145,952

	Other underwriting income	2,122				5,517				7,639

	Losses and loss adjustment expenses	(1,188,445		)		(490,979		)		(1,679,424		)
	Acquisition expenses, net	(311,904		)		(252,199		)		(564,103		)
	Other operating expenses	(315,387		)		(142,940		)		(458,327		)
	Underwriting income	$	62,400			$	389,337			451,737

	Net investment income									267,219

	Net realized gains									74,018

	Net impairment losses recognized in earnings									(3,786		)
	Equity in net income (loss) of investment funds									35,701
	accounted for using the equity method
	Other income (loss)									(586		)
	Other expenses									(42,403		)
	Interest expense									(27,060		)
	Net foreign exchange losses									(12,335		)
	Income before income taxes									742,505

	Income tax expense									(32,774		)
	Net income									709,731

	Preferred dividends									(21,938		)
	Net income available to common shareholders									$	687,793


	Underwriting Ratios
	Loss ratio	63.3		%		38.7		%		53.4		%
	Acquisition expense ratio (2)	16.5		%		19.9		%		17.9		%
	Other operating expense ratio	16.8		%		11.3		%		14.6		%
	Combined ratio	96.6		%		69.9		%		85.9		%

	-1	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

	-2	The acquisition expense ratio is adjusted to include certain other underwriting income.


		Year Ended December 31, 2012
		Insurance				Reinsurance				Total
	Gross premiums written (1)	$	2,593,959			$	1,282,000			$	3,869,161

	Net premiums written	1,825,334				1,226,901				3,052,235


	Net premiums earned	$	1,800,343			$	1,134,797			$	2,935,140

	Other underwriting income	2,335				5,755				8,090

	Losses and loss adjustment expenses	(1,283,841		)		(577,436		)		(1,861,277		)
	Acquisition expenses, net	(298,983		)		(209,901		)		(508,884		)
Other operating expenses	(307,489		)		(122,546		)		(430,035		)
Underwriting income (loss)	$	(87,635	)		$	230,669			143,034

Net investment income									294,895

Net realized gains									194,228

Net impairment losses recognized in earnings									(11,388		)
Equity in net income (loss) of investment funds									73,510
accounted for using the equity method
Other income (loss)									(12,094		)
Other expenses									(35,318		)
Interest expense									(28,525		)
Net foreign exchange losses									(28,955		)
Income before income taxes									589,387

Income tax benefit									4,010

Net income									593,397

Preferred dividends									(25,079		)
Loss on repurchase of preferred shares									$	(10,612	)
Net income available to common shareholders									$	557,706


Underwriting Ratios
Loss ratio	71.3		%		50.9		%		63.4		%
Acquisition expense ratio (2)	16.5		%		18.5		%		17.3		%
Other operating expense ratio	17.1		%		10.8		%		14.7		%
Combined ratio	104.9		%		80.2		%		95.4		%

-1	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

-2	The acquisition expense ratio is adjusted to include certain other underwriting income.


	Year Ended December 31, 2011
	Insurance				Reinsurance				Total
Gross premiums written (1)	$	2,444,485			$	998,520			$	3,436,456

Net premiums written	1,721,279				952,047				2,673,326


Net premiums earned	$	1,679,047			$	952,768			$	2,631,815

Other underwriting income	2,870				559				3,429

Losses and loss adjustment expenses	(1,172,742		)		(554,811		)		(1,727,553		)
Acquisition expenses, net	(278,696		)		(184,241		)		(462,937		)
Other operating expenses	(307,797		)		(92,945		)		(400,742		)
Underwriting income (loss)	$	(77,318	)		$	121,330			44,012

Net investment income									338,198

Net realized gains									110,646

Net impairment losses recognized in earnings									(9,062		)
Equity in net income (loss) of investment funds									(9,605		)
accounted for using the equity method
Other income									(2,114		)
Other expenses									(31,380		)
Interest expense									(31,691		)
Net foreign exchange gains									17,366

Income before income taxes									426,370

Income tax benefit									9,793

Net income									436,163

Preferred dividends									(25,844		)
Net income available to common shareholders									$	410,319


Underwriting Ratios
Loss ratio	69.8		%		58.2		%		65.6		%
Acquisition expense ratio (2)	16.4		%		19.3		%		17.5		%
Other operating expense ratio	18.3		%		9.8		%		15.2		%
Combined ratio	104.5		%		87.3		%		98.3		%

-1	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

-2	The acquisition expense ratio is adjusted to include certain other underwriting income.
Summary of information regarding net premiums written and earned by major line of business and net premiums written by location	'


	INSURANCE SEGMENT	Year Ended December 31,
		2013				2012				2011
	Net premiums written (1)
	Programs	$	419,673			$	340,130			$	290,378

	Property, energy, marine and aviation	280,551				294,690				335,589

	Professional liability	222,351				260,705				237,860

	Executive assurance	213,727				250,904				231,405

	Construction	161,877				130,201				120,405

	Casualty	112,094				112,307				114,235

	National accounts	109,233				80,929				80,973

	Lenders products	101,576				99,724				94,301

	Surety	64,911				53,271				42,475

	Travel and accident	63,209				80,489				71,940

	Healthcare	40,115				36,814				35,652

	Other (2)	159,479				85,170				66,066

	Total	$	1,948,796			$	1,825,334			$	1,721,279


	Net premiums earned (1)
	Programs	$	386,840			$	318,740			$	283,367

	Property, energy, marine and aviation	304,294				313,081				322,510

	Professional liability	231,014				258,401				252,037

	Executive assurance	221,925				241,791				228,623

	Construction	149,864				129,446				112,764

	Casualty	103,152				113,597				111,654

	National accounts	100,865				79,771				79,542

	Lenders products	99,847				103,478				79,522

	Surety	57,719				47,302				41,119

	Travel and accident	59,987				78,050				69,945

	Healthcare	38,852				36,779				35,906

	Other (2)	121,655				79,907				62,058

	Total	$	1,876,014			$	1,800,343			$	1,679,047


	Net premiums written by client location (1)
	United States	$	1,526,156			$	1,314,577			$	1,208,007

Europe	226,254				271,278				273,578

Asia and Pacific	95,970				120,492				119,523

Other	100,416				118,987				120,171

Total	$	1,948,796			$	1,825,334			$	1,721,279


Net premiums written by underwriting location (1)
United States	$	1,478,930			$	1,254,623			$	1,153,834

Europe	389,763				472,132				463,855

Other	80,103				98,579				103,590

Total	$	1,948,796			$	1,825,334			$	1,721,279


-1	Insurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

-2	Includes alternative markets, contract binding, accident and health and excess workers' compensation business.


REINSURANCE SEGMENT	Year Ended December 31,
	2013				2012				2011
Net premiums written (1)
Other specialty (2)	$	417,865			$	308,104			$	219,632

Casualty (3)	306,304				205,925				173,344

Property excluding property catastrophe (4)	292,536				265,783				226,013

Property catastrophe	220,749				283,677				246,793

Marine and aviation	64,380				84,649				77,309

Other (5)	100,737				78,763				8,956

Total	$	1,402,571			$	1,226,901			$	952,047


Net premiums earned (1)
Other specialty (2)	$	387,630			$	309,101			$	195,855

Casualty (3)	241,774				188,963				189,608

Property excluding property catastrophe (4)	274,719				254,338				243,702

Property catastrophe	232,423				280,185				238,748

Marine and aviation	70,105				76,145				77,819

Other (5)	63,287				26,065				7,036

Total	$	1,269,938			$	1,134,797			$	952,768


Net premiums written (1)
Pro rata	$	781,594			$	598,874			$	416,321

Excess of loss	620,977				628,027				535,726

Total	$	1,402,571			$	1,226,901			$	952,047


Net premiums earned (1)
Pro rata	$	659,852			$	515,764			$	435,311

Excess of loss	610,086				619,033				517,457

Total	$	1,269,938			$	1,134,797			$	952,768


Net premiums written by client location (1)
United States	$	770,080			$	629,614			$	512,319

Europe	327,172				341,674				250,809

Asia and Pacific	120,017				104,398				75,590

Bermuda	87,047				72,864				60,246

Other	98,255				78,351				53,083

Total	$	1,402,571			$	1,226,901			$	952,047


Net premiums written by underwriting location (1)
Bermuda	$	548,924			$	595,999			$	531,254

United States	507,183				379,239				323,731

Europe	309,242				225,491				84,919

Other	37,222				26,172				12,143

Total	$	1,402,571			$	1,226,901			$	952,047


-1	Reinsurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

-2	Includes U.K. motor, trade credit, surety, workers’ compensation catastrophe, accident and health, private passenger auto and other.

-3	Includes professional liability, executive assurance and healthcare business.

-4	Includes facultative business.

-5	Includes mortgage, life, casualty clash and other.

Reinsurance_Tables

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2013
Reinsurance Disclosures [Abstract]	'
Effects of reinsurance	'
	The effects of reinsurance on the Company’s written and earned premiums and losses and loss adjustment expenses with unaffiliated reinsurers were as follows:


		Year Ended December 31,
		2013			2012			2011
	Premiums Written
	Direct	$	2,754,582		$	2,673,864		$	2,402,153

	Assumed	1,442,041			1,195,297			1,034,303

	Ceded	(845,256		)	(816,926		)	(763,130		)
	Net	$	3,351,367		$	3,052,235		$	2,673,326


	Premiums Earned
	Direct	$	2,666,104		$	2,572,078		$	2,357,656

	Assumed	1,296,048			1,165,371			1,034,939

	Ceded	(816,200		)	(802,309		)	(760,780		)
	Net	$	3,145,952		$	2,935,140		$	2,631,815


	Losses and Loss Adjustment Expenses
	Direct	$	1,603,369		$	1,725,707		$	1,584,815

	Assumed	450,618			578,081			630,466

	Ceded	(374,563		)	(442,511		)	(487,728		)
	Net	$	1,679,424		$	1,861,277		$	1,727,553

Reserve_for_Losses_and_Loss_Ad1

Reserve for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2013
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]	'
Analysis of losses and loss adjustment expenses and reconciliation of beginning and ending reserve balances	'
	The following table represents an analysis of losses and loss adjustment expenses and a reconciliation of the beginning and ending reserve for losses and loss adjustment expenses:


		Year Ended December 31,
		2013			2012			2011
	Reserve for losses and loss adjustment expenses at beginning of year	$	8,933,292		$	8,456,210		$	8,098,454

	Unpaid losses and loss adjustment expenses recoverable	1,829,070			1,818,047			1,703,201

	Net reserve for losses and loss adjustment expenses at beginning of year	7,104,222			6,638,163			6,395,253


	Net incurred losses and loss adjustment expenses relating to losses
	occurring in:
	Current year	1,943,466			2,082,805			2,012,569

	Prior years	(264,042		)	(221,528		)	(285,016		)
	Total net incurred losses and loss adjustment expenses	1,679,424			1,861,277			1,727,553


	Net losses and loss adjustment expense reserves of acquired business	—			31,977			—


	Foreign exchange losses (gains)	1,617			38,184			(32,020		)


	Net paid losses and loss adjustment expenses relating to losses
	occurring in:
	Current year	(288,114		)	(295,984		)	(325,273		)
	Prior years	(1,420,703		)	(1,169,395		)	(1,127,350		)
	Total net paid losses and loss adjustment expenses	(1,708,817		)	(1,465,379		)	(1,452,623		)

	Net reserve for losses and loss adjustment expenses at end of year	7,076,446			7,104,222			6,638,163

	Unpaid losses and loss adjustment expenses recoverable	1,748,250			1,829,070			1,818,047

	Reserve for losses and loss adjustment expenses at end of year	$	8,824,696		$	8,933,292		$	8,456,210

Investment_Information_Tables

Investment Information (Tables)	12 Months Ended
	Dec. 31, 2013
Disclosure Investment Information [Abstract]	'
Summary of fair value and cost or amortized cost of available for sale securities	'
	The following table summarizes the fair value and cost or amortized cost of the Company’s securities classified as available for sale:


		Estimated			Gross			Gross			Cost or			OTTI
		Fair			Unrealized			Unrealized			Amortized			Unrealized
		Value			Gains			Losses			Cost			Losses (2)
	31-Dec-13
	Fixed maturities and fixed maturities pledged
	under securities lending agreements (1):
	Corporate bonds	$	2,267,263		$	35,289		$	(35,537	)	$	2,267,511		$	(16	)

	Mortgage backed securities	1,133,095			16,270			(22,209		)	1,139,034			(9,269		)

	Municipal bonds	1,481,738			29,378			(9,730		)	1,462,090			(17		)

	Commercial mortgage backed securities	1,074,497			13,972			(15,224		)	1,075,749			(199		)

	U.S. government and government agencies	1,301,809			3,779			(11,242		)	1,309,272			(19		)

	Non-U.S. government securities	1,085,861			14,729			(19,363		)	1,090,495			—

	Asset backed securities	1,332,594			20,033			(13,795		)	1,326,356			(3,422		)

	Total	9,676,857			133,450			(127,100		)	9,670,507			(12,942		)

	Equity securities	496,824			69,487			(5,938		)	433,275			—

	Other investments	498,310			28,082			(18,459		)	488,687			—

	Short-term investments	1,478,367			1,654			(871		)	1,477,584			—

	Total	$	12,150,358		$	232,673		$	(152,368	)	$	12,070,053		$	(12,942	)


	31-Dec-12
	Fixed maturities and fixed maturities pledged
	under securities lending agreements (1):
	Corporate bonds	$	2,857,513		$	105,798		$	(6,710	)	$	2,758,425		$	(62	)

	Mortgage backed securities	1,532,736			24,809			(7,484		)	1,515,411			(9,329		)

	Municipal bonds	1,463,586			62,322			(1,421		)	1,402,685			(17		)

	Commercial mortgage backed securities	824,165			37,514			(4,468		)	791,119			(270		)

	U.S. government and government agencies	1,131,688			20,178			(1,095		)	1,112,605			(19		)

	Non-U.S. government securities	998,901			33,701			(8,860		)	974,060			—

	Asset backed securities	1,073,999			25,528			(5,838		)	1,054,309			(3,346		)

	Total	9,882,588			309,850			(35,876		)	9,608,614			(13,043		)

	Equity securities	312,749			26,625			(12,290		)	298,414			—

	Other investments	549,280			32,582			(3,257		)	519,955			—

	Short-term investments	730,369			3,521			(1,248		)	728,096			—

	Total	$	11,474,986		$	372,578		$	(52,671	)	$	11,155,079		$	(13,043	)


	-1	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged. See “—Securities Lending Agreements.”

-2	Represents the total other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income (“AOCI”). It does not include the change in fair value subsequent to the impairment measurement date. At December 31, 2013, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $6.0 million, compared to a net unrealized gain of $2.0 million at December 31, 2012.
Summary of available for sale securities in a continual unrealized loss position	'
	The following table summarizes, for all available for sale securities in an unrealized loss position, the fair value and gross unrealized loss by length of time the security has been in a continual unrealized loss position:


		Less than 12 Months						12 Months or More						Total
		Estimated			Gross			Estimated			Gross			Estimated			Gross
		Fair			Unrealized			Fair			Unrealized			Fair			Unrealized
		Value			Losses			Value			Losses			Value			Losses
	31-Dec-13
	Fixed maturities and fixed maturities pledged under securities lending agreements (1):
	Corporate bonds	$	1,183,625		$	(32,837	)	$	46,673		$	(2,700	)	$	1,230,298		$	(35,537	)

	Mortgage backed securities	778,693			(20,253		)	43,634			(1,956		)	822,327			(22,209		)

	Municipal bonds	589,009			(9,422		)	6,092			(308		)	595,101			(9,730		)

	Commercial mortgage backed securities	677,617			(15,110		)	1,612			(114		)	679,229			(15,224		)

	U.S. government and government agencies	1,144,809			(11,242		)	—			—			1,144,809			(11,242		)

	Non-U.S. government securities	821,506			(15,776		)	24,334			(3,587		)	845,840			(19,363		)

	Asset backed securities	692,362			(10,431		)	88,629			(3,364		)	780,991			(13,795		)

	Total	5,887,621			(115,071		)	210,974			(12,029		)	6,098,595			(127,100		)

	Equity securities	76,563			(5,938		)	0			0			76,563			(5,938		)

	Other investments	165,891			(15,775		)	47,316			(2,684		)	213,207			(18,459		)

	Short-term investments	28,170			(871		)	—			—			28,170			(871		)

	Total	$	6,158,245		$	(137,655	)	$	258,290		$	(14,713	)	$	6,416,535		$	(152,368	)


	31-Dec-12
	Fixed maturities and fixed maturities pledged under securities lending agreements (1):
	Corporate bonds	$	490,784		$	(3,692	)	$	52,334		$	(3,018	)	$	543,118		$	(6,710	)

	Mortgage backed securities	537,883			(4,290		)	60,574			(3,194		)	598,457			(7,484		)

	Municipal bonds	147,766			(1,120		)	7,052			(301		)	154,818			(1,421		)

	Commercial mortgage backed securities	36,649			(2,261		)	8,878			(2,207		)	45,527			(4,468		)

	U.S. government and government agencies	146,526			(1,095		)	—			—			146,526			(1,095		)

	Non-U.S. government securities	244,827			(1,070		)	135,564			(7,790		)	380,391			(8,860		)

	Asset backed securities	234,584			(1,508		)	57,371			(4,330		)	291,955			(5,838		)

	Total	1,839,019			(15,036		)	321,773			(20,840		)	2,160,792			(35,876		)

	Equity securities	130,385			(10,200		)	16,469			(2,090		)	146,854			(12,290		)

	Other investments	23,849			(2,474		)	35,083			(783		)	58,932			(3,257		)

	Short-term investments	57,415			(1,248		)	—			—			57,415			(1,248		)

	Total	$	2,050,668		$	(28,958	)	$	373,325		$	(23,713	)	$	2,423,993		$	(52,671	)


	-1	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged. See “—Securities Lending Agreements.”
Contractual maturities of the Company's fixed maturities and fixed maturities pledged under securities lending arrangements	'


		December 31, 2013						December 31, 2012
	Maturity	Estimated Fair Value			Amortized Cost			Estimated Fair Value			Amortized Cost
	Due in one year or less	$	235,330		$	232,652		$	446,402		$	436,376

	Due after one year through five years	3,738,500			3,718,920			3,876,062			3,769,426

	Due after five years through 10 years	1,966,536			1,979,510			1,949,297			1,869,698

	Due after 10 years	196,305			198,286			179,927			172,275

		6,136,671			6,129,368			6,451,688			6,247,775

	Mortgage backed securities	1,133,095			1,139,034			1,532,736			1,515,411

	Commercial mortgage backed securities	1,074,497			1,075,749			824,165			791,119

	Asset backed securities	1,332,594			1,326,356			1,073,999			1,054,309

	Total	$	9,676,857		$	9,670,507		$	9,882,588		$	9,608,614

Summary of other investments, including available for sale and fair value option components	'
	The following table summarizes the Company’s other investments, including available for sale and fair value option components:


		December 31,
		2013			2012
	Available for sale securities:
	Asian and emerging markets	$	331,984		$	316,860

	Investment grade fixed income	159,115			220,410

	Other	7,211			12,010

	Total available for sale	498,310			549,280

	Fair value option:
	Term loan investments (par value: $494,502 and $307,016)	512,076			308,596

	Asian and emerging markets	14,054			24,035

	Investment grade fixed income	75,062			67,624

	Non-investment grade fixed income	—			11,093

	Other	172,088			116,623

	Total fair value option	773,280			527,971

	Total	$	1,271,590		$	1,077,251

Summary of assets and liabilities accounted for using the fair value option	'
	The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option:


		December 31,
		2013			2012
	Fixed maturities	$	448,254		$	363,541

	Other investments	773,280			527,971

	Equity securities	—			25,954

	Investments accounted for using the fair value option	1,221,534			917,466

	Securities sold but not yet purchased (1)	—			(6,924		)

	Net assets accounted for using the fair value option	$	1,221,534		$	910,542


	-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.
Components of net investment income	'
	The components of net investment income were derived from the following sources:


		Year Ended December 31,
		2013			2012			2011
	Fixed maturities	$	249,833		$	281,140		$	331,469

	Term loan investments	20,608			15,283			2,854

	Equity securities	8,919			7,963			7,332

	Short-term investments	1,259			1,980			2,174

	Other (1)	19,710			14,196			19,152

	Gross investment income	300,329			320,562			362,981

	Investment expenses	(33,110		)	(25,667		)	(24,783		)
	Net investment income	$	267,219		$	294,895		$	338,198


	-1	Includes dividends on investment funds and other items.
Summary of net realized gains (losses)	'
	Net realized gains (losses) were as follows, excluding the other-than-temporary impairment provisions discussed above:


		Year Ended December 31,
		2013			2012			2011
	Available for sale securities:
	Gross gains on investment sales	$	239,421		$	247,291		$	271,818

	Gross losses on investment sales	(203,077		)	(71,722		)	(132,166		)
	Change in fair value of assets and liabilities
	accounted for using the fair value option:
	Fixed maturities	54			13,195			(12,164		)

	Equity securities	704			(73		)	(31,519		)

	Other investments	17,503			7,383			(3,272		)

	Derivative instruments (1)	20,912			(1,326		)	19,851

	Other	(1,499		)	(520		)	(1,902		)
	Net realized gains	$	74,018		$	194,228		$	110,646


	-1	See Note 9 for information on the Company’s derivative instruments.
Summary of OTTI recognized in earnings by asset class	'
	The Company performs quarterly reviews of its available for sale investments in order to determine whether declines in fair value below the amortized cost basis were considered other-than-temporary in accordance with applicable guidance. The following table details the net impairment losses recognized in earnings by asset class:


		Year Ended December 31,
		2013			2012			2011
	Fixed maturities:
	Mortgage backed securities	$	(295	)	$	(2,491	)	$	(5,023	)
	Corporate bonds	(88		)	(1,512		)	(931		)
	Non-U.S. government securities	—			(261		)	—

	Commercial mortgage backed securities	—			(211		)	—

	Asset backed securities	(128		)	(127		)	(10		)
	U.S. government and government agencies	—			(10		)	—

	Total	(511		)	(4,612		)	(5,964		)
	Investment of funds received under securities lending agreements	—			(87		)	(1,623		)

	Equity securities	(3,275		)	(6,689		)	(1,475		)
	Net impairment losses recognized in earnings	$	(3,786	)	$	(11,388	)	$	(9,062	)
Rollforward of the amount related to credit losses recognized in earnings for which a portion was recognized in AOCI	'
	The following table provides a roll forward of the amount related to credit losses recognized in earnings for which a portion of an OTTI was recognized in accumulated other comprehensive income:


		Year Ended December 31,
		2013			2012			2011
	Balance at start of year	$	62,001		$	66,545		$	86,040

	Credit loss impairments recognized on securities not previously impaired	423			1,962			3,736

	Credit loss impairments recognized on securities previously impaired	88			2,735			3,850

	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	(2,450		)	(9,241		)	(27,081		)
	Balance at end of year	$	60,062		$	62,001		$	66,545

Summary of restricted assets	'
	The following table details the value of the Company’s restricted assets:


		December 31,
		2013			2012
	Assets used for collateral or guarantees:
	Affiliated transactions	$	4,060,533		$	4,062,097

	Third party agreements	856,890			771,631

	Deposits with U.S. regulatory authorities	302,809			290,441

	Deposits with non-U.S. regulatory authorities	6,546			247,321

	Trust funds	75,264			96,342

	Total restricted assets	$	5,302,042		$	5,467,832

Fair_Value_Tables

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair value hierarchy	'
	The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2013:


						Fair Value Measurement Using:
		Estimated				Quoted Prices in Active Markets for Identical Assets				Significant Other Observable Inputs				Significant Unobservable Inputs
		Fair Value				(Level 1)				(Level 2)				(Level 3)
	Assets measured at fair value:
	Available for sale securities:
	Fixed maturities and fixed maturities pledged under securities lending agreements (1):
	Corporate bonds	$	2,267,263			$	—			$	2,265,218			$	2,045

	Mortgage backed securities	1,133,095				—				1,133,095				—

	Municipal bonds	1,481,738				—				1,481,738				—

	Commercial mortgage backed securities	1,074,497				—				1,074,497				—

	U.S. government and government agencies	1,301,809				1,301,809				—				—

	Non-U.S. government securities	1,085,861				—				1,085,861				—

	Asset backed securities	1,332,594				—				1,332,594				—

	Total	9,676,857				1,301,809				8,373,003				2,045

	Equity securities	496,824				496,738				86				—

	Other investments	498,310				—				327,890				170,420

	Short-term investments	1,478,367				1,427,744				50,623				—

	Fair value option:
	Investments accounted for using the fair value option:
	Corporate bonds	334,065				—				334,065				—

	Non-U.S. government bonds	73,156				—				73,156				—

	Mortgage backed securities	41,033				—				41,033				—

	Other investments	773,280				—				395,755				377,525

	Total	1,221,534				—				844,009				377,525

	Total assets measured at fair value	$	13,371,892			$	3,226,291			$	9,595,611			$	549,990


	-1	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged.
	The following table presents the Company’s financial assets and liabilities measured at fair value by level at December 31, 2012:


						Fair Value Measurement Using:
		Estimated				Quoted Prices in Active Markets for Identical Assets				Significant Other Observable Inputs				Significant Unobservable Inputs
		Fair Value				(Level 1)				(Level 2)				(Level 3)
	Assets measured at fair value:
	Available for sale securities:
	Fixed maturities and fixed maturities pledged under securities lending agreements (1):
	Corporate bonds	$	2,857,513			$	—			$	2,759,109			$	98,404

	Mortgage backed securities	1,532,736				—				1,532,736				—

	Municipal bonds	1,463,586				—				1,463,586				—

	Commercial mortgage backed securities	824,165				—				824,165				—

U.S. government and government agencies	1,131,688				1,131,688				—				—

Non-U.S. government securities	998,901				—				998,901				—

Asset backed securities	1,073,999				—				1,073,999				—

Total	9,882,588				1,131,688				8,652,496				98,404

Equity securities	312,749				312,666				83				—

Other investments	549,280				—				365,078				184,202

Short-term investments	730,369				678,441				51,928				—

Fair value option:
Investments accounted for using the fair value option:
Corporate bonds	275,132				—				275,132				—

Non-U.S. government bonds	88,409				—				88,409				—

Equity securities	25,954				25,954				—				—

Other investments	527,971				—				332,621				195,350

Total	917,466				25,954				696,162				195,350

Total assets measured at fair value	$	12,392,452			$	2,148,749			$	9,765,747			$	477,956


Liabilities measured at fair value:
Fair value option:
Securities sold but not yet purchased (2)	6,924				6,924				—				—

Total liabilities measured at fair value	$	6,924			$	6,924			$	—			$	—


-1	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged.

-2	Represents the Company’s obligation 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.
Rollforward of Level 3 investments	'
	The following table presents a reconciliation of the beginning and ending balances for all investments measured at fair value on a recurring basis using Level 3 inputs for 2013, 2012 and 2011:


		Fair Value Measurements Using:
		Significant Unobservable Inputs (Level 3)
		Available for sale								Fair value option
		Corporate Bonds				Other Investments				Other Investments				Total
	Year Ended December 31, 2013
	Balance at beginning of year	$	98,404			$	184,202			$	195,350			$	477,956

	Total gains or (losses) (realized/unrealized)
	Included in earnings (1)	4,679				8,915				11,743				25,337

	Included in other comprehensive income	(3,051		)		473				—				(2,578		)

	Purchases, issuances and settlements
	Purchases	—				25,000				275,067				300,067

	Issuances	—				—				—				—

	Sales	(96,655		)		0				(20,156		)		(116,811		)

	Settlements	(1,332		)		(48,170		)		(84,479		)		(133,981		)
	Transfers in and/or out of Level 3	—				—				—				—

	Balance at end of year	$	2,045			$	170,420			$	377,525			$	549,990


	Year Ended December 31, 2012
	Balance at beginning of year	$	92,091			$	5,124			$	—			$	97,215

	Total gains or (losses) (realized/unrealized)
	Included in earnings (1)	4,419				1,829				(611		)		5,637

	Included in other comprehensive income	2,049				1,026				—				3,075

	Purchases, issuances and settlements
	Purchases	—				25,000				91,232				116,232

	Issuances	—				—				—				—

	Sales	0				0				—				0

	Settlements	(155		)		(1,830		)		—				(1,985		)

	Transfers in and/or out of Level 3	—				153,053				104,729				257,782

	Balance at end of year	$	98,404			$	184,202			$	195,350			$	477,956


	Year Ended December 31, 2011
	Balance at beginning of year	$	153,509			$	7,858			$	—			$	161,367

	Total gains or (losses) (realized/unrealized)
	Included in earnings (1)	2,276				1,709				—				3,985

	Included in other comprehensive income	(4,515		)		(3,777		)		—				(8,292		)

	Purchases, issuances and settlements
	Purchases	—				—				—				—

	Issuances	—				—				—				—

Sales	(49,947		)		(666		)		—				(50,613		)

Settlements	(9,232		)		—				—				(9,232		)

Transfers in and/or out of Level 3	—				—				—				—

Balance at end of year	$	92,091			$	5,124			$	—			$	97,215


-1	Gains or losses on corporate bonds and other investments were recorded in net realized gains (losses).

Derivative_Instruments_Tables

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2013
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. The fair value of TBAs is included in “fixed maturities available for sale, at fair value.”



		Asset			Liability Derivatives			Net
		Derivatives						Derivatives
		Fair Value			Fair Value			Fair Value			Notional Value
	31-Dec-13

	Futures contracts	$	461		$	(110	)	$	351		$	475,967

	Foreign currency forward contracts	5,023			(3,090		)	1,933			330,746

	TBAs	33,455			(21,731		)	11,724			56,160

	Other	920			(1,541		)	(621		)	347,916

	Total	$	39,859		$	(26,472	)	$	13,387


	31-Dec-12

	Futures contracts	$	52		$	(52	)	$	—		$	340,400

	Foreign currency forward contracts	2,809			(2,678		)	131			396,468

	TBAs	23,599			(4,346		)	19,253			26,000

	Other	448			(676		)	(228		)	50,341

	Total	$	26,908		$	(7,752	)	$	19,156

Summary of net realized gains (losses) recorded in the consolidated statements of income	'
	The following table summarizes derivative instrument activity, which is reflected as net realized gains or losses in the consolidated statements of operations:


	Derivatives not designated	Year Ended December 31,
	as hedging instruments	2013			2012			2011
	Futures contracts	$	10,742		$	(3,307	)	$	2,293

	Foreign currency forward contracts	9,762			(214		)	895

	TBAs	(1,623		)	4,413			12,329

	Other	2,031			(2,218		)	4,334

	Total	$	20,912		$	(1,326	)	$	19,851

Other_Comprehensive_Income_Los1

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2013
Comprehensive Income Note Disclosure [Abstract]	'
Schedule of changes in each component of AOCI	'
	The following table presents the changes in each component of accumulated other comprehensive income ("AOCI"), net of tax:


		Unrealized Appreciation on Available-For-Sale Investments				Foreign Currency Translation Adjustments				Total
	Year Ended December 31, 2013
	Beginning balance	$	289,956			$	(2,939	)		$	287,017

	Other comprehensive income (loss) before reclassifications	(176,578		)		(2,789		)		(179,367		)
	Amounts reclassified from accumulated other comprehensive income	(32,686		)		—				(32,686		)

	Net current period other comprehensive income (loss)	(209,264		)		(2,789		)		(212,053		)
	Ending balance	$	80,692			$	(5,728	)		$	74,964


	Year Ended December 31, 2012
	Beginning balance	$	174,636			$	(20,713	)		$	153,923

	Other comprehensive income (loss) before reclassifications	273,144				17,774				290,918

	Amounts reclassified from accumulated other comprehensive income	(157,824		)		—				(157,824		)

	Net current period other comprehensive income (loss)	115,320				17,774				133,094

	Ending balance	$	289,956			$	(2,939	)		$	287,017


	Year Ended December 31, 2011
	Beginning balance	$	213,927			$	(9,424	)		$	204,503

	Other comprehensive income (loss) before reclassifications	84,271				(11,289		)		72,982

	Amounts reclassified from accumulated other comprehensive income	(123,562		)		—				(123,562		)

	Net current period other comprehensive income (loss)	(39,291		)		(11,289		)		(50,580		)
	Ending balance	$	174,636			$	(20,713	)		$	153,923

Details about amounts reclassified from AOCI	'
	The following table presents details about amounts reclassified from accumulated other comprehensive income:


			Consolidated Statement of Income		Amounts Reclassed from AOCI
			Line Item That Includes		Year Ended December 31,
	Details About AOCI Components		Reclassification		2013				2012				2011

	Unrealized appreciation on available-for-sale investments
			Net realized gains		$	39,308			$	180,144			$	139,752

			Other-than-temporary impairment losses		(3,961		)		(12,175		)		(13,850		)
			Total before tax		35,347				167,969				125,902

			Income tax expense		(2,661		)		(10,145		)		(2,340		)
			Net of tax		$	32,686			$	157,824			$	123,562

Schedule of comprehensive income (loss)	'
	Following are the related tax effects allocated to each component of other comprehensive income (loss):


		Before				Tax				Net
		Tax				Expense				of Tax
		Amount				(Benefit)				Amount
	Year Ended December 31, 2013
	Unrealized appreciation (decline) in value of available-for-sale investments:
	Unrealized holding losses arising during period	$	(201,386	)		$	(24,983	)		$	(176,403	)
	Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss)	(175		)		—				(175		)

	Less reclassification of net realized gains included in net income	35,347				2,661				32,686

	Foreign currency translation adjustments	(2,789		)		—				(2,789		)

	Other comprehensive income (loss)	$	(239,697	)		$	(27,644	)		$	(212,053	)
	Year Ended December 31, 2012
	Unrealized appreciation (decline) in value of available-for-sale investments:
	Unrealized holding gains arising during period	$	278,917			$	4,986			$	273,931

	Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss)	(787		)		—				(787		)

	Less reclassification of net realized gains included in net income	167,969				10,145				157,824

	Foreign currency translation adjustments	18,748				974				17,774

	Other comprehensive income (loss)	$	128,909			$	(4,185	)		$	133,094

	Year Ended December 31, 2011
	Unrealized appreciation (decline) in value of available-for-sale investments:
	Unrealized holding gains arising during period	$	108,046			$	18,987			$	89,059

	Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss)	(4,788		)		—				(4,788		)

	Less reclassification of net realized gains included in net income	125,902				2,340				123,562

	Foreign currency translation adjustments	(12,461		)		(1,172		)		(11,289		)
	Other comprehensive income	$	(35,105	)		$	15,475			$	(50,580	)

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Schedule of computation of basic and diluted earnings per common share	'
	The following table sets forth the computation of basic and diluted earnings per common share:


		Year Ended December 31,
		2013			2012			2011
	Numerator:
	Net income	$	709,731		$	593,397		$	436,163

	Preferred dividends	(21,938		)	(25,079		)	(25,844		)
	Loss on repurchase of preferred shares	—			(10,612		)	—

	Net income available to common shareholders	$	687,793		$	557,706		$	410,319


	Denominator:
	Weighted average common shares outstanding – basic	131,355,392			134,446,158			132,221,970

	Effect of dilutive common share equivalents:
	Nonvested restricted shares	1,090,100			857,174			940,612

	Stock options (1)	3,331,691			2,955,515			5,127,120

	Weighted average common shares and common share	135,777,183			138,258,847			138,289,702
	equivalents outstanding – diluted

	Earnings per common share:
	Basic	$	5.24		$	4.15		$	3.1

	Diluted	$	5.07		$	4.03		$	2.97


	-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 2013, 2012 and 2011, the number of stock options excluded were 892,439, 839,414 and 462,020, respectively.

Income_Taxes_Income_Taxes_Tabl

Income Taxes Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	'
	The components of income taxes attributable to operations were as follows:


		Year Ended December 31,
		2013			2012			2011
	Current expense (benefit):
	United States	$	27,537		$	8,267		$	(214	)

	Non-U.S.	5,159			737			8,045

		32,696			9,004			7,831

	Deferred expense (benefit):
	United States	1,937			(9,779		)	(11,563		)

	Non-U.S.	(1,859		)	(3,235		)	(6,061		)
		78			(13,014		)	(17,624		)

	Income tax expense (benefit)	$	32,774		$	(4,010	)	$	(9,793	)

Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	'
	The Company’s income or loss before income taxes was earned in the following jurisdictions:


		Year Ended December 31,
		2013			2012			2011
	Income (Loss) Before Income Taxes:
	Bermuda	$	717,661		$	609,710		$	454,673

	United States	87,032			9,600			(18,662		)

	Other	(62,188		)	(29,923		)	(9,641		)
	Total	$	742,505		$	589,387		$	426,370

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	'
	A reconciliation of the difference between the provision for income taxes and the expected tax provision at the weighted average tax rate follows:


		Year Ended December 31,
		2013			2012			2011
	Expected income tax (benefit) expense computed on pre-tax income	$	17,506		$	(3,426	)	$	(5,388	)
	at weighted average income tax rate
	Addition (reduction) in income tax expense (benefit) resulting from:
	Tax-exempt investment income	(8,255		)	(9,257		)	(8,885		)
	Meals and entertainment	599			688			633

	State taxes, net of U.S. federal tax benefit	431			270			309

	U.S. operations’ foreign taxes, net of U.S. federal tax benefit	703			544			(402		)

	Prior year adjustment	2,810			(1,581		)	(91		)

	Non deductible foreign exchange gains & losses	(1,254		)	(436		)	978

	Changes in applicable tax rate	2,007			1,193			217

	Dividend withholding taxes	4,619			2,511			2,237

	Change in valuation allowance	11,795			4,281			—

	Other	1,813			1,203			599

	Income tax expense (benefit)	$	32,774		$	(4,010	)	$	(9,793	)

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	'
	Significant components of the Company’s deferred income tax assets and liabilities were as follows:


		December 31,
		2013			2012
	Deferred income tax assets:
	Net operating loss	$	15,294		$	4,925

	AMT credit carryforward	14,456			14,423

	Discounting of net loss reserves	53,293			54,860

	Net unearned premium reserve	30,698			30,614

	Compensation liabilities	26,481			22,713

	Foreign tax credit carryforward	4,343			8,229

	Interest expense	6,049			3,628

	Other, net	13,347			15,237

	Deferred tax assets before valuation allowance	163,961			154,629

	Valuation allowance	(15,548		)	(4,309		)
	Deferred tax assets net of valuation allowance	148,413			150,320

	Deferred income tax liabilities:
	Depreciation and amortization	(3,810		)	(4,896		)
	Deferred acquisition costs, net	(3,369		)	(5,988		)
	Deposit accounting liability	(4,581		)	(4,823		)
	Net unrealized foreign exchange gains	0			(2,825		)

	Net unrealized appreciation of investments	(6,354		)	(30,662		)
	Other, net	(1,738		)	(2,544		)
	Total deferred tax liabilities	(19,852		)	(51,738		)
	Net deferred income tax assets	$	128,561		$	98,582

Commitments_and_Contingencies_

Commitments and Contingencies Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Summary of future minimum lease payments	'
	At December 31, 2013, the future minimum rental commitments, exclusive of escalation clauses and maintenance costs and net of rental income, for all of the Company’s operating leases are as follows:


	2014	$	19,009

	2015	18,390

	2016	17,850

	2017	15,464

	2018	15,266

	Thereafter	54,406

	Total	$	140,385

Shareholders_Equity_Shareholde

Shareholders' Equity Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2013
Stockholders' Equity Note [Abstract]	'
Roll-forward of changes in issued and outstanding Common Shares	'
	The following table presents a roll-forward of changes in the Company’s issued and outstanding Common Shares:


		Year Ended December 31,
		2013		2012		2011
	Common Shares:
	Shares issued and outstanding, beginning of year	168,255,572		164,636,338		160,073,616

	Shares issued (1)	811,732		2,066,065		3,592,713

	Restricted shares issued, net of cancellations	493,287		1,553,169		970,009

	Shares issued, end of year	169,560,591		168,255,572		164,636,338

	Common shares in treasury, end of year	(35,885,707	)	(34,412,959	)	(30,277,993	)
	Shares issued and outstanding, end of year	133,674,884		133,842,613		134,358,345


	-1	Includes shares issued from the exercise of stock options and stock appreciation rights, and shares issued from the employee share purchase plan.

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Valuation assumptions	'


		Year Ended December 31,
		2013			2012			2011
	Dividend yield	0	%		0	%		0	%
	Expected volatility	23.6	%		24.3	%		24.6	%
	Risk free interest rate	1	%		1	%		2.2	%
	Expected option life	6.0 years			6.25 years			6.0 years

Option activity	'
	A summary of stock option and SAR activity under the Company’s Long Term Incentive and Share Award Plans during 2013 is presented below:


		Year Ended December 31, 2013
		Number of			Weighted Average Exercise Price
		Options / SARs
	Outstanding, beginning of year	8,221,444			$	25.87

	Granted	860,881			$	51.76

	Exercised	(695,756	)		$	21.62

	Forfeited or expired	(48,089	)		$	40.54

	Outstanding, end of year	8,338,480			$	28.82

	Exercisable, end of year	6,119,335			$	23.51

Unvested restricted share and unit activity	'
	A summary of unvested restricted share and unit activity under the Company’s Long Term Incentive and Share Award Plans for 2013 is presented below:


		Year Ended December 31, 2013
		Restricted				Restricted
		Common				Unit
		Shares				Awards
	Unvested Shares:
	Unvested balance, beginning of year	2,114,640				357,250

	Granted	513,832				76,286

	Vested	(664,802		)		(97,943		)
	Forfeited	(20,545		)		(27,271		)
	Unvested balance, end of year	1,943,125				308,322


	Weighted Average Grant Date Fair Value:
	Unvested balance, beginning of year	$	37.88			$	38.03

	Granted	$	53.21			$	53.26

	Vested	$	33.04			$	32.95

	Forfeited	$	42.21			$	39.06

	Unvested balance, end of year	$	43.55			$	43.32

Statutory_Information_Tables

Statutory Information (Tables)	12 Months Ended
	Dec. 31, 2013
Disclosure Statutory Information [Abstract]	'
Summary of statutory capital, surplus and net income	'
	The actual and required statutory capital and surplus for the Company’s principal operating subsidiaries at December 31, 2013 and 2012 was as follows:


		December 31, 2013						December 31, 2012
		Actual (1)			Required (1)			Actual (1)			Required (1)
	Statutory capital and surplus (1):
	Bermuda	$	5,416,948		$	2,096,428		$	5,010,386		$	2,175,191

	Ireland	$	533,283		$	458,666		$	539,326		$	377,340

	United States	$	1,013,228		$	335,442		$	822,615		$	319,129

	United Kingdom	$	250,688		$	237,555		$	231,387		$	206,764

	Canada	$	77,877		$	74,951		—			—


	-1	Such amounts include ownership interests in affiliated insurance and reinsurance subsidiaries.
	The statutory net income (loss) for the Company’s principal operating subsidiaries for 2013, 2012 and 2011 was as follows:


		Year Ended December 31,
		2013			2012			2011
	Statutory net income (loss):
	Bermuda	$	719,267		$	631,483		$	447,447

	Ireland	$	24,410		$	(1,940	)	$	9,123

	United States	$	62,605		$	(21,517	)	$	(37,252	)

	United Kingdom	$	(11,353	)	$	(4,449	)	$	1,637

	Canada	$	(36,203	)	—			—

Unaudited_Condensed_Quarterly_1

Unaudited Condensed Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Summary of condensed quarterly financial information	'
	The following table summarizes the Company’s 2013 and 2012 unaudited condensed quarterly financial information:


		Fourth			Third			Second			First
		Quarter			Quarter			Quarter			Quarter
	Year Ended December 31, 2013
	Net premiums written	$	748,921		$	839,135		$	810,535		$	952,776

	Net premiums earned	839,366			795,000			758,816			752,770

	Net investment income	67,095			66,083			68,369			65,672

	Net realized gains (losses)	9,048			(6,022		)	12,652			58,340

	Net impairment losses recognized in earnings	(88		)	(728		)	(724		)	(2,246		)
	Underwriting income	128,318			110,992			96,029			116,398

	Net income	161,490			114,825			176,940			256,476

	Preferred dividends	(5,485		)	(5,484		)	(5,485		)	(5,484		)
	Net income available to common shareholders	156,005			109,341			171,455			250,992

	Net income per common share -- basic	$	1.19		$	0.83		$	1.31		$	1.92

	Net income per common share -- diluted	$	1.14		$	0.8		$	1.26		$	1.85


	Year Ended December 31, 2012
	Net premiums written	$	613,142		$	755,249		$	820,233		$	863,611

	Net premiums earned	779,481			748,691			726,656			680,312

	Net investment income	73,769			73,221			73,608			74,297

	Net realized gains	54,849			60,391			34,867			44,121

	Net impairment losses recognized in earnings	(6,035		)	(2,379		)	(1,951		)	(1,023		)
	Underwriting income (loss)	(91,334		)	73,452			93,723			67,193

	Net income	19,217			189,656			220,268			164,256

	Preferred dividends	(5,485		)	(5,484		)	(7,649		)	(6,461		)
	Loss on repurchase of preferred shares	—			—			(10,612		)	—

	Net income available to common shareholders	13,732			184,172			202,007			157,795

	Net income per common share -- basic	$	0.1		$	1.36		$	1.5		$	1.18

	Net income per common share -- diluted	$	0.1		$	1.33		$	1.46		$	1.14

Guarantor_Financial_Informatio1

Guarantor Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Condensed consolidating balance sheet	'


		31-Dec-13
	Condensed Consolidating Balance Sheet	ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
	Assets
	Total investments	$	2,530			$	408,957			$	13,200,247			$	—			$	13,611,734

	Cash	3,223				509				430,325				—				434,057

	Investments in subsidiaries	6,046,060				1,258,889				—				(7,304,949		)		—

	Due from subsidiaries and affiliates	2,251				—				405,110				(407,361		)		—

	Premiums receivable	—				—				1,085,369				(331,445		)		753,924

	Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	—				—				5,645,156				(3,840,826		)		1,804,330

	Contractholder receivables	—				—				1,064,246				—				1,064,246

	Prepaid reinsurance premiums	—				—				1,109,312				(780,969		)		328,343

	Deferred acquisition costs, net	—				—				342,314				—				342,314

	Other assets	6,598				60,342				1,714,651				(554,445		)		1,227,146

	Total Assets	$	6,060,662			$	1,728,697			$	24,996,730			$	(13,219,995	)		$	19,566,094


	Liabilities
	Reserve for losses and loss adjustment expenses	$	—			$	—			$	12,625,766			$	(3,801,070	)		$	8,824,696

	Unearned premiums	—				—				2,677,334				(780,969		)		1,896,365

	Reinsurance balances payable	—				—				662,394				(466,227		)		196,167

	Contractholder payables	—				—				1,064,246				—				1,064,246

	Deposit accounting liabilities	—				—				758,490				(337,193		)		421,297

	Senior notes	300,000				500,000				—				—				800,000

	Revolving credit agreement borrowings	100,000				—				—				—				100,000

	Due to subsidiaries and affiliates	18				10,250				397,093				(407,361		)		—

	Other liabilities	13,148				33,206				691,699				(122,226		)		615,827

	Total Liabilities	413,166				543,456				18,877,022				(5,915,046		)		13,918,598


	Shareholders' Equity
	Total Shareholders' Equity	5,647,496				1,185,241				6,119,708				(7,304,949		)		5,647,496


	Total Liabilities and Shareholders' Equity	$	6,060,662			$	1,728,697			$	24,996,730			$	(13,219,995	)		$	19,566,094



		31-Dec-12
	Condensed Consolidating Balance Sheet	ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
	Assets
	Total investments	$	8,328			$	8,798			$	12,674,114			$	—			$	12,691,240

Cash	6,417				612				364,012				—				371,041

Investments in subsidiaries	5,560,655				1,155,839				—				(6,716,494		)		—

Due from subsidiaries and affiliates	254				—				352,063				(352,317		)		—

Premiums receivable	—				—				877,210				(188,337		)		688,873

Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	—				—				5,849,750				(3,979,713		)		1,870,037

Contractholder receivables	—				—				865,728				—				865,728

Prepaid reinsurance premiums	—				—				914,367				(615,883		)		298,484

Deferred acquisition costs, net	—				—				262,822				—				262,822

Other assets	6,430				48,571				662,186				51,350				768,537

Total Assets	$	5,582,084			$	1,213,820			$	22,822,252			$	(11,801,394	)		$	17,816,762


Liabilities
Reserve for losses and loss adjustment expenses	$	—			$	—			$	12,857,514			$	(3,924,222	)		$	8,933,292

Unearned premiums	—				—				2,263,861				(615,883		)		1,647,978

Reinsurance balances payable	—				—				529,562				(341,016		)		188,546

Contractholder payables	—				—				865,728				—				865,728

Deposit accounting liabilities	—				—				27,594				—				27,594

Senior notes	300,000				—				—				—				300,000

Revolving credit agreement borrowings	100,000				—				—				—				100,000

Due to subsidiaries and affiliates	2,397				—				349,920				(352,317		)		—

Other liabilities	10,809				31,193				394,206				148,538				584,746

Total Liabilities	413,206				31,193				17,288,385				(5,084,900		)		12,647,884


Shareholders' Equity
Total Shareholders' Equity	5,168,878				1,182,627				5,533,867				(6,716,494		)		5,168,878


Total Liabilities and Shareholders' Equity	$	5,582,084			$	1,213,820			$	22,822,252			$	(11,801,394	)		$	17,816,762

Condensed consolidating statement of income and comprehensive income	'


		Year Ended December 31, 2013
	Condensed Consolidating Statement of Income and Comprehensive Income	ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
	Revenues
	Net premiums earned	$	—			$	—			$	3,145,952			$	—			$	3,145,952

	Net investment income	(5		)		31				307,449				(40,256		)		267,219

	Net realized gains	—				—				74,018				—				74,018

	Net impairment losses recognized in earnings	—				—				(3,786		)		—				(3,786		)

	Other underwriting income	—				—				7,639				—				7,639

	Equity in net income (loss) of investment funds accounted for using the equity method	—				—				35,701				—				35,701

	Other income (loss)	—				—				(586		)		—				(586		)

	Total revenues	(5		)		31				3,566,387				(40,256		)		3,526,157


	Expenses
	Losses and loss adjustment expenses	—				—				1,679,424				—				1,679,424

	Acquisition expenses	—				—				564,103				—				564,103

	Other operating expenses	38,702				2,691				459,337				—				500,730

	Interest expense	23,267				1,316				42,733				(40,256		)		27,060

	Net foreign exchange losses	—				—				2,145				10,190				12,335

	Total expenses	61,969				4,007				2,747,742				(30,066		)		2,783,652


	Income (loss) before income taxes	(61,974		)		(3,976		)		818,645				(10,190		)		742,505

	Income tax benefit (expense)	—				1,383				(34,157		)		—				(32,774		)


	Income (loss) before equity in net income of subsidiaries	(61,974		)		(2,593		)		784,488				(10,190		)		709,731


	Equity in net income (loss) of subsidiaries	771,705				25,644				—				(797,349		)		—


	Net income	709,731				23,051				784,488				(807,539		)		709,731

	Preferred dividends	(21,938		)		—				—				—				(21,938		)


	Net income available to common shareholders	$	687,793			$	23,051			$	784,488			$	(807,539	)		$	687,793


	Comprehensive income (loss)	$	497,678			$	(28,330	)		$	562,245			$	(533,915	)		$	497,678



		Year Ended December 31, 2012
	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	$	—			$	—			$	2,935,140			$	—			$	2,935,140

Net investment income	4				8				321,805				(26,922		)		294,895

Net realized gains	—				—				194,228				—				194,228

Net impairment losses recognized in earnings	—				—				(11,388		)		—				(11,388		)

Other underwriting income	—				—				8,090				—				8,090

Equity in net income of investment funds accounted for using the equity method	—				—				73,510				—				73,510

Other income (loss)	—				—				(12,094		)		—				(12,094		)

Total revenues	4				8				3,509,291				(26,922		)		3,482,381


Expenses
Losses and loss adjustment expenses	—				—				1,861,277				—				1,861,277

Acquisition expenses	—				—				508,884				—				508,884

Other operating expenses	35,570				1,218				428,565				—				465,353

Interest expense	23,496				—				31,951				(26,922		)		28,525

Net foreign exchange losses	—				—				21,787				7,168				28,955

Total expenses	59,066				1,218				2,852,464				(19,754		)		2,892,994


Income before income taxes	(59,062		)		(1,210		)		656,827				(7,168		)		589,387

Income tax benefit	—				424				3,586				—				4,010


Income (loss) before equity in net income of subsidiaries	(59,062		)		(786		)		660,413				(7,168		)		593,397


Equity in net income (loss) of subsidiaries	652,459				9,738				—				(662,197		)		—


Net income	593,397				8,952				660,413				(669,365		)		593,397

Preferred dividends	(25,079		)		—				—				—				(25,079		)

Loss on repurchase of preferred shares	(10,612		)		—				—				—				(10,612		)


Net income available to common shareholders	$	557,706			$	8,952			$	660,413			$	(669,365	)		$	557,706


Comprehensive income (loss)	$	726,491			$	2,796			$	786,338			$	(789,134	)		$	726,491



	Year Ended December 31, 2011
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	$	—			$	—			$	2,631,815			$	—			$	2,631,815

Net investment income	—				3				350,412				(12,217		)		338,198

Net realized gains	63				—				107,021				3,562				110,646

Net impairment losses recognized in earnings	—				—				(9,062		)		—				(9,062		)

Other underwriting income	—				—				3,429				—				3,429

Equity in net income (loss) of investment funds accounted for using the equity method	—				—				(9,605		)		—				(9,605		)

Other income (loss)	—				—				(2,114		)		—				(2,114		)

Total revenues	63				3				3,071,896				(8,655		)		3,063,307


Expenses
Losses and loss adjustment expenses	—				—				1,727,553				—				1,727,553

Acquisition expenses	—				—				462,937				—				462,937

Other operating expenses	31,509				887				399,726				—				432,122

Interest expense	23,151				—				20,757				(12,217		)		31,691

Net foreign exchange gains	—				—				(9,024		)		(8,342		)		(17,366		)

Total expenses	54,660				887				2,601,949				(20,559		)		2,636,937


Income before income taxes	(54,597		)		(884		)		469,947				11,904				426,370

Income tax benefit	—				321				9,472				—				9,793


Income (loss) before equity in net income of subsidiaries	(54,597		)		(563		)		479,419				11,904				436,163


Equity in net income (loss) of subsidiaries	490,760				(134		)		—				(490,626		)		—


Net income	436,163				(697		)		479,419				(478,722		)		436,163

Preferred dividends	(25,844		)		—				—				—				(25,844		)


Net income available to common shareholders	$	410,319			$	(697	)		$	479,419			$	(478,722	)		$	410,319


Comprehensive income (loss)	$	385,583			$	23,155			$	440,745			$	(463,900	)		$	385,583

Condensed consolidating statement of cash flows	'


		Year Ended December 31, 2013
	Condensed Consolidating Statement	ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
	of Cash Flows
	Operating Activities
	Net Cash Provided By (Used For)	$	68,562			$	(6,569	)		$	908,375			$	(119,500	)		$	850,868
	Operating Activities
	Investing Activities
	Purchases of fixed maturity investments	—				—				(18,174,988		)		—				(18,174,988		)

	Purchases of equity securities	—				—				(535,857		)		—				(535,857		)

	Purchases of other investments	—				—				(1,326,729		)		—				(1,326,729		)

	Proceeds from the sales of fixed maturity investments	—				—				17,196,614				—				17,196,614

	Proceeds from the sales of equity securities	—				—				462,787				—				462,787

	Proceeds from the sales of other investments	—				—				1,162,707				—				1,162,707

	Proceeds from redemptions and maturities of fixed maturity investments	—				—				731,708				—				731,708

	Net (purchases) sales of short-term investments	5,799				(400,162		)		(356,250		)		—				(750,613		)

	Change in investment of securities lending collateral	—				—				(55,643		)		—				(55,643		)

	Contributions to subsidiaries	(160		)		(97,850		)		(20,250		)		118,260				—

	Intercompany loans issued	—				—				(10,250		)		10,250				—

	Purchase of business, net of cash acquired	—				—				—				—				—

	Purchases of furniture, equipment and other assets	(712		)		—				(16,787		)		—				(17,499		)

	Net Cash Provided By (Used For)	4,927				(498,012		)		(942,938		)		128,510				(1,307,513		)
	Investing Activities
	Financing Activities
	Purchases of common shares under share repurchase program	(57,796		)		—				—				—				(57,796		)

	Proceeds from common shares issued, net	3,051				—				118,260				(118,260		)		3,051

	Proceeds from intercompany borrowings	—				10,250				—				(10,250		)		—

	Proceeds from borrowings	—				494,228				—				—				494,228

	Repayments of intercompany borrowings	—				—				—				—				—

	Repayments of borrowings	—				—				—				—				—

	Change in securities lending collateral	—				—				55,643				—				55,643

	Dividends paid to parent (1)	—				—				(119,500		)		119,500				—

	Other	—				—				50,830				—				50,830

	Preferred dividends paid	(21,938		)		—				—				—				(21,938		)

	Net Cash Provided By (Used For)	(76,683		)		504,478				105,233				(9,010		)		524,018
	Financing Activities
	Effects of exchange rates changes on foreign currency cash	—				—				(4,357		)		—				(4,357		)


Increase (decrease) in cash	(3,194		)		(103		)		66,313				—				63,016

Cash beginning of year	6,417				612				364,012				—				371,041

Cash end of year	$	3,223			$	509			$	430,325			$	—			$	434,057


-1	Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.


	Year Ended December 31, 2012
Condensed Consolidating Statement	ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
of Cash Flows
Operating Activities
Net Cash Provided By (Used For)	$	209,500			$	(8,086	)		$	978,679			$	(258,490	)		$	921,603
Operating Activities
Investing Activities
Purchases of fixed maturity investments	—				—				(17,568,592		)		—				(17,568,592		)

Purchases of equity securities	—				—				(268,999		)		—				(268,999		)

Purchases of other investments	—				—				(1,000,049		)		—				(1,000,049		)

Proceeds from the sales of fixed maturity investments	—				—				16,366,306				—				16,366,306

Proceeds from the sales of equity securities	—				—				313,617				—				313,617

Proceeds from the sales of other investments	—				—				443,630				—				443,630

Proceeds from redemptions and maturities of fixed maturity investments	—				—				1,115,594				—				1,115,594

Net (purchases) sales of short-term investments	(5,094		)		1,986				189,027				—				185,919

Change in investment of securities lending collateral	—				—				6,190				—				6,190

Contributions to subsidiaries	—				—				(38,576		)		38,576				—

Purchase of business, net of cash acquired	—				—				28,948				—				28,948

Purchases of furniture, equipment and other assets	(65		)		—				(18,467		)		—				(18,532		)

Net Cash Provided By (Used For)	(5,159		)		1,986				(431,371		)		38,576				(395,968		)
Investing Activities
Financing Activities
Proceeds from issuance of Series C preferred shares, net	315,763				—				—				—				315,763

Repurchase of Series A and B preferred shares	(325,000		)		—				—				—				(325,000		)

Purchases of common shares under share repurchase program	(172,056		)		—				—				—				(172,056		)

Proceeds from common shares issued, net	7,033				—				38,576				(38,576		)		7,033

Repayments of borrowings	—				—				(310,868		)		—				(310,868		)

Change in securities lending collateral	—				—				(6,190		)		—				(6,190		)

Dividends paid to parent (1)	—				—				(258,490		)		258,490				—

Other	—				—				6,664				—				6,664

Preferred dividends paid	(28,381		)		—				—				—				(28,381		)

Net Cash Provided By (Used For)	(202,641		)		—				(530,308		)		219,914				(513,035		)
Financing Activities
Effects of exchange rates changes on foreign currency cash	—				—				6,742				—				6,742


Increase (decrease) in cash	1,700				(6,100		)		23,742				—				19,342

Cash beginning of year	4,717				6,712				340,270				—				351,699

Cash end of year	$	6,417			$	612			$	364,012			$	—			$	371,041


-1	Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.


	Year Ended December 31, 2011
Condensed Consolidating Statement	ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
of Cash Flows
Operating Activities
Net Cash Provided By (Used For)	$	300,764			$	5,606			$	901,252			$	(341,510	)		$	866,112
Operating Activities
Investing Activities
Purchases of fixed maturity investments	—				—				(13,875,635		)		—				(13,875,635		)

Purchases of equity securities	—				—				(413,024		)		—				(413,024		)

Purchases of other investments	—				—				(593,862		)		—				(593,862		)

Proceeds from the sales of fixed maturity investments	—				—				12,398,253				—				12,398,253

Proceeds from the sales of equity securities	—				—				369,503				—				369,503

Proceeds from the sales of other investments	—				—				543,757				—				543,757

Proceeds from redemptions and maturities of fixed maturity investments	—				—				1,034,489				—				1,034,489

Net (purchases) sales of short-term investments	4,441				487				(7,317		)		—				(2,389		)

Change in investment of securities lending collateral	—				—				19,475				—				19,475

Contributions to subsidiaries	—				—				(59,844		)		59,844				—

Intercompany loans issued	—				—				(185,289		)		185,289				—

Purchases of furniture, equipment and other assets	(196		)		—				(18,791		)		—				(18,987		)

Net Cash Provided By (Used For)	4,245				487				(788,285		)		245,133				(538,420		)
Investing Activities
Financing Activities
Purchases of common shares under share repurchase program	(287,561		)		—				—				—				(287,561		)

Proceeds from common shares issued, net	6,332				—				59,844				(59,844		)		6,332

Proceeds from intercompany borrowings	—				—				185,289				(185,289		)		—

Repayments of borrowings	—				—				(15,352		)		—				(15,352		)

Change in securities lending collateral	—				—				(19,475		)		—				(19,475		)

Dividends paid to parent (1)	—				—				(341,510		)		341,510				—

Other	—				—				4,765				—				4,765

Preferred dividends paid	(25,844		)		—				—				—				(25,844		)

Net Cash Provided By (Used For)	(307,073		)		—				(126,439		)		96,377				(337,135		)
Financing Activities
Effects of exchange rates changes on foreign currency cash	—				—				(1,598		)		—				(1,598		)


Increase (decrease) in cash	(2,064		)		6,093				(15,070		)		—				(11,041		)

Cash beginning of year	6,781				619				355,340				—				362,740

Cash end of year	$	4,717			$	6,712			$	340,270			$	—			$	351,699

General_Details

General (Details) (USD $)	1 Months Ended
In Millions, except Per Share data, unless otherwise specified	Oct. 30, 2001	Dec. 31, 2013	Dec. 31, 2012
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'	'	'
Proceeds from from common shares issued, net	$763.20	'	'
Common shares, par value per share	'	$0.00	$0.00

Significant_Accounting_Policie2

Significant Accounting Policies Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Line Items]	'	'
Premium revenue recognition period	'12 months	'
Deposit accounting liabilities	$421,297,000	$27,594,000
Deposit accounting assets	$370,500,000	$6,500,000
Securities lending rate of collateral required (percentage)	102.00%	'
Equity method investments, time lag for reporting - low end of range	'1 month	'
Equity method investments, time lag for reporting - high end of range	'3 months	'
Vesting period, share-based awards	'3 years	'
Requisite service period, share-based awards	'5 years	'
Losses occurring	'	'
Significant Accounting Policies [Line Items]	'	'
Premium revenue recognition period	'12 months	'
Risks attaching	'	'
Significant Accounting Policies [Line Items]	'	'
Premium revenue recognition period	'24 months	'

Segment_Information_Details

Segment Information (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

segment

Segment Reporting Information [Line Items]

Number of segments

Gross premiums written

$4,196,623

$3,869,161

$3,436,456

[1]

Net premiums written

748,921

839,135

810,535

952,776

613,142

755,249

820,233

863,611

3,351,367

3,052,235

2,673,326

Net premiums earned

839,366

795,000

758,816

752,770

779,481

748,691

726,656

680,312

3,145,952

2,935,140

2,631,815

Other underwriting income

7,639

8,090

3,429

Losses and loss adjustment expenses

-1,679,424

-1,861,277

-1,727,553

Acquisition expenses, net

-564,103

-508,884

-462,937

Other operating expenses

-458,327

-430,035

-400,742

Underwriting income (loss)

128,318

110,992

96,029

116,398

-91,334

73,452

93,723

67,193

451,737

143,034

44,012

Net investment income

67,095

66,083

68,369

65,672

73,769

73,221

73,608

74,297

267,219

294,895

338,198

Net realized gains

9,048

-6,022

12,652

58,340

54,849

60,391

34,867

44,121

74,018

194,228

110,646

Net impairment losses recognized in earnings

-88

-728

-724

-2,246

-6,035

-2,379

-1,951

-1,023

-3,786

-11,388

-9,062

Equity in net income (loss) of investment funds accounted for using the equity method

35,701

73,510

-9,605

Other income (loss)

-586

-12,094

-2,114

Other expenses

-42,403

-35,318

-31,380

Interest expense

-27,060

-28,525

-31,691

Net foreign exchange (gains) losses

-12,335

-28,955

17,366

Income before income taxes

742,505

589,387

426,370

Income tax (expense) benefit

-32,774

4,010

9,793

Net income

161,490

114,825

176,940

256,476

19,217

189,656

220,268

164,256

709,731

593,397

436,163

Preferred dividends

-5,485

-5,484

-5,485

-5,484

-5,485

-5,484

-7,649

-6,461

-21,938

-25,079

-25,844

Loss on repurchase of preferred shares

-10,612

Net income available to common shareholders

156,005

109,341

171,455

250,992

13,732

184,172

202,007

157,795

687,793

557,706

410,319

Underwriting Ratios

Loss ratio

53.40%

63.40%

65.60%

Acquisition expense ratio

17.90%

[2]

17.30%

[2]

17.50%

[2]

Other operating expense ratio

14.60%

14.70%

15.20%

Combined ratio

85.90%

95.40%

98.30%

Insurance

Segment Reporting Information [Line Items]

Gross premiums written

2,712,509

[1]

2,593,959

[1]

2,444,485

[1]

Net premiums written

1,948,796

1,825,334

1,721,279

Net premiums earned

1,876,014

1,800,343

1,679,047

Other underwriting income

2,122

2,335

2,870

Losses and loss adjustment expenses

-1,188,445

-1,283,841

-1,172,742

Acquisition expenses, net

-311,904

-298,983

-278,696

Other operating expenses

-315,387

-307,489

-307,797

Underwriting income (loss)

62,400

-87,635

-77,318

Underwriting Ratios

Loss ratio

63.30%

71.30%

69.80%

Acquisition expense ratio

16.50%

[2]

16.50%

[2]

16.40%

[2]

Other operating expense ratio

16.80%

17.10%

18.30%

Combined ratio

96.60%

104.90%

104.50%

Reinsurance

Segment Reporting Information [Line Items]

Gross premiums written

1,489,191

[1]

1,282,000

[1]

998,520

[1]

Net premiums written

1,402,571

1,226,901

952,047

Net premiums earned

1,269,938

1,134,797

952,768

Other underwriting income

5,517

5,755

559

Losses and loss adjustment expenses

-490,979

-577,436

-554,811

Acquisition expenses, net

-252,199

-209,901

-184,241

Other operating expenses

-142,940

-122,546

-92,945

Underwriting income (loss)

$389,337

$230,669

$121,330

Underwriting Ratios

Loss ratio

38.70%

50.90%

58.20%

Acquisition expense ratio

19.90%

[2]

18.50%

[2]

19.30%

[2]

Other operating expense ratio

11.30%

10.80%

9.80%

Combined ratio

69.90%

80.20%

87.30%

[1]

Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

[2]

The acquisition expense ratio is adjusted to include certain other underwriting income.

Segment_Information_By_line_of

Segment Information (By line of business and geographic) (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Segment Reporting Information [Line Items]

Net premiums written

$748,921

$839,135

$810,535

$952,776

$613,142

$755,249

$820,233

$863,611

$3,351,367

$3,052,235

$2,673,326

Net premiums earned

839,366

795,000

758,816

752,770

779,481

748,691

726,656

680,312

3,145,952

2,935,140

2,631,815

Reinsurance

Segment Reporting Information [Line Items]

Net premiums written

1,402,571

1,226,901

952,047

Net premiums earned

1,269,938

1,134,797

952,768

Reinsurance | Client Location [Member] | United States

Segment Reporting Information [Line Items]

Net premiums written

770,080

[1]

629,614

[1]

512,319

[1]

Reinsurance | Client Location [Member] | Bermuda

Segment Reporting Information [Line Items]

Net premiums written

87,047

[1]

72,864

[1]

60,246

[1]

Reinsurance | Client Location [Member] | Europe

Segment Reporting Information [Line Items]

Net premiums written

327,172

[1]

341,674

[1]

250,809

[1]

Reinsurance | Client Location [Member] | Asia and Pacific

Segment Reporting Information [Line Items]

Net premiums written

120,017

[1]

104,398

[1]

75,590

[1]

Reinsurance | Client Location [Member] | Other geographic location

Segment Reporting Information [Line Items]

Net premiums written

98,255

[1]

78,351

[1]

53,083

[1]

Reinsurance | Underwriting Location [Member] | United States

Segment Reporting Information [Line Items]

Net premiums written

507,183

[1]

379,239

[1]

323,731

[1]

Reinsurance | Underwriting Location [Member] | Bermuda

Segment Reporting Information [Line Items]

Net premiums written

548,924

[1]

595,999

[1]

531,254

[1]

Reinsurance | Underwriting Location [Member] | Europe

Segment Reporting Information [Line Items]

Net premiums written

309,242

[1]

225,491

[1]

84,919

[1]

Reinsurance | Underwriting Location [Member] | Other geographic location

Segment Reporting Information [Line Items]

Net premiums written

37,222

[1]

26,172

[1]

12,143

[1]

Reinsurance | Pro Rata [Member]

Segment Reporting Information [Line Items]

Net premiums written

781,594

[1]

598,874

[1]

416,321

[1]

Net premiums earned

659,852

[1]

515,764

[1]

435,311

[1]

Reinsurance | Excess Of Loss [Member]

Segment Reporting Information [Line Items]

Net premiums written

620,977

[1]

628,027

[1]

535,726

[1]

Net premiums earned

610,086

[1]

619,033

[1]

517,457

[1]

Reinsurance | Other specialty [Member]

Segment Reporting Information [Line Items]

Net premiums written

417,865

[1],[2]

308,104

[1],[2]

219,632

[1],[2]

Net premiums earned

387,630

[1],[2]

309,101

[1],[2]

195,855

[1],[2]

Reinsurance | Property excluding property catastrophe [Member]

Segment Reporting Information [Line Items]

Net premiums written

292,536

[1],[3]

265,783

[1],[3]

226,013

[1],[3]

Net premiums earned

274,719

[1],[3]

254,338

[1],[3]

243,702

[1],[3]

Reinsurance | Property catastrophe [Member]

Segment Reporting Information [Line Items]

Net premiums written

220,749

[1]

283,677

[1]

246,793

[1]

Net premiums earned

232,423

[1]

280,185

[1]

238,748

[1]

Reinsurance | Casualty [Member]

Segment Reporting Information [Line Items]

Net premiums written

306,304

[1],[4]

205,925

[1],[4]

173,344

[1],[4]

Net premiums earned

241,774

[1],[4]

188,963

[1],[4]

189,608

[1],[4]

Reinsurance | Marine and aviation [Member]

Segment Reporting Information [Line Items]

Net premiums written

64,380

[1]

84,649

[1]

77,309

[1]

Net premiums earned

70,105

[1]

76,145

[1]

77,819

[1]

Reinsurance | Other [Member]

Segment Reporting Information [Line Items]

Net premiums written

100,737

[1],[5]

78,763

[1],[5]

8,956

[1],[5]

Net premiums earned

63,287

[1],[5]

26,065

[1],[5]

7,036

[1],[5]

Insurance

Segment Reporting Information [Line Items]

Net premiums written

1,948,796

1,825,334

1,721,279

Net premiums earned

1,876,014

1,800,343

1,679,047

Insurance | Client Location [Member]

Segment Reporting Information [Line Items]

Net premiums written

1,948,796

1,825,334

1,721,279

Insurance | Client Location [Member] | United States

Segment Reporting Information [Line Items]

Net premiums written

1,526,156

[6]

1,314,577

[6]

1,208,007

[6]

Insurance | Client Location [Member] | Europe

Segment Reporting Information [Line Items]

Net premiums written

226,254

[6]

271,278

[6]

273,578

[6]

Insurance | Client Location [Member] | Asia and Pacific

Segment Reporting Information [Line Items]

Net premiums written

95,970

[6]

120,492

[6]

119,523

[6]

Insurance | Client Location [Member] | Other geographic location

Segment Reporting Information [Line Items]

Net premiums written

100,416

[6]

118,987

[6]

120,171

[6]

Insurance | Underwriting Location [Member]

Segment Reporting Information [Line Items]

Net premiums written

1,948,796

1,825,334

1,721,279

Insurance | Underwriting Location [Member] | United States

Segment Reporting Information [Line Items]

Net premiums written

1,478,930

[6]

1,254,623

[6]

1,153,834

[6]

Insurance | Underwriting Location [Member] | Europe

Segment Reporting Information [Line Items]

Net premiums written

389,763

[6]

472,132

[6]

463,855

[6]

Insurance | Underwriting Location [Member] | Other geographic location

Segment Reporting Information [Line Items]

Net premiums written

80,103

[6]

98,579

[6]

103,590

[6]

Insurance | Programs [Member]

Segment Reporting Information [Line Items]

Net premiums written

419,673

[6]

340,130

[6]

290,378

[6]

Net premiums earned

386,840

[6]

318,740

[6]

283,367

[6]

Insurance | Property, energy, marine and aviation [Member]

Segment Reporting Information [Line Items]

Net premiums written

280,551

[6]

294,690

[6]

335,589

[6]

Net premiums earned

304,294

[6]

313,081

[6]

322,510

[6]

Insurance | Professional liability [Member]

Segment Reporting Information [Line Items]

Net premiums written

222,351

[6]

260,705

[6]

237,860

[6]

Net premiums earned

231,014

[6]

258,401

[6]

252,037

[6]

Insurance | Executive assurance [Member]

Segment Reporting Information [Line Items]

Net premiums written

213,727

[6]

250,904

[6]

231,405

[6]

Net premiums earned

221,925

[6]

241,791

[6]

228,623

[6]

Insurance | Construction [Member]

Segment Reporting Information [Line Items]

Net premiums written

161,877

[6]

130,201

[6]

120,405

[6]

Net premiums earned

149,864

[6]

129,446

[6]

112,764

[6]

Insurance | Casualty [Member]

Segment Reporting Information [Line Items]

Net premiums written

112,094

[6]

112,307

[6]

114,235

[6]

Net premiums earned

103,152

[6]

113,597

[6]

111,654

[6]

Insurance | National accounts [Member]

Segment Reporting Information [Line Items]

Net premiums written

109,233

[6]

80,929

[6]

80,973

[6]

Net premiums earned

100,865

[6]

79,771

[6]

79,542

[6]

Insurance | Lenders products [Member]

Segment Reporting Information [Line Items]

Net premiums written

101,576

[6]

99,724

[6]

94,301

[6]

Net premiums earned

99,847

[6]

103,478

[6]

79,522

[6]

Insurance | Surety [Member]

Segment Reporting Information [Line Items]

Net premiums written

64,911

[6]

53,271

[6]

42,475

[6]

Net premiums earned

57,719

[6]

47,302

[6]

41,119

[6]

Insurance | Travel and accident [Member]

Segment Reporting Information [Line Items]

Net premiums written

63,209

[6]

80,489

[6]

71,940

[6]

Net premiums earned

59,987

[6]

78,050

[6]

69,945

[6]

Insurance | Healthcare [Member]

Segment Reporting Information [Line Items]

Net premiums written

40,115

[6]

36,814

[6]

35,652

[6]

Net premiums earned

38,852

[6]

36,779

[6]

35,906

[6]

Insurance | Other [Member]

Segment Reporting Information [Line Items]

Net premiums written

159,479

[6]

85,170

[6]

66,066

[6]

Net premiums earned

$121,655

[6],[7]

$79,907

[6],[7]

$62,058

[6],[7]

[1]

Reinsurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

[2]

Includes U.K. motor, trade credit, surety, workersâ€™ compensation catastrophe, accident and health, private passenger auto and other.

[3]

Includes facultative business.

[4]

Includes professional liability, executive assurance and healthcare business.

[5]

Includes mortgage, life, casualty clash and other.

[6]

Insurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

[7]

Includes alternative markets, contract binding, accident and health and excess workers' compensation business.

Reinsurance_Effects_of_reinsur

Reinsurance (Effects of reinsurance) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Premiums Written	'	'	'	'	'	'	'	'	'	'	'
Direct	'	'	'	'	'	'	'	'	$2,754,582	$2,673,864	$2,402,153
Assumed	'	'	'	'	'	'	'	'	1,442,041	1,195,297	1,034,303
Ceded	'	'	'	'	'	'	'	'	-845,256	-816,926	-763,130
Net	748,921	839,135	810,535	952,776	613,142	755,249	820,233	863,611	3,351,367	3,052,235	2,673,326
Premiums Earned	'	'	'	'	'	'	'	'	'	'	'
Direct	'	'	'	'	'	'	'	'	2,666,104	2,572,078	2,357,656
Assumed	'	'	'	'	'	'	'	'	1,296,048	1,165,371	1,034,939
Ceded	'	'	'	'	'	'	'	'	-816,200	-802,309	-760,780
Net premiums earned	839,366	795,000	758,816	752,770	779,481	748,691	726,656	680,312	3,145,952	2,935,140	2,631,815
Losses and Loss Adjustment Expenses	'	'	'	'	'	'	'	'	'	'	'
Direct	'	'	'	'	'	'	'	'	1,603,369	1,725,707	1,584,815
Assumed	'	'	'	'	'	'	'	'	450,618	578,081	630,466
Ceded	'	'	'	'	'	'	'	'	-374,563	-442,511	-487,728
Net	'	'	'	'	'	'	'	'	$1,679,424	$1,861,277	$1,727,553

Reinsurance_Ceded_credit_risk_

Reinsurance (Ceded credit risk) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Ceded Credit Risk [Line Items]	'	'
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	$1,804,330	$1,870,037
AM Best Aminus Or Better Rating [Member]	'	'
Ceded Credit Risk [Line Items]	'	'
Percentage of reinsurance recoverable	86.50%	87.50%

Reinsurance_Other_items_Detail

Reinsurance (Other items) (Details) (Reinsurance recoverables, Credit concentration risk, Stockholders' equity)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Reinsurance recoverables \| Credit concentration risk \| Stockholders' equity	'	'
Concentration Risk [Line Items]	'	'
Concentration risk percentage	4.20%	4.70%

Reserve_for_Losses_and_Loss_Ad2

Reserve for Losses and Loss Adjustment Expenses - Reconciliation of beginning and ending balances of losses and loss adjustment reserves (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]	'	'	'
Reserve for losses and loss adjustment expenses at beginning of year	$8,933,292	$8,456,210	$8,098,454
Unpaid losses and loss adjustment expenses recoverable	1,829,070	1,818,047	1,703,201
Net reserve for losses and loss adjustment expenses at beginning of year	7,104,222	6,638,163	6,395,253
Net incurred losses and loss adjustment expenses relating to losses occurring in:	'	'	'
Current year	1,943,466	2,082,805	2,012,569
Prior years	-264,042	-221,528	-285,016
Total net incurred losses and loss adjustment expenses	1,679,424	1,861,277	1,727,553
Net losses and loss adjustment expense reserves of acquired business	0	31,977	0
Foreign exchange losses (gains)	1,617	38,184	-32,020
Net paid losses and loss adjustment expenses relating to losses occurring in:	'	'	'
Current year	-288,114	-295,984	-325,273
Prior years	-1,420,703	-1,169,395	-1,127,350
Total net paid losses and loss adjustment expenses	1,708,817	1,465,379	1,452,623
Net reserve for losses and loss adjustment expenses at end of year	7,076,446	7,104,222	6,638,163
Unpaid losses and loss adjustment expenses recoverable	1,748,250	1,829,070	1,818,047
Reserve for losses and loss adjustment expenses at end of year	$8,824,696	$8,933,292	$8,456,210

Reserve_for_Losses_and_Loss_Ad3

Reserve for Losses and Loss Adjustment Expenses - Prior years reserve development (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	($264,042)	($221,528)	($285,016)
Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-218,900	-190,300	-232,900
Prior year reserve development (points)	17.20%	16.80%	24.40%
Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-45,100	-31,200	-52,100
Prior year reserve development (points)	2.40%	1.70%	3.10%
Short tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-112,100	-117,600	-118,500
Short tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-67,000	-79,300	-75,700
Medium tailed and long tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-106,800	-72,700	-114,400
Medium tailed and long tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	21,900	48,100	23,600
Casualty [Member] \| Medium tailed and long tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	32,300
Casualty [Member] \| Medium tailed and long tailed lines [Member] \| Insurance \| Other commercial claims [Member]	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	9,500
Specialty Casualty [Member] \| Medium tailed and long tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	28,000	'	'
Programs [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	26,200	'	'
Professional liability [Member] \| Medium tailed and long tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	19,800	'
2009-2012 \| Property catastrophe and property other than property catastrophe [Member] \| Short tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-110,100	'	'
2005-2012 \| Property catastrophe [Member] \| Short tailed lines [Member] \| Reinsurance \| Named catastrophic events [Member]	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-28,600	'	'
2005-2012 \| Property [Member] \| Short tailed lines [Member] \| Insurance \| Named catastrophic events [Member]	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-15,900	'	'
2003-2009 \| Casualty [Member] \| Medium tailed and long tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-98,800	-55,900	'
2007 and 2009 \| Marine and aviation [Member] \| Medium tailed and long tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-8,100	'	'
2008-2011 \| Property catastrophe and property other than property catastrophe [Member] \| Short tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	-92,100	'
2008-2011 \| Property [Member] \| Short tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	-62,400	'	'
2008-2010 \| Marine and aviation [Member] \| Medium tailed and long tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	-16,800	'
2008-2010 \| Property [Member] \| Short tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	-68,500
2007-2011 \| Property [Member] \| Short tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	-69,000	'
2005-2011 \| Property catastrophe [Member] \| Short tailed lines [Member] \| Reinsurance \| Named catastrophic events [Member]	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	-16,800	'
2005-2011 \| Property [Member] \| Short tailed lines [Member] \| Insurance \| Named catastrophic events [Member]	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	-19,100	'
2007-2010 \| Property catastrophe and property other than property catastrophe [Member] \| Short tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	-97,600
2003-2005 \| Specialty Casualty [Member] \| Medium tailed and long tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	23,000	'
2005-2010 \| Property catastrophe [Member] \| Short tailed lines [Member] \| Reinsurance \| Named catastrophic events [Member]	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	-19,400
2005-2010 \| Property [Member] \| Short tailed lines [Member] \| Insurance \| Named catastrophic events [Member]	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	-23,000
2002-2007 \| Casualty [Member] \| Medium tailed and long tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	-99,000
2006-2010 \| Marine and aviation [Member] \| Medium tailed and long tailed lines [Member] \| Reinsurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	-15,400
2005 and 2007 \| New York Residential Contractors [Member] \| Medium tailed and long tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	14,300
2010 \| New York Residential Contractors [Member] \| Medium tailed and long tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	8,500
2011 \| Programs [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development, percentage attributable to a singe cause	0.9	'	'
2003 and 2004 \| Programs [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	'	9,800
United Kingdom \| 2007-2010 \| Medium tailed and long tailed lines [Member] \| Insurance	'	'	'
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'
Prior year reserve development	'	$38,900	'

Investment_Information_Summary

Investment Information (Summary of Available for Sale Securities) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Available for sale securities:	'		'
Estimated Fair Value	$12,150,358,000		$11,474,986,000
Gross Unrealized Gains	232,673,000		372,578,000
Gross Unrealized Losses	-152,368,000		-52,671,000
Cost or Amortized Cost	12,070,053,000		11,155,079,000
OTTI Unrealized Losses	-12,942,000	[1]	-13,043,000	[1]
Available for sale securities, other information:	'		'
OTTI unrealized losses at current fair value	6,000,000		2,000,000
Fixed maturities and fixed maturities pledged under securities lending agreements	'		'
Available for sale securities:	'		'
Estimated Fair Value	9,676,857,000	[2]	9,882,588,000	[2]
Gross Unrealized Gains	133,450,000	[2]	309,850,000	[2]
Gross Unrealized Losses	-127,100,000	[2]	-35,876,000	[2]
Cost or Amortized Cost	9,670,507,000	[2]	9,608,614,000	[2]
OTTI Unrealized Losses	-12,942,000	[1],[2]	-13,043,000	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Corporate bonds	'		'
Available for sale securities:	'		'
Estimated Fair Value	2,267,263,000	[2]	2,857,513,000	[2]
Gross Unrealized Gains	35,289,000	[2]	105,798,000	[2]
Gross Unrealized Losses	-35,537,000	[2]	-6,710,000	[2]
Cost or Amortized Cost	2,267,511,000	[2]	2,758,425,000	[2]
OTTI Unrealized Losses	-16,000	[1],[2]	-62,000	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,133,095,000	[2]	1,532,736,000	[2]
Gross Unrealized Gains	16,270,000	[2]	24,809,000	[2]
Gross Unrealized Losses	-22,209,000	[2]	-7,484,000	[2]
Cost or Amortized Cost	1,139,034,000	[2]	1,515,411,000	[2]
OTTI Unrealized Losses	-9,269,000	[1],[2]	-9,329,000	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Municipal bonds	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,481,738,000	[2]	1,463,586,000	[2]
Gross Unrealized Gains	29,378,000	[2]	62,322,000	[2]
Gross Unrealized Losses	-9,730,000	[2]	-1,421,000	[2]
Cost or Amortized Cost	1,462,090,000	[2]	1,402,685,000	[2]
OTTI Unrealized Losses	-17,000	[1],[2]	-17,000	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,074,497,000	[2]	824,165,000	[2]
Gross Unrealized Gains	13,972,000	[2]	37,514,000	[2]
Gross Unrealized Losses	-15,224,000	[2]	-4,468,000	[2]
Cost or Amortized Cost	1,075,749,000	[2]	791,119,000	[2]
OTTI Unrealized Losses	-199,000	[1],[2]	-270,000	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| US government and government agencies	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,301,809,000	[2]	1,131,688,000	[2]
Gross Unrealized Gains	3,779,000	[2]	20,178,000	[2]
Gross Unrealized Losses	-11,242,000	[2]	-1,095,000	[2]
Cost or Amortized Cost	1,309,272,000	[2]	1,112,605,000	[2]
OTTI Unrealized Losses	-19,000	[1],[2]	-19,000	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Non-US government securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,085,861,000	[2]	998,901,000	[2]
Gross Unrealized Gains	14,729,000	[2]	33,701,000	[2]
Gross Unrealized Losses	-19,363,000	[2]	-8,860,000	[2]
Cost or Amortized Cost	1,090,495,000	[2]	974,060,000	[2]
OTTI Unrealized Losses	0	[1],[2]	0	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Asset backed securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,332,594,000	[2]	1,073,999,000	[2]
Gross Unrealized Gains	20,033,000	[2]	25,528,000	[2]
Gross Unrealized Losses	-13,795,000	[2]	-5,838,000	[2]
Cost or Amortized Cost	1,326,356,000	[2]	1,054,309,000	[2]
OTTI Unrealized Losses	-3,422,000	[1],[2]	-3,346,000	[1],[2]
Equity securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	496,824,000		312,749,000
Gross Unrealized Gains	69,487,000		26,625,000
Gross Unrealized Losses	-5,938,000		-12,290,000
Cost or Amortized Cost	433,275,000		298,414,000
OTTI Unrealized Losses	0	[1]	0	[1]
Other investments	'		'
Available for sale securities:	'		'
Estimated Fair Value	498,310,000		549,280,000
Gross Unrealized Gains	28,082,000		32,582,000
Gross Unrealized Losses	-18,459,000		-3,257,000
Cost or Amortized Cost	488,687,000		519,955,000
OTTI Unrealized Losses	0	[1]	0	[1]
Short-term investments	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,478,367,000		730,369,000
Gross Unrealized Gains	1,654,000		3,521,000
Gross Unrealized Losses	-871,000		-1,248,000
Cost or Amortized Cost	1,477,584,000		728,096,000
OTTI Unrealized Losses	$0	[1]	$0	[1]

[1]	Represents the total other-than-temporary impairments (â€œOTTIâ€) recognized in accumulated other comprehensive income (â€œAOCIâ€). It does not include the change in fair value subsequent to the impairment measurement date. At December 31, 2013, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $6.0 million, compared to a net unrealized gain of $2.0 million at December 31, 2012.
[2]	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged. See â€œâ€”Securities Lending Agreements.â€

Investment_Information_Aging_o

Investment Information (Aging of Available For Sale Securities in an Unrealized Loss Position) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	$6,158,245		$2,050,668
Gross Unrealized Losses - Less than 12 Months	-137,655		-28,958
Estimated Fair Value - 12 Months or More	258,290		373,325
Gross Unrealized Losses - 12 Months or More	-14,713		-23,713
Estimated Fair Value - Total	6,416,535		2,423,993
Gross Unrealized Losses - Total	-152,368		-52,671
Fixed maturities and fixed maturities pledged under securities lending agreements	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	5,887,621	[1]	1,839,019	[1]
Gross Unrealized Losses - Less than 12 Months	-115,071	[1]	-15,036	[1]
Estimated Fair Value - 12 Months or More	210,974	[1]	321,773	[1]
Gross Unrealized Losses - 12 Months or More	-12,029	[1]	-20,840	[1]
Estimated Fair Value - Total	6,098,595	[1]	2,160,792	[1]
Gross Unrealized Losses - Total	-127,100	[1]	-35,876	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Corporate bonds	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	1,183,625	[1]	490,784	[1]
Gross Unrealized Losses - Less than 12 Months	-32,837	[1]	-3,692	[1]
Estimated Fair Value - 12 Months or More	46,673	[1]	52,334	[1]
Gross Unrealized Losses - 12 Months or More	-2,700	[1]	-3,018	[1]
Estimated Fair Value - Total	1,230,298	[1]	543,118	[1]
Gross Unrealized Losses - Total	-35,537	[1]	-6,710	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	778,693	[1]	537,883	[1]
Gross Unrealized Losses - Less than 12 Months	-20,253	[1]	-4,290	[1]
Estimated Fair Value - 12 Months or More	43,634	[1]	60,574	[1]
Gross Unrealized Losses - 12 Months or More	-1,956	[1]	-3,194	[1]
Estimated Fair Value - Total	822,327	[1]	598,457	[1]
Gross Unrealized Losses - Total	-22,209	[1]	-7,484	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Municipal bonds	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	589,009	[1]	147,766	[1]
Gross Unrealized Losses - Less than 12 Months	-9,422	[1]	-1,120	[1]
Estimated Fair Value - 12 Months or More	6,092	[1]	7,052	[1]
Gross Unrealized Losses - 12 Months or More	-308	[1]	-301	[1]
Estimated Fair Value - Total	595,101	[1]	154,818	[1]
Gross Unrealized Losses - Total	-9,730	[1]	-1,421	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	677,617	[1]	36,649	[1]
Gross Unrealized Losses - Less than 12 Months	-15,110	[1]	-2,261	[1]
Estimated Fair Value - 12 Months or More	1,612	[1]	8,878	[1]
Gross Unrealized Losses - 12 Months or More	-114	[1]	-2,207	[1]
Estimated Fair Value - Total	679,229	[1]	45,527	[1]
Gross Unrealized Losses - Total	-15,224	[1]	-4,468	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| US government and government agencies	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	1,144,809	[1]	146,526	[1]
Gross Unrealized Losses - Less than 12 Months	-11,242	[1]	-1,095	[1]
Estimated Fair Value - 12 Months or More	0	[1]	0	[1]
Gross Unrealized Losses - 12 Months or More	0	[1]	0	[1]
Estimated Fair Value - Total	1,144,809	[1]	146,526	[1]
Gross Unrealized Losses - Total	-11,242	[1]	-1,095	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Non-US government securities	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	821,506	[1]	244,827	[1]
Gross Unrealized Losses - Less than 12 Months	-15,776	[1]	-1,070	[1]
Estimated Fair Value - 12 Months or More	24,334	[1]	135,564	[1]
Gross Unrealized Losses - 12 Months or More	-3,587	[1]	-7,790	[1]
Estimated Fair Value - Total	845,840	[1]	380,391	[1]
Gross Unrealized Losses - Total	-19,363	[1]	-8,860	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Asset backed securities	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	692,362	[1]	234,584	[1]
Gross Unrealized Losses - Less than 12 Months	-10,431	[1]	-1,508	[1]
Estimated Fair Value - 12 Months or More	88,629	[1]	57,371	[1]
Gross Unrealized Losses - 12 Months or More	-3,364	[1]	-4,330	[1]
Estimated Fair Value - Total	780,991	[1]	291,955	[1]
Gross Unrealized Losses - Total	-13,795	[1]	-5,838	[1]
Equity securities	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	76,563		130,385
Gross Unrealized Losses - Less than 12 Months	-5,938		-10,200
Estimated Fair Value - 12 Months or More	0		16,469
Gross Unrealized Losses - 12 Months or More	0		-2,090
Estimated Fair Value - Total	76,563		146,854
Gross Unrealized Losses - Total	-5,938		-12,290
Other investments	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	165,891		23,849
Gross Unrealized Losses - Less than 12 Months	-15,775		-2,474
Estimated Fair Value - 12 Months or More	47,316		35,083
Gross Unrealized Losses - 12 Months or More	-2,684		-783
Estimated Fair Value - Total	213,207		58,932
Gross Unrealized Losses - Total	-18,459		-3,257
Short-term investments	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	28,170		57,415
Gross Unrealized Losses - Less than 12 Months	-871		-1,248
Estimated Fair Value - 12 Months or More	0		0
Gross Unrealized Losses - 12 Months or More	0		0
Estimated Fair Value - Total	28,170		57,415
Gross Unrealized Losses - Total	($871)		($1,248)

[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged. See â€œâ€”Securities Lending Agreements.â€

Investment_Information_Maturit

Investment Information (Maturity Profile of Available For Sale Securities) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Estimated Fair Value:	'	'
Estimated fair value	$9,571,776	$9,839,988
Amortized Cost:	'	'
Amortized cost	9,564,634	9,567,290
Fixed maturities and fixed maturities pledged under securities lending agreements	'	'
Estimated Fair Value:	'	'
Due in one year or less	235,330	446,402
Due after one year through five years	3,738,500	3,876,062
Due after five years through 10 years	1,966,536	1,949,297
Due after 10 years	196,305	179,927
Single maturity date	6,136,671	6,451,688
Estimated fair value	9,676,857	9,882,588
Amortized Cost:	'	'
Due in one year or less	232,652	436,376
Due after one year through five years	3,718,920	3,769,426
Due after five years through 10 years	1,979,510	1,869,698
Due after 10 years	198,286	172,275
Single maturity date	6,129,368	6,247,775
Amortized cost	9,670,507	9,608,614
Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'	'
Estimated Fair Value:	'	'
Securities without single maturity date	1,133,095	1,532,736
Amortized Cost:	'	'
Securities without single maturity date	1,139,034	1,515,411
Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'	'
Estimated Fair Value:	'	'
Securities without single maturity date	1,074,497	824,165
Amortized Cost:	'	'
Securities without single maturity date	1,075,749	791,119
Fixed maturities and fixed maturities pledged under securities lending agreements \| Asset backed securities	'	'
Estimated Fair Value:	'	'
Securities without single maturity date	1,332,594	1,073,999
Amortized Cost:	'	'
Securities without single maturity date	$1,326,356	$1,054,309

Investment_Information_Other_I

Investment Information (Other Investments) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	$1,271,590	$1,077,251
Available for sale	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	498,310	549,280
Available for sale \| Asian and emerging markets	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	331,984	316,860
Available for sale \| Investment grade fixed income	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	159,115	220,410
Available for sale \| Other	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	7,211	12,010
Fair value option	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	773,280	527,971
Fair value option \| Asian and emerging markets	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	14,054	24,035
Fair value option \| Investment grade fixed income	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	75,062	67,624
Fair value option \| Non-investment grade fixed income	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	0	11,093
Fair value option \| Other	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	172,088	116,623
Fair value option \| Term loan investments	'	'
Schedule Of Other Investments [Line Items]	'	'
Other investments and fair value option investments	512,076	308,596
Other investments par	$494,502	$307,016

Investment_Information_Fair_Va

Investment Information (Fair Value Option) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]	'		'
Investments accounted for using the fair value option	$1,221,534		$917,466
Securities sold but not yet purchased	0	[1]	-6,924	[1]
Net assets accounting for using the fair value option	1,221,534		910,542
Fixed Maturities	'		'
Fair Value, Option, Quantitative Disclosures [Line Items]	'		'
Investments accounted for using the fair value option	448,254		363,541
Other investments	'		'
Fair Value, Option, Quantitative Disclosures [Line Items]	'		'
Investments accounted for using the fair value option	773,280		527,971
Equity securities	'		'
Fair Value, Option, Quantitative Disclosures [Line Items]	'		'
Investments accounted for using the fair value option	$0		$25,954

[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.

Investment_Information_Net_Inv

Investment Information (Net Investment Income) (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Net investment income:

Gross investment income

$300,329

$320,562

$362,981

Investment expenses

-33,110

-25,667

-24,783

Net investment income

67,095

66,083

68,369

65,672

73,769

73,221

73,608

74,297

267,219

294,895

338,198

Fixed Maturities

Net investment income:

Gross investment income

249,833

281,140

331,469

Term loan investments

Net investment income:

Gross investment income

20,608

15,283

2,854

Short-term investments

Net investment income:

Gross investment income

1,259

1,980

2,174

Equity securities

Net investment income:

Gross investment income

8,919

7,963

7,332

Other

Net investment income:

Gross investment income

$19,710

[1]

$14,196

[1]

$19,152

[1]

Includes dividends on investment funds and other items.

Investment_Information_Net_Rea

Investment Information (Net Realized Gains and Losses) (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Net realized gains and losses:

Available for sale securities, gross gains on investment sales

$239,421

$247,291

$271,818

Available for sale securities, gross losses on investment sales

-203,077

-71,722

-132,166

Change in fair value of assets and liabilities accounted for using the fair value option - derivatives

20,912

[1]

-1,326

[1]

19,851

[1]

Change in fair value of assets and liabilities accounted for using the fair value option - other investments

-1,499

-520

-1,902

Net realized gains

9,048

-6,022

12,652

58,340

54,849

60,391

34,867

44,121

74,018

194,228

110,646

Fixed Maturities

Net realized gains and losses:

Change in fair value of assets and liabilities accounted for using the fair value option

13,195

-12,164

Equity securities

Net realized gains and losses:

Change in fair value of assets and liabilities accounted for using the fair value option

704

-73

-31,519

Other investments

Net realized gains and losses:

Change in fair value of assets and liabilities accounted for using the fair value option

$17,503

$7,383

($3,272)

[1]

See Note 9 for information on the Companyâ€™s derivative instruments.

Investment_Information_Other_T

Investment Information (Other Than Temporary Impairments Recognized in Earnings) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	($88)	($728)	($724)	($2,246)	($6,035)	($2,379)	($1,951)	($1,023)	($3,786)	($11,388)	($9,062)
Fixed Maturities	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	-511	-4,612	-5,964
Fixed Maturities \| Mortgage backed securities	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	-295	-2,491	-5,023
Fixed Maturities \| Corporate bonds	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	-88	-1,512	-931
Fixed Maturities \| Non-US government securities	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	0	-261	0
Fixed Maturities \| Commercial mortgage backed securities	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	0	-211	0
Fixed Maturities \| Asset backed securities	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	-128	-127	-10
Fixed Maturities \| US government and government agencies	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	0	-10	0
Investment of funds received under securities lending arrangements	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	0	-87	-1,623
Equity securities	'	'	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	($3,275)	($6,689)	($1,475)

Investment_Information_Other_T1

Investment Information (Other Than Temporary Impairments Rollforward) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Rollforward:	'	'	'
Balance at start of period	$62,001	$66,545	$86,040
Credit loss impairments recognized on securities not previously impaired	423	1,962	3,736
Credit loss impairments recognized on securities previously impaired	88	2,735	3,850
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	0	0	0
Reductions for securities sold during the period	-2,450	-9,241	-27,081
Balance at end of period	$60,062	$62,001	$66,545

Investment_Information_Restric

Investment Information (Restricted Assets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Restricted Assets [Line Items]	'	'
Restricted assets	$5,302,042	$5,467,832
Collateral or guarantees - affiliated transactions	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	4,060,533	4,062,097
Collateral or guarantees - third party agreements	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	856,890	771,631
Deposits with US regulatory authorities	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	302,809	290,441
Deposits with non-US regulatory authorities	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	6,546	247,321
Trust funds	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	$75,264	$96,342

Investment_Information_Text_It

Investment Information (Text Items) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
	lots		lots		Dec. 31, 2011
Disclosure Investment Information [Abstract]	'		'		'
OTTI Unrealized Losses	$12,942,000	[1]	$13,043,000	[1]	'
Continuous unrealized loss, qualitative disclosures:	'		'		'
Number of positions in an unrealized loss position (lots)	2,080		910		'
Total number of positions (lots)	4,400		4,580		'
Largest single loss	3,500,000		2,500,000		'
Securities lending, qualitative disclosures:	'		'		'
Fair value of fixed maturities and short-term investments pledged under securities lending agreements	105,100,000		50,800,000		'
Amortized cost of fixed maturities and short-term investments pledged under securities lending agreements	105,900,000		49,600,000		'
Approximate fair value of sub-prime securities backing the securities lending program	6,300,000		5,400,000		'
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]	'		'		'
Equity in net income (loss) of investment funds accounted for using the equity method	35,701,000		73,510,000		-9,605,000
Equity method investments, time lag for reporting - low end of range	'1 month		'		'
Equity method investments, time lag for reporting - high end of range	'3 months		'		'
Investment Of Funds Accounted For Using Equity Method Excluding Investments In Related Parties	$242,300,000		$302,500,000		'

[1]	Represents the total other-than-temporary impairments (â€œOTTIâ€) recognized in accumulated other comprehensive income (â€œAOCIâ€). It does not include the change in fair value subsequent to the impairment measurement date. At December 31, 2013, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $6.0 million, compared to a net unrealized gain of $2.0 million at December 31, 2012.

Investment_in_Joint_Venture_De

Investment in Joint Venture (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	31-May-08
Investment in Joint Venture (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Gulf Re
Schedule of Equity Method Investments [Line Items]	'	'	'
Investment in joint venture, at cost	$100,000,000	$100,000,000	$100,000,000
Joint venture, ownership percentage	'	'	50.00%
Initial capital amount	'	'	200,000,000
Additional funding commitment	'	'	$200,000,000

Fair_Value_Fair_Value_Hierarch

Fair Value (Fair Value Hierarchy) (Details) (Recurring, USD $)	Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Estimated Fair Value	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	$13,371,892		$12,392,452
Liabilities measured at fair value	'		6,924
Estimated Fair Value \| Fixed maturities and fixed maturities pledged under securities lending agreements	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	9,676,857	[1]	9,882,588	[1]
Estimated Fair Value \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Corporate bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	2,267,263	[1]	2,857,513	[1]
Estimated Fair Value \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,133,095	[1]	1,532,736	[1]
Estimated Fair Value \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Municipal bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,481,738	[1]	1,463,586	[1]
Estimated Fair Value \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,074,497	[1]	824,165	[1]
Estimated Fair Value \| Fixed maturities and fixed maturities pledged under securities lending agreements \| US government and government agencies	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,301,809	[1]	1,131,688	[1]
Estimated Fair Value \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Non-US government securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,085,861	[1]	998,901	[1]
Estimated Fair Value \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Asset backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,332,594	[1]	1,073,999	[1]
Estimated Fair Value \| Equity securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	496,824		312,749
Estimated Fair Value \| Other investments	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	498,310		549,280
Estimated Fair Value \| Short-term investments	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,478,367		730,369
Estimated Fair Value \| Fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,221,534		917,466
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	334,065		275,132
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	41,033		'
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	73,156		88,409
Estimated Fair Value \| Fair value option \| Equity securities fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	'		25,954
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	773,280		527,971
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	'		6,924
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	3,226,291		2,148,749
Liabilities measured at fair value	'		6,924
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities and fixed maturities pledged under securities lending agreements	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,301,809	[1]	1,131,688	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Corporate bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Municipal bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| US government and government agencies	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,301,809	[1]	1,131,688	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Non-US government securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Asset backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
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	496,738		312,666
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	0		0
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	1,427,744		678,441
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	0		25,954
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		'
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 \| Equity securities fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	'		25,954
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	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	'		6,924
Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	9,595,611		9,765,747
Liabilities measured at fair value	'		0
Significant Other Observable Inputs (Level 2) \| Fixed maturities and fixed maturities pledged under securities lending agreements	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	8,373,003	[1]	8,652,496	[1]
Significant Other Observable Inputs (Level 2) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Corporate bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	2,265,218	[1]	2,759,109	[1]
Significant Other Observable Inputs (Level 2) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,133,095	[1]	1,532,736	[1]
Significant Other Observable Inputs (Level 2) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Municipal bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,481,738	[1]	1,463,586	[1]
Significant Other Observable Inputs (Level 2) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,074,497	[1]	824,165	[1]
Significant Other Observable Inputs (Level 2) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| US government and government agencies	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Significant Other Observable Inputs (Level 2) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Non-US government securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,085,861	[1]	998,901	[1]
Significant Other Observable Inputs (Level 2) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Asset backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,332,594	[1]	1,073,999	[1]
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	86		83
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	327,890		365,078
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	50,623		51,928
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	844,009		696,162
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	334,065		275,132
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	41,033		'
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	73,156		88,409
Significant Other Observable Inputs (Level 2) \| Fair value option \| Equity securities fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	'		0
Significant Other Observable Inputs (Level 2) \| Fair value option \| Other investments fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	395,755		332,621
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	'		0
Significant Unobservable Inputs (Level 3)	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	549,990		477,956
Liabilities measured at fair value	'		0
Significant Unobservable Inputs (Level 3) \| Fixed maturities and fixed maturities pledged under securities lending agreements	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	2,045	[1]	98,404	[1]
Significant Unobservable Inputs (Level 3) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Corporate bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	2,045	[1]	98,404	[1]
Significant Unobservable Inputs (Level 3) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Municipal bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| US government and government agencies	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Non-US government securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) \| Fixed maturities and fixed maturities pledged under securities lending agreements \| Asset backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0	[1]	0	[1]
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) \| Other investments	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	170,420		184,202
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) \| Fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	377,525		195,350
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		'
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 \| Equity securities fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	'		0
Significant Unobservable Inputs (Level 3) \| Fair value option \| Other investments fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	377,525		195,350
Significant Unobservable Inputs (Level 3) \| Securities sold but not yet purchased	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Liabilities measured at fair value	'		$0

[1]	In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities and short-term investments pledged. For purposes of this table, the Company has excluded the collateral received and reinvested and included the fixed maturities and short-term investments pledged.

Fair_Value_Rollforward_of_Leve

Fair Value (Rollforward of Level 3 assets) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'
Balance at beginning of period	$477,956,000		$97,215,000		$161,367,000
Total gains or (losses) (realized/unrealized) - included in earnings	25,337,000	[1]	5,637,000	[1]	3,985,000
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	-2,578,000		3,075,000		-8,292,000
Purchases, issuances, sales and settlements	'		'		'
Purchases	300,067,000		116,232,000		0
Issuances	0		0		0
Sales	-116,811,000		0		-50,613,000
Settlements	-133,981,000		-1,985,000		-9,232,000
Transfers in and/or out of Level 3	0		257,782,000		0
Balance at end of period	549,990,000		477,956,000		97,215,000
Available for sale \| Corporate bonds	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'
Balance at beginning of period	98,404,000		92,091,000		153,509,000
Total gains or (losses) (realized/unrealized) - included in earnings	4,679,000	[1]	4,419,000	[1]	2,276,000
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	-3,051,000		2,049,000		-4,515,000
Purchases, issuances, sales and settlements	'		'		'
Purchases	0		0		0
Issuances	0		0		0
Sales	-96,655,000		0		-49,947,000
Settlements	-1,332,000		-155,000		-9,232,000
Transfers in and/or out of Level 3	0		0		0
Balance at end of period	2,045,000		98,404,000		92,091,000
Available for sale \| Other investments	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'
Balance at beginning of period	184,202,000		5,124,000		7,858,000
Total gains or (losses) (realized/unrealized) - included in earnings	8,915,000	[1]	1,829,000	[1]	1,709,000
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	473,000		1,026,000		-3,777,000
Purchases, issuances, sales and settlements	'		'		'
Purchases	25,000,000		25,000,000		0
Issuances	0		0		0
Sales	0		0		-666,000
Settlements	-48,170,000		-1,830,000		0
Transfers in and/or out of Level 3	0		153,053,000		0
Balance at end of period	170,420,000		184,202,000		5,124,000
Fair value option \| Other investments	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'
Balance at beginning of period	195,350,000		0		0
Total gains or (losses) (realized/unrealized) - included in earnings	11,743,000	[1]	-611,000	[1]	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0		0		0
Purchases, issuances, sales and settlements	'		'		'
Purchases	275,067,000		91,232,000		0
Issuances	0		0		0
Sales	-20,156,000		0		0
Settlements	-84,479,000		0		0
Transfers in and/or out of Level 3	0		104,729,000		0
Balance at end of period	$377,525,000		$195,350,000		$0

[1]	Gains or losses on corporate bonds and other investments were recorded in net realized gains (losses).

Fair_Value_Text_Items_Details

Fair Value (Text Items) (Details) (USD $)	3 Months Ended	12 Months Ended
Fair Value (Text Items) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair Value Disclosures [Abstract]	'	'	'	'
Total assets and liabilities measured at fair value	$12,400,000,000	$13,400,000,000	$12,400,000,000	'
Total assets and liabilities measured at fair value priced using non-binding broker quotes	927,900,000	1,330,000,000	927,900,000	'
Total assets and liabilities measured at fair value priced using non-binding broker quotes (percentage)	7.50%	9.90%	7.50%	'
Gains (losses) including in earnings attributable to the change in unrealized gains or losses related to assets still held at balance sheet date	'	22,000,000	5,600,000	600,000
Senior notes	300,000,000	800,000,000	300,000,000	'
Transfers from Level 2 to Level 3	257,800,000	'	'	'
Goodwill and intangible assets	$38,300,000	$27,300,000	$38,300,000	'

Derivative_Instruments_Details

Derivative Instruments (Details) (USD $)	12 Months Ended
Derivative Instruments (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Derivative offsetting [Abstract]	'		'		'
Derivative assets subject to master netting agreements	$28,000,000		$26,900,000		'
Derivative liabilities subject to master netting agreements	14,600,000		7,800,000		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	20,912,000	[1]	-1,326,000	[1]	19,851,000	[1]
Not Designated as Hedging Instrument [Member]	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	39,859,000		26,908,000		'
Liability derivatives - fair value	-26,472,000		-7,752,000		'
Net derivatives - fair value	13,387,000		19,156,000		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	20,912,000		-1,326,000		19,851,000
Not Designated as Hedging Instrument [Member] \| Futures contracts	'		'		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	10,742,000		-3,307,000		2,293,000
Not Designated as Hedging Instrument [Member] \| Futures contracts \| Other investments available for sale, at fair value	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	461,000		52,000		'
Liability derivatives - fair value	-110,000		-52,000		'
Net derivatives - fair value	351,000		0		'
Net derivatives - notional value	475,967,000		340,400,000		'
Not Designated as Hedging Instrument [Member] \| Foreign currency forward contracts	'		'		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	9,762,000		-214,000		895,000
Not Designated as Hedging Instrument [Member] \| Foreign currency forward contracts \| Other investments available for sale, at fair value	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	5,023,000		2,809,000		'
Liability derivatives - fair value	-3,090,000		-2,678,000		'
Net derivatives - fair value	1,933,000		131,000		'
Net derivatives - notional value	330,746,000		396,468,000		'
Not Designated as Hedging Instrument [Member] \| TBAs	'		'		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	-1,623,000		4,413,000		12,329,000
Not Designated as Hedging Instrument [Member] \| TBAs \| Fixed maturities available for sale, at fair value	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	33,455,000		23,599,000		'
Liability derivatives - fair value	-21,731,000		-4,346,000		'
Net derivatives - fair value	11,724,000		19,253,000		'
Net derivatives - notional value	56,160,000		26,000,000		'
Not Designated as Hedging Instrument [Member] \| Other	'		'		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	2,031,000		-2,218,000		4,334,000
Not Designated as Hedging Instrument [Member] \| Other \| Other investments available for sale, at fair value	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	920,000		448,000		'
Liability derivatives - fair value	-1,541,000		-676,000		'
Net derivatives - fair value	-621,000		-228,000		'
Net derivatives - notional value	$347,916,000		$50,341,000		'

[1]	See Note 9 for information on the Companyâ€™s derivative instruments.

Other_Comprehensive_Income_Los2

Other Comprehensive Income (Loss) - Components of accumulated other comprehensive income (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Beginning balance	$287,017	$153,923	$204,503
Other comprehensive income (loss) before reclassifications	-179,367	290,918	72,982
Amounts reclassified from accumulated other comprehensive income	-32,686	-157,824	-123,562
Net current period other comprehensive income (loss)	-212,053	133,094	-50,580
Ending balance	74,964	287,017	153,923
Unrealized Appreciation on Available-For-Sale Investments	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Beginning balance	289,956	174,636	213,927
Other comprehensive income (loss) before reclassifications	-176,578	273,144	84,271
Amounts reclassified from accumulated other comprehensive income	-32,686	-157,824	-123,562
Net current period other comprehensive income (loss)	-209,264	115,320	-39,291
Ending balance	80,692	289,956	174,636
Foreign Currency Translation Adjustments	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Beginning balance	-2,939	-20,713	-9,424
Other comprehensive income (loss) before reclassifications	-2,789	17,774	-11,289
Amounts reclassified from accumulated other comprehensive income	0	0	0
Net current period other comprehensive income (loss)	-2,789	17,774	-11,289
Ending balance	($5,728)	($2,939)	($20,713)

Other_Comprehensive_Income_Los3

Other Comprehensive Income (Loss) - Amounts reclassified from accumulated other comprehensive income (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reclassification out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Other-than-temporary impairment losses	($88)	($728)	($724)	($2,246)	($6,035)	($2,379)	($1,951)	($1,023)	($3,786)	($11,388)	($9,062)
Income before income taxes	'	'	'	'	'	'	'	'	742,505	589,387	426,370
Income tax expense	'	'	'	'	'	'	'	'	-32,774	4,010	9,793
Net of tax	161,490	114,825	176,940	256,476	19,217	189,656	220,268	164,256	709,731	593,397	436,163
Reclassification out of accumulated other comprehensive income \| Unrealized Appreciation on Available-For-Sale Investments	'	'	'	'	'	'	'	'	'	'	'
Reclassification out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net realized gains	'	'	'	'	'	'	'	'	39,308	180,144	139,752
Other-than-temporary impairment losses	'	'	'	'	'	'	'	'	-3,961	-12,175	-13,850
Income before income taxes	'	'	'	'	'	'	'	'	35,347	167,969	125,902
Income tax expense	'	'	'	'	'	'	'	'	-2,661	-10,145	-2,340
Net of tax	'	'	'	'	'	'	'	'	$32,686	$157,824	$123,562

Other_Comprehensive_Income_Los4

Other Comprehensive Income (Loss) - Components of other comprehensive income (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Before tax amount:	'	'	'
Unrealized holding gains (losses) arising during period, before tax	($201,386)	$278,917	$108,046
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), before tax	-175	-787	-4,788
Less reclassification of net realized gains included in net income, before tax	35,347	167,969	125,902
Foreign currency translation adjustments, before tax	-2,789	18,748	-12,461
Other comprehensive income (loss), before tax	-239,697	128,909	-35,105
Tax expense (benefit):	'	'	'
Unrealized holding gains (losses) arising during period, tax	-24,983	4,986	18,987
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), tax	0	0	0
Less reclassification of net realized gains included in net income, tax	2,661	10,145	2,340
Foreign currency translation adjustments, tax	0	974	-1,172
Other comprehensive income (loss), tax	-27,644	-4,185	15,475
Net of tax amount:	'	'	'
Unrealized holding gains (losses) arising during period, net of tax	-176,403	273,931	89,059
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), net of tax	-175	-787	-4,788
Less reclassification of net realized gains included in net income, net of tax	32,686	157,824	123,562
Foreign currency translation adjustments, net of tax	-2,789	17,774	-11,289
Net current period other comprehensive income (loss)	($212,053)	$133,094	($50,580)

Earnings_Per_Common_Share_Deta

Earnings Per Common Share (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, except Share data, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Numerator:

Net income

$161,490

$114,825

$176,940

$256,476

$19,217

$189,656

$220,268

$164,256

$709,731

$593,397

$436,163

Preferred dividends

5,485

5,484

5,485

5,484

5,485

5,484

7,649

6,461

21,938

25,079

25,844

Loss on repurchase of preferred shares

-10,612

Net income available to common shareholders

$156,005

$109,341

$171,455

$250,992

$13,732

$184,172

$202,007

$157,795

$687,793

$557,706

$410,319

Denominator:

Weighted average common shares outstanding â€” basic

131,355,392

134,446,158

132,221,970

Effect of dilutive common share equivalents:

Nonvested restricted shares

1,090,100

857,174

940,612

Stock options

3,331,691

[1]

2,955,515

[1]

5,127,120

[1]

Weighted average common shares and common share equivalents outstanding â€” diluted

135,777,183

138,258,847

138,289,702

Earnings per common share:

Basic (per share)

$1.19

$0.83

$1.31

$1.92

$0.10

$1.36

$1.50

$1.18

$5.24

$4.15

$3.10

Diluted (per share)

$1.14

$0.80

$1.26

$1.85

$0.10

$1.33

$1.46

$1.14

$5.07

$4.03

$2.97

Stock Options

Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]

Antidilutive securities excluded from computation of earnings per common share (shares)

892,439

839,414

462,020

[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 2013, 2012 and 2011, the number of stock options excluded were 892,439, 839,414 and 462,020, respectively.

Income_Taxes_Components_of_inc

Income Taxes (Components of income tax) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current expense (benefit):	'	'	'
United States	$27,537	$8,267	($214)
Non-U.S.	5,159	737	8,045
Current Income Tax Expense (Benefit)	32,696	9,004	7,831
Deferred expense (benefit):	'	'	'
United States	1,937	-9,779	-11,563
Non-U.S.	-1,859	-3,235	-6,061
Deferred Income Tax Expense (Benefit)	78	-13,014	-17,624
Income tax expense (benefit)	$32,774	($4,010)	($9,793)

Income_Taxes_Income_before_tax

Income Taxes (Income before taxes by jurisdiction) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Line Items]	'	'	'
Income (loss) before income taxes	$742,505	$589,387	$426,370
Bermuda	'	'	'
Income Tax Disclosure [Line Items]	'	'	'
Income (loss) before income taxes	717,661	609,710	454,673
United States	'	'	'
Income Tax Disclosure [Line Items]	'	'	'
Income (loss) before income taxes	87,032	9,600	-18,662
Other	'	'	'
Income Tax Disclosure [Line Items]	'	'	'
Income (loss) before income taxes	($62,188)	($29,923)	($9,641)

Income_Taxes_Statutory_tax_rat

Income Taxes (Statutory tax rate by jurisdiction) (Details)	12 Months Ended
Income Taxes (Statutory tax rate by jurisdiction) (Details)	Dec. 31, 2013
Bermuda	'
Income Tax Disclosure [Line Items]	'
Statutory tax rate (percentage)	0.00%
United States	'
Income Tax Disclosure [Line Items]	'
Statutory tax rate (percentage)	35.00%
United Kingdom	'
Income Tax Disclosure [Line Items]	'
Statutory tax rate (percentage)	23.25%
Ireland	'
Income Tax Disclosure [Line Items]	'
Statutory tax rate (percentage)	12.50%
Denmark	'
Income Tax Disclosure [Line Items]	'
Statutory tax rate (percentage)	25.00%
Canada	'
Income Tax Disclosure [Line Items]	'
Statutory tax rate (percentage)	24.00%
Gibraltar	'
Income Tax Disclosure [Line Items]	'
Statutory tax rate (percentage)	10.00%
Netherlands	'
Income Tax Disclosure [Line Items]	'
Statutory tax rate (percentage)	22.60%

Income_Taxes_Reconciliation_of

Income Taxes (Reconciliation of effective tax rate) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Expected income tax (benefit) expense computed on pre-tax income at weighted average income tax rate	$17,506	($3,426)	($5,388)
Addition (reduction) in income tax expense (benefit) resulting from:	'	'	'
Tax-exempt investment income	-8,255	-9,257	-8,885
Meals and entertainment	599	688	633
State taxes, net of U.S. federal tax benefit	431	270	309
U.S. operationsâ€™ foreign taxes, net of U.S. federal tax benefit	703	544	-402
Prior year adjustment	2,810	-1,581	-91
Non deductible foreign exchange gains & losses	-1,254	-436	978
Changes in applicable tax rate	2,007	1,193	217
Dividend withholding taxes	4,619	2,511	2,237
Change in valuation allowance	11,795	4,281	0
Other	1,813	1,203	599
Income tax expense (benefit)	$32,774	($4,010)	($9,793)

Income_Taxes_Components_of_def

Income Taxes (Components of deferred tax assets and liabilities) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred income tax assets:	'	'
Net operating loss	$15,294	$4,925
AMT credit carryforward	14,456	14,423
Discounting of net loss reserves	53,293	54,860
Net unearned premium reserve	30,698	30,614
Compensation liabilities	26,481	22,713
Foreign tax credit carryforward	4,343	8,229
Interest expense	6,049	3,628
Other, net	13,347	15,237
Deferred tax assets before valuation allowance	163,961	154,629
Valuation allowance	-15,548	-4,309
Deferred tax assets net of valuation allowance	148,413	150,320
Deferred income tax liabilities:	'	'
Depreciation and amortization	-3,810	-4,896
Deferred acquisition costs, net	-3,369	-5,988
Deposit accounting liability	-4,581	-4,823
Net unrealized foreign exchange gains	0	-2,825
Net unrealized appreciation of investments	-6,354	-30,662
Other, net	-1,738	-2,544
Total deferred tax liabilities	-19,852	-51,738
Net deferred income tax assets	$128,561	$98,582

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)	12 Months Ended
Income Taxes (Narrative) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Loss Carryforwards [Line Items]	'	'	'
Operating Loss Carryforward Expiration Period	'20 years	'	'
Deferred Tax Assets, Valuation Allowance	$15,548,000	$4,309,000	'
Income taxes paid	15,300,000	1,800,000	1,900,000
Current income tax payable	4,200,000	'	'
Federal excise taxes incurred	9,500,000	8,600,000	9,300,000
Foreign tax credit carryforward	4,343,000	8,229,000	'
AMT credit carryforward	14,456,000	14,423,000	'
United Kingdom	'	'	'
Operating Loss Carryforwards [Line Items]	'	'	'
Operating Loss Carryforwards	24,000,000	'	'
Ireland	'	'	'
Operating Loss Carryforwards [Line Items]	'	'	'
Operating Loss Carryforwards	15,500,000	'	'
Canada	'	'	'
Operating Loss Carryforwards [Line Items]	'	'	'
Operating Loss Carryforwards	$32,200,000	'	'

Transactions_with_Related_Part1

Transactions with Related Parties (Details) (Aeolus LP, Investee, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2006
Aeolus LP \| Investee	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Initial contribution amount	'	'	'	$50
Ownership percentage	4.00%	'	'	'
Dividends received	$2.10	$19.80	$33.20	'

Commitments_and_Contingencies_1

Commitments and Contingencies - Concentrations of credit risk (Details) (USD $)	12 Months Ended
In Billions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Concentration Risk [Line Items]	'	'	'
Net reinsurance recoverables	1.94	1.98	'
Aon Corporation [Member] \| Customer Concentration Risk [Member] \| Gross Written Premiums [Member]	'	'	'
Concentration Risk [Line Items]	'	'	'
Concentration risk percentage	16.00%	20.30%	19.40%
Marsh And McLennan Companies [Member] \| Customer Concentration Risk [Member] \| Gross Written Premiums [Member]	'	'	'
Concentration Risk [Line Items]	'	'	'
Concentration risk percentage	17.00%	14.10%	14.20%

Commitments_and_Contingencies_2

Commitments and Contingencies - Future minimum rental payments (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Rent expense	'	'	'
Rental expense net of income from subleases	$18,700,000	$17,100,000	$16,400,000
Office Space [Member]	'	'	'
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]	'	'	'
2014	19,009,000	'	'
2015	18,390,000	'	'
2016	17,850,000	'	'
2017	15,464,000	'	'
2018	15,266,000	'	'
Thereafter	54,406,000	'	'
Total	$140,385,000	'	'

Commitments_and_Contingencies_3

Commitments and Contingencies - Credit facilities and other commitments (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013
	Dec. 31, 2013	Dec. 31, 2012	LOC Facilities	Aggregate limit on unsecured letters of credit	Credit Agreement	Unsecured revolving loan and letter of credit facility	Secured letter of credit facility	Other secured letter of credit facilities
Line of Credit Facility [Line Items]	'	'	'	'	'	'	'	'
Investment commitments	$807,600,000	'	'	'	'	'	'	'
Estimated purchase commitments, primarily related to software and computerized systems	35,900,000	21,500,000	'	'	'	'	'	'
Line of Credit Facility [Abstract]	'	'	'	'	'	'	'	'
Maximum borrowing capacity	'	'	'	100,000,000	'	300,000,000	500,000,000	197,600,000
Debt to total capital ratio (expressed as a percent)	'	'	'	'	0.35	'	'	'
Minimum tangible net worth	'	'	'	'	3,090,000,000	'	'	'
Percentage of aggregate future net income for each quarterly period	'	'	'	'	25.00%	'	'	'
Percentage of future aggregate proceeds from issuance of common or preferred equity	'	'	'	'	25.00%	'	'	'
Amount outstanding	'	'	459,700,000	'	'	'	'	'
Investments pledged as collateral	'	'	537,700,000	'	'	'	'	'
Revolving credit agreement borrowings	$100,000,000	$100,000,000	'	'	'	'	'	'

Senior_Notes_Details

Senior Notes (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	4-May-04	Dec. 31, 2013	Dec. 13, 2013
				Unsecured debt	Unsecured debt	Unsecured debt	Unsecured debt	Unsecured debt
				7.35% senior notes due 2034	7.35% senior notes due 2034	7.35% senior notes due 2034	5.144% senior notes due 2043	5.144% senior notes due 2043
Debt Instrument [Line Items]	'	'	'	'	'	'	'	'
Face amount of issued debt	'	'	'	'	'	$300	'	$500
Stated interest rate (percentage)	'	'	'	'	'	7.35%	'	5.14%
Estimated fair value of senior notes	'	'	'	381	379.1	'	514.1	'
Interest paid on senior notes	$23.70	$29.10	$30.50	'	'	'	'	'

Shareholders_Equity_Rollforwar

Shareholders' Equity - Roll-forward of changes in issued and outstanding Common Shares (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Authorized and Issued:	'		'		'
Common shares authorized	600,000,000		'		'
Common shares, par value per share	$0.00		$0.00		'
Preferred shares authorized	50,000,000		'		'
Preferred shares, par value per share	$0.01		'		'
Common Shares:	'		'		'
Shares issued, beginning of year	168,255,572		164,636,338		160,073,616
Shares issued	811,732	[1]	2,066,065	[1]	3,592,713	[1]
Restricted shares issued, net of cancellations	493,287		1,553,169		970,009
Shares issued, end of year	169,560,591		168,255,572		164,636,338
Common shares held in treasury, end of year	-35,885,707		-34,412,959		-30,277,993
Common shares outstanding, end of year	133,674,884		133,842,613		134,358,345

[1]	Includes shares issued from the exercise of stock options and stock appreciation rights, and shares issued from the employee share purchase plan.

Shareholders_Equity_Share_repu

Shareholders' Equity - Share repurchases and treasury shares (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Class of Stock [Line Items]	'	'	'
Common shares held in treasury (shares)	35,885,707	34,412,959	30,277,993
Common shares held in treasury, at cost	$1,094,704,000	$1,025,839,000	'
Common Shares	'	'	'
Class of Stock [Line Items]	'	'	'
Cumulative number of shares acquired since inception of share repurchase program	109,900,000	'	'
Aggregate purchase price of shares acquired since inception of share repurchase program	2,790,000,000	'	'
Treasury stock, shares acquired (shares)	1,300,000	3,900,000	9,600,000
Treasury stock, value of shares acquired	57,800,000	172,100,000	287,600,000
Reduction to weighted average shares outstanding as a result of share repurchases	109,600,000	105,000,000	103,200,000
Remaining authorized repurchase amount	712,100,000	'	'
February 2007 \| Common Shares	'	'	'
Class of Stock [Line Items]	'	'	'
Share repurchase authorizations, amount	1,000,000,000	'	'
May 2008 \| Common Shares	'	'	'
Class of Stock [Line Items]	'	'	'
Share repurchase authorizations, amount	500,000,000	'	'
November 2009 \| Common Shares	'	'	'
Class of Stock [Line Items]	'	'	'
Share repurchase authorizations, amount	1,000,000,000	'	'
February 2011 \| Common Shares	'	'	'
Class of Stock [Line Items]	'	'	'
Share repurchase authorizations, amount	$1,000,000,000	'	'

Shareholders_Equity_Preferred_

Shareholders' Equity - Preferred shares (Details) (USD $)	12 Months Ended				0 Months Ended			12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	2-May-12	2-May-12	2-May-12	Apr. 02, 2012	Dec. 31, 2013
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Series A and B Preferred Shares	Series A Preferred Stock	Series B Preferred Stock	Series C Preferred Stock	Series C Preferred Stock
Class of Stock [Line Items]	'	'	'	'	'	'	'	'
Shares issued - Series C	$0	$315,763	$0	'	'	'	$325,000	'
Shares redeemed during period, value	'	'	'	'	200,000	125,000	'	'
Preferred shares, dividend rate (as a percent)	'	'	'	'	8.00%	7.88%	6.75%	6.75%
Preferred shares, redemption price per share	'	'	'	$25	'	'	'	$25
Preferred dividends paid	$21,938	$28,381	$25,844	'	'	'	'	'

ShareBased_Compensation_Long_T

Share-Based Compensation - Long Term Incentive Plan (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
2002 Long Term Incentive and Share Award Plan	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Number of shares reserved for issuance	9,497,490	'	'
2007 Long Term Incentive and Share Award Plan	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Shares available for issuance transferred	3,153,924	'	'
2007 Employee Share Purchase Plan	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Number of shares reserved for issuance	2,250,000	'	'
Shares available for issuance	944,766	'	'
Length of offering period, in months	'27 months	'	'
Maximum employee subscription rate	20.00%	'	'
Purchase price (percentage of market value)	85.00%	'	'
Maximum number of shares per employee	3,000	'	'
Maximum accumulation per calendar year	$25,000	'	'
Share based compensation expense	1,100,000	900,000	700,000
Tax benefit	$400,000	$300,000	$300,000
2012 Long Term Incentive and Share Award Plan	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Number of shares reserved for issuance	4,280,000	'	'
Total number of shares reserved under plan	7,433,924	'	'
Maximum percentage of awards to be issued in connection with full value awarrds	50.00%	'	'
Maximum number of incentive stock options	2,000,000	'	'
Shares available for issuance	2,692,267	'	'

ShareBased_Compensation_Valuat

Share-Based Compensation - Valuation assumptions (Details)	12 Months Ended
Share-Based Compensation - Valuation assumptions (Details)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'	'	'
Dividend yield	0.00%	0.00%	0.00%
Expected volatility	23.60%	24.30%	24.60%
Risk free interest rate	1.00%	1.00%	2.20%
Expected option life	'6 years	'6 years 3 months	'6 years

ShareBased_Compensation_Stock_

Share-Based Compensation - Stock option activity (Details) (Stock Options, USD $)	12 Months Ended
	Dec. 31, 2013
Stock Options	'
Number of Options / SARs	'
Outstanding, beginning of year (in shares)	8,221,444
Granted (in shares)	860,881
Exercised (in shares)	-695,756
Forfeited or expired (in shares)	-48,089
Outstanding, end of year (in shares)	8,338,480
Exercisable, end of year (in shares)	6,119,335
Weighted Average Exercise Price	'
Outstanding, beginning of year, weighted average exercise price	$25.87
Granted, weighted average exercise price	$51.76
Exercised, weighted average exercise price	$21.62
Forfeited or expired, weighted average exercise price	$40.54
Outstanding, end of year, weighted average exercise price	$28.82
Exercisable, end of year, weighted average exercise price	$23.51

ShareBased_Compensation_Restri

Share-Based Compensation - Restricted common shares and restricted stock units activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2013
Restricted Common Shares	'
Unvested Shares:	'
Unvested balance, beginning of year (in shares)	2,114,640
Granted (in shares)	513,832
Vested (in shares)	-664,802
Forfeited (in shares)	-20,545
Unvested balance, end of year (in shares)	1,943,125
Weighted Average Grant Date Fair Value:	'
Unvested balance, beginning of year, weighted average grant date fair value	$37.88
Granted, weighted average grant date fair value	$53.21
Vested, weighted average grant date fair value	$33.04
Forfeited, weighted average grant date fair value	$42.21
Unvested balance, end of year, weighted average grant date fair value	$43.55
Restricted Unit Awards	'
Unvested Shares:	'
Unvested balance, beginning of year (in shares)	357,250
Granted (in shares)	76,286
Vested (in shares)	-97,943
Forfeited (in shares)	-27,271
Unvested balance, end of year (in shares)	308,322
Weighted Average Grant Date Fair Value:	'
Unvested balance, beginning of year, weighted average grant date fair value	$38.03
Granted, weighted average grant date fair value	$53.26
Vested, weighted average grant date fair value	$32.95
Forfeited, weighted average grant date fair value	$39.06
Unvested balance, end of year, weighted average grant date fair value	$43.32

ShareBased_Compensation_Additi

Share-Based Compensation - Additional information (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Vesting period	'3 years	'	'
Stock Options	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Vesting period	'3 years	'	'
Life of award	'10 years	'	'
Share based compensation expense	$10.60	$8.50	$5.30
Tax benefit	2	1.8	1.5
Unrecognized compensation cost related to unvested awards	14.1	'	'
Expected period for recognition (years)	'2 years 1 month 2 days	'	'
Weighted average grant date fair value	$12.96	$10.61	$9.73
Aggregate intrinsic value of options exercised	21.7	64	106
Aggregate intrinsic value of options outstanding	257.4	'	'
Aggregate intrinsic value of options exercisable	221.4	'	'
Options outstanding, weighted average remaining contractual term (in years)	'5 years 4 months 24 days	'	'
Options exercisable, weighted average remaining contractual term (in years)	'4 years 3 months 18 days	'	'
Proceeds from stock options exercised	6.4	'	'
Tax benefit from stock options exercised	5	'	'
Restricted Common Shares And Restricted Units	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Vesting period	'3 years	'	'
Share based compensation expense	27.4	24.6	18.2
Tax benefit	7.8	6.3	5
Granted (in shares)	590,118	1,819,657	779,541
Granted, weighted average grant date fair value	$53.21	$40.75	$33.82
Aggregate fair value of awards that vested in the period	41	33.2	31.7
Restricted Common Shares	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Unrecognized compensation cost related to unvested awards	46.3	'	'
Expected period for recognition (years)	'2 years 21 days	'	'
Granted (in shares)	513,832	'	'
Granted, weighted average grant date fair value	$53.21	'	'
Restricted Unit Awards	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Unrecognized compensation cost related to unvested awards	8.3	'	'
Expected period for recognition (years)	'2 years 2 months 12 days	'	'
Granted (in shares)	76,286	'	'
Granted, weighted average grant date fair value	$53.26	'	'
Aggregate intrinsic value of awards outstanding	26.5	'	'
Aggregate intrinsic value of awards exercisable	$8.10	'	'

Retirement_Plans_Details

Retirement Plans (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Compensation and Retirement Disclosure [Abstract]	'	'	'
Defined Contribution Plan, Cost Recognized	$21.50	$19.30	$18.20

Statutory_Information_Summary_

Statutory Information - Summary of statutory capital, surplus and net income (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Bermuda	'		'		'
Statutory Accounting Practices [Line Items]	'		'		'
Actual statutory capital and surplus	$5,416,948	[1]	$5,010,386	[1]	'
Required statutory capital and surplus	2,096,428		2,175,191	[1]	'
Statutory net income (loss)	719,267		631,483		447,447
Ireland	'		'		'
Statutory Accounting Practices [Line Items]	'		'		'
Actual statutory capital and surplus	533,283	[1]	539,326	[1]	'
Required statutory capital and surplus	458,666		377,340	[1]	'
Statutory net income (loss)	24,410		-1,940		9,123
United States	'		'		'
Statutory Accounting Practices [Line Items]	'		'		'
Actual statutory capital and surplus	1,013,228	[1]	822,615	[1]	'
Required statutory capital and surplus	335,442		319,129	[1]	'
Statutory net income (loss)	62,605		-21,517		-37,252
United Kingdom	'		'		'
Statutory Accounting Practices [Line Items]	'		'		'
Actual statutory capital and surplus	250,688	[1]	231,387	[1]	'
Required statutory capital and surplus	237,555		206,764	[1]	'
Statutory net income (loss)	-11,353		-4,449		1,637
Canada	'		'		'
Statutory Accounting Practices [Line Items]	'		'		'
Actual statutory capital and surplus	77,877		0	[1]	'
Required statutory capital and surplus	74,951		0	[1]	'
Statutory net income (loss)	($36,203)		$0		$0

[1]	Such amounts include ownership interests in affiliated insurance and reinsurance subsidiaries.

Statutory_Information_Text_ite

Statutory Information - Text items (Details) (USD $)	12 Months Ended
Statutory Information - Text items (Details) (USD $)	Dec. 31, 2013
Arch Re Bermuda \| Bermuda	'
Statutory Accounting Practices [Line Items]	'
Dividends, percentage permitted	25.00%
Notice period required for dividends to be paid	'7 days
Capital reduction, percentage permitted	15.00%
Dividends available for payment in 2014 without prior regulatory approval	$1,350,000,000
Arch Re US \| United States	'
Statutory Accounting Practices [Line Items]	'
Notice period required for dividends to be paid	'10 days
Notice period required for dividends declared	'5 days
Dividends available for payment in 2014, total	$101,300,000

Unaudited_Condensed_Quarterly_2

Unaudited Condensed Quarterly Financial Information (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Net premiums written	$748,921	$839,135	$810,535	$952,776	$613,142	$755,249	$820,233	$863,611	$3,351,367	$3,052,235	$2,673,326
Net premiums earned	839,366	795,000	758,816	752,770	779,481	748,691	726,656	680,312	3,145,952	2,935,140	2,631,815
Net investment income	67,095	66,083	68,369	65,672	73,769	73,221	73,608	74,297	267,219	294,895	338,198
Net realized gains	9,048	-6,022	12,652	58,340	54,849	60,391	34,867	44,121	74,018	194,228	110,646
Net impairment losses recognized in earnings	-88	-728	-724	-2,246	-6,035	-2,379	-1,951	-1,023	-3,786	-11,388	-9,062
Underwriting Income Loss Segment	128,318	110,992	96,029	116,398	-91,334	73,452	93,723	67,193	451,737	143,034	44,012
Net income	161,490	114,825	176,940	256,476	19,217	189,656	220,268	164,256	709,731	593,397	436,163
Dividends declared on preferred shares	-5,485	-5,484	-5,485	-5,484	-5,485	-5,484	-7,649	-6,461	-21,938	-25,079	-25,844
Net income available to common shareholders	156,005	109,341	171,455	250,992	13,732	184,172	202,007	157,795	687,793	557,706	410,319
Loss on repurchase of preferred shares	'	'	'	'	$0	$0	$10,612	$0	$0	$10,612	$0
Basic (per share)	$1.19	$0.83	$1.31	$1.92	$0.10	$1.36	$1.50	$1.18	$5.24	$4.15	$3.10
Diluted (per share)	$1.14	$0.80	$1.26	$1.85	$0.10	$1.33	$1.46	$1.14	$5.07	$4.03	$2.97

Guarantor_Financial_Informatio2

Guarantor Financial Information - Condensed consolidating balance sheet (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets	'	'	'	'
Total investments	$13,611,734	$12,691,240	'	'
Cash	434,057	371,041	351,699	362,740
Investment in subsidiaries	0	0	'	'
Due from subsidiaries and affiliates	0	0	'	'
Premiums receivable	753,924	688,873	'	'
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	1,804,330	1,870,037	'	'
Contractholder receivables	1,064,246	865,728	'	'
Prepaid reinsurance premiums	328,343	298,484	'	'
Deferred acquisition costs, net	342,314	262,822	'	'
Other assets	1,227,146	768,537	'	'
Total Assets	19,566,094	17,816,762	'	'
Liabilities	'	'	'	'
Reserve for losses and loss adjustment expenses	8,824,696	8,933,292	8,456,210	8,098,454
Unearned premiums	1,896,365	1,647,978	'	'
Reinsurance balances payable	196,167	188,546	'	'
Contractholder payables	1,064,246	865,728	'	'
Deposit accounting liabilities	421,297	27,594	'	'
Senior notes	800,000	300,000	'	'
Revolving credit agreement borrowings	100,000	100,000	'	'
Due to subsidiaries and affiliates	0	0	'	'
Other liabilities	615,827	584,746	'	'
Total Liabilities	13,918,598	12,647,884	'	'
Shareholdersâ€™ Equity	'	'	'	'
Total Shareholders' Equity	5,647,496	5,168,878	4,592,074	'
Total Liabilities and Shareholders' Equity	19,566,094	17,816,762	'	'
Reportable legal entities \| ACGL (Parent Guarantor)	'	'	'	'
Assets	'	'	'	'
Total investments	2,530	8,328	'	'
Cash	3,223	6,417	4,717	6,781
Investment in subsidiaries	6,046,060	5,560,655	'	'
Due from subsidiaries and affiliates	2,251	254	'	'
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	6,598	6,430	'	'
Total Assets	6,060,662	5,582,084	'	'
Liabilities	'	'	'	'
Reserve for losses and loss adjustment expenses	0	0	'	'
Unearned premiums	0	0	'	'
Reinsurance balances payable	0	0	'	'
Contractholder payables	0	0	'	'
Deposit accounting liabilities	0	0	'	'
Senior notes	300,000	300,000	'	'
Revolving credit agreement borrowings	100,000	100,000	'	'
Due to subsidiaries and affiliates	18	2,397	'	'
Other liabilities	13,148	10,809	'	'
Total Liabilities	413,166	413,206	'	'
Shareholdersâ€™ Equity	'	'	'	'
Total Shareholders' Equity	5,647,496	5,168,878	'	'
Total Liabilities and Shareholders' Equity	6,060,662	5,582,084	'	'
Reportable legal entities \| Arch-U.S. (Subsidiary Issuer)	'	'	'	'
Assets	'	'	'	'
Total investments	408,957	8,798	'	'
Cash	509	612	6,712	619
Investment in subsidiaries	1,258,889	1,155,839	'	'
Due from subsidiaries and affiliates	0	0	'	'
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	60,342	48,571	'	'
Total Assets	1,728,697	1,213,820	'	'
Liabilities	'	'	'	'
Reserve for losses and loss adjustment expenses	0	0	'	'
Unearned premiums	0	0	'	'
Reinsurance balances payable	0	0	'	'
Contractholder payables	0	0	'	'
Deposit accounting liabilities	0	0	'	'
Senior notes	500,000	0	'	'
Revolving credit agreement borrowings	0	0	'	'
Due to subsidiaries and affiliates	10,250	0	'	'
Other liabilities	33,206	31,193	'	'
Total Liabilities	543,456	31,193	'	'
Shareholdersâ€™ Equity	'	'	'	'
Total Shareholders' Equity	1,185,241	1,182,627	'	'
Total Liabilities and Shareholders' Equity	1,728,697	1,213,820	'	'
Reportable legal entities \| Other ACGL Subsidiaries	'	'	'	'
Assets	'	'	'	'
Total investments	13,200,247	12,674,114	'	'
Cash	430,325	364,012	340,270	355,340
Investment in subsidiaries	0	0	'	'
Due from subsidiaries and affiliates	405,110	352,063	'	'
Premiums receivable	1,085,369	877,210	'	'
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	5,645,156	5,849,750	'	'
Contractholder receivables	1,064,246	865,728	'	'
Prepaid reinsurance premiums	1,109,312	914,367	'	'
Deferred acquisition costs, net	342,314	262,822	'	'
Other assets	1,714,651	662,186	'	'
Total Assets	24,996,730	22,822,252	'	'
Liabilities	'	'	'	'
Reserve for losses and loss adjustment expenses	12,625,766	12,857,514	'	'
Unearned premiums	2,677,334	2,263,861	'	'
Reinsurance balances payable	662,394	529,562	'	'
Contractholder payables	1,064,246	865,728	'	'
Deposit accounting liabilities	758,490	27,594	'	'
Senior notes	0	0	'	'
Revolving credit agreement borrowings	0	0	'	'
Due to subsidiaries and affiliates	397,093	349,920	'	'
Other liabilities	691,699	394,206	'	'
Total Liabilities	18,877,022	17,288,385	'	'
Shareholdersâ€™ Equity	'	'	'	'
Total Shareholders' Equity	6,119,708	5,533,867	'	'
Total Liabilities and Shareholders' Equity	24,996,730	22,822,252	'	'
Consolidating adjustments and eliminations	'	'	'	'
Assets	'	'	'	'
Total investments	0	0	'	'
Cash	0	0	0	0
Investment in subsidiaries	-7,304,949	-6,716,494	'	'
Due from subsidiaries and affiliates	-407,361	-352,317	'	'
Premiums receivable	-331,445	-188,337	'	'
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	-3,840,826	-3,979,713	'	'
Contractholder receivables	0	0	'	'
Prepaid reinsurance premiums	-780,969	-615,883	'	'
Deferred acquisition costs, net	0	0	'	'
Other assets	-554,445	51,350	'	'
Total Assets	-13,219,995	-11,801,394	'	'
Liabilities	'	'	'	'
Reserve for losses and loss adjustment expenses	-3,801,070	-3,924,222	'	'
Unearned premiums	-780,969	-615,883	'	'
Reinsurance balances payable	-466,227	-341,016	'	'
Contractholder payables	0	0	'	'
Deposit accounting liabilities	-337,193	0	'	'
Senior notes	0	0	'	'
Revolving credit agreement borrowings	0	0	'	'
Due to subsidiaries and affiliates	-407,361	-352,317	'	'
Other liabilities	-122,226	148,538	'	'
Total Liabilities	-5,915,046	-5,084,900	'	'
Shareholdersâ€™ Equity	'	'	'	'
Total Shareholders' Equity	-7,304,949	-6,716,494	'	'
Total Liabilities and Shareholders' Equity	($13,219,995)	($11,801,394)	'	'

Guarantor_Financial_Informatio3

Guarantor Financial Information - Condensed consolidating statement of income and comprehensive income (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues	'	'	'	'	'	'	'	'	'	'	'
Net premiums earned	$839,366	$795,000	$758,816	$752,770	$779,481	$748,691	$726,656	$680,312	$3,145,952	$2,935,140	$2,631,815
Net investment income	67,095	66,083	68,369	65,672	73,769	73,221	73,608	74,297	267,219	294,895	338,198
Net realized gains	9,048	-6,022	12,652	58,340	54,849	60,391	34,867	44,121	74,018	194,228	110,646
Net impairment losses recognized in earnings	-88	-728	-724	-2,246	-6,035	-2,379	-1,951	-1,023	-3,786	-11,388	-9,062
Other underwriting income	'	'	'	'	'	'	'	'	7,639	8,090	3,429
Equity in net income (loss) of investment funds accounted for using the equity method	'	'	'	'	'	'	'	'	35,701	73,510	-9,605
Other income (loss)	'	'	'	'	'	'	'	'	-586	-12,094	-2,114
Total revenues	'	'	'	'	'	'	'	'	3,526,157	3,482,381	3,063,307
Expenses	'	'	'	'	'	'	'	'	'	'	'
Losses and loss adjustment expenses	'	'	'	'	'	'	'	'	1,679,424	1,861,277	1,727,553
Acquisition expenses	'	'	'	'	'	'	'	'	564,103	508,884	462,937
Other operating expenses	'	'	'	'	'	'	'	'	500,730	465,353	432,122
Interest expense	'	'	'	'	'	'	'	'	27,060	28,525	31,691
Net foreign exchange losses (gains)	'	'	'	'	'	'	'	'	12,335	28,955	-17,366
Total expenses	'	'	'	'	'	'	'	'	2,783,652	2,892,994	2,636,937
Income (loss) before income taxes	'	'	'	'	'	'	'	'	742,505	589,387	426,370
Income tax (expense) benefit	'	'	'	'	'	'	'	'	-32,774	4,010	9,793
Income (loss) before equity in net income of subsidiaries	'	'	'	'	'	'	'	'	709,731	593,397	436,163
Equity in net income (loss) of subsidiaries	'	'	'	'	'	'	'	'	0	0	0
Net income	161,490	114,825	176,940	256,476	19,217	189,656	220,268	164,256	709,731	593,397	436,163
Preferred dividends	-5,485	-5,484	-5,485	-5,484	-5,485	-5,484	-7,649	-6,461	-21,938	-25,079	-25,844
Loss on repurchase of preferred shares	'	'	'	'	0	0	-10,612	0	0	-10,612	0
Net income available to common shareholders	156,005	109,341	171,455	250,992	13,732	184,172	202,007	157,795	687,793	557,706	410,319
Comprehensive Income	'	'	'	'	'	'	'	'	497,678	726,491	385,583
Reportable legal entities \| ACGL (Parent Guarantor)	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	'	'	'
Net premiums earned	'	'	'	'	'	'	'	'	0	0	0
Net investment income	'	'	'	'	'	'	'	'	-5	4	0
Net realized gains	'	'	'	'	'	'	'	'	0	0	63
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	0	0	0
Other underwriting income	'	'	'	'	'	'	'	'	0	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	'	'	'	'	'	'	'	'	0	0	0
Other income (loss)	'	'	'	'	'	'	'	'	0	0	0
Total revenues	'	'	'	'	'	'	'	'	-5	4	63
Expenses	'	'	'	'	'	'	'	'	'	'	'
Losses and loss adjustment expenses	'	'	'	'	'	'	'	'	0	0	0
Acquisition expenses	'	'	'	'	'	'	'	'	0	0	0
Other operating expenses	'	'	'	'	'	'	'	'	38,702	35,570	31,509
Interest expense	'	'	'	'	'	'	'	'	23,267	23,496	23,151
Net foreign exchange losses (gains)	'	'	'	'	'	'	'	'	0	0	0
Total expenses	'	'	'	'	'	'	'	'	61,969	59,066	54,660
Income (loss) before income taxes	'	'	'	'	'	'	'	'	-61,974	-59,062	-54,597
Income tax (expense) benefit	'	'	'	'	'	'	'	'	0	0	0
Income (loss) before equity in net income of subsidiaries	'	'	'	'	'	'	'	'	-61,974	-59,062	-54,597
Equity in net income (loss) of subsidiaries	'	'	'	'	'	'	'	'	771,705	652,459	490,760
Net income	'	'	'	'	'	'	'	'	709,731	593,397	436,163
Preferred dividends	'	'	'	'	'	'	'	'	-21,938	-25,079	-25,844
Loss on repurchase of preferred shares	'	'	'	'	'	'	'	'	'	-10,612	'
Net income available to common shareholders	'	'	'	'	'	'	'	'	687,793	557,706	410,319
Comprehensive Income	'	'	'	'	'	'	'	'	497,678	726,491	385,583
Reportable legal entities \| Arch-U.S. (Subsidiary Issuer)	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	'	'	'
Net premiums earned	'	'	'	'	'	'	'	'	0	0	0
Net investment income	'	'	'	'	'	'	'	'	31	8	3
Net realized gains	'	'	'	'	'	'	'	'	0	0	0
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	0	0	0
Other underwriting income	'	'	'	'	'	'	'	'	0	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	'	'	'	'	'	'	'	'	0	0	0
Other income (loss)	'	'	'	'	'	'	'	'	0	0	0
Total revenues	'	'	'	'	'	'	'	'	31	8	3
Expenses	'	'	'	'	'	'	'	'	'	'	'
Losses and loss adjustment expenses	'	'	'	'	'	'	'	'	0	0	0
Acquisition expenses	'	'	'	'	'	'	'	'	0	0	0
Other operating expenses	'	'	'	'	'	'	'	'	2,691	1,218	887
Interest expense	'	'	'	'	'	'	'	'	1,316	0	0
Net foreign exchange losses (gains)	'	'	'	'	'	'	'	'	0	0	0
Total expenses	'	'	'	'	'	'	'	'	4,007	1,218	887
Income (loss) before income taxes	'	'	'	'	'	'	'	'	-3,976	-1,210	-884
Income tax (expense) benefit	'	'	'	'	'	'	'	'	1,383	424	321
Income (loss) before equity in net income of subsidiaries	'	'	'	'	'	'	'	'	-2,593	-786	-563
Equity in net income (loss) of subsidiaries	'	'	'	'	'	'	'	'	25,644	9,738	-134
Net income	'	'	'	'	'	'	'	'	23,051	8,952	-697
Preferred dividends	'	'	'	'	'	'	'	'	0	0	0
Loss on repurchase of preferred shares	'	'	'	'	'	'	'	'	'	0	'
Net income available to common shareholders	'	'	'	'	'	'	'	'	23,051	8,952	-697
Comprehensive Income	'	'	'	'	'	'	'	'	-28,330	2,796	23,155
Reportable legal entities \| Other ACGL Subsidiaries	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	'	'	'
Net premiums earned	'	'	'	'	'	'	'	'	3,145,952	2,935,140	2,631,815
Net investment income	'	'	'	'	'	'	'	'	307,449	321,805	350,412
Net realized gains	'	'	'	'	'	'	'	'	74,018	194,228	107,021
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	-3,786	-11,388	-9,062
Other underwriting income	'	'	'	'	'	'	'	'	7,639	8,090	3,429
Equity in net income (loss) of investment funds accounted for using the equity method	'	'	'	'	'	'	'	'	35,701	73,510	-9,605
Other income (loss)	'	'	'	'	'	'	'	'	-586	-12,094	-2,114
Total revenues	'	'	'	'	'	'	'	'	3,566,387	3,509,291	3,071,896
Expenses	'	'	'	'	'	'	'	'	'	'	'
Losses and loss adjustment expenses	'	'	'	'	'	'	'	'	1,679,424	1,861,277	1,727,553
Acquisition expenses	'	'	'	'	'	'	'	'	564,103	508,884	462,937
Other operating expenses	'	'	'	'	'	'	'	'	459,337	428,565	399,726
Interest expense	'	'	'	'	'	'	'	'	42,733	31,951	20,757
Net foreign exchange losses (gains)	'	'	'	'	'	'	'	'	2,145	21,787	-9,024
Total expenses	'	'	'	'	'	'	'	'	2,747,742	2,852,464	2,601,949
Income (loss) before income taxes	'	'	'	'	'	'	'	'	818,645	656,827	469,947
Income tax (expense) benefit	'	'	'	'	'	'	'	'	-34,157	3,586	9,472
Income (loss) before equity in net income of subsidiaries	'	'	'	'	'	'	'	'	784,488	660,413	479,419
Equity in net income (loss) of subsidiaries	'	'	'	'	'	'	'	'	0	0	0
Net income	'	'	'	'	'	'	'	'	784,488	660,413	479,419
Preferred dividends	'	'	'	'	'	'	'	'	0	0	0
Loss on repurchase of preferred shares	'	'	'	'	'	'	'	'	'	0	'
Net income available to common shareholders	'	'	'	'	'	'	'	'	784,488	660,413	479,419
Comprehensive Income	'	'	'	'	'	'	'	'	562,245	786,338	440,745
Consolidating adjustments and eliminations	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	'	'	'
Net premiums earned	'	'	'	'	'	'	'	'	0	0	0
Net investment income	'	'	'	'	'	'	'	'	-40,256	-26,922	-12,217
Net realized gains	'	'	'	'	'	'	'	'	0	0	3,562
Net impairment losses recognized in earnings	'	'	'	'	'	'	'	'	0	0	0
Other underwriting income	'	'	'	'	'	'	'	'	0	0	0
Equity in net income (loss) of investment funds accounted for using the equity method	'	'	'	'	'	'	'	'	0	0	0
Other income (loss)	'	'	'	'	'	'	'	'	0	0	0
Total revenues	'	'	'	'	'	'	'	'	-40,256	-26,922	-8,655
Expenses	'	'	'	'	'	'	'	'	'	'	'
Losses and loss adjustment expenses	'	'	'	'	'	'	'	'	0	0	0
Acquisition expenses	'	'	'	'	'	'	'	'	0	0	0
Other operating expenses	'	'	'	'	'	'	'	'	0	0	0
Interest expense	'	'	'	'	'	'	'	'	-40,256	-26,922	-12,217
Net foreign exchange losses (gains)	'	'	'	'	'	'	'	'	10,190	7,168	-8,342
Total expenses	'	'	'	'	'	'	'	'	-30,066	-19,754	-20,559
Income (loss) before income taxes	'	'	'	'	'	'	'	'	-10,190	-7,168	11,904
Income tax (expense) benefit	'	'	'	'	'	'	'	'	0	0	0
Income (loss) before equity in net income of subsidiaries	'	'	'	'	'	'	'	'	-10,190	-7,168	11,904
Equity in net income (loss) of subsidiaries	'	'	'	'	'	'	'	'	-797,349	-662,197	-490,626
Net income	'	'	'	'	'	'	'	'	-807,539	-669,365	-478,722
Preferred dividends	'	'	'	'	'	'	'	'	0	0	0
Loss on repurchase of preferred shares	'	'	'	'	'	'	'	'	'	0	'
Net income available to common shareholders	'	'	'	'	'	'	'	'	-807,539	-669,365	-478,722
Comprehensive Income	'	'	'	'	'	'	'	'	($533,915)	($789,134)	($463,900)

Guarantor_Financial_Informatio4

Guarantor Financial Information - Condensed consolidating statement of cash flows (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Operating Activities	'		'		'
Net Cash Provided by (Used in) Operating Activities	$850,868		$921,603		$866,112
Investing Activities	'		'		'
Purchases of fixed maturity investments	-18,174,988		-17,568,592		-13,875,635
Purchases of equity securities	-535,857		-268,999		-413,024
Purchases of other investments	-1,326,729		-1,000,049		-593,862
Proceeds from the sale of fixed maturity investments	17,196,614		16,366,306		12,398,253
Proceeds from the sale of equity securities	462,787		313,617		369,503
Proceeds from the sale of other investments	1,162,707		443,630		543,757
Proceeds from redemptions and maturities of fixed maturity investments	731,708		1,115,594		1,034,489
Net (purchases) sales of short-term investments	-750,613		185,919		-2,389
Change in investment of securities lending collateral	-55,643		6,190		19,475
Contributions to subsidiaries	0		0		0
Intercompany loans issued	0		'		0
Purchase of business, net of cash acquired	0		28,948		0
Purchases of furniture, equipment and other assets	-17,499		-18,532		-18,987
Net Cash Used For Investing Activities	-1,307,513		-395,968		-538,420
Financing Activities	'		'		'
Proceeds from issuance of Series C preferred shares, net	0		315,763		0
Repurchase of Series A and B preferred shares	0		-325,000		0
Purchases of common shares under share repurchase program	-57,796		-172,056		-287,561
Proceeds from common shares issued, net	3,051		7,033		6,332
Proceeds from intercompany borrowings	0		'		0
Proceeds from borrowings	494,228		0		0
Repayments of intercompany borrowings	0		'		'
Repayments of borrowings	0		-310,868		-15,352
Change in securities lending collateral	55,643		-6,190		-19,475
Dividends paid to parent	0	[1]	0	[1]	0	[1]
Other	50,830		6,664		4,765
Preferred dividends paid	-21,938		-28,381		-25,844
Net Cash Used For Financing Activities	524,018		-513,035		-337,135
Effects of exchange rate changes on foreign currency cash	-4,357		6,742		-1,598
Increase (decrease) in cash	63,016		19,342		-11,041
Cash beginning of year	371,041		351,699		362,740
Cash end of period	434,057		371,041		351,699
Reportable legal entities \| ACGL (Parent Guarantor)	'		'		'
Operating Activities	'		'		'
Net Cash Provided by (Used in) Operating Activities	68,562		209,500		300,764
Investing Activities	'		'		'
Purchases of fixed maturity investments	0		0		0
Purchases of equity securities	0		0		0
Purchases of other investments	0		0		0
Proceeds from the sale of fixed maturity investments	0		0		0
Proceeds from the sale of equity securities	0		0		0
Proceeds from the sale of other investments	0		0		0
Proceeds from redemptions and maturities of fixed maturity investments	0		0		0
Net (purchases) sales of short-term investments	5,799		-5,094		4,441
Change in investment of securities lending collateral	0		0		0
Contributions to subsidiaries	-160		0		0
Intercompany loans issued	0		'		0
Purchase of business, net of cash acquired	0		0		'
Purchases of furniture, equipment and other assets	-712		-65		-196
Net Cash Used For Investing Activities	4,927		-5,159		4,245
Financing Activities	'		'		'
Proceeds from issuance of Series C preferred shares, net	'		315,763		'
Repurchase of Series A and B preferred shares	'		-325,000		'
Purchases of common shares under share repurchase program	-57,796		-172,056		-287,561
Proceeds from common shares issued, net	3,051		7,033		6,332
Proceeds from intercompany borrowings	0		'		0
Proceeds from borrowings	0		'		'
Repayments of intercompany borrowings	0		'		'
Repayments of borrowings	0		0		0
Change in securities lending collateral	0		0		0
Dividends paid to parent	0	[1]	0	[1]	0	[1]
Other	0		0		0
Preferred dividends paid	-21,938		-28,381		-25,844
Net Cash Used For Financing Activities	-76,683		-202,641		-307,073
Effects of exchange rate changes on foreign currency cash	0		0		0
Increase (decrease) in cash	-3,194		1,700		-2,064
Cash beginning of year	6,417		4,717		6,781
Cash end of period	3,223		6,417		4,717
Reportable legal entities \| Arch-U.S. (Subsidiary Issuer)	'		'		'
Operating Activities	'		'		'
Net Cash Provided by (Used in) Operating Activities	-6,569		-8,086		5,606
Investing Activities	'		'		'
Purchases of fixed maturity investments	0		0		0
Purchases of equity securities	0		0		0
Purchases of other investments	0		0		0
Proceeds from the sale of fixed maturity investments	0		0		0
Proceeds from the sale of equity securities	0		0		0
Proceeds from the sale of other investments	0		0		0
Proceeds from redemptions and maturities of fixed maturity investments	0		0		0
Net (purchases) sales of short-term investments	-400,162		1,986		487
Change in investment of securities lending collateral	0		0		0
Contributions to subsidiaries	-97,850		0		0
Intercompany loans issued	0		'		0
Purchase of business, net of cash acquired	0		0		'
Purchases of furniture, equipment and other assets	0		0		0
Net Cash Used For Investing Activities	-498,012		1,986		487
Financing Activities	'		'		'
Proceeds from issuance of Series C preferred shares, net	'		0		'
Repurchase of Series A and B preferred shares	'		0		'
Purchases of common shares under share repurchase program	0		0		0
Proceeds from common shares issued, net	0		0		0
Proceeds from intercompany borrowings	10,250		'		0
Proceeds from borrowings	494,228		'		'
Repayments of intercompany borrowings	0		'		'
Repayments of borrowings	0		0		0
Change in securities lending collateral	0		0		0
Dividends paid to parent	0	[1]	0	[1]	0	[1]
Other	0		0		0
Preferred dividends paid	0		0		0
Net Cash Used For Financing Activities	504,478		0		0
Effects of exchange rate changes on foreign currency cash	0		0		0
Increase (decrease) in cash	-103		-6,100		6,093
Cash beginning of year	612		6,712		619
Cash end of period	509		612		6,712
Reportable legal entities \| Other ACGL Subsidiaries	'		'		'
Operating Activities	'		'		'
Net Cash Provided by (Used in) Operating Activities	908,375		978,679		901,252
Investing Activities	'		'		'
Purchases of fixed maturity investments	-18,174,988		-17,568,592		-13,875,635
Purchases of equity securities	-535,857		-268,999		-413,024
Purchases of other investments	-1,326,729		-1,000,049		-593,862
Proceeds from the sale of fixed maturity investments	17,196,614		16,366,306		12,398,253
Proceeds from the sale of equity securities	462,787		313,617		369,503
Proceeds from the sale of other investments	1,162,707		443,630		543,757
Proceeds from redemptions and maturities of fixed maturity investments	731,708		1,115,594		1,034,489
Net (purchases) sales of short-term investments	-356,250		189,027		-7,317
Change in investment of securities lending collateral	-55,643		6,190		19,475
Contributions to subsidiaries	-20,250		-38,576		-59,844
Intercompany loans issued	-10,250		'		-185,289
Purchase of business, net of cash acquired	0		28,948		'
Purchases of furniture, equipment and other assets	-16,787		-18,467		-18,791
Net Cash Used For Investing Activities	-942,938		-431,371		-788,285
Financing Activities	'		'		'
Proceeds from issuance of Series C preferred shares, net	'		0		'
Repurchase of Series A and B preferred shares	'		0		'
Purchases of common shares under share repurchase program	0		0		0
Proceeds from common shares issued, net	118,260		38,576		59,844
Proceeds from intercompany borrowings	0		'		185,289
Proceeds from borrowings	0		'		'
Repayments of intercompany borrowings	0		'		'
Repayments of borrowings	0		-310,868		-15,352
Change in securities lending collateral	55,643		-6,190		-19,475
Dividends paid to parent	-119,500	[1]	-258,490	[1]	-341,510	[1]
Other	50,830		6,664		4,765
Preferred dividends paid	0		0		0
Net Cash Used For Financing Activities	105,233		-530,308		-126,439
Effects of exchange rate changes on foreign currency cash	-4,357		6,742		-1,598
Increase (decrease) in cash	66,313		23,742		-15,070
Cash beginning of year	364,012		340,270		355,340
Cash end of period	430,325		364,012		340,270
Consolidating adjustments and eliminations	'		'		'
Operating Activities	'		'		'
Net Cash Provided by (Used in) Operating Activities	-119,500		-258,490		-341,510
Investing Activities	'		'		'
Purchases of fixed maturity investments	0		0		0
Purchases of equity securities	0		0		0
Purchases of other investments	0		0		0
Proceeds from the sale of fixed maturity investments	0		0		0
Proceeds from the sale of equity securities	0		0		0
Proceeds from the sale of other investments	0		0		0
Proceeds from redemptions and maturities of fixed maturity investments	0		0		0
Net (purchases) sales of short-term investments	0		0		0
Change in investment of securities lending collateral	0		0		0
Contributions to subsidiaries	118,260		38,576		59,844
Intercompany loans issued	10,250		'		185,289
Purchase of business, net of cash acquired	0		0		'
Purchases of furniture, equipment and other assets	0		0		0
Net Cash Used For Investing Activities	128,510		38,576		245,133
Financing Activities	'		'		'
Proceeds from issuance of Series C preferred shares, net	'		0		'
Repurchase of Series A and B preferred shares	'		0		'
Purchases of common shares under share repurchase program	0		0		0
Proceeds from common shares issued, net	-118,260		-38,576		-59,844
Proceeds from intercompany borrowings	-10,250		'		-185,289
Proceeds from borrowings	0		'		'
Repayments of intercompany borrowings	0		'		'
Repayments of borrowings	0		0		0
Change in securities lending collateral	0		0		0
Dividends paid to parent	119,500	[1]	258,490	[1]	341,510	[1]
Other	0		0		0
Preferred dividends paid	0		0		0
Net Cash Used For Financing Activities	-9,010		219,914		96,377
Effects of exchange rate changes on foreign currency cash	0		0		0
Increase (decrease) in cash	0		0		0
Cash beginning of year	0		0		0
Cash end of period	$0		$0		$0

[1]	Included in net cash provided by (used for) operating activities in the ACGL (Parent Guarantor) column.

Subsequent_Events_Details

Subsequent Events (Details) (Subsequent Event [Member], CMG Mortgage Insurance Company [Member], USD $)	0 Months Ended
In Millions, unless otherwise specified	Jan. 30, 2014
Subsequent Event [Member] \| CMG Mortgage Insurance Company [Member]	'
Subsequent Event [Line Items]	'
Aggregate consideration on property acquisition	$253

Schedule_III_Supplementary_Ins1

Schedule III - Supplementary Insurance Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Supplementary Insurance Information, by Segment [Line Items]	'		'		'
Deferred Acquisition Costs, Net	$342,314		$262,822		$227,884
Reserves for Losses and Loss Adjustment Expenses	8,824,696		8,933,292		8,456,210
Unearned Premiums	1,896,365		1,647,978		1,411,872
Net Premiums Earned	3,145,952		2,935,140		2,631,815
Net Losses and Loss Adjustment Expenses Incurred	1,679,424		1,861,277		1,727,553
Amortization of Deferred Acquisition Costs	564,103		508,884		462,937
Other Operating Expenses	458,327	[1]	430,035	[1]	400,742	[1]
Net Premiums Written	3,351,367		3,052,235		2,673,326
Insurance	'		'		'
Supplementary Insurance Information, by Segment [Line Items]	'		'		'
Deferred Acquisition Costs, Net	158,121		141,962		161,907
Reserves for Losses and Loss Adjustment Expenses	6,137,121		6,149,247		5,762,533
Unearned Premiums	1,192,188		1,077,211		1,039,081
Net Premiums Earned	1,876,014		1,800,343		1,679,047
Net Losses and Loss Adjustment Expenses Incurred	1,188,445		1,283,841		1,172,742
Amortization of Deferred Acquisition Costs	311,904		298,983		278,696
Other Operating Expenses	315,387	[1]	307,489	[1]	307,797	[1]
Net Premiums Written	1,948,796		1,825,334		1,721,279
Reinsurance	'		'		'
Supplementary Insurance Information, by Segment [Line Items]	'		'		'
Deferred Acquisition Costs, Net	184,193		120,860		65,977
Reserves for Losses and Loss Adjustment Expenses	2,687,575		2,784,045		2,693,677
Unearned Premiums	704,177		570,767		372,791
Net Premiums Earned	1,269,938		1,134,797		952,768
Net Losses and Loss Adjustment Expenses Incurred	490,979		577,436		554,811
Amortization of Deferred Acquisition Costs	252,199		209,901		184,241
Other Operating Expenses	142,940	[1]	122,546	[1]	92,945	[1]
Net Premiums Written	$1,402,571		$1,226,901		$952,047

[1]	Certain other operating expenses relate to the Companyâ€™s corporate and other segment (non-underwriting). Such amounts are not reflected in the table above. See Note 3.

Schedule_IV_Reinsurance_Detail

Schedule IV - Reinsurance (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross Amount	'	'	'	'	'	'	'	'	$2,754,582	$2,673,864	$2,402,153
Ceded to other Companies	'	'	'	'	'	'	'	'	-845,256	-816,926	-763,130
Assumed From Other Companies	'	'	'	'	'	'	'	'	1,442,041	1,195,297	1,034,303
Net Amount	748,921	839,135	810,535	952,776	613,142	755,249	820,233	863,611	3,351,367	3,052,235	2,673,326
Percentage of Amount Assumed to Net	'	'	'	'	'	'	'	'	43.00%	39.20%	38.70%
Insurance	'	'	'	'	'	'	'	'	'	'	'
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross Amount	'	'	'	'	'	'	'	'	2,682,446	2,562,788	2,402,153
Ceded to other Companies	'	'	'	'	'	'	'	'	-763,713	-768,625	-723,206
Assumed From Other Companies	'	'	'	'	'	'	'	'	30,063	31,171	42,332
Net Amount	'	'	'	'	'	'	'	'	1,948,796	1,825,334	1,721,279
Percentage of Amount Assumed to Net	'	'	'	'	'	'	'	'	1.50%	1.70%	2.50%
Reinsurance	'	'	'	'	'	'	'	'	'	'	'
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross Amount	'	'	'	'	'	'	'	'	72,136	111,076	0
Ceded to other Companies	'	'	'	'	'	'	'	'	-86,620	-55,099	-46,473
Assumed From Other Companies	'	'	'	'	'	'	'	'	1,417,055	1,170,924	998,520
Net Amount	'	'	'	'	'	'	'	'	$1,402,571	$1,226,901	$952,047
Percentage of Amount Assumed to Net	'	'	'	'	'	'	'	'	101.00%	95.40%	104.90%

Schedule_VI_Supplementary_Info1

Schedule VI - Supplementary Information For Property and Casualty Insurance Underwriters (Details) (Operating Segments, USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Insurance	'	'	'
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]	'	'	'
Deferred Acquisition Costs, Net	$158,121	$141,962	$161,907
Reserves for Losses and Loss Adjustment Expenses	6,137,121	6,191,705	5,762,533
Discount, if any, deducted in Column C	12,539	10,485	9,834
Unearned Premiums	1,192,188	1,077,211	1,039,081
Net Premiums Earned	1,876,014	1,800,343	1,679,047
Net Losses And Loss Adjustment Expenses Incurred Related to Current Years	1,233,593	1,315,088	1,224,861
Net Losses And Loss Adjustment Expenses Incurred Related to Prior Years	-45,148	-31,247	-52,119
Amortization of Deferred Acquisition Costs	311,904	298,983	278,696
Net Paid Losses and Loss Adjustment Expenses	1,068,699	981,790	900,398
Net Premiums Written	1,948,796	1,825,334	1,721,279
Reinsurance	'	'	'
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]	'	'	'
Deferred Acquisition Costs, Net	184,193	120,860	65,977
Reserves for Losses and Loss Adjustment Expenses	2,687,575	2,741,587	2,693,677
Discount, if any, deducted in Column C	0	0	0
Unearned Premiums	704,177	570,767	372,791
Net Premiums Earned	1,269,938	1,134,797	952,768
Net Losses And Loss Adjustment Expenses Incurred Related to Current Years	709,873	767,717	787,707
Net Losses And Loss Adjustment Expenses Incurred Related to Prior Years	-218,894	-190,281	-232,896
Amortization of Deferred Acquisition Costs	252,199	209,901	184,241
Net Paid Losses and Loss Adjustment Expenses	640,118	483,589	552,225
Net Premiums Written	$1,402,571	$1,226,901	$952,047