Arch Capital (ACGL) 10-Q12 May 142014 Q1 Quarterly reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information Document and Entity Information	3 Months Ended
	Mar. 31, 2014	1-May-14
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	'Accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	134,099,536

Unaudited_Consolidated_Balance

Unaudited Consolidated Balance Sheets (USD $)	Mar. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Investments:	'		'		'
Fixed maturities available for sale, at fair value (amortized cost: $9,722,364 and $9,564,634)	$9,775,730		$9,571,776		'
Short-term investments available for sale, at fair value (amortized cost: $1,485,378 and $1,477,584)	1,484,280		1,478,367		'
Investment of funds received under securities lending, at fair value (amortized cost: $93,274 and $97,943)	96,264		100,584		'
Equity securities available for sale, at fair value (cost: $475,868 and $433,275)	548,168		496,824		'
Other investments available for sale, at fair value (cost: $417,762 and $488,687)	426,917		498,310		'
Investments accounted for using the fair value option	1,256,650		1,221,534		'
Investments accounted for using the equity method	255,488		244,339		'
Total investments	13,843,497		13,611,734		'
Cash	1,569,605		434,057		371,041
Accrued investment income	59,701		66,848		'
Investment in joint venture (cost: $100,000)	102,803		104,856		'
Fixed maturities and short-term investments pledged under securities lending, at fair value	100,590		105,081		'
Premiums receivable	1,008,375		753,924		'
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	1,790,025		1,804,330		'
Contractholder receivables	1,118,991		1,064,246		'
Prepaid reinsurance premiums	349,077		328,343		'
Deferred acquisition costs, net	384,294		342,314		'
Receivable for securities sold	426,431		50,555		'
Goodwill and intangible assets	120,875		27,319		'
Other assets	926,094		872,487		'
Total assets	21,800,358		19,566,094		'
Liabilities	'		'		'
Reserve for losses and loss adjustment expenses	8,938,958		8,824,696		'
Unearned premiums	2,148,475		1,896,365		'
Reinsurance balances payable	201,794		196,167		'
Contractholder payables	1,118,991		1,064,246		'
Deposit accounting liabilities	409,080		421,297		'
Senior notes	800,000		800,000		'
Revolving credit agreement borrowings	100,000		100,000		'
Securities lending payable	103,330		107,999		'
Payable for securities purchased	499,473		51,318		'
Other liabilities	575,394		456,510		'
Total liabilities	14,895,495		13,918,598		'
Commitments and Contingencies	'		'		'
Redeemable noncontrolling interests	219,234	[1]	0	[1]	'
Shareholdersâ€™ Equity	'		'		'
Non-cumulative preferred shares	325,000		325,000		'
Common shares ($0.0033 par, shares issued: 170,006,958 and 169,560,591)	567		565		'
Additional paid-in capital	320,503		299,517		'
Retained earnings	6,219,170		6,042,154		'
Accumulated other comprehensive income, net of deferred income tax	123,719		74,964		'
Common shares held in treasury, at cost (shares: 35,922,820 and 35,885,707)	-1,096,826		-1,094,704		'
Total shareholders' equity available to Arch	5,892,133		5,647,496		'
Non-redeemable noncontrolling interests	793,496	[1]	0	[1]	'
Total shareholders' equity	6,685,629		5,647,496		'
Total liabilities, noncontrolling interests and shareholders' equity	$21,800,358		$19,566,094		'

[1]	See Note 4.

Unaudited_Consolidated_Balance1

Unaudited Consolidated Balance Sheets (Parentheticals) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fixed maturities available for sale, at amortized cost	$9,722,364	$9,564,634
Short-term investments available for sale, at amortized cost	1,485,378	1,477,584
Investment of funds received under securities lending agreements, at cost	93,274	97,943
Equity securities, at cost	475,868	433,275
Other investments, at cost	417,762	488,687
Investment in joint venture, at cost	$100,000	$100,000
Common shares, par value per share	$0.00	$0.00
Common shares issued (shares)	170,006,958	169,560,591
Common shares held in treasury (shares)	35,922,820	35,885,707

Unaudited_Consolidated_Stateme

Unaudited Consolidated Statements of Income (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Revenues	'		'
Net premiums written	$1,064,990		$952,776
Change in unearned premiums	-205,210		-200,006
Net premiums earned	859,780		752,770
Net investment income	66,994		65,672
Net realized gains	19,697		58,340
Other-than-temporary impairment losses	-2,971		-2,248
Less investment impairments recognized in other comprehensive income, before taxes	0		2
Net impairment losses recognized in earnings	-2,971		-2,246
Other underwriting income	1,582		538
Equity in net income of investment funds accounted for using the equity method	3,253		13,823
Other income (loss)	-2,104		1,244
Total revenues	946,231		890,141
Expenses	'		'
Losses and loss adjustment expenses	436,240		399,403
Acquisition expenses	160,342		127,592
Other operating expenses	145,799		120,183
Interest expense	14,404		5,898
Net foreign exchange losses (gains)	6,563		-24,264
Total expenses	763,348		628,812
Income before income taxes	182,883		261,329
Income tax expense	3,738		4,853
Net income	179,145		256,476
Net (income) loss attributable to noncontrolling interests	3,355	[1]	0	[1]
Net income available to Arch	182,500		256,476
Preferred dividends	5,484		5,484
Net income available to common shareholders	$177,016		$250,992
Net income per common share	'		'
Basic (per share)	$1.34		$1.92
Diluted (per share)	$1.30		$1.85
Weighted average common shares and common share equivalents outstanding	'		'
Basic (shares)	131,857,910		130,907,902
Diluted (shares)	136,562,717		135,409,288

[1]	See Note 4.

Unaudited_Consolidated_Stateme1

Unaudited Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Comprehensive Income	'		'
Net income	$179,145		$256,476
Unrealized appreciation in value of available-for-sale investments:	'		'
Unrealized holding gains arising during period	71,353		9,471
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0		-2
Reclassification of net realized gains, net of income taxes, included in net income	-21,249		-38,701
Foreign currency translation adjustments	-1,349		-28,222
Comprehensive income	227,900		199,022
Net (income) loss attributable to noncontrolling interests	3,355	[1]	0	[1]
Other comprehensive (income) loss attributable to noncontrolling interests	0		0
Comprehensive (income) loss attributable to noncontrolling interests	3,355		0
Comprehensive income available to Arch	$231,255		$199,022

[1]	See Note 4.

Unaudited_Consolidated_Stateme2

Unaudited 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	Unrealized gains on available-for-sale securities	Foreign currency translation adjustments	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	Unrealized gains on available-for-sale securities	Foreign currency translation adjustments	Common Shares Held in Treasury, at Cost
Balance at beginning of year at Dec. 31, 2012		'	$325,000	$561	$227,778	$5,354,361	$287,017	$289,956	($2,939)	($1,025,839)
Common shares issued, net		'	'	0	'	'	'	'	'	'
Exercise of stock options		'	'	'	3,093	'	'	'	'	'
Amortization of share-based compensation		'	'	'	11,543	'	'	'	'	'
Other		'	'	'	78	'	'	'	'	'
Net income		256,476	'	'	'	256,476	'	'	'	'
Net (income) loss attributable to noncontrolling interests	[1]	0	'	'	'	0	'	'	'	'
Preferred share dividends		-5,484	'	'	'	-5,484	'	'	'	'
Unrealized holding gains (losses) arising during period, net of reclassification adjustment		'	'	'	'	'	'	-29,230	'	'
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax		-2	'	'	'	'	'	-2	'	'
Foreign currency translation adjustments		-28,222	'	'	'	'	'	'	-28,222	'
Shares repurchased for treasury		'	'	'	'	'	'	'	'	-41,600
Noncontrolling interest	[1]	0	'	'	'	'	'	'	'	'
Total shareholders' equity at Mar. 31, 2013		5,335,530	'	'	'	'	'	'	'	'
Balance at end of period at Mar. 31, 2013		5,335,530	325,000	561	242,492	5,605,353	229,563	260,724	-31,161	-1,067,439
Balance at beginning of year at Dec. 31, 2013		5,647,496	325,000	565	299,517	6,042,154	74,964	80,692	-5,728	-1,094,704
Common shares issued, net		'	'	2	'	'	'	'	'	'
Exercise of stock options		'	'	'	8,054	'	'	'	'	'
Amortization of share-based compensation		'	'	'	14,175	'	'	'	'	'
Other		'	'	'	-1,243	'	'	'	'	'
Net income		179,145	'	'	'	179,145	'	'	'	'
Net (income) loss attributable to noncontrolling interests	[1]	3,355	'	'	'	3,355	'	'	'	'
Preferred share dividends		-5,484	'	'	'	-5,484	'	'	'	'
Unrealized holding gains (losses) arising during period, net of reclassification adjustment		'	'	'	'	'	'	50,104	'	'
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax		0	'	'	'	'	'	0	'	'
Foreign currency translation adjustments		-1,349	'	'	'	'	'	'	-1,349	'
Shares repurchased for treasury		'	'	'	'	'	'	'	'	-2,122
Noncontrolling interest	[1]	793,496	'	'	'	'	'	'	'	'
Total shareholders' equity at Mar. 31, 2014		6,685,629	'	'	'	'	'	'	'	'
Balance at end of period at Mar. 31, 2014		$5,892,133	$325,000	$567	$320,503	$6,219,170	$123,719	$130,796	($7,077)	($1,096,826)

[1]	See Note 4.

Unaudited_Consolidated_Stateme3

Unaudited Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Operating Activities	'		'
Net income	$179,145		$256,476
Adjustments to reconcile net income to net cash provided by operating activities:	'		'
Net realized gains	-22,367		-59,504
Net impairment losses recognized in earnings	2,971		2,246
Equity in net income or loss of investment funds accounted for using the equity method and other income or loss	9,559		23,052
Share-based compensation	14,175		11,543
Changes in:	'		'
Reserve for losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable	10,326		-22,182
Unearned premiums, net of prepaid reinsurance premiums	205,210		200,006
Premiums receivable	-242,616		-198,814
Deferred acquisition costs, net	-41,988		-45,159
Reinsurance balances payable	5,428		17,365
Other liabilities	59,285		23,811
Other items	19,041		-3,181
Net Cash Provided By Operating Activities	198,169		205,659
Investing Activities	'		'
Purchases of fixed maturity investments	-7,131,071		-3,970,320
Purchases of equity securities	-89,227		-63,353
Purchases of other investments	-304,454		-250,442
Proceeds from the sale of fixed maturity investments	7,014,281		3,796,638
Proceeds from the sale of equity securities	49,614		81,513
Proceeds from the sale of other investments	331,176		280,010
Proceeds from redemptions and maturities of fixed maturity investments	168,484		181,727
Net (purchases) sales of short-term investments	156,262		-221,444
Change in investment of securities lending collateral	4,669		-41,019
Purchase of business, net of cash acquired	-235,578	[1]	0	[1]
Purchases of furniture, equipment and other assets	-5,382		-3,742
Net Cash Used For Investing Activities	-41,226		-210,432
Financing Activities	'		'
Purchases of common shares under share repurchase program	0		-40,964
Proceeds from common shares issued, net	3,021		1,280
Change in securities lending collateral	-4,669		41,019
Third party investment in non-redeemable noncontrolling interests	796,903	[2]	0	[2]
Third party investment in redeemable noncontrolling interests	186,893	[2]	0	[2]
Other	1,700		1,084
Preferred dividends paid	-5,484		-5,484
Net Cash Provided By (Used For) Financing Activities	978,364		-3,065
Effects of exchange rate changes on foreign currency cash	241		-6,436
Increase (decrease) in cash	1,135,548		-14,274
Cash beginning of year	434,057		371,041
Cash end of period	$1,569,605		$356,767

[1]	See Note 2.
[2]	See Note 4.

General

General	3 Months Ended
General	Mar. 31, 2014
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 subsidiaries (together with ACGL, the “Company”).

	On January 30, 2014, the Company acquired CMG Mortgage Insurance Company and its affiliated mortgage insurance companies (together, “CMG Entities”) and the mortgage insurance platform and related assets from PMI Mortgage Insurance Co. (“PMI”) (see Note 2).

	On March 20, 2014, the Company acquired approximately 11% of Watford Holdings Ltd.’s common equity and a warrant to purchase additional common equity for $100 million. Watford Holdings Ltd. is the parent of Watford Re Ltd., a newly-formed multi-line Bermuda reinsurance company (together with Watford Holdings Ltd., “Watford”). Watford is considered a variable interest entity (“VIE”) and the Company concluded that it is the primary beneficiary of Watford. As such, the results of Watford are included in the Company’s consolidated financial statements (see Note 4).

	The interim 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 the Company and Watford. All significant intercompany transactions and balances have been eliminated in consolidation. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates and assumptions. In the opinion of management, the accompanying unaudited interim consolidated financial statements reflect all adjustments (consisting of normally recurring accruals) necessary for a fair statement of results on an interim basis. The results of any interim period are not necessarily indicative of the results for a full year or any future periods.

	Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted; however, management believes that the disclosures are adequate to make the information presented not misleading. This report should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2013 (“2013 Form 10-K”), including the Company’s audited consolidated financial statements and related notes.

	The Company has reclassified the presentation of certain prior year information to conform to the current presentation. Such reclassifications had no effect on the Company’s net income, comprehensive income, shareholders’ equity or cash flows. Tabular amounts are in U.S. Dollars in thousands, except share amounts, unless otherwise noted.

Business_Acquired

Business Acquired	3 Months Ended
	Mar. 31, 2014
Business Combinations [Abstract]	'
Business Acquired	'
	Business Acquired

	On January 30, 2014, the Company’s U.S.-based subsidiaries completed the acquisition of the CMG Entities through a stock purchase agreement (“SPA”) from its previous owners, PMI, which has been in rehabilitation under the receivership of the Arizona Department of Insurance since 2011, and CMFG Life Insurance Company (“CUNA Mutual”). In addition, the Company entered into a distribution agreement with CUNA Mutual and a reinsurance agreement with an affiliate of CUNA Mutual. CMG Mortgage Insurance Company has been renamed “Arch Mortgage Insurance Company” (“Arch MI U.S.”). As part of the transaction, Arch MI U.S. obtained approval as an eligible mortgage insurer from Fannie Mae and Freddie Mac (each a government sponsored enterprise or “GSE”), subject to maintaining certain ongoing requirements.

	In addition, through an asset purchase agreement (“APA”) with PMI, the Company acquired the mortgage insurance operating platform of PMI, 100% of the capital stock of PMI Mortgage Assurance Co., a mortgage insurance company licensed in all 50 states (renamed Arch Mortgage Guaranty Company), and entered into a quota share reinsurance agreement pursuant to which Arch Reinsurance Ltd. agreed to provide 100% quota share indemnity reinsurance to PMI for all certificates of insurance that were issued by PMI between and including January 1, 2009 and December 31, 2011 that were not in default as of an agreed upon effective date. Other than this quota share, no PMI legacy exposures were assumed in the transaction. As part of the transaction, the Company entered into a services agreement with PMI to provide certain necessary operational services to administer the run-off of PMI’s legacy business at the direction of PMI. Arch MI U.S. also entered into a quota share reinsurance agreement whereby it will cede 20% of all new primary flow mortgage insurance business post-closing (both credit union and non-credit union business) on the first $25 billion in original loan amounts to PMI, on a funds-withheld basis.

	The completion of the SPA and APA transactions enabled the Company to enter the U.S. mortgage insurance marketplace and serve all lenders nationwide. The arrangements with CUNA Mutual also provided a seamless transition and enabled the Company to provide uninterrupted access and services to the credit union marketplace.

	At closing, the Company paid aggregate consideration of $160.6 million (80% of the actual closing date book value of the CMG Entities) under the SPA and $84.6 million under the APA. Additionally, the SPA contains provisions for additional contingent consideration payments, subject to an overall maximum payment of 150% of closing book value of the pre-closing portfolio of the CMG Entities as re-calculated over an earn-out period and payable at the third, fifth and sixth anniversaries after closing (subject to a one time extension period of one to three years at the sellers’ discretion). The maximum amount of contingent consideration payments is $136.3 million. To the extent that the adjusted book value of the CMG Entities drops below the cumulative amount paid by the Company, no additional payments would be due. To determine the fair value of the contingent consideration liability, the Company estimated future payments using a weighted average cost of capital approach at a rate of return of 15% which reflects the industry-weighted average rate of return on debt and equity as required by market participants. The fair value of the contingent consideration liability was $41.8 million at closing. The contingent consideration liability, which is included in ‘other liabilities’ in the consolidated balance sheets, is remeasured at fair value at each balance sheet date ($43.2 million at March 31, 2014) until the contingency is resolved with changes in fair value recognized in ‘net realized gains (losses).’

	The following table summarizes the fair value of net assets acquired and allocation of purchase price:


		Total		Useful Life
	Purchase price
	Cash paid	$	245,157

	Contingent consideration liability	41,762

	Total purchase price (a)	$	286,919


	Assets acquired
	Cash	$	9,579

	Investments, at fair value	312,093

	Intangible asset -- acquired insurance contracts	46,473		5 years

	Intangible asset -- operating platform	29,900		5 years

	Intangible asset -- favorable lease contract	1,056		5 years

	Intangible asset -- insurance licenses	16,858		Indefinite

	Other assets acquired	21,691

	Total assets acquired	437,650


	Liabilities acquired
	Reserves for losses and loss adjustment expenses	$	121,572

	Unearned premiums	26,261

	Intangible liability -- unfavorable service contract	9,533		9 years

	Other liabilities acquired	7,217

	Total liabilities acquired	164,583

	Net assets acquired (b)	$	273,067

	Goodwill (a)-(b)	$	13,852


	The Company recognized goodwill of $13.9 million that is primarily attributed to PMI’s assembled workforce, access to the mortgage insurance market through an existing operating platform, and additional synergies to be realized in the future. Under U.S. tax principles, which differentiate between taxable and non-taxable business combinations, the Company estimates that $48.0 million of goodwill is expected to be deductible for tax purposes.

	The Company includes the operations of Arch MI U.S. in its mortgage segment (see Note 6).

Significant_Accounting_Policie

Significant Accounting Policies	3 Months Ended
Significant Accounting Policies	Mar. 31, 2014
Accounting Policies [Abstract]	'
Significant Accounting Policies	'
	Significant Accounting Policies

	As discussed in Note 2, the Company completed its acquisition of the CMG Entities on January 30, 2014. As such, the Company has added relevant sections pertaining to mortgage insurance to its significant accounting policies as described in Note 2, “Significant Accounting Policies,” of its audited consolidated financial statements and related notes of the 2013 Form 10-K.

	(b) Premium Revenues and Related Expenses

	Insurance. Insurance premiums written are generally recorded at the policy inception and are primarily earned on a pro rata basis over the terms of the policies for all products, usually 12 months. Premiums written include estimates in the Company’s programs, specialty lines, lenders products business and for participation in involuntary pools. Such premium estimates are derived from multiple sources which include the historical experience of the underlying business, similar business and available industry information. Unearned premium reserves represent the portion of premiums written that relates to the unexpired terms of in-force insurance policies.

	Reinsurance. Reinsurance premiums written include amounts reported by brokers and ceding companies, supplemented by the Company’s own estimates of premiums where reports have not been received. The determination of premium estimates requires a review of the Company’s experience with the ceding companies, familiarity with each market, the timing of the reported information, an analysis and understanding of the characteristics of each line of business, and management’s judgment of the impact of various factors, including premium or loss trends, on the volume of business written and ceded to the Company. On an ongoing basis, the Company’s underwriters review the amounts reported by these third parties for reasonableness based on their experience and knowledge of the subject class of business, taking into account the Company’s historical experience with the brokers or ceding companies. In addition, reinsurance contracts under which the Company assumes business generally contain specific provisions which allow the Company to perform audits of the ceding company to ensure compliance with the terms and conditions of the contract, including accurate and timely reporting of information. Based on a review of all available information, management establishes premium estimates where reports have not been received. Premium estimates are updated when new information is received and differences between such estimates and actual amounts are recorded in the period in which estimates are changed or the actual amounts are determined.

	Reinsurance premiums written are recorded based on the type of contracts the Company writes. Premiums on the Company’s excess of loss and pro rata reinsurance contracts are estimated when the business is underwritten. For excess of loss contracts, premiums are recorded as written based on the terms of the contract. Estimates of premiums written under pro rata contracts are recorded in the period in which the underlying risks are expected to incept and are based on information provided by the brokers and the ceding companies. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term.

	Reinstatement premiums for the Company’s insurance and reinsurance operations are recognized at the time a loss event occurs, where coverage limits for the remaining life of the contract are reinstated under pre-defined contract terms. Reinstatement premiums, if obligatory, are fully earned when recognized. The accrual of reinstatement premiums is based on an estimate of losses and loss adjustment expenses, which reflects management’s judgment. Premium estimates are reviewed by management at least quarterly. Such review includes a comparison of actual reported premiums to expected ultimate premiums along with a review of the aging and collection of premium estimates. Based on management’s review, the appropriateness of the premium estimates is evaluated, and any adjustment to these estimates is recorded in the period in which it becomes known. Adjustments to premium estimates could be material and such adjustments could directly and significantly impact earnings favorably or unfavorably in the period they are determined because the estimated premium may be fully or substantially earned. A significant portion of amounts included as premiums receivable, which represent estimated premiums written, net of commissions, are not currently due based on the terms of the underlying contracts.

	Reinsurance premiums written, irrespective of the class of business, are generally earned on a pro rata basis over the terms of the underlying policies or reinsurance contracts. Contracts and policies written on a “losses occurring” basis cover claims that may occur during the term of the contract or policy, which is typically 12 months. Accordingly, the premium is earned evenly over the term. Contracts which are written on a “risks attaching” basis cover claims which attach to the underlying insurance policies written during the terms of such contracts. Premiums earned on such contracts usually extend beyond the original term of the reinsurance contract, typically resulting in recognition of premiums earned over a 24-month period. Certain of the Company’s reinsurance contracts include provisions that adjust premiums or acquisition expenses based upon the experience under the contracts. Premiums written and earned, as well as related acquisition expenses, are recorded based upon the projected experience under such contracts.

	The Company also writes certain reinsurance business that is intended to provide insurers with risk management solutions that complement traditional reinsurance. Under these contracts, the Company assumes a measured amount of insurance risk in exchange for an anticipated margin, which is typically lower than on traditional reinsurance contracts. The terms and conditions of these contracts may include additional or return premiums based on loss experience, loss corridors, sublimits and caps. Examples of such business include aggregate stop-loss coverages, financial quota share coverages and multi- year retrospectively rated excess of loss coverages. If these contracts are deemed to transfer risk, they are accounted for as reinsurance.

	Mortgage. Mortgage guaranty insurance policies are contracts that are generally non-cancelable by the insurer, are renewable at a fixed price, and provide for payment of premiums on a monthly, annual or single basis. Upon renewal, the Company is not able to re-underwrite or re-price its policies. Consistent with industry accounting practices, premiums written on a monthly basis are earned as coverage is provided. Premiums written on an annual basis are amortized on a monthly pro rata basis over the year of coverage. Primary mortgage insurance premiums written on policies covering more than one year are referred to as single premiums. A portion of the revenue from single premiums is recognized in premiums earned in the current period, and the remaining portion is deferred as unearned premiums and earned over the expected life of the policy. If single premium policies related to insured loans are canceled due to repayment by the borrower, and the premium is non-refundable, the remaining unearned premium related to each canceled policy is recognized as earned premium upon notification of the cancellation.

	Unearned premiums represent the portion of premiums written that is applicable to the estimated unexpired risk of insured loans. A portion of premium payments may be refundable if the insured cancels coverage, which generally occurs when the loan is repaid, the loan amortizes to a sufficiently low amount to trigger a lender permitted or legally required cancellation, or the value of the property has increased sufficiently in accordance with the terms of the contract. Premium refunds reduce premiums earned in the consolidated statements of operations.

	Acquisition Costs. Acquisition expenses and other expenses related to the Company’s underwriting operations that vary with, and are directly related to, the successful acquisition or renewal of business are deferred and amortized based on the type of contract. For property and casualty insurance and reinsurance contracts, deferred acquisition costs are amortized over the period in which the related premiums are earned. Consistent with mortgage insurance industry accounting practice, amortization of acquisition costs related to the mortgage insurance contracts for each underwriting year’s book of business is charged against revenue in proportion to estimated gross profits. Estimated gross profits are comprised of earned premiums, interest income, losses and loss adjustment expenses. For each underwriting year, the Company estimates the rate of amortization to reflect actual experience and any changes to persistency or loss development.

	Acquisition expenses, net of ceding commissions received from reinsurers, consist principally of commissions and premium taxes paid to obtain the Company’s business. Other operating expenses also include expenses that vary with, and are directly related to, the acquisition of business. Deferred acquisition costs are carried at their estimated realizable value and take into account anticipated losses and loss adjustment expenses, based on historical and current experience, and anticipated investment income. A premium deficiency occurs if the sum of anticipated losses and loss adjustment expenses, unamortized acquisition costs and maintenance costs exceed unearned premiums 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.

	(i) Reserves for Losses and Loss Adjustment Expenses

	Insurance and Reinsurance. The reserve for losses and loss adjustment expenses consists of estimates of unpaid reported losses and loss adjustment expenses and estimates for losses incurred but not reported. The reserve for unpaid reported losses and loss adjustment expenses, established by management based on reports from ceding companies and claims from insureds, excludes estimates of amounts 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.

	Mortgage. The reserves for mortgage guaranty insurance losses and loss adjustment expenses are the estimated claim settlement costs on notices of default that have been received by the Company, as well as loan defaults that have been incurred but have not been reported by the lenders. Consistent with industry accounting practice, the Company does not establish loss reserves for future claims on insured loans that are not currently in default (defined as two consecutive missed payments). The Company establishes loss reserves on a case-by-case basis when insured loans are identified as currently in default using estimated claim rates and average claim sizes for each report year, net of any salvage recoverable. The Company also reserves for defaults that have occurred but have not yet been reported to the Company prior to the close of an accounting period. To determine this reserve, the Company estimates the number of defaults not yet reported using historical information regarding late reported delinquencies and applies estimated claim rates and claim sizes for the estimated defaults not yet reported.

	The establishment of reserves across the Company’s segments is an inherently uncertain process, are necessarily based on estimates, and the ultimate net cost may vary from such estimates. The methods for making such estimates and for establishing the resulting liability are reviewed and updated using the most current information available. Any resulting adjustments, which may be material, are reflected in current operations

	(q) Goodwill and Intangible Assets

	Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired and is assigned to the applicable reporting unit at acquisition. Goodwill is not amortized and is evaluated for impairment on an annual basis. Impairment tests may be performed more frequently if the facts and circumstances indicate a possible impairment. In performing impairment tests, the Company may first assess qualitative factors to determine whether it is more likely than not (that is, more than a 50% probability) that the fair value of a reporting unit exceeds its carrying amount as a basis for determining whether it is necessary to perform the two-step goodwill impairment test described in the accounting guidance.

	Indefinite-lived intangible assets, such as insurance licenses, are not amortized and are evaluated for impairment similar to goodwill. Finite-lived intangible assets and liabilities include the value of insurance and reinsurance contracts, which are estimated based on the present value of future expected cash flows and amortized in ‘acquisition expenses’ in proportion to the estimated profits expected to be realized. Other finite-lived intangible assets or liabilities, including favorable or unfavorable contracts, are amortized in ‘other operating expenses’ over their useful lives. Finite-lived intangible assets and liabilities are periodically reviewed for indicators of impairment. An impairment is recognized when the carrying amount is not recoverable from its undiscounted cash flows and is measured as the difference between the carrying amount and fair value.

	If goodwill or intangible assets are impaired, such assets are written down to their realizable values with the related expense recorded in the Company’s results of operations.

Variable_Interest_Entities_and

Variable Interest Entities and Noncontrolling Interests	3 Months Ended
	Mar. 31, 2014
Noncontrolling Interest [Abstract]	'
Variable Interest Entity and Noncontrolling Interests	'
	Variable Interest Entity and Noncontrolling Interests

	Variable interest entity

	A VIE refers to an entity that has characteristics such as (i) insufficient equity at risk to allow the entity to finance its activities without additional financial support or (ii) instances where the equity investors, as a group, do not have characteristics of a controlling financial interest. The primary beneficiary of a VIE is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (i) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (ii) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. If a company is determined to be the primary beneficiary, it is required to consolidate the VIE in its financial statements.

	In March 2014, Watford raised approximately $1.1 billion of capital consisting of $907.3 million in common equity ($895.6 million net of issuance costs) and $226.6 million in preference equity ($219.2 million net of issuance costs and discount). The Company invested $100.0 million and acquired approximately 11% of Watford Holdings Ltd.’s common equity and a warrant to purchase additional common equity. Arch Underwriters Ltd. (“AUL”), a subsidiary of the Company, acts as Watford’s reinsurance manager, and Highbridge Principal Strategies, LLC (“Highbridge”), a subsidiary of JPMorgan Chase & Co., manages Watford’s investment assets, each under separate long term services agreements. John Rathgeber, previously Vice Chairman of Arch Worldwide Reinsurance Group, was named CEO of Watford. In addition, Marc Grandisson, Chairman and CEO of Arch Worldwide Reinsurance and Mortgage Groups, and Nicolas Papadopoulo, Chairman and CEO of Arch Reinsurance Ltd., were appointed to the board of directors of Watford.

	The Company concluded that Watford is a VIE due to both the reinsurance management services agreement with AUL and the investment management agreement with Highbridge. Both of these agreements provide for services for an extended period of time with limited termination rights by Watford. In addition, these agreements allow for both AUL and Highbridge to participate in the favorable results of Watford in the form of performance fees. To determine if the Company is the primary beneficiary of Watford, the Company concluded that the most significant activity of Watford pertains to the insurance activities arising from the reinsurance management services agreement, as these activities will ultimately generate the investable assets required by Highbridge to execute the investment strategy. In addition, the Company factored into its analysis qualitative aspects of the relationship with Watford that are indicative of power to direct the insurance activities. These aspects coupled with the Company’s board seats and a former executive of the Company serving as Watford’s CEO resulted in the Company concluding that it is the primary beneficiary of Watford. As such, the results of Watford are included in the Company’s consolidated financial statements.

	The Company concluded that Watford represents a separate operating segment and provides the income statement and total investable assets, total assets and total liabilities of Watford within Note 6. Because Watford is an independent company, the assets of Watford can be used only to settle obligations of Watford and Watford is solely responsible for its own liabilities and commitments. The Company’s financial exposure to Watford is limited to its investment in Watford’s common shares and counterparty credit risk (mitigated by collateral) arising from the reinsurance transactions.

	Non-redeemable noncontrolling interests

	The Company accounts for the portion of Watford’s common equity attributable to third party investors in the shareholders’ equity section of its consolidated balance sheets. The noncontrolling ownership in Watford’s common shares was approximately 89% at March 31, 2014. The portion of Watford’s income or loss attributable to third party investors is recorded in the consolidated statements of income as ‘net (income) loss attributable to noncontrolling interests.’ The following table sets forth activity in the non-redeemable noncontrolling interests:


		Three Months Ended March 31, 2014
	Balance, beginning of year	$	—

	Sale of shares to noncontrolling interests	796,903

	Net (loss) income attributable to noncontrolling interests	(3,407		)
	Balance, end of period	$	793,496


	Redeemable noncontrolling interests

	The Company accounts for redeemable noncontrolling interests in the mezzanine section of its consolidated balance sheets in accordance with applicable accounting guidance. Such redeemable noncontrolling interests represent the 9,065,200 cumulative redeemable preference shares (“Watford Preference Shares”) issued in late March 2014 with a par value of $0.01 per share and a liquidation preference of $25.00 per share. The Watford Preference Shares were issued at a discounted amount of $24.50 per share. Due to the timing of the issuance, not all amounts subscribed were collected by Watford by March 31, 2014. Holders of the Watford Preference Shares will be entitled to receive, if declared by Watford’s board, quarterly cash dividends on the last day of March, June, September, and December commencing June 30, 2014. Dividends will accrue from the closing date to June 30, 2019 at a fixed rate of 8.5% per annum. From June 30, 2019 and subsequent, dividends will accrue based on a floating rate equal to the 3 month U.S. dollar LIBOR (with a 1% floor) plus a margin based on the difference between the fixed rate and the 5 year mid swap rate to the floating rate as set out on the IRSB18. The Watford Preference Shares may be redeemed by Watford on or after June 30, 2019 or at the option of the preferred shareholders at any time on or after June 30, 2034. Because the redemption features are not solely within the control of Watford, the Company accounts for the redeemable noncontrolling interests in the Watford Preference Shares in the mezzanine section of its consolidated balance sheets. Third party investors own 100% of the Watford Preference Shares at March 31, 2014. Preferred dividends, including the accretion of the discount and issuance costs, are included as ‘net (income) loss attributable to noncontrolling interests’ in the Company’s consolidated statements of income.

Earnings_Per_Common_Share

Earnings Per Common Share	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
Earnings Per Common Share	'
	Earnings Per Common Share

	The following table sets forth the computation of basic and diluted earnings per common share:


		Three Months Ended
		March 31,
		2014			2013

	Numerator:

	Net income	$	179,145		$	256,476

	Net (income) loss attributable to noncontrolling interests	3,355			—

	Net income available to Arch	182,500			256,476

	Preferred dividends	(5,484		)	(5,484		)
	Net income available to Arch common shareholders	$	177,016		$	250,992


	Denominator:

	Weighted average common shares outstanding — basic	131,857,910			130,907,902

	Effect of dilutive common share equivalents:

	Nonvested restricted shares	1,346,401			1,290,161

	Stock options (1)	3,358,406			3,211,225

	Weighted average common shares and common share equivalents outstanding — diluted	136,562,717			135,409,288


	Earnings per common share:

	Basic	$	1.34		$	1.92

	Diluted	$	1.3		$	1.85

	_________________________________________________

	-1	Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2014 first quarter and 2013 first quarter, the number of stock options excluded were 759,172 and 1,016,043, respectively.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Segment Information	'
	Segment Information

	During the 2014 first quarter, to reflect activity during the period as described below, the Company changed its segment structure and added two new segments (mortgage and ‘other’). The Company now classifies its businesses into three underwriting segments — insurance, reinsurance and mortgage — and two other operating segments — ‘other’ and corporate (non-underwriting). The Company determined its reportable segments using the management approach described in accounting guidance regarding disclosures about segments of an enterprise and related information. The accounting policies of the segments are the same as those used for the preparation of the Company’s consolidated financial statements. Intersegment business is allocated to the segment accountable for the underwriting results.

	The Company’s insurance, reinsurance and mortgage segments each have managers who are responsible for the overall profitability of their respective segments and who are directly accountable to the Company’s chief operating decision makers, the Chairman, 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. Management measures segment performance for its three underwriting segments based on underwriting income or loss. The Company does not manage its assets by underwriting segment and, accordingly, investment income is not allocated to each underwriting segment.

	The corporate (non-underwriting) segment results include net investment income, other income (loss), other expenses incurred by the Company, interest expense, net realized gains or losses, net impairment losses included in earnings, equity in net income (loss) of investment funds accounted for using the equity method, net foreign exchange gains or losses, income taxes and items related to the Company’s non-cumulative preferred shares. Such amounts exclude the results of the ‘other’ segment.

	The ‘other’ segment includes the results of Watford (see Note 4). Watford has its own management and board of directors that is responsible for the overall profitability of the ‘other’ segment. For the ‘other’ segment, performance is measured based on net income or loss.


	The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income or loss to net income available to common shareholders:


		Three Months Ended
		31-Mar-14
		Insurance				Reinsurance				Mortgage				Sub-Total				Other				Total

	Gross premiums written (1)	$	730,646			$	517,053			$	47,907			$	1,295,136			$	32,194			$	1,295,136

	Premiums ceded	(185,044		)		(73,127		)		(4,639		)		(262,340		)		—				(230,146		)

	Net premiums written	545,602				443,926				43,268				1,032,796				32,194				1,064,990

	Change in unearned premiums	(68,101		)		(102,578		)		(4,503		)		(175,182		)		(30,028		)		(205,210		)
	Net premiums earned	477,501				341,348				38,765				857,614				2,166				859,780

	Other underwriting income	500				316				766				1,582				—				1,582

	Losses and loss adjustment expenses	(286,770		)		(139,636		)		(8,478		)		(434,884		)		(1,356		)		(436,240		)
	Acquisition expenses, net	(76,932		)		(73,433		)		(9,154		)		(159,519		)		(823		)		(160,342		)
	Other operating expenses	(81,144		)		(36,195		)		(13,876		)		(131,215		)		(1,109		)		(132,324		)
	Underwriting income (loss)	$	33,155			$	92,400			$	8,023			133,578				(1,122		)		132,456


	Net investment income													66,993				1				66,994

	Net realized gains													19,697				—				19,697

	Net impairment losses recognized in earnings													(2,971		)		—				(2,971		)

	Equity in net income of investment funds accounted for using the equity method													3,253				—				3,253

	Other income (loss)													(2,104		)		—				(2,104		)

	Other expenses													(10,799		)		(2,676		)		(13,475		)

	Interest expense													(14,404		)		—				(14,404		)

	Net foreign exchange gains (losses)													(6,656		)		93				(6,563		)

	Income before income taxes													186,587				(3,704		)		182,883

	Income tax expense													(3,738		)		—				(3,738		)

	Net income (loss)													182,849				(3,704		)		179,145

	Net (income) loss attributable to noncontrolling interests													—				3,355				3,355

	Net income available to Arch													182,849				(349		)		182,500

	Preferred dividends													(5,484		)		—				(5,484		)

Net income available to Arch common shareholders													$	177,365			$	(349	)		$	177,016


Underwriting Ratios

Loss ratio	60.1		%		40.9		%		21.9		%		50.7		%		62.6		%		50.7		%
Acquisition expense ratio (2)	16		%		21.5		%		23.6		%		18.5		%		38		%		18.6		%
Other operating expense ratio	17		%		10.6		%		35.8		%		15.3		%		51.2		%		15.4		%
Combined ratio	93.1		%		73		%		81.3		%		84.5		%		151.8		%		84.7		%

Total investable assets													$	14,261,106			$	1,083,280			$	15,344,386

Total assets													20,653,897				1,146,461				21,800,358

Total liabilities													14,860,124				35,371				14,895,495

_________________________________________________

-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.



	Three Months Ended
	31-Mar-13
	Insurance				Reinsurance				Mortgage				Sub-Total				Other				Total

Gross premiums written (1)	$	688,817			$	450,447			$	25,758			$	1,163,699			$	—			$	1,163,699

Premiums ceded	(184,267		)		(27,979		)		—				(210,923		)		—				(210,923		)

Net premiums written	504,550				422,468				25,758				952,776				—				952,776

Change in unearned premiums	(59,585		)		(126,315		)		(14,106		)		(200,006		)		—				(200,006		)

Net premiums earned	444,965				296,153				11,652				752,770				—				752,770

Other underwriting income	525				13				—				538				—				538

Losses and loss adjustment expenses	(283,467		)		(113,857		)		(2,079		)		(399,403		)		—				(399,403		)

Acquisition expenses, net	(70,758		)		(53,143		)		(3,691		)		(127,592		)		—				(127,592		)

Other operating expenses	(76,315		)		(32,197		)		(1,403		)		(109,915		)		—				(109,915		)

Underwriting income	$	14,950			$	96,969			$	4,479			116,398				—				116,398


Net investment income													65,672				—				65,672

Net realized gains													58,340				—				58,340

Net impairment losses recognized in earnings													(2,246		)		—				(2,246		)

Equity in net income of investment funds accounted for using the equity method													13,823				—				13,823

Other income (loss)													1,244				—				1,244

Other expenses													(10,268		)		—				(10,268		)

Interest expense													(5,898		)		—				(5,898		)

Net foreign exchange gains													24,264				—				24,264

Income before income taxes													261,329				—				261,329

Income tax expense													(4,853		)		—				(4,853		)

Net income													256,476				—				256,476

Net (income) loss attributable to noncontrolling interests													—				—				—

Net income available to Arch													256,476				—				256,476

Preferred dividends													(5,484		)		—				(5,484		)

Net income available to Arch common shareholders													$	250,992			$	—			$	250,992


Underwriting Ratios

Loss ratio	63.7		%		38.4		%		17.8		%		53.1		%		—		%		53.1		%
Acquisition expense ratio (2)	15.8		%		17.9		%		31.7		%		16.9		%		—		%		16.9		%
Other operating expense ratio	17.2		%		10.9		%		12		%		14.6		%		—		%		14.6		%
Combined ratio	96.7		%		67.2		%		61.5		%		84.6		%		—		%		84.6		%

Total investable assets													$	13,132,116			$	—			$	13,132,116

Total assets													18,757,061				—				18,757,061

Total liabilities													13,421,531				—				13,421,531

_________________________________________________

-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 other underwriting income.

Investment_Information

Investment Information	3 Months Ended
	Mar. 31, 2014
Disclosure Investment Information [Abstract]	'
Investment Information	'
	Investment Information

	At March 31, 2014, total investable assets of $15.34 billion included $14.26 billion managed by the Company and $1.08 billion attributable to Watford. Due to the timing of Watford’s launch, the cash proceeds received from Watford’s capital raising activities was not invested at March 31, 2014 and, as such, Watford’s investable assets were included in the Company’s cash balance at such date. As such, the tables in this footnote do not reflect any Watford balances except for the net investment income table. See Note 4 for further details on Watford.

	Available For Sale Investments

	The following table summarizes the fair value and cost or amortized cost of the Company’s investments classified as available for sale:


		Fair			Gross			Gross				Cost or			OTTI
		Value			Unrealized			Unrealized				Amortized			Unrealized
					Gains			Losses				Cost			Losses (2)
	31-Mar-14

	Fixed maturities and fixed maturities pledged under securities lending agreements (1):

	Corporate bonds	$	2,514,129		$	39,704		$	(20,047	)		$	2,494,472		$	(16	)

	Mortgage backed securities	1,087,840			21,700			(14,253		)		1,080,393			(8,217		)

	Municipal bonds	1,410,043			28,494			(3,742		)		1,385,291			(17		)

	Commercial mortgage backed securities	1,023,055			11,769			(9,031		)		1,020,317			—

	U.S. government and government agencies	1,153,120			4,048			(5,932		)		1,155,004			(19		)

	Non-U.S. government securities	1,114,382			14,538			(12,978		)		1,112,822			—

	Asset backed securities	1,573,751			11,143			(12,385		)		1,574,993			(2,902		)

	Total	9,876,320			131,396			(78,368		)		9,823,292			(11,171		)


	Equity securities	548,168			78,896			(6,596		)		475,868			—

	Other investments	426,917			24,398			(15,243		)		417,762			—

	Short-term investments	1,484,280			955			(2,053		)		1,485,378			—

	Total	$	12,335,685		$	235,645		$	(102,260	)		$	12,202,300		$	(11,171	)


	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	)

_________________________________________________

-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 March 31, 2014, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $4.8 million, compared to a net unrealized gain of $6.0 million at December 31, 2013.

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
	Fair			Gross			Fair				Gross			Fair				Gross
	Value			Unrealized			Value				Unrealized			Value				Unrealized
				Losses							Losses							Losses
31-Mar-14

Fixed maturities and fixed maturities pledged under securities lending agreements (1):

Corporate bonds	$	1,012,076		$	(17,780	)	$	40,352			$	(2,267	)	$	1,052,428			$	(20,047	)

Mortgage backed securities	434,286			(11,841		)	23,033				(2,412		)	457,319				(14,253		)

Municipal bonds	340,349			(3,484		)	3,741				(258		)	344,090				(3,742		)

Commercial mortgage backed securities	398,428			(8,977		)	581				(54		)	399,009				(9,031		)

U.S. government and government agencies	764,802			(5,932		)	—				—			764,802				(5,932		)

Non-U.S. government securities	541,534			(10,940		)	36,298				(2,038		)	577,832				(12,978		)

Asset backed securities	904,539			(8,424		)	99,179				(3,961		)	1,003,718				(12,385		)

Total	4,396,014			(67,378		)	203,184				(10,990		)	4,599,198				(78,368		)

Equity securities	102,589			(6,596		)	—				—			102,589				(6,596		)

Other investments	156,468			(15,243		)	—				—			156,468				(15,243		)

Short-term investments	180,233			(2,053		)	—				—			180,233				(2,053		)

Total	$	4,835,304		$	(91,270	)	$	203,184			$	(10,990	)	$	5,038,488			$	(102,260	)


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		)	—				—			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	)

_________________________________________________

-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 March 31, 2014, on a lot level basis, approximately 1,580 security lots out of a total of approximately 4,310 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 $3.6 million. 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.

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.


		31-Mar-14						31-Dec-13
Maturity		Fair Value			Amortized			Fair Value				Amortized
					Cost							Cost
Due in one year or less		$	286,950		$	282,281		$	235,330			$	232,652

Due after one year through five years		3,757,966			3,731,777			3,738,500				3,718,920

Due after five years through 10 years		1,883,374			1,872,047			1,966,536				1,979,510

Due after 10 years		263,384			261,484			196,305				198,286

		6,191,674			6,147,589			6,136,671				6,129,368

Mortgage backed securities		1,087,840			1,080,393			1,133,095				1,139,034

Commercial mortgage backed securities		1,023,055			1,020,317			1,074,497				1,075,749

Asset backed securities		1,573,751			1,574,993			1,332,594				1,326,356

Total		$	9,876,320		$	9,823,292		$	9,676,857			$	9,670,507


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 fair value and amortized cost of fixed maturities and short-term investments pledged under securities lending agreements were $100.6 million and $100.9 million, respectively, at March 31, 2014, compared to $105.1 million and $105.9 million, respectively, at December 31, 2013. The fair value of the portfolio of collateral backing the Company’s securities lending program was $96.3 million at March 31, 2014, compared to $100.6 million at December 31, 2013. Such amounts included approximately $6.3 million of sub-prime securities at March 31, 2014, compared to $6.3 million at December 31, 2013. The Company maintains legal control over the securities it lends, retains the earnings and cash flows associated with the loaned securities and receives a fee from the borrower for the temporary use of the securities. An indemnification agreement with the lending agent protects the Company in the event a borrower becomes insolvent or fails to return any of the securities on loan to the Company.

Other Investments

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


	March 31,			December 31,
	2014			2013
Available for sale:
Asian and emerging markets	$	266,023		$	331,984

Investment grade fixed income	160,894			159,115

Other	—			7,211

Total available for sale	426,917			498,310

Fair value option:
Term loan investments (par value: $403,383 and $494,502)	410,430			512,076

Asian and emerging markets	14,817			14,054

Investment grade fixed income	91,907			75,062

Other (1)	282,670			172,088

Total fair value option	799,824			773,280

Total	$	1,226,741		$	1,271,590

_________________________________________________

-1	Includes fund investments with strategies in mortgage servicing rights, transportation and infrastructure assets and other.

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

Fair Value Option

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


	March 31,			December 31,
	2014			2013
Fixed maturities	$	456,826		$	448,254

Other investments	799,824			773,280

Investments accounted for using the fair value option	$	1,256,650		$	1,221,534


Net Investment Income

The components of net investment income were derived from the following sources:


	Three Months Ended
	March 31,
	2014			2013
Fixed maturities	$	62,449		$	62,006

Term loan investments	5,669			4,217

Equity securities (dividends)	2,921			1,423

Short-term investments	406			392

Other (1)	4,718			6,299

Gross investment income	76,163			74,337

Investment expenses	(9,169		)	(8,665		)
Net investment income	$	66,994		$	65,672

_________________________________________________

-1	Includes dividends on investment funds and other items.

Net Realized Gains (Losses)

Net realized gains (losses) were as follows, excluding other-than-temporary impairment provisions:


	Three Months Ended
	March 31,
	2014			2013
Available for sale securities:

Gross gains on investment sales	$	66,051		$	67,020

Gross losses on investment sales	(40,013		)	(25,056		)
Change in fair value of assets and liabilities accounted for using the fair value option:

Fixed maturities	(1,643		)	5,058

Other investments	10,776			9,951

Equity securities	—			699

Derivative instruments (1)	(12,768		)	(378		)
Other (2)	(2,706		)	1,046

Net realized gains (losses)	$	19,697		$	58,340

_________________________________________________

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

-2	Includes accretion of contingent liability amounts related to the acquisition of the CMG Entities (see Note 2 for further details).

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:


	Three Months Ended
	March 31,
	2014			2013
Fixed maturities:

Mortgage backed securities	$	—		$	(15	)

Asset backed securities	(6		)	(20		)
Total	(6		)	(35		)
Equity securities	—			(2,211		)

Other investments	(2,965		)	—

Net impairment losses recognized in earnings	$	(2,971	)	$	(2,246	)

The Company’s net impairment losses recognized in earnings in the 2014 first quarter primarily related to one investment fund. The Company analyzed available positive and negative evidence on the fund, including the business prospects, recent events, industry and market data and other factors. Following such review, 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 and, as such, the cost basis of such securities was adjusted down accordingly.

The Company believes that the $11.2 million of OTTI included in accumulated other comprehensive income at March 31, 2014 on the securities which were considered by the Company to be impaired was due to market and sector-related factors (i.e., not credit losses). At March 31, 2014, 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:


	Three Months Ended
	March 31,
	2014			2013
Balance at start of period	$	60,062		$	62,001

Credit loss impairments recognized on securities not previously impaired	—			33

Credit loss impairments recognized on securities previously impaired	6			2

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	(12,812		)	(80		)
Balance at end of period	$	47,256		$	61,956


Restricted Assets

The Company is required to maintain assets on deposit, which primarily consist of fixed maturities, with various regulatory authorities to support its insurance and reinsurance operations. The Company’s insurance and reinsurance subsidiaries maintain assets in trust accounts as collateral for insurance and reinsurance transactions with affiliated companies and also have investments in segregated portfolios primarily to provide collateral or guarantees for letters of credit to third parties. See Note 10 for further details. The following table details the value of the Company’s restricted assets:


	March 31,			December 31,
	2014			2013
Assets used for collateral or guarantees:

Affiliated transactions	$	4,346,385		$	4,060,533

Third party agreements	951,609			856,890

Deposits with U.S. regulatory authorities	350,284			302,809

Deposits with non-U.S. regulatory authorities	2			6,546

Trust funds	92,108			75,264

Total restricted assets	$	5,740,388		$	5,302,042

Fair_Value

Fair Value	3 Months Ended
	Mar. 31, 2014
Fair Value Disclosures [Abstract]	'
Fair Value	'
	Fair Value

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

	The levels in the hierarchy are defined as follows:


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


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


	Level 3:	Inputs to the valuation methodology are unobservable and significant to the fair value measurement

	Following is a description of the valuation methodologies used for securities measured at fair value, as well as the general classification of such securities pursuant to the valuation hierarchy.

	The Company 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) 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. The Company did not adjust any of the prices obtained from the pricing services at March 31, 2014.

	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 $13.64 billion of financial assets and liabilities measured at fair value at March 31, 2014, approximately $544.4 million, or 4.0%, were priced using non-binding broker-dealer quotes. Of the $13.37 billion of financial assets and liabilities measured at fair value at December 31, 2013, approximately $601.9 million, or 4.5%, 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 advisers and others. No transfers were made in the periods presented. 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.

	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.

	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.

	Contingent consideration liability. The contingent consideration liability (included in ‘other liabilities’ in the consolidated balance sheets) resulted from the acquisition of the CMG Entities and is remeasured at fair value at each balance sheet date. Changes in fair value are recognized in ‘net realized gains (losses).’ To determine the fair value of the contingent consideration liability, the Company estimates future payments using an income approach based on modeled inputs which include a weighted average cost of capital. The Company determined that the contingent consideration liability would be included in Level 3 of the valuation hierarchy.

	The following table presents the Company’s financial assets and liabilities measured at fair value by level at March 31, 2014:


					Fair Value Measurement Using:
		Fair			Quoted Prices in			Significant			Significant
		Value			Active Markets			Other			Unobservable
					for Identical			Observable			Inputs
					Assets			Inputs			(Level 3)
					(Level 1)			(Level 2)
	Assets measured at fair value:

	Available for sale securities:

	Fixed maturities and fixed maturities pledged under securities lending agreements (1):

	Corporate bonds	$	2,514,129		$	—		$	2,514,129		$	—

	Mortgage backed securities	1,087,840			—			1,087,840			—

	Municipal bonds	1,410,043			—			1,410,043			—

	Commercial mortgage backed securities	1,023,055			—			1,023,055			—

	U.S. government and government agencies	1,153,120			1,153,120			—			—

	Non-U.S. government securities	1,114,382			—			1,114,382			—

	Asset backed securities	1,573,751			—			1,573,751			—

Total	9,876,320			1,153,120			8,723,200			—


Equity securities	548,168			548,099			69			—

Other investments	426,917			—			322,582			104,335

Short-term investments	1,484,280			1,457,349			26,931			—


Fair value option:

Investments accounted for using the fair value option:

Corporate bonds	353,644			—			353,644			—

Non-U.S. government bonds	63,538			—			63,538			—

Mortgage backed securities	39,644			—			39,644			—

Other investments	799,824			—			380,678			419,146

Total	1,256,650			—			837,504			419,146

Total assets measured at fair value	$	13,592,335		$	3,158,568		$	9,910,286		$	523,481


Liabilities measured at fair value:

Contingent consideration liability	$	43,156		$	—		$	—		$	43,156

Total liabilities measured at fair value	$	43,156		$	—		$	—		$	43,156

_________________________________________________

-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, 2013:


				Fair Value Measurement Using:
	Fair			Quoted Prices in			Significant			Significant
	Value			Active Markets			Other			Unobservable
				for Identical			Observable			Inputs
				Assets			Inputs			(Level 3)
				(Level 1)			(Level 2)
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 tables present a reconciliation of the beginning and ending balances for all financial assets and liabilities measured at fair value on a recurring basis using Level 3 inputs:


	Fair Value Measurements Using:
	Significant Unobservable Inputs (Level 3)
	Assets												Liabilities
s	Available-For-Sale						Fair Value Option
	Corporate			Other			Other			Total			Contingent Consideration Liability
	Bonds			Investments			Investments
Three Months Ended March 31, 2014

Balance at beginning of period	$	2,045		$	170,420		$	377,525		$	549,990		$	—

Total gains or (losses) (realized/unrealized)

Included in earnings (1)	—			2,275			6,310			8,585			(1,394		)

Included in other comprehensive income	—			(2,196		)	—			(2,196		)	—

Purchases, issuances, sales and settlements

Purchases	—			—			40,110			40,110			—

Issuances	—			—			—			—			(41,762		)

Sales	(2,045		)	(66,164		)	—			(68,209		)	—

Settlements	—			—			(4,799		)	(4,799		)	—

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

Balance at end of period	$	—		$	104,335		$	419,146		$	523,481		$	(43,156	)


Three Months Ended March 31, 2013

Balance at beginning of period	$	98,404		$	184,202		$	195,350		$	477,956		$	—

Total gains or (losses) (realized/unrealized)

Included in earnings (1)	1,492			4,762			373			6,627			—

Included in other comprehensive income	(1,688		)	1,912			—			224			—

Purchases, issuances, sales and settlements

Purchases	—			5,000			41,654			46,654			—

Issuances	—			—			—			—			—

Sales	—			—			—			—			—

Settlements	(910		)	(9,942		)	(58,007		)	(68,859		)	—

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

Balance at end of period	$	97,298		$	185,934		$	179,370		$	462,602		$	—

_________________________________________________

-1	Gains or losses on corporate bonds were included in net realized gains (losses) while gains or losses on other investments were included in net realized gains (losses) or net investment income. Gains or losses on the contingent consideration liability were included in net realized gains (losses).

The amount of total gains for the 2014 first quarter included in earnings attributable to the change in unrealized gains or losses relating to assets still held at March 31, 2014 was $3.3 million, while the amount of total gains for the 2013 first quarter included in earnings attributable to the change in unrealized gains or losses relating to assets still held at March 31, 2013 was $6.6 million.

Financial Instruments Disclosed, But Not Carried, At Fair Value

The Company uses various financial instruments in the normal course of its business. The carrying values of cash, accrued investment income, receivable for securities sold, certain other assets, payable for securities purchased and certain other liabilities approximated their fair values at March 31, 2014, due to their respective short maturities. As these financial instruments are not actively traded, their respective fair values are classified within Level 2.

At March 31, 2014, the senior notes of ACGL were carried at their cost of $300.0 million and had a fair value of $394.7 million while the senior notes of Arch-U.S. were carried at their cost of $500.0 million and had a fair value of $530.3 million. The fair values of the senior notes were obtained from a third party pricing service and are based on observable market inputs. As such, the fair value of the senior notes is classified within Level 2.

Derivative_Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments	'
	Derivative Instruments

	The Company’s investment strategy allows for the use of derivative securities. The Company’s derivative instruments are recorded on its consolidated balance sheets at fair value. The fair values of those derivatives are based on quoted market prices. All realized and unrealized contract gains and losses are reflected in the Company’s results of operations. 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 Company did not hold any derivatives which were designated as hedging instruments at March 31, 2014 or December 31, 2013.

	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 (1)
	31-Mar-14

	Futures contracts	$	469			$	(769	)		$	(300	)	$	1,056,045

	Foreign currency forward contracts	693				(1,565		)		(872		)	244,614

	TBAs	216,548				(211,763		)		4,785			412,800

	Other	1,349				(844		)		505			690,029

	Total	$	219,059			$	(214,941	)		$	4,118


	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

	_________________________________________________

	-1	Represents the absolute notional value of all outstanding contracts, consisting of long and short positions.

	The Company’s derivative instruments are generally traded under master netting agreements, which establish terms that apply to all derivative transactions with a counterparty. In the event of a bankruptcy or other stipulated event of default, such agreements provide that the non-defaulting party may elect to terminate all outstanding derivative transactions, in which case all individual derivative positions (loss or gain) with a counterparty are closed out and netted and replaced with a single amount, usually referred to as the termination amount, which is expressed in a single currency. The resulting single net amount, where positive, is payable to the party “in-the-money” regardless of whether or not it is the defaulting party, unless the parties have agreed that only the non-defaulting party is entitled to receive a termination payment where the net amount is positive and is in its favor. Effectively, contractual close-out netting reduces derivatives credit exposure from gross to net exposure. At March 31, 2014, asset derivatives and liability derivatives of $147.7 million and $143.0 million, respectively, were subject to a master netting agreement, compared to $28.0 million and $14.6 million, respectively, at December 31, 2013. The remaining derivatives included in the table above were not subject to a master netting agreement.

	The following table summarizes net realized gains (losses) recorded on the Company’s derivative instruments in the consolidated statements of income:


			Three Months Ended
	Derivatives not designated as		March 31,
	hedging instruments		2014				2013
	Futures contracts		$	(9,862	)		$	(829	)
	Foreign currency forward contracts		(2,257		)		(725		)
	TBAs		(37		)		541

	Other		(612		)		635

	Total		$	(12,768	)		$	(378	)

Commitments_and_Contingencies

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Commitments and Contingencies

	Letter of Credit and Revolving Credit Facilities

	As of March 31, 2014, the Company had a $300 million unsecured revolving loan and letter of credit facility and a $500 million secured letter of credit facility (the “Credit Agreement”). The Credit Agreement expires on August 18, 2014. In addition, the Company had access to secured letter of credit facilities of approximately $192.0 million as of March 31, 2014, 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”). At March 31, 2014, the Company had $430.0 million in outstanding letters of credit under the LOC Facilities, which were secured by investments with a fair value of $493.1 million, and had $100.0 million of borrowings outstanding under the Credit Agreement. The Company was in compliance with all covenants contained in the LOC Facilities at March 31, 2014.

	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 $966.1 million at March 31, 2014.

Share_Transactions

Share Transactions	3 Months Ended
Share Transactions	Mar. 31, 2014
Stockholders' Equity Note [Abstract]	'
Share Transactions	'
	Share Transactions

	Share Repurchases

	The board of directors of ACGL has authorized the investment in ACGL’s common shares through a share repurchase program. Repurchases under the program may be effected from time to time in open market or privately negotiated transactions through December 2014. Since the inception of the share repurchase program, ACGL has repurchased approximately 109.9 million common shares for an aggregate purchase price of $2.79 billion. During the 2014 first quarter, ACGL did not repurchase any common shares, compared to 930,759 common shares for an aggregate purchase price of $41.0 million for the 2013 period. At March 31, 2014, $712.1 million of share repurchases were available under the program. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations.

Income_Taxes

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes

	ACGL is incorporated under the laws of Bermuda and, under current Bermuda law, is not obligated to pay any taxes in Bermuda based upon income or capital gains. The Company has received a written undertaking from the Minister of Finance in Bermuda under the Exempted Undertakings Tax Protection Act 1966 that, in the event that any legislation is enacted in Bermuda imposing any tax computed on profits, income, gain or appreciation on any capital asset, or any tax in the nature of estate duty or inheritance tax, such tax will not be applicable to ACGL or any of its operations until March 31, 2035. This undertaking does not, however, prevent the imposition of taxes on any person ordinarily resident in Bermuda or any company in respect of its ownership of real property or leasehold interests in Bermuda.

	ACGL and its non-U.S. subsidiaries will be subject to U.S. federal income tax only to the extent that they derive U.S. source income that is subject to U.S. withholding tax or income that is effectively connected with the conduct of a trade or business within the U.S. and is not exempt from U.S. tax under an applicable income tax treaty with the U.S. ACGL and its non-U.S. subsidiaries will be subject to a withholding tax on dividends from U.S. investments and interest from certain U.S. payors (subject to reduction by any applicable income tax treaty). ACGL and its non-U.S. subsidiaries intend to conduct their operations in a manner that will not cause them to be treated as engaged in a trade or business in the United States and, therefore, will not be required to pay U.S. federal income taxes (other than U.S. excise taxes on insurance and reinsurance premium and withholding taxes on dividends and certain other U.S. source investment income). However, because there is uncertainty as to the activities which constitute being engaged in a trade or business within the United States, there can be no assurances that the U.S. Internal Revenue Service will not contend successfully that ACGL or its non-U.S. subsidiaries are engaged in a trade or business in the United States. If ACGL or any of its non-U.S. subsidiaries were subject to U.S. income tax, ACGL’s shareholders’ equity and earnings could be materially adversely affected. ACGL has subsidiaries and branches that operate in various jurisdictions around the world that are subject to tax in the jurisdictions in which they operate. The significant jurisdictions in which ACGL’s subsidiaries and branches are subject to tax are the United States, United Kingdom, Ireland, Canada, Switzerland and Denmark.

	The Company’s income tax provision on income before income taxes resulted in an expense of 2.0% for the three months ended March 31, 2014, compared to an expense of 1.9% for the 2013 period. The Company’s effective tax rate, which is based upon the expected annual effective tax rate, may fluctuate from period to period based on the relative mix of income or loss reported by jurisdiction and the varying tax rates in each jurisdiction. The Company had a net deferred tax asset of $151.2 million at March 31, 2014, compared to $128.6 million at December 31, 2013. In addition, the Company paid $1.6 million in income taxes for the three months ended March 31, 2014, while the Company paid $1.3 million for the 2013 period.

Other_Comprehensive_Income_Los

Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2014
Comprehensive Income Note Disclosure [Abstract]	'
Other Comprehensive Income (Loss)	'
	Other Comprehensive Income (Loss)

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


					Amounts Reclassed from AOCI
			Consolidated Statement of Income		Three Months Ended
			Line Item That Includes		March 31,
	Details About AOCI Components		Reclassification		2014				2013

	Unrealized appreciation on available-for-sale investments
			Net realized gains		$	26,038			$	44,367

			Other-than-temporary impairment losses		(2,971		)		(2,248		)
			Total before tax		23,067				42,119

			Income tax expense		(1,818		)		(3,418		)
			Net of tax		$	21,249			$	38,701


	The following table presents the tax effects allocated to each component of other comprehensive income (loss):


		Before Tax Amount				Tax Expense (Benefit)				Net of Tax Amount
	Three Months Ended March 31, 2014
	Unrealized appreciation (decline) in value of investments:
	Unrealized holding gains (losses) arising during period	$	75,400			$	4,047			$	71,353

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

	Less reclassification of net realized gains included in net income	23,067				1,818				21,249

	Foreign currency translation adjustments	(1,349		)		—				(1,349		)

	Other comprehensive income (loss)	$	50,984			$	2,229			$	48,755


	Three Months Ended March 31, 2013
	Unrealized appreciation (decline) in value of investments:
	Unrealized holding gains (losses) arising during period	$	10,347			$	876			$	9,471

	Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss)	(2		)		—				(2		)

	Less reclassification of net realized gains included in net income	42,119				3,418				38,701

	Foreign currency translation adjustments	(28,222		)		—				(28,222		)

	Other comprehensive income (loss)	$	(59,996	)		$	(2,542	)		$	(57,454	)

Guarantor_Financial_Informatio

Guarantor Financial Information	3 Months Ended
	Mar. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Guarantor Financial Information	'
	Guarantor Financial Information

	The following tables present condensed financial information for ACGL, Arch Capital Group (U.S.) Inc. (“Arch-U.S.”), a 100% owned subsidiary of ACGL, and ACGL’s other subsidiaries.


			31-Mar-14
	Condensed Consolidating Balance Sheet		ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
	Assets
	Total investments		$	2,546			$	48,689			$	13,792,262			$	—			$	13,843,497

	Cash		12,353				45,472				1,511,780				—				1,569,605

	Investments in subsidiaries		6,288,035				1,598,732				—				(7,886,767		)		—

	Due from subsidiaries and affiliates		503				—				401,987				(402,490		)		—

	Premiums receivable		—				—				1,399,825				(391,450		)		1,008,375

	Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses		—				—				5,617,877				(3,827,852		)		1,790,025

	Contractholder receivables		—				—				1,118,991				—				1,118,991

	Prepaid reinsurance premiums		—				—				1,293,460				(944,383		)		349,077

	Deferred acquisition costs, net		—				—				384,294				—				384,294

	Other assets		6,309				62,500				2,211,353				(543,668		)		1,736,494

		Total assets	$	6,309,746			$	1,755,393			$	27,731,829			$	(13,996,610	)		$	21,800,358


	Liabilities
	Reserve for losses and loss adjustment expenses		$	—			$	—			$	12,749,908			$	(3,810,950	)		$	8,938,958

	Unearned premiums		—				—				3,092,858				(944,383		)		2,148,475

	Reinsurance balances payable		—				—				742,630				(540,836		)		201,794

	Contractholder payables		—				—				1,118,991				—				1,118,991

	Deposit accounting liabilities		—				—				735,993				(326,913		)		409,080

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

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

	Due to subsidiaries and affiliates		2,091				1,167				399,232				(402,490		)		—

	Other liabilities		15,522				46,040				1,200,906				(84,271		)		1,178,197

		Total liabilities	417,613				547,207				20,040,518				(6,109,843		)		14,895,495


	Redeemable noncontrolling interests (1)		—				—				219,234				—				219,234


	Shareholders’ Equity
	Total shareholders’ equity available to Arch		5,892,133				1,208,186				6,678,581				(7,886,767		)		5,892,133

	Non-redeemable noncontrolling interests (1)		—				—				793,496				—				793,496

		Total shareholders’ equity	5,892,133				1,208,186				7,472,077				(7,886,767		)		6,685,629


	Total liabilities, noncontrolling interests and shareholders’ equity	$	6,309,746			$	1,755,393			$	27,731,829			$	(13,996,610	)		$	21,800,358


(1) See Note 4.





		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


Redeemable noncontrolling interests		—				—				—				—				—


Shareholders’ Equity
Total shareholders’ equity available to Arch		5,647,496				1,185,241				6,119,708				(7,304,949		)		5,647,496

Non-redeemable noncontrolling interests		—				—				—				—				—

	Total shareholders’ equity	5,647,496				1,185,241				6,119,708				(7,304,949		)		5,647,496


	Total liabilities, noncontrolling interests and shareholders’ equity	$	6,060,662			$	1,728,697			$	24,996,730			$	(13,219,995	)		$	19,566,094








		Three Months Ended March 31, 2014
Condensed Consolidating Statement of Income and Comprehensive Income		ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
Revenues
Net premiums earned		$	—			$	—			$	859,780			$	—			$	859,780

Net investment income		—				—				77,001				(10,007		)		66,994

Net realized gains		—				—				19,697				—				19,697

Net impairment losses recognized in earnings		—				—				(2,971		)		—				(2,971		)

Other underwriting income		—				—				1,582				—				1,582

Equity in net income of investment funds accounted for using the equity method		—				—				3,253				—				3,253

Other income (loss)		—				—				(2,104		)		—				(2,104		)

	Total revenues	—				—				956,238				(10,007		)		946,231


Expenses
Losses and loss adjustment expenses		—				—				436,240				—				436,240

Acquisition expenses		—				—				160,342				—				160,342

Other operating expenses		10,307				977				134,515				—				145,799

Interest expense		5,853				6,514				12,044				(10,007		)		14,404

Net foreign exchange losses		—				—				5,741				822				6,563

	Total expenses	16,160				7,491				748,882				(9,185		)		763,348


Income (loss) before income taxes		(16,160		)		(7,491		)		207,356				(822		)		182,883

Income tax benefit (expense)		—				2,788				(6,526		)		—				(3,738		)

Income (loss) before equity in net income of subsidiaries		(16,160		)		(4,703		)		200,830				(822		)		179,145

Equity in net income of subsidiaries		198,660				22,152				—				(220,812		)		—

Net income		182,500				17,449				200,830				(221,634		)		179,145

Net (income) loss attributable to noncontrolling interests (1)		—				—				3,355				—				3,355

Net income available to Arch		182,500				17,449				204,185				(221,634		)		182,500

Preferred dividends		(5,484		)		—				—				—				(5,484		)

Net income available to Arch common shareholders		$	177,016			$	17,449			$	204,185			$	(221,634	)		$	177,016


Comprehensive income available to Arch		$	231,255			$	17,220			$	252,119			$	(269,339	)		$	231,255


(1) See Note 4.




		Three Months Ended March 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		$	—			$	—			$	752,770			$	—			$	752,770

Net investment income		—				—				72,322				(6,650		)		65,672

Net realized gains		—				—				58,340				—				58,340

Net impairment losses recognized in earnings		—				—				(2,246		)		—				(2,246		)

Other underwriting income		—				—				538				—				538

Equity in net income of investment funds accounted for using the equity method		—				—				13,823				—				13,823

Other income		—				—				1,244				—				1,244

	Total revenues	—				—				896,791				(6,650		)		890,141


Expenses
Losses and loss adjustment expenses		—				—				399,403				—				399,403

Acquisition expenses		—				—				127,592				—				127,592

Other operating expenses		9,942				777				109,464				—				120,183

Interest expense		5,820				3				6,725				(6,650		)		5,898

Net foreign exchange (gains) losses		—				—				(12,772		)		(11,492		)		(24,264		)

	Total expenses	15,762				780				630,412				(18,142		)		628,812


Income (loss) before income taxes		(15,762		)		(780		)		266,379				11,492				261,329

Income tax benefit (expense)		—				235				(5,088		)		—				(4,853		)

Income (loss) before equity in net income of subsidiaries		(15,762		)		(545		)		261,291				11,492				256,476

Equity in net income (loss) of subsidiaries		272,238				18,482				—				(290,720		)		—

Net income		256,476				17,937				261,291				(279,228		)		256,476

Net (income) loss attributable to noncontrolling interests		—				—				—				—				—

Net income available to Arch		256,476				17,937				261,291				(279,228		)		256,476

Preferred dividends		(5,484		)		—				—				—				(5,484		)

Net income available to Arch common shareholders		$	250,992			$	17,937			$	261,291			$	(279,228	)		$	250,992


Comprehensive income available to Arch		$	199,022			$	6,152			$	215,329			$	(221,481	)		$	199,022







				Three Months Ended March 31, 2014
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 Operating Activities			$	11,685			$	7,151			$	194,833			$	(15,500	)		$	198,169

Investing Activities
Purchases of fixed maturity investments				—				—				(7,131,071		)		—				(7,131,071		)

Purchases of equity securities				—				—				(89,227		)		—				(89,227		)

Purchases of other investments				—				—				(304,454		)		—				(304,454		)

Proceeds from the sales of fixed maturity investments				—				—				7,014,281				—				7,014,281

Proceeds from the sales of equity securities				—				—				49,614				—				49,614

Proceeds from the sales of other investments				—				—				331,176				—				331,176

Proceeds from redemptions and maturities of fixed maturity investments				—				—				168,484				—				168,484

Net (purchases) sales of short-term investments				(16		)		360,269				(203,991		)		—				156,262

Change in investment of securities lending collateral				—				—				4,669				—				4,669

Contributions to subsidiaries				—				(312,207		)		(100,000		)		412,207				—

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

Purchase of business, net of cash acquired				—				—				(235,578		)		—				(235,578		)

Purchases of furniture, equipment and other assets				(76		)		—				(5,306		)		—				(5,382		)

	Net Cash Provided By (Used For) Investing Activities			(92		)		48,062				(491,153		)		401,957				(41,226		)

Financing Activities
Proceeds from common shares issued, net				3,021				—				412,207				(412,207		)		3,021

Repayments of intercompany borrowings				—				(10,250		)		—				10,250				—

Change in securities lending collateral				—				—				(4,669		)		—				(4,669		)

Third party investment in non-redeemable noncontrolling interests (1)				—				—				796,903				—				796,903

Third party investment in redeemable noncontrolling interests (1				—				—				186,893				—				186,893

Dividends paid to parent				—				—				(15,500		)		15,500				—

Other				—				—				1,700				—				1,700

Preferred dividends paid				(5,484		)		—				—				—				(5,484		)

	Net Cash Provided By (Used For) Financing Activities			(2,463		)		(10,250		)		1,377,534				(386,457		)		978,364

Effects of exchange rates changes on foreign currency cash				—				—				241				—				241

Increase in cash				9,130				44,963				1,081,455				—				1,135,548

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

Cash end of period				$	12,353			$	45,472			$	1,511,780			$	—			$	1,569,605


(1) See Note 4.




				Three Months Ended March 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) Operating Activities			$	34,432			$	(254	)		$	216,481			$	(45,000	)		$	205,659

Investing Activities
Purchases of fixed maturity investments				—				—				(3,970,320		)		—				(3,970,320		)

Purchases of equity securities				—				—				(63,353		)		—				(63,353		)

Purchases of other investments				—				—				(250,442		)		—				(250,442		)

Proceeds from the sales of fixed maturity investments				—				—				3,796,638				—				3,796,638

Proceeds from the sales of equity securities				—				—				81,513				—				81,513

Proceeds from the sales of other investments				—				—				280,010				—				280,010

Proceeds from redemptions and maturities of fixed maturity investments				—				—				181,727				—				181,727

Net (purchases) sales of short-term investments				7,964				(2		)		(229,406		)		—				(221,444		)

Change in investment of securities lending collateral				—				—				(41,019		)		—				(41,019		)

Contributions to subsidiaries				—				(10,250		)		(250		)		10,500				—

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

Purchases of furniture, equipment and other assets				(31		)		—				(3,711		)		—				(3,742		)

	Net Cash Provided By (Used For) Investing Activities			7,933				(10,252		)		(228,863		)		20,750				(210,432		)

Financing Activities
Purchases of common shares under share repurchase program				(40,964		)		—				—				—				(40,964		)

Proceeds from common shares issued, net				1,280				—				10,500				(10,500		)		1,280

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

Change in securities lending collateral				—				—				41,019				—				41,019

Dividends paid to parent				—				—				(45,000		)		45,000				—

Other				—				—				1,084				—				1,084

Preferred dividends paid				(5,484		)		—				—				—				(5,484		)

	Net Cash Provided By (Used For) Financing Activities			(45,168		)		10,250				7,603				24,250				(3,065		)

Effects of exchange rates changes on foreign currency cash				—				—				(6,436		)		—				(6,436		)

Increase (decrease) in cash				(2,803		)		(256		)		(11,215		)		—				(14,274		)

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

Cash end of period				$	3,614			$	356			$	352,797			$	—			$	356,767

Legal_Proceedings

Legal Proceedings	3 Months Ended
Legal Proceedings	Mar. 31, 2014
Disclosure Legal Proceedings [Abstract]	'
Legal Proceedings	'
	Legal Proceedings

	The Company, in common with the insurance industry in general, is subject to litigation and arbitration in the normal course of its business. As of March 31, 2014, 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.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	3 Months Ended
Significant Accounting Policies (Policies)	Mar. 31, 2014
Accounting Policies [Abstract]	'
Basis of presentation	'
Basis of presentation	The interim consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and Watford. All significant intercompany transactions and balances have been eliminated in consolidation.
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. In the opinion of management, the accompanying unaudited interim consolidated financial statements reflect all adjustments (consisting of normally recurring accruals) necessary for a fair statement of results on an interim basis. The results of any interim period are not necessarily indicative of the results for a full year or any future periods.
Premium revenues	'
	Insurance. Insurance premiums written are generally recorded at the policy inception and are primarily earned on a pro rata basis over the terms of the policies for all products, usually 12 months. Premiums written include estimates in the Company’s programs, specialty lines, lenders products business and for participation in involuntary pools. Such premium estimates are derived from multiple sources which include the historical experience of the underlying business, similar business and available industry information. Unearned premium reserves represent the portion of premiums written that relates to the unexpired terms of in-force insurance policies.

	Reinsurance. Reinsurance premiums written include amounts reported by brokers and ceding companies, supplemented by the Company’s own estimates of premiums where reports have not been received. The determination of premium estimates requires a review of the Company’s experience with the ceding companies, familiarity with each market, the timing of the reported information, an analysis and understanding of the characteristics of each line of business, and management’s judgment of the impact of various factors, including premium or loss trends, on the volume of business written and ceded to the Company. On an ongoing basis, the Company’s underwriters review the amounts reported by these third parties for reasonableness based on their experience and knowledge of the subject class of business, taking into account the Company’s historical experience with the brokers or ceding companies. In addition, reinsurance contracts under which the Company assumes business generally contain specific provisions which allow the Company to perform audits of the ceding company to ensure compliance with the terms and conditions of the contract, including accurate and timely reporting of information. Based on a review of all available information, management establishes premium estimates where reports have not been received. Premium estimates are updated when new information is received and differences between such estimates and actual amounts are recorded in the period in which estimates are changed or the actual amounts are determined.

	Reinsurance premiums written are recorded based on the type of contracts the Company writes. Premiums on the Company’s excess of loss and pro rata reinsurance contracts are estimated when the business is underwritten. For excess of loss contracts, premiums are recorded as written based on the terms of the contract. Estimates of premiums written under pro rata contracts are recorded in the period in which the underlying risks are expected to incept and are based on information provided by the brokers and the ceding companies. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term.

	Reinstatement premiums for the Company’s insurance and reinsurance operations are recognized at the time a loss event occurs, where coverage limits for the remaining life of the contract are reinstated under pre-defined contract terms. Reinstatement premiums, if obligatory, are fully earned when recognized. The accrual of reinstatement premiums is based on an estimate of losses and loss adjustment expenses, which reflects management’s judgment. Premium estimates are reviewed by management at least quarterly. Such review includes a comparison of actual reported premiums to expected ultimate premiums along with a review of the aging and collection of premium estimates. Based on management’s review, the appropriateness of the premium estimates is evaluated, and any adjustment to these estimates is recorded in the period in which it becomes known. Adjustments to premium estimates could be material and such adjustments could directly and significantly impact earnings favorably or unfavorably in the period they are determined because the estimated premium may be fully or substantially earned. A significant portion of amounts included as premiums receivable, which represent estimated premiums written, net of commissions, are not currently due based on the terms of the underlying contracts.

	Reinsurance premiums written, irrespective of the class of business, are generally earned on a pro rata basis over the terms of the underlying policies or reinsurance contracts. Contracts and policies written on a “losses occurring” basis cover claims that may occur during the term of the contract or policy, which is typically 12 months. Accordingly, the premium is earned evenly over the term. Contracts which are written on a “risks attaching” basis cover claims which attach to the underlying insurance policies written during the terms of such contracts. Premiums earned on such contracts usually extend beyond the original term of the reinsurance contract, typically resulting in recognition of premiums earned over a 24-month period. Certain of the Company’s reinsurance contracts include provisions that adjust premiums or acquisition expenses based upon the experience under the contracts. Premiums written and earned, as well as related acquisition expenses, are recorded based upon the projected experience under such contracts.

	The Company also writes certain reinsurance business that is intended to provide insurers with risk management solutions that complement traditional reinsurance. Under these contracts, the Company assumes a measured amount of insurance risk in exchange for an anticipated margin, which is typically lower than on traditional reinsurance contracts. The terms and conditions of these contracts may include additional or return premiums based on loss experience, loss corridors, sublimits and caps. Examples of such business include aggregate stop-loss coverages, financial quota share coverages and multi- year retrospectively rated excess of loss coverages. If these contracts are deemed to transfer risk, they are accounted for as reinsurance.

	Mortgage. Mortgage guaranty insurance policies are contracts that are generally non-cancelable by the insurer, are renewable at a fixed price, and provide for payment of premiums on a monthly, annual or single basis. Upon renewal, the Company is not able to re-underwrite or re-price its policies. Consistent with industry accounting practices, premiums written on a monthly basis are earned as coverage is provided. Premiums written on an annual basis are amortized on a monthly pro rata basis over the year of coverage. Primary mortgage insurance premiums written on policies covering more than one year are referred to as single premiums. A portion of the revenue from single premiums is recognized in premiums earned in the current period, and the remaining portion is deferred as unearned premiums and earned over the expected life of the policy. If single premium policies related to insured loans are canceled due to repayment by the borrower, and the premium is non-refundable, the remaining unearned premium related to each canceled policy is recognized as earned premium upon notification of the cancellation.

	Unearned premiums represent the portion of premiums written that is applicable to the estimated unexpired risk of insured loans. A portion of premium payments may be refundable if the insured cancels coverage, which generally occurs when the loan is repaid, the loan amortizes to a sufficiently low amount to trigger a lender permitted or legally required cancellation, or the value of the property has increased sufficiently in accordance with the terms of the contract. Premium refunds reduce premiums earned in the consolidated statements of operations.
Deferred acquisition costs	'
	Acquisition Costs. Acquisition expenses and other expenses related to the Company’s underwriting operations that vary with, and are directly related to, the successful acquisition or renewal of business are deferred and amortized based on the type of contract. For property and casualty insurance and reinsurance contracts, deferred acquisition costs are amortized over the period in which the related premiums are earned. Consistent with mortgage insurance industry accounting practice, amortization of acquisition costs related to the mortgage insurance contracts for each underwriting year’s book of business is charged against revenue in proportion to estimated gross profits. Estimated gross profits are comprised of earned premiums, interest income, losses and loss adjustment expenses. For each underwriting year, the Company estimates the rate of amortization to reflect actual experience and any changes to persistency or loss development.

	Acquisition expenses, net of ceding commissions received from reinsurers, consist principally of commissions and premium taxes paid to obtain the Company’s business. Other operating expenses also include expenses that vary with, and are directly related to, the acquisition of business. Deferred acquisition costs are carried at their estimated realizable value and take into account anticipated losses and loss adjustment expenses, based on historical and current experience, and anticipated investment income. A premium deficiency occurs if the sum of anticipated losses and loss adjustment expenses, unamortized acquisition costs and maintenance costs exceed unearned premiums 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.
Reserve for losses and loss adjustment expenses	'
	Insurance and Reinsurance. The reserve for losses and loss adjustment expenses consists of estimates of unpaid reported losses and loss adjustment expenses and estimates for losses incurred but not reported. The reserve for unpaid reported losses and loss adjustment expenses, established by management based on reports from ceding companies and claims from insureds, excludes estimates of amounts 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.

	Mortgage. The reserves for mortgage guaranty insurance losses and loss adjustment expenses are the estimated claim settlement costs on notices of default that have been received by the Company, as well as loan defaults that have been incurred but have not been reported by the lenders. Consistent with industry accounting practice, the Company does not establish loss reserves for future claims on insured loans that are not currently in default (defined as two consecutive missed payments). The Company establishes loss reserves on a case-by-case basis when insured loans are identified as currently in default using estimated claim rates and average claim sizes for each report year, net of any salvage recoverable. The Company also reserves for defaults that have occurred but have not yet been reported to the Company prior to the close of an accounting period. To determine this reserve, the Company estimates the number of defaults not yet reported using historical information regarding late reported delinquencies and applies estimated claim rates and claim sizes for the estimated defaults not yet reported.

	The establishment of reserves across the Company’s segments is an inherently uncertain process, are necessarily based on estimates, and the ultimate net cost may vary from such estimates. The methods for making such estimates and for establishing the resulting liability are reviewed and updated using the most current information available. Any resulting adjustments, which may be material, are reflected in current operations
Goodwill and intangible assets	'
	Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired and is assigned to the applicable reporting unit at acquisition. Goodwill is not amortized and is evaluated for impairment on an annual basis. Impairment tests may be performed more frequently if the facts and circumstances indicate a possible impairment. In performing impairment tests, the Company may first assess qualitative factors to determine whether it is more likely than not (that is, more than a 50% probability) that the fair value of a reporting unit exceeds its carrying amount as a basis for determining whether it is necessary to perform the two-step goodwill impairment test described in the accounting guidance.

	Indefinite-lived intangible assets, such as insurance licenses, are not amortized and are evaluated for impairment similar to goodwill. Finite-lived intangible assets and liabilities include the value of insurance and reinsurance contracts, which are estimated based on the present value of future expected cash flows and amortized in ‘acquisition expenses’ in proportion to the estimated profits expected to be realized. Other finite-lived intangible assets or liabilities, including favorable or unfavorable contracts, are amortized in ‘other operating expenses’ over their useful lives. Finite-lived intangible assets and liabilities are periodically reviewed for indicators of impairment. An impairment is recognized when the carrying amount is not recoverable from its undiscounted cash flows and is measured as the difference between the carrying amount and fair value.

	If goodwill or intangible assets are impaired, such assets are written down to their realizable values with the related expense recorded in the Company’s results of operations.

Business_Acquired_Tables

Business Acquired (Tables)	3 Months Ended
	Mar. 31, 2014
Business Combinations [Abstract]	'
Summary of fair value of net assets acquired and allocation of purchase price	'
	The following table summarizes the fair value of net assets acquired and allocation of purchase price:


		Total		Useful Life
	Purchase price
	Cash paid	$	245,157

	Contingent consideration liability	41,762

	Total purchase price (a)	$	286,919


	Assets acquired
	Cash	$	9,579

	Investments, at fair value	312,093

	Intangible asset -- acquired insurance contracts	46,473		5 years

	Intangible asset -- operating platform	29,900		5 years

	Intangible asset -- favorable lease contract	1,056		5 years

	Intangible asset -- insurance licenses	16,858		Indefinite

	Other assets acquired	21,691

	Total assets acquired	437,650


	Liabilities acquired
	Reserves for losses and loss adjustment expenses	$	121,572

	Unearned premiums	26,261

	Intangible liability -- unfavorable service contract	9,533		9 years

	Other liabilities acquired	7,217

	Total liabilities acquired	164,583

	Net assets acquired (b)	$	273,067

	Goodwill (a)-(b)	$	13,852

Variable_Interest_Entities_and1

Variable Interest Entities and Noncontrolling Interests (Tables)	3 Months Ended
	Mar. 31, 2014
Noncontrolling Interest [Abstract]	'
Activity in non-redeemable noncontrolling interests	'
	The following table sets forth activity in the non-redeemable noncontrolling interests:


		Three Months Ended March 31, 2014
	Balance, beginning of year	$	—

	Sale of shares to noncontrolling interests	796,903

	Net (loss) income attributable to noncontrolling interests	(3,407		)
	Balance, end of period	$	793,496

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
Schedule of computation of basic and diluted earnings per common share	'
	The following table sets forth the computation of basic and diluted earnings per common share:


		Three Months Ended
		March 31,
		2014			2013

	Numerator:

	Net income	$	179,145		$	256,476

	Net (income) loss attributable to noncontrolling interests	3,355			—

	Net income available to Arch	182,500			256,476

	Preferred dividends	(5,484		)	(5,484		)
	Net income available to Arch common shareholders	$	177,016		$	250,992


	Denominator:

	Weighted average common shares outstanding — basic	131,857,910			130,907,902

	Effect of dilutive common share equivalents:

	Nonvested restricted shares	1,346,401			1,290,161

	Stock options (1)	3,358,406			3,211,225

	Weighted average common shares and common share equivalents outstanding — diluted	136,562,717			135,409,288


	Earnings per common share:

	Basic	$	1.34		$	1.92

	Diluted	$	1.3		$	1.85

	_________________________________________________

	-1	Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2014 first quarter and 2013 first quarter, the number of stock options excluded were 759,172 and 1,016,043, respectively.

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Analysis of underwriting income by segment and reconciliation to net income available to common shareholders	'
	The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income or loss to net income available to common shareholders:


		Three Months Ended
		31-Mar-14
		Insurance				Reinsurance				Mortgage				Sub-Total				Other				Total

	Gross premiums written (1)	$	730,646			$	517,053			$	47,907			$	1,295,136			$	32,194			$	1,295,136

	Premiums ceded	(185,044		)		(73,127		)		(4,639		)		(262,340		)		—				(230,146		)

	Net premiums written	545,602				443,926				43,268				1,032,796				32,194				1,064,990

	Change in unearned premiums	(68,101		)		(102,578		)		(4,503		)		(175,182		)		(30,028		)		(205,210		)
	Net premiums earned	477,501				341,348				38,765				857,614				2,166				859,780

	Other underwriting income	500				316				766				1,582				—				1,582

	Losses and loss adjustment expenses	(286,770		)		(139,636		)		(8,478		)		(434,884		)		(1,356		)		(436,240		)
	Acquisition expenses, net	(76,932		)		(73,433		)		(9,154		)		(159,519		)		(823		)		(160,342		)
	Other operating expenses	(81,144		)		(36,195		)		(13,876		)		(131,215		)		(1,109		)		(132,324		)
	Underwriting income (loss)	$	33,155			$	92,400			$	8,023			133,578				(1,122		)		132,456


	Net investment income													66,993				1				66,994

	Net realized gains													19,697				—				19,697

	Net impairment losses recognized in earnings													(2,971		)		—				(2,971		)

	Equity in net income of investment funds accounted for using the equity method													3,253				—				3,253

	Other income (loss)													(2,104		)		—				(2,104		)

	Other expenses													(10,799		)		(2,676		)		(13,475		)

	Interest expense													(14,404		)		—				(14,404		)

	Net foreign exchange gains (losses)													(6,656		)		93				(6,563		)

	Income before income taxes													186,587				(3,704		)		182,883

	Income tax expense													(3,738		)		—				(3,738		)

	Net income (loss)													182,849				(3,704		)		179,145

	Net (income) loss attributable to noncontrolling interests													—				3,355				3,355

	Net income available to Arch													182,849				(349		)		182,500

	Preferred dividends													(5,484		)		—				(5,484		)

	Net income available to Arch common shareholders													$	177,365			$	(349	)		$	177,016


	Underwriting Ratios

	Loss ratio	60.1		%		40.9		%		21.9		%		50.7		%		62.6		%		50.7		%
	Acquisition expense ratio (2)	16		%		21.5		%		23.6		%		18.5		%		38		%		18.6		%
	Other operating expense ratio	17		%		10.6		%		35.8		%		15.3		%		51.2		%		15.4		%
	Combined ratio	93.1		%		73		%		81.3		%		84.5		%		151.8		%		84.7		%

	Total investable assets													$	14,261,106			$	1,083,280			$	15,344,386

Total assets													20,653,897				1,146,461				21,800,358

Total liabilities													14,860,124				35,371				14,895,495

_________________________________________________

-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.



	Three Months Ended
	31-Mar-13
	Insurance				Reinsurance				Mortgage				Sub-Total				Other				Total

Gross premiums written (1)	$	688,817			$	450,447			$	25,758			$	1,163,699			$	—			$	1,163,699

Premiums ceded	(184,267		)		(27,979		)		—				(210,923		)		—				(210,923		)

Net premiums written	504,550				422,468				25,758				952,776				—				952,776

Change in unearned premiums	(59,585		)		(126,315		)		(14,106		)		(200,006		)		—				(200,006		)

Net premiums earned	444,965				296,153				11,652				752,770				—				752,770

Other underwriting income	525				13				—				538				—				538

Losses and loss adjustment expenses	(283,467		)		(113,857		)		(2,079		)		(399,403		)		—				(399,403		)

Acquisition expenses, net	(70,758		)		(53,143		)		(3,691		)		(127,592		)		—				(127,592		)

Other operating expenses	(76,315		)		(32,197		)		(1,403		)		(109,915		)		—				(109,915		)

Underwriting income	$	14,950			$	96,969			$	4,479			116,398				—				116,398


Net investment income													65,672				—				65,672

Net realized gains													58,340				—				58,340

Net impairment losses recognized in earnings													(2,246		)		—				(2,246		)

Equity in net income of investment funds accounted for using the equity method													13,823				—				13,823

Other income (loss)													1,244				—				1,244

Other expenses													(10,268		)		—				(10,268		)

Interest expense													(5,898		)		—				(5,898		)

Net foreign exchange gains													24,264				—				24,264

Income before income taxes													261,329				—				261,329

Income tax expense													(4,853		)		—				(4,853		)

Net income													256,476				—				256,476

Net (income) loss attributable to noncontrolling interests													—				—				—

Net income available to Arch													256,476				—				256,476

Preferred dividends													(5,484		)		—				(5,484		)

Net income available to Arch common shareholders													$	250,992			$	—			$	250,992


Underwriting Ratios

Loss ratio	63.7		%		38.4		%		17.8		%		53.1		%		—		%		53.1		%
Acquisition expense ratio (2)	15.8		%		17.9		%		31.7		%		16.9		%		—		%		16.9		%
Other operating expense ratio	17.2		%		10.9		%		12		%		14.6		%		—		%		14.6		%
Combined ratio	96.7		%		67.2		%		61.5		%		84.6		%		—		%		84.6		%

Total investable assets													$	13,132,116			$	—			$	13,132,116

Total assets													18,757,061				—				18,757,061

Total liabilities													13,421,531				—				13,421,531

_________________________________________________

-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 other underwriting income.

Investment_Information_Tables

Investment Information (Tables)	3 Months Ended
	Mar. 31, 2014
Disclosure Investment Information [Abstract]	'
Summary of fair value and cost or amortized cost of available for sale securities	'
	The following table summarizes the fair value and cost or amortized cost of the Company’s investments classified as available for sale:


		Fair				Gross				Gross				Cost or				OTTI
		Value				Unrealized				Unrealized				Amortized				Unrealized
						Gains				Losses				Cost				Losses (2)
	31-Mar-14

	Fixed maturities and fixed maturities pledged under securities lending agreements (1):

	Corporate bonds	$	2,514,129			$	39,704			$	(20,047	)		$	2,494,472			$	(16	)

	Mortgage backed securities	1,087,840				21,700				(14,253		)		1,080,393				(8,217		)

	Municipal bonds	1,410,043				28,494				(3,742		)		1,385,291				(17		)

	Commercial mortgage backed securities	1,023,055				11,769				(9,031		)		1,020,317				—

	U.S. government and government agencies	1,153,120				4,048				(5,932		)		1,155,004				(19		)

	Non-U.S. government securities	1,114,382				14,538				(12,978		)		1,112,822				—

	Asset backed securities	1,573,751				11,143				(12,385		)		1,574,993				(2,902		)

	Total	9,876,320				131,396				(78,368		)		9,823,292				(11,171		)


	Equity securities	548,168				78,896				(6,596		)		475,868				—

	Other investments	426,917				24,398				(15,243		)		417,762				—

	Short-term investments	1,484,280				955				(2,053		)		1,485,378				—

	Total	$	12,335,685			$	235,645			$	(102,260	)		$	12,202,300			$	(11,171	)


	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	)

_________________________________________________

-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 March 31, 2014, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $4.8 million, compared to a net unrealized gain of $6.0 million at December 31, 2013.
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
		Fair				Gross				Fair				Gross				Fair			Gross
		Value				Unrealized				Value				Unrealized				Value			Unrealized
						Losses								Losses							Losses
	31-Mar-14

	Fixed maturities and fixed maturities pledged under securities lending agreements (1):

	Corporate bonds	$	1,012,076			$	(17,780	)		$	40,352			$	(2,267	)		$	1,052,428		$	(20,047	)

	Mortgage backed securities	434,286				(11,841		)		23,033				(2,412		)		457,319			(14,253		)

	Municipal bonds	340,349				(3,484		)		3,741				(258		)		344,090			(3,742		)

	Commercial mortgage backed securities	398,428				(8,977		)		581				(54		)		399,009			(9,031		)

	U.S. government and government agencies	764,802				(5,932		)		—				—				764,802			(5,932		)

	Non-U.S. government securities	541,534				(10,940		)		36,298				(2,038		)		577,832			(12,978		)

	Asset backed securities	904,539				(8,424		)		99,179				(3,961		)		1,003,718			(12,385		)

	Total	4,396,014				(67,378		)		203,184				(10,990		)		4,599,198			(78,368		)

	Equity securities	102,589				(6,596		)		—				—				102,589			(6,596		)

	Other investments	156,468				(15,243		)		—				—				156,468			(15,243		)

	Short-term investments	180,233				(2,053		)		—				—				180,233			(2,053		)

	Total	$	4,835,304			$	(91,270	)		$	203,184			$	(10,990	)		$	5,038,488		$	(102,260	)


	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		)		—				—				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	)

_________________________________________________

-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	'
	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.


			31-Mar-14								31-Dec-13
	Maturity		Fair Value				Amortized				Fair Value				Amortized
							Cost								Cost
	Due in one year or less		$	286,950			$	282,281			$	235,330			$	232,652

	Due after one year through five years		3,757,966				3,731,777				3,738,500				3,718,920

	Due after five years through 10 years		1,883,374				1,872,047				1,966,536				1,979,510

	Due after 10 years		263,384				261,484				196,305				198,286

			6,191,674				6,147,589				6,136,671				6,129,368

	Mortgage backed securities		1,087,840				1,080,393				1,133,095				1,139,034

	Commercial mortgage backed securities		1,023,055				1,020,317				1,074,497				1,075,749

	Asset backed securities		1,573,751				1,574,993				1,332,594				1,326,356

	Total		$	9,876,320			$	9,823,292			$	9,676,857			$	9,670,507

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


		March 31,				December 31,
		2014				2013
	Available for sale:
	Asian and emerging markets	$	266,023			$	331,984

	Investment grade fixed income	160,894				159,115

	Other	—				7,211

	Total available for sale	426,917				498,310

	Fair value option:
	Term loan investments (par value: $403,383 and $494,502)	410,430				512,076

	Asian and emerging markets	14,817				14,054

	Investment grade fixed income	91,907				75,062

	Other (1)	282,670				172,088

	Total fair value option	799,824				773,280

	Total	$	1,226,741			$	1,271,590

	_________________________________________________

	-1	Includes fund investments with strategies in mortgage servicing rights, transportation and infrastructure assets and other.
Summary of assets and liabilities accounted for using the fair value option	'
	The following table summarizes the Company’s assets and liabilities which are accounted for using the fair value option:


		March 31,				December 31,
		2014				2013
	Fixed maturities	$	456,826			$	448,254

	Other investments	799,824				773,280

	Investments accounted for using the fair value option	$	1,256,650			$	1,221,534


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


		Three Months Ended
		March 31,
		2014				2013
	Fixed maturities	$	62,449			$	62,006

	Term loan investments	5,669				4,217

	Equity securities (dividends)	2,921				1,423

	Short-term investments	406				392

	Other (1)	4,718				6,299

	Gross investment income	76,163				74,337

	Investment expenses	(9,169		)		(8,665		)
	Net investment income	$	66,994			$	65,672

	_________________________________________________

	-1	Includes dividends on investment funds and other items.
Summary of net realized gains (losses)	'
	Net realized gains (losses) were as follows, excluding other-than-temporary impairment provisions:


		Three Months Ended
		March 31,
		2014				2013
	Available for sale securities:

	Gross gains on investment sales	$	66,051			$	67,020

	Gross losses on investment sales	(40,013		)		(25,056		)
	Change in fair value of assets and liabilities accounted for using the fair value option:

	Fixed maturities	(1,643		)		5,058

	Other investments	10,776				9,951

	Equity securities	—				699

	Derivative instruments (1)	(12,768		)		(378		)
	Other (2)	(2,706		)		1,046

	Net realized gains (losses)	$	19,697			$	58,340

	_________________________________________________

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

	-2	Includes accretion of contingent liability amounts related to the acquisition of the CMG Entities (see Note 2 for further details).
Summary of OTTI recognized in earnings by asset class	'
	The following table details the net impairment losses recognized in earnings by asset class:


		Three Months Ended
		March 31,
		2014				2013
	Fixed maturities:

	Mortgage backed securities	$	—			$	(15	)

	Asset backed securities	(6		)		(20		)
	Total	(6		)		(35		)
	Equity securities	—				(2,211		)

	Other investments	(2,965		)		—

	Net impairment losses recognized in earnings	$	(2,971	)		$	(2,246	)
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:


		Three Months Ended
		March 31,
		2014				2013
	Balance at start of period	$	60,062			$	62,001

	Credit loss impairments recognized on securities not previously impaired	—				33

	Credit loss impairments recognized on securities previously impaired	6				2

	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	(12,812		)		(80		)
	Balance at end of period	$	47,256			$	61,956

Summary of restricted assets	'
	The following table details the value of the Company’s restricted assets:


		March 31,				December 31,
		2014				2013
	Assets used for collateral or guarantees:

	Affiliated transactions	$	4,346,385			$	4,060,533

	Third party agreements	951,609				856,890

	Deposits with U.S. regulatory authorities	350,284				302,809

	Deposits with non-U.S. regulatory authorities	2				6,546

	Trust funds	92,108				75,264

	Total restricted assets	$	5,740,388			$	5,302,042

Fair_Value_Tables

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2014
Fair Value Disclosures [Abstract]	'
Fair value hierarchy	'
	The following table presents the Company’s financial assets and liabilities measured at fair value by level at March 31, 2014:


						Fair Value Measurement Using:
		Fair				Quoted Prices in				Significant				Significant
		Value				Active Markets				Other				Unobservable
						for Identical				Observable				Inputs
						Assets				Inputs				(Level 3)
						(Level 1)				(Level 2)
	Assets measured at fair value:

	Available for sale securities:

	Fixed maturities and fixed maturities pledged under securities lending agreements (1):

	Corporate bonds	$	2,514,129			$	—			$	2,514,129			$	—

	Mortgage backed securities	1,087,840				—				1,087,840				—

	Municipal bonds	1,410,043				—				1,410,043				—

	Commercial mortgage backed securities	1,023,055				—				1,023,055				—

	U.S. government and government agencies	1,153,120				1,153,120				—				—

	Non-U.S. government securities	1,114,382				—				1,114,382				—

	Asset backed securities	1,573,751				—				1,573,751				—

	Total	9,876,320				1,153,120				8,723,200				—


	Equity securities	548,168				548,099				69				—

	Other investments	426,917				—				322,582				104,335

	Short-term investments	1,484,280				1,457,349				26,931				—


	Fair value option:

	Investments accounted for using the fair value option:

	Corporate bonds	353,644				—				353,644				—

	Non-U.S. government bonds	63,538				—				63,538				—

	Mortgage backed securities	39,644				—				39,644				—

	Other investments	799,824				—				380,678				419,146

	Total	1,256,650				—				837,504				419,146

	Total assets measured at fair value	$	13,592,335			$	3,158,568			$	9,910,286			$	523,481


	Liabilities measured at fair value:

	Contingent consideration liability	$	43,156			$	—			$	—			$	43,156

	Total liabilities measured at fair value	$	43,156			$	—			$	—			$	43,156

	_________________________________________________

-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, 2013:


					Fair Value Measurement Using:
	Fair				Quoted Prices in				Significant				Significant
	Value				Active Markets				Other				Unobservable
					for Identical				Observable				Inputs
					Assets				Inputs				(Level 3)
					(Level 1)				(Level 2)
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.
Rollforward of Level 3 investments	'
	The following tables present a reconciliation of the beginning and ending balances for all financial assets and liabilities measured at fair value on a recurring basis using Level 3 inputs:


		Fair Value Measurements Using:
		Significant Unobservable Inputs (Level 3)
		Assets															Liabilities
	s	Available-For-Sale								Fair Value Option
		Corporate				Other				Other				Total			Contingent Consideration Liability
		Bonds				Investments				Investments
	Three Months Ended March 31, 2014

	Balance at beginning of period	$	2,045			$	170,420			$	377,525			$	549,990		$	—

	Total gains or (losses) (realized/unrealized)

	Included in earnings (1)	—				2,275				6,310				8,585			(1,394		)

	Included in other comprehensive income	—				(2,196		)		—				(2,196		)	—

	Purchases, issuances, sales and settlements

	Purchases	—				—				40,110				40,110			—

	Issuances	—				—				—				—			(41,762		)

	Sales	(2,045		)		(66,164		)		—				(68,209		)	—

	Settlements	—				—				(4,799		)		(4,799		)	—

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

	Balance at end of period	$	—			$	104,335			$	419,146			$	523,481		$	(43,156	)


	Three Months Ended March 31, 2013

	Balance at beginning of period	$	98,404			$	184,202			$	195,350			$	477,956		$	—

	Total gains or (losses) (realized/unrealized)

	Included in earnings (1)	1,492				4,762				373				6,627			—

	Included in other comprehensive income	(1,688		)		1,912				—				224			—

	Purchases, issuances, sales and settlements

	Purchases	—				5,000				41,654				46,654			—

	Issuances	—				—				—				—			—

	Sales	—				—				—				—			—

	Settlements	(910		)		(9,942		)		(58,007		)		(68,859		)	—

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

	Balance at end of period	$	97,298			$	185,934			$	179,370			$	462,602		$	—

	_________________________________________________

	-1	Gains or losses on corporate bonds were included in net realized gains (losses) while gains or losses on other investments were included in net realized gains (losses) or net investment income. Gains or losses on the contingent consideration liability were included in net realized gains (losses).

Derivative_Instruments_Tables

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2014
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 (1)
	31-Mar-14

	Futures contracts	$	469			$	(769	)		$	(300	)	$	1,056,045

	Foreign currency forward contracts	693				(1,565		)		(872		)	244,614

	TBAs	216,548				(211,763		)		4,785			412,800

	Other	1,349				(844		)		505			690,029

	Total	$	219,059			$	(214,941	)		$	4,118


	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

Summary of net realized gains (losses) recorded in the consolidated statements of income	'
	The following table summarizes net realized gains (losses) recorded on the Company’s derivative instruments in the consolidated statements of income:


			Three Months Ended
	Derivatives not designated as		March 31,
	hedging instruments		2014				2013
	Futures contracts		$	(9,862	)		$	(829	)
	Foreign currency forward contracts		(2,257		)		(725		)
	TBAs		(37		)		541

	Other		(612		)		635

	Total		$	(12,768	)		$	(378	)

Other_Comprehensive_Income_Los1

Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2014
Comprehensive Income Note Disclosure [Abstract]	'
Details about amounts reclassified from AOCI	'
	The following table presents details about amounts reclassified from accumulated other comprehensive income:


					Amounts Reclassed from AOCI
			Consolidated Statement of Income		Three Months Ended
			Line Item That Includes		March 31,
	Details About AOCI Components		Reclassification		2014				2013

	Unrealized appreciation on available-for-sale investments
			Net realized gains		$	26,038			$	44,367

			Other-than-temporary impairment losses		(2,971		)		(2,248		)
			Total before tax		23,067				42,119

			Income tax expense		(1,818		)		(3,418		)
			Net of tax		$	21,249			$	38,701

Schedule of comprehensive income (loss)	'
	The following table presents the tax effects allocated to each component of other comprehensive income (loss):


		Before Tax Amount				Tax Expense (Benefit)				Net of Tax Amount
	Three Months Ended March 31, 2014
	Unrealized appreciation (decline) in value of investments:
	Unrealized holding gains (losses) arising during period	$	75,400			$	4,047			$	71,353

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

	Less reclassification of net realized gains included in net income	23,067				1,818				21,249

	Foreign currency translation adjustments	(1,349		)		—				(1,349		)

	Other comprehensive income (loss)	$	50,984			$	2,229			$	48,755


	Three Months Ended March 31, 2013
	Unrealized appreciation (decline) in value of investments:
	Unrealized holding gains (losses) arising during period	$	10,347			$	876			$	9,471

	Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss)	(2		)		—				(2		)

	Less reclassification of net realized gains included in net income	42,119				3,418				38,701

	Foreign currency translation adjustments	(28,222		)		—				(28,222		)

	Other comprehensive income (loss)	$	(59,996	)		$	(2,542	)		$	(57,454	)

Guarantor_Financial_Informatio1

Guarantor Financial Information (Tables)	3 Months Ended
	Mar. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Condensed consolidating balance sheet	'


			31-Mar-14
	Condensed Consolidating Balance Sheet		ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
	Assets
	Total investments		$	2,546			$	48,689			$	13,792,262			$	—			$	13,843,497

	Cash		12,353				45,472				1,511,780				—				1,569,605

	Investments in subsidiaries		6,288,035				1,598,732				—				(7,886,767		)		—

	Due from subsidiaries and affiliates		503				—				401,987				(402,490		)		—

	Premiums receivable		—				—				1,399,825				(391,450		)		1,008,375

	Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses		—				—				5,617,877				(3,827,852		)		1,790,025

	Contractholder receivables		—				—				1,118,991				—				1,118,991

	Prepaid reinsurance premiums		—				—				1,293,460				(944,383		)		349,077

	Deferred acquisition costs, net		—				—				384,294				—				384,294

	Other assets		6,309				62,500				2,211,353				(543,668		)		1,736,494

		Total assets	$	6,309,746			$	1,755,393			$	27,731,829			$	(13,996,610	)		$	21,800,358


	Liabilities
	Reserve for losses and loss adjustment expenses		$	—			$	—			$	12,749,908			$	(3,810,950	)		$	8,938,958

	Unearned premiums		—				—				3,092,858				(944,383		)		2,148,475

	Reinsurance balances payable		—				—				742,630				(540,836		)		201,794

	Contractholder payables		—				—				1,118,991				—				1,118,991

	Deposit accounting liabilities		—				—				735,993				(326,913		)		409,080

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

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

	Due to subsidiaries and affiliates		2,091				1,167				399,232				(402,490		)		—

	Other liabilities		15,522				46,040				1,200,906				(84,271		)		1,178,197

		Total liabilities	417,613				547,207				20,040,518				(6,109,843		)		14,895,495


	Redeemable noncontrolling interests (1)		—				—				219,234				—				219,234


	Shareholders’ Equity
	Total shareholders’ equity available to Arch		5,892,133				1,208,186				6,678,581				(7,886,767		)		5,892,133

	Non-redeemable noncontrolling interests (1)		—				—				793,496				—				793,496

		Total shareholders’ equity	5,892,133				1,208,186				7,472,077				(7,886,767		)		6,685,629


		Total liabilities, noncontrolling interests and shareholders’ equity	$	6,309,746			$	1,755,393			$	27,731,829			$	(13,996,610	)		$	21,800,358


(1) See Note 4.





		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


Redeemable noncontrolling interests		—				—				—				—				—


Shareholders’ Equity
Total shareholders’ equity available to Arch		5,647,496				1,185,241				6,119,708				(7,304,949		)		5,647,496

Non-redeemable noncontrolling interests		—				—				—				—				—

	Total shareholders’ equity	5,647,496				1,185,241				6,119,708				(7,304,949		)		5,647,496


	Total liabilities, noncontrolling interests and shareholders’ equity	$	6,060,662			$	1,728,697			$	24,996,730			$	(13,219,995	)		$	19,566,094


Condensed consolidating statement of income and comprehensive income	'


			Three Months Ended March 31, 2014
	Condensed Consolidating Statement of Income and Comprehensive Income		ACGL (Parent Guarantor)				Arch-U.S. (Subsidiary Issuer)				Other ACGL Subsidiaries				Consolidating Adjustments and Eliminations				ACGL Consolidated
	Revenues
	Net premiums earned		$	—			$	—			$	859,780			$	—			$	859,780

	Net investment income		—				—				77,001				(10,007		)		66,994

	Net realized gains		—				—				19,697				—				19,697

	Net impairment losses recognized in earnings		—				—				(2,971		)		—				(2,971		)

	Other underwriting income		—				—				1,582				—				1,582

	Equity in net income of investment funds accounted for using the equity method		—				—				3,253				—				3,253

	Other income (loss)		—				—				(2,104		)		—				(2,104		)

		Total revenues	—				—				956,238				(10,007		)		946,231


	Expenses
	Losses and loss adjustment expenses		—				—				436,240				—				436,240

	Acquisition expenses		—				—				160,342				—				160,342

	Other operating expenses		10,307				977				134,515				—				145,799

	Interest expense		5,853				6,514				12,044				(10,007		)		14,404

	Net foreign exchange losses		—				—				5,741				822				6,563

		Total expenses	16,160				7,491				748,882				(9,185		)		763,348


	Income (loss) before income taxes		(16,160		)		(7,491		)		207,356				(822		)		182,883

	Income tax benefit (expense)		—				2,788				(6,526		)		—				(3,738		)

	Income (loss) before equity in net income of subsidiaries		(16,160		)		(4,703		)		200,830				(822		)		179,145

	Equity in net income of subsidiaries		198,660				22,152				—				(220,812		)		—

	Net income		182,500				17,449				200,830				(221,634		)		179,145

	Net (income) loss attributable to noncontrolling interests (1)		—				—				3,355				—				3,355

	Net income available to Arch		182,500				17,449				204,185				(221,634		)		182,500

	Preferred dividends		(5,484		)		—				—				—				(5,484		)

	Net income available to Arch common shareholders		$	177,016			$	17,449			$	204,185			$	(221,634	)		$	177,016


	Comprehensive income available to Arch		$	231,255			$	17,220			$	252,119			$	(269,339	)		$	231,255


	(1) See Note 4.




		Three Months Ended March 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		$	—			$	—			$	752,770			$	—			$	752,770

Net investment income		—				—				72,322				(6,650		)		65,672

Net realized gains		—				—				58,340				—				58,340

Net impairment losses recognized in earnings		—				—				(2,246		)		—				(2,246		)

Other underwriting income		—				—				538				—				538

Equity in net income of investment funds accounted for using the equity method		—				—				13,823				—				13,823

Other income		—				—				1,244				—				1,244

	Total revenues	—				—				896,791				(6,650		)		890,141


Expenses
Losses and loss adjustment expenses		—				—				399,403				—				399,403

Acquisition expenses		—				—				127,592				—				127,592

Other operating expenses		9,942				777				109,464				—				120,183

Interest expense		5,820				3				6,725				(6,650		)		5,898

Net foreign exchange (gains) losses		—				—				(12,772		)		(11,492		)		(24,264		)

	Total expenses	15,762				780				630,412				(18,142		)		628,812


Income (loss) before income taxes		(15,762		)		(780		)		266,379				11,492				261,329

Income tax benefit (expense)		—				235				(5,088		)		—				(4,853		)

Income (loss) before equity in net income of subsidiaries		(15,762		)		(545		)		261,291				11,492				256,476

Equity in net income (loss) of subsidiaries		272,238				18,482				—				(290,720		)		—

Net income		256,476				17,937				261,291				(279,228		)		256,476

Net (income) loss attributable to noncontrolling interests		—				—				—				—				—

Net income available to Arch		256,476				17,937				261,291				(279,228		)		256,476

Preferred dividends		(5,484		)		—				—				—				(5,484		)

Net income available to Arch common shareholders		$	250,992			$	17,937			$	261,291			$	(279,228	)		$	250,992


Comprehensive income available to Arch		$	199,022			$	6,152			$	215,329			$	(221,481	)		$	199,022


Condensed consolidating statement of cash flows	'


					Three Months Ended March 31, 2014
	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 Operating Activities			$	11,685			$	7,151			$	194,833			$	(15,500	)		$	198,169

	Investing Activities
	Purchases of fixed maturity investments				—				—				(7,131,071		)		—				(7,131,071		)

	Purchases of equity securities				—				—				(89,227		)		—				(89,227		)

	Purchases of other investments				—				—				(304,454		)		—				(304,454		)

	Proceeds from the sales of fixed maturity investments				—				—				7,014,281				—				7,014,281

	Proceeds from the sales of equity securities				—				—				49,614				—				49,614

	Proceeds from the sales of other investments				—				—				331,176				—				331,176

	Proceeds from redemptions and maturities of fixed maturity investments				—				—				168,484				—				168,484

	Net (purchases) sales of short-term investments				(16		)		360,269				(203,991		)		—				156,262

	Change in investment of securities lending collateral				—				—				4,669				—				4,669

	Contributions to subsidiaries				—				(312,207		)		(100,000		)		412,207				—

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

	Purchase of business, net of cash acquired				—				—				(235,578		)		—				(235,578		)

	Purchases of furniture, equipment and other assets				(76		)		—				(5,306		)		—				(5,382		)

		Net Cash Provided By (Used For) Investing Activities			(92		)		48,062				(491,153		)		401,957				(41,226		)

	Financing Activities
	Proceeds from common shares issued, net				3,021				—				412,207				(412,207		)		3,021

	Repayments of intercompany borrowings				—				(10,250		)		—				10,250				—

	Change in securities lending collateral				—				—				(4,669		)		—				(4,669		)

	Third party investment in non-redeemable noncontrolling interests (1)				—				—				796,903				—				796,903

	Third party investment in redeemable noncontrolling interests (1				—				—				186,893				—				186,893

	Dividends paid to parent				—				—				(15,500		)		15,500				—

	Other				—				—				1,700				—				1,700

	Preferred dividends paid				(5,484		)		—				—				—				(5,484		)

		Net Cash Provided By (Used For) Financing Activities			(2,463		)		(10,250		)		1,377,534				(386,457		)		978,364

	Effects of exchange rates changes on foreign currency cash				—				—				241				—				241

	Increase in cash				9,130				44,963				1,081,455				—				1,135,548

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

	Cash end of period				$	12,353			$	45,472			$	1,511,780			$	—			$	1,569,605


(1) See Note 4.




				Three Months Ended March 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) Operating Activities			$	34,432			$	(254	)		$	216,481			$	(45,000	)		$	205,659

Investing Activities
Purchases of fixed maturity investments				—				—				(3,970,320		)		—				(3,970,320		)

Purchases of equity securities				—				—				(63,353		)		—				(63,353		)

Purchases of other investments				—				—				(250,442		)		—				(250,442		)

Proceeds from the sales of fixed maturity investments				—				—				3,796,638				—				3,796,638

Proceeds from the sales of equity securities				—				—				81,513				—				81,513

Proceeds from the sales of other investments				—				—				280,010				—				280,010

Proceeds from redemptions and maturities of fixed maturity investments				—				—				181,727				—				181,727

Net (purchases) sales of short-term investments				7,964				(2		)		(229,406		)		—				(221,444		)

Change in investment of securities lending collateral				—				—				(41,019		)		—				(41,019		)

Contributions to subsidiaries				—				(10,250		)		(250		)		10,500				—

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

Purchases of furniture, equipment and other assets				(31		)		—				(3,711		)		—				(3,742		)

	Net Cash Provided By (Used For) Investing Activities			7,933				(10,252		)		(228,863		)		20,750				(210,432		)

Financing Activities
Purchases of common shares under share repurchase program				(40,964		)		—				—				—				(40,964		)

Proceeds from common shares issued, net				1,280				—				10,500				(10,500		)		1,280

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

Change in securities lending collateral				—				—				41,019				—				41,019

Dividends paid to parent				—				—				(45,000		)		45,000				—

Other				—				—				1,084				—				1,084

Preferred dividends paid				(5,484		)		—				—				—				(5,484		)

	Net Cash Provided By (Used For) Financing Activities			(45,168		)		10,250				7,603				24,250				(3,065		)

Effects of exchange rates changes on foreign currency cash				—				—				(6,436		)		—				(6,436		)

Increase (decrease) in cash				(2,803		)		(256		)		(11,215		)		—				(14,274		)

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

Cash end of period				$	3,614			$	356			$	352,797			$	—			$	356,767

General_Details

General (Details) (Watford Holdings Ltd, Variable Interest Entity, Primary Beneficiary, USD $)	1 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014
Watford Holdings Ltd \| Variable Interest Entity, Primary Beneficiary	'
Variable Interest Entity [Line Items]	'
Percentage ownership	11.00%
Initial investment contribution amount	$100

Business_Acquired_Summary_of_f

Business Acquired - Summary of fair value of net assets acquired and allocation of purchase price(Details) (CMG Mortgage Insurance Company, USD $)	0 Months Ended
In Thousands, unless otherwise specified	Jan. 30, 2014	Mar. 31, 2014
Business Acquisition [Line Items]	'	'
Cash paid	$245,157	'
Contingent consideration liability	41,762	43,156
Total purchase price (a)	286,919	'
Cash	9,579	'
Investments, at fair value	312,093	'
Other assets acquired	21,691	'
Total assets acquired	437,650	'
Reserves for losses and loss adjustment expenses	121,572	'
Unearned premiums	26,261	'
Intangible liability -- unfavorable service contract	9,533	'
Other liabilities acquired	7,217	'
Total liabilities acquired	164,583	'
Net assets acquired	273,067	'
Goodwill	13,852	'
Useful life of finite lived intangible liabilities acquired	'9 years	'
Insurance licenses	'	'
Business Acquisition [Line Items]	'	'
Intangible asset -- insurance licenses	16,858	'
Acquired insurance contracts	'	'
Business Acquisition [Line Items]	'	'
Intangible asset	46,473	'
Useful life of finite lived intangible assets acquired	'5 years	'
Operating platform	'	'
Business Acquisition [Line Items]	'	'
Intangible asset	29,900	'
Useful life of finite lived intangible assets acquired	'5 years	'
Favorable lease contract	'	'
Business Acquisition [Line Items]	'	'
Intangible asset	$1,056	'
Useful life of finite lived intangible assets acquired	'5 years	'

Business_Acquired_Narrative_De

Business Acquired - Narrative (Details) (CMG Mortgage Insurance Company, USD $)	0 Months Ended	3 Months Ended
	Jan. 30, 2014	Mar. 31, 2014
Business Acquisition [Line Items]	'	'
Percentage of voting interests acquired	100.00%	'
Quota share agreement percentage	'	100.00%
Cash paid	$245,157,000	'
Contingent consideration, upper bound	'	136,300,000
Discount rate, percentage	15.00%	'
Contingent consideration liability	41,762,000	43,156,000
Goodwill	13,852,000	'
Goodwill, deferred tax asset	'	48,000,000
Stock Purchase Agreement (SPA)	'	'
Business Acquisition [Line Items]	'	'
Cash paid	160,600,000	'
Percentage of book value	80.00%	'
Asset Purchase Agreement (APA)	'	'
Business Acquisition [Line Items]	'	'
Cash paid	84,600,000	'
Maximum	'	'
Business Acquisition [Line Items]	'	'
Percentage of book value	150.00%	'
Extension period	'	'3 years
Minimum	'	'
Business Acquisition [Line Items]	'	'
Extension period	'	'1 year
New mortgage insurance business (post closing)	'	'
Business Acquisition [Line Items]	'	'
Quota share agreement percentage	'	20.00%
Quota share reinsurance agreement limit	'	$25,000,000,000

Significant_Accounting_Policie2

Significant Accounting Policies (Details)	3 Months Ended
Significant Accounting Policies (Details)	Mar. 31, 2014
Significant Accounting Policies [Line Items]	'
Premium revenue recognition period	'12 months
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

Variable_Interest_Entities_and2

Variable Interest Entities and Noncontrolling Interests - Variable interest entity (Details) (Variable Interest Entity, Primary Beneficiary, Watford Holdings Ltd, USD $)	1 Months Ended
	Mar. 31, 2014
Variable Interest Entity, Primary Beneficiary \| Watford Holdings Ltd	'
Variable Interest Entity [Line Items]	'
Initial capitalization amount	$1,100,000,000
Proceeds from issuance of common shares	907,300,000
Net proceeds from issuance of common shares	895,600,000
Proceeds on issuance of preference shares	226,600,000
Net proceeds on issuance of preference shares	219,200,000
Initial investment contribution amount	$100,000,000
Ownership percentage	11.00%

Variable_Interest_Entities_and3

Variable Interest Entities and Noncontrolling Interests - Non-redeemable noncontrolling interests (Details) (USD $)	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013		Mar. 31, 2014		Mar. 31, 2014
In Thousands, unless otherwise specified							Watford Holdings Ltd		Common shares
							Noncontrolling Interest		Watford Holdings Ltd
									Noncontrolling Interest
Noncontrolling Interest [Line Items]	'		'		'		'		'
Noncontrolling interest, ownership percentage by noncontrolling owners	'		'		'		'		89.00%
Non-redeemable noncontrolling interests, beginning of year	$793,496	[1]	$0	[1]	$0	[1]	$0	[1]	'
Sale of shares to noncontrolling interests	'		'		'		796,903		'
Net (loss) income attributable to noncontrolling interests	'		'		'		-3,407		'
Non-redeemable noncontrolling interests, end of period	$793,496	[1]	$0	[1]	$0	[1]	$793,496	[1]	'

[1]	See Note 4.

Variable_Interest_Entities_and4

Variable Interest Entities and Noncontrolling Interests - Redeemable noncontrolling interests (Details) (Watford Holdings Ltd, USD $)	3 Months Ended
	Mar. 31, 2014
Redeemable Noncontrolling Interest [Line Items]	'
Par value per share	$0.01
Liquidation preference per share	$25
Issue price per share	$24.50
Preference shares, number of shares issued	9,065,200
Preference shares, dividend rate (percentage)	8.50%
3 month US dollar LIBOR	'
Redeemable Noncontrolling Interest [Line Items]	'
Preference shares, dividend rate (percentage)	1.00%
Cumulative redeemable preference shares	'
Redeemable Noncontrolling Interest [Line Items]	'
Noncontrolling interest, ownership percentage by noncontrolling owners	100.00%

Earnings_Per_Common_Share_Deta

Earnings Per Common Share (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Numerator:	'		'
Net income	$179,145		$256,476
Net (income) loss attributable to noncontrolling interests	3,355	[1]	0	[1]
Net income available to Arch	182,500		256,476
Preferred dividends	-5,484		-5,484
Net income available to Arch common shareholders	$177,016		$250,992
Denominator:	'		'
Weighted average common shares outstanding â€” basic	131,857,910		130,907,902
Effect of dilutive common share equivalents:	'		'
Nonvested restricted shares	1,346,401		1,290,161
Stock options	3,358,406	[2]	3,211,225	[2]
Weighted average common shares and common share equivalents outstanding â€” diluted	136,562,717		135,409,288
Earnings per common share:	'		'
Basic (per share)	$1.34		$1.92
Diluted (per share)	$1.30		$1.85
Stock Options	'		'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'		'
Antidilutive securities excluded from computation of earnings per common share (shares)	759,172		1,016,043

[1]	See Note 4.
[2]	Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For the 2014 first quarter and 2013 first quarter, the number of stock options excluded were 759,172 and 1,016,043, respectively.

Segment_Information_Summary_of

Segment Information - Summary of underwriting income or loss by segment (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]	'		'		'
Gross premiums written	$1,295,136	[1]	$1,163,699	[1]	'
Premiums ceded	-230,146		-210,923		'
Net premiums written	1,064,990		952,776		'
Change in unearned premiums	-205,210		-200,006		'
Net premiums earned	859,780		752,770		'
Other underwriting income	1,582		538		'
Losses and loss adjustment expenses	-436,240		-399,403		'
Acquisition expenses, net	-160,342		-127,592		'
Other operating expenses	-132,324		-109,915		'
Underwriting income (loss)	132,456		116,398		'
Net investment income	66,994		65,672		'
Net realized gains	19,697		58,340		'
Net impairment losses recognized in earnings	-2,971		-2,246		'
Equity in net income (loss) of investment funds accounted for using the equity method	3,253		13,823		'
Other income (loss)	-2,104		1,244		'
Other expenses	-13,475		-10,268		'
Interest expense	-14,404		-5,898		'
Net foreign exchange gains (losses)	-6,563		24,264		'
Income before income taxes	182,883		261,329		'
Income tax expense (benefit)	-3,738		-4,853		'
Net income	179,145		256,476		'
Net (income) loss attributable to noncontrolling interests	3,355	[2]	0	[2]	'
Net income available to Arch	182,500		256,476		'
Preferred dividends	-5,484		-5,484		'
Net income available to Arch common shareholders	177,016		250,992		'
Underwriting Ratios	'		'		'
Loss ratio	50.70%		53.10%		'
Acquisition expense ratio	18.60%		16.90%		'
Other operating expense ratio	15.40%	[3]	14.60%	[3]	'
Combined ratio	84.70%		84.60%		'
Investable assets	15,344,386		13,132,116		'
Total assets	21,800,358		18,757,061		19,566,094
Total liabilities	14,895,495		13,421,531		13,918,598
Underwriting segments	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premiums written	1,295,136		1,163,699		'
Premiums ceded	-262,340		-210,923		'
Net premiums written	1,032,796		952,776		'
Change in unearned premiums	-175,182		-200,006		'
Net premiums earned	857,614		752,770		'
Other underwriting income	1,582		538		'
Losses and loss adjustment expenses	-434,884		-399,403		'
Acquisition expenses, net	-159,519		-127,592		'
Other operating expenses	-131,215		-109,915		'
Underwriting income (loss)	133,578		116,398		'
Net investment income	66,993		65,672		'
Net realized gains	19,697		58,340		'
Net impairment losses recognized in earnings	-2,971		-2,246		'
Equity in net income (loss) of investment funds accounted for using the equity method	3,253		13,823		'
Other income (loss)	-2,104		1,244		'
Other expenses	-10,799		-10,268		'
Interest expense	-14,404		-5,898		'
Net foreign exchange gains (losses)	-6,656		24,264		'
Income before income taxes	186,587		261,329		'
Income tax expense (benefit)	-3,738		-4,853		'
Net income	182,849		256,476		'
Net (income) loss attributable to noncontrolling interests	0		0		'
Net income available to Arch	182,849		256,476		'
Preferred dividends	-5,484		-5,484		'
Net income available to Arch common shareholders	177,365		250,992		'
Underwriting Ratios	'		'		'
Loss ratio	50.70%		53.10%		'
Acquisition expense ratio	18.50%		16.90%		'
Other operating expense ratio	15.30%		14.60%		'
Combined ratio	84.50%		84.60%		'
Investable assets	14,261,106		13,132,116		'
Total assets	20,653,897		18,757,061		'
Total liabilities	14,860,124		13,421,531		'
Underwriting segments \| Insurance	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premiums written	730,646	[1]	688,817	[1]	'
Premiums ceded	-185,044		-184,267		'
Net premiums written	545,602		504,550		'
Change in unearned premiums	-68,101		-59,585		'
Net premiums earned	477,501		444,965		'
Other underwriting income	500		525		'
Losses and loss adjustment expenses	-286,770		-283,467		'
Acquisition expenses, net	-76,932		-70,758		'
Other operating expenses	-81,144		-76,315		'
Underwriting income (loss)	33,155		14,950		'
Underwriting Ratios	'		'		'
Loss ratio	60.10%		63.70%		'
Acquisition expense ratio	16.00%		15.80%		'
Other operating expense ratio	17.00%	[3]	17.20%	[3]	'
Combined ratio	93.10%		96.70%		'
Underwriting segments \| Reinsurance	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premiums written	517,053	[1]	450,447	[1]	'
Premiums ceded	-73,127		-27,979		'
Net premiums written	443,926		422,468		'
Change in unearned premiums	-102,578		-126,315		'
Net premiums earned	341,348		296,153		'
Other underwriting income	316		13		'
Losses and loss adjustment expenses	-139,636		-113,857		'
Acquisition expenses, net	-73,433		-53,143		'
Other operating expenses	-36,195		-32,197		'
Underwriting income (loss)	92,400		96,969		'
Underwriting Ratios	'		'		'
Loss ratio	40.90%		38.40%		'
Acquisition expense ratio	21.50%		17.90%		'
Other operating expense ratio	10.60%	[3]	10.90%	[3]	'
Combined ratio	73.00%		67.20%		'
Underwriting segments \| Mortgage	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premiums written	47,907		25,758		'
Premiums ceded	-4,639		0		'
Net premiums written	43,268		25,758		'
Change in unearned premiums	-4,503		-14,106		'
Net premiums earned	38,765		11,652		'
Other underwriting income	766		0		'
Losses and loss adjustment expenses	-8,478		-2,079		'
Acquisition expenses, net	-9,154		-3,691		'
Other operating expenses	-13,876		-1,403		'
Underwriting income (loss)	8,023		4,479		'
Underwriting Ratios	'		'		'
Loss ratio	21.90%		17.80%		'
Acquisition expense ratio	23.60%		31.70%		'
Other operating expense ratio	35.80%		12.00%		'
Combined ratio	81.30%		61.50%		'
Other	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premiums written	32,194	[1]	0	[1]	'
Premiums ceded	0		0		'
Net premiums written	32,194		0		'
Change in unearned premiums	-30,028		0		'
Net premiums earned	2,166		0		'
Other underwriting income	0		0		'
Losses and loss adjustment expenses	-1,356		0		'
Acquisition expenses, net	-823		0		'
Other operating expenses	-1,109		0		'
Underwriting income (loss)	-1,122		0		'
Net investment income	1		0		'
Net realized gains	0		0		'
Net impairment losses recognized in earnings	0		0		'
Equity in net income (loss) of investment funds accounted for using the equity method	0		0		'
Other income (loss)	0		0		'
Other expenses	-2,676		0		'
Interest expense	0		0		'
Net foreign exchange gains (losses)	93		0		'
Income before income taxes	-3,704		0		'
Income tax expense (benefit)	0		0		'
Net income	-3,704		0		'
Net (income) loss attributable to noncontrolling interests	3,355		0		'
Net income available to Arch	-349		0		'
Preferred dividends	0		0		'
Net income available to Arch common shareholders	-349		0		'
Underwriting Ratios	'		'		'
Loss ratio	62.60%		0.00%		'
Acquisition expense ratio	38.00%		0.00%		'
Other operating expense ratio	51.20%	[3]	0.00%	[3]	'
Combined ratio	151.80%		0.00%		'
Investable assets	1,083,280		0		'
Total assets	1,146,461		0		'
Total liabilities	$35,371		$0		'

[1]	Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.
[2]	See Note 4.
[3]	The acquisition expense ratio is adjusted to include certain other underwriting income.

Segment_Information_Narrative_

Segment Information - Narrative (Details)	3 Months Ended
	Mar. 31, 2014
	segment
Underwriting segments	'
Segment Reporting Information [Line Items]	'
Number of underwriting segments	3
Other	'
Segment Reporting Information [Line Items]	'
Number of underwriting segments	2

Investment_Information_Summary

Investment Information - Summary of available for sale securities (Details) (USD $)	3 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Available for sale securities:	'		'
Estimated Fair Value	$12,335,685		$12,150,358
Gross Unrealized Gains	235,645		232,673
Gross Unrealized Losses	-102,260		-152,368
Cost or Amortized Cost	12,202,300		12,070,053
OTTI Unrealized Losses	-11,171	[1]	-12,942	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements	'		'
Available for sale securities:	'		'
Estimated Fair Value	9,876,320	[2]	9,676,857	[2]
Gross Unrealized Gains	131,396	[2]	133,450	[2]
Gross Unrealized Losses	-78,368	[2]	-127,100	[2]
Cost or Amortized Cost	9,823,292	[2]	9,670,507	[2]
OTTI Unrealized Losses	-11,171	[1],[2]	-12,942	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Corporate bonds	'		'
Available for sale securities:	'		'
Estimated Fair Value	2,514,129	[2]	2,267,263	[2]
Gross Unrealized Gains	39,704	[2]	35,289	[2]
Gross Unrealized Losses	-20,047	[2]	-35,537	[2]
Cost or Amortized Cost	2,494,472	[2]	2,267,511	[2]
OTTI Unrealized Losses	-16	[1],[2]	-16	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,087,840	[2]	1,133,095	[2]
Gross Unrealized Gains	21,700	[2]	16,270	[2]
Gross Unrealized Losses	-14,253	[2]	-22,209	[2]
Cost or Amortized Cost	1,080,393	[2]	1,139,034	[2]
OTTI Unrealized Losses	-8,217	[1],[2]	-9,269	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Municipal bonds	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,410,043	[2]	1,481,738	[2]
Gross Unrealized Gains	28,494	[2]	29,378	[2]
Gross Unrealized Losses	-3,742	[2]	-9,730	[2]
Cost or Amortized Cost	1,385,291	[2]	1,462,090	[2]
OTTI Unrealized Losses	-17	[1],[2]	-17	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,023,055	[2]	1,074,497	[2]
Gross Unrealized Gains	11,769	[2]	13,972	[2]
Gross Unrealized Losses	-9,031	[2]	-15,224	[2]
Cost or Amortized Cost	1,020,317	[2]	1,075,749	[2]
OTTI Unrealized Losses	0	[1],[2]	-199	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| US government and government agencies	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,153,120	[2]	1,301,809	[2]
Gross Unrealized Gains	4,048	[2]	3,779	[2]
Gross Unrealized Losses	-5,932	[2]	-11,242	[2]
Cost or Amortized Cost	1,155,004	[2]	1,309,272	[2]
OTTI Unrealized Losses	-19	[1],[2]	-19	[1],[2]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Non-US government securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,114,382	[2]	1,085,861	[2]
Gross Unrealized Gains	14,538	[2]	14,729	[2]
Gross Unrealized Losses	-12,978	[2]	-19,363	[2]
Cost or Amortized Cost	1,112,822	[2]	1,090,495	[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	1,573,751	[2]	1,332,594	[2]
Gross Unrealized Gains	11,143	[2]	20,033	[2]
Gross Unrealized Losses	-12,385	[2]	-13,795	[2]
Cost or Amortized Cost	1,574,993	[2]	1,326,356	[2]
OTTI Unrealized Losses	-2,902	[1],[2]	-3,422	[1],[2]
Equity securities	'		'
Available for sale securities:	'		'
Estimated Fair Value	548,168		496,824
Gross Unrealized Gains	78,896		69,487
Gross Unrealized Losses	-6,596		-5,938
Cost or Amortized Cost	475,868		433,275
OTTI Unrealized Losses	0	[1]	0	[1]
Other investments	'		'
Available for sale securities:	'		'
Estimated Fair Value	426,917		498,310
Gross Unrealized Gains	24,398		28,082
Gross Unrealized Losses	-15,243		-18,459
Cost or Amortized Cost	417,762		488,687
OTTI Unrealized Losses	0	[1]	0	[1]
Short-term investments	'		'
Available for sale securities:	'		'
Estimated Fair Value	1,484,280		1,478,367
Gross Unrealized Gains	955		1,654
Gross Unrealized Losses	-2,053		-871
Cost or Amortized Cost	1,485,378		1,477,584
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 March 31, 2014, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $4.8 million, compared to a net unrealized gain of $6.0 million at December 31, 2013.
[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 $)	Mar. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	$4,835,304		$6,158,245
Gross Unrealized Losses - Less than 12 Months	-91,270		-137,655
Estimated Fair Value - 12 Months or More	203,184		258,290
Gross Unrealized Losses - 12 Months or More	-10,990		-14,713
Estimated Fair Value - Total	5,038,488		6,416,535
Gross Unrealized Losses - Total	-102,260		-152,368
Fixed maturities and fixed maturities pledged under securities lending agreements	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	4,396,014	[1]	5,887,621	[1]
Gross Unrealized Losses - Less than 12 Months	-67,378	[1]	-115,071	[1]
Estimated Fair Value - 12 Months or More	203,184	[1]	210,974	[1]
Gross Unrealized Losses - 12 Months or More	-10,990	[1]	-12,029	[1]
Estimated Fair Value - Total	4,599,198	[1]	6,098,595	[1]
Gross Unrealized Losses - Total	-78,368	[1]	-127,100	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Corporate bonds	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	1,012,076	[1]	1,183,625	[1]
Gross Unrealized Losses - Less than 12 Months	-17,780	[1]	-32,837	[1]
Estimated Fair Value - 12 Months or More	40,352	[1]	46,673	[1]
Gross Unrealized Losses - 12 Months or More	-2,267	[1]	-2,700	[1]
Estimated Fair Value - Total	1,052,428	[1]	1,230,298	[1]
Gross Unrealized Losses - Total	-20,047	[1],[2]	-35,537	[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	434,286	[1]	778,693	[1]
Gross Unrealized Losses - Less than 12 Months	-11,841	[1]	-20,253	[1]
Estimated Fair Value - 12 Months or More	23,033	[1]	43,634	[1]
Gross Unrealized Losses - 12 Months or More	-2,412	[1]	-1,956	[1]
Estimated Fair Value - Total	457,319	[1]	822,327	[1]
Gross Unrealized Losses - Total	-14,253	[1]	-22,209	[1]
Fixed maturities and fixed maturities pledged under securities lending agreements \| Municipal bonds	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	340,349	[1]	589,009	[1]
Gross Unrealized Losses - Less than 12 Months	-3,484	[1]	-9,422	[1]
Estimated Fair Value - 12 Months or More	3,741	[1]	6,092	[1]
Gross Unrealized Losses - 12 Months or More	-258	[1]	-308	[1]
Estimated Fair Value - Total	344,090	[1]	595,101	[1]
Gross Unrealized Losses - Total	-3,742	[1]	-9,730	[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	398,428	[1]	677,617	[1]
Gross Unrealized Losses - Less than 12 Months	-8,977	[1]	-15,110	[1]
Estimated Fair Value - 12 Months or More	581	[1]	1,612	[1]
Gross Unrealized Losses - 12 Months or More	-54	[1]	-114	[1]
Estimated Fair Value - Total	399,009	[1]	679,229	[1]
Gross Unrealized Losses - Total	-9,031	[1]	-15,224	[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	764,802	[1]	1,144,809	[1]
Gross Unrealized Losses - Less than 12 Months	-5,932	[1]	-11,242	[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	764,802	[1]	1,144,809	[1]
Gross Unrealized Losses - Total	-5,932	[1]	-11,242	[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	541,534	[1]	821,506	[1]
Gross Unrealized Losses - Less than 12 Months	-10,940	[1]	-15,776	[1]
Estimated Fair Value - 12 Months or More	36,298	[1]	24,334	[1]
Gross Unrealized Losses - 12 Months or More	-2,038	[1]	-3,587	[1]
Estimated Fair Value - Total	577,832	[1]	845,840	[1]
Gross Unrealized Losses - Total	-12,978	[1]	-19,363	[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	904,539	[1]	692,362	[1]
Gross Unrealized Losses - Less than 12 Months	-8,424	[1]	-10,431	[1]
Estimated Fair Value - 12 Months or More	99,179	[1]	88,629	[1]
Gross Unrealized Losses - 12 Months or More	-3,961	[1]	-3,364	[1]
Estimated Fair Value - Total	1,003,718	[1]	780,991	[1]
Gross Unrealized Losses - Total	-12,385	[1]	-13,795	[1]
Equity securities	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	102,589		76,563
Gross Unrealized Losses - Less than 12 Months	-6,596		-5,938
Estimated Fair Value - 12 Months or More	0		0
Gross Unrealized Losses - 12 Months or More	0		0
Estimated Fair Value - Total	102,589		76,563
Gross Unrealized Losses - Total	-6,596		-5,938
Other investments	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	156,468		165,891
Gross Unrealized Losses - Less than 12 Months	-15,243		-15,775
Estimated Fair Value - 12 Months or More	0		47,316
Gross Unrealized Losses - 12 Months or More	0		-2,684
Estimated Fair Value - Total	156,468		213,207
Gross Unrealized Losses - Total	-15,243		-18,459
Short-term investments	'		'
Available for sale securities:	'		'
Estimated Fair Value - Less than 12 Months	180,233		28,170
Gross Unrealized Losses - Less than 12 Months	-2,053		-871
Estimated Fair Value - 12 Months or More	0		0
Gross Unrealized Losses - 12 Months or More	0		0
Estimated Fair Value - Total	180,233		28,170
Gross Unrealized Losses - Total	($2,053)		($871)

[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€
[2]	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 March 31, 2014, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $4.8 million, compared to a net unrealized gain of $6.0 million at December 31, 2013.

Investment_Information_Maturit

Investment Information - Maturity profile of available for sale securities) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Estimated Fair Value:	'	'
Estimated fair value	$9,775,730	$9,571,776
Amortized Cost:	'	'
Amortized cost	9,722,364	9,564,634
Fixed maturities and fixed maturities pledged under securities lending agreements	'	'
Estimated Fair Value:	'	'
Due in one year or less	286,950	235,330
Due after one year through five years	3,757,966	3,738,500
Due after five years through 10 years	1,883,374	1,966,536
Due after 10 years	263,384	196,305
Single maturity date	6,191,674	6,136,671
Estimated fair value	9,876,320	9,676,857
Amortized Cost:	'	'
Due in one year or less	282,281	232,652
Due after one year through five years	3,731,777	3,718,920
Due after five years through 10 years	1,872,047	1,979,510
Due after 10 years	261,484	198,286
Single maturity date	6,147,589	6,129,368
Amortized cost	9,823,292	9,670,507
Fixed maturities and fixed maturities pledged under securities lending agreements \| Mortgage backed securities	'	'
Estimated Fair Value:	'	'
Securities without single maturity date	1,087,840	1,133,095
Amortized Cost:	'	'
Securities without single maturity date	1,080,393	1,139,034
Fixed maturities and fixed maturities pledged under securities lending agreements \| Commercial mortgage backed securities	'	'
Estimated Fair Value:	'	'
Securities without single maturity date	1,023,055	1,074,497
Amortized Cost:	'	'
Securities without single maturity date	1,020,317	1,075,749
Fixed maturities and fixed maturities pledged under securities lending agreements \| Asset backed securities	'	'
Estimated Fair Value:	'	'
Securities without single maturity date	1,573,751	1,332,594
Amortized Cost:	'	'
Securities without single maturity date	$1,574,993	$1,326,356

Investment_Information_Other_i

Investment Information - Other investments (Details) (USD $)	Mar. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	$1,226,741		$1,271,590
Available for sale	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	426,917		498,310
Available for sale \| Asian and emerging markets	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	266,023		331,984
Available for sale \| Investment grade fixed income	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	160,894		159,115
Available for sale \| Other	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	0		7,211
Fair value option	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	799,824		773,280
Fair value option \| Term loan investments	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	410,430		512,076
Other investments par	403,383		494,502
Fair value option \| Asian and emerging markets	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	14,817		14,054
Fair value option \| Investment grade fixed income	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	91,907		75,062
Fair value option \| Other	'		'
Schedule Of Other Investments [Line Items]	'		'
Other investments and fair value option investments	$282,670	[1]	$172,088	[1]

[1]	Includes fund investments with strategies in mortgage servicing rights, transportation and infrastructure assets and other.

Investment_Information_Fair_va

Investment Information - Fair value option (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Option, Quantitative Disclosures [Line Items]	'	'
Investments accounted for using the fair value option	$1,256,650	$1,221,534
Fixed Maturities	'	'
Fair Value, Option, Quantitative Disclosures [Line Items]	'	'
Investments accounted for using the fair value option	456,826	448,254
Other investments	'	'
Fair Value, Option, Quantitative Disclosures [Line Items]	'	'
Investments accounted for using the fair value option	$799,824	$773,280

Investment_Information_Net_inv

Investment Information - Net investment income (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Net investment income:	'		'
Gross investment income	$76,163		$74,337
Investment expenses	-9,169		-8,665
Net investment income	66,994		65,672
Fixed Maturities	'		'
Net investment income:	'		'
Gross investment income	62,449		62,006
Term loan investments	'		'
Net investment income:	'		'
Gross investment income	5,669		4,217
Equity securities (dividends)	'		'
Net investment income:	'		'
Gross investment income	2,921		1,423
Short-term investments	'		'
Net investment income:	'		'
Gross investment income	406		392
Other	'		'
Net investment income:	'		'
Gross investment income	$4,718	[1]	$6,299	[1]

[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
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Net realized gains and losses:	'		'
Available for sale securities, gross gains on investment sales	$66,051		$67,020
Available for sale securities, gross losses on investment sales	-40,013		-25,056
Derivative instruments	-12,768	[1]	-378	[1]
Other	-2,706	[2]	1,046	[2]
Net realized gains	19,697		58,340
Fixed Maturities	'		'
Net realized gains and losses:	'		'
Change in fair value of assets and liabilities accounted for using the fair value option	-1,643		5,058
Other investments	'		'
Net realized gains and losses:	'		'
Change in fair value of assets and liabilities accounted for using the fair value option	10,776		9,951
Equity securities	'		'
Net realized gains and losses:	'		'
Change in fair value of assets and liabilities accounted for using the fair value option	$0		$699

[1]	See Note 9 for information on the Companyâ€™s derivative instruments.
[2]	Includes accretion of contingent liability amounts related to the acquisition of the CMG Entities (see Note 2 for further details).

Investment_Information_Other_t

Investment Information - Other than temporary impairments recognized in earnings (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'
Net impairment losses recognized in earnings	($2,971)	($2,246)
Fixed Maturities	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'
Net impairment losses recognized in earnings	-6	-35
Fixed Maturities \| Mortgage backed securities	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'
Net impairment losses recognized in earnings	0	-15
Fixed Maturities \| Asset backed securities	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'
Net impairment losses recognized in earnings	-6	-20
Equity securities	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'
Net impairment losses recognized in earnings	0	-2,211
Other investments	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'
Net impairment losses recognized in earnings	($2,965)	$0

Investment_Information_Other_t1

Investment Information - Other than temporary impairments rollforward (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Rollforward:	'	'
Balance at start of period	$60,062	$62,001
Credit loss impairments recognized on securities not previously impaired	0	33
Credit loss impairments recognized on securities previously impaired	6	2
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	0	0
Reductions for securities sold during the period	-12,812	-80
Balance at end of period	$47,256	$61,956

Investment_Information_Restric

Investment Information - Restricted assets (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Restricted Assets [Line Items]	'	'
Restricted assets	$5,740,388	$5,302,042
Collateral or guarantees - affiliated transactions	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	4,346,385	4,060,533
Collateral or guarantees - third party agreements	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	951,609	856,890
Deposits with US regulatory authorities	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	350,284	302,809
Deposits with non-US regulatory authorities	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	2	6,546
Trust funds	'	'
Restricted Assets [Line Items]	'	'
Restricted assets	$92,108	$75,264

Investment_Information_Narrati

Investment Information - Narrative (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013
	lots		lots		Mar. 31, 2013
Narrative items:	'		'		'
Investable assets	$15,344,386,000		'		$13,132,116,000
OTTI unrealized losses at current fair value	4,800,000		6,000,000		'
Continuous unrealized loss, qualitative disclosures:	'		'		'
Number of positions in an unrealized loss position (lots)	1,580		2,080		'
Total number of positions (lots)	4,310		4,400		'
Largest single loss	3,600,000		3,500,000		'
Securities lending, qualitative disclosures:	'		'		'
Fair value of fixed maturities and short-term investments pledged under securities lending agreements	100,600,000		105,100,000		'
Amortized cost of fixed maturities and short-term investments pledged under securities lending agreements	100,900,000		105,900,000		'
Fair value of securities backing securities lending program	96,264,000		100,584,000		'
Approximate fair value of sub-prime securities backing the securities lending program	6,300,000		6,300,000		'
OTTI Unrealized Losses	11,171,000	[1]	12,942,000	[1]	'
Underwriting segments	'		'		'
Narrative items:	'		'		'
Investable assets	14,261,106,000		'		13,132,116,000
Other	'		'		'
Narrative items:	'		'		'
Investable assets	$1,083,280,000		'		$0

[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 March 31, 2014, the net unrealized gain related to securities for which a non-credit OTTI was recognized in AOCI was $4.8 million, compared to a net unrealized gain of $6.0 million at December 31, 2013.

Fair_Value_Fair_Value_Hierarch

Fair Value - Fair Value Hierarchy (Details) (Recurring, USD $)	Mar. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Estimated Fair Value	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	$13,592,335		$13,371,892
Liabilities measured at fair value	43,156		'
Estimated Fair Value \| Contingent consideration liability	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Liabilities measured at fair value	43,156		'
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	9,876,320	[1]	9,676,857
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	2,514,129	[1]	2,267,263	[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	1,087,840	[1]	1,133,095	[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	1,410,043	[1]	1,481,738	[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	1,023,055	[1]	1,074,497	[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	1,153,120	[1]	1,301,809	[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	1,114,382	[1]	1,085,861	[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	1,573,751	[1]	1,332,594	[1]
Estimated Fair Value \| Equity securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	548,168		496,824
Estimated Fair Value \| Other investments	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	426,917		498,310
Estimated Fair Value \| Short-term investments	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,484,280		1,478,367
Estimated Fair Value \| Fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	1,256,650		1,221,534
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	353,644		334,065
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	39,644		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	63,538		73,156
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	799,824		773,280
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	3,158,568		3,226,291
Liabilities measured at fair value	0		'
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Contingent consideration liability	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Liabilities measured at fair value	0		'
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	1,153,120	[1]	1,301,809
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	1,153,120	[1]	1,301,809	[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	548,099		496,738
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	1,457,349		1,427,744
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		0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair value option \| Corporate bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair value option \| Mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair value option \| 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 \| 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
Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	9,910,286		9,595,611
Liabilities measured at fair value	0		'
Significant Other Observable Inputs (Level 2) \| Contingent consideration liability	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Liabilities measured at fair value	0		'
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	8,723,200	[1]	8,373,003
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	2,514,129	[1]	2,265,218	[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	1,087,840	[1]	1,133,095	[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	1,410,043	[1]	1,481,738	[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	1,023,055	[1]	1,074,497	[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	1,114,382	[1]	1,085,861	[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	1,573,751	[1]	1,332,594	[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	69		86
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	322,582		327,890
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	26,931		50,623
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	837,504		844,009
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	353,644		334,065
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	39,644		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	63,538		73,156
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	380,678		395,755
Significant Unobservable Inputs (Level 3)	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	523,481		549,990
Liabilities measured at fair value	43,156		'
Significant Unobservable Inputs (Level 3) \| Contingent consideration liability	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Liabilities measured at fair value	43,156		'
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	0	[1]	2,045
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	0	[1]	2,045	[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	104,335		170,420
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	419,146		377,525
Significant Unobservable Inputs (Level 3) \| Fair value option \| Corporate bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0		0
Significant Unobservable Inputs (Level 3) \| Fair value option \| Mortgage backed securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	0		0
Significant Unobservable Inputs (Level 3) \| Fair value option \| 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 \| Other investments fair value option	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Assets measured at fair value	$419,146		$377,525

[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 and liabilities (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance at beginning of period	$549,990	$477,956
Total gains or (losses) (realized/unrealized) - included in earnings	8,585	6,627
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	-2,196	224
Purchases, issuances, sales and settlements	'	'
Purchases	40,110	46,654
Issuances	0	0
Sales	-68,209	0
Settlements	-4,799	-68,859
Transfers in and/or out of Level 3	0	0
Balance at end of period	523,481	462,602
Contingent consideration liability	'	'
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance at beginning of period	0	0
Total gains or (losses) (realized/unrealized) - included in earnings	-1,394	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	0
Purchases, issuances, sales and settlements	'	'
Purchases	0	0
Issuances	-41,762	0
Sales	0	0
Settlements	0	0
Transfers in and/or out of Level 3	0	0
Balance at end of period	-43,156	0
Available for sale \| Corporate bonds	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance at beginning of period	2,045	98,404
Total gains or (losses) (realized/unrealized) - included in earnings	0	1,492
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	-1,688
Purchases, issuances, sales and settlements	'	'
Purchases	0	0
Issuances	0	0
Sales	-2,045	0
Settlements	0	-910
Transfers in and/or out of Level 3	0	0
Balance at end of period	0	97,298
Available for sale \| Other investments	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance at beginning of period	170,420	184,202
Total gains or (losses) (realized/unrealized) - included in earnings	2,275	4,762
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	-2,196	1,912
Purchases, issuances, sales and settlements	'	'
Purchases	0	5,000
Issuances	0	0
Sales	-66,164	0
Settlements	0	-9,942
Transfers in and/or out of Level 3	0	0
Balance at end of period	104,335	185,934
Fair value option \| Other investments	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance at beginning of period	377,525	195,350
Total gains or (losses) (realized/unrealized) - included in earnings	6,310	373
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	0
Purchases, issuances, sales and settlements	'	'
Purchases	40,110	41,654
Issuances	0	0
Sales	0	0
Settlements	-4,799	-58,007
Transfers in and/or out of Level 3	0	0
Balance at end of period	$419,146	$179,370

Fair_Value_Narrative_Details

Fair Value - Narrative (Details) (USD $)	3 Months Ended
Fair Value - Narrative (Details) (USD $)	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'	'	'
Total assets and liabilities measured at fair value	$13,640,000,000	'	$13,370,000,000
Total assets and liabilities measured at fair value priced using non-binding broker quotes	544,400,000	'	601,900,000
Total assets and liabilities measured at fair value priced using non-binding broker quotes (percentage)	4.00%	'	4.50%
Gains (losses) including in earnings attributable to the change in unrealized gains or losses related to assets still held at balance sheet date	3,300,000	6,600,000	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'	'
Senior notes	800,000,000	'	800,000,000
Reportable Legal Entities \| ACGL (Parent Guarantor)	'	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'	'
Senior notes	300,000,000	'	300,000,000
Estimated fair value of senior notes	394,700,000	'	'
Reportable Legal Entities \| Arch-U.S. (Subsidiary Issuer)	'	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'	'
Senior notes	500,000,000	'	500,000,000
Estimated fair value of senior notes	$530,300,000	'	'

Derivative_Instruments_Details

Derivative Instruments (Details) (USD $)	3 Months Ended
Derivative Instruments (Details) (USD $)	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Derivative offsetting [Abstract]	'		'		'
Derivative assets subject to master netting agreements	$147,700,000		'		$28,000,000
Derivative liabilities subject to master netting agreements	143,000,000		'		14,600,000
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	-12,768,000	[1]	-378,000	[1]	'
Not Designated as Hedging Instrument [Member]	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	219,059,000		'		39,859,000
Liability derivatives - fair value	-214,941,000		'		-26,472,000
Net derivatives - fair value	4,118,000		'		13,387,000
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	-12,768,000		-378,000		'
Not Designated as Hedging Instrument [Member] \| Futures contracts	'		'		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	-9,862,000		-829,000		'
Not Designated as Hedging Instrument [Member] \| Futures contracts \| Other investments available for sale, at fair value	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	469,000		'		461,000
Liability derivatives - fair value	-769,000		'		-110,000
Net derivatives - fair value	-300,000		'		351,000
Net derivatives - notional value	1,056,045,000	[2]	'		475,967,000	[2]
Not Designated as Hedging Instrument [Member] \| Foreign currency forward contracts	'		'		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	-2,257,000		-725,000		'
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	693,000		'		5,023,000
Liability derivatives - fair value	-1,565,000		'		-3,090,000
Net derivatives - fair value	-872,000		'		1,933,000
Net derivatives - notional value	244,614,000	[2]	'		330,746,000	[2]
Not Designated as Hedging Instrument [Member] \| TBAs	'		'		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	-37,000		541,000		'
Not Designated as Hedging Instrument [Member] \| TBAs \| Fixed maturities available for sale, at fair value	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	216,548,000		'		33,455,000
Liability derivatives - fair value	-211,763,000		'		-21,731,000
Net derivatives - fair value	4,785,000		'		11,724,000
Net derivatives - notional value	412,800,000	[2]	'		56,160,000	[2]
Not Designated as Hedging Instrument [Member] \| Other	'		'		'
Net realized gains (losses) on derivative instruments	'		'		'
Net realized gains (losses) on derivative instruments	-612,000		635,000		'
Not Designated as Hedging Instrument [Member] \| Other \| Other investments available for sale, at fair value	'		'		'
Derivative [Line Items]	'		'		'
Asset derivatives - fair value	1,349,000		'		920,000
Liability derivatives - fair value	-844,000		'		-1,541,000
Net derivatives - fair value	505,000		'		-621,000
Net derivatives - notional value	$690,029,000	[2]	'		$347,916,000	[2]

[1]	See Note 9 for information on the Companyâ€™s derivative instruments.
[2]	Represents the absolute notional value of all outstanding contracts, consisting of long and short positions.

Commitments_and_Contingencies_

Commitments and Contingencies (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014
Unfunded Investment Commitments [Abstract]	'
Investment commitments	$966.10
LOC Facilities [Member]	'
Line of Credit Facility [Abstract]	'
Amount outstanding	430
Investments pledged as collateral	493.1
Other secured letter of credit facilities	'
Line of Credit Facility [Abstract]	'
Maximum borrowing capacity	192
Credit Agreement	'
Line of Credit Facility [Abstract]	'
Credit facility expiration date	18-Aug-14
Amount outstanding	100
Unsecured revolving loan and letter of credit facility	'
Line of Credit Facility [Abstract]	'
Maximum borrowing capacity	300
Secured letter of credit facility	'
Line of Credit Facility [Abstract]	'
Maximum borrowing capacity	$500

Share_Transactions_Details

Share Transactions (Details) (Common Shares, USD $)	3 Months Ended
Share Transactions (Details) (Common Shares, USD $)	Mar. 31, 2014	Mar. 31, 2013
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)	'	930,759
Treasury stock, value of shares acquired	'	41,000,000
Remaining authorized repurchase amount	$712,100,000	'

Income_Taxes_Details

Income Taxes (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'	'	'
Effective tax rate on income before income taxes (percentage)	2.00%	1.90%	'
Net deferred tax assets	$151.20	'	$128.60
Income taxes paid	$1.60	$1.30	'

Other_Comprehensive_Income_Los2

Other Comprehensive Income (Loss) - Amounts reclassified from accumulated other comprehensive income (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'
Other-than-temporary impairment losses	($2,971)	($2,246)
Income before income taxes	182,883	261,329
Income tax expense	-3,738	-4,853
Net of tax	182,500	256,476
Reclassification out of accumulated other comprehensive income \| Unrealized appreciation on available-for-sale investments	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'
Net realized gains	26,038	44,367
Other-than-temporary impairment losses	-2,971	-2,248
Income before income taxes	23,067	42,119
Income tax expense	-1,818	-3,418
Net of tax	$21,249	$38,701

Other_Comprehensive_Income_Los3

Other Comprehensive Income (Loss) - Components of other comprehensive income (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Before tax amount:	'	'
Unrealized holding gains arising during period, before tax	$75,400	$10,347
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), before tax	0	-2
Less reclassification of net realized gains included in net income, before tax	23,067	42,119
Foreign currency translation adjustments, before tax	-1,349	-28,222
Other comprehensive income (loss), before tax	50,984	-59,996
Tax expense (benefit):	'	'
Unrealized holding gains arising during period, tax	4,047	876
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), tax	0	0
Less reclassification of net realized gains included in net income, tax	1,818	3,418
Foreign currency translation adjustments, tax	0	0
Other comprehensive income (loss), tax	2,229	-2,542
Net of tax amount:	'	'
Unrealized holding gains arising during period, net of tax	71,353	9,471
Portion of other-than-temporary impairment losses recognized in other comprehensive income (loss), net of tax	0	-2
Less reclassification of net realized gains included in net income, net of tax	21,249	38,701
Foreign currency translation adjustments, net of tax	-1,349	-28,222
Net current period other comprehensive income (loss)	$48,755	($57,454)

Guarantor_Financial_Informatio2

Guarantor Financial Information - Condensed consolidating balance sheet (Details) (USD $)	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013		Dec. 31, 2012
Assets	'		'		'		'
Total investments	$13,843,497		$13,611,734		'		'
Cash	1,569,605		434,057		356,767		371,041
Investments in subsidiaries	0		0		'		'
Due from subsidiaries and affiliates	0		0		'		'
Premiums receivable	1,008,375		753,924		'		'
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	1,790,025		1,804,330		'		'
Contractholder receivables	1,118,991		1,064,246		'		'
Prepaid reinsurance premiums	349,077		328,343		'		'
Deferred acquisition costs, net	384,294		342,314		'		'
Other assets	1,736,494		1,227,146		'		'
Total assets	21,800,358		19,566,094		18,757,061		'
Liabilities	'		'		'		'
Reserve for losses and loss adjustment expenses	8,938,958		8,824,696		'		'
Unearned premiums	2,148,475		1,896,365		'		'
Reinsurance balances payable	201,794		196,167		'		'
Contractholder payables	1,118,991		1,064,246		'		'
Deposit accounting liabilities	409,080		421,297		'		'
Senior notes	800,000		800,000		'		'
Revolving credit agreement borrowings	100,000		100,000		'		'
Due to subsidiaries and affiliates	0		0		'		'
Other liabilities	1,178,197		615,827		'		'
Total liabilities	14,895,495		13,918,598		13,421,531		'
Redeemable noncontrolling interests	219,234	[1]	0	[1]	'		'
Shareholders' Equity	'		'		'		'
Total shareholders' equity available to Arch	5,892,133		5,647,496		5,335,530		'
Non-redeemable noncontrolling interests	793,496	[1]	0	[1]	0	[1]	'
Total shareholders' equity	6,685,629		5,647,496		5,335,530		'
Total liabilities, noncontrolling interests and shareholders' equity	21,800,358		19,566,094		'		'
Reportable Legal Entities \| ACGL (Parent Guarantor)	'		'		'		'
Assets	'		'		'		'
Total investments	2,546		2,530		'		'
Cash	12,353		3,223		3,614		6,417
Investments in subsidiaries	6,288,035		6,046,060		'		'
Due from subsidiaries and affiliates	503		2,251		'		'
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	6,309		6,598		'		'
Total assets	6,309,746		6,060,662		'		'
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	2,091		18		'		'
Other liabilities	15,522		13,148		'		'
Total liabilities	417,613		413,166		'		'
Redeemable noncontrolling interests	0	[1]	0		'		'
Shareholders' Equity	'		'		'		'
Total shareholders' equity available to Arch	5,892,133		5,647,496		'		'
Non-redeemable noncontrolling interests	0	[1]	0		'		'
Total shareholders' equity	5,892,133		5,647,496		'		'
Total liabilities, noncontrolling interests and shareholders' equity	6,309,746		6,060,662		'		'
Reportable Legal Entities \| Arch-U.S. (Subsidiary Issuer)	'		'		'		'
Assets	'		'		'		'
Total investments	48,689		408,957		'		'
Cash	45,472		509		356		612
Investments in subsidiaries	1,598,732		1,258,889		'		'
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	62,500		60,342		'		'
Total assets	1,755,393		1,728,697		'		'
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		500,000		'		'
Revolving credit agreement borrowings	0		0		'		'
Due to subsidiaries and affiliates	1,167		10,250		'		'
Other liabilities	46,040		33,206		'		'
Total liabilities	547,207		543,456		'		'
Redeemable noncontrolling interests	0	[1]	0		'		'
Shareholders' Equity	'		'		'		'
Total shareholders' equity available to Arch	1,208,186		1,185,241		'		'
Non-redeemable noncontrolling interests	0	[1]	0		'		'
Total shareholders' equity	1,208,186		1,185,241		'		'
Total liabilities, noncontrolling interests and shareholders' equity	1,755,393		1,728,697		'		'
Reportable Legal Entities \| Other ACGL Subsidiaries	'		'		'		'
Assets	'		'		'		'
Total investments	13,792,262		13,200,247		'		'
Cash	1,511,780		430,325		352,797		364,012
Investments in subsidiaries	0		0		'		'
Due from subsidiaries and affiliates	401,987		405,110		'		'
Premiums receivable	1,399,825		1,085,369		'		'
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	5,617,877		5,645,156		'		'
Contractholder receivables	1,118,991		1,064,246		'		'
Prepaid reinsurance premiums	1,293,460		1,109,312		'		'
Deferred acquisition costs, net	384,294		342,314		'		'
Other assets	2,211,353		1,714,651		'		'
Total assets	27,731,829		24,996,730		'		'
Liabilities	'		'		'		'
Reserve for losses and loss adjustment expenses	12,749,908		12,625,766		'		'
Unearned premiums	3,092,858		2,677,334		'		'
Reinsurance balances payable	742,630		662,394		'		'
Contractholder payables	1,118,991		1,064,246		'		'
Deposit accounting liabilities	735,993		758,490		'		'
Senior notes	0		0		'		'
Revolving credit agreement borrowings	0		0		'		'
Due to subsidiaries and affiliates	399,232		397,093		'		'
Other liabilities	1,200,906		691,699		'		'
Total liabilities	20,040,518		18,877,022		'		'
Redeemable noncontrolling interests	219,234	[1]	0		'		'
Shareholders' Equity	'		'		'		'
Total shareholders' equity available to Arch	6,678,581		6,119,708		'		'
Non-redeemable noncontrolling interests	793,496	[1]	0		'		'
Total shareholders' equity	7,472,077		6,119,708		'		'
Total liabilities, noncontrolling interests and shareholders' equity	27,731,829		24,996,730		'		'
Consolidating Adjustments and Eliminations	'		'		'		'
Assets	'		'		'		'
Total investments	0		0		'		'
Cash	0		0		0		0
Investments in subsidiaries	-7,886,767		-7,304,949		'		'
Due from subsidiaries and affiliates	-402,490		-407,361		'		'
Premiums receivable	-391,450		-331,445		'		'
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	-3,827,852		-3,840,826		'		'
Contractholder receivables	0		0		'		'
Prepaid reinsurance premiums	-944,383		-780,969		'		'
Deferred acquisition costs, net	0		0		'		'
Other assets	-543,668		-554,445		'		'
Total assets	-13,996,610		-13,219,995		'		'
Liabilities	'		'		'		'
Reserve for losses and loss adjustment expenses	-3,810,950		-3,801,070		'		'
Unearned premiums	-944,383		-780,969		'		'
Reinsurance balances payable	-540,836		-466,227		'		'
Contractholder payables	0		0		'		'
Deposit accounting liabilities	-326,913		-337,193		'		'
Senior notes	0		0		'		'
Revolving credit agreement borrowings	0		0		'		'
Due to subsidiaries and affiliates	-402,490		-407,361		'		'
Other liabilities	-84,271		-122,226		'		'
Total liabilities	-6,109,843		-5,915,046		'		'
Redeemable noncontrolling interests	0	[1]	0		'		'
Shareholders' Equity	'		'		'		'
Total shareholders' equity available to Arch	-7,886,767		-7,304,949		'		'
Non-redeemable noncontrolling interests	0	[1]	0		'		'
Total shareholders' equity	-7,886,767		-7,304,949		'		'
Total liabilities, noncontrolling interests and shareholders' equity	($13,996,610)		($13,219,995)		'		'

[1]	See Note 4.

Guarantor_Financial_Informatio3

Guarantor Financial Information - Condensed consolidating statement of income and comprehensive income (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Revenues	'		'
Premiums Earned, Net	$859,780		$752,770
Net investment income	66,994		65,672
Net realized gains	19,697		58,340
Net impairment losses recognized in earnings	-2,971		-2,246
Other underwriting income	1,582		538
Equity in net income of investment funds accounted for using the equity method	3,253		13,823
Other income (loss)	-2,104		1,244
Total revenues	946,231		890,141
Expenses	'		'
Losses and loss adjustment expenses	436,240		399,403
Acquisition expenses	160,342		127,592
Other operating expenses	145,799		120,183
Interest expense	14,404		5,898
Net foreign exchange losses (gains)	6,563		-24,264
Total expenses	763,348		628,812
Income (loss) before income taxes	182,883		261,329
Income tax expense (benefit)	-3,738		-4,853
Income Loss Net Of Income Taxes And Before Equity In Net Income Of Subsidiaries	179,145		256,476
Income (Loss) from Subsidiaries, Net of Tax	0		0
Net income	179,145		256,476
Net (income) loss attributable to noncontrolling interests	3,355	[1]	0	[1]
Net income available to Arch	182,500		256,476
Preferred dividends	-5,484		-5,484
Net income available to Arch common shareholders	177,016		250,992
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	231,255		199,022
Reportable Legal Entities \| ACGL (Parent Guarantor)	'		'
Revenues	'		'
Premiums Earned, Net	0		0
Net investment income	0		0
Net realized gains	0		0
Net impairment losses recognized in earnings	0		0
Other underwriting income	0		0
Equity in net income of investment funds accounted for using the equity method	0		0
Other income (loss)	0		0
Total revenues	0		0
Expenses	'		'
Losses and loss adjustment expenses	0		0
Acquisition expenses	0		0
Other operating expenses	10,307		9,942
Interest expense	5,853		5,820
Net foreign exchange losses (gains)	0		0
Total expenses	16,160		15,762
Income (loss) before income taxes	-16,160		-15,762
Income tax expense (benefit)	0		0
Income Loss Net Of Income Taxes And Before Equity In Net Income Of Subsidiaries	-16,160		-15,762
Income (Loss) from Subsidiaries, Net of Tax	198,660		272,238
Net income	182,500		256,476
Net (income) loss attributable to noncontrolling interests	0	[1]	0
Net income available to Arch	182,500		256,476
Preferred dividends	-5,484		-5,484
Net income available to Arch common shareholders	177,016		250,992
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	231,255		199,022
Reportable Legal Entities \| Arch-U.S. (Subsidiary Issuer)	'		'
Revenues	'		'
Premiums Earned, Net	0		0
Net investment income	0		0
Net realized gains	0		0
Net impairment losses recognized in earnings	0		0
Other underwriting income	0		0
Equity in net income of investment funds accounted for using the equity method	0		0
Other income (loss)	0		0
Total revenues	0		0
Expenses	'		'
Losses and loss adjustment expenses	0		0
Acquisition expenses	0		0
Other operating expenses	977		777
Interest expense	6,514		3
Net foreign exchange losses (gains)	0		0
Total expenses	7,491		780
Income (loss) before income taxes	-7,491		-780
Income tax expense (benefit)	2,788		235
Income Loss Net Of Income Taxes And Before Equity In Net Income Of Subsidiaries	-4,703		-545
Income (Loss) from Subsidiaries, Net of Tax	22,152		18,482
Net income	17,449		17,937
Net (income) loss attributable to noncontrolling interests	0	[1]	0
Net income available to Arch	17,449		17,937
Preferred dividends	0		0
Net income available to Arch common shareholders	17,449		17,937
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	17,220		6,152
Reportable Legal Entities \| Other ACGL Subsidiaries	'		'
Revenues	'		'
Premiums Earned, Net	859,780		752,770
Net investment income	77,001		72,322
Net realized gains	19,697		58,340
Net impairment losses recognized in earnings	-2,971		-2,246
Other underwriting income	1,582		538
Equity in net income of investment funds accounted for using the equity method	3,253		13,823
Other income (loss)	-2,104		1,244
Total revenues	956,238		896,791
Expenses	'		'
Losses and loss adjustment expenses	436,240		399,403
Acquisition expenses	160,342		127,592
Other operating expenses	134,515		109,464
Interest expense	12,044		6,725
Net foreign exchange losses (gains)	5,741		-12,772
Total expenses	748,882		630,412
Income (loss) before income taxes	207,356		266,379
Income tax expense (benefit)	-6,526		-5,088
Income Loss Net Of Income Taxes And Before Equity In Net Income Of Subsidiaries	200,830		261,291
Income (Loss) from Subsidiaries, Net of Tax	0		0
Net income	200,830		261,291
Net (income) loss attributable to noncontrolling interests	3,355	[1]	0
Net income available to Arch	204,185		261,291
Preferred dividends	0		0
Net income available to Arch common shareholders	204,185		261,291
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	252,119		215,329
Consolidating Adjustments and Eliminations	'		'
Revenues	'		'
Premiums Earned, Net	0		0
Net investment income	-10,007		-6,650
Net realized gains	0		0
Net impairment losses recognized in earnings	0		0
Other underwriting income	0		0
Equity in net income of investment funds accounted for using the equity method	0		0
Other income (loss)	0		0
Total revenues	-10,007		-6,650
Expenses	'		'
Losses and loss adjustment expenses	0		0
Acquisition expenses	0		0
Other operating expenses	0		0
Interest expense	-10,007		-6,650
Net foreign exchange losses (gains)	822		-11,492
Total expenses	-9,185		-18,142
Income (loss) before income taxes	-822		11,492
Income tax expense (benefit)	0		0
Income Loss Net Of Income Taxes And Before Equity In Net Income Of Subsidiaries	-822		11,492
Income (Loss) from Subsidiaries, Net of Tax	-220,812		-290,720
Net income	-221,634		-279,228
Net (income) loss attributable to noncontrolling interests	0	[1]	0
Net income available to Arch	-221,634		-279,228
Preferred dividends	0		0
Net income available to Arch common shareholders	-221,634		-279,228
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	($269,339)		($221,481)

[1]	See Note 4.

Guarantor_Financial_Informatio4

Guarantor Financial Information - Condensed consolidating statement of cash flows (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]	'		'
Net Cash Provided by (Used in) Operating Activities	$198,169		$205,659
Purchases of fixed maturity investments	-7,131,071		-3,970,320
Purchases of equity securities	-89,227		-63,353
Purchases of other investments	-304,454		-250,442
Proceeds from the sale of fixed maturity investments	7,014,281		3,796,638
Proceeds from the sale of equity securities	49,614		81,513
Proceeds from the sale of other investments	331,176		280,010
Proceeds from redemptions and maturities of fixed maturity investments	168,484		181,727
Net (purchases) sales of short-term investments	156,262		-221,444
Change in investment of securities lending collateral	4,669		-41,019
Contributions to subsidiaries	0		0
Intercompany loans issued	0		0
Purchase of business, net of cash acquired	-235,578	[1]	0	[1]
Purchases of furniture, equipment and other assets	-5,382		-3,742
Net Cash Used For Investing Activities	-41,226		-210,432
Purchases of common shares under share repurchase program	0		-40,964
Proceeds from common shares issued, net	3,021		1,280
Proceeds from intercompany borrowings	'		0
Repayments of intercompany borrowings	0		'
Change in securities lending collateral	-4,669		41,019
Third party investment in non-redeemable noncontrolling interests	796,903	[2]	0	[2]
Third party investment in redeemable noncontrolling interests	186,893	[2]	0	[2]
Dividends paid to parent	0		0
Other	1,700		1,084
Preferred dividends paid	-5,484		-5,484
Net Cash Provided By (Used For) Financing Activities	978,364		-3,065
Effects of exchange rate changes on foreign currency cash	241		-6,436
Cash and Cash Equivalents, Period Increase (Decrease)	1,135,548		-14,274
Cash	1,569,605		356,767
Reportable Legal Entities \| ACGL (Parent Guarantor)	'		'
Condensed Cash Flow Statements, Captions [Line Items]	'		'
Net Cash Provided by (Used in) Operating Activities	11,685		34,432
Purchases of fixed maturity investments	0		0
Purchases of equity securities	0		0
Purchases of other investments	0		0
Proceeds from the sale of fixed maturity investments	0		0
Proceeds from the sale of equity securities	0		0
Proceeds from the sale of other investments	0		0
Proceeds from redemptions and maturities of fixed maturity investments	0		0
Net (purchases) sales of short-term investments	-16		7,964
Change in investment of securities lending collateral	0		0
Contributions to subsidiaries	0		0
Intercompany loans issued	0		0
Purchase of business, net of cash acquired	0		'
Purchases of furniture, equipment and other assets	-76		-31
Net Cash Used For Investing Activities	-92		7,933
Purchases of common shares under share repurchase program	'		-40,964
Proceeds from common shares issued, net	3,021		1,280
Proceeds from intercompany borrowings	'		0
Repayments of intercompany borrowings	0		'
Change in securities lending collateral	0		0
Third party investment in non-redeemable noncontrolling interests	0	[2]	'
Third party investment in redeemable noncontrolling interests	0	[2]	'
Dividends paid to parent	0		0
Other	0		0
Preferred dividends paid	-5,484		-5,484
Net Cash Provided By (Used For) Financing Activities	-2,463		-45,168
Effects of exchange rate changes on foreign currency cash	0		0
Cash and Cash Equivalents, Period Increase (Decrease)	9,130		-2,803
Cash	12,353		3,614
Reportable Legal Entities \| Arch-U.S. (Subsidiary Issuer)	'		'
Condensed Cash Flow Statements, Captions [Line Items]	'		'
Net Cash Provided by (Used in) Operating Activities	7,151		-254
Purchases of fixed maturity investments	0		0
Purchases of equity securities	0		0
Purchases of other investments	0		0
Proceeds from the sale of fixed maturity investments	0		0
Proceeds from the sale of equity securities	0		0
Proceeds from the sale of other investments	0		0
Proceeds from redemptions and maturities of fixed maturity investments	0		0
Net (purchases) sales of short-term investments	360,269		-2
Change in investment of securities lending collateral	0		0
Contributions to subsidiaries	-312,207		-10,250
Intercompany loans issued	0		0
Purchase of business, net of cash acquired	0		'
Purchases of furniture, equipment and other assets	0		0
Net Cash Used For Investing Activities	48,062		-10,252
Purchases of common shares under share repurchase program	'		0
Proceeds from common shares issued, net	0		0
Proceeds from intercompany borrowings	'		10,250
Repayments of intercompany borrowings	-10,250		'
Change in securities lending collateral	0		0
Third party investment in non-redeemable noncontrolling interests	0	[2]	'
Third party investment in redeemable noncontrolling interests	0	[2]	'
Dividends paid to parent	0		0
Other	0		0
Preferred dividends paid	0		0
Net Cash Provided By (Used For) Financing Activities	-10,250		10,250
Effects of exchange rate changes on foreign currency cash	0		0
Cash and Cash Equivalents, Period Increase (Decrease)	44,963		-256
Cash	45,472		356
Reportable Legal Entities \| Other ACGL Subsidiaries	'		'
Condensed Cash Flow Statements, Captions [Line Items]	'		'
Net Cash Provided by (Used in) Operating Activities	194,833		216,481
Purchases of fixed maturity investments	-7,131,071		-3,970,320
Purchases of equity securities	-89,227		-63,353
Purchases of other investments	-304,454		-250,442
Proceeds from the sale of fixed maturity investments	7,014,281		3,796,638
Proceeds from the sale of equity securities	49,614		81,513
Proceeds from the sale of other investments	331,176		280,010
Proceeds from redemptions and maturities of fixed maturity investments	168,484		181,727
Net (purchases) sales of short-term investments	-203,991		-229,406
Change in investment of securities lending collateral	4,669		-41,019
Contributions to subsidiaries	-100,000		-250
Intercompany loans issued	10,250		-10,250
Purchase of business, net of cash acquired	-235,578		'
Purchases of furniture, equipment and other assets	-5,306		-3,711
Net Cash Used For Investing Activities	-491,153		-228,863
Purchases of common shares under share repurchase program	'		0
Proceeds from common shares issued, net	412,207		10,500
Proceeds from intercompany borrowings	'		0
Repayments of intercompany borrowings	0		'
Change in securities lending collateral	-4,669		41,019
Third party investment in non-redeemable noncontrolling interests	796,903	[2]	'
Third party investment in redeemable noncontrolling interests	186,893	[2]	'
Dividends paid to parent	-15,500		-45,000
Other	1,700		1,084
Preferred dividends paid	0		0
Net Cash Provided By (Used For) Financing Activities	1,377,534		7,603
Effects of exchange rate changes on foreign currency cash	241		-6,436
Cash and Cash Equivalents, Period Increase (Decrease)	1,081,455		-11,215
Cash	1,511,780		352,797
Consolidating Adjustments and Eliminations	'		'
Condensed Cash Flow Statements, Captions [Line Items]	'		'
Net Cash Provided by (Used in) Operating Activities	-15,500		-45,000
Purchases of fixed maturity investments	0		0
Purchases of equity securities	0		0
Purchases of other investments	0		0
Proceeds from the sale of fixed maturity investments	0		0
Proceeds from the sale of equity securities	0		0
Proceeds from the sale of other investments	0		0
Proceeds from redemptions and maturities of fixed maturity investments	0		0
Net (purchases) sales of short-term investments	0		0
Change in investment of securities lending collateral	0		0
Contributions to subsidiaries	412,207		10,500
Intercompany loans issued	-10,250		10,250
Purchase of business, net of cash acquired	0		'
Purchases of furniture, equipment and other assets	0		0
Net Cash Used For Investing Activities	401,957		20,750
Purchases of common shares under share repurchase program	'		0
Proceeds from common shares issued, net	-412,207		-10,500
Proceeds from intercompany borrowings	'		-10,250
Repayments of intercompany borrowings	10,250		'
Change in securities lending collateral	0		0
Third party investment in non-redeemable noncontrolling interests	0	[2]	'
Third party investment in redeemable noncontrolling interests	0	[2]	'
Dividends paid to parent	15,500		45,000
Other	0		0
Preferred dividends paid	0		0
Net Cash Provided By (Used For) Financing Activities	-386,457		24,250
Effects of exchange rate changes on foreign currency cash	0		0
Cash and Cash Equivalents, Period Increase (Decrease)	0		0
Cash	$0		$0

[1]	See Note 2.
[2]	See Note 4.