Allied World Assurance 10-Q 22 Apr 15 2015 Q1 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 13, 2015
Document And Entity Information [Abstract]
Entity Registrant Name	Allied World Assurance Co Holdings, AG
Entity Central Index Key	1163348
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		95,444,669

Unaudited_Condensed_Consolidat

Unaudited Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
ASSETS:
Fixed maturity investments trading, at fair value (amortized cost: 2015: $6,229,608; 2014: $6,035,240)	$6,288,897	$6,069,010
Equity securities trading, at fair value (cost: 2015: $798,275; 2014: $791,206)	856,652	844,163
Other invested assets	926,407	955,509
Total investments	8,071,956	7,868,682
Cash and cash equivalents	515,070	589,339
Restricted cash	49,931	80,971
Insurance balances receivable	773,394	664,815
Funds held	479,909	724,021
Prepaid reinsurance	318,838	360,732
Reinsurance recoverable	1,350,311	1,340,256
Reinsurance recoverable on paid losses	107,071	86,075
Accrued investment income	28,267	28,456
Net deferred acquisition costs	187,246	151,546
Goodwill	280,725	278,258
Intangible assets	49,274	46,298
Balances receivable on sale of investments	46,822	47,149
Net deferred tax assets	29,922	33,615
Other assets	329,050	121,350
Total assets	12,617,786	12,421,563
LIABILITIES:
Reserve for losses and loss expenses	5,905,110	5,881,165
Unearned premiums	1,717,399	1,555,313
Reinsurance balances payable	184,322	180,060
Balances due on purchases of investments	34,396	5,428
Senior notes	798,881	798,802
Other long-term debt	19,730	19,213
Dividends payable	21,528	21,669
Accounts payable and accrued liabilities	107,353	181,622
Total liabilities	8,788,719	8,643,272
Commitments and contingencies
SHAREHOLDERS’ EQUITY:
Common shares: 2015 and 2014: par value CHF 4.10 per share (2015: 100,299,454; 2014: 100,775,256 shares issued and 2015: 95,444,669; 2014: 96,195,482 shares outstanding)	406,088	408,020
Treasury shares, at cost (2015: 4,854,785; 2014: 4,579,774)	-162,356	-143,075
Retained earnings	3,585,335	3,513,346
Total shareholders’ equity	3,829,067	3,778,291
Total liabilities and shareholders’ equity	$12,617,786	$12,421,563

Unaudited_Condensed_Consolidat1

Unaudited Condensed Consolidated Balance Sheets (Parenthetical)(USD ($))	Mar. 31, 2015	Dec. 31, 2014
In Thousands, except Share data, unless otherwise specified
Fixed maturity investments trading, amortized cost	$6,229,608	$6,035,240
Equity securities trading - cost	$798,275	$791,206
Common stock, shares issued	100,299,454	100,775,256
Common stock, shares outstanding	95,444,669	96,195,482
Treasury stock (shares)	4,854,785	4,579,774

Unaudited_Condensed_Consolidat2

Unaudited Condensed Consolidated Statements Of Operations And Comprehensive Income (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
REVENUES:
Gross premiums written	$880,614	$901,393
Premiums ceded	-108,086	-129,779
Net premiums written	772,528	771,614
Change in unearned premiums	-203,980	-241,329
Net premiums earned	568,548	530,285
Net investment income	44,551	47,619
Net realized investment gains	45,025	54,205
Other income	854	0
Total revenues	658,978	632,109
EXPENSES:
Net losses and loss expenses	325,176	275,286
Acquisition costs	78,699	67,722
General and administrative expenses	97,138	80,340
Other expense	1,823	0
Amortization of intangible assets	633	633
Interest expense	14,337	14,534
Foreign exchange loss	9,897	49
Total expenses	527,703	438,564
Income before income taxes	131,275	193,545
Income tax expense	6,919	16,573
NET INCOME	124,356	176,972
Other comprehensive income	0	0
COMPREHENSIVE INCOME	$124,356	$176,972
PER SHARE DATA
Basic earnings per share	$1.30	$1.78
Diluted earnings per share	$1.27	$1.74
Weighted average common shares outstanding	95,935,551	99,545,187
Weighted average common shares and common share equivalents outstanding	97,577,029	101,584,662
Dividends paid per share	$0.23	$0.17

Unaudited_Condensed_Consolidat3

Unaudited Condensed Consolidated Statements Of Shareholders' Equity (USD $)	Total	Common shares	Treasury shares	Retained earnings
In Thousands
Balance, at beginning of period at Dec. 31, 2013	$3,519,826	$418,988	($79,992)	$3,180,830
Net income	176,972			176,972
Dividends	-16,489			-16,489
Stock compensation	5,028		11,236	-6,208
Share repurchases	-68,659		-68,659
Shares cancelled	0	-8,168	68,659	-60,491
Balance, at end of period at Mar. 31, 2014	3,616,678	410,820	-68,756	3,274,614
Balance, at beginning of period at Dec. 31, 2014	3,778,291	408,020	-143,075	3,513,346
Net income	124,356			124,356
Dividends	-21,522			-21,522
Stock compensation	-1,109		12,288	-13,397
Share repurchases	-50,949		-50,949
Shares cancelled	0	-1,932	19,380	-17,448
Balance, at end of period at Mar. 31, 2015	$3,829,067	$406,088	($162,356)	$3,585,335

Unaudited_Condensed_Consolidat4

Unaudited Condensed Consolidated Statements Of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:
Net income	$124,356	$176,972
Adjustments to reconcile net income to cash provided by operating activities:
Net realized gains on sales of investments	-32,536	-49,756
Mark to market adjustments	-22,694	-13,956
Stock compensation expense	4,002	4,240
Undistributed income of equity method investments	9,767	-2,292
Changes in:
Reserve for losses and loss expenses, net of reinsurance recoverables	13,890	44,248
Unearned premiums, net of prepaid reinsurance	203,980	241,329
Insurance balances receivable	-108,579	-175,739
Reinsurance recoverable on paid losses	-20,996	840
Funds held	244,112	184,629
Reinsurance balances payable	4,262	-12,982
Net deferred acquisition costs	-35,700	-40,443
Net deferred tax assets	3,693	521
Accounts payable and accrued liabilities	-75,008	-83,745
Other items, net	5,027	29,230
Net cash provided by operating activities	317,576	303,096
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	-1,723,443	-1,568,993
Purchases of other invested assets	-233,252	-779,934
Sales of trading securities	1,561,890	1,494,648
Sales of other invested assets	56,535	663,237
Purchases of fixed assets	-8,374	-2,336
Net cash paid on acquisition	-3,543	0
Change in restricted cash	31,040	4,823
Net cash used in investing activities	-319,147	-188,555
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	-21,669	-16,732
Proceeds from the exercise of stock options	4,223	3,030
Share repurchases	-50,273	-68,659
Net cash used in financing activities	-67,719	-82,361
Effect of exchange rate changes on foreign currency cash	-4,979	1,686
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	-74,269	33,866
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	589,339	531,936
CASH AND CASH EQUIVALENTS, END OF PERIOD	515,070	565,802
Supplemental disclosure of cash flow information:
Cash paid for income taxes	717	529
Cash paid for interest expense	$18,750	$18,750

General

General	3 Months Ended
	Mar. 31, 2015
General [Abstract]
General	GENERAL
	Allied World Assurance Company Holdings, AG, a Swiss holding company (“Allied World Switzerland”), through its wholly-owned subsidiaries (collectively, the “Company”), is a global provider of a diversified portfolio of property and casualty insurance and reinsurance products with operations in Australia, Bermuda, Canada, Europe Hong Kong, Singapore and the United States as well as Lloyd's Syndicate 2232. References to $ are to the lawful currency of the United States and to CHF are to the lawful currency of Switzerland.
	In January 2015, the Company acquired Latin American Underwriters Holdings Ltd. ("LAU") for $5,105. LAU had previously underwritten trade credit insurance and political risk coverages solely for the Company since 2010. As part of the acquisition, the Company recorded goodwill of $2,467 and customer relationship intangibles of $3,610, which have a five-year amortization period. The Company also recorded $1,000 of contingent consideration related to certain earn-out payments.
	During the fourth quarter of 2014, the Company reorganized how it manages its business, and as a result it realigned its executive management team and changed its reportable segments to correspond to the reorganization. The Company's Bermuda insurance operations, except for the trade credit line of business, which had previously been included in the international insurance segment, was combined with the U.S. insurance segment, with the new segment renamed the "North American Insurance" segment. The remaining direct insurance operations of the international insurance segment was renamed the "Global Markets Insurance" segment. The Reinsurance segment remained unchanged. The newly created segments are included in Note 12 and prior periods have been recast to conform to the new presentation.
	On May 1, 2014, the shareholders approved a 3-for-1 stock split of the Company's common shares. All historical share and per share amounts reflect the effect of the stock split.

Basis_of_Preparation_and_Conso

Basis of Preparation and Consolidation	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Preparation and Consolidation	BASIS OF PREPARATION AND CONSOLIDATION
	These unaudited condensed consolidated financial statements include the accounts of the Company and have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial information and with Article 10 of Regulation S-X as promulgated by the U.S. Securities and Exchange Commission (“SEC”). Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the opinion of management, these unaudited condensed consolidated financial statements reflect all adjustments that are normal and recurring in nature and necessary for a fair presentation of financial position and results of operations as of the end of and for the periods presented. The results of operations for any interim period are not necessarily indicative of the results for a full year.
	The preparation of financial statements in conformity with U.S. 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. The significant estimates reflected in the Company’s financial statements, include, but are not limited to:
	•	The premium estimates for certain reinsurance agreements,
	•	Recoverability of deferred acquisition costs,
	•	The reserve for outstanding losses and loss expenses,
	•	Valuation of ceded reinsurance recoverables,
	•	Determination of impairment of goodwill and other intangible assets, and
	•	Valuation of financial instruments.
	Intercompany accounts and transactions have been eliminated on consolidation and all entities meeting consolidation requirements have been included in the unaudited condensed consolidated financial statements.
	These unaudited condensed consolidated financial statements, including these notes, should be read in conjunction with the Company’s audited consolidated financial statements, and related notes thereto, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014.

New_Accounting_Pronouncements

New Accounting Pronouncements	3 Months Ended
	Mar. 31, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncements	NEW ACCOUNTING PRONOUNCEMENTS
	In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update 2014-09, "Revenue from Contracts with Customers" ("ASU 2014-09"). ASU 2014-09 provides a framework, through a five-step process, for recognizing revenue from customers, improves comparability and consistency of recognizing revenue across entities, industries, jurisdictions and capital markets, and requires enhanced disclosures. Certain contracts with customers are specifically excluded from the scope of ASU 2014-09, including, among others, insurance contracts accounted for under Accounting Standard Codification 944, Financial Services - Insurance. ASU 2014-09 is effective on January 1, 2017 with retrospective adoption required for the comparative periods. In recent re-deliberations, the FASB has decided to propose a one-year deferral of the effective date of ASU 2014-09, such that it will become effective on January 1, 2018. The Company is currently assessing the impact the adoption of ASU 2014-09 will have on future financial statements and related disclosures.
	In August 2014, the FASB issued Accounting Standards Update 2014-15, "Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern" ("ASU 2014-15"). Currently, there is no guidance under U.S. GAAP regarding management's responsibility to assess whether there is substantial doubt about an entity's ability to continue as a going concern. Under ASU 2014-15, the Company will be required to assess its ability to continue as a going concern each interim and annual reporting period and provide certain disclosures if there is substantial doubt about the entity's ability to continue as a going concern, including management's plan to alleviate the substantial doubt. ASU 2014-15 is effective for the year ended December 31, 2016 and early adoption is permitted. The Company early adopted ASU 2014-15 on January 1, 2015.
	In February 2015, the FASB issued Accounting Standards Update 2015-02, "Amendments to the Consolidation Analysis" ("ASU 2015-02"). ASU 2015-02 amends certain aspects of the consolidation guidance in U.S. GAAP. In particular, it will modify the evaluation of whether limited partnerships and similar legal entities are variable interest entities ("VIEs") or voting interest entities and also eliminates the presumption that a general partner should consolidate a limited partnership. The new guidance will also affect the consolidation analysis of the Company's interests in VIEs, particularly those that have fee arrangements and related party relationships. ASU 2015-02 is effective on January 1, 2016 and retrospectively adoption is required either through a modified retrospective approach by recording a cumulative-effect adjustment to equity as of the beginning of the year of adoption or retrospectively for all comparative periods. Early adoption is permitted. The Company is currently assessing the impact the adoption of ASU 2015-02 will have on future financial statements and related disclosures.

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Investments [Abstract]
Investments	INVESTMENTS
	a) Trading Securities
	Securities accounted for at fair value with changes in fair value recognized in the unaudited condensed consolidated statements of operations and comprehensive income (“consolidated income statements”) by category are as follows:
		March 31, 2015						December 31, 2014
		Fair Value			Amortized Cost			Fair Value				Amortized Cost
	U.S. government and government agencies	$	1,577,775		$	1,569,317		$	1,610,502			$	1,610,880
	Non-U.S. government and government agencies	189,448			204,867			188,199				196,332
	States, municipalities and political subdivisions	178,551			172,339			170,567				165,615
	Corporate debt:
	Financial institutions	1,107,108			1,094,338			1,024,667				1,018,777
	Industrials	1,107,548			1,105,744			1,029,729				1,037,820
	Utilities	113,383			113,280			110,997				111,599
	Mortgage-backed	1,286,210			1,238,165			1,263,517				1,219,712
	Asset-backed	728,874			731,558			670,832				674,505
	Total fixed maturity investments	$	6,288,897		$	6,229,608		$	6,069,010			$	6,035,240
		March 31, 2015						December 31, 2014
		Fair Value			Original Cost			Fair Value				Original Cost
	Equity securities	$	856,652		$	798,275		$	844,163			$	791,206
	Other invested assets	792,569			701,637			812,543				725,069
		$	1,649,221		$	1,499,912		$	1,656,706			$	1,516,275
	Other invested assets, included in the table above, include investments in private equity funds, hedge funds and a high yield loan fund that are accounted for at fair value, but exclude other private securities described below in Note 4(b) that are accounted for using the equity method of accounting.
	b) Other Invested Assets
	Details regarding the carrying value, redemption characteristics and unfunded investment commitments of the other invested assets portfolio as of March 31, 2015 and December 31, 2014 were as follows:
	Investment Type	Carrying Value as of March 31, 2015			Investments			Estimated		Investments				Redemption	Redemption	Unfunded
					with			Remaining		without				Frequency(1)	Notice	Commitments
					Redemption			Restriction		Redemption					Period(1)
					Restrictions			Period		Restrictions
	Private equity	$	196,090		$	196,090		2 - 8 Years		$	—					$	191,382
	Mezzanine debt	163,357			163,357			5 - 9 Years		—						200,804
	Distressed	5,545			5,545			3 Years		—						5,347
	Real estate	—			—			9 Years		—						150,000
	Total private equity	364,992			364,992					—						547,533
	Distressed	173,122			173,122					—				Based on net asset value	60 Days	—
	Equity long/short	87,644			—			1 Year		87,644				Quarterly	30 -60 Days	—
	Multi-strategy	15,996			—					15,996				Quarterly	45 -90 Days	—
	Relative value credit	120,460			—					120,460				Quarterly	60 Days	—
	Total hedge funds	397,222			173,122					224,100						—
	High yield loan fund	30,355			—					30,355				Monthly	30 days	—
	Total other invested assets at fair value	792,569			538,114					254,455						547,533
	Other private securities	133,838			—					133,838						—
	Total other invested assets	$	926,407		$	538,114				$	388,293					$	547,533
	Investment Type	Carrying Value as of December 31, 2014			Investments			Estimated		Investments				Redemption	Redemption	Unfunded
					with			Remaining		without				Frequency(1)	Notice	Commitments
					Redemption			Restriction		Redemption					Period(1)
					Restrictions			Period		Restrictions
	Private equity	$	184,576		$	184,576		2 - 8 Years		$	—					$	223,802
	Mezzanine debt	166,905			166,905			5 - 9 Years		—						204,232
	Distressed	5,869			5,869			3 Years		—						5,180
	Real estate	—			—			9 Years		—						50,000
	Total private equity	357,350			357,350					—						483,214
	Distressed	170,169			170,169					—				Based on net asset value	60 Days	—
	Equity long/short	84,198			—					84,198				Quarterly	30 -60 Days	—
	Multi-strategy	51,507			—					51,507				Quarterly	45 -90 Days	—
	Relative value credit	119,156			—					119,156				Quarterly	60 Days	—
	Total hedge funds	425,030			170,169					254,861						—
	High yield loan fund	30,163			—					30,163				Monthly	30 days	—
	Total other invested assets at fair value	812,543			527,519					285,024						483,214
	Other private securities	142,966			—					142,966						—
	Total other invested assets	$	955,509		$	527,519				$	427,990					$	483,214
	_______________________
	-1	The redemption frequency and notice periods only apply to the investments without redemption restrictions. Some or all of these investments may be subject to a gate as described below.
	In general, the Company has invested in hedge funds that require at least 30 days’ notice of redemption and may be redeemed on a monthly, quarterly, semi-annual, annual or longer basis, depending on the fund. Certain hedge funds have lock-up periods ranging from one to three years from initial investment. A lock-up period refers to the initial amount of time an investor is contractually required to invest before having the ability to redeem. Funds that provide for periodic redemptions may, depending on the funds’ governing documents, have the ability to deny or delay a redemption request, called a “gate.” The fund may implement this restriction because the aggregate amount of redemption requests as of a particular date exceeds a specified level, generally ranging from 15% to 25% of the fund’s net assets. The gate is a method for executing an orderly redemption process to reduce the possibility of adversely affecting investors in the fund. Typically, the imposition of a gate delays a portion of the requested redemption, with the remaining portion settled in cash sometime after the redemption date. Certain funds may impose a redemption fee on early redemptions. Interests in private equity funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
	The following describes each investment type:
	•	Private equity funds: Primary funds may invest in companies and general partnership interests. Secondary funds buy limited partnership interests from existing limited partners of primary private equity funds. As owners of private equity funds seek liquidity, they can sell their existing investments, plus any remaining commitment, to secondary market participants. These funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
•	Mezzanine debt funds: Mezzanine debt funds primarily focus on providing capital to upper middle market and middle market companies and private equity sponsors, in connection with leveraged buyouts, mergers and acquisitions, recapitalizations, growth financings and other corporate transactions. The most common position in the capital structure will be between the senior secured debt holder and the equity; however, the funds will utilize a flexible approach when structuring investments, which may include secured debt, subordinated debt, preferred stock and/or private equity. These funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
•	Distressed funds: In distressed debt investing, managers take positions in the debt of companies experiencing significant financial difficulties, including bankruptcy, or in certain positions of the capital structure of structured securities. The manager relies on the fundamental analysis of these securities, including the claims on the assets and the likely return to bondholders. Certain funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
•	Real estate funds: Private real estate funds invest directly in commercial real estate (multifamily units, industrial buildings, office spaces and retail stores) and some residential property.  Real estate managers have diversified portfolios that generally follow core, core-plus, value-added or opportunistic strategies.  These funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
•	Equity long/short funds: In equity long/short funds, managers take long positions in companies they deem to be undervalued and short positions in companies they deem to be overvalued. Long/short managers may invest in countries, regions or sectors and vary by their use of leverage and by their targeted net long position.
•	Multi-strategy funds: These funds may utilize many strategies employed by specialized funds including distressed investing, equity long/short, merger arbitrage, convertible arbitrage, fixed income arbitrage and macro trading.
•	Relative value credit funds: These funds seek to take exposure to credit-sensitive securities, long and/or short, based upon credit analysis of issuers and securities and credit market views.
•	High yield loan fund: A long-only private mutual fund that invests in high yield fixed income securities.
•	Other private securities: These securities mostly include strategic non-controlling minority investments in private asset management companies and other insurance related investments that are accounted for using the equity method of accounting.
c) Net Investment Income
	Three Months Ended
	March 31,
	2015			2014
Fixed maturity investments	$	36,258		$	36,299
Equity securities	3,563			3,253
Other invested assets: hedge funds and private equity	8,380			3,992
Other invested assets: other private securities	866			7,416
Cash and cash equivalents	462			439
Expenses	(4,978		)	(3,780		)
Net investment income	$	44,551		$	47,619
d) Components of Realized Gains and Losses
	Three Months Ended
	March 31,
	2015			2014
Gross realized gains on sale of invested assets	$	45,289		$	62,292
Gross realized losses on sale of invested assets	(13,004		)	(12,247		)
Net realized and unrealized losses on derivatives	(11,632		)	(12,920		)
Mark-to-market gains (losses):
Fixed maturity investments, trading	25,517			22,455
Equity securities, trading	5,420			(21,605		)
Other invested assets, trading	(6,565		)	16,230
Net realized investment gains	$	45,025		$	54,205
e) Pledged Assets
As of March 31, 2015 and December 31, 2014, $3,114,066 and $3,585,792, respectively, of cash and cash equivalents and investments were deposited, pledged or held in trust accounts in favor of ceding companies and other counterparties or government authorities to comply with reinsurance contract provisions, insurance laws and other contract provisions.
In addition, as of March 31, 2015 and December 31, 2014, a further $599,724 and $571,750, respectively, of cash and cash equivalents and investments were pledged as collateral for the Company’s letter of credit facilities. See Note 10(f) to the Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014 for details on the Company’s credit facilities.

Derivative_Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	DERIVATIVE INSTRUMENTS
	As of March 31, 2015 and December 31, 2014, none of the Company’s derivatives were designated as hedges for accounting purposes. The following table summarizes information on the location and amounts of derivative fair values on the unaudited condensed consolidated balance sheets (“consolidated balance sheets”):
		March 31, 2015										December 31, 2014
		Asset			Asset			Liability		Liability		Asset		Asset		Liability		Liability
		Derivative			Derivative			Derivative		Derivative		Derivative		Derivative		Derivative		Derivative
		Notional			Fair Value			Notional		Fair Value		Notional		Fair Value		Notional		Fair Value
		Amount						Amount				Amount				Amount
	Foreign exchange contracts	$	32,833		$	123		$	24,857	$	203	$	33,875	$	1,274	$	167,376	$	991
	Interest rate swaps	—			—			662,200		1,119		—		—		571,500		683
	Total derivatives	$	32,833		$	123		$	687,057	$	1,322	$	33,875	$	1,274	$	738,876	$	1,674
	Derivative assets and derivative liabilities are classified within “other assets” or “accounts payable and accrued liabilities” on the consolidated balance sheets.
	The following table provides the net realized and unrealized gains (losses) on derivatives not designated as hedges recorded on the consolidated income statements:
		Three Months Ended
		March 31,
		2015			2014
	Foreign exchange contracts	$	(7,352	)	$	(868	)
	Total included in foreign exchange loss	(7,352		)	(868		)
	Foreign exchange contracts	1,050			(558		)
	Interest rate futures	(12,682		)	(12,362		)
	Total included in net realized investment gains	(11,632		)	(12,920		)
	Total realized and unrealized losses on derivatives	$	(18,984	)	$	(13,788	)
	Derivative Instruments Not Designated as Hedging Instruments
	The Company is exposed to foreign currency risk in its investment portfolio. Accordingly, the fair values of the Company’s investment portfolio are partially influenced by the change in foreign exchange rates. These foreign currency hedging activities have not been designated as specific hedges for financial reporting purposes.
	The Company’s insurance and reinsurance subsidiaries and branches operate in various foreign countries and consequently the Company’s underwriting portfolio is exposed to foreign currency risk. The Company manages foreign currency risk by seeking to match liabilities under the insurance policies and reinsurance contracts that it writes and that are payable in foreign currencies with cash and investments that are denominated in such currencies. When necessary, the Company may also use derivatives to economically hedge un-matched foreign currency exposures, specifically forward contracts and currency options. For example, the Company purchased a forward contract to hedge a portion of its foreign currency exposure related to the consideration that was paid for the Hong Kong and Singapore operations of RSA.
	The Company also purchases and sells interest rate future and interest rate swap contracts to actively manage the duration and yield curve positioning of its fixed income portfolio. Interest rate futures and interest rate swaps can efficiently increase or decrease the overall duration of the portfolio. Additionally, interest rate future and interest rate swap contracts can be utilized to obtain the desired position along the yield curve in order to protect against certain future yield curve shapes.
	The Company also purchases options to actively manage its equity portfolio.

Fair_Value_Of_Financial_Instru

Fair Value Of Financial Instruments	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	FAIR VALUE OF FINANCIAL INSTRUMENTS
	In accordance with U.S. GAAP, fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. There is a three-level valuation hierarchy for disclosure of fair value measurements. The valuation hierarchy is based upon whether the inputs to the valuation of an asset or liability are observable or unobservable in the market at the measurement date, with quoted market prices being the highest level (Level 1) and unobservable inputs being the lowest level (Level 3). A fair value measurement will fall within the level of the hierarchy based on the input that is significant to determining such measurement. The three levels are defined as follows:
	•	Level 1: Observable inputs to the valuation methodology that are quoted prices (unadjusted) for identical assets or liabilities in active markets.
	•	Level 2: Observable inputs to the valuation methodology other than quoted market prices (unadjusted) for identical assets or liabilities in active markets. Level 2 inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical assets in markets that are not active and inputs other than quoted prices that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the asset or liability.
	•	Level 3: Inputs to the valuation methodology that are unobservable for the asset or liability.
	The following table shows the fair value of the Company’s financial instruments and where in the fair value hierarchy the fair value measurements are included as of the dates indicated below:
	March 31, 2015		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. government and government agencies		$	1,577,775		$	1,577,775		$	1,467,357		$	110,418	$	—
	Non-U.S. government and government agencies		189,448			189,448			—			189,448		—
	States, municipalities and political subdivisions		178,551			178,551			—			178,551		—
	Corporate debt		2,328,039			2,328,039			—			2,328,039		—
	Mortgage-backed		1,286,210			1,286,210			—			1,153,512		132,698
	Asset-backed		728,874			728,874			—			635,942		92,932
	Total fixed maturity investments		6,288,897			6,288,897			1,467,357			4,595,910		225,630
	Equity securities		856,652			856,652			807,885			—		48,767
	Other invested assets		792,569			792,569			—			—		792,569
	Total investments		$	7,938,118		$	7,938,118		$	2,275,242		$	4,595,910	$	1,066,966
	Derivative assets:
	Foreign exchange contracts		$	123		$	123		$	—		$	123	$	—
	Derivative liabilities:
	Foreign exchange contracts		$	203		$	203		$	—		$	203	$	—
	Interest rate swaps		1,119			1,119			—			1,119		—
	Senior notes		$	798,881		$	877,027		$	—		$	877,027	$	—
	Other long-term debt		$	19,730		$	27,175		$	—		$	27,175	$	—
	December 31, 2014		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. Government and Government agencies		$	1,610,502		$	1,610,502		$	1,499,347		$	111,155	$	—
	Non-U.S. Government and Government agencies		188,199			188,199			—			188,199		—
	States, municipalities and political subdivisions		170,567			170,567			—			170,567		—
	Corporate debt		2,165,393			2,165,393			—			2,165,393		—
	Mortgage-backed		1,263,517			1,263,517			—			1,081,734		181,783
	Asset-backed		670,832			670,832			—			615,419		55,413
	Total fixed maturity investments		6,069,010			6,069,010			1,499,347			4,332,467		237,196
	Equity securities		844,163			844,163			800,833			—		43,330
	Other invested assets		812,543			812,543			—			—		812,543
	Total investments		$	7,725,716		$	7,725,716		$	2,300,180		$	4,332,467	$	1,093,069
	Derivative assets:
	Foreign exchange contracts		$	1,274		$	1,274		$	—		$	1,274	$	—
	Derivative liabilities:
	Foreign exchange contracts		$	991		$	991		$	—		$	991	$	—
	Interest rate swaps		$	683		$	683		$	—		$	683	$	—
	Senior notes		$	798,802		$	879,317		$	—		$	879,317	$	—
	Other long-term debt		$	19,213		$	22,583		$	—		$	22,583	$	—
	“Other invested assets” exclude other private securities that the Company did not measure at fair value, but are accounted for using the equity method of accounting. Derivative assets and derivative liabilities relating to foreign exchange contracts and interest rate swaps are classified within “other assets” or “accounts payable and accrued liabilities” on the consolidated balance sheets.
	The following describes the valuation techniques used by the Company to determine the fair value of financial instruments held as of the balance sheet date.
	Recurring Fair Value of Financial Instruments
	U.S. government and government agencies: Comprised primarily of bonds issued by the U.S. Treasury, the Federal Home Loan Bank, the Federal Home Loan Mortgage Corporation and the Federal National Mortgage Association. The fair values of the Company’s U.S. government securities are based on quoted market prices in active markets and are included in the Level 1 fair value hierarchy. The Company believes the market for U.S. Treasury securities is an actively traded market given the high level of daily trading volume. The fair values of U.S. government agency securities are priced using the spread above the risk-free yield curve. As the yields for the risk-free yield curve and the spreads for these securities are observable market inputs, the fair values of U.S. government agency securities are included in the Level 2 fair value hierarchy.
	Non-U.S. government and government agencies: Comprised of fixed income obligations of non-U.S. governmental entities. The fair values of these securities are based on prices obtained from international indices and are included in the Level 2 fair value hierarchy.
	States, municipalities and political subdivisions: Comprised of fixed income obligations of U.S.-domiciled state and municipality entities. The fair values of these securities are based on prices obtained from the new issue market, and are included in the Level 2 fair value hierarchy.
	Corporate debt: Comprised of bonds issued by or loan obligations of corporations that are diversified across a wide range of issuers and industries. The fair values of corporate debt that are short-term are priced using the spread above the LIBOR yield curve, and the fair values of corporate debt that are long-term are priced using the spread above the risk-free yield curve. The spreads are sourced from broker-dealers, trade prices and the new issue market. As the significant inputs used to price corporate bonds are observable market inputs, the fair values of corporate debt are included in the Level 2 fair value hierarchy.
	Mortgage-backed: Primarily comprised of residential and commercial mortgages originated by both U.S. government agencies (such as the Federal National Mortgage Association) and non-U.S. government agencies. The fair values of mortgage-backed securities originated by U.S. government agencies and non-U.S. government agencies are based on a pricing model that incorporates prepayment speeds and spreads to determine the appropriate average life of mortgage-backed securities. The spreads are sourced from broker-dealers, trade prices and the new issue market. As the significant inputs used to price the mortgage-backed securities are observable market inputs, the fair values of these securities are included in the Level 2 fair value hierarchy, unless the significant inputs used to price the mortgage-backed securities are broker-dealer quotes and the Company is not able to determine if those quotes are based on observable market inputs, in which case the fair value is included in the Level 3 hierarchy.
	Asset-backed: Principally comprised of bonds backed by pools of automobile loan receivables, home equity loans, credit card receivables and collateralized loan obligations originated by a variety of financial institutions. The fair values of asset-backed securities are priced using prepayment speed and spread inputs that are sourced from the new issue market or broker-dealer quotes. As the significant inputs used to price the asset-backed securities are observable market inputs, the fair values of these securities are included in the Level 2 fair value hierarchy, unless the significant inputs used to price the asset-backed securities are broker-dealer quotes and the Company is not able to determine if those quotes are based on observable market inputs, in which case the fair value is included in the Level 3 hierarchy.
	Equity securities: Comprised of common and preferred stocks and mutual funds. Equities are generally included in the Level 1 fair value hierarchy as prices are obtained from market exchanges in active markets. Non-U.S. mutual funds where the net asset value ("NAV") is not provided on a daily basis are included in the Level 3 fair value hierarchy.
	Other invested assets: Comprised of funds invested in a range of diversified strategies. In accordance with U.S. GAAP, the fair values of the funds are based on the NAV of the funds as reported by the fund manager. The fair value of these investments are included in Level 3 fair value hierarchy as the Company believes NAV is an unobservable input and these securities are not redeemable in the near term. The Company does not measure its investments that are accounted for using the equity method of accounting at fair value.
	Derivative instruments: The fair value of foreign exchange contracts, interest rate futures and interest rate swaps are priced from quoted market prices for similar exchange-traded derivatives and pricing valuation models that utilize independent market data inputs. The fair value of derivatives are included in the Level 2 fair value hierarchy.
	Senior notes: The fair value of the senior notes is based on reported trades. The fair value of the senior notes is included in the Level 2 fair value hierarchy.
	Other long-term debt: Comprised of the mortgage and credit facility associated with the purchase of office space in Switzerland. The fair value of the other long-term debt is based on the value of the debt using current interest rates. The fair value of the long-term debt is included in the Level 2 fair value hierarchy.
	Non-recurring Fair Value of Financial Instruments
	The Company measures the fair value of certain assets on a non-recurring basis, generally quarterly, annually or when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. These assets include investments accounted for using the equity method, goodwill and intangible assets. The Company uses a variety of techniques to measure the fair value of these assets when appropriate, as described below:
	Investments accounted for using the equity method: When the Company determines that the carrying value of these assets may not be recoverable, the Company records the assets at fair value with the loss recognized in income. In such cases, the Company measures the fair value of these assets using discounted cash flow models.
	Goodwill and intangible assets: The Company tests goodwill and intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount may not be recoverable, but at least annually for goodwill and indefinite-lived intangibles. If the Company determines that goodwill and intangible assets may be impaired, the Company uses techniques, including discounted expected future cash flows and market multiple models, to measure fair value.
Rollforward of Level 3 Financial Instruments
The following is a reconciliation of the beginning and ending balance of financial instruments using significant unobservable inputs (Level 3):
Three Months Ended March 31, 2015	Other invested			Mortgage-backed			Asset-backed			Equities
	assets
Opening balance	$	812,543		$	181,783		$	55,413		$	43,330
Realized and unrealized gains included in net income	14,101			1,337			352			5,437
Purchases	39,364			20,170			25,341			—
Sales	(73,439		)	(70,592		)	(2,669		)	—
Transfers into Level 3 from Level 2	—			—			43,610			—
Transfers out of Level 3 into Level 2 (1)	—			—			(29,115		)	—
Ending balance	$	792,569		$	132,698		$	92,932		$	48,767
Three Months Ended March 31, 2014
Opening balance	$	764,081		$	147,338		$	93,413		$	73,904
Realized and unrealized gains (losses) included in net income	22,626			1,368			(864		)	(9,821		)
Purchases	89,199			14,110			7,493			—
Sales	(35,919		)	(17,956		)	(3,176		)	(29,297		)
Transfers into Level 3 from Level 2	—			—			606			—
Transfers out of Level 3 into Level 2 (1)	—			(10,799		)	(16,238		)	—
Ending balance	$	839,987		$	134,061		$	81,234		$	34,786
_______________________
-1	Transfers out of Level 3 are primarily attributable to the availability of market observable information.
The Company attempts to verify the significant inputs used by broker-dealers in determining the fair value of the securities priced by them. If the Company could not obtain sufficient information to determine if the broker-dealers were using significant observable inputs, then such securities have been transferred to the Level 3 fair value hierarchy. The Company believes the prices obtained from the broker-dealers are the best estimate of fair value of the securities being priced as the broker-dealers are typically involved in the initial pricing of the security, and the Company has compared the price per the broker-dealer to other pricing sources and noted no material differences. The Company recognizes transfers between levels at the end of the reporting period. There were no transfers between Level 1 and Level 2 during the period.
The Company’s external investment accounting service provider receives prices from internationally recognized independent pricing services to measure the fair values of its fixed maturity investments. Pricing sources are evaluated and selected in a manner to ensure that the most reliable sources are used. The Company uses a pricing service ranking to consistently select the most appropriate pricing service in instances where it receives multiple quotes on the same security. The Company obtains multiple quotes for the majority of its securities. The independent pricing sources obtain market quotations and actual transaction prices for securities that have quoted prices in active markets. Each pricing service 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 service uses observable market inputs, including, but not limited to, reported trades, benchmark yields, broker-dealer quotes, interest rates, prepayment speeds, default rates and such other inputs as are available from market sources to determine a reasonable fair value.
All of the Company’s securities classified as Level 3, other than investments in other invested assets, are valued based on unadjusted broker-dealer quotes. This includes less liquid securities such as lower quality asset-backed securities, commercial mortgage-backed securities and residential mortgage-backed securities. The primary valuation inputs include monthly payment information, the probability of default, loss severity rates and estimated prepayment rates. Significant changes in these inputs in isolation would result in a significantly lower or higher fair value measurement. In general, a change in the assumption of the probability of default is accompanied by a directionally similar change in the assumption used for the loss severity in an event of default and prepayment rates.
The Company records the unadjusted price provided and validates this price through a process that includes, but is not limited to, monthly and/or quarterly: (i) comparison of prices between two independent sources, with significant differences requiring additional price sources; (ii) quantitative analysis (e.g., comparing the quarterly return for each managed portfolio to their target benchmark, with significant differences identified and investigated); (iii) evaluation of methodologies used by external parties to calculate fair value, including a review of the inputs used for pricing; (iv) comparing the price to the Company’s knowledge of the current investment market; and (v) back-testing, which includes randomly selecting purchased or sold securities and comparing the executed prices to the fair value estimates from the pricing service. In addition to internal controls, management relies on the effectiveness of the valuation controls in place at the Company’s external investment accounting service provider (supported by a Statement on Standards for Attestation Engagements No. 16 report) in conjunction with regular discussion and analysis of the investment portfolio’s structure and performance.

Reserve_For_Losses_And_Loss_Ex

Reserve For Losses And Loss Expenses	3 Months Ended
	Mar. 31, 2015
Insurance Loss Reserves [Abstract]
Reserve for Losses and Loss Expenses	RESERVE FOR LOSSES AND LOSS EXPENSES
	The reserve for losses and loss expenses consists of the following:
		March 31,			December 31,
		2015			2014
	Outstanding loss reserves	$	1,414,512		$	1,514,051
	Reserves for losses incurred but not reported	4,490,598			4,367,114
	Reserve for losses and loss expenses	$	5,905,110		$	5,881,165
	The table below is a reconciliation of the beginning and ending liability for unpaid losses and loss expenses. Losses incurred and paid are reflected net of reinsurance recoverables.
		Three Months Ended
		March 31,
		2015			2014
	Gross liability at beginning of period	$	5,881,165		$	5,766,529
	Reinsurance recoverable at beginning of period	(1,340,256		)	(1,234,504		)
	Net liability at beginning of period	4,540,909			4,532,025
	Net losses incurred related to:
	Current year	388,817			324,147
	Prior years	(63,641		)	(48,861		)
	Total incurred	325,176			275,286
	Net paid losses related to:
	Current year	6,557			3,743
	Prior years	293,098			228,594
	Total paid	299,655			232,337
	Foreign exchange revaluation	(11,631		)	1,299
	Net liability at end of period	4,554,799			4,576,273
	Reinsurance recoverable at end of period	1,350,311			1,280,525
	Gross liability at end of period	$	5,905,110		$	5,856,798
	For the three months ended March 31, 2015, the Company recorded net favorable prior year reserve development in each of its operating segments due to actual loss emergence being lower than initially expected. The net favorable prior year reserve development in the North American Insurance segment was primarily related to the professional liability and general casualty lines of business, partially offset by net unfavorable prior year reserve development in the healthcare line of business. The Global Markets Insurance segment had favorable prior year reserve development across most major lines of business. The net favorable prior year reserve development in the Reinsurance segment was primarily related to the property reinsurance and casualty reinsurance lines of business partially offset by unfavorable reserve development in the specialty line of business.
	For the three months ended March 31, 2014, the Company recorded net favorable prior year reserve development in each of its operating segments due to actual loss emergence being lower than initially expected. The net favorable prior year reserve development in the North American Insurance segment primarily related to the professional liability, general casualty and general property lines of business, partially offset by net unfavorable prior year reserve development in the healthcare line of business. The Global Markets Insurance segment had favorable prior year reserve development across all major lines of business. The net favorable prior year reserve development in the Reinsurance segment was primarily due to benign property loss activity.
	While the Company has experienced favorable reserve development in its insurance and reinsurance lines, there is no assurance that conditions and trends that have affected the development of liabilities in the past will continue. It is not appropriate to extrapolate future redundancies based on prior years’ development. The methodology of estimating loss reserves is periodically reviewed to ensure that the key assumptions used in the actuarial models continue to be appropriate.

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES
	Under Swiss law, a resident company is subject to income tax at the federal, cantonal and communal levels that is levied on net income. Income attributable to permanent establishments or real estate located abroad is excluded from the Swiss tax base. Allied World Switzerland is a holding company and, therefore, is exempt from cantonal and communal income tax. As a result, Allied World Switzerland is subject to Swiss income tax only at the federal level. Allied World Switzerland is a resident of the Canton of Zug and, as such, is subject to an annual cantonal and communal capital tax on the taxable equity of Allied World Switzerland. Allied World Switzerland has a Swiss operating company resident in the Canton of Zug. The operating company is subject to federal, cantonal and communal income tax and to annual cantonal and communal capital tax.
	Under current Bermuda law, Allied World Assurance Company Holdings, Ltd (“Allied World Bermuda”) and its Bermuda subsidiaries are not required to pay taxes in Bermuda on either income or capital gains. Allied World Bermuda and Allied World Assurance Company, Ltd have received an assurance from the Bermuda Minister of Finance under the Exempted Undertakings Tax Protection Act 1966 of Bermuda, that in the event of any such taxes being imposed, Allied World Bermuda and Allied World Assurance Company, Ltd will be exempted until March 2035.
	Certain subsidiaries of Allied World Switzerland file U.S. federal income tax returns and various U.S. state income tax returns, as well as income tax returns in Canada, Hong Kong, Ireland, Singapore, Switzerland and the United Kingdom. The U.S. Internal Revenue Service is currently conducting an audit of the 2012 tax return of the Company's U.S. subsidiaries. To the best of the Company’s knowledge, there are no other examinations pending by any other tax authority.
	Management has deemed all material tax positions to have a greater than 50% likelihood of being sustained based on technical merits if challenged. The Company does not expect any material unrecognized tax benefits within 12 months of March 31, 2015.

Shareholders_Equity

Shareholders' Equity	3 Months Ended
	Mar. 31, 2015
Stockholders' Equity Note [Abstract]
Shareholders' Equity	SHAREHOLDERS’ EQUITY
	a) Authorized shares
	The issued share capital consists of the following:
		March 31,			December 31,
		2015			2014
	Common shares issued and fully paid, 2015 and 2014: CHF 4.10 per share	100,299,454			100,775,256
	Share capital at end of period	$	406,088		$	408,020
		Three Months Ended
		March 31, 2015
	Shares issued at beginning of period	100,775,256
	Shares canceled	(475,802	)
	Total shares issued at end of period	100,299,454
	Treasury shares issued at beginning of period	4,579,774
	Shares repurchased	1,271,213
	Shares issued out of treasury	(520,400	)
	Shares canceled	(475,802	)
	Total treasury shares at end of period	4,854,785
	Total shares outstanding at end of period	95,444,669
	During the three months ended March 31, 2015, 475,802 shares repurchased and designated for cancellation were constructively retired and canceled.
	b) Dividends
	The Company paid the following dividends during the three months ended March 31, 2015:
	Dividend Paid		Dividend			Total
			Per			Amount
			Share			Paid
	2-Jan-15		$	0.225		$	21,669
	On May 1, 2014, the shareholders approved the Company’s proposal to pay cash dividends in the form of a distribution out of general legal reserve from capital contributions. The distribution amount was paid to shareholders in quarterly dividends of $0.225 per share. The first dividend was on July 2, 2014, the second dividend was on October 2, 2014, the third dividend was on January 2, 2015 and the last quarterly dividend on April 2, 2015.
	c) Share Repurchases
	On May 1, 2014, the shareholders approved a share repurchase program in order for the Company to repurchase up to $500,000 of Allied World Switzerland's common shares. Repurchases may be effected from time to time through open market purchases, privately negotiated transactions, tender offers or otherwise. The timing, form and amount of the share repurchases under the program will depend on a variety of factors, including market conditions, the Company’s capital position, legal requirements and other factors. Under the terms of the share repurchase program, the first three million of common shares repurchased will remain in treasury and will be used by Allied World Switzerland to satisfy share delivery obligations under its equity-based compensation plans. Any additional common shares repurchased will be designated for cancellation at acquisition and will be canceled upon shareholder approval. Shares repurchased and designated for cancellation are constructively retired and recorded as a share cancellation.
	The Company’s share repurchases were as follows:
		Three Months Ended
		March 31,
		2015			2014
	Common shares repurchased	1,271,213			2,012,196
	Total cost of shares repurchased	$	50,949		$	68,659
	Average price per share	$	40.08		$	34.12

Employee_Benefit_Plans

Employee Benefit Plans	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS
	a) Restricted stock units and performance-based equity awards
	Restricted stock units ("RSUs") vest pro-rata over four years from the date of grant. The compensation expense for the RSUs is based on the fair market value of Allied World Switzerland’s common shares at the date of grant. The Company estimates the expected forfeitures of RSUs at the date of grant and recognizes compensation expense only for those awards that the Company expects to vest. The forfeiture assumption is ultimately adjusted to the actual forfeiture rate.
	Performance-based equity awards represent the right to receive a number of common shares in the future, based upon the achievement of established performance criteria during an applicable performance period. For the performance-based equity awards granted in 2015, 2014 and 2013, the Company anticipates that the performance goals are likely to be achieved. Based on the performance goals, the performance-based equity awards granted in 2015, 2014 and 2013 are expensed at 100%, 100% and 110%, respectively, of the fair value of Allied World Switzerland's common shares on the date of grant. The expense is recognized over the performance period.
	The activity related to the Company’s RSUs awards is as follows:
		Three Months Ended March 31, 2015
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	502,506		$	32.1
	RSUs granted	502,543		40.24
	RSUs forfeited	(1,458	)	(24.02		)
	RSUs fully vested	(159,984	)	(30.59		)
	Outstanding at end of period	843,607		$	37.25
	The activity related to the Company’s performance-based equity awards is as follows:
		Three Months Ended March 31, 2015
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	616,641		$	27.52
	Performance-based equity awards granted	234,361		40.24
	Additional awards granted due to achievement of performance criteria	91,737		22.29
	Performance-based equity awards fully vested	(346,515	)	(22.29		)
	Outstanding at end of period	596,224		$	34.76
	b) Cash-equivalent stock awards
	As part of the Company’s annual year-end compensation awards, the Company granted both awards classified as equity and cash-equivalent stock awards. The cash-equivalent awards were granted to employees who received RSUs and performance-based equity awards in tandem with stock-based awards. The cash-equivalent RSU awards vest pro-rata over four years from the date of grant. The cash-equivalent performance-based equity awards vest after a three-year performance period. The amount payable per unit awarded will be equal to the price per share of Allied World Switzerland’s common shares, and as such the Company measures the value of the award each reporting period based on the period-ending share price. The effects of changes in the share price at each period-end during the service period are recognized as changes in compensation expense ratably over the service period. The liability is included in “accounts payable and accrued liabilities” in the consolidated balance sheets and changes in the liability are recorded in “general and administrative expenses” in the consolidated income statements.
	The activity related to the Company's cash-equivalent RSUs and performance-based awards is as follows:
		RSU's					Performance-based Awards
	Three Months Ended March 31, 2015	Number of Awards		Weighted Average Grant Date Fair Value			Number of Awards		Weighted Average Grant Date Fair Value
	Outstanding at beginning of period	1,654,064		$	27.99		924,906		27.52
	Granted	325,805		40.24			156,238		40.24
	Additional awards granted due to achievement of performance criteria	—		—			137,585		22.29
	Forfeited	(9,525	)	(26.90		)	(1,404	)	(22.29		)
	Fully vested	(649,102	)	(26.17		)	(519,725	)	(22.29		)
	Outstanding at end of period	1,321,242		$	31.92		697,600		$	33.25
	c) Total Stock Related Compensation Expense
	The following table shows the total stock-related compensation expense relating to the stock options, RSUs and cash equivalent awards.
		Three Months Ended
		March 31,
		2015			2014
	Stock options	$	277		$	727
	RSUs and performance-based equity awards	3,725			3,513
	Cash-equivalent stock awards	12,523			4,629
	Total	$	16,525		$	8,869

Earnings_Per_Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Share	EARNINGS PER SHARE
	The following table sets forth the comparison of basic and diluted earnings per share:
		Three Months Ended
		March 31,
		2015		2014
	Basic earnings per share:
	Net income	$	124,356	$	176,972
	Weighted average common shares outstanding	95,935,551		99,545,187
	Basic earnings per share	$	1.3	$	1.78
		Three Months Ended
		March 31,
		2015		2014
	Diluted earnings per share:
	Net income	$	124,356	$	176,972
	Weighted average common shares outstanding	95,935,551		99,545,187
	Share equivalents:
	Stock options	1,116,871		1,463,958
	RSUs and performance-based equity awards	509,971		565,611
	Employee share purchase plan	14,636		9,906
	Weighted average common shares and common share equivalents outstanding - diluted	97,577,029		101,584,662
	Diluted earnings per share	$	1.27	$	1.74
	For the three months ended March 31, 2015 and 2014, a weighted average of 175,175 and 75 RSUs, respectively, were considered anti-dilutive and were therefore excluded from the calculation of the diluted earnings per share.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION
	The determination of reportable segments is based on how senior management monitors the Company’s underwriting operations. Management monitors the performance of its direct underwriting operations based on the geographic location of the Company’s offices, the markets and customers served and the type of accounts written. The Company is currently organized into three operating segments: North American Insurance, Global Markets Insurance and Reinsurance. All product lines fall within these classifications.
	The North American Insurance segment includes the Company’s direct specialty insurance operations in the United States, Bermuda and Canada, as well as the Company's claim administration services operation. This segment provides both direct property and casualty insurance primarily to North American domiciled accounts. The Global Markets Insurance segment includes the Company’s insurance operations in Europe and Asia Pacific, which includes offices in Australia, Hong Kong, Singapore and a Lloyd's coverholder operation in Miami, which services business from Latin America and the Caribbean. This segment provides both direct property and casualty insurance primarily to non-North American domiciled accounts. The Reinsurance segment includes the Company’s reinsurance operations in the United States, Bermuda, Europe and Singapore. This segment provides reinsurance of property, general casualty, professional liability, specialty lines and property catastrophe coverages written by insurance companies. The Company presently writes reinsurance on both a treaty and a facultative basis, targeting several niche reinsurance markets.
	Responsibility and accountability for the results of underwriting operations are assigned by major line of business within each segment. Because the Company does not manage its assets by segment, investment income, interest expense and total assets are not allocated to individual reportable segments. General and administrative expenses are allocated to segments based on various factors, including staff count and each segment’s proportional share of gross premiums written.
	The Company measures its segment profit or loss as underwriting income or loss plus other insurance-related income and expenses, which may include the net earnings from our claims administration services operations and other income or expense that is not directly related to our underwriting operations. Management measures results for each segment's underwriting income on the basis of the “loss and loss expense ratio,” “acquisition cost ratio,” “general and administrative expense ratio,” “expense ratio” and the “combined ratio.” The “loss and loss expense ratio” is derived by dividing net losses and loss expenses by net premiums earned. The “acquisition cost ratio” is derived by dividing acquisition costs by net premiums earned. The “general and administrative expense ratio” is derived by dividing general and administrative expenses by net premiums earned. The expense ratio is the sum of the “acquisition cost ratio” and the “general and administrative expense ratio”. The “combined ratio” is the sum of the “loss and loss expense ratio,” the “acquisition cost ratio” and the “general and administrative expense ratio.”
	The following tables provide a summary of the segment results:
	Three Months Ended March 31, 2015		North American				Global Markets			Reinsurance			Total
			Insurance				Insurance
	Gross premiums written		$	380,767			$	60,562		$	439,285		$	880,614
	Net premiums written		296,883				42,895			432,750			772,528
	Net premiums earned		312,970				50,040			205,538			568,548
	Net losses and loss expenses		(195,479		)		(20,510		)	(109,187		)	(325,176		)
	Acquisition costs		(31,032		)		(7,008		)	(40,659		)	(78,699		)
	General and administrative expenses		(59,288		)		(18,025		)	(19,825		)	(97,138		)
	Underwriting income		27,171				4,497			35,867			67,535
	Other insurance-related income		854				—			—			854
	Other insurance-related expenses		(855		)		(968		)	—			(1,823		)
	Segment income		27,170				3,529			35,867			66,566
	Net investment income												44,551
	Net realized investment gains												45,025
	Amortization of intangible assets												(633		)
	Interest expense												(14,337		)
	Foreign exchange loss												(9,897		)
	Income before income taxes												$	131,275
	Loss and loss expense ratio		62.5		%		41		%	53.1		%	57.2		%
	Acquisition cost ratio		9.9		%		14		%	19.8		%	13.8		%
	General and administrative expense ratio		18.9		%		36		%	9.6		%	17.1		%
	Expense ratio		28.8		%		50		%	29.4		%	30.9		%
	Combined ratio		91.3		%		91		%	82.5		%	88.1		%
	Three Months Ended March 31, 2014		North American				Global Markets			Reinsurance			Total
			Insurance				Insurance
	Gross premiums written		$	345,912			$	58,397		$	497,084		$	901,393
	Net premiums written		247,152				31,047			493,415			771,614
	Net premiums earned		265,451				35,011			229,823			530,285
	Net losses and loss expenses		(161,172		)		(4,389		)	(109,725		)	(275,286		)
	Acquisition costs		(23,675		)		(2,879		)	(41,168		)	(67,722		)
	General and administrative expenses		(47,615		)		(14,582		)	(18,143		)	(80,340		)
	Underwriting income		32,989				13,161			60,787			106,937
	Other insurance-related income		—				—			—			—
	Other insurance-related expenses		—				—			—			—
	Segment income		32,989				13,161			60,787			106,937
	Net investment income												47,619
	Net realized investment gains												54,205
	Amortization of intangible assets												(633		)
	Interest expense												(14,534		)
	Foreign exchange loss												(49		)
	Income before income taxes												$	193,545
	Loss and loss expense ratio		60.7		%		12.5		%	47.7		%	51.9		%
	Acquisition cost ratio		8.9		%		8.2		%	17.9		%	12.8		%
	General and administrative expense ratio		17.9		%		41.6		%	7.9		%	15.2		%
	Expense ratio		26.8		%		49.8		%	25.8		%	28		%
	Combined ratio		87.5		%		62.3		%	73.5		%	79.9		%
	The following table shows an analysis of the Company’s gross premiums written by geographic location of the Company’s subsidiaries and branches. All intercompany premiums have been eliminated.
		Three Months Ended
		March 31,
		2015				2014
	United States	$	536,632			$	520,773
	Bermuda	196,628				229,631
	Europe	103,969				103,336
	Asia Pacific	40,058				46,823
	Canada	3,327				830
	Total gross premiums written	$	880,614			$	901,393
	Europe includes gross premiums written attributable to Switzerland of $40,383 and $44,293 for the three months ended March 31, 2015 and 2014, respectively.
	The following table shows the Company’s net premiums earned by line of business for each segment for the three months ended March 31, 2015 and 2014, respectively.
		Three Months Ended
		March 31,
		2015				2014
North American Insurance:
General casualty		$	104,924			$	76,302
Professional liability		78,916				64,271
Healthcare		38,041				42,493
Programs		34,147				30,469
General property		28,000				34,939
Inland marine		13,349				8,890
Environmental		6,822				4,586
Other		8,771				3,501
Total		312,970				265,451
Global Markets Insurance:
Professional liability		19,503				11,720
General property		8,232				8,239
Aviation		5,953				5,637
General casualty		5,913				2,693
Trade credit		4,276				4,012
Healthcare		3,606				2,502
Other		2,557				208
Total		50,040				35,011
Reinsurance:
Property		104,351				137,084
Specialty		44,285				45,225
Casualty		56,902				47,514
Total		205,538				229,823
Total net premiums earned		$	568,548			$	530,285

Commitments_And_Contingencies

Commitments And Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	COMMITMENTS AND CONTINGENCIES
	The Company, in common with the insurance industry in general, is subject to litigation and arbitration in the normal course of its business. These legal proceedings generally relate to claims asserted by or against the Company in the ordinary course of insurance or reinsurance operations. Estimated amounts payable under these proceedings are included in the reserve for losses and loss expenses in the Company’s consolidated balance sheets. As of March 31, 2015, the Company was not a party to any material legal proceedings arising outside the ordinary course of business that management believes will have a material adverse effect on the Company’s results of operations, financial position or cash flow.

Condensed_Consolidated_Guarant

Condensed Consolidated Guarantor Financial Statements	3 Months Ended
	Mar. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Consolidated Guarantor Financial Statements	CONDENSED CONSOLIDATED GUARANTOR FINANCIAL STATEMENTS
	The following tables present unaudited condensed consolidating financial information as of March 31, 2015 and December 31, 2014 and for the three months ended March 31, 2015 and 2014 for Allied World Switzerland (the “Parent Guarantor”) and Allied World Bermuda (the “Subsidiary Issuer”). The Subsidiary Issuer is a direct, 100%-owned subsidiary of the Parent Guarantor. Investments in subsidiaries are accounted for by the Parent Guarantor under the equity method for purposes of the supplemental consolidating presentation. Earnings of subsidiaries are reflected in the Parent Guarantor’s investment accounts and earnings. The Parent Guarantor fully and unconditionally guarantees the senior notes issued by the Subsidiary Issuer.
	Unaudited Condensed Consolidating Balance Sheet:
	As of March 31, 2015	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	8,071,956		$	—		$	8,071,956
	Cash and cash equivalents	36,499			2,109			476,462			—			515,070
	Insurance balances receivable	—			—			773,394			—			773,394
	Funds held	—			—			479,909			—			479,909
	Reinsurance recoverable	—			—			1,350,311			—			1,350,311
	Reinsurance recoverable on paid losses	—			—			107,071			—			107,071
	Net deferred acquisition costs	—			—			187,246			—			187,246
	Goodwill and intangible assets	—			—			329,999			—			329,999
	Balances receivable on sale of investments	—			—			46,822			—			46,822
	Investments in subsidiaries	3,600,273			4,170,400			—			(7,770,673		)	—
	Due from subsidiaries	226,081			27,963			16,454			(270,498		)	—
	Other assets	2,128			2,838			751,042			—			756,008
	Total assets	$	3,864,981		$	4,203,310		$	12,590,666		$	(8,041,171	)	$	12,617,786
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,905,110		$	—		$	5,905,110
	Unearned premiums	—			—			1,717,399			—			1,717,399
	Reinsurance balances payable	—			—			184,322			—			184,322
	Balances due on purchases of investments	—			—			34,396			—			34,396
	Senior notes	—			798,881			—			—			798,881
	Other long-term debt	—			—			19,730			—			19,730
	Due to subsidiaries	10,009			6,445			254,044			(270,498		)	—
	Other liabilities	25,905			14,303			88,673			—			128,881
	Total liabilities	35,914			819,629			8,203,674			(270,498		)	8,788,719
	Total shareholders’ equity	3,829,067			3,383,681			4,386,992			(7,770,673		)	3,829,067
	Total liabilities and shareholders’ equity	$	3,864,981		$	4,203,310		$	12,590,666		$	(8,041,171	)	$	12,617,786
	As of December 31, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	7,868,682		$	—		$	7,868,682
	Cash and cash equivalents	32,579			1,734			555,026			—			589,339
	Insurance balances receivable	—			—			664,815			—			664,815
	Funds held	—			—			724,021			—			724,021
	Reinsurance recoverable	—			—			1,340,256			—			1,340,256
	Reinsurance recoverable on paid losses	—			—			86,075			—			86,075
	Net deferred acquisition costs	—			—			151,546			—			151,546
	Goodwill and intangible assets	—			—			324,556			—			324,556
	Balances receivable on sale of investments	—			—			47,149			—			47,149
	Investments in subsidiaries	3,629,301			4,218,028			—			(7,847,329		)	—
	Due from subsidiaries	147,072			19,190			14,396			(180,658		)	—
	Other assets	1,470			3,192			620,462			—			625,124
	Total assets	$	3,810,422		$	4,242,144		$	12,396,984		$	(8,027,987	)	$	12,421,563
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,881,165		$	—		$	5,881,165
	Unearned premiums	—			—			1,555,313			—			1,555,313
	Reinsurance balances payable	—			—			180,060			—			180,060
	Balances due on purchases of investments	—			—			5,428			—			5,428
	Senior notes	—			798,802			—			—			798,802
	Other long-term debt	—			—			19,213						19,213
	Due to subsidiaries	7,599			6,797			166,262			(180,658		)	—
	Other liabilities	24,532			19,618			159,141			—			203,291
	Total liabilities	32,131			825,217			7,966,582			(180,658		)	8,643,272
	Total shareholders’ equity	3,778,291			3,416,927			4,430,402			(7,847,329		)	3,778,291
	Total liabilities and shareholders’ equity	$	3,810,422		$	4,242,144		$	12,396,984		$	(8,027,987	)	$	12,421,563
	Unaudited Condensed Consolidating Statement of Operations and Comprehensive Income:
Three Months Ended March 31, 2015	Allied World			Allied World			Other Allied			Consolidating			Allied World
	Switzerland			Bermuda			World			Adjustments			Switzerland
	(Parent			(Subsidiary			Subsidiaries						Consolidated
	Guarantor)			Issuer)
Net premiums earned	$	—		$	—		$	568,548		$	—		$	568,548
Net investment income	2			—			44,549			—			44,551
Net realized investment losses	—			—			45,025			—			45,025
Other income	—			—			854			—			854
Net losses and loss expenses	—			—			(325,176		)	—			(325,176		)
Acquisition costs	—			—			(78,699		)	—			(78,699		)
General and administrative expenses	(9,462		)	240			(87,916		)	—			(97,138		)
Other expense	—			—			(1,823		)	—			(1,823		)
Amortization of intangible assets	—			—			(633		)	—			(633		)
Interest expense	—			(13,866		)	(471		)	—			(14,337		)
Foreign exchange gain (loss)	5			10			(9,912		)	—			(9,897		)
Income tax (expense) benefit	(639		)	—			(6,280		)	—			(6,919		)
Equity in earnings of consolidated subsidiaries	134,450			143,696			—			(278,146		)	—
NET INCOME (LOSS)	$	124,356		$	130,080		$	148,066		$	(278,146	)	$	124,356
Other comprehensive income	—			—			—			—			—
COMPREHENSIVE INCOME (LOSS)	$	124,356		$	130,080		$	148,066		$	(278,146	)	$	124,356
Three Months Ended March 31, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
	Switzerland			Bermuda			World			Adjustments			Switzerland
	(Parent			(Subsidiary			Subsidiaries						Consolidated
	Guarantor)			Issuer)
Net premiums earned	$	—		$	—		$	530,285		$	—		$	530,285
Net investment income	2			—			47,617			—			47,619
Net realized investment gains	—			—			54,205			—			54,205
Other income	—			—			—			—			—
Net losses and loss expenses	—			—			(275,286		)	—			(275,286		)
Acquisition costs	—			—			(67,722		)	—			(67,722		)
General and administrative expenses	(8,914		)	(2,391		)	(69,035		)	—			(80,340		)
Other expense	—			—			—			—			—
Amortization of intangible assets	—			—			(633		)	—			(633		)
Interest expense	—			(13,848		)	(686		)	—			(14,534		)
Foreign exchange gain (loss)	(2		)	33			(80		)	—			(49		)
Income tax (expense) benefit	(409		)	—			(16,164		)	—			(16,573		)
Equity in earnings of consolidated subsidiaries	186,295			199,007			—			(385,302		)	—
NET INCOME (LOSS)	$	176,972		$	182,801		$	202,501		$	(385,302	)	$	176,972
Other comprehensive income	—			—			—			—			—
COMPREHENSIVE INCOME (LOSS)	$	176,972		$	182,801		$	202,501		$	(385,302	)	$	176,972
Unaudited Condensed Consolidating Statement of Cash Flows:
Three Months Ended March 31, 2015	Allied World			Allied World			Other Allied			Consolidating			Allied World
	Switzerland			Bermuda			World			Adjustments			Switzerland
	(Parent			(Subsidiary			Subsidiaries						Consolidated
	Guarantor)			Issuer)
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES	$	71,639		$	80,375		$	339,583		$	(179,000	)	$	312,597
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases trading securities	—			—			(1,723,443		)	—			(1,723,443		)
Purchases of other invested assets	—			—			(233,252		)	—			(233,252		)
Sales of trading securities	—			—			1,561,890			—			1,561,890
Sales of other invested assets	—			—			56,535			—			56,535
Other	—			—			19,123			—			19,123
Net cash provided by (used in) investing activities	—			—			(319,147		)	—			(319,147		)
CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Dividends paid	(21,669		)	—			—			—			(21,669		)
Intercompany dividends paid	—			(80,000		)	(99,000		)	179,000			—
Proceeds from the exercise of stock options	4,223			—			—			—			4,223
Share repurchases	(50,273		)	—			—			—			(50,273		)
Net cash provided by (used in) financing activities	(67,719		)	(80,000		)	(99,000		)	179,000			(67,719		)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	3,920			375			(78,564		)	—			(74,269		)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	32,579			1,734			555,026			—			589,339
CASH AND CASH EQUIVALENTS, END OF PERIOD	$	36,499		$	2,109		$	476,462		$	—		$	515,070
Three Months Ended March 31, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
	Switzerland			Bermuda			World			Adjustments			Switzerland
	(Parent			(Subsidiary			Subsidiaries						Consolidated
	Guarantor)			Issuer)
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$	94,128		$	92,272		$	324,382		$	(206,000	)	$	304,782
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	—			—			(1,568,993		)	—			(1,568,993		)
Purchases of other invested assets	—			—			(779,934		)	—			(779,934		)
Sales of trading securities	—			—			1,494,648			—			1,494,648
Sales of other invested assets	—			—			663,237			—			663,237
Other	—			—			2,487			—			2,487
Net cash provided by (used in) investing activities	—			—			(188,555		)	—			(188,555		)
CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Dividends paid	(16,732		)	—			—			—			(16,732		)
Intercompany dividends paid	—			(94,000		)	(112,000		)	206,000			—
Proceeds from the exercise of stock options	3,030			—			—			—			3,030
Share repurchases	(68,659		)	—			—			—			(68,659		)
Net cash provided by (used in) financing activities	(82,361		)	(94,000		)	(112,000		)	206,000			(82,361		)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	11,767			(1,728		)	23,827			—			33,866
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790			2,775			518,371			—			531,936
CASH AND CASH EQUIVALENTS, END OF PERIOD	$	22,557		$	1,047		$	542,198		$	—		$	565,802
Notes to Parent Company Condensed Financial Information
a) Dividends
Allied World Switzerland received cash dividends from its subsidiaries of $80,000 and $94,000 for the three months ended March 31, 2015 and 2014, respectively. Such dividends are included in “cash flows provided by (used in) operating activities” in the unaudited condensed consolidating cash flows.

Subsequent_events

Subsequent events	3 Months Ended
	Mar. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS
	On April 1, 2015, the Company completed its acquisitions of the Hong Kong and Singapore operations of Royal & Sun Alliance Insurance plc ("RSA") for approximately $192,692, subject to post-closing adjustments. In addition to the purchase price, the Company contributed an additional $90,000 to capitalize the businesses on an ongoing basis. Completion of the valuation of the assets acquired and liabilities assumed is currently in process, in particular related to insurance-related contract intangibles and other intangibles acquired. The required disclosures related to this acquisition will be provided upon the completion of the valuation of the assets acquired and liabilities assumed in the second quarter of 2015. In addition, the Company has entered into a contract to acquire the Labuan operations of RSA for one British pound sterling. This transaction is expected to close in the second quarter of 2015.
	On April 2, 2015, the Company paid a quarterly dividend of $0.225 per share to shareholders of record on March 24, 2015.

Basis_of_Preparation_and_Conso1

Basis of Preparation and Consolidation (Policies)	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of accounting	These unaudited condensed consolidated financial statements include the accounts of the Company and have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial information and with Article 10 of Regulation S-X as promulgated by the U.S. Securities and Exchange Commission (“SEC”). Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the opinion of management, these unaudited condensed consolidated financial statements reflect all adjustments that are normal and recurring in nature and necessary for a fair presentation of financial position and results of operations as of the end of and for the periods presented. The results of operations for any interim period are not necessarily indicative of the results for a full year.
	Intercompany accounts and transactions have been eliminated on consolidation and all entities meeting consolidation requirements have been included in the unaudited condensed consolidated financial statements.
Use of estimates	The preparation of financial statements in conformity with U.S. 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. The significant estimates reflected in the Company’s financial statements, include, but are not limited to:
	•	The premium estimates for certain reinsurance agreements,
	•	Recoverability of deferred acquisition costs,
	•	The reserve for outstanding losses and loss expenses,
	•	Valuation of ceded reinsurance recoverables,
	•	Determination of impairment of goodwill and other intangible assets, and
	•	Valuation of financial instruments.

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Investments [Abstract]
Schedule of trading securities	Securities accounted for at fair value with changes in fair value recognized in the unaudited condensed consolidated statements of operations and comprehensive income (“consolidated income statements”) by category are as follows:
		March 31, 2015						December 31, 2014
		Fair Value			Amortized Cost			Fair Value				Amortized Cost
	U.S. government and government agencies	$	1,577,775		$	1,569,317		$	1,610,502			$	1,610,880
	Non-U.S. government and government agencies	189,448			204,867			188,199				196,332
	States, municipalities and political subdivisions	178,551			172,339			170,567				165,615
	Corporate debt:
	Financial institutions	1,107,108			1,094,338			1,024,667				1,018,777
	Industrials	1,107,548			1,105,744			1,029,729				1,037,820
	Utilities	113,383			113,280			110,997				111,599
	Mortgage-backed	1,286,210			1,238,165			1,263,517				1,219,712
	Asset-backed	728,874			731,558			670,832				674,505
	Total fixed maturity investments	$	6,288,897		$	6,229,608		$	6,069,010			$	6,035,240
		March 31, 2015						December 31, 2014
		Fair Value			Original Cost			Fair Value				Original Cost
	Equity securities	$	856,652		$	798,275		$	844,163			$	791,206
	Other invested assets	792,569			701,637			812,543				725,069
		$	1,649,221		$	1,499,912		$	1,656,706			$	1,516,275
Schedule of other invested assets	Details regarding the carrying value, redemption characteristics and unfunded investment commitments of the other invested assets portfolio as of March 31, 2015 and December 31, 2014 were as follows:
	Investment Type	Carrying Value as of March 31, 2015			Investments			Estimated		Investments				Redemption	Redemption	Unfunded
					with			Remaining		without				Frequency(1)	Notice	Commitments
					Redemption			Restriction		Redemption					Period(1)
					Restrictions			Period		Restrictions
	Private equity	$	196,090		$	196,090		2 - 8 Years		$	—					$	191,382
	Mezzanine debt	163,357			163,357			5 - 9 Years		—						200,804
	Distressed	5,545			5,545			3 Years		—						5,347
	Real estate	—			—			9 Years		—						150,000
	Total private equity	364,992			364,992					—						547,533
	Distressed	173,122			173,122					—				Based on net asset value	60 Days	—
	Equity long/short	87,644			—			1 Year		87,644				Quarterly	30 -60 Days	—
	Multi-strategy	15,996			—					15,996				Quarterly	45 -90 Days	—
	Relative value credit	120,460			—					120,460				Quarterly	60 Days	—
	Total hedge funds	397,222			173,122					224,100						—
	High yield loan fund	30,355			—					30,355				Monthly	30 days	—
	Total other invested assets at fair value	792,569			538,114					254,455						547,533
	Other private securities	133,838			—					133,838						—
	Total other invested assets	$	926,407		$	538,114				$	388,293					$	547,533
	Investment Type	Carrying Value as of December 31, 2014			Investments			Estimated		Investments				Redemption	Redemption	Unfunded
					with			Remaining		without				Frequency(1)	Notice	Commitments
					Redemption			Restriction		Redemption					Period(1)
					Restrictions			Period		Restrictions
	Private equity	$	184,576		$	184,576		2 - 8 Years		$	—					$	223,802
	Mezzanine debt	166,905			166,905			5 - 9 Years		—						204,232
	Distressed	5,869			5,869			3 Years		—						5,180
	Real estate	—			—			9 Years		—						50,000
	Total private equity	357,350			357,350					—						483,214
	Distressed	170,169			170,169					—				Based on net asset value	60 Days	—
	Equity long/short	84,198			—					84,198				Quarterly	30 -60 Days	—
	Multi-strategy	51,507			—					51,507				Quarterly	45 -90 Days	—
	Relative value credit	119,156			—					119,156				Quarterly	60 Days	—
	Total hedge funds	425,030			170,169					254,861						—
	High yield loan fund	30,163			—					30,163				Monthly	30 days	—
	Total other invested assets at fair value	812,543			527,519					285,024						483,214
	Other private securities	142,966			—					142,966						—
	Total other invested assets	$	955,509		$	527,519				$	427,990					$	483,214
	_______________________
	-1	The redemption frequency and notice periods only apply to the investments without redemption restrictions. Some or all of these investments may be subject to a gate as described below.
Schedule of net investment income
		Three Months Ended
		March 31,
		2015			2014
	Fixed maturity investments	$	36,258		$	36,299
	Equity securities	3,563			3,253
	Other invested assets: hedge funds and private equity	8,380			3,992
	Other invested assets: other private securities	866			7,416
	Cash and cash equivalents	462			439
	Expenses	(4,978		)	(3,780		)
	Net investment income	$	44,551		$	47,619
Components of realized gains and losses
		Three Months Ended
		March 31,
		2015			2014
	Gross realized gains on sale of invested assets	$	45,289		$	62,292
	Gross realized losses on sale of invested assets	(13,004		)	(12,247		)
	Net realized and unrealized losses on derivatives	(11,632		)	(12,920		)
	Mark-to-market gains (losses):
	Fixed maturity investments, trading	25,517			22,455
	Equity securities, trading	5,420			(21,605		)
	Other invested assets, trading	(6,565		)	16,230
	Net realized investment gains	$	45,025		$	54,205

Derivative_Instruments_Tables

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Location and amounts of derivative fair values on the unaudited condensed consolidated balance sheets	The following table summarizes information on the location and amounts of derivative fair values on the unaudited condensed consolidated balance sheets (“consolidated balance sheets”):
		March 31, 2015										December 31, 2014
		Asset			Asset			Liability		Liability		Asset		Asset		Liability		Liability
		Derivative			Derivative			Derivative		Derivative		Derivative		Derivative		Derivative		Derivative
		Notional			Fair Value			Notional		Fair Value		Notional		Fair Value		Notional		Fair Value
		Amount						Amount				Amount				Amount
	Foreign exchange contracts	$	32,833		$	123		$	24,857	$	203	$	33,875	$	1,274	$	167,376	$	991
	Interest rate swaps	—			—			662,200		1,119		—		—		571,500		683
	Total derivatives	$	32,833		$	123		$	687,057	$	1,322	$	33,875	$	1,274	$	738,876	$	1,674
Unrealized and realized gains (losses) on derivatives recorded in the unaudited condensed consolidated income statements	The following table provides the net realized and unrealized gains (losses) on derivatives not designated as hedges recorded on the consolidated income statements:
		Three Months Ended
		March 31,
		2015			2014
	Foreign exchange contracts	$	(7,352	)	$	(868	)
	Total included in foreign exchange loss	(7,352		)	(868		)
	Foreign exchange contracts	1,050			(558		)
	Interest rate futures	(12,682		)	(12,362		)
	Total included in net realized investment gains	(11,632		)	(12,920		)
	Total realized and unrealized losses on derivatives	$	(18,984	)	$	(13,788	)

Fair_Value_Of_Financial_Instru1

Fair Value Of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair value hierarchy and related disclosures	The following table shows the fair value of the Company’s financial instruments and where in the fair value hierarchy the fair value measurements are included as of the dates indicated below:
	March 31, 2015		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. government and government agencies		$	1,577,775		$	1,577,775		$	1,467,357		$	110,418	$	—
	Non-U.S. government and government agencies		189,448			189,448			—			189,448		—
	States, municipalities and political subdivisions		178,551			178,551			—			178,551		—
	Corporate debt		2,328,039			2,328,039			—			2,328,039		—
	Mortgage-backed		1,286,210			1,286,210			—			1,153,512		132,698
	Asset-backed		728,874			728,874			—			635,942		92,932
	Total fixed maturity investments		6,288,897			6,288,897			1,467,357			4,595,910		225,630
	Equity securities		856,652			856,652			807,885			—		48,767
	Other invested assets		792,569			792,569			—			—		792,569
	Total investments		$	7,938,118		$	7,938,118		$	2,275,242		$	4,595,910	$	1,066,966
	Derivative assets:
	Foreign exchange contracts		$	123		$	123		$	—		$	123	$	—
	Derivative liabilities:
	Foreign exchange contracts		$	203		$	203		$	—		$	203	$	—
	Interest rate swaps		1,119			1,119			—			1,119		—
	Senior notes		$	798,881		$	877,027		$	—		$	877,027	$	—
	Other long-term debt		$	19,730		$	27,175		$	—		$	27,175	$	—
	December 31, 2014		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. Government and Government agencies		$	1,610,502		$	1,610,502		$	1,499,347		$	111,155	$	—
	Non-U.S. Government and Government agencies		188,199			188,199			—			188,199		—
	States, municipalities and political subdivisions		170,567			170,567			—			170,567		—
	Corporate debt		2,165,393			2,165,393			—			2,165,393		—
	Mortgage-backed		1,263,517			1,263,517			—			1,081,734		181,783
	Asset-backed		670,832			670,832			—			615,419		55,413
	Total fixed maturity investments		6,069,010			6,069,010			1,499,347			4,332,467		237,196
	Equity securities		844,163			844,163			800,833			—		43,330
	Other invested assets		812,543			812,543			—			—		812,543
	Total investments		$	7,725,716		$	7,725,716		$	2,300,180		$	4,332,467	$	1,093,069
	Derivative assets:
	Foreign exchange contracts		$	1,274		$	1,274		$	—		$	1,274	$	—
	Derivative liabilities:
	Foreign exchange contracts		$	991		$	991		$	—		$	991	$	—
	Interest rate swaps		$	683		$	683		$	—		$	683	$	—
	Senior notes		$	798,802		$	879,317		$	—		$	879,317	$	—
	Other long-term debt		$	19,213		$	22,583		$	—		$	22,583	$	—
Fair value measurements using significant unobservable inputs (Level 3)	The following is a reconciliation of the beginning and ending balance of financial instruments using significant unobservable inputs (Level 3):
	Three Months Ended March 31, 2015	Other invested			Mortgage-backed			Asset-backed			Equities
		assets
	Opening balance	$	812,543		$	181,783		$	55,413		$	43,330
	Realized and unrealized gains included in net income	14,101			1,337			352			5,437
	Purchases	39,364			20,170			25,341			—
	Sales	(73,439		)	(70,592		)	(2,669		)	—
	Transfers into Level 3 from Level 2	—			—			43,610			—
	Transfers out of Level 3 into Level 2 (1)	—			—			(29,115		)	—
	Ending balance	$	792,569		$	132,698		$	92,932		$	48,767
	Three Months Ended March 31, 2014
	Opening balance	$	764,081		$	147,338		$	93,413		$	73,904
	Realized and unrealized gains (losses) included in net income	22,626			1,368			(864		)	(9,821		)
	Purchases	89,199			14,110			7,493			—
	Sales	(35,919		)	(17,956		)	(3,176		)	(29,297		)
	Transfers into Level 3 from Level 2	—			—			606			—
	Transfers out of Level 3 into Level 2 (1)	—			(10,799		)	(16,238		)	—
	Ending balance	$	839,987		$	134,061		$	81,234		$	34,786
	_______________________
	-1	Transfers out of Level 3 are primarily attributable to the availability of market observable information.

Reserve_For_Losses_And_Loss_Ex1

Reserve For Losses And Loss Expenses (Tables)	3 Months Ended
	Mar. 31, 2015
Insurance Loss Reserves [Abstract]
Components of liabilty for unpaid losses and loss expenses	The reserve for losses and loss expenses consists of the following:
		March 31,			December 31,
		2015			2014
	Outstanding loss reserves	$	1,414,512		$	1,514,051
	Reserves for losses incurred but not reported	4,490,598			4,367,114
	Reserve for losses and loss expenses	$	5,905,110		$	5,881,165
Reconciliation of beginning and ending liability for unpaid losses and loss expenses	The table below is a reconciliation of the beginning and ending liability for unpaid losses and loss expenses. Losses incurred and paid are reflected net of reinsurance recoverables.
		Three Months Ended
		March 31,
		2015			2014
	Gross liability at beginning of period	$	5,881,165		$	5,766,529
	Reinsurance recoverable at beginning of period	(1,340,256		)	(1,234,504		)
	Net liability at beginning of period	4,540,909			4,532,025
	Net losses incurred related to:
	Current year	388,817			324,147
	Prior years	(63,641		)	(48,861		)
	Total incurred	325,176			275,286
	Net paid losses related to:
	Current year	6,557			3,743
	Prior years	293,098			228,594
	Total paid	299,655			232,337
	Foreign exchange revaluation	(11,631		)	1,299
	Net liability at end of period	4,554,799			4,576,273
	Reinsurance recoverable at end of period	1,350,311			1,280,525
	Gross liability at end of period	$	5,905,110		$	5,856,798

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2015
Stockholders' Equity Note [Abstract]
Issued share capital	The issued share capital consists of the following:
		March 31,			December 31,
		2015			2014
	Common shares issued and fully paid, 2015 and 2014: CHF 4.10 per share	100,299,454			100,775,256
	Share capital at end of period	$	406,088		$	408,020
Schedule of common stock outstanding roll forward
		Three Months Ended
		March 31, 2015
	Shares issued at beginning of period	100,775,256
	Shares canceled	(475,802	)
	Total shares issued at end of period	100,299,454
	Treasury shares issued at beginning of period	4,579,774
	Shares repurchased	1,271,213
	Shares issued out of treasury	(520,400	)
	Shares canceled	(475,802	)
	Total treasury shares at end of period	4,854,785
	Total shares outstanding at end of period	95,444,669
Dividends paid	The Company paid the following dividends during the three months ended March 31, 2015:
	Dividend Paid		Dividend			Total
			Per			Amount
			Share			Paid
	2-Jan-15		$	0.225		$	21,669
Share repurchases	The Company’s share repurchases were as follows:
		Three Months Ended
		March 31,
		2015			2014
	Common shares repurchased	1,271,213			2,012,196
	Total cost of shares repurchased	$	50,949		$	68,659
	Average price per share	$	40.08		$	34.12

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of stock-related compensation expense	The following table shows the total stock-related compensation expense relating to the stock options, RSUs and cash equivalent awards.
		Three Months Ended
		March 31,
		2015			2014
	Stock options	$	277		$	727
	RSUs and performance-based equity awards	3,725			3,513
	Cash-equivalent stock awards	12,523			4,629
	Total	$	16,525		$	8,869
Rsus Other Than Performance Based Rsus [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of activity of stock awards	The activity related to the Company’s RSUs awards is as follows:
		Three Months Ended March 31, 2015
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	502,506		$	32.1
	RSUs granted	502,543		40.24
	RSUs forfeited	(1,458	)	(24.02		)
	RSUs fully vested	(159,984	)	(30.59		)
	Outstanding at end of period	843,607		$	37.25
Performance Based Rsus [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of activity of stock awards	The activity related to the Company’s performance-based equity awards is as follows:
		Three Months Ended March 31, 2015
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	616,641		$	27.52
	Performance-based equity awards granted	234,361		40.24
	Additional awards granted due to achievement of performance criteria	91,737		22.29
	Performance-based equity awards fully vested	(346,515	)	(22.29		)
	Outstanding at end of period	596,224		$	34.76
Cash Equivalent Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of activity of cash equivalent awards	The activity related to the Company's cash-equivalent RSUs and performance-based awards is as follows:
		RSU's					Performance-based Awards
	Three Months Ended March 31, 2015	Number of Awards		Weighted Average Grant Date Fair Value			Number of Awards		Weighted Average Grant Date Fair Value
	Outstanding at beginning of period	1,654,064		$	27.99		924,906		27.52
	Granted	325,805		40.24			156,238		40.24
	Additional awards granted due to achievement of performance criteria	—		—			137,585		22.29
	Forfeited	(9,525	)	(26.90		)	(1,404	)	(22.29		)
	Fully vested	(649,102	)	(26.17		)	(519,725	)	(22.29		)
	Outstanding at end of period	1,321,242		$	31.92		697,600		$	33.25

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Comparison Of Basic And Diluted Earnings Per Share	The following table sets forth the comparison of basic and diluted earnings per share:
		Three Months Ended
		March 31,
		2015		2014
	Basic earnings per share:
	Net income	$	124,356	$	176,972
	Weighted average common shares outstanding	95,935,551		99,545,187
	Basic earnings per share	$	1.3	$	1.78
		Three Months Ended
		March 31,
		2015		2014
	Diluted earnings per share:
	Net income	$	124,356	$	176,972
	Weighted average common shares outstanding	95,935,551		99,545,187
	Share equivalents:
	Stock options	1,116,871		1,463,958
	RSUs and performance-based equity awards	509,971		565,611
	Employee share purchase plan	14,636		9,906
	Weighted average common shares and common share equivalents outstanding - diluted	97,577,029		101,584,662
	Diluted earnings per share	$	1.27	$	1.74

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Summary of segment results	The following tables provide a summary of the segment results:
	Three Months Ended March 31, 2015		North American				Global Markets			Reinsurance			Total
			Insurance				Insurance
	Gross premiums written		$	380,767			$	60,562		$	439,285		$	880,614
	Net premiums written		296,883				42,895			432,750			772,528
	Net premiums earned		312,970				50,040			205,538			568,548
	Net losses and loss expenses		(195,479		)		(20,510		)	(109,187		)	(325,176		)
	Acquisition costs		(31,032		)		(7,008		)	(40,659		)	(78,699		)
	General and administrative expenses		(59,288		)		(18,025		)	(19,825		)	(97,138		)
	Underwriting income		27,171				4,497			35,867			67,535
	Other insurance-related income		854				—			—			854
	Other insurance-related expenses		(855		)		(968		)	—			(1,823		)
	Segment income		27,170				3,529			35,867			66,566
	Net investment income												44,551
	Net realized investment gains												45,025
	Amortization of intangible assets												(633		)
	Interest expense												(14,337		)
	Foreign exchange loss												(9,897		)
	Income before income taxes												$	131,275
	Loss and loss expense ratio		62.5		%		41		%	53.1		%	57.2		%
	Acquisition cost ratio		9.9		%		14		%	19.8		%	13.8		%
	General and administrative expense ratio		18.9		%		36		%	9.6		%	17.1		%
	Expense ratio		28.8		%		50		%	29.4		%	30.9		%
	Combined ratio		91.3		%		91		%	82.5		%	88.1		%
	Three Months Ended March 31, 2014		North American				Global Markets			Reinsurance			Total
			Insurance				Insurance
	Gross premiums written		$	345,912			$	58,397		$	497,084		$	901,393
	Net premiums written		247,152				31,047			493,415			771,614
	Net premiums earned		265,451				35,011			229,823			530,285
	Net losses and loss expenses		(161,172		)		(4,389		)	(109,725		)	(275,286		)
	Acquisition costs		(23,675		)		(2,879		)	(41,168		)	(67,722		)
	General and administrative expenses		(47,615		)		(14,582		)	(18,143		)	(80,340		)
	Underwriting income		32,989				13,161			60,787			106,937
	Other insurance-related income		—				—			—			—
	Other insurance-related expenses		—				—			—			—
	Segment income		32,989				13,161			60,787			106,937
	Net investment income												47,619
	Net realized investment gains												54,205
	Amortization of intangible assets												(633		)
	Interest expense												(14,534		)
	Foreign exchange loss												(49		)
	Income before income taxes												$	193,545
	Loss and loss expense ratio		60.7		%		12.5		%	47.7		%	51.9		%
	Acquisition cost ratio		8.9		%		8.2		%	17.9		%	12.8		%
	General and administrative expense ratio		17.9		%		41.6		%	7.9		%	15.2		%
	Expense ratio		26.8		%		49.8		%	25.8		%	28		%
	Combined ratio		87.5		%		62.3		%	73.5		%	79.9		%
Analysis of gross written premium by geographic location	The following table shows an analysis of the Company’s gross premiums written by geographic location of the Company’s subsidiaries and branches. All intercompany premiums have been eliminated.
		Three Months Ended
		March 31,
		2015				2014
	United States	$	536,632			$	520,773
	Bermuda	196,628				229,631
	Europe	103,969				103,336
	Asia Pacific	40,058				46,823
	Canada	3,327				830
	Total gross premiums written	$	880,614			$	901,393
Premiums earned by segment and line of business	The following table shows the Company’s net premiums earned by line of business for each segment for the three months ended March 31, 2015 and 2014, respectively.
			Three Months Ended
			March 31,
			2015				2014
	North American Insurance:
	General casualty		$	104,924			$	76,302
	Professional liability		78,916				64,271
	Healthcare		38,041				42,493
	Programs		34,147				30,469
	General property		28,000				34,939
	Inland marine		13,349				8,890
	Environmental		6,822				4,586
	Other		8,771				3,501
	Total		312,970				265,451
	Global Markets Insurance:
	Professional liability		19,503				11,720
	General property		8,232				8,239
	Aviation		5,953				5,637
	General casualty		5,913				2,693
	Trade credit		4,276				4,012
	Healthcare		3,606				2,502
	Other		2,557				208
	Total		50,040				35,011
	Reinsurance:
	Property		104,351				137,084
	Specialty		44,285				45,225
	Casualty		56,902				47,514
	Total		205,538				229,823
	Total net premiums earned		$	568,548			$	530,285

Condensed_Consolidated_Guarant1

Condensed Consolidated Guarantor Financial Statements (Tables)	3 Months Ended
	Mar. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule of condensed consolidating balance sheet	Unaudited Condensed Consolidating Balance Sheet:
	As of March 31, 2015	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	8,071,956		$	—		$	8,071,956
	Cash and cash equivalents	36,499			2,109			476,462			—			515,070
	Insurance balances receivable	—			—			773,394			—			773,394
	Funds held	—			—			479,909			—			479,909
	Reinsurance recoverable	—			—			1,350,311			—			1,350,311
	Reinsurance recoverable on paid losses	—			—			107,071			—			107,071
	Net deferred acquisition costs	—			—			187,246			—			187,246
	Goodwill and intangible assets	—			—			329,999			—			329,999
	Balances receivable on sale of investments	—			—			46,822			—			46,822
	Investments in subsidiaries	3,600,273			4,170,400			—			(7,770,673		)	—
	Due from subsidiaries	226,081			27,963			16,454			(270,498		)	—
	Other assets	2,128			2,838			751,042			—			756,008
	Total assets	$	3,864,981		$	4,203,310		$	12,590,666		$	(8,041,171	)	$	12,617,786
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,905,110		$	—		$	5,905,110
	Unearned premiums	—			—			1,717,399			—			1,717,399
	Reinsurance balances payable	—			—			184,322			—			184,322
	Balances due on purchases of investments	—			—			34,396			—			34,396
	Senior notes	—			798,881			—			—			798,881
	Other long-term debt	—			—			19,730			—			19,730
	Due to subsidiaries	10,009			6,445			254,044			(270,498		)	—
	Other liabilities	25,905			14,303			88,673			—			128,881
	Total liabilities	35,914			819,629			8,203,674			(270,498		)	8,788,719
	Total shareholders’ equity	3,829,067			3,383,681			4,386,992			(7,770,673		)	3,829,067
	Total liabilities and shareholders’ equity	$	3,864,981		$	4,203,310		$	12,590,666		$	(8,041,171	)	$	12,617,786
	As of December 31, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	7,868,682		$	—		$	7,868,682
	Cash and cash equivalents	32,579			1,734			555,026			—			589,339
	Insurance balances receivable	—			—			664,815			—			664,815
	Funds held	—			—			724,021			—			724,021
	Reinsurance recoverable	—			—			1,340,256			—			1,340,256
	Reinsurance recoverable on paid losses	—			—			86,075			—			86,075
	Net deferred acquisition costs	—			—			151,546			—			151,546
	Goodwill and intangible assets	—			—			324,556			—			324,556
	Balances receivable on sale of investments	—			—			47,149			—			47,149
	Investments in subsidiaries	3,629,301			4,218,028			—			(7,847,329		)	—
	Due from subsidiaries	147,072			19,190			14,396			(180,658		)	—
	Other assets	1,470			3,192			620,462			—			625,124
	Total assets	$	3,810,422		$	4,242,144		$	12,396,984		$	(8,027,987	)	$	12,421,563
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,881,165		$	—		$	5,881,165
	Unearned premiums	—			—			1,555,313			—			1,555,313
	Reinsurance balances payable	—			—			180,060			—			180,060
	Balances due on purchases of investments	—			—			5,428			—			5,428
	Senior notes	—			798,802			—			—			798,802
	Other long-term debt	—			—			19,213						19,213
	Due to subsidiaries	7,599			6,797			166,262			(180,658		)	—
	Other liabilities	24,532			19,618			159,141			—			203,291
	Total liabilities	32,131			825,217			7,966,582			(180,658		)	8,643,272
	Total shareholders’ equity	3,778,291			3,416,927			4,430,402			(7,847,329		)	3,778,291
	Total liabilities and shareholders’ equity	$	3,810,422		$	4,242,144		$	12,396,984		$	(8,027,987	)	$	12,421,563
Schedule of condensed consolidating statement of operations and comprehensive income	Unaudited Condensed Consolidating Statement of Operations and Comprehensive Income:
	Three Months Ended March 31, 2015	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	Net premiums earned	$	—		$	—		$	568,548		$	—		$	568,548
	Net investment income	2			—			44,549			—			44,551
	Net realized investment losses	—			—			45,025			—			45,025
	Other income	—			—			854			—			854
	Net losses and loss expenses	—			—			(325,176		)	—			(325,176		)
	Acquisition costs	—			—			(78,699		)	—			(78,699		)
	General and administrative expenses	(9,462		)	240			(87,916		)	—			(97,138		)
	Other expense	—			—			(1,823		)	—			(1,823		)
	Amortization of intangible assets	—			—			(633		)	—			(633		)
	Interest expense	—			(13,866		)	(471		)	—			(14,337		)
	Foreign exchange gain (loss)	5			10			(9,912		)	—			(9,897		)
	Income tax (expense) benefit	(639		)	—			(6,280		)	—			(6,919		)
	Equity in earnings of consolidated subsidiaries	134,450			143,696			—			(278,146		)	—
	NET INCOME (LOSS)	$	124,356		$	130,080		$	148,066		$	(278,146	)	$	124,356
	Other comprehensive income	—			—			—			—			—
	COMPREHENSIVE INCOME (LOSS)	$	124,356		$	130,080		$	148,066		$	(278,146	)	$	124,356
	Three Months Ended March 31, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	Net premiums earned	$	—		$	—		$	530,285		$	—		$	530,285
	Net investment income	2			—			47,617			—			47,619
	Net realized investment gains	—			—			54,205			—			54,205
	Other income	—			—			—			—			—
	Net losses and loss expenses	—			—			(275,286		)	—			(275,286		)
	Acquisition costs	—			—			(67,722		)	—			(67,722		)
	General and administrative expenses	(8,914		)	(2,391		)	(69,035		)	—			(80,340		)
	Other expense	—			—			—			—			—
	Amortization of intangible assets	—			—			(633		)	—			(633		)
	Interest expense	—			(13,848		)	(686		)	—			(14,534		)
	Foreign exchange gain (loss)	(2		)	33			(80		)	—			(49		)
	Income tax (expense) benefit	(409		)	—			(16,164		)	—			(16,573		)
	Equity in earnings of consolidated subsidiaries	186,295			199,007			—			(385,302		)	—
	NET INCOME (LOSS)	$	176,972		$	182,801		$	202,501		$	(385,302	)	$	176,972
	Other comprehensive income	—			—			—			—			—
	COMPREHENSIVE INCOME (LOSS)	$	176,972		$	182,801		$	202,501		$	(385,302	)	$	176,972
Schedule of condensed consolidating statement of cash flows	Unaudited Condensed Consolidating Statement of Cash Flows:
	Three Months Ended March 31, 2015	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES	$	71,639		$	80,375		$	339,583		$	(179,000	)	$	312,597
	CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
	Purchases trading securities	—			—			(1,723,443		)	—			(1,723,443		)
	Purchases of other invested assets	—			—			(233,252		)	—			(233,252		)
	Sales of trading securities	—			—			1,561,890			—			1,561,890
	Sales of other invested assets	—			—			56,535			—			56,535
	Other	—			—			19,123			—			19,123
	Net cash provided by (used in) investing activities	—			—			(319,147		)	—			(319,147		)
	CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
	Dividends paid	(21,669		)	—			—			—			(21,669		)
	Intercompany dividends paid	—			(80,000		)	(99,000		)	179,000			—
	Proceeds from the exercise of stock options	4,223			—			—			—			4,223
	Share repurchases	(50,273		)	—			—			—			(50,273		)
	Net cash provided by (used in) financing activities	(67,719		)	(80,000		)	(99,000		)	179,000			(67,719		)
	NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	3,920			375			(78,564		)	—			(74,269		)
	CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	32,579			1,734			555,026			—			589,339
	CASH AND CASH EQUIVALENTS, END OF PERIOD	$	36,499		$	2,109		$	476,462		$	—		$	515,070
	Three Months Ended March 31, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$	94,128		$	92,272		$	324,382		$	(206,000	)	$	304,782
	CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
	Purchases of trading securities	—			—			(1,568,993		)	—			(1,568,993		)
	Purchases of other invested assets	—			—			(779,934		)	—			(779,934		)
	Sales of trading securities	—			—			1,494,648			—			1,494,648
	Sales of other invested assets	—			—			663,237			—			663,237
	Other	—			—			2,487			—			2,487
	Net cash provided by (used in) investing activities	—			—			(188,555		)	—			(188,555		)
	CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
	Dividends paid	(16,732		)	—			—			—			(16,732		)
	Intercompany dividends paid	—			(94,000		)	(112,000		)	206,000			—
	Proceeds from the exercise of stock options	3,030			—			—			—			3,030
	Share repurchases	(68,659		)	—			—			—			(68,659		)
	Net cash provided by (used in) financing activities	(82,361		)	(94,000		)	(112,000		)	206,000			(82,361		)
	NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	11,767			(1,728		)	23,827			—			33,866
	CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790			2,775			518,371			—			531,936
	CASH AND CASH EQUIVALENTS, END OF PERIOD	$	22,557		$	1,047		$	542,198		$	—		$	565,802

General_Details

General (Details) (USD $)	0 Months Ended	1 Months Ended
In Thousands, unless otherwise specified	1-May-14	Jan. 31, 2015
Business Acquisition [Line Items]
Stock split conversion ratio	3
Latin American Underwriters Holdings Ltd. (LAU)
Business Acquisition [Line Items]
Business acquisition, consideration transferred		$5,105
Goodwill acquired during the period		2,467
Intangible assets acquired during the period		3,610
Useful life of intangible assets		5 years
Contingent consideration		$1,000

Investments_Narrative_Details

Investments (Narrative) (Details)	3 Months Ended
	Mar. 31, 2015
Minimum [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Redemption Restriction, Period in Effect	1 year
Minimum [Member] | Investments without redemption restrictions [Member] | Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	30 days
Gate trigger, percentage	15.00%
Maximum [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Redemption Restriction, Period in Effect	3 years
Maximum [Member] | Investments without redemption restrictions [Member] | Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Gate trigger, percentage	25.00%

Investments_Schedule_Of_Tradin

Investments (Schedule Of Trading Securities) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Equity securities and other invested assets [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	$1,649,221	$1,656,706
Trading securities, Amortized Cost	1,499,912	1,516,275
Equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	856,652	844,163
Trading securities, Amortized Cost	798,275	791,206
Other invested assets
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	792,569	812,543
Trading securities, Amortized Cost	701,637	725,069
Fixed Maturities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	6,288,897	6,069,010
Trading securities, Amortized Cost	6,229,608	6,035,240
U.S. Government And Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,577,775	1,610,502
Trading securities, Amortized Cost	1,569,317	1,610,880
Non-U.S. Government And Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	189,448	188,199
Trading securities, Amortized Cost	204,867	196,332
States, Municipalities And Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	178,551	170,567
Trading securities, Amortized Cost	172,339	165,615
Corporate Debt, Financial Institutions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,107,108	1,024,667
Trading securities, Amortized Cost	1,094,338	1,018,777
Corporate Debt, Industrials [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,107,548	1,029,729
Trading securities, Amortized Cost	1,105,744	1,037,820
Corporate Debt, Utilities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	113,383	110,997
Trading securities, Amortized Cost	113,280	111,599
Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,286,210	1,263,517
Trading securities, Amortized Cost	1,238,165	1,219,712
Asset-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	728,874	670,832
Trading securities, Amortized Cost	$731,558	$674,505

Investments_Schedule_Of_Other_

Investments (Schedule Of Other Investments) (Details) (USD $)	3 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	926,407		955,509
Unfunded Commitments	547,533		483,214
Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	538,114		527,519
Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	388,293		427,990
Private Equity [Member] | Investments with redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	2 years		2 years
Private Equity [Member] | Investments with redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	8 years		8 years
Mezzanine Debt [Member] | Investments with redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	5 years		5 years
Mezzanine Debt [Member] | Investments with redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	9 years		9 years
Distressed [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	3 years		3 years
Real Estate [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	9 years		9 years
Hedge Funds [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	30 days
Distressed Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	60 days		60 days
Equity Long/Short [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	1 year
Equity Long/Short [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	30 days	[1]	30 days	[1]
Equity Long/Short [Member] | Investments without redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	60 days	[1]	60 days	[1]
Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	45 days	[1]	45 days	[1]
Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	90 days	[1]	90 days	[1]
Relative Value Credit [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	60 days	[1]	60 days
High Yield Loan Fund [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	30 days	[1]	30 days	[1]
Total Fair Value [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	792,569		812,543
Unfunded Commitments	547,533		483,214
Total Fair Value [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	538,114		527,519
Total Fair Value [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	254,455		285,024
Total Fair Value [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	364,992		357,350
Unfunded Commitments	547,533		483,214
Total Fair Value [Member] | Private Equity Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	364,992		357,350
Total Fair Value [Member] | Private Equity Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Private Equity [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	196,090		184,576
Unfunded Commitments	191,382		223,802
Total Fair Value [Member] | Private Equity [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	196,090		184,576
Total Fair Value [Member] | Private Equity [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Mezzanine Debt [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	163,357		166,905
Unfunded Commitments	200,804		204,232
Total Fair Value [Member] | Mezzanine Debt [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	163,357		166,905
Total Fair Value [Member] | Mezzanine Debt [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Distressed [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	5,545		5,869
Unfunded Commitments	5,347		5,180
Total Fair Value [Member] | Distressed [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	5,545		5,869
Total Fair Value [Member] | Distressed [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Real Estate [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Unfunded Commitments	150,000		50,000
Total Fair Value [Member] | Real Estate [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Real Estate [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	397,222		425,030
Unfunded Commitments	0		0
Total Fair Value [Member] | Hedge Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	173,122		170,169
Total Fair Value [Member] | Hedge Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	224,100		254,861
Total Fair Value [Member] | Distressed Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	173,122		170,169
Unfunded Commitments	0		0
Total Fair Value [Member] | Distressed Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	173,122		170,169
Total Fair Value [Member] | Distressed Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Equity Long/Short [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	87,644		84,198
Unfunded Commitments	0		0
Total Fair Value [Member] | Equity Long/Short [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Equity Long/Short [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	87,644		84,198
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Total Fair Value [Member] | Multi-Strategy Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	15,996		51,507
Unfunded Commitments	0		0
Total Fair Value [Member] | Multi-Strategy Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	15,996		51,507
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Total Fair Value [Member] | Relative Value Credit [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	120,460		119,156
Unfunded Commitments	0		0
Total Fair Value [Member] | Relative Value Credit [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | Relative Value Credit [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	120,460		119,156
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Total Fair Value [Member] | High Yield Loan Fund [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	30,355		30,163
Unfunded Commitments	0		0
Total Fair Value [Member] | High Yield Loan Fund [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Total Fair Value [Member] | High Yield Loan Fund [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	30,355		30,163
Redemption frequency	Monthly	[1]	Monthly	[1]
Carrying Value [Member] | Other invested assets: other private securities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	133,838		142,966
Unfunded Commitments	0		0
Carrying Value [Member] | Other invested assets: other private securities | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Carrying Value [Member] | Other invested assets: other private securities | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	133,838		142,966
[1]	The redemption frequency and notice periods only apply to the investments without redemption restrictions. Some or all of these investments may be subject to a gate as described below.

Investments_Schedule_Of_Net_In

Investments (Schedule Of Net Investment Income) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net Investment Income [Line Items]
Net investment income	$44,551	$47,619
Fixed maturity investments
Net Investment Income [Line Items]
Net investment income	36,258	36,299
Equity securities
Net Investment Income [Line Items]
Net investment income	3,563	3,253
Other invested assets: hedge funds and private equity
Net Investment Income [Line Items]
Net investment income	8,380	3,992
Other invested assets: other private securities
Net Investment Income [Line Items]
Net investment income	866	7,416
Cash and cash equivalents
Net Investment Income [Line Items]
Net investment income	462	439
Expenses
Net Investment Income [Line Items]
Net investment income	($4,978)	($3,780)

Investments_Components_Of_Real

Investments (Components Of Realized Gains And Losses) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Gain (Loss) on Investments [Line Items]
Gross realized gains on sale of invested assets	$45,289	$62,292
Gross realized losses on sale of invested assets	-13,004	-12,247
Net realized and unrealized losses on derivatives	-11,632	-12,920
Net realized investment gains	45,025	54,205
Fixed maturity investments, trading
Gain (Loss) on Investments [Line Items]
Mark-to-market changes	25,517	22,455
Equity securities, trading
Gain (Loss) on Investments [Line Items]
Mark-to-market changes	5,420	-21,605
Other invested assets
Gain (Loss) on Investments [Line Items]
Mark-to-market changes	($6,565)	$16,230

Investments_Pledged_Assets_Det

Investments (Pledged Assets) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Compliance With Reinsurance Contract Provisions Or Insurance Laws [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Restricted Cash and Investments	$3,114,066	$3,585,792
Pledged As Collateral For Letter Of Credit Facilities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Restricted Cash and Investments	$599,724	$571,750

Derivative_Instruments_Locatio

Derivative Instruments (Location and Amounts of Derivative Fair Values On The Condensed Consolidated Balance Sheets) (Details) (Not Designated as Hedging Instrument [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	$32,833	$33,875
Asset Derivative Fair Value	123	1,274
Liability Derivative Notional Amount	687,057	738,876
Liability Derivative Fair Value	1,322	1,674
Foreign exchange contracts | Other assets
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	32,833	33,875
Asset Derivative Fair Value	123	1,274
Foreign exchange contracts | Accounts payable and accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	24,857	167,376
Liability Derivative Fair Value	203	991
Interest rate swaps | Other assets
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	0	0
Asset Derivative Fair Value	0	0
Interest rate swaps | Accounts payable and accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	662,200	571,500
Liability Derivative Fair Value	$1,119	$683

Derivative_Instruments_Locatio1

Derivative Instruments (Location and Amounts of Unrealized And Realized Gains (Losses) On Derivatives Recorded In The Condensed Consolidated Income Statements) (Details) (Not Designated as Hedging Instrument [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	($18,984)	($13,788)
Foreign exchange (loss) gain
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	-7,352	-868
Foreign exchange (loss) gain | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	-7,352	-868
Net realized investment gains
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	-11,632	-12,920
Net realized investment gains | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	1,050	-558
Net realized investment gains | Interest rate futures
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	($12,682)	($12,362)

Fair_Value_Of_Financial_Instru2

Fair Value Of Financial Instruments (Schedule Of Fair Value Of Financial Instruments) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	$6,288,897	$6,069,010
Equity securities	856,652	844,163
Other invested assets	926,407	955,509
Total investments	8,071,956	7,868,682
Senior notes	798,881	798,802
Other long-term debt	19,730	19,213
Total Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	792,569	812,543
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	6,288,897	6,069,010
Equity securities	856,652	844,163
Other invested assets	792,569	812,543
Total investments	7,938,118	7,725,716
Senior notes		798,802
Other long-term debt	19,730	19,213
Fair Value, Measurements, Recurring [Member] | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	123	1,274
Derivative liabilities	203	991
Fair Value, Measurements, Recurring [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	1,119	683
Fair Value, Measurements, Recurring [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,577,775	1,610,502
Fair Value, Measurements, Recurring [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	189,448	188,199
Fair Value, Measurements, Recurring [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	178,551	170,567
Fair Value, Measurements, Recurring [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	2,328,039	2,165,393
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,286,210	1,263,517
Fair Value, Measurements, Recurring [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	728,874	670,832
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,467,357	1,499,347
Equity securities	807,885	800,833
Other invested assets	0	0
Total investments	2,275,242	2,300,180
Senior notes	0	0
Other long-term debt	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,467,357	1,499,347
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	4,595,910	4,332,467
Equity securities	0	0
Other invested assets	0	0
Total investments	4,595,910	4,332,467
Senior notes	877,027	879,317
Other long-term debt	27,175	22,583
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	123	1,274
Derivative liabilities	203	991
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	1,119	683
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	110,418	111,155
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	189,448	188,199
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	178,551	170,567
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	2,328,039	2,165,393
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,153,512	1,081,734
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	635,942	615,419
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	225,630	237,196
Equity securities	48,767	43,330
Other invested assets	792,569	812,543
Total investments	1,066,966	1,093,069
Senior notes	0	0
Other long-term debt	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	132,698	181,783
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	92,932	55,413
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	6,288,897	6,069,010
Equity securities	856,652	844,163
Other invested assets	792,569	812,543
Total investments	7,938,118	7,725,716
Senior notes	877,027	879,317
Other long-term debt	27,175	22,583
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	123	1,274
Derivative liabilities	203	991
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	1,119	683
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,577,775	1,610,502
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	189,448	188,199
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	178,551	170,567
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	2,328,039	2,165,393
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,286,210	1,263,517
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	$728,874	$670,832

Fair_Value_Of_Financial_Instru3

Fair Value Of Financial Instruments (Schedule Of Fair Value Measurement Using Significant Unobservable Inputs Level Three) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Other invested assets: hedge funds and private equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	$812,543		$764,081
Realized and unrealized gains (losses) included in net income	14,101		22,626
Purchases	39,364		89,199
Sales	-73,439		-35,919
Transfers into Level 3 from Level 2	0		0
Transfers out of Level 3 to Level 2	0	[1]	0	[1]
Ending balance	792,569		839,987
Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	181,783		147,338
Realized and unrealized gains (losses) included in net income	1,337		1,368
Purchases	20,170		14,110
Sales	-70,592		-17,956
Transfers into Level 3 from Level 2	0		0
Transfers out of Level 3 to Level 2	0	[1]	-10,799	[1]
Ending balance	132,698		134,061
Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	55,413		93,413
Realized and unrealized gains (losses) included in net income	352		-864
Purchases	25,341		7,493
Sales	-2,669		-3,176
Transfers into Level 3 from Level 2	43,610		606
Transfers out of Level 3 to Level 2	-29,115	[1]	-16,238	[1]
Ending balance	92,932		81,234
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	43,330		73,904
Realized and unrealized gains (losses) included in net income	5,437		-9,821
Purchases	0		0
Sales	0		-29,297
Transfers into Level 3 from Level 2	0		0
Transfers out of Level 3 to Level 2	0	[1]	0	[1]
Ending balance	$48,767		$34,786
[1]	Transfers out of Level 3 are primarily attributable to the availability of market observable information.

Reserve_For_Losses_And_Loss_Ex2

Reserve For Losses And Loss Expenses (Schedule Of Reserve For Losses And Loss Expenses) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Insurance Loss Reserves [Abstract]
Outstanding loss reserves	$1,414,512	$1,514,051
Reserves for losses incurred but not reported	4,490,598	4,367,114
Reserve for losses and loss expenses	$5,905,110	$5,881,165	$5,856,798	$5,766,529

Reserve_For_Losses_And_Loss_Ex3

Reserve For Losses And Loss Expenses (Schedule Of Reconciliation Of Unpaid Losses And Loss Expenses) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Insurance Loss Reserves [Abstract]
Gross liability at beginning of year	$5,881,165	$5,766,529
Reinsurance recoverable at beginning of year	-1,340,256	-1,234,504
Net liability at beginning of year	4,540,909	4,532,025
Net losses incurred related to:
Current year	388,817	324,147
Prior years	-63,641	-48,861
Total incurred	325,176	275,286
Net paid losses related to:
Current year	6,557	3,743
Prior years	293,098	228,594
Total paid	299,655	232,337
Foreign exchange revaluation	-11,631	1,299
Net liability at end of year	4,554,799	4,576,273
Reinsurance recoverable at end of year	1,350,311	1,280,525
Gross liability at end of year	$5,905,110	$5,856,798

Shareholders_Equity_Issued_Sha

Shareholders' Equity (Issued Share Capital) (Details)	Mar. 31, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2014
In Thousands, except Share data, unless otherwise specified	USD ($)	CHF	USD ($)	CHF
Stockholders' Equity Note [Abstract]
Common shares issued and fully paid, 2014 and 2013: CHF 4.10 per share	100,299,454	100,299,454	100,775,256	100,775,256
Common shares, par value		4.1		4.1
Total share capital	$406,088		$408,020

Shareholders_Equity_Schedule_O

Shareholders' Equity (Schedule Of Common Stock Outstanding Roll Forward) (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued at beginning of year	100,775,256
Shares cancelled, shares	-475,802
Shares issued at end of year	100,299,454
Treasury Stock Transactions, Excluding Value of Shares Reissued [Abstract]
Treasury shares issued at beginning of year	4,579,774
Shares repurchased, shares	1,271,213	2,012,196
Shares issued out of treasury, shares	-520,400
Shares cancelled, shares	-475,802
Total treasury shares at end of year	4,854,785
Total shares outstanding at end of year	95,444,669		96,195,482

Shareholders_Equity_Schedule_O1

Shareholders' Equity (Schedule Of Dividends Paid) (Details) (USD $)	3 Months Ended		0 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Jan. 02, 2015	Oct. 02, 2014	Jul. 02, 2014	Apr. 02, 2015
Dividends, Common Stock [Abstract]
Dividends paid per common share	$0.23	$0.17
Common shares
Dividends, Common Stock [Abstract]
Dividends paid per common share			$0.23	$0.23	$0.23
Payment of quarterly dividends			$21,669
Subsequent event | Common shares
Dividends, Common Stock [Abstract]
Dividends paid per common share						$0.23

Shareholders_Equity_Schedule_O2

Shareholders' Equity (Schedule Of Share Repurchases) (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	1-May-14
Stockholders' Equity Note [Abstract]
Stock Repurchase Program, Authorized Amount			$500,000
Equity Compensation Plans Treasury Shares Reserved For Future Issuance	3,000,000
Shares repurchased, shares	1,271,213	2,012,196
Cost of shares repurchased	$50,949	$68,659
Shares repurchased, average price per share	$40.08	$34.12

Employee_Benefit_Plans_Restric

Employee Benefit Plans (Restricted Stock Units) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Vesting period	4 years
Rsus Other Than Performance Based Rsus [Member]
Activity:
Outstanding, beginning of year, shares	502,506
Granted, shares	502,543
Forfeited, shares	-1,458
Fully vested, shares	-159,984
Outstanding, end of year, shares	843,607
Weighted average grant date fair value:
Outstanding, beginning of year - weighted average grant date fair value	32.1
Granted - weighted average grant date fair value	40.24
Forfeited - weighted average grant date fair value	-24.02
Vested - weighted average grant date fair value	-30.59
Outstanding, end of year - weighted average grant date fair value	37.25
Performance Based Rsus [Member]
Activity:
Outstanding, beginning of year, shares	616,641
Granted, shares	234,361
Additional awards granted due to achievement of performance criteria, shares	91,737
Fully vested, shares	-346,515
Outstanding, end of year, shares	596,224
Weighted average grant date fair value:
Outstanding, beginning of year - weighted average grant date fair value	27.52
Granted - weighted average grant date fair value	40.24
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	22.29
Vested - weighted average grant date fair value	-22.29
Outstanding, end of year - weighted average grant date fair value	34.76
Awards 2015 [Member] | Performance Based Rsus [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
The rate at which performance awards are expensed	100.00%
Awards 2014 [Member] | Performance Based Rsus [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
The rate at which performance awards are expensed	100.00%
Awards 2013 [Member] | Performance Based Rsus [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
The rate at which performance awards are expensed	110.00%

Employee_Benefit_Plans_CashEqu

Employee Benefit Plans (Cash-Equivalent Stock Awards) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Cash Equivalent Stock Awards Rsus [Member]
Activity:
Outstanding, beginning of year, shares	1,654,064
Granted, shares	325,805
Additional awards granted due to achievement of performance criteria, shares	0
Forfeited, shares	-9,525
Fully vested, shares	-649,102
Outstanding, end of year, shares	1,321,242
Weighted average grant date fair value:
Outstanding, beginning of year - weighted average grant date fair value	$27.99
Granted - weighted average grant date fair value	$40.24
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	$0
Forfeited - weighted average grant date fair value	($26.90)
Vested - weighted average grant date fair value	($26.17)
Outstanding, end of year - weighted average grant date fair value	$31.92
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Vesting period	4 years
Cash Equivalent Stock Awards Performance Based [Member]
Activity:
Outstanding, beginning of year, shares	924,906
Granted, shares	156,238
Additional awards granted due to achievement of performance criteria, shares	137,585
Forfeited, shares	-1,404
Fully vested, shares	-519,725
Outstanding, end of year, shares	697,600
Weighted average grant date fair value:
Outstanding, beginning of year - weighted average grant date fair value	$27.52
Granted - weighted average grant date fair value	$40.24
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	$22.29
Forfeited - weighted average grant date fair value	($22.29)
Vested - weighted average grant date fair value	($22.29)
Outstanding, end of year - weighted average grant date fair value	$33.25
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Vesting period	3 years

Employee_Benefit_Plans_Other_D

Employee Benefit Plans (Other Details) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$16,525	$8,869
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	277	727
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	3,725	3,513
Cash Equivalent Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$12,523	$4,629

Earnings_Per_Share_Narrative_D

Earnings Per Share (Narrative) (Details) (Stock Compensation Plan [Member])	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Stock Compensation Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	175,175	75

Earnings_Per_Share_Comparison_

Earnings Per Share (Comparison Of Basic And Diluted Earnings Per Share) (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Basic earnings per share:
Net income	$124,356	$176,972
Weighted average common shares outstanding	95,935,551	99,545,187
Basic earnings per share	$1.30	$1.78
Diluted earnings per share:
Net income	$124,356	$176,972
Weighted average common shares outstanding	95,935,551	99,545,187
Share equivalents:
Warrants and options	1,116,871	1,463,958
RSUs and performance-based equity awards	509,971	565,611
Employee share purchase plan	14,636	9,906
Weighted average common shares and common share equivalents outstanding - diluted	97,577,029	101,584,662
Diluted earnings per share	$1.27	$1.74

Segment_Information_Summary_Of

Segment Information (Summary Of Segment Results) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	segments
Segment Reporting Information [Line Items]
Gross premiums written	$880,614	$901,393
Net premiums written	772,528	771,614
Net premiums earned	568,548	530,285
Net losses and loss expenses	-325,176	-275,286
Acquisition costs	-78,699	-67,722
General and administrative expenses	-97,138	-80,340
Underwriting income (loss)	67,535	106,937
Other insurance-related income	854	0
Other insurance-related expenses	-1,823	0
Segment income	66,566	106,937
Net investment income	44,551	47,619
Net realized investment gains	45,025	54,205
Amortization of intangible assets	-633	-633
Interest expense	-14,337	-14,534
Foreign exchange loss	-9,897	-49
Income before income taxes	131,275	193,545
Loss and loss expense ratio	57.20%	51.90%
Acquisition cost ratio	13.80%	12.80%
General and administrative expense ratio	17.10%	15.20%
Underwriting Expense Ratio	30.90%	28.00%
Combined ratio	88.10%	79.90%
Number of Operating Segments	3
Operating segments | North American Insurance
Segment Reporting Information [Line Items]
Gross premiums written	380,767	345,912
Net premiums written	296,883	247,152
Net premiums earned	312,970	265,451
Net losses and loss expenses	-195,479	-161,172
Acquisition costs	-31,032	-23,675
General and administrative expenses	-59,288	-47,615
Underwriting income (loss)	27,171	32,989
Other insurance-related income	854	0
Other insurance-related expenses	-855	0
Segment income	27,170	32,989
Loss and loss expense ratio	62.50%	60.70%
Acquisition cost ratio	9.90%	8.90%
General and administrative expense ratio	18.90%	17.90%
Underwriting Expense Ratio	28.80%	26.80%
Combined ratio	91.30%	87.50%
Operating segments | Global Markets Insurance
Segment Reporting Information [Line Items]
Gross premiums written	60,562	58,397
Net premiums written	42,895	31,047
Net premiums earned	50,040	35,011
Net losses and loss expenses	-20,510	-4,389
Acquisition costs	-7,008	-2,879
General and administrative expenses	-18,025	-14,582
Underwriting income (loss)	4,497	13,161
Other insurance-related income	0	0
Other insurance-related expenses	-968	0
Segment income	3,529	13,161
Loss and loss expense ratio	41.00%	12.50%
Acquisition cost ratio	14.00%	8.20%
General and administrative expense ratio	36.00%	41.60%
Underwriting Expense Ratio	50.00%	49.80%
Combined ratio	91.00%	62.30%
Operating segments | Reinsurance
Segment Reporting Information [Line Items]
Gross premiums written	439,285	497,084
Net premiums written	432,750	493,415
Net premiums earned	205,538	229,823
Net losses and loss expenses	-109,187	-109,725
Acquisition costs	-40,659	-41,168
General and administrative expenses	-19,825	-18,143
Underwriting income (loss)	35,867	60,787
Other insurance-related income	0	0
Other insurance-related expenses	0	0
Segment income	$35,867	$60,787
Loss and loss expense ratio	53.10%	47.70%
Acquisition cost ratio	19.80%	17.90%
General and administrative expense ratio	9.60%	7.90%
Underwriting Expense Ratio	29.40%	25.80%
Combined ratio	82.50%	73.50%

Segment_Information_Gross_Prem

Segment Information (Gross Premiums Written By Geographic Location) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	$880,614	$901,393
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	536,632	520,773
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	196,628	229,631
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	103,969	103,336
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	40,058	46,823
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	3,327	830
Switzerland
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	$40,383	$44,293

Segment_Information_Net_Premiu

Segment Information (Net Premiums Earned by Line of Business) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Net premiums earned	$568,548	$530,285
Operating segments | North American Insurance
Segment Reporting Information [Line Items]
Net premiums earned	312,970	265,451
Operating segments | North American Insurance | General casualty
Segment Reporting Information [Line Items]
Net premiums earned	104,924	76,302
Operating segments | North American Insurance | Professional liability
Segment Reporting Information [Line Items]
Net premiums earned	78,916	64,271
Operating segments | North American Insurance | Healthcare
Segment Reporting Information [Line Items]
Net premiums earned	38,041	42,493
Operating segments | North American Insurance | Programs
Segment Reporting Information [Line Items]
Net premiums earned	34,147	30,469
Operating segments | North American Insurance | General property
Segment Reporting Information [Line Items]
Net premiums earned	28,000	34,939
Operating segments | North American Insurance | Inland marine
Segment Reporting Information [Line Items]
Net premiums earned	13,349	8,890
Operating segments | North American Insurance | Environmental
Segment Reporting Information [Line Items]
Net premiums earned	6,822	4,586
Operating segments | North American Insurance | Other
Segment Reporting Information [Line Items]
Net premiums earned	8,771	3,501
Operating segments | Global Markets Insurance
Segment Reporting Information [Line Items]
Net premiums earned	50,040	35,011
Operating segments | Global Markets Insurance | General casualty
Segment Reporting Information [Line Items]
Net premiums earned	5,913	2,693
Operating segments | Global Markets Insurance | Professional liability
Segment Reporting Information [Line Items]
Net premiums earned	19,503	11,720
Operating segments | Global Markets Insurance | Healthcare
Segment Reporting Information [Line Items]
Net premiums earned	3,606	2,502
Operating segments | Global Markets Insurance | General property
Segment Reporting Information [Line Items]
Net premiums earned	8,232	8,239
Operating segments | Global Markets Insurance | Other
Segment Reporting Information [Line Items]
Net premiums earned	2,557	208
Operating segments | Global Markets Insurance | Aviation
Segment Reporting Information [Line Items]
Net premiums earned	5,953	5,637
Operating segments | Global Markets Insurance | Trade credit
Segment Reporting Information [Line Items]
Net premiums earned	4,276	4,012
Operating segments | Reinsurance
Segment Reporting Information [Line Items]
Net premiums earned	205,538	229,823
Operating segments | Reinsurance | Property
Segment Reporting Information [Line Items]
Net premiums earned	104,351	137,084
Operating segments | Reinsurance | Specialty
Segment Reporting Information [Line Items]
Net premiums earned	44,285	45,225
Operating segments | Reinsurance | Casualty
Segment Reporting Information [Line Items]
Net premiums earned	$56,902	$47,514

Condensed_Consolidated_Guarant2

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Balance Sheet) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
ASSETS:
Investments	$8,071,956	$7,868,682
Cash and cash equivalents	515,070	589,339	565,802	531,936
Insurance balances receivable	773,394	664,815
Funds held	479,909	724,021
Reinsurance recoverable	1,350,311	1,340,256	1,280,525	1,234,504
Reinsurance recoverable on paid losses	107,071	86,075
Net deferred acquisition costs	187,246	151,546
Goodwill and intangible assets	329,999	324,556
Balances receivable on sale of investments	46,822	47,149
Investments in subsidiaries	0	0
Due from subsidiaries	0	0
Other assets	756,008	625,124
Total assets	12,617,786	12,421,563
LIABILITIES:
Reserve for losses and loss expenses	5,905,110	5,881,165	5,856,798	5,766,529
Unearned premiums	1,717,399	1,555,313
Reinsurance balances payable	184,322	180,060
Balances due on purchases of investments	34,396	5,428
Senior notes	798,881	798,802
Other long-term debt	19,730	19,213
Due to subsidiaries	0	0
Other liabilities	128,881	203,291
Total liabilities	8,788,719	8,643,272
Total shareholders’ equity	3,829,067	3,778,291	3,616,678	3,519,826
Total liabilities and shareholders’ equity	12,617,786	12,421,563
Percentage ownership of Subsidiary Issuer	100.00%
Consolidation, Eliminations [Member]
ASSETS:
Investments	0	0
Cash and cash equivalents	0	0	0	0
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses	0	0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	-7,770,673	-7,847,329
Due from subsidiaries	-270,498	-180,658
Other assets	0	0
Total assets	-8,041,171	-8,027,987
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments	0	0
Senior notes	0	0
Other long-term debt	0
Due to subsidiaries	-270,498	-180,658
Other liabilities	0	0
Total liabilities	-270,498	-180,658
Total shareholders’ equity	-7,770,673	-7,847,329
Total liabilities and shareholders’ equity	-8,041,171	-8,027,987
Allied World Switzerland (Parent Guarantor) [Member]
ASSETS:
Investments	0	0
Cash and cash equivalents	36,499	32,579	22,557	10,790
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses	0	0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	3,600,273	3,629,301
Due from subsidiaries	226,081	147,072
Other assets	2,128	1,470
Total assets	3,864,981	3,810,422
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments	0	0
Senior notes	0	0
Other long-term debt	0	0
Due to subsidiaries	10,009	7,599
Other liabilities	25,905	24,532
Total liabilities	35,914	32,131
Total shareholders’ equity	3,829,067	3,778,291
Total liabilities and shareholders’ equity	3,864,981	3,810,422
Allied World Bermuda (Subsidiary Issuer) [Member]
ASSETS:
Investments	0	0
Cash and cash equivalents	2,109	1,734	1,047	2,775
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses	0	0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	4,170,400	4,218,028
Due from subsidiaries	27,963	19,190
Other assets	2,838	3,192
Total assets	4,203,310	4,242,144
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments	0	0
Senior notes	798,881	798,802
Other long-term debt	0	0
Due to subsidiaries	6,445	6,797
Other liabilities	14,303	19,618
Total liabilities	819,629	825,217
Total shareholders’ equity	3,383,681	3,416,927
Total liabilities and shareholders’ equity	4,203,310	4,242,144
Other Allied World Subsidiaries [Member]
ASSETS:
Investments	8,071,956	7,868,682
Cash and cash equivalents	476,462	555,026	542,198	518,371
Insurance balances receivable	773,394	664,815
Funds held	479,909	724,021
Reinsurance recoverable	1,350,311	1,340,256
Reinsurance recoverable on paid losses	107,071	86,075
Net deferred acquisition costs	187,246	151,546
Goodwill and intangible assets	329,999	324,556
Balances receivable on sale of investments	46,822	47,149
Investments in subsidiaries	0	0
Due from subsidiaries	16,454	14,396
Other assets	751,042	620,462
Total assets	12,590,666	12,396,984
LIABILITIES:
Reserve for losses and loss expenses	5,905,110	5,881,165
Unearned premiums	1,717,399	1,555,313
Reinsurance balances payable	184,322	180,060
Balances due on purchases of investments	34,396	5,428
Senior notes	0	0
Other long-term debt	19,730	19,213
Due to subsidiaries	254,044	166,262
Other liabilities	88,673	159,141
Total liabilities	8,203,674	7,966,582
Total shareholders’ equity	4,386,992	4,430,402
Total liabilities and shareholders’ equity	$12,590,666	$12,396,984

Condensed_Consolidated_Guarant3

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Income Statement) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Condensed Income Statements, Captions [Line Items]
Net premiums earned	$568,548	$530,285
Net investment income	44,551	47,619
Net realized investment gains (losses)	45,025	54,205
Other income	854	0
Net losses and loss expenses	-325,176	-275,286
Acquisition costs	-78,699	-67,722
General and administrative expenses	-97,138	-80,340
Other insurance-related expenses	-1,823	0
Amortization of intangible assets	-633	-633
Interest expense	-14,337	-14,534
Foreign exchange loss	-9,897	-49
Income tax (expense) benefit	-6,919	-16,573
Equity in earnings of consolidated subsidiaries	0	0
NET INCOME	124,356	176,972
Other comprehensive income	0	0
COMPREHENSIVE INCOME (LOSS)	124,356	176,972
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	0	0
Net investment income	0	0
Net realized investment gains (losses)	0	0
Other income	0	0
Net losses and loss expenses	0	0
Acquisition costs	0	0
General and administrative expenses	0	0
Other insurance-related expenses	0	0
Amortization of intangible assets	0	0
Interest expense	0	0
Foreign exchange loss	0	0
Income tax (expense) benefit	0	0
Equity in earnings of consolidated subsidiaries	-278,146	-385,302
NET INCOME	-278,146	-385,302
Other comprehensive income	0	0
COMPREHENSIVE INCOME (LOSS)	-278,146	-385,302
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	0	0
Net investment income	2	2
Net realized investment gains (losses)	0	0
Other income	0	0
Net losses and loss expenses	0	0
Acquisition costs	0	0
General and administrative expenses	-9,462	-8,914
Other insurance-related expenses	0	0
Amortization of intangible assets	0	0
Interest expense	0	0
Foreign exchange loss	5	-2
Income tax (expense) benefit	-639	-409
Equity in earnings of consolidated subsidiaries	134,450	186,295
NET INCOME	124,356	176,972
Other comprehensive income	0	0
COMPREHENSIVE INCOME (LOSS)	124,356	176,972
Allied World Bermuda (Subsidiary Issuer) [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	0	0
Net investment income	0	0
Net realized investment gains (losses)	0	0
Other income	0	0
Net losses and loss expenses	0	0
Acquisition costs	0	0
General and administrative expenses	240	-2,391
Other insurance-related expenses	0	0
Amortization of intangible assets	0	0
Interest expense	-13,866	-13,848
Foreign exchange loss	10	33
Income tax (expense) benefit	0	0
Equity in earnings of consolidated subsidiaries	143,696	199,007
NET INCOME	130,080	182,801
Other comprehensive income	0	0
COMPREHENSIVE INCOME (LOSS)	130,080	182,801
Other Allied World Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	568,548	530,285
Net investment income	44,549	47,617
Net realized investment gains (losses)	45,025	54,205
Other income	854	0
Net losses and loss expenses	-325,176	-275,286
Acquisition costs	-78,699	-67,722
General and administrative expenses	-87,916	-69,035
Other insurance-related expenses	-1,823	0
Amortization of intangible assets	-633	-633
Interest expense	-471	-686
Foreign exchange loss	-9,912	-80
Income tax (expense) benefit	-6,280	-16,164
Equity in earnings of consolidated subsidiaries	0	0
NET INCOME	148,066	202,501
Other comprehensive income	0	0
COMPREHENSIVE INCOME (LOSS)	$148,066	$202,501

Condensed_Consolidated_Guarant4

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Cash Flows) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$312,597	$304,782
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	-1,723,443	-1,568,993
Purchases of other invested assets	-233,252	-779,934
Sales of trading securities	1,561,890	1,494,648
Sales of other invested assets	56,535	663,237
Other	19,123	2,487
Net cash used in investing activities	-319,147	-188,555
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	-21,669	-16,732
Intercompany dividends paid	0	0
Proceeds from the exercise of stock options	4,223	3,030
Share repurchases	-50,273	-68,659
Net cash used in financing activities	-67,719	-82,361
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	-74,269	33,866
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	589,339	531,936
CASH AND CASH EQUIVALENTS, END OF PERIOD	515,070	565,802
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	-179,000	-206,000
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash used in investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	0	0
Intercompany dividends paid	179,000	206,000
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	179,000	206,000
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	0	0
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	0	0
CASH AND CASH EQUIVALENTS, END OF PERIOD	0	0
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	71,639	94,128
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash used in investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	-21,669	-16,732
Intercompany dividends paid	0	0
Proceeds from the exercise of stock options	4,223	3,030
Share repurchases	-50,273	-68,659
Net cash used in financing activities	-67,719	-82,361
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	3,920	11,767
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	32,579	10,790
CASH AND CASH EQUIVALENTS, END OF PERIOD	36,499	22,557
Allied World Bermuda (Subsidiary Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	80,375	92,272
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash used in investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	0	0
Intercompany dividends paid	-80,000	-94,000
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	-80,000	-94,000
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	375	-1,728
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	1,734	2,775
CASH AND CASH EQUIVALENTS, END OF PERIOD	2,109	1,047
Other Allied World Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	339,583	324,382
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	-1,723,443	-1,568,993
Purchases of other invested assets	-233,252	-779,934
Sales of trading securities	1,561,890	1,494,648
Sales of other invested assets	56,535	663,237
Other	19,123	2,487
Net cash used in investing activities	-319,147	-188,555
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	0	0
Intercompany dividends paid	-99,000	-112,000
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	-99,000	-112,000
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	-78,564	23,827
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	555,026	518,371
CASH AND CASH EQUIVALENTS, END OF PERIOD	$476,462	$542,198

Condensed_Consolidated_Guarant5

Condensed Consolidated Guarantor Financial Statements (Notes to Consolidated Guarantor Financial Statements) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	$80,000	$94,000

Subsequent_Events_Details

Subsequent Events (Details) (USD $)	3 Months Ended		0 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Jan. 02, 2015	Oct. 02, 2014	Jul. 02, 2014	Apr. 02, 2015	Apr. 01, 2015
Subsequent Event [Line Items]
Dividends paid per common share	$0.23	$0.17
Common shares
Subsequent Event [Line Items]
Dividends paid per common share			$0.23	$0.23	$0.23
Common shares | Subsequent event
Subsequent Event [Line Items]
Dividends paid per common share						$0.23
Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc [Member]
Subsequent Event [Line Items]
Business Acquisition Preliminary Purchase Price							$192,692
Business Acquisition Expected Additional Capitalization							$90,000