Allied World Assurance 10-Q 23 Apr 14 2014 Q1 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 14, 2014
Document And Entity Information [Abstract]	'	'
Entity Registrant Name	'Allied World Assurance Co Holdings, AG	'
Entity Central Index Key	'0001163348	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	32,851,429

Unaudited_Condensed_Consolidat

Unaudited Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
ASSETS:	'	'
Fixed maturity investments trading, at fair value (amortized cost: 2014: $6,010,765; 2013: $6,065,350)	$6,068,666	$6,100,798
Equity securities trading, at fair value (cost: 2014: $803,954; 2013: $647,301)	834,893	699,846
Other invested assets	989,791	911,392
Total investments	7,893,350	7,712,036
Cash and cash equivalents	565,802	531,936
Restricted cash	144,570	149,393
Insurance balances receivable	839,630	664,731
Funds held	447,801	632,430
Prepaid reinsurance	331,065	340,992
Reinsurance recoverable	1,280,525	1,234,504
Accrued investment income	29,539	32,236
Net deferred acquisition costs	167,104	126,661
Goodwill	268,376	268,376
Intangible assets	48,198	48,831
Balances receivable on sale of investments	198,640	76,544
Net deferred tax assets	36,948	37,469
Other assets	82,617	89,691
Total assets	12,334,165	11,945,830
LIABILITIES:	'	'
Reserve for losses and loss expenses	5,856,798	5,766,529
Unearned premiums	1,627,658	1,396,256
Reinsurance balances payable	160,041	173,023
Balances due on purchases of investments	171,442	104,740
Senior notes	798,573	798,499
Dividends payable	16,495	16,732
Accounts payable and accrued liabilities	86,480	170,225
Total liabilities	8,717,487	8,426,004
Commitments and contingencies	'	'
SHAREHOLDERS’ EQUITY:	'	'
Common shares: 2014: par value CHF 12.30 per share and 2013: par value CHF 12.30 per share (2014: 33,821,752; 2013: 34,492,484 shares issued and 2014: 32,908,821; 2013: 33,417,882 shares outstanding)	410,820	418,988
Treasury shares, at cost (2014: 912,931; 2013: 1,074,602)	-68,756	-79,992
Retained earnings	3,274,614	3,180,830
Total shareholders’ equity	3,616,678	3,519,826
Total liabilities and shareholders’ equity	$12,334,165	$11,945,830

Unaudited_Condensed_Consolidat1

Unaudited Condensed Consolidated Balance Sheets (Parenthetical)(USD ($))	Mar. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Fixed maturity investments trading, amortized cost	$6,010,765	$6,065,350
Equity securities trading - cost	$803,954	$647,301
Common stock, shares issued	33,821,752	34,492,484
Common stock, shares outstanding	32,908,821	33,417,882
Treasury stock (shares)	912,931	1,074,602

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, 2014	Mar. 31, 2013
REVENUES:	'	'
Gross premiums written	$901,393	$837,081
Premiums ceded	-129,779	-142,029
Net premiums written	771,614	695,052
Change in unearned premiums	-241,329	-231,824
Net premiums earned	530,285	463,228
Net investment income	47,619	33,388
Net realized investment gains	54,205	79,637
Total revenues	632,109	576,253
EXPENSES:	'	'
Net losses and loss expenses	275,286	255,178
Acquisition costs	67,722	56,685
General and administrative expenses	80,340	82,680
Amortization of intangible assets	633	633
Interest expense	14,534	14,134
Foreign exchange loss	49	2,518
Total expenses	438,564	411,828
Income before income taxes	193,545	164,425
Income tax expense	16,573	5,433
NET INCOME	176,972	158,992
Other comprehensive loss:	'	'
Other comprehensive loss	0	0
COMPREHENSIVE INCOME	$176,972	$158,992
PER SHARE DATA	'	'
Basic earnings per share	$5.33	$4.59
Diluted earnings per share	$5.23	$4.49
Weighted average common shares outstanding	33,181,729	34,613,606
Weighted average common shares and common share equivalents outstanding	33,861,554	35,431,843
Dividends paid per share	$0.50	$0.38

Unaudited_Condensed_Consolidat3

Unaudited Condensed Consolidated Statements Of Shareholders' Equity (USD $)	Total	Common shares	Treasury Shares	Retained Earnings [Member]
In Thousands
Balance, at beginning of period at Dec. 31, 2012	$3,326,335	$454,980	($113,818)	$2,985,173
Net income	158,992	'	'	158,992
Dividends — par value reduction	-12,981	-12,981	'	'
Other comprehensive loss	0	'	'	'
Stock compensation	-4,138	'	17,465	-21,603
Share repurchases	-36,245	'	-36,245	'
Shares cancelled	0	-5,412	36,245	-30,833
Balance, at end of period at Mar. 31, 2013	3,431,963	436,587	-96,353	3,091,729
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
Other comprehensive loss	0	'	'	'
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

Unaudited_Condensed_Consolidat4

Unaudited Condensed Consolidated Statements Of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:	'	'
Net income	$176,972	$158,992
Adjustments to reconcile net income to cash provided by operating activities:	'	'
Net realized gains on sales of investments	-49,756	-38,533
Mark to market adjustments	-13,956	-46,112
Stock compensation expense	4,240	3,995
Undistributed income of equity method investments	-2,292	0
Changes in:	'	'
Reserve for losses and loss expenses, net of reinsurance recoverables	44,248	5,278
Unearned premiums, net of prepaid reinsurance	241,329	231,824
Insurance balances receivable	-174,899	-156,967
Funds held	184,629	-34,212
Reinsurance balances payable	-12,982	-17,803
Net deferred acquisition costs	-40,443	-34,141
Net deferred tax assets	521	-2,157
Accounts payable and accrued liabilities	-83,745	-70,780
Other items, net	29,230	14,185
Net cash provided by operating activities	303,096	13,569
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:	'	'
Purchases of trading securities	-1,568,993	-1,330,735
Purchases of other invested assets	-779,934	-54,026
Sales of trading securities	1,494,648	1,188,307
Sales of other invested assets	663,237	97,989
Purchases of fixed assets	-2,336	-2,378
Change in restricted cash	4,823	116,785
Net cash (used in) provided by investing activities	-188,555	15,942
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid - partial par value reduction	0	-12,981
Dividends paid	-16,732	0
Proceeds from the exercise of stock options	3,030	2,472
Share repurchases	-68,659	-36,245
Net cash used in financing activities	-82,361	-46,754
Effect of exchange rate changes on foreign currency cash	1,686	-2,055
NET INCREASE IN CASH AND CASH EQUIVALENTS	33,866	-19,298
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	531,936	681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	565,802	662,581
Supplemental disclosure of cash flow information:	'	'
Cash paid for income taxes	529	6,953
Cash paid for interest expense	$18,750	$18,750

General

General	3 Months Ended
	Mar. 31, 2014
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”), provides property and casualty insurance and reinsurance on a worldwide basis. References to $ are to the lawful currency of the United States and to CHF are to the lawful currency of Switzerland.

Basis_of_Preparation_and_Conso

Basis of Preparation and Consolidation	3 Months Ended
	Mar. 31, 2014
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, including, but 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, 2013.

New_Accounting_Pronouncements

New Accounting Pronouncements	3 Months Ended
	Mar. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
New Accounting Pronouncements	'
	NEW ACCOUNTING PRONOUNCEMENTS
	There were no recently issued accounting pronouncements that had a material impact on the Company's financial statements or disclosures.

Investments

Investments	3 Months Ended
	Mar. 31, 2014
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, 2014						December 31, 2013
		Fair Value			Amortized Cost			Fair Value				Amortized Cost
	U.S. Government and Government agencies	$	1,476,463		$	1,480,371		$	1,676,788			$	1,684,832
	Non-U.S. Government and Government agencies	182,415			187,632			191,776				197,082
	States, municipalities and political subdivisions	230,669			228,284			231,555				234,406
	Corporate debt:
	Financial institutions	1,097,649			1,083,131			958,794				943,518
	Industrials	1,116,004			1,105,613			1,174,047				1,165,448
	Utilities	96,807			96,403			69,426				69,658
	Mortgage-backed	1,304,130			1,266,663			1,292,502				1,267,863
	Asset-backed	564,529			562,668			505,910				502,543
	Total fixed maturity investments	$	6,068,666		$	6,010,765		$	6,100,798			$	6,065,350
		March 31, 2014						December 31, 2013
		Fair Value			Original Cost			Fair Value				Original Cost
	Equity securities	$	834,893		$	803,954		$	699,846			$	647,301
	Other invested assets	839,987			718,358			764,081				658,683
		$	1,674,880		$	1,522,312		$	1,463,927			$	1,305,984
	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 excludes 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, 2014 and December 31, 2013 were as follows:
	Investment Type	Carrying Value as of March 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	$	144,582		$	144,582		2 - 9 Years		$	—					$	262,450
	Mezzanine debt	81,474			81,474			8 - 9 Years		—						182,562
	Distressed	9,752			9,752			4 Years		—						5,249
	Total private equity	235,808			235,808					—						450,261
	Distressed	161,033			161,033			1 Year		—						—
	Equity long/short	163,964			52,149			1 Year		111,815				Quarterly	30 -60 Days	—
	Multi-strategy	122,584			—					122,584				Quarterly	45 -90 Days	—
	Event driven	6,407			—					6,407				Annual	60 Days	—
	Relative value credit	117,271			—					117,271				Quarterly	60 Days	—
	Total hedge funds	571,259			213,182					358,077						—
	High yield loan fund	32,920			—					32,920				Monthly	30 days	—
	Total other invested assets at fair value	839,987			448,990					390,997						450,261
	Other private securities	149,804			—					149,804						—
	Total other invested assets	$	989,791		$	448,990				$	540,801					$	450,261
	Investment Type	Carrying Value as of December 31, 2013			Investments			Estimated		Investments				Redemption	Redemption	Unfunded
					with			Remaining		without				Frequency(1)	Notice	Commitments
					Redemption			Restriction		Redemption					Period(1)
					Restrictions			Period		Restrictions
	Private equity	$	144,422		$	144,422		2 - 9 Years		$	—					$	263,519
	Mezzanine debt	64,627			64,627			8 - 9 Years		—						198,756
	Distressed	7,776			7,776			4 Years		—						5,249
	Total private equity	216,825			216,825					—						467,524
	Distressed	151,227			151,227			1 - 2 Years		—						—
	Equity long/short	99,365			—					99,365				Quarterly	30 -60 Days	—
	Multi-strategy	136,958			—					136,958				Quarterly	45 -90 Days	—
	Event driven	14,018			—					14,018				Annual	60 Days	—
	Relative value credit	113,730			—					113,730				Quarterly	60 Days	—
	Total hedge funds	515,298			151,227					364,071						—
	High yield loan fund	31,958			—					31,958				Monthly	30 days	—
	Total other invested assets at fair value	764,081			368,052					396,029						467,524
	Other private securities	147,311			—					147,311						—
	Total other invested assets	$	911,392		$	368,052				$	543,340					$	467,524
	_______________________
	-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.
	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.
•	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.
•	Event driven funds: Event driven strategies seek to deploy capital into specific securities whose returns are affected by a specific event that affects the value of one or more securities of a company. Returns for such securities are linked primarily to the specific outcome of the events and not by the overall direction of the bond or stock markets. Examples could include mergers and acquisitions (arbitrage), corporate restructurings and spin-offs, and capital structure arbitrage.
•	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 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,
	2014			2013
Fixed maturity investments	$	36,299		$	32,525
Equity securities	3,253			3,199
Other invested assets	11,408			1,464
Cash and cash equivalents	439			488
Expenses	(3,780		)	(4,288		)
Net investment income	$	47,619		$	33,388
Net investment income from other invested assets included the distributed and undistributed net income from investments accounted for using the equity method of accounting for the three months ended March 31, 2014 and 2013.
d) Components of Realized Gains and Losses
	Three Months Ended
	March 31,
	2014			2013
Gross realized gains on sale of invested assets	$	62,292		$	44,249
Gross realized losses on sale of invested assets	(12,247		)	(6,965		)
Net realized and unrealized losses on derivatives	(12,920		)	(977		)
Mark-to-market gains (losses):
Fixed maturity investments, trading	22,455			(16,475		)
Equity securities, trading	(21,605		)	32,973
Other invested assets, trading	16,230			26,832
Net realized investment gains	$	54,205		$	79,637
e) Pledged Assets
As of March 31, 2014 and December 31, 2013, $2,635,901 and $2,894,401, 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, 2014 and December 31, 2013, a further $1,004,926 and $1,053,632, respectively, of cash and cash equivalents and investments were pledged as collateral for the Company’s letter of credit facilities. See Note 10(d) to the Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013 for details on the Company’s credit facilities.

Derivative_Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments	'
	DERIVATIVE INSTRUMENTS
	As of March 31, 2014 and December 31, 2013, 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, 2014										December 31, 2013
		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	$	194,081		$	1,408		$	117,757	$	3,145	$	294,788	$	6,254	$	122,439	$	1,176
	Interest rate swaps	581,400			860			95,000		15		491,400		6,829		40,000		4,214
	Total derivatives	$	775,481		$	2,268		$	212,757	$	3,160	$	786,188	$	13,083	$	162,439	$	5,390
	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,
		2014			2013
	Foreign exchange contracts	$	(868	)	$	(744	)
	Total included in foreign exchange loss	(868		)	(744		)
	Put options	—			(3,732		)
	Foreign exchange contracts	(558		)	1,815
	Interest rate futures	(12,362		)	940
	Total included in net realized investment gains	(12,920		)	(977		)
	Total realized and unrealized losses on derivatives	$	(13,788	)	$	(1,721	)
	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.
	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, 2014
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, 2014		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. Government and Government agencies		$	1,476,463		$	1,476,463		$	1,135,246		$	341,217	$	—
	Non-U.S. Government and Government agencies		182,415			182,415			—			182,415		—
	States, municipalities and political subdivisions		230,669			230,669			—			230,669		—
	Corporate debt		2,310,460			2,310,460			—			2,310,460		—
	Mortgage-backed		1,304,130			1,304,130			—			1,170,069		134,061
	Asset-backed		564,529			564,529			—			483,295		81,234
	Total fixed maturity investments		6,068,666			6,068,666			1,135,246			4,718,125		215,295
	Equity securities		834,893			834,893			800,107			—		34,786
	Other invested assets		839,987			839,987			—			—		839,987
	Total investments		$	7,743,546		$	7,743,546		$	1,935,353		$	4,718,125	$	1,090,068
	Derivative assets:
	Foreign exchange contracts		$	1,408		$	1,408		$	—		$	1,408	$	—
	Interest rate swaps		860			860			—			860		—
	Derivative liabilities:
	Foreign exchange contracts		$	3,145		$	3,145		$	—		$	3,145	$	—
	Interest rate swaps		15			15			—			15		—
	Senior notes		$	798,573		$	906,448		$	—		$	906,448	$	—
	December 31, 2013		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. Government and Government agencies		$	1,676,788		$	1,676,788		$	1,370,088		$	306,700	$	—
	Non-U.S. Government and Government agencies		191,776			191,776			—			191,776		—
	States, municipalities and political subdivisions		231,555			231,555			—			231,555		—
	Corporate debt		2,202,267			2,202,267			—			2,202,267		—
	Mortgage-backed		1,292,502			1,292,502			—			1,145,164		147,338
	Asset-backed		505,910			505,910			—			412,497		93,413
	Total fixed maturity investments		6,100,798			6,100,798			1,370,088			4,489,959		240,751
	Equity securities		699,846			699,846			625,942			—		73,904
	Other invested assets		764,081			764,081			—			—		764,081
	Total investments		$	7,564,725		$	7,564,725		$	1,996,030		$	4,489,959	$	1,078,736
	Derivative assets:
	Foreign exchange contracts		$	6,254		$	6,254		$	—		$	6,254	$	—
	Interest rate swaps		6,829			6,829			—			6,829		—
	Derivative liabilities:
	Foreign exchange contracts		$	1,176		$	1,176		$	—		$	1,176	$	—
	Interest rate swaps		$	4,214		$	4,214		$	—		$	4,214	$	—
	Senior notes		$	798,499		$	897,601		$	—		$	897,601	$	—
	“Other invested assets” excluded 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 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 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 net asset value of the funds as reported by the fund manager that the Company believes is an unobservable input, and as such, the fair values of those funds are included in the Level 3 fair value hierarchy.
	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.
	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, 2014	Other invested			Mortgage-backed			Asset-backed			Equities
	assets
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
Three Months Ended March 31, 2013
Opening balance	$	655,888		$	167,825		$	62,246		$	54,680
Realized and unrealized gains included in net income	32,253			(1,189		)	(97		)	3,107
Purchases	73,210			—			2,461			—
Sales	(51,211		)	(21,645		)	(16,622		)	—
Transfers into Level 3 from Level 2	—			19,813			—			—
Transfers out of Level 3 into Level 2 (1)	—			(9,384		)	(7,085		)	—
Ending balance	$	710,140		$	155,420		$	40,903		$	57,787
_______________________
-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, 2014
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,
		2014			2013
	Outstanding loss reserves	$	1,474,376		$	1,520,867
	Reserves for losses incurred but not reported	4,382,422			4,245,662
	Reserve for losses and loss expenses	$	5,856,798		$	5,766,529
	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,
		2014			2013
	Gross liability at beginning of period	$	5,766,529		$	5,645,549
	Reinsurance recoverable at beginning of period	(1,234,504		)	(1,141,110		)
	Net liability at beginning of period	4,532,025			4,504,439
	Net losses incurred related to:
	Current year	324,147			299,248
	Prior years	(48,861		)	(44,070		)
	Total incurred	275,286			255,178
	Net paid losses related to:
	Current year	3,743			3,581
	Prior years	228,594			241,121
	Total paid	232,337			244,702
	Foreign exchange revaluation	1,299			(5,198		)
	Net liability at end of period	4,576,273			4,509,717
	Reinsurance recoverable at end of period	1,280,525			1,163,503
	Gross liability at end of period	$	5,856,798		$	5,673,220
	For the three months ended March 31, 2014, the Company recorded net unfavorable reserve development in its U.S. insurance segment and net favorable prior year development in its international insurance and reinsurance segments. The net unfavorable prior year reserve development in the U.S. insurance segment for the 2011 loss year was in the Company's healthcare line of business and was due to adverse development on several claims above its previous expectations in the managed care errors and omissions class of business and higher than expected loss frequency in the medical malpractice class of business. The international insurance segment had favorable prior year reserve development for the 2007 loss year due to favorable development on an individual professional liability claim, and unfavorable reserve development for the 2013 loss year due to a single claim in the healthcare line of business. The net favorable prior year reserve development in the reinsurance segment for the 2013 loss year was primarily due to benign property loss activity.
	For the three months ended March 31, 2013, the Company had net favorable reserve development in its international and reinsurance segments due to actual loss emergence being lower than initially expected. The U.S. insurance segment had net unfavorable reserve development primarily due to adverse loss emergence trends for the 2011 and 2012 loss years for certain errors and omissions and directors’ and officers’ classes of business.
	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, 2014
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, Labuan, the United Kingdom, Singapore and Switzerland. To the best of the Company’s knowledge, there are no income tax examinations pending by any 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, 2014.

Shareholders_Equity

Shareholders' Equity	3 Months Ended
	Mar. 31, 2014
Stockholders' Equity Note [Abstract]	'
Shareholders' Equity	'
	SHAREHOLDERS’ EQUITY
	a) Authorized shares
	The issued share capital consists of the following:
		March 31,			December 31,
		2014			2013
	Common shares issued and fully paid, 2014: CHF 12.30 per share; 2013: CHF 12.30 per share	33,821,752			34,492,484
	Share capital at end of period	$	410,820		$	418,988
		Three Months Ended
		March 31, 2014
	Shares issued at beginning of period	34,492,484
	Shares cancelled	(670,732	)
	Total shares issued at end of period	33,821,752
	Treasury shares issued at beginning of period	1,074,602
	Shares repurchased	670,732
	Shares issued out of treasury	(161,671	)
	Shares cancelled	(670,732	)
	Total treasury shares at end of period	912,931
	Total shares outstanding at end of period	32,908,821
	During the three months ended March 31, 2014, 670,732 shares repurchased and designated for cancellation were constructively retired and cancelled.
	b) Dividends
	The Company paid the following dividends during the three months ended March 31, 2014:
	Dividend Paid		Dividend			Total
			Per			Amount
			Share			Paid
	2-Jan-14		$	0.5		$	16,732
	On May 2, 2013, 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 amounts were paid to shareholders in quarterly dividends of $0.50 per share in July 2013, October 2013, January 2014 and April 2014.
	c) Share Repurchases
	In May 2012, the Company established a share repurchase program in order to repurchase up to $500,000 of its 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 this share repurchase program, common shares repurchased shall be designated for cancellation at acquisition and shall be cancelled 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,
		2014			2013
	Common shares repurchased	670,732			432,117
	Total cost of shares repurchased	$	68,659		$	36,245
	Average price per share	$	102.36		$	83.88

Employee_Benefit_Plans

Employee Benefit Plans	3 Months Ended
	Mar. 31, 2014
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 2014, 2013 and 2012, the Company anticipates that the performance goals are likely to be achieved. Based on the performance goals, the performance-based equity awards granted in 2014, 2013 and 2012 are expensed at 100%, 100% and 130%, 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, 2014
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	47,899		$	65.07
	RSUs granted	151,392		100.68
	RSUs forfeited	—		—
	RSUs fully vested	(24,876	)	(65.06		)
	Outstanding at end of period	174,415		$	95.98
	The activity related to the Company’s performance-based equity awards is as follows:
		Three Months Ended March 31, 2014
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	268,173		$	69.64
	Performance-based equity awards granted	55,434		100.67
	Additional awards granted due to achievement of performance criteria	34,965		61.51
	Performance-based equity awards forfeited	—		—
	Performance-based equity awards fully vested	(151,480	)	(61.51		)
	Outstanding at end of period	207,092		$	82.52
	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, 2014	Number of Awards		Weighted Average Grant Date Fair Value			Number of Awards		Weighted Average Grant Date Fair Value
	Outstanding at beginning of period	683,028		$	74.1		343,987		71.02
	Granted	146,054		100.67			83,146		100.67
	Additional awards granted due to achievement of performance criteria	—		—			34,965		61.51
	Forfeited	(960	)	(77.72		)	—		—
	Fully vested	(250,640	)	(64.41		)	(151,480	)	(61.51		)
	Outstanding at end of period	577,482		$	83.81		310,618		$	82.52
	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,
		2014			2013
	Stock options	$	727		$	1,335
	RSUs and performance-based equity awards	3,513			2,660
	Cash-equivalent stock awards	4,629			12,756
	Total	$	8,869		$	16,751

Earnings_Per_Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2014
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,
		2014		2013
	Basic earnings per share:
	Net income	$	176,972	$	158,992
	Weighted average common shares outstanding	33,181,729		34,613,606
	Basic earnings per share	$	5.33	$	4.59
		Three Months Ended
		March 31,
		2014		2013
	Diluted earnings per share:
	Net income	$	176,972	$	158,992
	Weighted average common shares outstanding	33,181,729		34,613,606
	Share equivalents:
	Stock options	487,986		482,207
	RSUs and performance-based equity awards	188,537		335,575
	Employee share purchase plan	3,302		455
	Weighted average common shares and common share equivalents outstanding - diluted	33,861,554		35,431,843
	Diluted earnings per share	$	5.23	$	4.49
	For the three months ended March 31, 2014 and 2013, a weighted average of 25 and 333 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, 2014
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: U.S. insurance, international insurance and reinsurance. All product lines fall within these classifications.
	The U.S. insurance segment includes the Company’s direct specialty insurance operations in the United States and Canada. This segment provides both direct property and specialty casualty insurance primarily to non-Fortune 1000 North American domiciled accounts. The international insurance segment includes the Company’s direct insurance operations in Bermuda, Europe, Singapore and Hong Kong. This segment provides both direct property and casualty insurance primarily to Fortune 1000 North American domiciled accounts from the Bermuda office and direct property and specialty casualty insurance to non-North American domiciled accounts from the European, Singapore and Hong Kong offices. 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.
	Management measures results for each segment on the basis of the “loss and loss expense ratio,” “acquisition cost ratio,” “general and administrative 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 “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, 2014		U.S. Insurance				International			Reinsurance			Total
							Insurance
	Gross premiums written		$	269,945			$	134,364		$	497,084		$	901,393
	Net premiums written		202,740				75,459			493,415			771,614
	Net premiums earned		212,123				88,339			229,823			530,285
	Net losses and loss expenses		(141,995		)		(23,566		)	(109,725		)	(275,286		)
	Acquisition costs		(27,501		)		947			(41,168		)	(67,722		)
	General and administrative expenses		(37,436		)		(24,761		)	(18,143		)	(80,340		)
	Underwriting income		5,191				40,959			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		66.9		%		26.7		%	47.7		%	51.9		%
	Acquisition cost ratio		13		%		(1.1		)%	17.9		%	12.8		%
	General and administrative expense ratio		17.6		%		28		%	7.9		%	15.2		%
	Combined ratio		97.5		%		53.6		%	73.5		%	79.9		%
	Three Months Ended March 31, 2013		U.S. Insurance				International			Reinsurance			Total
							Insurance
	Gross premiums written		$	256,018			$	128,516		$	452,547		$	837,081
	Net premiums written		192,253				77,745			425,054			695,052
	Net premiums earned		188,439				84,214			190,575			463,228
	Net losses and loss expenses		(133,324		)		(28,935		)	(92,919		)	(255,178		)
	Acquisition costs		(23,128		)		849			(34,406		)	(56,685		)
	General and administrative expenses		(39,596		)		(24,789		)	(18,295		)	(82,680		)
	Underwriting (loss) income		(7,609		)		31,339			44,955			68,685
	Net investment income												33,388
	Net realized investment gains												79,637
	Amortization of intangible assets												(633		)
	Interest expense												(14,134		)
	Foreign exchange loss												(2,518		)
	Income before income taxes												$	164,425
	Loss and loss expense ratio		70.8		%		34.4		%	48.8		%	55.1		%
	Acquisition cost ratio		12.3		%		(1.0		)%	18.1		%	12.2		%
	General and administrative expense ratio		21		%		29.4		%	9.6		%	17.8		%
	Combined ratio		104.1		%		62.8		%	76.5		%	85.1		%
	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,
		2014				2013
	United States	$	520,773			$	478,443
	Bermuda	229,631				228,672
	Europe	103,336				86,509
	Singapore	41,940				38,113
	Hong Kong	4,883				5,344
	Canada	830				—
	Total gross premiums written	$	901,393			$	837,081
	Europe includes gross premiums written attributable to Switzerland of $44,293 and $40,806 for the three months ended March 31, 2014 and 2013, respectively.

Commitments_And_Contingencies

Commitments And Contingencies	3 Months Ended
	Mar. 31, 2014
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, 2014, 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.
	The Company entered into a 20-year mortgage commitment with a Swiss bank for a company-used office building in Zug, Switzerland. The total proceeds to be received under the mortgage are CHF 18,000 with a fixed annual interest rate of 3.2% payable quarterly. The mortgage payments will be CHF 300 per year, plus accrued interest, for the first 19 years with the remaining balance payable at the end of the mortgage. The Company will receive the proceeds from the bank during the fourth quarter of 2014 at which time the Company will recognize the mortgage loan liability in its consolidated balance sheets.
	In conjunction with the above mortgage commitment, the Company entered into a three-year credit facility with a Swiss bank that provides up to CHF 5,000 for general corporate purposes; however, the Company will use the proceeds from the credit facility to fund the purchase of the office building in Zug, Switzerland. The interest rate for the credit facility is 2.5%.

Condensed_Consolidated_Guarant

Condensed Consolidated Guarantor Financial Statements	3 Months Ended
	Mar. 31, 2014
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, 2014 and December 31, 2013 and for the three months ended March 31, 2014 and 2013 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, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	7,893,350		$	—		$	7,893,350
	Cash and cash equivalents	22,557			1,047			542,198			—			565,802
	Insurance balances receivable	—			—			839,630			—			839,630
	Funds held	—			—			447,801			—			447,801
	Reinsurance recoverable	—			—			1,280,525			—			1,280,525
	Net deferred acquisition costs	—			—			167,104			—			167,104
	Goodwill and intangible assets	—			—			316,574			—			316,574
	Balances receivable on sale of investments	—			—			198,640			—			198,640
	Investments in subsidiaries	3,434,192			4,026,535			—			(7,460,727		)	—
	Due from subsidiaries	187,571			30,569			20,751			(238,891		)	—
	Other assets	2,079			4,321			618,339			—			624,739
	Total assets	$	3,646,399		$	4,062,472		$	12,324,912		$	(7,699,618	)	$	12,334,165
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,856,798		$	—		$	5,856,798
	Unearned premiums	—			—			1,627,658			—			1,627,658
	Reinsurance balances payable	—			—			160,041			—			160,041
	Balances due on purchases of investments	—			—			171,442			—			171,442
	Senior notes	—			798,573			—			—			798,573
	Due to subsidiaries	10,565			10,186			218,140			(238,891		)	—
	Other liabilities	19,156			14,583			69,236			—			102,975
	Total liabilities	29,721			823,342			8,103,315			(238,891		)	8,717,487
	Total shareholders’ equity	3,616,678			3,239,130			4,221,597			(7,460,727		)	3,616,678
	Total liabilities and shareholders’ equity	$	3,646,399		$	4,062,472		$	12,324,912		$	(7,699,618	)	$	12,334,165
	As of December 31, 2013	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	7,712,036		$	—		$	7,712,036
	Cash and cash equivalents	10,790			2,775			518,371			—			531,936
	Insurance balances receivable	—			—			664,731			—			664,731
	Funds held	—			—			632,430			—			632,430
	Reinsurance recoverable	—			—			1,234,504			—			1,234,504
	Net deferred acquisition costs	—			—			126,661			—			126,661
	Goodwill and intangible assets	—			—			317,207			—			317,207
	Balances receivable on sale of investments	—			—			76,544			—			76,544
	Investments in subsidiaries	3,413,001			4,018,619			—			(7,431,620		)	—
	Due from subsidiaries	111,172			122,846			123,479			(357,497		)	—
	Other assets	1,757			4,671			643,353			—			649,781
	Total assets	$	3,536,720		$	4,148,911		$	12,049,316		$	(7,789,117	)	$	11,945,830
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,766,529		$	—		$	5,766,529
	Unearned premiums	—			—			1,396,256			—			1,396,256
	Reinsurance balances payable	—			—			173,023			—			173,023
	Balances due on purchases of investments	—			—			104,740			—			104,740
	Senior notes	—			798,499			—			—			798,499
	Due to subsidiaries	12,945			110,534			234,018			(357,497		)	—
	Other liabilities	3,949			17,797			165,211			—			186,957
	Total liabilities	16,894			926,830			7,839,777			(357,497		)	8,426,004
	Total shareholders’ equity	3,519,826			3,222,081			4,209,539			(7,431,620		)	3,519,826
	Total liabilities and shareholders’ equity	$	3,536,720		$	4,148,911		$	12,049,316		$	(7,789,117	)	$	11,945,830
	The investment in subsidiaries and total shareholders' equity balances reported above in the Unaudited Condensed Consolidating Balance Sheet for Allied World Bermuda (Subsidiary Issuer) as of December 31, 2013 were reduced by $776,000 from the previously reported amounts to properly record intercompany dividends as a reduction in the investment in subsidiaries balance due to a miscalculation. Since the intercompany dividends were eliminated in consolidation there was no impact to consolidated total shareholders' equity.
	Unaudited Condensed Consolidating Statement of Operations and Comprehensive Income:
	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 losses	—			—			54,205			—			54,205
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		)
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
Three Months Ended March 31, 2013	Allied World			Allied World			Other Allied			Consolidating			Allied World
	Switzerland			Bermuda			World			Adjustments			Switzerland
	(Parent			(Subsidiary			Subsidiaries						Consolidated
	Guarantor)			Issuer)
Net premiums earned	$	—		$	—		$	463,228		$	—		$	463,228
Net investment income	7			2			33,379			—			33,388
Net realized investment gains	—			—			79,637			—			79,637
Net losses and loss expenses	—			—			(255,178		)	—			(255,178		)
Acquisition costs	—			—			(56,685		)	—			(56,685		)
General and administrative expenses	(10,986		)	(457		)	(71,237		)	—			(82,680		)
Amortization of intangible assets	—			—			(633		)	—			(633		)
Interest expense	—			(13,830		)	(304		)	—			(14,134		)
Foreign exchange gain (loss)	272			(95		)	(2,695		)	—			(2,518		)
Income tax (expense) benefit	—			—			(5,433		)	—			(5,433		)
Equity in earnings of consolidated subsidiaries	169,699			181,480			—			(351,179		)	—
NET INCOME (LOSS)	$	158,992		$	167,100		$	184,079		$	(351,179	)	$	158,992
Other comprehensive income	—			—			—			—			—
COMPREHENSIVE INCOME (LOSS)	$	158,992		$	167,100		$	184,079		$	(351,179	)	$	158,992
Unaudited Condensed Consolidating Statement of Cash Flows:
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		$	(1,728	)	$	212,382		$	—		$	304,782
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases 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		)
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		)	—			—			—			(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
Three Months Ended March 31, 2013	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:	$	59,772		$	5,859		$	(54,117	)	$	—		$	11,514
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	—			—			(1,330,735		)	—			(1,330,735		)
Purchases of other invested assets	—			—			(54,026		)	—			(54,026		)
Sales of trading securities	—			—			1,188,307			—			1,188,307
Sales of other invested assets	—			—			97,989			—			97,989
Other	—			—			114,407			—			114,407
Net cash provided by (used in) investing activities	—			—			15,942			—			15,942
CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Partial par value reduction	(12,981		)	—			—			—			(12,981		)
Proceeds from the exercise of stock options	2,472			—			—			—			2,472
Share repurchases	(36,245		)	—			—			—			(36,245		)
Net cash provided by (used in) financing activities	(46,754		)	—			—			—			(46,754		)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	13,018			5,859			(38,175		)	—			(19,298		)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	19,997			11,324			650,558			—			681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	$	33,015		$	17,183		$	612,383		$	—		$	662,581
Notes to Parent Company Condensed Financial Information
a) Dividends
Allied World Switzerland received cash dividends from its subsidiaries of $94,000 and $90,000 for the three months ended March 31, 2014 and 2013, 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, 2014
Subsequent Events [Abstract]	'
Subsequent Events	'
	SUBSEQUENT EVENTS
	On April 3, 2014, the Company paid a quarterly dividend of $0.50 per share to shareholders of record on March 25, 2014.

Basis_of_Preparation_and_Conso1

Basis of Preparation and Consolidation (Policies)	3 Months Ended
	Mar. 31, 2014
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, including, but 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, 2014
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, 2014						December 31, 2013
		Fair Value			Amortized Cost			Fair Value				Amortized Cost
	U.S. Government and Government agencies	$	1,476,463		$	1,480,371		$	1,676,788			$	1,684,832
	Non-U.S. Government and Government agencies	182,415			187,632			191,776				197,082
	States, municipalities and political subdivisions	230,669			228,284			231,555				234,406
	Corporate debt:
	Financial institutions	1,097,649			1,083,131			958,794				943,518
	Industrials	1,116,004			1,105,613			1,174,047				1,165,448
	Utilities	96,807			96,403			69,426				69,658
	Mortgage-backed	1,304,130			1,266,663			1,292,502				1,267,863
	Asset-backed	564,529			562,668			505,910				502,543
	Total fixed maturity investments	$	6,068,666		$	6,010,765		$	6,100,798			$	6,065,350
		March 31, 2014						December 31, 2013
		Fair Value			Original Cost			Fair Value				Original Cost
	Equity securities	$	834,893		$	803,954		$	699,846			$	647,301
	Other invested assets	839,987			718,358			764,081				658,683
		$	1,674,880		$	1,522,312		$	1,463,927			$	1,305,984
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, 2014 and December 31, 2013 were as follows:
	Investment Type	Carrying Value as of March 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	$	144,582		$	144,582		2 - 9 Years		$	—					$	262,450
	Mezzanine debt	81,474			81,474			8 - 9 Years		—						182,562
	Distressed	9,752			9,752			4 Years		—						5,249
	Total private equity	235,808			235,808					—						450,261
	Distressed	161,033			161,033			1 Year		—						—
	Equity long/short	163,964			52,149			1 Year		111,815				Quarterly	30 -60 Days	—
	Multi-strategy	122,584			—					122,584				Quarterly	45 -90 Days	—
	Event driven	6,407			—					6,407				Annual	60 Days	—
	Relative value credit	117,271			—					117,271				Quarterly	60 Days	—
	Total hedge funds	571,259			213,182					358,077						—
	High yield loan fund	32,920			—					32,920				Monthly	30 days	—
	Total other invested assets at fair value	839,987			448,990					390,997						450,261
	Other private securities	149,804			—					149,804						—
	Total other invested assets	$	989,791		$	448,990				$	540,801					$	450,261
	Investment Type	Carrying Value as of December 31, 2013			Investments			Estimated		Investments				Redemption	Redemption	Unfunded
					with			Remaining		without				Frequency(1)	Notice	Commitments
					Redemption			Restriction		Redemption					Period(1)
					Restrictions			Period		Restrictions
	Private equity	$	144,422		$	144,422		2 - 9 Years		$	—					$	263,519
	Mezzanine debt	64,627			64,627			8 - 9 Years		—						198,756
	Distressed	7,776			7,776			4 Years		—						5,249
	Total private equity	216,825			216,825					—						467,524
	Distressed	151,227			151,227			1 - 2 Years		—						—
	Equity long/short	99,365			—					99,365				Quarterly	30 -60 Days	—
	Multi-strategy	136,958			—					136,958				Quarterly	45 -90 Days	—
	Event driven	14,018			—					14,018				Annual	60 Days	—
	Relative value credit	113,730			—					113,730				Quarterly	60 Days	—
	Total hedge funds	515,298			151,227					364,071						—
	High yield loan fund	31,958			—					31,958				Monthly	30 days	—
	Total other invested assets at fair value	764,081			368,052					396,029						467,524
	Other private securities	147,311			—					147,311						—
	Total other invested assets	$	911,392		$	368,052				$	543,340					$	467,524
	_______________________
	-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.
Schedule of net investment income	'
		Three Months Ended
		March 31,
		2014			2013
	Fixed maturity investments	$	36,299		$	32,525
	Equity securities	3,253			3,199
	Other invested assets	11,408			1,464
	Cash and cash equivalents	439			488
	Expenses	(3,780		)	(4,288		)
	Net investment income	$	47,619		$	33,388
Components of realized gains and losses	'
		Three Months Ended
		March 31,
		2014			2013
	Gross realized gains on sale of invested assets	$	62,292		$	44,249
	Gross realized losses on sale of invested assets	(12,247		)	(6,965		)
	Net realized and unrealized losses on derivatives	(12,920		)	(977		)
	Mark-to-market gains (losses):
	Fixed maturity investments, trading	22,455			(16,475		)
	Equity securities, trading	(21,605		)	32,973
	Other invested assets, trading	16,230			26,832
	Net realized investment gains	$	54,205		$	79,637

Derivative_Instruments_Tables

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2014
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, 2014										December 31, 2013
		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	$	194,081		$	1,408		$	117,757	$	3,145	$	294,788	$	6,254	$	122,439	$	1,176
	Interest rate swaps	581,400			860			95,000		15		491,400		6,829		40,000		4,214
	Total derivatives	$	775,481		$	2,268		$	212,757	$	3,160	$	786,188	$	13,083	$	162,439	$	5,390
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,
		2014			2013
	Foreign exchange contracts	$	(868	)	$	(744	)
	Total included in foreign exchange loss	(868		)	(744		)
	Put options	—			(3,732		)
	Foreign exchange contracts	(558		)	1,815
	Interest rate futures	(12,362		)	940
	Total included in net realized investment gains	(12,920		)	(977		)
	Total realized and unrealized losses on derivatives	$	(13,788	)	$	(1,721	)

Fair_Value_Of_Financial_Instru1

Fair Value Of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2014
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, 2014		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. Government and Government agencies		$	1,476,463		$	1,476,463		$	1,135,246		$	341,217	$	—
	Non-U.S. Government and Government agencies		182,415			182,415			—			182,415		—
	States, municipalities and political subdivisions		230,669			230,669			—			230,669		—
	Corporate debt		2,310,460			2,310,460			—			2,310,460		—
	Mortgage-backed		1,304,130			1,304,130			—			1,170,069		134,061
	Asset-backed		564,529			564,529			—			483,295		81,234
	Total fixed maturity investments		6,068,666			6,068,666			1,135,246			4,718,125		215,295
	Equity securities		834,893			834,893			800,107			—		34,786
	Other invested assets		839,987			839,987			—			—		839,987
	Total investments		$	7,743,546		$	7,743,546		$	1,935,353		$	4,718,125	$	1,090,068
	Derivative assets:
	Foreign exchange contracts		$	1,408		$	1,408		$	—		$	1,408	$	—
	Interest rate swaps		860			860			—			860		—
	Derivative liabilities:
	Foreign exchange contracts		$	3,145		$	3,145		$	—		$	3,145	$	—
	Interest rate swaps		15			15			—			15		—
	Senior notes		$	798,573		$	906,448		$	—		$	906,448	$	—
	December 31, 2013		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. Government and Government agencies		$	1,676,788		$	1,676,788		$	1,370,088		$	306,700	$	—
	Non-U.S. Government and Government agencies		191,776			191,776			—			191,776		—
	States, municipalities and political subdivisions		231,555			231,555			—			231,555		—
	Corporate debt		2,202,267			2,202,267			—			2,202,267		—
	Mortgage-backed		1,292,502			1,292,502			—			1,145,164		147,338
	Asset-backed		505,910			505,910			—			412,497		93,413
	Total fixed maturity investments		6,100,798			6,100,798			1,370,088			4,489,959		240,751
	Equity securities		699,846			699,846			625,942			—		73,904
	Other invested assets		764,081			764,081			—			—		764,081
	Total investments		$	7,564,725		$	7,564,725		$	1,996,030		$	4,489,959	$	1,078,736
	Derivative assets:
	Foreign exchange contracts		$	6,254		$	6,254		$	—		$	6,254	$	—
	Interest rate swaps		6,829			6,829			—			6,829		—
	Derivative liabilities:
	Foreign exchange contracts		$	1,176		$	1,176		$	—		$	1,176	$	—
	Interest rate swaps		$	4,214		$	4,214		$	—		$	4,214	$	—
	Senior notes		$	798,499		$	897,601		$	—		$	897,601	$	—
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, 2014	Other invested			Mortgage-backed			Asset-backed			Equities
		assets
	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
	Three Months Ended March 31, 2013
	Opening balance	$	655,888		$	167,825		$	62,246		$	54,680
	Realized and unrealized gains included in net income	32,253			(1,189		)	(97		)	3,107
	Purchases	73,210			—			2,461			—
	Sales	(51,211		)	(21,645		)	(16,622		)	—
	Transfers into Level 3 from Level 2	—			19,813			—			—
	Transfers out of Level 3 into Level 2 (1)	—			(9,384		)	(7,085		)	—
	Ending balance	$	710,140		$	155,420		$	40,903		$	57,787
	_______________________
	-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, 2014
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,
		2014			2013
	Outstanding loss reserves	$	1,474,376		$	1,520,867
	Reserves for losses incurred but not reported	4,382,422			4,245,662
	Reserve for losses and loss expenses	$	5,856,798		$	5,766,529
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,
		2014			2013
	Gross liability at beginning of period	$	5,766,529		$	5,645,549
	Reinsurance recoverable at beginning of period	(1,234,504		)	(1,141,110		)
	Net liability at beginning of period	4,532,025			4,504,439
	Net losses incurred related to:
	Current year	324,147			299,248
	Prior years	(48,861		)	(44,070		)
	Total incurred	275,286			255,178
	Net paid losses related to:
	Current year	3,743			3,581
	Prior years	228,594			241,121
	Total paid	232,337			244,702
	Foreign exchange revaluation	1,299			(5,198		)
	Net liability at end of period	4,576,273			4,509,717
	Reinsurance recoverable at end of period	1,280,525			1,163,503
	Gross liability at end of period	$	5,856,798		$	5,673,220

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2014
Stockholders' Equity Note [Abstract]	'
Issued share capital	'
	The issued share capital consists of the following:
		March 31,			December 31,
		2014			2013
	Common shares issued and fully paid, 2014: CHF 12.30 per share; 2013: CHF 12.30 per share	33,821,752			34,492,484
	Share capital at end of period	$	410,820		$	418,988
Schedule of common stock outstanding roll forward	'
		Three Months Ended
		March 31, 2014
	Shares issued at beginning of period	34,492,484
	Shares cancelled	(670,732	)
	Total shares issued at end of period	33,821,752
	Treasury shares issued at beginning of period	1,074,602
	Shares repurchased	670,732
	Shares issued out of treasury	(161,671	)
	Shares cancelled	(670,732	)
	Total treasury shares at end of period	912,931
	Total shares outstanding at end of period	32,908,821
Dividends paid	'
	The Company paid the following dividends during the three months ended March 31, 2014:
	Dividend Paid		Dividend			Total
			Per			Amount
			Share			Paid
	2-Jan-14		$	0.5		$	16,732
Share repurchases	'
	The Company’s share repurchases were as follows:
		Three Months Ended
		March 31,
		2014			2013
	Common shares repurchased	670,732			432,117
	Total cost of shares repurchased	$	68,659		$	36,245
	Average price per share	$	102.36		$	83.88

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2014
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,
		2014			2013
	Stock options	$	727		$	1,335
	RSUs and performance-based equity awards	3,513			2,660
	Cash-equivalent stock awards	4,629			12,756
	Total	$	8,869		$	16,751
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, 2014
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	47,899		$	65.07
	RSUs granted	151,392		100.68
	RSUs forfeited	—		—
	RSUs fully vested	(24,876	)	(65.06		)
	Outstanding at end of period	174,415		$	95.98
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, 2014
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	268,173		$	69.64
	Performance-based equity awards granted	55,434		100.67
	Additional awards granted due to achievement of performance criteria	34,965		61.51
	Performance-based equity awards forfeited	—		—
	Performance-based equity awards fully vested	(151,480	)	(61.51		)
	Outstanding at end of period	207,092		$	82.52
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, 2014	Number of Awards		Weighted Average Grant Date Fair Value			Number of Awards		Weighted Average Grant Date Fair Value
	Outstanding at beginning of period	683,028		$	74.1		343,987		71.02
	Granted	146,054		100.67			83,146		100.67
	Additional awards granted due to achievement of performance criteria	—		—			34,965		61.51
	Forfeited	(960	)	(77.72		)	—		—
	Fully vested	(250,640	)	(64.41		)	(151,480	)	(61.51		)
	Outstanding at end of period	577,482		$	83.81		310,618		$	82.52

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2014
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,
		2014		2013
	Basic earnings per share:
	Net income	$	176,972	$	158,992
	Weighted average common shares outstanding	33,181,729		34,613,606
	Basic earnings per share	$	5.33	$	4.59
		Three Months Ended
		March 31,
		2014		2013
	Diluted earnings per share:
	Net income	$	176,972	$	158,992
	Weighted average common shares outstanding	33,181,729		34,613,606
	Share equivalents:
	Stock options	487,986		482,207
	RSUs and performance-based equity awards	188,537		335,575
	Employee share purchase plan	3,302		455
	Weighted average common shares and common share equivalents outstanding - diluted	33,861,554		35,431,843
	Diluted earnings per share	$	5.23	$	4.49

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Summary of segment results	'
	The following tables provide a summary of the segment results:
	Three Months Ended March 31, 2014		U.S. Insurance				International			Reinsurance			Total
							Insurance
	Gross premiums written		$	269,945			$	134,364		$	497,084		$	901,393
	Net premiums written		202,740				75,459			493,415			771,614
	Net premiums earned		212,123				88,339			229,823			530,285
	Net losses and loss expenses		(141,995		)		(23,566		)	(109,725		)	(275,286		)
	Acquisition costs		(27,501		)		947			(41,168		)	(67,722		)
	General and administrative expenses		(37,436		)		(24,761		)	(18,143		)	(80,340		)
	Underwriting income		5,191				40,959			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		66.9		%		26.7		%	47.7		%	51.9		%
	Acquisition cost ratio		13		%		(1.1		)%	17.9		%	12.8		%
	General and administrative expense ratio		17.6		%		28		%	7.9		%	15.2		%
	Combined ratio		97.5		%		53.6		%	73.5		%	79.9		%
	Three Months Ended March 31, 2013		U.S. Insurance				International			Reinsurance			Total
							Insurance
	Gross premiums written		$	256,018			$	128,516		$	452,547		$	837,081
	Net premiums written		192,253				77,745			425,054			695,052
	Net premiums earned		188,439				84,214			190,575			463,228
	Net losses and loss expenses		(133,324		)		(28,935		)	(92,919		)	(255,178		)
	Acquisition costs		(23,128		)		849			(34,406		)	(56,685		)
	General and administrative expenses		(39,596		)		(24,789		)	(18,295		)	(82,680		)
	Underwriting (loss) income		(7,609		)		31,339			44,955			68,685
	Net investment income												33,388
	Net realized investment gains												79,637
	Amortization of intangible assets												(633		)
	Interest expense												(14,134		)
	Foreign exchange loss												(2,518		)
	Income before income taxes												$	164,425
	Loss and loss expense ratio		70.8		%		34.4		%	48.8		%	55.1		%
	Acquisition cost ratio		12.3		%		(1.0		)%	18.1		%	12.2		%
	General and administrative expense ratio		21		%		29.4		%	9.6		%	17.8		%
	Combined ratio		104.1		%		62.8		%	76.5		%	85.1		%
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,
		2014				2013
	United States	$	520,773			$	478,443
	Bermuda	229,631				228,672
	Europe	103,336				86,509
	Singapore	41,940				38,113
	Hong Kong	4,883				5,344
	Canada	830				—
	Total gross premiums written	$	901,393			$	837,081

Condensed_Consolidated_Guarant1

Condensed Consolidated Guarantor Financial Statements (Tables)	3 Months Ended
	Mar. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Schedule of condensed consolidating balance sheet	'
	Unaudited Condensed Consolidating Balance Sheet:
	As of March 31, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	7,893,350		$	—		$	7,893,350
	Cash and cash equivalents	22,557			1,047			542,198			—			565,802
	Insurance balances receivable	—			—			839,630			—			839,630
	Funds held	—			—			447,801			—			447,801
	Reinsurance recoverable	—			—			1,280,525			—			1,280,525
	Net deferred acquisition costs	—			—			167,104			—			167,104
	Goodwill and intangible assets	—			—			316,574			—			316,574
	Balances receivable on sale of investments	—			—			198,640			—			198,640
	Investments in subsidiaries	3,434,192			4,026,535			—			(7,460,727		)	—
	Due from subsidiaries	187,571			30,569			20,751			(238,891		)	—
	Other assets	2,079			4,321			618,339			—			624,739
	Total assets	$	3,646,399		$	4,062,472		$	12,324,912		$	(7,699,618	)	$	12,334,165
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,856,798		$	—		$	5,856,798
	Unearned premiums	—			—			1,627,658			—			1,627,658
	Reinsurance balances payable	—			—			160,041			—			160,041
	Balances due on purchases of investments	—			—			171,442			—			171,442
	Senior notes	—			798,573			—			—			798,573
	Due to subsidiaries	10,565			10,186			218,140			(238,891		)	—
	Other liabilities	19,156			14,583			69,236			—			102,975
	Total liabilities	29,721			823,342			8,103,315			(238,891		)	8,717,487
	Total shareholders’ equity	3,616,678			3,239,130			4,221,597			(7,460,727		)	3,616,678
	Total liabilities and shareholders’ equity	$	3,646,399		$	4,062,472		$	12,324,912		$	(7,699,618	)	$	12,334,165
	As of December 31, 2013	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	7,712,036		$	—		$	7,712,036
	Cash and cash equivalents	10,790			2,775			518,371			—			531,936
	Insurance balances receivable	—			—			664,731			—			664,731
	Funds held	—			—			632,430			—			632,430
	Reinsurance recoverable	—			—			1,234,504			—			1,234,504
	Net deferred acquisition costs	—			—			126,661			—			126,661
	Goodwill and intangible assets	—			—			317,207			—			317,207
	Balances receivable on sale of investments	—			—			76,544			—			76,544
	Investments in subsidiaries	3,413,001			4,018,619			—			(7,431,620		)	—
	Due from subsidiaries	111,172			122,846			123,479			(357,497		)	—
	Other assets	1,757			4,671			643,353			—			649,781
	Total assets	$	3,536,720		$	4,148,911		$	12,049,316		$	(7,789,117	)	$	11,945,830
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,766,529		$	—		$	5,766,529
	Unearned premiums	—			—			1,396,256			—			1,396,256
	Reinsurance balances payable	—			—			173,023			—			173,023
	Balances due on purchases of investments	—			—			104,740			—			104,740
	Senior notes	—			798,499			—			—			798,499
	Due to subsidiaries	12,945			110,534			234,018			(357,497		)	—
	Other liabilities	3,949			17,797			165,211			—			186,957
	Total liabilities	16,894			926,830			7,839,777			(357,497		)	8,426,004
	Total shareholders’ equity	3,519,826			3,222,081			4,209,539			(7,431,620		)	3,519,826
	Total liabilities and shareholders’ equity	$	3,536,720		$	4,148,911		$	12,049,316		$	(7,789,117	)	$	11,945,830
Schedule of condensed consolidating income statement	'
	Unaudited Condensed Consolidating Statement of Operations and Comprehensive Income:
	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 losses	—			—			54,205			—			54,205
	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		)
	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
	Three Months Ended March 31, 2013	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	Net premiums earned	$	—		$	—		$	463,228		$	—		$	463,228
	Net investment income	7			2			33,379			—			33,388
	Net realized investment gains	—			—			79,637			—			79,637
	Net losses and loss expenses	—			—			(255,178		)	—			(255,178		)
	Acquisition costs	—			—			(56,685		)	—			(56,685		)
	General and administrative expenses	(10,986		)	(457		)	(71,237		)	—			(82,680		)
	Amortization of intangible assets	—			—			(633		)	—			(633		)
	Interest expense	—			(13,830		)	(304		)	—			(14,134		)
	Foreign exchange gain (loss)	272			(95		)	(2,695		)	—			(2,518		)
	Income tax (expense) benefit	—			—			(5,433		)	—			(5,433		)
	Equity in earnings of consolidated subsidiaries	169,699			181,480			—			(351,179		)	—
	NET INCOME (LOSS)	$	158,992		$	167,100		$	184,079		$	(351,179	)	$	158,992
	Other comprehensive income	—			—			—			—			—
	COMPREHENSIVE INCOME (LOSS)	$	158,992		$	167,100		$	184,079		$	(351,179	)	$	158,992
Schedule of condensed consolidating statement of cash flows	'
	Unaudited Condensed Consolidating Statement of Cash Flows:
	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		$	(1,728	)	$	212,382		$	—		$	304,782
	CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
	Purchases 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		)
	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		)	—			—			—			(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
	Three Months Ended March 31, 2013	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:	$	59,772		$	5,859		$	(54,117	)	$	—		$	11,514
	CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
	Purchases of trading securities	—			—			(1,330,735		)	—			(1,330,735		)
	Purchases of other invested assets	—			—			(54,026		)	—			(54,026		)
	Sales of trading securities	—			—			1,188,307			—			1,188,307
	Sales of other invested assets	—			—			97,989			—			97,989
	Other	—			—			114,407			—			114,407
	Net cash provided by (used in) investing activities	—			—			15,942			—			15,942
	CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
	Partial par value reduction	(12,981		)	—			—			—			(12,981		)
	Proceeds from the exercise of stock options	2,472			—			—			—			2,472
	Share repurchases	(36,245		)	—			—			—			(36,245		)
	Net cash provided by (used in) financing activities	(46,754		)	—			—			—			(46,754		)
	NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	13,018			5,859			(38,175		)	—			(19,298		)
	CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	19,997			11,324			650,558			—			681,879
	CASH AND CASH EQUIVALENTS, END OF PERIOD	$	33,015		$	17,183		$	612,383		$	—		$	662,581

Investments_Narrative_Details

Investments (Narrative) (Details)	3 Months Ended
	Mar. 31, 2014
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	'P30D
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, 2014	Dec. 31, 2013
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	$1,674,880	$1,463,927
Trading securities, Amortized Cost	1,522,312	1,305,984
Equity securities [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	834,893	699,846
Trading securities, Amortized Cost	803,954	647,301
Other invested assets [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	839,987	764,081
Trading securities, Amortized Cost	718,358	658,683
Fixed Maturities [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	6,068,666	6,100,798
Trading securities, Amortized Cost	6,010,765	6,065,350
U.S. Government And Government Agencies [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	1,476,463	1,676,788
Trading securities, Amortized Cost	1,480,371	1,684,832
Non-U.S. Government And Government Agencies [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	182,415	191,776
Trading securities, Amortized Cost	187,632	197,082
States, Municipalities And Political Subdivisions [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	230,669	231,555
Trading securities, Amortized Cost	228,284	234,406
Corporate Debt, Financial Institutions [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	1,097,649	958,794
Trading securities, Amortized Cost	1,083,131	943,518
Corporate Debt, Industrials [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	1,116,004	1,174,047
Trading securities, Amortized Cost	1,105,613	1,165,448
Corporate Debt, Utilities [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	96,807	69,426
Trading securities, Amortized Cost	96,403	69,658
Mortgage-Backed [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	1,304,130	1,292,502
Trading securities, Amortized Cost	1,266,663	1,267,863
Asset-Backed [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	564,529	505,910
Trading securities, Amortized Cost	$562,668	$502,543

Investments_Schedule_Of_Other_

Investments (Schedule Of Other Investments) (Details) (USD $)	3 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	989,791		911,392
Unfunded Commitments	450,261		467,524
Investments with redemption restrictions [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	448,990		368,052
Investments without redemption restrictions [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	540,801		543,340
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	'P30D		'
Portion at Fair Value, Fair Value Disclosure [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	839,987		764,081
Unfunded Commitments	450,261		467,524
Portion at Fair Value, Fair Value Disclosure [Member] | Investments with redemption restrictions [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	448,990		368,052
Portion at Fair Value, Fair Value Disclosure [Member] | Investments without redemption restrictions [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	390,997		396,029
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity Funds [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	235,808		216,825
Unfunded Commitments	450,261		467,524
Portion at Fair Value, Fair Value Disclosure [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	235,808		216,825
Portion at Fair Value, Fair Value Disclosure [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
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	144,582		144,422
Unfunded Commitments	262,450		263,519
Portion at Fair Value, Fair Value Disclosure [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	144,582		144,422
Portion at Fair Value, Fair Value Disclosure [Member] | 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
Portion at Fair Value, Fair Value Disclosure [Member] | 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	'9 years		'9 years
Portion at Fair Value, Fair Value Disclosure [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
Portion at Fair Value, Fair Value Disclosure [Member] | Mezzanine Debt [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	81,474		64,627
Unfunded Commitments	182,562		198,756
Portion at Fair Value, Fair Value Disclosure [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	81,474		64,627
Portion at Fair Value, Fair Value Disclosure [Member] | 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	'8 years		'8 years
Portion at Fair Value, Fair Value Disclosure [Member] | 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
Portion at Fair Value, Fair Value Disclosure [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
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	9,752		7,776
Unfunded Commitments	5,249		5,249
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed [Member] | Investments with redemption restrictions [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	9,752		7,776
Estimated remaining restriction period	'4 years		'4 years
Portion at Fair Value, Fair Value Disclosure [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
Portion at Fair Value, Fair Value Disclosure [Member] | Hedge Funds [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	571,259		515,298
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [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	213,182		151,227
Portion at Fair Value, Fair Value Disclosure [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	358,077		364,071
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed Funds [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	161,033		151,227
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [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	161,033		151,227
Estimated remaining restriction period	'1 year		'
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed Funds [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	'		'1 year
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed Funds [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	'		'2 years
Portion at Fair Value, Fair Value Disclosure [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
Portion at Fair Value, Fair Value Disclosure [Member] | Equity Long/Short [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	163,964		99,365
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [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	52,149		0
Estimated remaining restriction period	'1 year		'
Portion at Fair Value, Fair Value Disclosure [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	111,815		99,365
Redemption frequency	'Quarterly	[1]	'Quarterly	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | 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	'P30D	[1]	'P30D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | 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	'P60D	[1]	'P60D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Multi-Strategy Funds [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	122,584		136,958
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [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
Portion at Fair Value, Fair Value Disclosure [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	122,584		136,958
Redemption frequency	'Quarterly	[1]	'Quarterly	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | 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	'P45D	[1]	'P45D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | 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	'P90D	[1]	'P90D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Event Driven Funds [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	6,407		14,018
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Event Driven 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
Portion at Fair Value, Fair Value Disclosure [Member] | Event Driven Funds [Member] | Investments without redemption restrictions [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	6,407		14,018
Redemption frequency	'Annual	[1]	'Annual	[1]
Redemption notice period	'P60D	[1]	'P60D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Relative Value Credit [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	117,271		113,730
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [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
Portion at Fair Value, Fair Value Disclosure [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	117,271		113,730
Redemption frequency	'Quarterly	[1]	'Quarterly	[1]
Redemption notice period	'P60D	[1]	'P60D
Portion at Fair Value, Fair Value Disclosure [Member] | High Yield Loan Fund [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	32,920		31,958
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [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
Portion at Fair Value, Fair Value Disclosure [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	32,920		31,958
Redemption frequency	'Monthly	[1]	'Monthly	[1]
Redemption notice period	'P30D	[1]	'P30D	[1]
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Other Private Securities [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	149,804		147,311
Unfunded Commitments	0		0
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Other Private Securities [Member] | Investments with redemption restrictions [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	0		0
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Other Private Securities [Member] | Investments without redemption restrictions [Member]	'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'
Other invested assets	149,804		147,311
[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.

Investments_Schedule_Of_Net_In

Investments (Schedule Of Net Investment Income) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Net Investment Income [Line Items]	'	'
Net investment income	$47,619	$33,388
Fixed maturity investments [Member]	'	'
Net Investment Income [Line Items]	'	'
Net investment income	36,299	32,525
Equity securities [Member]	'	'
Net Investment Income [Line Items]	'	'
Net investment income	3,253	3,199
Other invested assets [Member]	'	'
Net Investment Income [Line Items]	'	'
Net investment income	11,408	1,464
Cash and cash equivalents [Member]	'	'
Net Investment Income [Line Items]	'	'
Net investment income	439	488
Expenses [Member]	'	'
Net Investment Income [Line Items]	'	'
Net investment income	($3,780)	($4,288)

Investments_Components_Of_Real

Investments (Components Of Realized Gains And Losses) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Gain (Loss) on Investments [Line Items]	'	'
Gross realized gains on sale of invested assets	$62,292	$44,249
Gross realized losses on sale of invested assets	-12,247	-6,965
Net realized and unrealized losses on derivatives	-12,920	-977
Net realized investment gains	54,205	79,637
Debt Securities [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Mark-to-market changes	22,455	-16,475
Equity securities [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Mark-to-market changes	-21,605	32,973
Other invested assets [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Mark-to-market changes	$16,230	$26,832

Investments_Pledged_Assets_Det

Investments (Pledged Assets) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
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	$2,635,901	$2,894,401
Pledged As Collateral For Letter Of Credit Facilities [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Restricted Cash and Investments	$1,004,926	$1,053,632

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, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Derivatives, Fair Value [Line Items]	'	'
Asset Derivative Notional Amount	$775,481	$786,188
Asset Derivative Fair Value	2,268	13,083
Liability Derivative Notional Amount	212,757	162,439
Liability Derivative Fair Value	3,160	5,390
Foreign exchange contracts | Other assets	'	'
Derivatives, Fair Value [Line Items]	'	'
Asset Derivative Notional Amount	194,081	294,788
Asset Derivative Fair Value	1,408	6,254
Foreign exchange contracts | Accounts payable and accrued liabilities	'	'
Derivatives, Fair Value [Line Items]	'	'
Liability Derivative Notional Amount	117,757	122,439
Liability Derivative Fair Value	3,145	1,176
Interest rate swaps | Other assets	'	'
Derivatives, Fair Value [Line Items]	'	'
Asset Derivative Notional Amount	581,400	491,400
Asset Derivative Fair Value	860	6,829
Interest rate swaps | Accounts payable and accrued liabilities	'	'
Derivatives, Fair Value [Line Items]	'	'
Liability Derivative Notional Amount	95,000	40,000
Liability Derivative Fair Value	$15	$4,214

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, 2014	Mar. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Total realized and unrealized losses on derivatives	($13,788)	($1,721)
Foreign exchange (loss) gain	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Total realized and unrealized losses on derivatives	-868	-744
Foreign exchange (loss) gain | Foreign exchange contracts	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Total realized and unrealized losses on derivatives	-868	-744
Net realized investment gains	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Total realized and unrealized losses on derivatives	-12,920	-977
Net realized investment gains | Put options	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Total realized and unrealized losses on derivatives	0	-3,732
Net realized investment gains | Foreign exchange contracts	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Total realized and unrealized losses on derivatives	-558	1,815
Net realized investment gains | Interest rate futures	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Total realized and unrealized losses on derivatives	($12,362)	$940

Fair_Value_Of_Financial_Instru2

Fair Value Of Financial Instruments (Schedule Of Fair Value Of Financial Instruments) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Trading fixed maturity investments	$6,068,666	$6,100,798
Equity securities	834,893	699,846
Other invested assets	989,791	911,392
Total investments	7,893,350	7,712,036
Senior notes	798,573	798,499
Fair Value, Measurements, Recurring [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Trading fixed maturity investments	6,068,666	6,100,798
Equity securities	834,893	699,846
Other invested assets	839,987	764,081
Total investments	7,743,546	7,564,725
Senior notes	798,573	798,499
Fair Value, Measurements, Recurring [Member] | Foreign exchange contracts	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Derivative assets	1,408	6,254
Derivative liabilities	3,145	1,176
Fair Value, Measurements, Recurring [Member] | Interest rate swaps	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Derivative assets	860	6,829
Derivative liabilities	15	4,214
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	1,476,463	1,676,788
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	182,415	191,776
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	230,669	231,555
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	2,310,460	2,202,267
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	1,304,130	1,292,502
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	564,529	505,910
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	6,068,666	6,100,798
Equity securities	834,893	699,846
Other invested assets	839,987	764,081
Total investments	7,743,546	7,564,725
Senior notes	906,448	897,601
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	1,408	6,254
Derivative liabilities	3,145	1,176
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 assets	860	6,829
Derivative liabilities	15	4,214
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	1,476,463	1,676,788
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	182,415	191,776
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	230,669	231,555
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	2,310,460	2,202,267
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	1,304,130	1,292,502
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	564,529	505,910
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	1,135,246	1,370,088
Equity securities	800,107	625,942
Other invested assets	0	0
Total investments	1,935,353	1,996,030
Senior notes	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 assets	0	0
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	1,135,246	1,370,088
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	4,718,125	4,489,959
Equity securities	0	0
Other invested assets	0	0
Total investments	4,718,125	4,489,959
Senior notes	906,448	897,601
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	1,408	6,254
Derivative liabilities	3,145	1,176
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 assets	860	6,829
Derivative liabilities	15	4,214
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	341,217	306,700
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	182,415	191,776
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	230,669	231,555
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	2,310,460	2,202,267
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	1,170,069	1,145,164
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	483,295	412,497
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	215,295	240,751
Equity securities	34,786	73,904
Other invested assets	839,987	764,081
Total investments	1,090,068	1,078,736
Senior notes	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 assets	0	0
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	134,061	147,338
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	$81,234	$93,413

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, 2014		Mar. 31, 2013
Other invested assets [Member]	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Opening balance	$764,081		$655,888
Realized and unrealized gains (losses) included in net income	22,626		32,253
Purchases	89,199		73,210
Sales	-35,919		-51,211
Transfers into Level 3 from Level 2	0		0
Transfers out of Level 3 to Level 2	0	[1]	0	[1]
Ending balance	839,987		710,140
Mortgage-Backed [Member]	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Opening balance	147,338		167,825
Realized and unrealized gains (losses) included in net income	1,368		-1,189
Purchases	14,110		0
Sales	-17,956		-21,645
Transfers into Level 3 from Level 2	0		19,813
Transfers out of Level 3 to Level 2	-10,799	[1]	-9,384	[1]
Ending balance	134,061		155,420
Asset-Backed [Member]	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Opening balance	93,413		62,246
Realized and unrealized gains (losses) included in net income	-864		-97
Purchases	7,493		2,461
Sales	-3,176		-16,622
Transfers into Level 3 from Level 2	606		0
Transfers out of Level 3 to Level 2	-16,238	[1]	-7,085	[1]
Ending balance	81,234		40,903
Equity securities [Member]	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'
Opening balance	73,904		54,680
Realized and unrealized gains (losses) included in net income	-9,821		3,107
Purchases	0		0
Sales	-29,297		0
Transfers into Level 3 from Level 2	0		0
Transfers out of Level 3 to Level 2	0	[1]	0	[1]
Ending balance	$34,786		$57,787
[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, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Insurance Loss Reserves [Abstract]	'	'	'	'
Outstanding loss reserves	$1,474,376	$1,520,867	'	'
Reserves for losses incurred but not reported	4,382,422	4,245,662	'	'
Reserve for losses and loss expenses	$5,856,798	$5,766,529	$5,673,220	$5,645,549

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, 2014	Mar. 31, 2013
Insurance Loss Reserves [Abstract]	'	'
Gross liability at beginning of year	$5,766,529	$5,645,549
Reinsurance recoverable at beginning of year	-1,234,504	-1,141,110
Net liability at beginning of year	4,532,025	4,504,439
Net losses incurred related to:	'	'
Current year	324,147	299,248
Prior years	-48,861	-44,070
Total incurred	275,286	255,178
Net paid losses related to:	'	'
Current year	3,743	3,581
Prior years	228,594	241,121
Total paid	232,337	244,702
Foreign exchange revaluation	1,299	-5,198
Net liability at end of year	4,576,273	4,509,717
Reinsurance recoverable at end of year	1,280,525	1,163,503
Gross liability at end of year	$5,856,798	$5,673,220

Shareholders_Equity_Issued_Sha

Shareholders' Equity (Issued Share Capital) (Details)	Mar. 31, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified	USD ($)	CHF	USD ($)	CHF
Stockholders' Equity Note [Abstract]	'	'	'	'
Common shares issued and fully paid, 2014: CHF 12.30 per share; 2013: CHF 12.30 per share	33,821,752	33,821,752	34,492,484	34,492,484
Common shares, par value	'	12.3	'	12.3
Total share capital	$410,820	'	$418,988	'

Shareholders_Equity_Schedule_O

Shareholders' Equity (Schedule Of Common Stock Outstanding Roll Forward) (Details)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'	'	'
Shares issued at beginning of year	34,492,484	'	'
Shares cancelled, shares	-670,732	'	'
Shares issued at end of year	33,821,752	'	'
Treasury Stock Transactions, Excluding Value of Shares Reissued [Abstract]	'	'	'
Treasury shares issued at beginning of year	1,074,602	'	'
Shares repurchased, shares	670,732	432,117	'
Shares issued out of treasury, shares	-161,671	'	'
Shares cancelled, shares	-670,732	'	'
Total treasury shares at end of year	912,931	'	'
Total shares outstanding at end of year	32,908,821	'	33,417,882

Shareholders_Equity_Schedule_O1

Shareholders' Equity (Schedule Of Dividends Paid) (Details) (USD $)	3 Months Ended		0 Months Ended	1 Months Ended		0 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Jan. 02, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 03, 2014
			Common shares	Common shares	Common shares	Subsequent event
						Common shares
Dividends, Common Stock [Abstract]	'	'	'	'	'	'
Dividends paid per common share	$0.50	$0.38	$0.50	$0.50	$0.50	$0.50
Payment of quarterly dividends	'	'	$16,732	'	'	'

Shareholders_Equity_Schedule_O2

Shareholders' Equity (Schedule Of Share Repurchases) (Details) (USD $)	1 Months Ended	3 Months Ended
In Thousands, except Share data, unless otherwise specified	31-May-12	Mar. 31, 2014	Mar. 31, 2013
Stockholders' Equity Note [Abstract]	'	'	'
Stock Repurchase Program, Authorized Amount	$500,000	'	'
Shares repurchased, shares	'	670,732	432,117
Cost of shares repurchased	'	$68,659	$36,245
Shares repurchased, average price per share	'	$102.36	$83.88

Employee_Benefit_Plans_Restric

Employee Benefit Plans (Restricted Stock Units) (Details) (USD $)	12 Months Ended	3 Months Ended
	Dec. 31, 2013	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014
	Restricted Stock Units (RSUs) [Member]	Rsus Other Than Performance Based Rsus [Member]	Performance Based Rsus [Member]	Awards 2014 [Member]	Awards 2013 [Member]	Awards 2012 [Member]
				Performance Based Rsus [Member]	Performance Based Rsus [Member]	Performance Based Rsus [Member]
Activity:	'	'	'	'	'	'
Outstanding, beginning of year, shares	'	47,899	268,173	'	'	'
Granted, shares	'	151,392	55,434	'	'	'
Additional awards granted due to achievement of performance criteria, shares	'	'	34,965	'	'	'
Forfeited, shares	'	0	0	'	'	'
Fully vested, shares	'	-24,876	-151,480	'	'	'
Outstanding, end of year, shares	'	174,415	207,092	'	'	'
Weighted average grant date fair value:	'	'	'	'	'	'
Outstanding, beginning of year - weighted average grant date fair value	'	$65.07	$69.64	'	'	'
Granted - weighted average grant date fair value	'	$100.68	$100.67	'	'	'
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	'	'	$61.51	'	'	'
Forfeited - weighted average grant date fair value	'	$0	$0	'	'	'
Vested - weighted average grant date fair value	'	($65.06)	($61.51)	'	'	'
Outstanding, end of year - weighted average grant date fair value	'	$95.98	$82.52	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]	'	'	'	'	'	'
Vesting period	'4 years	'	'	'	'	'
The rate at which performance awards are expensed	'	'	'	100.00%	100.00%	130.00%

Employee_Benefit_Plans_CashEqu

Employee Benefit Plans (Cash-Equivalent Stock Awards) (Details) (USD $)	12 Months Ended	3 Months Ended
	Dec. 31, 2013	Mar. 31, 2014	Mar. 31, 2014
	Cash Equivalent Stock Awards [Member]	Cash Equivalent Stock Awards Rsus [Member]	Cash Equivalent Stock Awards Performance Based [Member]
Activity:	'	'	'
Outstanding, beginning of year, shares	'	683,028	343,987
Granted, shares	'	146,054	83,146
Additional awards granted due to achievement of performance criteria, shares	'	0	34,965
Forfeited, shares	'	-960	0
Fully vested, shares	'	-250,640	-151,480
Outstanding, end of year, shares	'	577,482	310,618
Weighted average grant date fair value:	'	'	'
Outstanding, beginning of year - weighted average grant date fair value	'	$74.10	$71.02
Granted - weighted average grant date fair value	'	$100.67	$100.67
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	'	$0	$61.51
Forfeited - weighted average grant date fair value	'	($77.72)	$0
Vested - weighted average grant date fair value	'	($64.41)	($61.51)
Outstanding, end of year - weighted average grant date fair value	'	$83.81	$82.52
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]	'	'	'
Vesting period	'4 years	'	'

Employee_Benefit_Plans_Other_D

Employee Benefit Plans (Other Details) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Share-based compensation expense	$8,869	$16,751
Employee Stock Option [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Share-based compensation expense	727	1,335
Restricted Stock Units (RSUs) [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Share-based compensation expense	3,513	2,660
Cash Equivalent Stock Awards [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Share-based compensation expense	$4,629	$12,756

Earnings_Per_Share_Narrative_D

Earnings Per Share (Narrative) (Details) (Stock Compensation Plan [Member])	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
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	25	333

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, 2014	Mar. 31, 2013
Earnings Per Share, Basic [Abstract]	'	'
Net income	$176,972	$158,992
Weighted average common shares outstanding	33,181,729	34,613,606
Basic earnings per share	$5.33	$4.59
Earnings Per Share, Diluted [Abstract]	'	'
Net income	$176,972	$158,992
Weighted average common shares outstanding	33,181,729	34,613,606
Share equivalents:	'	'
Warrants and options	487,986	482,207
RSUs and LTIP awards	188,537	335,575
Employee share purchase plan	3,302	455
Weighted average common shares and common share equivalents outstanding - diluted	33,861,554	35,431,843
Diluted earnings per share	$5.23	$4.49

Segment_Information_Summary_Of

Segment Information (Summary Of Segment Results) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
	segments
Segment Reporting Information [Line Items]	'	'
Gross premiums written	$901,393	$837,081
Net premiums written	771,614	695,052
Net premiums earned	530,285	463,228
Net losses and loss expenses	-275,286	-255,178
Acquisition costs	-67,722	-56,685
General and administrative expenses	-80,340	-82,680
Underwriting income (loss)	106,937	68,685
Net investment income	47,619	33,388
Net realized investment gains	54,205	79,637
Amortization of intangible assets	-633	-633
Interest expense	-14,534	-14,134
Foreign exchange loss	-49	-2,518
Income before income taxes	193,545	164,425
Loss and loss expense ratio	51.90%	55.10%
Acquisition cost ratio	12.80%	12.20%
General and administrative expense ratio	15.20%	17.80%
Combined ratio	79.90%	85.10%
Number of Operating Segments	3	'
Operating Segments [Member] | U S Insurance [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Gross premiums written	269,945	256,018
Net premiums written	202,740	192,253
Net premiums earned	212,123	188,439
Net losses and loss expenses	-141,995	-133,324
Acquisition costs	-27,501	-23,128
General and administrative expenses	-37,436	-39,596
Underwriting income (loss)	5,191	-7,609
Loss and loss expense ratio	66.90%	70.80%
Acquisition cost ratio	13.00%	12.30%
General and administrative expense ratio	17.60%	21.00%
Combined ratio	97.50%	104.10%
Operating Segments [Member] | International Insurance [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Gross premiums written	134,364	128,516
Net premiums written	75,459	77,745
Net premiums earned	88,339	84,214
Net losses and loss expenses	-23,566	-28,935
Acquisition costs	947	849
General and administrative expenses	-24,761	-24,789
Underwriting income (loss)	40,959	31,339
Loss and loss expense ratio	26.70%	34.40%
Acquisition cost ratio	-1.10%	-1.00%
General and administrative expense ratio	28.00%	29.40%
Combined ratio	53.60%	62.80%
Operating Segments [Member] | Reinsurance [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Gross premiums written	497,084	452,547
Net premiums written	493,415	425,054
Net premiums earned	229,823	190,575
Net losses and loss expenses	-109,725	-92,919
Acquisition costs	-41,168	-34,406
General and administrative expenses	-18,143	-18,295
Underwriting income (loss)	$60,787	$44,955
Loss and loss expense ratio	47.70%	48.80%
Acquisition cost ratio	17.90%	18.10%
General and administrative expense ratio	7.90%	9.60%
Combined ratio	73.50%	76.50%

Segment_Information_Gross_Prem

Segment Information (Gross Premiums Written By Geographic Location) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'
Gross premiums written	$901,393	$837,081
United States	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'
Gross premiums written	520,773	478,443
Bermuda	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'
Gross premiums written	229,631	228,672
Europe	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'
Gross premiums written	103,336	86,509
Singapore	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'
Gross premiums written	41,940	38,113
Hong Kong	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'
Gross premiums written	4,883	5,344
Canada	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'
Gross premiums written	830	0
Switzerland	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'
Gross premiums written	$44,293	$40,806

Commitments_And_Contingencies_

Commitments And Contingencies (Details) (Switzerland, CHF)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
Mortgages [Member]	'
Other Commitments [Line Items]	'
Mortgage Term	'20 years
Mortgage Commitment	18,000
Debt Instrument, Interest Rate, Stated Percentage	3.20%
Debt Instrument, Annual Principal Payment	300
Period of Annual Payments on Mortgages	'19 years
Line of Credit [Member]	'
Other Commitments [Line Items]	'
Debt Instrument, Interest Rate, Stated Percentage	2.50%
Credit Facility Term	'3 years
Line of Credit Facility, Maximum Borrowing Capacity	5,000

Condensed_Consolidated_Guarant2

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Balance Sheet) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
ASSETS:	'	'	'	'
Investments	$7,893,350	$7,712,036	'	'
Cash and cash equivalents	565,802	531,936	662,581	681,879
Insurance balances receivable	839,630	664,731	'	'
Funds held	447,801	632,430	'	'
Reinsurance recoverable	1,280,525	1,234,504	1,163,503	1,141,110
Net deferred acquisition costs	167,104	126,661	'	'
Goodwill and intangible assets	316,574	317,207	'	'
Balances receivable on sale of investments	198,640	76,544	'	'
Investments in subsidiaries	0	0	'	'
Due from subsidiaries	0	0	'	'
Other assets	624,739	649,781	'	'
Total assets	12,334,165	11,945,830	'	'
LIABILITIES:	'	'	'	'
Reserve for losses and loss expenses	5,856,798	5,766,529	5,673,220	5,645,549
Unearned premiums	1,627,658	1,396,256	'	'
Reinsurance balances payable	160,041	173,023	'	'
Balances due on purchases of investments	171,442	104,740	'	'
Senior notes	798,573	798,499	'	'
Due to subsidiaries	0	0	'	'
Other liabilities	102,975	186,957	'	'
Total liabilities	8,717,487	8,426,004	'	'
Total shareholders’ equity	3,616,678	3,519,826	3,431,963	3,326,335
Total liabilities and shareholders’ equity	12,334,165	11,945,830	'	'
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	'	'
Net deferred acquisition costs	0	0	'	'
Goodwill and intangible assets	0	0	'	'
Balances receivable on sale of investments	0	0	'	'
Investments in subsidiaries	-7,460,727	-7,431,620	'	'
Due from subsidiaries	-238,891	-357,497	'	'
Other assets	0	0	'	'
Total assets	-7,699,618	-7,789,117	'	'
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	'	'
Due to subsidiaries	-238,891	-357,497	'	'
Other liabilities	0	0	'	'
Total liabilities	-238,891	-357,497	'	'
Total shareholders’ equity	-7,460,727	-7,431,620	'	'
Total liabilities and shareholders’ equity	-7,699,618	-7,789,117	'	'
Allied World Switzerland (Parent Guarantor) [Member]	'	'	'	'
ASSETS:	'	'	'	'
Investments	0	0	'	'
Cash and cash equivalents	22,557	10,790	33,015	19,997
Insurance balances receivable	0	0	'	'
Funds held	0	0	'	'
Reinsurance recoverable	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	3,434,192	3,413,001	'	'
Due from subsidiaries	187,571	111,172	'	'
Other assets	2,079	1,757	'	'
Total assets	3,646,399	3,536,720	'	'
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	'	'
Due to subsidiaries	10,565	12,945	'	'
Other liabilities	19,156	3,949	'	'
Total liabilities	29,721	16,894	'	'
Total shareholders’ equity	3,616,678	3,519,826	'	'
Total liabilities and shareholders’ equity	3,646,399	3,536,720	'	'
Allied World Bermuda (Subsidiary Issuer) [Member]	'	'	'	'
ASSETS:	'	'	'	'
Investments	0	0	'	'
Cash and cash equivalents	1,047	2,775	17,183	11,324
Insurance balances receivable	0	0	'	'
Funds held	0	0	'	'
Reinsurance recoverable	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	4,026,535	4,018,619	'	'
Due from subsidiaries	30,569	122,846	'	'
Other assets	4,321	4,671	'	'
Total assets	4,062,472	4,148,911	'	'
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	798,573	798,499	'	'
Due to subsidiaries	10,186	110,534	'	'
Other liabilities	14,583	17,797	'	'
Total liabilities	823,342	926,830	'	'
Total shareholders’ equity	3,239,130	3,222,081	'	'
Total liabilities and shareholders’ equity	4,062,472	4,148,911	'	'
Other Allied World Subsidiaries [Member]	'	'	'	'
ASSETS:	'	'	'	'
Investments	7,893,350	7,712,036	'	'
Cash and cash equivalents	542,198	518,371	612,383	650,558
Insurance balances receivable	839,630	664,731	'	'
Funds held	447,801	632,430	'	'
Reinsurance recoverable	1,280,525	1,234,504	'	'
Net deferred acquisition costs	167,104	126,661	'	'
Goodwill and intangible assets	316,574	317,207	'	'
Balances receivable on sale of investments	198,640	76,544	'	'
Investments in subsidiaries	0	0	'	'
Due from subsidiaries	20,751	123,479	'	'
Other assets	618,339	643,353	'	'
Total assets	12,324,912	12,049,316	'	'
LIABILITIES:	'	'	'	'
Reserve for losses and loss expenses	5,856,798	5,766,529	'	'
Unearned premiums	1,627,658	1,396,256	'	'
Reinsurance balances payable	160,041	173,023	'	'
Balances due on purchases of investments	171,442	104,740	'	'
Senior notes	0	0	'	'
Due to subsidiaries	218,140	234,018	'	'
Other liabilities	69,236	165,211	'	'
Total liabilities	8,103,315	7,839,777	'	'
Total shareholders’ equity	4,221,597	4,209,539	'	'
Total liabilities and shareholders’ equity	$12,324,912	$12,049,316	'	'

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, 2014	Mar. 31, 2013
Condensed Income Statements, Captions [Line Items]	'	'
Net premiums earned	$530,285	$463,228
Net investment income	47,619	33,388
Net realized investment gains (losses)	54,205	79,637
Net losses and loss expenses	-275,286	-255,178
Acquisition costs	-67,722	-56,685
General and administrative expenses	-80,340	-82,680
Amortization of intangible assets	-633	-633
Interest expense	-14,534	-14,134
Foreign exchange loss	-49	-2,518
Income tax (expense) benefit	-16,573	-5,433
Equity in earnings of consolidated subsidiaries	0	0
NET INCOME	176,972	158,992
Other comprehensive loss	0	0
COMPREHENSIVE INCOME (LOSS)	176,972	158,992
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
Net losses and loss expenses	0	0
Acquisition costs	0	0
General and administrative 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	-385,302	-351,179
NET INCOME	-385,302	-351,179
Other comprehensive loss	0	0
COMPREHENSIVE INCOME (LOSS)	-385,302	-351,179
Allied World Switzerland (Parent Guarantor) [Member]	'	'
Condensed Income Statements, Captions [Line Items]	'	'
Net premiums earned	0	0
Net investment income	2	7
Net realized investment gains (losses)	0	0
Net losses and loss expenses	0	0
Acquisition costs	0	0
General and administrative expenses	-8,914	-10,986
Amortization of intangible assets	0	0
Interest expense	0	0
Foreign exchange loss	-2	272
Income tax (expense) benefit	-409	0
Equity in earnings of consolidated subsidiaries	186,295	169,699
NET INCOME	176,972	158,992
Other comprehensive loss	0	0
COMPREHENSIVE INCOME (LOSS)	176,972	158,992
Allied World Bermuda (Subsidiary Issuer) [Member]	'	'
Condensed Income Statements, Captions [Line Items]	'	'
Net premiums earned	0	0
Net investment income	0	2
Net realized investment gains (losses)	0	0
Net losses and loss expenses	0	0
Acquisition costs	0	0
General and administrative expenses	-2,391	-457
Amortization of intangible assets	0	0
Interest expense	-13,848	-13,830
Foreign exchange loss	33	-95
Income tax (expense) benefit	0	0
Equity in earnings of consolidated subsidiaries	199,007	181,480
NET INCOME	182,801	167,100
Other comprehensive loss	0	0
COMPREHENSIVE INCOME (LOSS)	182,801	167,100
Other Allied World Subsidiaries [Member]	'	'
Condensed Income Statements, Captions [Line Items]	'	'
Net premiums earned	530,285	463,228
Net investment income	47,617	33,379
Net realized investment gains (losses)	54,205	79,637
Net losses and loss expenses	-275,286	-255,178
Acquisition costs	-67,722	-56,685
General and administrative expenses	-69,035	-71,237
Amortization of intangible assets	-633	-633
Interest expense	-686	-304
Foreign exchange loss	-80	-2,695
Income tax (expense) benefit	-16,164	-5,433
Equity in earnings of consolidated subsidiaries	0	0
NET INCOME	202,501	184,079
Other comprehensive loss	0	0
COMPREHENSIVE INCOME (LOSS)	$202,501	$184,079

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, 2014	Mar. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]	'	'
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$304,782	$11,514
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:	'	'
Purchases of trading securities	-1,568,993	-1,330,735
Purchases of other invested assets	-779,934	-54,026
Sales of trading securities	1,494,648	1,188,307
Sales of other invested assets	663,237	97,989
Other	2,487	114,407
Net cash (used in) provided by investing activities	-188,555	15,942
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	-16,732	0
Dividends paid - par value reduction	0	-12,981
Proceeds from the exercise of stock options	3,030	2,472
Share repurchases	-68,659	-36,245
Net cash used in financing activities	-82,361	-46,754
NET INCREASE IN CASH AND CASH EQUIVALENTS	33,866	-19,298
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	531,936	681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	565,802	662,581
Consolidation, Eliminations [Member]	'	'
Condensed Cash Flow Statements, Captions [Line Items]	'	'
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	0	0
CASH FLOWS (USED IN) PROVIDED BY 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) provided by investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	0	'
Dividends paid - par value reduction	'	0
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	0	0
NET 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:	94,128	59,772
CASH FLOWS (USED IN) PROVIDED BY 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) provided by investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	-16,732	'
Dividends paid - par value reduction	'	-12,981
Proceeds from the exercise of stock options	3,030	2,472
Share repurchases	-68,659	-36,245
Net cash used in financing activities	-82,361	-46,754
NET INCREASE IN CASH AND CASH EQUIVALENTS	11,767	13,018
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790	19,997
CASH AND CASH EQUIVALENTS, END OF PERIOD	22,557	33,015
Allied World Bermuda (Subsidiary Issuer) [Member]	'	'
Condensed Cash Flow Statements, Captions [Line Items]	'	'
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	-1,728	5,859
CASH FLOWS (USED IN) PROVIDED BY 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) provided by investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	0	'
Dividends paid - par value reduction	'	0
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	0	0
NET INCREASE IN CASH AND CASH EQUIVALENTS	-1,728	5,859
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	2,775	11,324
CASH AND CASH EQUIVALENTS, END OF PERIOD	1,047	17,183
Other Allied World Subsidiaries [Member]	'	'
Condensed Cash Flow Statements, Captions [Line Items]	'	'
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	212,382	-54,117
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:	'	'
Purchases of trading securities	-1,568,993	-1,330,735
Purchases of other invested assets	-779,934	-54,026
Sales of trading securities	1,494,648	1,188,307
Sales of other invested assets	663,237	97,989
Other	2,487	114,407
Net cash (used in) provided by investing activities	-188,555	15,942
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	0	'
Dividends paid - par value reduction	'	0
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	0	0
NET INCREASE IN CASH AND CASH EQUIVALENTS	23,827	-38,175
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	518,371	650,558
CASH AND CASH EQUIVALENTS, END OF PERIOD	$542,198	$612,383

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, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Investments in subsidiaries	$0	'	$0	'
Total shareholders’ equity	3,616,678	3,431,963	3,519,826	3,326,335
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	94,000	90,000	'	'
Allied World Bermuda (Subsidiary Issuer) [Member]	'	'	'	'
Investments in subsidiaries	4,026,535	'	4,018,619	'
Total shareholders’ equity	3,239,130	'	3,222,081	'
Adjustment to correct for miscalculation | Restatement Adjustment | Allied World Bermuda (Subsidiary Issuer) [Member]	'	'	'	'
Investments in subsidiaries	'	'	776,000	'
Total shareholders’ equity	'	'	$0	'

Subsequent_Events_Details

Subsequent Events (Details) (USD $)	3 Months Ended		0 Months Ended	1 Months Ended		0 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Jan. 02, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 03, 2014
			Common shares	Common shares	Common shares	Common shares
						Subsequent event
Subsequent Event [Line Items]	'	'	'	'	'	'
Dividends paid per common share	$0.50	$0.38	$0.50	$0.50	$0.50	$0.50