Allied World Assurance 10-Q 23 Jul 14 2014 Q2 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	6 Months Ended
	Jun. 30, 2014	Jul. 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	30-Jun-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q2	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	96,823,713

Unaudited_Condensed_Consolidat

Unaudited Condensed Consolidated Balance Sheets (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
ASSETS:	'	'
Fixed maturity investments trading, at fair value (amortized cost: 2014: $6,062,758; 2013: $6,065,350)	$6,157,084	$6,100,798
Equity securities trading, at fair value (cost: 2014: $885,861; 2013: $647,301)	938,117	699,846
Other invested assets	932,639	911,392
Total investments	8,027,840	7,712,036
Cash and cash equivalents	635,138	531,936
Restricted cash	127,755	149,393
Insurance balances receivable	976,441	664,731
Funds held	414,445	632,430
Prepaid reinsurance	390,414	340,992
Reinsurance recoverable	1,301,742	1,234,504
Accrued investment income	30,968	32,236
Net deferred acquisition costs	163,259	126,661
Goodwill	277,761	268,376
Intangible assets	47,564	48,831
Balances receivable on sale of investments	164,713	76,544
Net deferred tax assets	35,867	37,469
Other assets	75,740	89,691
Total assets	12,669,647	11,945,830
LIABILITIES:	'	'
Reserve for losses and loss expenses	5,935,678	5,766,529
Unearned premiums	1,703,684	1,396,256
Reinsurance balances payable	224,182	173,023
Balances due on purchases of investments	180,378	104,740
Senior notes	798,648	798,499
Dividends payable	21,870	16,732
Accounts payable and accrued liabilities	122,445	170,225
Total liabilities	8,986,885	8,426,004
Commitments and contingencies	'	'
SHAREHOLDERS’ EQUITY:	'	'
Common shares: 2014: par value CHF 4.10 per share and 2013: par value CHF 4.10 per share (2014: 99,515,760; 2013: 103,477,452 shares issued and 2014: 96,929,091; 2013: 100,253,646 shares outstanding)	402,907	418,988
Treasury shares, at cost (2014: 2,586,669; 2013: 3,223,806)	-65,258	-79,992
Retained earnings	3,345,113	3,180,830
Total shareholders’ equity	3,682,762	3,519,826
Total liabilities and shareholders’ equity	$12,669,647	$11,945,830

Unaudited_Condensed_Consolidat1

Unaudited Condensed Consolidated Balance Sheets (Parenthetical)(USD ($))	Jun. 30, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Fixed maturity investments trading, amortized cost	$6,062,758	$6,065,350
Equity securities trading - cost	$885,861	$647,301
Common stock, shares issued	99,515,760	103,477,452
Common stock, shares outstanding	96,929,091	100,253,646
Treasury stock (shares)	2,586,669	3,223,806

Unaudited_Condensed_Consolidat2

Unaudited Condensed Consolidated Statements Of Operations And Comprehensive Income (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
REVENUES:	'	'	'	'
Gross premiums written	$760,405	$765,200	$1,661,798	$1,602,281
Premiums ceded	-206,481	-183,978	-336,260	-326,007
Net premiums written	553,924	581,222	1,325,538	1,276,274
Change in unearned premiums	-16,677	-73,951	-258,006	-305,775
Net premiums earned	537,247	507,271	1,067,532	970,499
Net investment income	36,793	37,635	84,412	71,023
Net realized investment gains	85,217	-115,198	139,422	-35,561
Total revenues	659,257	429,708	1,291,366	1,005,961
EXPENSES:	'	'	'	'
Net losses and loss expenses	314,855	275,128	590,141	530,306
Acquisition costs	74,279	64,617	142,001	121,302
General and administrative expenses	96,188	80,585	176,528	163,265
Amortization of intangible assets	634	634	1,267	1,267
Interest expense	14,592	14,188	29,126	28,322
Foreign exchange loss	651	490	700	3,008
Total expenses	501,199	435,642	939,763	847,470
Income before income taxes	158,058	-5,934	351,603	158,491
Income tax expense	6,195	-4,072	22,768	1,361
NET INCOME	151,863	-1,862	328,835	157,130
Other comprehensive loss:	'	'	'	'
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME	$151,863	($1,862)	$328,835	$157,130
PER SHARE DATA	'	'	'	'
Basic earnings per share	$1.55	($0.02)	$3.33	$1.52
Diluted earnings per share	$1.52	($0.02)	$3.27	$1.48
Weighted average common shares outstanding	97,809,639	103,267,659	98,672,618	103,552,656
Weighted average common shares and common share equivalents outstanding	99,724,802	103,267,659	100,691,568	105,949,785
Dividends paid per share	$0.17	$0	$0.33	$0.13

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	157,130	'	'	157,130
Dividends — par value reduction	-12,981	-12,981	'	'
Dividends	-17,127	'	'	-17,127
Other comprehensive loss	0	'	'	'
Stock compensation	2,443	'	22,157	-19,714
Share repurchases	-82,571	'	-82,571	'
Shares cancelled	0	-11,602	82,571	-70,969
Balance, at end of period at Jun. 30, 2013	3,373,229	430,397	-91,661	3,034,493
Balance, at beginning of period at Dec. 31, 2013	3,519,826	418,988	-79,992	3,180,830
Net income	328,835	'	'	328,835
Dividends	-38,345	'	'	-38,345
Other comprehensive loss	0	'	'	'
Stock compensation	11,978	'	14,734	-2,756
Share repurchases	-139,532	'	-139,532	'
Shares cancelled	0	-16,081	139,532	-123,451
Balance, at end of period at Jun. 30, 2014	$3,682,762	$402,907	($65,258)	$3,345,113

Unaudited_Condensed_Consolidat4

Unaudited Condensed Consolidated Statements Of Cash Flows (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:	'	'
Net income	$328,835	$157,130
Adjustments to reconcile net income to cash provided by operating activities:	'	'
Net realized gains on sales of investments	-99,781	-62,921
Mark to market adjustments	-59,113	95,698
Stock compensation expense	7,631	6,566
Undistributed income of equity method investments	13,744	-2,316
Changes in:	'	'
Reserve for losses and loss expenses, net of reinsurance recoverables	101,911	12,901
Unearned premiums, net of prepaid reinsurance	258,006	305,776
Insurance balances receivable	-310,885	-304,088
Funds held	217,985	-51,231
Reinsurance balances payable	51,159	69,620
Net deferred acquisition costs	-36,598	-45,802
Net deferred tax assets	1,934	-14,970
Accounts payable and accrued liabilities	-53,397	-45,601
Other items, net	27,507	12,880
Net cash provided by operating activities	448,938	133,642
CASH FLOWS USED IN INVESTING ACTIVITIES:	'	'
Purchases of trading securities	-3,905,650	-3,186,162
Purchases of other invested assets	-181,419	-141,805
Sales of trading securities	3,705,229	3,171,977
Sales of other invested assets	184,166	126,491
Purchases of fixed assets	-5,601	-3,363
Change in restricted cash	21,638	-10,561
Payments to Acquire Businesses, Net of Cash Acquired	-2,565	0
Net cash used in investing activities	-184,202	-43,423
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid - partial par value reduction	0	-12,981
Dividends paid	-33,207	0
Proceeds from the exercise of stock options	6,313	5,293
Share repurchases	-137,810	-82,571
Net cash used in financing activities	-164,704	-90,259
Effect of exchange rate changes on foreign currency cash	3,170	-7,736
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	103,202	-7,776
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	531,936	681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	635,138	674,103
Supplemental disclosure of cash flow information:	'	'
Cash paid for income taxes	18,061	12,671
Cash paid for interest expense	$27,000	$27,000

General

General	6 Months Ended
	Jun. 30, 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	6 Months Ended
	Jun. 30, 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.
	On May 1, 2014, the shareholders approved a 3-for-1 stock split of the Company's common shares. All historical share and per share amounts reflect the effect of the stock split.
	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	6 Months Ended
	Jun. 30, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
New Accounting Pronouncements	'
	NEW ACCOUNTING PRONOUNCEMENTS
	In April 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update 2014-08, "Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity" ("ASU 2014-08"). ASU 2014-08 changes the requirements for reporting discontinued operations, such that a disposal of a component of the Company's operations is required to be reported as discontinued operations if the disposal represents a strategic shift that has, or will have, a major effect on the Company's operations and financial results. Examples of strategic shifts that could have a major effect on the Company's operations could include a disposal of a major geographical area, a major line of business, a major equity method investment, or other major parts of the Company. ASU 2014-08 is effective for all disposals that occur after January 1, 2015. The Company is currently assessing the impact the adoption of ASU 2014-08 will have on future financial statements.
	In May 2014, the FASB issued Accounting Standards Update 2014-09, "Revenue from Contracts with Customers" ("ASU 2014-09"). ASU 2014-09 provides a framework, through a five-step process, for recognizing revenue from customers, improves comparability and consistency of recognizing revenue across entities, industries, jurisdictions and capital markets, and requires enhanced disclosures. Certain contracts with customers are specifically excluded from the scope of ASU 2014-09, including amongst others, insurance contracts accounted for under Accounting Standard Codification 944, Financial Services - Insurance. ASU 2014-09 is effective on January 1, 2017 with retrospective adoption required for the comparative periods. The Company is currently assessing the impact the adoption of ASU 2014-09 will have on future financial statements.

Investments

Investments	6 Months Ended
	Jun. 30, 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:
		June 30, 2014						December 31, 2013
		Fair Value			Amortized Cost			Fair Value				Amortized Cost
	U.S. Government and Government agencies	$	1,274,331		$	1,273,469		$	1,676,788			$	1,684,832
	Non-U.S. Government and Government agencies	185,071			186,142			191,776				197,082
	States, municipalities and political subdivisions	261,267			256,698			231,555				234,406
	Corporate debt:
	Financial institutions	1,168,937			1,149,005			958,794				943,518
	Industrials	1,167,470			1,152,858			1,174,047				1,165,448
	Utilities	98,878			97,457			69,426				69,658
	Mortgage-backed	1,323,763			1,272,824			1,292,502				1,267,863
	Asset-backed	677,367			674,305			505,910				502,543
	Total fixed maturity investments	$	6,157,084		$	6,062,758		$	6,100,798			$	6,065,350
		June 30, 2014						December 31, 2013
		Fair Value			Original Cost			Fair Value				Original Cost
	Equity securities	$	938,117		$	885,861		$	699,846			$	647,301
	Other invested assets	804,505			693,370			764,081				658,683
		$	1,742,622		$	1,579,231		$	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 June 30, 2014 and December 31, 2013 were as follows:
	Investment Type	Carrying Value as of June 30, 2014			Investments			Estimated		Investments				Redemption	Redemption	Unfunded
					with			Remaining		without				Frequency(1)	Notice	Commitments
					Redemption			Restriction		Redemption					Period(1)
					Restrictions			Period		Restrictions
	Private equity	$	161,667		$	161,667		2 - 9 Years		$	—					$	239,697
	Mezzanine debt	95,162			95,162			5 - 9 Years		—						206,856
	Distressed	10,008			10,008			4 Years		—						4,941
	Total private equity	266,837			266,837					—						451,494
	Distressed	165,253			165,253			1 Year		—						—
	Equity long/short	134,036			58,568			1 Year		75,468				Quarterly	30 -60 Days	—
	Multi-strategy	100,263			—					100,263				Quarterly	45 -90 Days	—
	Relative value credit	105,624			—					105,624				Quarterly	60 Days	—
	Total hedge funds	505,176			223,821					281,355						—
	High yield loan fund	32,492			—					32,492				Monthly	30 days	—
	Total other invested assets at fair value	804,505			490,658					313,847						451,494
	Other private securities	128,134			—					128,134						—
	Total other invested assets	$	932,639		$	490,658				$	441,981					$	451,494
	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 as described below.
	In general, the Company has invested in hedge funds that require at least 30 days’ notice of redemption and may be redeemed on a monthly, quarterly, semi-annual, annual or longer basis, depending on the fund. Certain hedge funds have lock-up periods ranging from one to three years from initial investment. A lock-up period refers to the initial amount of time an investor is contractually required to invest before having the ability to redeem. Funds that provide for periodic redemptions may, depending on the funds’ governing documents, have the ability to deny or delay a redemption request, called a “gate.” The fund may implement this restriction because the aggregate amount of redemption requests as of a particular date exceeds a specified level, generally ranging from 15% to 25% of the fund’s net assets. The gate is a method for executing an orderly redemption process to reduce the possibility of adversely affecting investors in the fund. Typically, the imposition of a gate delays a portion of the requested redemption, with the remaining portion settled in cash sometime after the redemption date. Certain funds may impose a redemption fee on early redemptions. Interests in private equity funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
	The following describes each investment type:
	•	Private equity funds: Primary funds may invest in companies and general partnership interests. Secondary funds buy limited partnership interests from existing limited partners of primary private equity funds. As owners of private equity funds seek liquidity, they can sell their existing investments, plus any remaining commitment, to secondary market participants. These funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
•	Mezzanine debt funds: Mezzanine debt funds primarily focus on providing capital to upper middle market and middle market companies and private equity sponsors, in connection with leveraged buyouts, mergers and acquisitions, recapitalizations, growth financings and other corporate transactions. The most common position in the capital structure will be between the senior secured debt holder and the equity; however, the funds will utilize a flexible approach when structuring investments, which may include secured debt, subordinated debt, preferred stock and/or private equity. These funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
•	Distressed funds: In distressed debt investing, managers take positions in the debt of companies experiencing significant financial difficulties, including bankruptcy, or in certain positions of the capital structure of structured securities. The manager relies on the fundamental analysis of these securities, including the claims on the assets and the likely return to bondholders. Certain funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund.
•	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						Six Months Ended
	June 30,						June 30,
	2014			2013			2014				2013
Fixed maturity investments	$	35,936		$	32,662		$	72,235			$	65,187
Equity securities	5,912			4,409			9,165				7,608
Other invested assets	(890		)	3,843			10,518				5,307
Cash and cash equivalents	571			529			1,010				1,017
Expenses	(4,736		)	(3,808		)	(8,516		)		(8,096		)
Net investment income	$	36,793		$	37,635		$	84,412			$	71,023
Net investment income from other invested assets included the distributed and undistributed net income from investments accounted for using the equity method of accounting. The loss reported for other invested assets for the three months ended June 30, 2014 was due to a loss of $9,348 recorded for an equity method investment due to impairment charges that it recorded.
d) Components of Realized Gains and Losses
	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2014			2013			2014				2013
Gross realized gains on sale of invested assets	$	55,714		$	58,223		$	118,006			$	102,472
Gross realized losses on sale of invested assets	(4,025		)	(35,077		)	(16,273		)		(42,042		)
Net realized and unrealized (losses) gains on derivatives	(13,720		)	8,538			(26,640		)		7,561
Mark-to-market gains (losses):
Fixed maturity investments, trading	36,426			(115,113		)	58,882				(131,588		)
Equity securities, trading	21,316			(34,330		)	(289		)		(1,357		)
Other invested assets, trading	(10,494		)	2,561			5,736				29,393
Net realized investment gains (losses)	$	85,217		$	(115,198	)	$	139,422			$	(35,561	)
e) Pledged Assets
As of June 30, 2014 and December 31, 2013, $2,745,352 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 June 30, 2014 and December 31, 2013, a further $886,220 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	6 Months Ended
	Jun. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments	'
	DERIVATIVE INSTRUMENTS
	As of June 30, 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”):
		June 30, 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	$	57,761		$	430		$	158,762		$	1,996		$	294,788	$	6,254	$	122,439	$	1,176
	Interest rate swaps	105,000			87			664,500			1,126			491,400		6,829		40,000		4,214
	Total derivatives	$	162,761		$	517		$	823,262		$	3,122		$	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						Six Months Ended
		June 30,						June 30,
		2014			2013			2014			2013
	Foreign exchange contracts	$	(1,598	)	$	1,989		$	(2,466	)	$	1,245
	Total included in foreign exchange loss	(1,598		)	1,989			(2,466		)	1,245
	Put options	—			(90		)	—			(3,822		)
	Foreign exchange contracts	(286		)	4,274			(844		)	6,089
	Interest rate futures and swaps	(13,434		)	4,354			(25,796		)	5,294
	Total included in net realized investment gains (losses)	(13,720		)	8,538			(26,640		)	7,561
	Total realized and unrealized (losses) gains on derivatives	$	(15,318	)	$	10,527		$	(29,106	)	$	8,806
	The losses related to interest rate future and swap contracts for the three and six months ended June 30, 2014 were the result of selling interest rate future and swap contracts to reduce the duration of the investment portfolio. Given the decrease in interest rates during the year, the Company recorded a loss related to these interest rate future and swap contracts.
	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	6 Months Ended
	Jun. 30, 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:
	June 30, 2014		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. Government and Government agencies		$	1,274,331		$	1,274,331		$	1,058,607		$	215,724	$	—
	Non-U.S. Government and Government agencies		185,071			185,071						185,071		—
	States, municipalities and political subdivisions		261,267			261,267			—			261,267		—
	Corporate debt		2,435,285			2,435,285			—			2,435,285		—
	Mortgage-backed		1,323,763			1,323,763			—			1,176,962		146,801
	Asset-backed		677,367			677,367			—			606,135		71,232
	Total fixed maturity investments		6,157,084			6,157,084			1,058,607			4,880,444		218,033
	Equity securities		938,117			938,117			903,254			—		34,863
	Other invested assets		804,505			804,505			—			—		804,505
	Total investments		$	7,899,706		$	7,899,706		$	1,961,861		$	4,880,444	$	1,057,401
	Derivative assets:
	Foreign exchange contracts		$	430		$	430		$	—		$	430	$	—
	Interest rate swaps		87			87			—			87		—
	Derivative liabilities:
	Foreign exchange contracts		$	1,996		$	1,996		$	—		$	1,996	$	—
	Interest rate swaps		1,126			1,126			—			1,126		—
	Senior notes		$	798,648		$	907,005		$	—		$	907,005	$	—
	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 June 30, 2014	Other invested			Mortgage-backed			Asset-backed			Equities
	assets
Opening balance	$	839,986		$	134,061		$	81,234		$	34,786
Realized and unrealized gains (losses) included in net income	22,498			2,721			450			77
Purchases	99,722			20,928			9,409			—
Sales	(157,701		)	(26,734		)	(3,743		)	—
Transfers into Level 3 from Level 2	—			17,437			—			—
Transfers out of Level 3 into Level 2 (1)	—			(1,612		)	(16,118		)	—
Ending balance	$	804,505		$	146,801		$	71,232		$	34,863
Three Months Ended June 30, 2013
Opening balance	$	710,140		$	155,420		$	40,903		$	57,787
Realized and unrealized gains (losses) included in net income	11,709			(6,188		)	(289		)	(4,288		)
Purchases	96,742			72,261			23,527			—
Sales	(104,200		)	(27,887		)	(1,727		)	—
Transfers into Level 3 from Level 2	—			11,197			—			—
Transfers out of Level 3 into Level 2 (1)	—			(6,800		)	(1,129		)	—
Ending balance	$	714,391		$	198,003		$	61,285		$	53,499
Six Months Ended June 30, 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	45,124			4,479			(355		)	(9,744		)
Purchases	188,920			50,840			16,938			—
Sales	(193,620		)	(54,419		)	(8,225		)	(29,297		)
Transfers into Level 3 from Level 2	—			103			—			—
Transfers out of Level 3 into Level 2 (1)	—			(1,540		)	(30,539		)	—
Ending balance	$	804,505		$	146,801		$	71,232		$	34,863
Six Months Ended June 30, 2013
Opening balance	$	655,888		$	167,825		$	62,246		$	54,680
Realized and unrealized gains (losses) included in net income	43,962			(7,613		)	(382		)	(1,181		)
Purchases	169,952			71,752			24,782			—
Sales	(155,411		)	(29,864		)	(18,478		)	—
Transfers into Level 3 from Level 2	—			7,109			—			—
Transfers out of Level 3 into Level 2 (1)	—			(11,206		)	(6,883		)	—
Ending balance	$	714,391		$	198,003		$	61,285		$	53,499
_______________________
-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	6 Months Ended
	Jun. 30, 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:
		June 30,			December 31,
		2014			2013
	Outstanding loss reserves	$	1,543,506		$	1,520,867
	Reserves for losses incurred but not reported	4,392,172			4,245,662
	Reserve for losses and loss expenses	$	5,935,678		$	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						Six Months Ended
		June 30,						June 30,
		2014			2013			2014			2013
	Gross liability at beginning of period	$	5,856,798		$	5,673,220		$	5,766,529		$	5,645,549
	Reinsurance recoverable at beginning of period	(1,280,525		)	(1,163,503		)	(1,234,504		)	(1,141,110		)
	Net liability at beginning of period	4,576,273			4,509,717			4,532,025			4,504,439
	Net losses incurred related to:
	Current year	359,994			323,556			684,141			622,804
	Prior years	(45,139		)	(48,428		)	(94,000		)	(92,498		)
	Total incurred	314,855			275,128			590,141			530,306
	Net paid losses related to:
	Current year	23,065			21,003			26,808			24,584
	Prior years	235,335			241,764			463,929			482,885
	Total paid	258,400			262,767			490,737			507,469
	Foreign exchange revaluation	1,208			(4,738		)	2,507			(9,936		)
	Net liability at end of period	4,633,936			4,517,340			4,633,936			4,517,340
	Reinsurance recoverable at end of period	1,301,742			1,179,525			1,301,742			1,179,525
	Gross liability at end of period	$	5,935,678		$	5,696,865		$	5,935,678		$	5,696,865
	For the three months ended June 30, 2014, the Company had net unfavorable prior year reserve development in the U.S. insurance segment and recorded net favorable prior year reserve development in the international insurance and reinsurance segments. The net unfavorable prior year reserve development in the U.S. insurance segment related primarily to the healthcare line of business, as well as adverse development on reported claims in the lawyers errors and omissions ("E&O") and primary casualty classes of business. The net favorable prior year reserve development in the international insurance and reinsurance segments was due to actual loss emergence being lower than initially expected.
	For the six months ended June 30, 2014, the Company had net unfavorable prior year reserve development in the U.S. insurance segment and recorded net favorable prior year reserve development in the international insurance and reinsurance segments. The net unfavorable prior year reserve development in the U.S. insurance segment related to the healthcare line of business due to higher than expected loss frequency and severity in the medical malpractice class of business. The U.S. insurance segment also experienced adverse development on reported claims in the lawyers E&O class of business and the primary casualty class of business in the 2013 loss year. The net favorable prior year reserve development in the international insurance and reinsurance segments was due to actual loss emergence being lower than initially expected.
	For the three months ended June 30, 2013, the Company had net favorable reserve development in each of its segments due to actual loss emergence being lower than initially expected. The majority of the net favorable reserve development was recognized in the 2007 through 2010 loss years across most lines of business. In addition, the reinsurance segment recognized net favorable reserve development for the 2012 loss year due to the low level of reported property losses. This was partially offset by adverse development in the U.S. insurance segment in the 2011 and 2012 loss years.
	For the six months ended June 30, 2013, the Company had net favorable reserve development in its international and reinsurance segments due to actual loss emergence being lower than initially expected, primarily for loss years 2004 to 2008. The reinsurance segment recognized net favorable reserve development for the 2012 loss year due to the low level of reported property losses. This was partially offset by adverse development in the U.S. insurance segment in the 2011 and 2012 loss years for certain E&O and director’s and officers’ classes of business.
	While the Company at times 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	6 Months Ended
	Jun. 30, 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 June 30, 2014.

Shareholders_Equity

Shareholders' Equity	6 Months Ended
	Jun. 30, 2014
Stockholders' Equity Note [Abstract]	'
Shareholders' Equity	'
	SHAREHOLDERS’ EQUITY
	a) Authorized shares
	The issued share capital consists of the following:
		June 30,			December 31,
		2014			2013
	Common shares issued and fully paid, 2014: CHF 4.10 per share; 2013: CHF 4.10 per share	99,515,760			103,477,452
	Share capital at end of period	$	402,907		$	418,988
		Six Months Ended June 30, 2014
	Shares issued at beginning of period	103,477,452
	Shares cancelled	(3,961,692	)
	Total shares issued at end of period	99,515,760
	Treasury shares issued at beginning of period	3,223,806
	Shares repurchased	3,961,692
	Shares issued out of treasury	(637,137	)
	Shares cancelled	(3,961,692	)
	Total treasury shares at end of period	2,586,669
	Total shares outstanding at end of period	96,929,091
	During the six months ended June 30, 2014, 3,961,692 shares repurchased and designated for cancellation were constructively retired and cancelled.
	b) Dividends
	The Company paid the following dividends during the six months ended June 30, 2014:
	Dividend Paid		Dividend			Total
			Per			Amount
			Share			Paid
	2-Jan-14		$	0.167		$	16,732
	3-Apr-14		$	0.167		$	16,495
	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 $0.167 per share in July 2013, October 2013, January 2014 and April 2014.
	On May 1, 2014, the shareholders approved the Company’s proposal to pay cash dividends in the form of a distribution out of general legal reserve from capital contributions. The distribution amount will be paid to shareholders in quarterly installments of $0.225 per share. The first installment of the dividend was on July 2, 2014. The Company expects to distribute the remaining installments of the dividend in October 2014, January 2015 and April 2015.
	c) Share Repurchases
	On May 1, 2014, the shareholders approved a new share repurchase program in order for the Company to repurchase up to $500,000 of its common shares. This new share repurchase program supersedes the 2012 share repurchase program and no further repurchases will be made under the 2012 share repurchase program. 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, the first three million of common shares repurchased will remain in treasury and will be used by the Company to satisfy share delivery obligations under its equity-based compensation plans. Any additional common shares repurchased will be designated for cancellation at acquisition and will be canceled upon shareholder approval. Shares repurchased and designated for cancellation are constructively retired and recorded as a share cancellation.
	The Company’s share repurchases were as follows:
		Three Months Ended						Six Months Ended
		June 30,						June 30,
		2014			2013			2014		2013
	Common shares repurchased	1,949,496			1,524,984			3,961,692		2,821,335
	Total cost of shares repurchased	$	70,874		$	46,326		$	139,532	$	82,571
	Average price per share	$	36.36		$	30.38		$	35.22	$	29.27

Employee_Benefit_Plans

Employee Benefit Plans	6 Months Ended
	Jun. 30, 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 135%, 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:
		Six Months Ended June 30, 2014
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	143,697		$	21.69
	RSUs granted	454,176		33.56
	RSUs forfeited	(5,097	)	(30.64		)
	RSUs fully vested	(76,230	)	(21.75		)
	Outstanding at end of period	516,546		$	32.03
	The activity related to the Company’s performance-based equity awards is as follows:
		Six Months Ended June 30, 2014
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	804,519		$	23.21
	Performance-based equity awards granted	166,302		33.56
	Additional awards granted due to achievement of performance criteria	104,895		(20.50		)
	Performance-based equity awards forfeited	(1,848	)	(25.28		)
	Performance-based equity awards fully vested	(454,440	)	(20.50		)
	Outstanding at end of period	619,428		$	27.51
	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
	Six Months Ended June 30, 2014	Number of Awards		Weighted Average Grant Date Fair Value			Number of Awards			Weighted Average Grant Date Fair Value
	Outstanding at beginning of period	2,049,084		$	24.69		1,031,961			23.67
	Granted	438,162		33.56			249,438			33.56
	Additional awards granted due to achievement of performance criteria	—		—			104,895			20.5
	Forfeited	(38,886	)	(26.36		)	(2,769	)		(25.28		)
	Fully vested	(751,920	)	(22.47		)	(454,440	)		(20.50		)
	Outstanding at end of period	1,696,440		$	27.93		929,085			$	27.51
	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						Six Months Ended
		June 30,						June 30,
		2014			2013			2014				2013
	Stock options	$	413		$	679		$	1,140			$	2,014
	RSUs and performance-based equity awards	2,977			1,891			6,490				4,551
	Cash-equivalent stock awards	12,868			8,212			17,497				20,968
	Total	$	16,258		$	10,782		$	25,127			$	27,533

Earnings_Per_Share

Earnings Per Share	6 Months Ended
	Jun. 30, 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					Six Months Ended
		June 30,					June 30,
		2014		2013			2014		2013
	Basic earnings (loss) per share:
	Net income (loss)	$	151,863	$	(1,862	)	$	328,835	$	157,130
	Weighted average common shares outstanding	97,809,639		103,267,659			98,672,618		103,552,656
	Basic earnings (loss) per share	$	1.55	$	(0.02	)	$	3.33	$	1.52
		Three Months Ended					Six Months Ended
		June 30,					June 30,
		2014		2013			2014		2013
	Diluted earnings (loss) per share:
	Net income (loss)	$	151,863	$	(1,862	)	$	328,835	$	157,130
	Weighted average common shares outstanding	97,809,639		103,267,659			98,672,618		103,552,656
	Share equivalents:
	Stock options	1,448,071		—			1,456,439		1,479,675
	RSUs and performance-based equity awards	455,744		—			550,224		913,587
	Employee share purchase plan	11,348		—			12,287		3,867
	Weighted average common shares and common share equivalents outstanding - diluted	99,724,802		103,267,659			100,691,568		105,949,785
	Diluted earnings (loss) per share	$	1.52	$	(0.02	)	$	3.27	$	1.48
	For the three months ended June 30, 2014, there were no common shares considered anti-dilutive and therefore excluded from the calculation of the diluted earnings per share. For the three months ended June 30, 2013, there were no common share equivalents included in calculating diluted earnings per share as there was a net loss and any additional shares would be anti-dilutive.
	For the six months ended June 30, 2014 and 2013, there were no common shares considered anti-dilutive and therefore excluded from the calculation of the diluted earnings per share.

Segment_Information

Segment Information	6 Months Ended
	Jun. 30, 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 lines of business fall within these classifications.
	The U.S. insurance segment includes the Company’s direct specialty insurance operations in the United States and Canada, as well as the Company's claim administration services operations. The Company acquired the remaining interest in a claims administration services company it did not own in May 2014 and recorded goodwill of $9,385 related to the transaction. The U.S. insurance segment provides both direct property and specialty casualty insurance primarily to non-Fortune 1000 North American domiciled accounts, as well as third-party claims administration services. The international insurance segment includes the Company’s direct insurance operations in Bermuda, Europe, and Asia Pacific, which includes offices in Australia, Hong Kong and Singapore. 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 and Asia Pacific 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”, “expense ratio” and the “combined ratio.” The “loss and loss expense ratio” is derived by dividing net losses and loss expenses by net premiums earned. The “acquisition cost ratio” is derived by dividing acquisition costs by net premiums earned. The “general and administrative expense ratio” is derived by dividing general and administrative expenses by net premiums earned. The expense ratio is the sum of the acquisition cost ratio and the general and administrative expense ratio. The “combined ratio” is the sum of the “loss and loss expense ratio,” the “acquisition cost ratio” and the “general and administrative expense ratio.”
	The following tables provide a summary of the segment results:
	Three Months Ended June 30, 2014		U.S. Insurance				International				Reinsurance				Total
							Insurance
	Gross premiums written		$	341,426			$	204,478			$	214,501			$	760,405
	Net premiums written		221,950				122,171				209,803				553,924
	Net premiums earned		214,593				89,205				233,449				537,247
	Net losses and loss expenses		(145,485		)		(35,920		)		(133,450		)		(314,855		)
	Acquisition costs		(29,677		)		(575		)		(44,027		)		(74,279		)
	General and administrative expenses		(46,593		)		(29,411		)		(20,184		)		(96,188		)
	Underwriting (loss) income		(7,162		)		23,299				35,788				51,925
	Net investment income														36,793
	Net realized investment gains														85,217
	Amortization of intangible assets														(634		)
	Interest expense														(14,592		)
	Foreign exchange loss														(651		)
	Income before income taxes														$	158,058
	Loss and loss expense ratio		67.8		%		40.3		%		57.2		%		58.6		%
	Acquisition cost ratio		13.8		%		0.6		%		18.9		%		13.8		%
	General and administrative expense ratio		21.7		%		33		%		8.6		%		17.9		%
	Expense ratio		35.5		%		33.6		%		27.5		%		31.7		%
	Combined ratio		103.3		%		73.9		%		84.7		%		90.3		%
	Three Months Ended June 30, 2013		U.S. Insurance				International				Reinsurance				Total
							Insurance
	Gross premiums written		$	307,297			$	192,593			$	265,310			$	765,200
	Net premiums written		221,419				106,394				253,409				581,222
	Net premiums earned		197,436				87,041				222,794				507,271
	Net losses and loss expenses		(124,364		)		(30,968		)		(119,796		)		(275,128		)
	Acquisition costs		(27,270		)		358				(37,705		)		(64,617		)
	General and administrative expenses		(38,302		)		(24,135		)		(18,148		)		(80,585		)
	Underwriting income		7,500				32,296				47,145				86,941
	Net investment income														37,635
	Net realized investment losses														(115,198		)
	Amortization of intangible assets														(634		)
	Interest expense														(14,188		)
	Foreign exchange loss														(490		)
	Loss before income taxes														$	(5,934	)
	Loss and loss expense ratio		63		%		35.6		%		53.8		%		54.2		%
	Acquisition cost ratio		13.8		%		(0.4		)%		16.9		%		12.7		%
	General and administrative expense ratio		19.4		%		27.7		%		8.1		%		15.9		%
	Expense ratio		33.2		%		27.3		%		25		%		28.6		%
	Combined ratio		96.2		%		62.9		%		78.8		%		82.8		%
	Six Months Ended June 30, 2014		U.S. Insurance				International				Reinsurance				Total
							Insurance
	Gross premiums written		$	611,371			$	338,842			$	711,585			$	1,661,798
	Net premiums written		424,690				197,630				703,218				1,325,538
	Net premiums earned		426,716				177,544				463,272				1,067,532
	Net losses and loss expenses		(287,480		)		(59,486		)		(243,175		)		(590,141		)
	Acquisition costs		(57,180		)		374				(85,195		)		(142,001		)
	General and administrative expenses		(84,030		)		(54,171		)		(38,327		)		(176,528		)
	Underwriting (loss) income		(1,974		)		64,261				96,575				158,862
	Net investment income														84,412
	Net realized investment gains														139,422
	Amortization of intangible assets														(1,267		)
	Interest expense														(29,126		)
	Foreign exchange loss														(700		)
	Income before income taxes														$	351,603
	Loss and loss expense ratio		67.4		%		33.5		%		52.5		%		55.3		%
	Acquisition cost ratio		13.4		%		(0.2		)%		18.4		%		13.3		%
General and administrative expense ratio		19.7		%		30.5		%		8.3		%		16.5		%
Expense ratio		33.1		%		30.3		%		26.7		%		29.8		%
Combined ratio		100.5		%		63.8		%		79.2		%		85.1		%
Six Months Ended June 30, 2013		U.S. Insurance				International				Reinsurance				Total
						Insurance
Gross premiums written		$	563,315			$	321,109			$	717,857			$	1,602,281
Net premiums written		413,672				184,139				678,463				1,276,274
Net premiums earned		385,875				171,255				413,369				970,499
Net losses and loss expenses		(257,688		)		(59,903		)		(212,715		)		(530,306		)
Acquisition costs		(50,398		)		1,207				(72,111		)		(121,302		)
General and administrative expenses		(77,898		)		(48,924		)		(36,443		)		(163,265		)
Underwriting (loss) income		(109		)		63,635				92,100				155,626
Net investment income														71,023
Net realized investment losses														(35,561		)
Amortization of intangible assets														(1,267		)
Interest expense														(28,322		)
Foreign exchange loss														(3,008		)
Income before income taxes														$	158,491
Loss and loss expense ratio		66.8		%		35		%		51.5		%		54.6		%
Acquisition cost ratio		13.1		%		(0.7		)%		17.4		%		12.5		%
General and administrative expense ratio		20.2		%		28.6		%		8.8		%		16.8		%
Expense ratio		33.3		%		27.9		%		26.2		%		29.3		%
Combined ratio		100.1		%		62.9		%		77.7		%		83.9		%
The following table shows an analysis of the Company’s gross premiums written by geographic location of the Company’s subsidiaries and branches. All intercompany premiums have been eliminated.
	Three Months Ended								Six Months Ended
	June 30,								June 30,
	2014				2013				2014				2013
United States	$	442,549			$	440,151			$	963,321			$	918,594
Bermuda	185,872				211,040				415,503				439,712
Europe	77,985				60,234				181,321				146,743
Singapore	45,375				48,918				87,316				87,031
Hong Kong	3,756				4,857				8,639				10,201
Canada	3,094				—				3,924				—
Australia	1,774				—				1,774				—
Total gross premiums written	$	760,405			$	765,200			$	1,661,798			$	1,602,281
Europe includes gross premiums written attributable to Switzerland of $10,261 and $5,868 for the three months ended June 30, 2014 and 2013, respectively and $54,554 and $46,674 for the six months ended June 30, 2014 and 2013.

Commitments_And_Contingencies

Commitments And Contingencies	6 Months Ended
	Jun. 30, 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 June 30, 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	6 Months Ended
	Jun. 30, 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 June 30, 2014 and December 31, 2013 and for the three and six months ended June 30, 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 June 30, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	8,027,840		$	—		$	8,027,840
	Cash and cash equivalents	40,976			1,286			592,876			—			635,138
	Insurance balances receivable	—			—			976,441			—			976,441
	Funds held	—			—			414,445			—			414,445
	Reinsurance recoverable	—			—			1,301,742			—			1,301,742
	Net deferred acquisition costs	—			—			163,259			—			163,259
	Goodwill and intangible assets	—			—			325,325			—			325,325
	Balances receivable on sale of investments	—			—			164,713			—			164,713
	Investments in subsidiaries	3,600,731			4,201,054			—			(7,801,785		)	—
	Due from subsidiaries	75,813			18,859			15,536			(110,208		)	—
	Other assets	1,090			4,026			655,628			—			660,744
	Total assets	$	3,718,610		$	4,225,225		$	12,637,805		$	(7,911,993	)	$	12,669,647
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,935,678		$	—		$	5,935,678
	Unearned premiums	—			—			1,703,684			—			1,703,684
	Reinsurance balances payable	—			—			224,182			—			224,182
	Balances due on purchases of investments	—			—			180,378			—			180,378
	Senior notes	—			798,648			—			—			798,648
	Due to subsidiaries	8,373			7,163			94,672			(110,208		)	—
	Other liabilities	27,475			17,976			98,864			—			144,315
	Total liabilities	35,848			823,787			8,237,458			(110,208		)	8,986,885
	Total shareholders’ equity	3,682,762			3,401,438			4,400,347			(7,801,785		)	3,682,762
	Total liabilities and shareholders’ equity	$	3,718,610		$	4,225,225		$	12,637,805		$	(7,911,993	)	$	12,669,647
	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 June 30, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
(Parent			(Subsidiary			Subsidiaries						Consolidated
Guarantor)			Issuer)
Net premiums earned	$	—		$	—		$	537,247		$	—		$	537,247
Net investment income	2			—			36,791			—			36,793
Net realized investment gains (losses)	—			—			85,217			—			85,217
Net losses and loss expenses	—			—			(314,855		)	—			(314,855		)
Acquisition costs	—			—			(74,279		)	—			(74,279		)
General and administrative expenses	(10,813		)	1,654			(87,029		)	—			(96,188		)
Amortization of intangible assets	—			—			(634		)	—			(634		)
Interest expense	—			(13,853		)	(739		)	—			(14,592		)
Foreign exchange gain (loss)	(2		)	(12		)	(637		)	—			(651		)
Income tax (expense) benefit	323			—			(6,518		)	—			(6,195		)
Equity in earnings of consolidated subsidiaries	162,353			170,796			—			(333,149		)	—
NET INCOME (LOSS)	$	151,863		$	158,585		$	174,564		$	(333,149	)	$	151,863
Other comprehensive income	—			—			—			—			—
COMPREHENSIVE INCOME (LOSS)	$	151,863		$	158,585		$	174,564		$	(333,149	)	$	151,863
Three Months Ended June 30, 2013	Allied World			Allied World			Other Allied			Consolidating			Allied World
	Switzerland			Bermuda			World			Adjustments			Switzerland
	(Parent			(Subsidiary			Subsidiaries						Consolidated
	Guarantor)			Issuer)
Net premiums earned	$	—		$	—		$	507,271		$	—		$	507,271
Net investment income	1			2			37,632			—			37,635
Net realized investment gains (losses)	—			—			(115,198		)	—			(115,198		)
Net losses and loss expenses	—			—			(275,128		)	—			(275,128		)
Acquisition costs	—			—			(64,617		)	—			(64,617		)
General and administrative expenses	(8,566		)	(455		)	(71,564		)	—			(80,585		)
Amortization of intangible assets	—			—			(634		)	—			(634		)
Interest expense	—			(13,835		)	(353		)	—			(14,188		)
Foreign exchange gain (loss)	2			(628		)	136			—			(490		)
Income tax (expense) benefit	—			—			4,072			—			4,072
Equity in earnings of consolidated subsidiaries	6,701			21,147			—			(27,848		)	—
NET INCOME (LOSS)	$	(1,862	)	$	6,231		$	21,617		$	(27,848	)	$	(1,862	)
Other comprehensive income	—			—			—			—			—
COMPREHENSIVE INCOME (LOSS)	$	(1,862	)	$	6,231		$	21,617		$	(27,848	)	$	(1,862	)
Six Months Ended June 30, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
	Switzerland			Bermuda			World			Adjustments			Switzerland
	(Parent			(Subsidiary			Subsidiaries						Consolidated
	Guarantor)			Issuer)
Net premiums earned	$	—		$	—		$	1,067,532		$	—		$	1,067,532
Net investment income	4			—			84,408			—			84,412
Net realized investment gains (losses)	—			—			139,422			—			139,422
Net losses and loss expenses	—			—			(590,141		)	—			(590,141		)
Acquisition costs	—			—			(142,001		)	—			(142,001		)
General and administrative expenses	(19,727		)	(737		)	(156,064		)	—			(176,528		)
Amortization of intangible assets	—			—			(1,267		)	—			(1,267		)
Interest expense	—			(27,700		)	(1,426		)	—			(29,126		)
Foreign exchange gain (loss)	(4		)	21			(717		)	—			(700		)
Income tax (expense) benefit	(86		)	—			(22,682		)	—			(22,768		)
Equity in earnings of consolidated subsidiaries	348,648			369,803			—			(718,451		)	—
NET INCOME (LOSS)	$	328,835		$	341,387		$	377,064		$	(718,451	)	$	328,835
Other comprehensive income	—			—			—			—			—
COMPREHENSIVE INCOME (LOSS)	$	328,835		$	341,387		$	377,064		$	(718,451	)	$	328,835
Six Months Ended June 30, 2013	Allied World			Allied World			Other Allied			Consolidating			Allied World
	Switzerland			Bermuda			World			Adjustments			Switzerland
	(Parent			(Subsidiary			Subsidiaries						Consolidated
	Guarantor)			Issuer)
Net premiums earned	$	—		$	—		$	970,499		$	—		$	970,499
Net investment income	8			4			71,011			—			71,023
Net realized investment gains (losses)	—			—			(35,561		)	—			(35,561		)
Net losses and loss expenses	—			—			(530,306		)	—			(530,306		)
Acquisition costs	—			—			(121,302		)	—			(121,302		)
General and administrative expenses	(19,552		)	(912		)	(142,801		)	—			(163,265		)
Amortization of intangible assets	—			—			(1,267		)	—			(1,267		)
Interest expense	—			(27,665		)	(657		)	—			(28,322		)
Foreign exchange gain (loss)	274			(723		)	(2,559		)	—			(3,008		)
Income tax (expense) benefit	—			—			(1,361		)	—			(1,361		)
Equity in earnings of consolidated subsidiaries	176,400			202,627			—			(379,027		)	—
NET INCOME (LOSS)	$	157,130		$	173,331		$	205,696		$	(379,027	)	$	157,130
Other comprehensive income	—			—			—			—			—
COMPREHENSIVE INCOME (LOSS)	$	157,130		$	173,331		$	205,696		$	(379,027	)	$	157,130
Unaudited Condensed Consolidating Statement of Cash Flows:
Six Months Ended June 30, 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	$	194,890		$	(1,489	)	$	258,707		$	—		$	452,108
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases trading securities	—			—			(3,905,650		)	—			(3,905,650		)
Purchases of other invested assets	—			—			(181,419		)	—			(181,419		)
Sales of trading securities	—			—			3,705,229			—			3,705,229
Sales of other invested assets	—			—			184,166			—			184,166
Other	—			—			13,472			—			13,472
Net cash provided by (used in) investing activities	—			—			(184,202		)	—			(184,202		)
CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Dividends paid	(33,207		)	—			—			—			(33,207		)
Proceeds from the exercise of stock options	6,313			—			—			—			6,313
Share repurchases	(137,810		)	—			—			—			(137,810		)
Net cash provided by (used in) financing activities	(164,704		)	—			—			—			(164,704		)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	30,186			(1,489		)	74,505			—			103,202
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790			2,775			518,371			—			531,936
CASH AND CASH EQUIVALENTS, END OF PERIOD	$	40,976		$	1,286		$	592,876		$	—		$	635,138
Six Months Ended June 30, 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:	$	73,938		$	(3,025	)	$	54,993		$	—		$	125,906
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	—			—			(3,186,162		)	—			(3,186,162		)
Purchases of other invested assets	—			—			(141,805		)	—			(141,805		)
Sales of trading securities	—			—			3,171,977			—			3,171,977
Sales of other invested assets	—			—			126,491			—			126,491
Other	—			—			(13,924		)	—			(13,924		)
Net cash provided by (used in) investing activities	—			—			(43,423		)	—			(43,423		)
CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Partial par value reduction	(12,981		)	—			—			—			(12,981		)
Proceeds from the exercise of stock options	5,293			—			—			—			5,293
Share repurchases	(82,571		)	—			—			—			(82,571		)
Net cash provided by (used in) financing activities	(90,259		)	—			—			—			(90,259		)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(16,321		)	(3,025		)	11,570			—			(7,776		)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	19,997			11,324			650,558			—			681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	$	3,676		$	8,299		$	662,128		$	—		$	674,103
Notes to Parent Company Condensed Financial Information
a) Dividends
Allied World Switzerland received cash dividends from its subsidiaries of $205,000 and $155,000 for the six months ended June 30, 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	6 Months Ended
	Jun. 30, 2014
Subsequent Events [Abstract]	'
Subsequent Events	'
	SUBSEQUENT EVENTS
	On July 2, 2014, the Company paid a quarterly dividend of $0.225 per share to shareholders of record on June 24, 2014.

Basis_of_Preparation_and_Conso1

Basis of Preparation and Consolidation (Policies)	6 Months Ended
	Jun. 30, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Basis of accounting	'
	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 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.
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)	6 Months Ended
	Jun. 30, 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:
		June 30, 2014						December 31, 2013
		Fair Value			Amortized Cost			Fair Value				Amortized Cost
	U.S. Government and Government agencies	$	1,274,331		$	1,273,469		$	1,676,788			$	1,684,832
	Non-U.S. Government and Government agencies	185,071			186,142			191,776				197,082
	States, municipalities and political subdivisions	261,267			256,698			231,555				234,406
	Corporate debt:
	Financial institutions	1,168,937			1,149,005			958,794				943,518
	Industrials	1,167,470			1,152,858			1,174,047				1,165,448
	Utilities	98,878			97,457			69,426				69,658
	Mortgage-backed	1,323,763			1,272,824			1,292,502				1,267,863
	Asset-backed	677,367			674,305			505,910				502,543
	Total fixed maturity investments	$	6,157,084		$	6,062,758		$	6,100,798			$	6,065,350
		June 30, 2014						December 31, 2013
		Fair Value			Original Cost			Fair Value				Original Cost
	Equity securities	$	938,117		$	885,861		$	699,846			$	647,301
	Other invested assets	804,505			693,370			764,081				658,683
		$	1,742,622		$	1,579,231		$	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 June 30, 2014 and December 31, 2013 were as follows:
	Investment Type	Carrying Value as of June 30, 2014			Investments			Estimated		Investments				Redemption	Redemption	Unfunded
					with			Remaining		without				Frequency(1)	Notice	Commitments
					Redemption			Restriction		Redemption					Period(1)
					Restrictions			Period		Restrictions
	Private equity	$	161,667		$	161,667		2 - 9 Years		$	—					$	239,697
	Mezzanine debt	95,162			95,162			5 - 9 Years		—						206,856
	Distressed	10,008			10,008			4 Years		—						4,941
	Total private equity	266,837			266,837					—						451,494
	Distressed	165,253			165,253			1 Year		—						—
	Equity long/short	134,036			58,568			1 Year		75,468				Quarterly	30 -60 Days	—
	Multi-strategy	100,263			—					100,263				Quarterly	45 -90 Days	—
	Relative value credit	105,624			—					105,624				Quarterly	60 Days	—
	Total hedge funds	505,176			223,821					281,355						—
	High yield loan fund	32,492			—					32,492				Monthly	30 days	—
	Total other invested assets at fair value	804,505			490,658					313,847						451,494
	Other private securities	128,134			—					128,134						—
	Total other invested assets	$	932,639		$	490,658				$	441,981					$	451,494
	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 as described below.
Schedule of net investment income	'
		Three Months Ended						Six Months Ended
		June 30,						June 30,
		2014			2013			2014				2013
	Fixed maturity investments	$	35,936		$	32,662		$	72,235			$	65,187
	Equity securities	5,912			4,409			9,165				7,608
	Other invested assets	(890		)	3,843			10,518				5,307
	Cash and cash equivalents	571			529			1,010				1,017
	Expenses	(4,736		)	(3,808		)	(8,516		)		(8,096		)
	Net investment income	$	36,793		$	37,635		$	84,412			$	71,023
Components of realized gains and losses	'
		Three Months Ended						Six Months Ended
		June 30,						June 30,
		2014			2013			2014				2013
	Gross realized gains on sale of invested assets	$	55,714		$	58,223		$	118,006			$	102,472
	Gross realized losses on sale of invested assets	(4,025		)	(35,077		)	(16,273		)		(42,042		)
	Net realized and unrealized (losses) gains on derivatives	(13,720		)	8,538			(26,640		)		7,561
	Mark-to-market gains (losses):
	Fixed maturity investments, trading	36,426			(115,113		)	58,882				(131,588		)
	Equity securities, trading	21,316			(34,330		)	(289		)		(1,357		)
	Other invested assets, trading	(10,494		)	2,561			5,736				29,393
	Net realized investment gains (losses)	$	85,217		$	(115,198	)	$	139,422			$	(35,561	)

Derivative_Instruments_Tables

Derivative Instruments (Tables)	6 Months Ended
	Jun. 30, 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”):
		June 30, 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	$	57,761		$	430		$	158,762		$	1,996		$	294,788	$	6,254	$	122,439	$	1,176
	Interest rate swaps	105,000			87			664,500			1,126			491,400		6,829		40,000		4,214
	Total derivatives	$	162,761		$	517		$	823,262		$	3,122		$	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						Six Months Ended
		June 30,						June 30,
		2014			2013			2014			2013
	Foreign exchange contracts	$	(1,598	)	$	1,989		$	(2,466	)	$	1,245
	Total included in foreign exchange loss	(1,598		)	1,989			(2,466		)	1,245
	Put options	—			(90		)	—			(3,822		)
	Foreign exchange contracts	(286		)	4,274			(844		)	6,089
	Interest rate futures and swaps	(13,434		)	4,354			(25,796		)	5,294
	Total included in net realized investment gains (losses)	(13,720		)	8,538			(26,640		)	7,561
	Total realized and unrealized (losses) gains on derivatives	$	(15,318	)	$	10,527		$	(29,106	)	$	8,806

Fair_Value_Of_Financial_Instru1

Fair Value Of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 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:
	June 30, 2014		Carrying			Total			Level 1			Level 2		Level 3
			Amount			Fair Value
	Fixed maturity investments:
	U.S. Government and Government agencies		$	1,274,331		$	1,274,331		$	1,058,607		$	215,724	$	—
	Non-U.S. Government and Government agencies		185,071			185,071						185,071		—
	States, municipalities and political subdivisions		261,267			261,267			—			261,267		—
	Corporate debt		2,435,285			2,435,285			—			2,435,285		—
	Mortgage-backed		1,323,763			1,323,763			—			1,176,962		146,801
	Asset-backed		677,367			677,367			—			606,135		71,232
	Total fixed maturity investments		6,157,084			6,157,084			1,058,607			4,880,444		218,033
	Equity securities		938,117			938,117			903,254			—		34,863
	Other invested assets		804,505			804,505			—			—		804,505
	Total investments		$	7,899,706		$	7,899,706		$	1,961,861		$	4,880,444	$	1,057,401
	Derivative assets:
	Foreign exchange contracts		$	430		$	430		$	—		$	430	$	—
	Interest rate swaps		87			87			—			87		—
	Derivative liabilities:
	Foreign exchange contracts		$	1,996		$	1,996		$	—		$	1,996	$	—
	Interest rate swaps		1,126			1,126			—			1,126		—
	Senior notes		$	798,648		$	907,005		$	—		$	907,005	$	—
	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 June 30, 2014	Other invested			Mortgage-backed			Asset-backed			Equities
		assets
	Opening balance	$	839,986		$	134,061		$	81,234		$	34,786
	Realized and unrealized gains (losses) included in net income	22,498			2,721			450			77
	Purchases	99,722			20,928			9,409			—
	Sales	(157,701		)	(26,734		)	(3,743		)	—
	Transfers into Level 3 from Level 2	—			17,437			—			—
	Transfers out of Level 3 into Level 2 (1)	—			(1,612		)	(16,118		)	—
	Ending balance	$	804,505		$	146,801		$	71,232		$	34,863
	Three Months Ended June 30, 2013
	Opening balance	$	710,140		$	155,420		$	40,903		$	57,787
	Realized and unrealized gains (losses) included in net income	11,709			(6,188		)	(289		)	(4,288		)
	Purchases	96,742			72,261			23,527			—
	Sales	(104,200		)	(27,887		)	(1,727		)	—
	Transfers into Level 3 from Level 2	—			11,197			—			—
	Transfers out of Level 3 into Level 2 (1)	—			(6,800		)	(1,129		)	—
	Ending balance	$	714,391		$	198,003		$	61,285		$	53,499
	Six Months Ended June 30, 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	45,124			4,479			(355		)	(9,744		)
	Purchases	188,920			50,840			16,938			—
	Sales	(193,620		)	(54,419		)	(8,225		)	(29,297		)
	Transfers into Level 3 from Level 2	—			103			—			—
	Transfers out of Level 3 into Level 2 (1)	—			(1,540		)	(30,539		)	—
	Ending balance	$	804,505		$	146,801		$	71,232		$	34,863
	Six Months Ended June 30, 2013
	Opening balance	$	655,888		$	167,825		$	62,246		$	54,680
	Realized and unrealized gains (losses) included in net income	43,962			(7,613		)	(382		)	(1,181		)
	Purchases	169,952			71,752			24,782			—
	Sales	(155,411		)	(29,864		)	(18,478		)	—
	Transfers into Level 3 from Level 2	—			7,109			—			—
	Transfers out of Level 3 into Level 2 (1)	—			(11,206		)	(6,883		)	—
	Ending balance	$	714,391		$	198,003		$	61,285		$	53,499
	_______________________
	-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)	6 Months Ended
	Jun. 30, 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:
		June 30,			December 31,
		2014			2013
	Outstanding loss reserves	$	1,543,506		$	1,520,867
	Reserves for losses incurred but not reported	4,392,172			4,245,662
	Reserve for losses and loss expenses	$	5,935,678		$	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						Six Months Ended
		June 30,						June 30,
		2014			2013			2014			2013
	Gross liability at beginning of period	$	5,856,798		$	5,673,220		$	5,766,529		$	5,645,549
	Reinsurance recoverable at beginning of period	(1,280,525		)	(1,163,503		)	(1,234,504		)	(1,141,110		)
	Net liability at beginning of period	4,576,273			4,509,717			4,532,025			4,504,439
	Net losses incurred related to:
	Current year	359,994			323,556			684,141			622,804
	Prior years	(45,139		)	(48,428		)	(94,000		)	(92,498		)
	Total incurred	314,855			275,128			590,141			530,306
	Net paid losses related to:
	Current year	23,065			21,003			26,808			24,584
	Prior years	235,335			241,764			463,929			482,885
	Total paid	258,400			262,767			490,737			507,469
	Foreign exchange revaluation	1,208			(4,738		)	2,507			(9,936		)
	Net liability at end of period	4,633,936			4,517,340			4,633,936			4,517,340
	Reinsurance recoverable at end of period	1,301,742			1,179,525			1,301,742			1,179,525
	Gross liability at end of period	$	5,935,678		$	5,696,865		$	5,935,678		$	5,696,865

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2014
Stockholders' Equity Note [Abstract]	'
Issued share capital	'
	The issued share capital consists of the following:
		June 30,			December 31,
		2014			2013
	Common shares issued and fully paid, 2014: CHF 4.10 per share; 2013: CHF 4.10 per share	99,515,760			103,477,452
	Share capital at end of period	$	402,907		$	418,988
Schedule of common stock outstanding roll forward	'
		Six Months Ended June 30, 2014
	Shares issued at beginning of period	103,477,452
	Shares cancelled	(3,961,692	)
	Total shares issued at end of period	99,515,760
	Treasury shares issued at beginning of period	3,223,806
	Shares repurchased	3,961,692
	Shares issued out of treasury	(637,137	)
	Shares cancelled	(3,961,692	)
	Total treasury shares at end of period	2,586,669
	Total shares outstanding at end of period	96,929,091
Dividends paid	'
	The Company paid the following dividends during the six months ended June 30, 2014:
	Dividend Paid		Dividend			Total
			Per			Amount
			Share			Paid
	2-Jan-14		$	0.167		$	16,732
	3-Apr-14		$	0.167		$	16,495
Share repurchases	'
	The Company’s share repurchases were as follows:
		Three Months Ended						Six Months Ended
		June 30,						June 30,
		2014			2013			2014		2013
	Common shares repurchased	1,949,496			1,524,984			3,961,692		2,821,335
	Total cost of shares repurchased	$	70,874		$	46,326		$	139,532	$	82,571
	Average price per share	$	36.36		$	30.38		$	35.22	$	29.27

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 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						Six Months Ended
		June 30,						June 30,
		2014			2013			2014				2013
	Stock options	$	413		$	679		$	1,140			$	2,014
	RSUs and performance-based equity awards	2,977			1,891			6,490				4,551
	Cash-equivalent stock awards	12,868			8,212			17,497				20,968
	Total	$	16,258		$	10,782		$	25,127			$	27,533
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:
		Six Months Ended June 30, 2014
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	143,697		$	21.69
	RSUs granted	454,176		33.56
	RSUs forfeited	(5,097	)	(30.64		)
	RSUs fully vested	(76,230	)	(21.75		)
	Outstanding at end of period	516,546		$	32.03
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:
		Six Months Ended June 30, 2014
		Number of Awards		Weighted
				Average
				Grant Date
				Fair Value
	Outstanding at beginning of period	804,519		$	23.21
	Performance-based equity awards granted	166,302		33.56
	Additional awards granted due to achievement of performance criteria	104,895		(20.50		)
	Performance-based equity awards forfeited	(1,848	)	(25.28		)
	Performance-based equity awards fully vested	(454,440	)	(20.50		)
	Outstanding at end of period	619,428		$	27.51
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
	Six Months Ended June 30, 2014	Number of Awards		Weighted Average Grant Date Fair Value			Number of Awards			Weighted Average Grant Date Fair Value
	Outstanding at beginning of period	2,049,084		$	24.69		1,031,961			23.67
	Granted	438,162		33.56			249,438			33.56
	Additional awards granted due to achievement of performance criteria	—		—			104,895			20.5
	Forfeited	(38,886	)	(26.36		)	(2,769	)		(25.28		)
	Fully vested	(751,920	)	(22.47		)	(454,440	)		(20.50		)
	Outstanding at end of period	1,696,440		$	27.93		929,085			$	27.51

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 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					Six Months Ended
		June 30,					June 30,
		2014		2013			2014		2013
	Basic earnings (loss) per share:
	Net income (loss)	$	151,863	$	(1,862	)	$	328,835	$	157,130
	Weighted average common shares outstanding	97,809,639		103,267,659			98,672,618		103,552,656
	Basic earnings (loss) per share	$	1.55	$	(0.02	)	$	3.33	$	1.52
		Three Months Ended					Six Months Ended
		June 30,					June 30,
		2014		2013			2014		2013
	Diluted earnings (loss) per share:
	Net income (loss)	$	151,863	$	(1,862	)	$	328,835	$	157,130
	Weighted average common shares outstanding	97,809,639		103,267,659			98,672,618		103,552,656
	Share equivalents:
	Stock options	1,448,071		—			1,456,439		1,479,675
	RSUs and performance-based equity awards	455,744		—			550,224		913,587
	Employee share purchase plan	11,348		—			12,287		3,867
	Weighted average common shares and common share equivalents outstanding - diluted	99,724,802		103,267,659			100,691,568		105,949,785
	Diluted earnings (loss) per share	$	1.52	$	(0.02	)	$	3.27	$	1.48

Segment_Information_Tables

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2014																	Jun. 30, 2013
Segment Reporting [Abstract]	'																	'
Summary of segment results	'																	'
	The following tables provide a summary of the segment results:
																		Six Months Ended June 30, 2013	U.S. Insurance			International			Reinsurance			Total
	Three Months Ended June 30, 2014		U.S. Insurance				International				Reinsurance				Total							Insurance
							Insurance											Gross premiums written	$	563,315		$	321,109		$	717,857		$	1,602,281
	Gross premiums written		$	341,426			$	204,478			$	214,501			$	760,405
																		Net premiums written	413,672			184,139			678,463			1,276,274
	Net premiums written		221,950				122,171				209,803				553,924
																		Net premiums earned	385,875			171,255			413,369			970,499
	Net premiums earned		214,593				89,205				233,449				537,247
																		Net losses and loss expenses	(257,688		)	(59,903		)	(212,715		)	(530,306		)
	Net losses and loss expenses		(145,485		)		(35,920		)		(133,450		)		(314,855		)	Acquisition costs	(50,398		)	1,207			(72,111		)	(121,302		)
	Acquisition costs		(29,677		)		(575		)		(44,027		)		(74,279		)
	General and administrative expenses		(46,593		)		(29,411		)		(20,184		)		(96,188		)	General and administrative expenses	(77,898		)	(48,924		)	(36,443		)	(163,265		)
	Underwriting (loss) income		(7,162		)		23,299				35,788				51,925			Underwriting (loss) income	(109		)	63,635			92,100			155,626
	Net investment income														36,793			Net investment income										71,023
	Net realized investment gains														85,217			Net realized investment losses										(35,561		)
																		Amortization of intangible assets										(1,267		)
	Amortization of intangible assets														(634		)	Interest expense										(28,322		)
	Interest expense														(14,592		)	Foreign exchange loss										(3,008		)
	Foreign exchange loss														(651		)	Income before income taxes										$	158,491
	Income before income taxes														$	158,058
																		Loss and loss expense ratio	66.8		%	35		%	51.5		%	54.6		%
	Loss and loss expense ratio		67.8		%		40.3		%		57.2		%		58.6		%	Acquisition cost ratio	13.1		%	(0.7		)%	17.4		%	12.5		%
	Acquisition cost ratio		13.8		%		0.6		%		18.9		%		13.8		%	General and administrative expense ratio	20.2		%	28.6		%	8.8		%	16.8		%
	General and administrative expense ratio		21.7		%		33		%		8.6		%		17.9		%	Expense ratio	33.3		%	27.9		%	26.2		%	29.3		%
	Expense ratio		35.5		%		33.6		%		27.5		%		31.7		%	Combined ratio	100.1		%	62.9		%	77.7		%	83.9		%
	Combined ratio		103.3		%		73.9		%		84.7		%		90.3		%
	Three Months Ended June 30, 2013		U.S. Insurance				International				Reinsurance				Total
							Insurance
	Gross premiums written		$	307,297			$	192,593			$	265,310			$	765,200
	Net premiums written		221,419				106,394				253,409				581,222
	Net premiums earned		197,436				87,041				222,794				507,271
	Net losses and loss expenses		(124,364		)		(30,968		)		(119,796		)		(275,128		)
	Acquisition costs		(27,270		)		358				(37,705		)		(64,617		)
	General and administrative expenses		(38,302		)		(24,135		)		(18,148		)		(80,585		)
	Underwriting income		7,500				32,296				47,145				86,941
	Net investment income														37,635
	Net realized investment losses														(115,198		)
	Amortization of intangible assets														(634		)
	Interest expense														(14,188		)
	Foreign exchange loss														(490		)
	Loss before income taxes														$	(5,934	)
	Loss and loss expense ratio		63		%		35.6		%		53.8		%		54.2		%
	Acquisition cost ratio		13.8		%		(0.4		)%		16.9		%		12.7		%
	General and administrative expense ratio		19.4		%		27.7		%		8.1		%		15.9		%
	Expense ratio		33.2		%		27.3		%		25		%		28.6		%
	Combined ratio		96.2		%		62.9		%		78.8		%		82.8		%
	Six Months Ended June 30, 2014		U.S. Insurance				International				Reinsurance				Total
							Insurance
	Gross premiums written		$	611,371			$	338,842			$	711,585			$	1,661,798
	Net premiums written		424,690				197,630				703,218				1,325,538
	Net premiums earned		426,716				177,544				463,272				1,067,532
	Net losses and loss expenses		(287,480		)		(59,486		)		(243,175		)		(590,141		)
	Acquisition costs		(57,180		)		374				(85,195		)		(142,001		)
	General and administrative expenses		(84,030		)		(54,171		)		(38,327		)		(176,528		)
	Underwriting (loss) income		(1,974		)		64,261				96,575				158,862
	Net investment income														84,412
	Net realized investment gains														139,422
	Amortization of intangible assets														(1,267		)
	Interest expense														(29,126		)
	Foreign exchange loss														(700		)
	Income before income taxes														$	351,603
	Loss and loss expense ratio		67.4		%		33.5		%		52.5		%		55.3		%
Acquisition cost ratio		13.4		%		(0.2		)%		18.4		%		13.3		%
General and administrative expense ratio		19.7		%		30.5		%		8.3		%		16.5		%
Expense ratio		33.1		%		30.3		%		26.7		%		29.8		%
Combined ratio		100.5		%		63.8		%		79.2		%		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								Six Months Ended
		June 30,								June 30,
		2014				2013				2014				2013
	United States	$	442,549			$	440,151			$	963,321			$	918,594
	Bermuda	185,872				211,040				415,503				439,712
	Europe	77,985				60,234				181,321				146,743
	Singapore	45,375				48,918				87,316				87,031
	Hong Kong	3,756				4,857				8,639				10,201
	Canada	3,094				—				3,924				—
	Australia	1,774				—				1,774				—
	Total gross premiums written	$	760,405			$	765,200			$	1,661,798			$	1,602,281

Condensed_Consolidated_Guarant1

Condensed Consolidated Guarantor Financial Statements (Tables)	6 Months Ended
	Jun. 30, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Schedule of condensed consolidating balance sheet	'
	Unaudited Condensed Consolidating Balance Sheet:
	As of June 30, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	ASSETS:
	Investments	$	—		$	—		$	8,027,840		$	—		$	8,027,840
	Cash and cash equivalents	40,976			1,286			592,876			—			635,138
	Insurance balances receivable	—			—			976,441			—			976,441
	Funds held	—			—			414,445			—			414,445
	Reinsurance recoverable	—			—			1,301,742			—			1,301,742
	Net deferred acquisition costs	—			—			163,259			—			163,259
	Goodwill and intangible assets	—			—			325,325			—			325,325
	Balances receivable on sale of investments	—			—			164,713			—			164,713
	Investments in subsidiaries	3,600,731			4,201,054			—			(7,801,785		)	—
	Due from subsidiaries	75,813			18,859			15,536			(110,208		)	—
	Other assets	1,090			4,026			655,628			—			660,744
	Total assets	$	3,718,610		$	4,225,225		$	12,637,805		$	(7,911,993	)	$	12,669,647
	LIABILITIES:
	Reserve for losses and loss expenses	$	—		$	—		$	5,935,678		$	—		$	5,935,678
	Unearned premiums	—			—			1,703,684			—			1,703,684
	Reinsurance balances payable	—			—			224,182			—			224,182
	Balances due on purchases of investments	—			—			180,378			—			180,378
	Senior notes	—			798,648			—			—			798,648
	Due to subsidiaries	8,373			7,163			94,672			(110,208		)	—
	Other liabilities	27,475			17,976			98,864			—			144,315
	Total liabilities	35,848			823,787			8,237,458			(110,208		)	8,986,885
	Total shareholders’ equity	3,682,762			3,401,438			4,400,347			(7,801,785		)	3,682,762
	Total liabilities and shareholders’ equity	$	3,718,610		$	4,225,225		$	12,637,805		$	(7,911,993	)	$	12,669,647
	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 June 30, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	Net premiums earned	$	—		$	—		$	537,247		$	—		$	537,247
	Net investment income	2			—			36,791			—			36,793
	Net realized investment gains (losses)	—			—			85,217			—			85,217
	Net losses and loss expenses	—			—			(314,855		)	—			(314,855		)
	Acquisition costs	—			—			(74,279		)	—			(74,279		)
	General and administrative expenses	(10,813		)	1,654			(87,029		)	—			(96,188		)
	Amortization of intangible assets	—			—			(634		)	—			(634		)
	Interest expense	—			(13,853		)	(739		)	—			(14,592		)
	Foreign exchange gain (loss)	(2		)	(12		)	(637		)	—			(651		)
	Income tax (expense) benefit	323			—			(6,518		)	—			(6,195		)
	Equity in earnings of consolidated subsidiaries	162,353			170,796			—			(333,149		)	—
	NET INCOME (LOSS)	$	151,863		$	158,585		$	174,564		$	(333,149	)	$	151,863
	Other comprehensive income	—			—			—			—			—
	COMPREHENSIVE INCOME (LOSS)	$	151,863		$	158,585		$	174,564		$	(333,149	)	$	151,863
	Three Months Ended June 30, 2013	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	Net premiums earned	$	—		$	—		$	507,271		$	—		$	507,271
	Net investment income	1			2			37,632			—			37,635
	Net realized investment gains (losses)	—			—			(115,198		)	—			(115,198		)
	Net losses and loss expenses	—			—			(275,128		)	—			(275,128		)
	Acquisition costs	—			—			(64,617		)	—			(64,617		)
	General and administrative expenses	(8,566		)	(455		)	(71,564		)	—			(80,585		)
	Amortization of intangible assets	—			—			(634		)	—			(634		)
	Interest expense	—			(13,835		)	(353		)	—			(14,188		)
	Foreign exchange gain (loss)	2			(628		)	136			—			(490		)
	Income tax (expense) benefit	—			—			4,072			—			4,072
	Equity in earnings of consolidated subsidiaries	6,701			21,147			—			(27,848		)	—
	NET INCOME (LOSS)	$	(1,862	)	$	6,231		$	21,617		$	(27,848	)	$	(1,862	)
	Other comprehensive income	—			—			—			—			—
	COMPREHENSIVE INCOME (LOSS)	$	(1,862	)	$	6,231		$	21,617		$	(27,848	)	$	(1,862	)
	Six Months Ended June 30, 2014	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	Net premiums earned	$	—		$	—		$	1,067,532		$	—		$	1,067,532
	Net investment income	4			—			84,408			—			84,412
	Net realized investment gains (losses)	—			—			139,422			—			139,422
	Net losses and loss expenses	—			—			(590,141		)	—			(590,141		)
	Acquisition costs	—			—			(142,001		)	—			(142,001		)
	General and administrative expenses	(19,727		)	(737		)	(156,064		)	—			(176,528		)
	Amortization of intangible assets	—			—			(1,267		)	—			(1,267		)
	Interest expense	—			(27,700		)	(1,426		)	—			(29,126		)
	Foreign exchange gain (loss)	(4		)	21			(717		)	—			(700		)
	Income tax (expense) benefit	(86		)	—			(22,682		)	—			(22,768		)
	Equity in earnings of consolidated subsidiaries	348,648			369,803			—			(718,451		)	—
	NET INCOME (LOSS)	$	328,835		$	341,387		$	377,064		$	(718,451	)	$	328,835
	Other comprehensive income	—			—			—			—			—
	COMPREHENSIVE INCOME (LOSS)	$	328,835		$	341,387		$	377,064		$	(718,451	)	$	328,835
	Six Months Ended June 30, 2013	Allied World			Allied World			Other Allied			Consolidating			Allied World
		Switzerland			Bermuda			World			Adjustments			Switzerland
		(Parent			(Subsidiary			Subsidiaries						Consolidated
		Guarantor)			Issuer)
	Net premiums earned	$	—		$	—		$	970,499		$	—		$	970,499
	Net investment income	8			4			71,011			—			71,023
	Net realized investment gains (losses)	—			—			(35,561		)	—			(35,561		)
	Net losses and loss expenses	—			—			(530,306		)	—			(530,306		)
Acquisition costs	—			—			(121,302		)	—			(121,302		)
General and administrative expenses	(19,552		)	(912		)	(142,801		)	—			(163,265		)
Amortization of intangible assets	—			—			(1,267		)	—			(1,267		)
Interest expense	—			(27,665		)	(657		)	—			(28,322		)
Foreign exchange gain (loss)	274			(723		)	(2,559		)	—			(3,008		)
Income tax (expense) benefit	—			—			(1,361		)	—			(1,361		)
Equity in earnings of consolidated subsidiaries	176,400			202,627			—			(379,027		)	—
NET INCOME (LOSS)	$	157,130		$	173,331		$	205,696		$	(379,027	)	$	157,130
Other comprehensive income	—			—			—			—			—
COMPREHENSIVE INCOME (LOSS)	$	157,130		$	173,331		$	205,696		$	(379,027	)	$	157,130
Schedule of condensed consolidating statement of cash flows	'
	Unaudited Condensed Consolidating Statement of Cash Flows:
	Six Months Ended June 30, 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	$	194,890		$	(1,489	)	$	258,707		$	—		$	452,108
	CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
	Purchases trading securities	—			—			(3,905,650		)	—			(3,905,650		)
	Purchases of other invested assets	—			—			(181,419		)	—			(181,419		)
	Sales of trading securities	—			—			3,705,229			—			3,705,229
	Sales of other invested assets	—			—			184,166			—			184,166
	Other	—			—			13,472			—			13,472
	Net cash provided by (used in) investing activities	—			—			(184,202		)	—			(184,202		)
	CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
	Dividends paid	(33,207		)	—			—			—			(33,207		)
	Proceeds from the exercise of stock options	6,313			—			—			—			6,313
	Share repurchases	(137,810		)	—			—			—			(137,810		)
	Net cash provided by (used in) financing activities	(164,704		)	—			—			—			(164,704		)
	NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	30,186			(1,489		)	74,505			—			103,202
	CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790			2,775			518,371			—			531,936
	CASH AND CASH EQUIVALENTS, END OF PERIOD	$	40,976		$	1,286		$	592,876		$	—		$	635,138
	Six Months Ended June 30, 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:	$	73,938		$	(3,025	)	$	54,993		$	—		$	125,906
	CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
	Purchases of trading securities	—			—			(3,186,162		)	—			(3,186,162		)
	Purchases of other invested assets	—			—			(141,805		)	—			(141,805		)
	Sales of trading securities	—			—			3,171,977			—			3,171,977
	Sales of other invested assets	—			—			126,491			—			126,491
	Other	—			—			(13,924		)	—			(13,924		)
	Net cash provided by (used in) investing activities	—			—			(43,423		)	—			(43,423		)
	CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
	Partial par value reduction	(12,981		)	—			—			—			(12,981		)
	Proceeds from the exercise of stock options	5,293			—			—			—			5,293
	Share repurchases	(82,571		)	—			—			—			(82,571		)
	Net cash provided by (used in) financing activities	(90,259		)	—			—			—			(90,259		)
	NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(16,321		)	(3,025		)	11,570			—			(7,776		)
	CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	19,997			11,324			650,558			—			681,879
	CASH AND CASH EQUIVALENTS, END OF PERIOD	$	3,676		$	8,299		$	662,128		$	—		$	674,103

Basis_of_Preparation_and_Conso2

Basis of Preparation and Consolidation (Details)	0 Months Ended
	1-May-14
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Stockholders' Equity Note, Stock Split, Conversion Ratio	3

Investments_Narrative_Details

Investments (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2014
	Other invested assets [Member]	Minimum [Member]	Minimum [Member]	Maximum [Member]	Maximum [Member]
		Investments with redemption restrictions [Member]	Investments without redemption restrictions [Member]	Investments with redemption restrictions [Member]	Investments without redemption restrictions [Member]
			Hedge Funds [Member]		Hedge Funds [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	'	'3 years	'
Redemption notice period	'	'	'P30D	'	'
Gate trigger, percentage	'	'	15.00%	'	25.00%
Loss on equity method investments	($9,348)	'	'	'	'

Investments_Schedule_Of_Tradin

Investments (Schedule Of Trading Securities) (Details) (USD $)	Jun. 30, 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	$1,742,622	$1,463,927
Trading securities, Amortized Cost	1,579,231	1,305,984
Equity securities [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	938,117	699,846
Trading securities, Amortized Cost	885,861	647,301
Other invested assets [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	804,505	764,081
Trading securities, Amortized Cost	693,370	658,683
Fixed Maturities [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	6,157,084	6,100,798
Trading securities, Amortized Cost	6,062,758	6,065,350
U.S. Government And Government Agencies [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	1,274,331	1,676,788
Trading securities, Amortized Cost	1,273,469	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	185,071	191,776
Trading securities, Amortized Cost	186,142	197,082
States, Municipalities And Political Subdivisions [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	261,267	231,555
Trading securities, Amortized Cost	256,698	234,406
Corporate Debt, Financial Institutions [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	1,168,937	958,794
Trading securities, Amortized Cost	1,149,005	943,518
Corporate Debt, Industrials [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	1,167,470	1,174,047
Trading securities, Amortized Cost	1,152,858	1,165,448
Corporate Debt, Utilities [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	98,878	69,426
Trading securities, Amortized Cost	97,457	69,658
Mortgage-Backed [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	1,323,763	1,292,502
Trading securities, Amortized Cost	1,272,824	1,267,863
Asset-Backed [Member]	'	'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'	'
Trading securities, Fair Value	677,367	505,910
Trading securities, Amortized Cost	$674,305	$502,543

Investments_Schedule_Of_Other_

Investments (Schedule Of Other Investments) (Details) (USD $)	6 Months Ended				12 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	$932,639		'		$911,392
Unfunded Commitments	451,494		'		467,524
Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	490,658		'		368,052
Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	441,981		'		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		'		'
Total Fair Value [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	804,505		'		764,081
Unfunded Commitments	451,494		'		467,524
Total Fair Value [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	490,658		'		368,052
Total Fair Value [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	313,847		'		396,029
Total Fair Value [Member] | Private Equity Funds [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	266,837		'		216,825
Unfunded Commitments	451,494		'		467,524
Total Fair Value [Member] | Private Equity Funds [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	266,837		'		216,825
Total Fair Value [Member] | Private Equity Funds [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	0		'		0
Total Fair Value [Member] | Private Equity [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	161,667		'		144,422
Unfunded Commitments	239,697		'		263,519
Total Fair Value [Member] | Private Equity [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	161,667		'		144,422
Total Fair Value [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		'
Total Fair Value [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		'
Total Fair Value [Member] | Private Equity [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	0		'		0
Total Fair Value [Member] | Mezzanine Debt [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	95,162		'		64,627
Unfunded Commitments	206,856		'		198,756
Total Fair Value [Member] | Mezzanine Debt [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	95,162		'		64,627
Total Fair Value [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	'5 years		'8 years		'
Total Fair Value [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		'
Total Fair Value [Member] | Mezzanine Debt [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	0		'		0
Total Fair Value [Member] | Distressed [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	10,008		'		7,776
Unfunded Commitments	4,941		'		5,249
Total Fair Value [Member] | Distressed [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	10,008		'		7,776
Estimated remaining restriction period	'4 years		'4 years		'
Total Fair Value [Member] | Distressed [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	0		'		0
Total Fair Value [Member] | Hedge Funds [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	505,176		'		515,298
Unfunded Commitments	0		'		0
Total Fair Value [Member] | Hedge Funds [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	223,821		'		151,227
Total Fair Value [Member] | Hedge Funds [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	281,355		'		364,071
Total Fair Value [Member] | Distressed Funds [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	165,253		'		151,227
Unfunded Commitments	0		'		0
Total Fair Value [Member] | Distressed Funds [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	165,253		'		151,227
Estimated remaining restriction period	'1 year		'		'
Total Fair Value [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		'
Total Fair Value [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		'
Total Fair Value [Member] | Distressed Funds [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	0		'		0
Total Fair Value [Member] | Equity Long/Short [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	134,036		'		99,365
Unfunded Commitments	0		'		0
Total Fair Value [Member] | Equity Long/Short [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	58,568		'		0
Estimated remaining restriction period	'1 year		'		'
Total Fair Value [Member] | Equity Long/Short [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	75,468		'		99,365
Redemption frequency	'Quarterly	[1]	'		'Quarterly	[1]
Total Fair Value [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]	'
Total Fair Value [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]	'
Total Fair Value [Member] | Multi-Strategy Funds [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	100,263		'		136,958
Unfunded Commitments	0		'		0
Total Fair Value [Member] | Multi-Strategy Funds [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	0		'		0
Total Fair Value [Member] | Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	100,263		'		136,958
Redemption frequency	'Quarterly	[1]	'		'Quarterly	[1]
Total Fair Value [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]	'
Total Fair Value [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]	'
Total Fair Value [Member] | Event Driven Funds [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	'		'		14,018
Unfunded Commitments	'		'		0
Total Fair Value [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
Total Fair Value [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	'		'		14,018
Redemption frequency	'		'		'Annual	[1]
Redemption notice period	'		'P60D	[1]	'
Total Fair Value [Member] | Relative Value Credit [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	105,624		'		113,730
Unfunded Commitments	0		'		0
Total Fair Value [Member] | Relative Value Credit [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	0		'		0
Total Fair Value [Member] | Relative Value Credit [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	105,624		'		113,730
Redemption frequency	'Quarterly	[1]	'		'Quarterly	[1]
Redemption notice period	'P60D	[1]	'P60D		'
Total Fair Value [Member] | High Yield Loan Fund [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	32,492		'		31,958
Unfunded Commitments	0		'		0
Total Fair Value [Member] | High Yield Loan Fund [Member] | Investments with redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	0		'		0
Total Fair Value [Member] | High Yield Loan Fund [Member] | Investments without redemption restrictions [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	32,492		'		31,958
Redemption frequency	'Monthly	[1]	'		'Monthly	[1]
Redemption notice period	'P30D	[1]	'P30D	[1]	'
Carrying Value [Member] | Other Private Securities [Member]	'		'		'
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]	'		'		'
Other invested assets	128,134		'		147,311
Unfunded Commitments	0		'		0
Carrying Value [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 Value [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	$128,134		'		$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 as described below.

Investments_Schedule_Of_Net_In

Investments (Schedule Of Net Investment Income) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net Investment Income [Line Items]	'	'	'	'
Net investment income	$36,793	$37,635	$84,412	$71,023
Fixed maturity investments [Member]	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Net investment income	35,936	32,662	72,235	65,187
Equity securities [Member]	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Net investment income	5,912	4,409	9,165	7,608
Other invested assets [Member]	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Net investment income	-890	3,843	10,518	5,307
Cash and cash equivalents [Member]	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Net investment income	571	529	1,010	1,017
Expenses [Member]	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Net investment income	($4,736)	($3,808)	($8,516)	($8,096)

Investments_Components_Of_Real

Investments (Components Of Realized Gains And Losses) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on sale of invested assets	$55,714	$58,223	$118,006	$102,472
Gross realized losses on sale of invested assets	-4,025	-35,077	-16,273	-42,042
Net realized and unrealized losses on derivatives	-13,720	8,538	-26,640	7,561
Net realized investment gains	85,217	-115,198	139,422	-35,561
Debt Securities [Member]	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Mark-to-market changes	36,426	-115,113	58,882	-131,588
Equity securities [Member]	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Mark-to-market changes	21,316	-34,330	-289	-1,357
Other invested assets [Member]	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Mark-to-market changes	($10,494)	$2,561	$5,736	$29,393

Investments_Pledged_Assets_Det

Investments (Pledged Assets) (Details) (USD $)	Jun. 30, 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	$2,745,352	$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	$886,220	$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 $)	Jun. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Derivatives, Fair Value [Line Items]	'	'
Asset Derivative Notional Amount	$162,761	$786,188
Asset Derivative Fair Value	517	13,083
Liability Derivative Notional Amount	823,262	162,439
Liability Derivative Fair Value	3,122	5,390
Foreign exchange contracts | Other assets	'	'
Derivatives, Fair Value [Line Items]	'	'
Asset Derivative Notional Amount	57,761	294,788
Asset Derivative Fair Value	430	6,254
Foreign exchange contracts | Accounts payable and accrued liabilities	'	'
Derivatives, Fair Value [Line Items]	'	'
Liability Derivative Notional Amount	158,762	122,439
Liability Derivative Fair Value	1,996	1,176
Interest rate swaps | Other assets	'	'
Derivatives, Fair Value [Line Items]	'	'
Asset Derivative Notional Amount	105,000	491,400
Asset Derivative Fair Value	87	6,829
Interest rate swaps | Accounts payable and accrued liabilities	'	'
Derivatives, Fair Value [Line Items]	'	'
Liability Derivative Notional Amount	664,500	40,000
Liability Derivative Fair Value	$1,126	$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		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Total realized and unrealized losses on derivatives	($15,318)	$10,527	($29,106)	$8,806
Foreign exchange (loss) gain	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Total realized and unrealized losses on derivatives	-1,598	1,989	-2,466	1,245
Foreign exchange (loss) gain | Foreign exchange contracts	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Total realized and unrealized losses on derivatives	-1,598	1,989	-2,466	1,245
Net realized investment gains	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Total realized and unrealized losses on derivatives	-13,720	8,538	-26,640	7,561
Net realized investment gains | Put options	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Total realized and unrealized losses on derivatives	0	-90	0	-3,822
Net realized investment gains | Foreign exchange contracts	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Total realized and unrealized losses on derivatives	-286	4,274	-844	6,089
Net realized investment gains | Interest rate futures	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Total realized and unrealized losses on derivatives	($13,434)	$4,354	($25,796)	$5,294

Fair_Value_Of_Financial_Instru2

Fair Value Of Financial Instruments (Schedule Of Fair Value Of Financial Instruments) (Details) (USD $)	Jun. 30, 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	$6,157,084	$6,100,798
Equity securities	938,117	699,846
Other invested assets	932,639	911,392
Total investments	8,027,840	7,712,036
Senior notes	798,648	798,499
Fair Value, Measurements, Recurring [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Trading fixed maturity investments	6,157,084	6,100,798
Equity securities	938,117	699,846
Other invested assets	804,505	764,081
Total investments	7,899,706	7,564,725
Senior notes	798,648	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	430	6,254
Derivative liabilities	1,996	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	87	6,829
Derivative liabilities	1,126	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	1,274,331	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	185,071	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	261,267	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	2,435,285	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	1,323,763	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	677,367	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	6,157,084	6,100,798
Equity securities	938,117	699,846
Other invested assets	804,505	764,081
Total investments	7,899,706	7,564,725
Senior notes	907,005	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	430	6,254
Derivative liabilities	1,996	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	87	6,829
Derivative liabilities	1,126	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	1,274,331	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	185,071	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	261,267	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	2,435,285	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	1,323,763	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	677,367	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	1,058,607	1,370,088
Equity securities	903,254	625,942
Other invested assets	0	0
Total investments	1,961,861	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	1,058,607	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
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	4,880,444	4,489,959
Equity securities	0	0
Other invested assets	0	0
Total investments	4,880,444	4,489,959
Senior notes	907,005	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	430	6,254
Derivative liabilities	1,996	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	87	6,829
Derivative liabilities	1,126	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	215,724	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	185,071	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	261,267	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	2,435,285	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	1,176,962	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	606,135	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	218,033	240,751
Equity securities	34,863	73,904
Other invested assets	804,505	764,081
Total investments	1,057,401	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	146,801	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	$71,232	$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				6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Other invested assets [Member]	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'		'
Opening balance	$839,986		$710,140		$764,081		$655,888
Realized and unrealized gains (losses) included in net income	22,498		11,709		45,124		43,962
Purchases	99,722		96,742		188,920		169,952
Sales	-157,701		-104,200		-193,620		-155,411
Transfers into Level 3 from Level 2	0		0		0		0
Transfers out of Level 3 to Level 2	0	[1]	0	[1]	0	[1]	0	[1]
Ending balance	804,505		714,391		804,505		714,391
Mortgage-Backed [Member]	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'		'
Opening balance	134,061		155,420		147,338		167,825
Realized and unrealized gains (losses) included in net income	2,721		-6,188		4,479		-7,613
Purchases	20,928		72,261		50,840		71,752
Sales	-26,734		-27,887		-54,419		-29,864
Transfers into Level 3 from Level 2	17,437		11,197		103		7,109
Transfers out of Level 3 to Level 2	-1,612	[1]	-6,800	[1]	-1,540	[1]	-11,206	[1]
Ending balance	146,801		198,003		146,801		198,003
Asset-Backed [Member]	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'		'
Opening balance	81,234		40,903		93,413		62,246
Realized and unrealized gains (losses) included in net income	450		-289		-355		-382
Purchases	9,409		23,527		16,938		24,782
Sales	-3,743		-1,727		-8,225		-18,478
Transfers into Level 3 from Level 2	0		0		0		0
Transfers out of Level 3 to Level 2	-16,118	[1]	-1,129	[1]	-30,539	[1]	-6,883	[1]
Ending balance	71,232		61,285		71,232		61,285
Equity securities [Member]	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'		'
Opening balance	34,786		57,787		73,904		54,680
Realized and unrealized gains (losses) included in net income	77		-4,288		-9,744		-1,181
Purchases	0		0		0		0
Sales	0		0		-29,297		0
Transfers into Level 3 from Level 2	0		0		0		0
Transfers out of Level 3 to Level 2	0	[1]	0	[1]	0	[1]	0	[1]
Ending balance	$34,863		$53,499		$34,863		$53,499
[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 $)	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Insurance Loss Reserves [Abstract]	'	'	'	'	'	'
Outstanding loss reserves	$1,543,506	'	$1,520,867	'	'	'
Reserves for losses incurred but not reported	4,392,172	'	4,245,662	'	'	'
Reserve for losses and loss expenses	$5,935,678	$5,856,798	$5,766,529	$5,696,865	$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		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Insurance Loss Reserves [Abstract]	'	'	'	'
Gross liability at beginning of year	$5,856,798	$5,673,220	$5,766,529	$5,645,549
Reinsurance recoverable at beginning of year	-1,280,525	-1,163,503	-1,234,504	-1,141,110
Net liability at beginning of year	4,576,273	4,509,717	4,532,025	4,504,439
Net losses incurred related to:	'	'	'	'
Current year	359,994	323,556	684,141	622,804
Prior years	-45,139	-48,428	-94,000	-92,498
Total incurred	314,855	275,128	590,141	530,306
Net paid losses related to:	'	'	'	'
Current year	23,065	21,003	26,808	24,584
Prior years	235,335	241,764	463,929	482,885
Total paid	258,400	262,767	490,737	507,469
Foreign exchange revaluation	1,208	-4,738	2,507	-9,936
Net liability at end of year	4,633,936	4,517,340	4,633,936	4,517,340
Reinsurance recoverable at end of year	1,301,742	1,179,525	1,301,742	1,179,525
Gross liability at end of year	$5,935,678	$5,696,865	$5,935,678	$5,696,865

Shareholders_Equity_Issued_Sha

Shareholders' Equity (Issued Share Capital) (Details)	Jun. 30, 2014	Jun. 30, 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 4.10 per share; 2013: CHF 4.10 per share	99,515,760	99,515,760	103,477,452	103,477,452
Common shares, par value	'	4.1	'	4.1
Total share capital	$402,907	'	$418,988	'

Shareholders_Equity_Schedule_O

Shareholders' Equity (Schedule Of Common Stock Outstanding Roll Forward) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'	'	'	'	'
Shares issued at beginning of year	'	'	103,477,452	'	'
Shares cancelled, shares	'	'	-3,961,692	'	'
Shares issued at end of year	99,515,760	'	99,515,760	'	'
Treasury Stock Transactions, Excluding Value of Shares Reissued [Abstract]	'	'	'	'	'
Treasury shares issued at beginning of year	'	'	3,223,806	'	'
Shares repurchased, shares	1,949,496	1,524,984	3,961,692	2,821,335	'
Shares issued out of treasury, shares	'	'	-637,137	'	'
Shares cancelled, shares	'	'	-3,961,692	'	'
Total treasury shares at end of year	2,586,669	'	2,586,669	'	'
Total shares outstanding at end of year	96,929,091	'	96,929,091	'	100,253,646

Shareholders_Equity_Schedule_O1

Shareholders' Equity (Schedule Of Dividends Paid) (Details) (USD $)	3 Months Ended		6 Months Ended		0 Months Ended			1 Months Ended		0 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	1-May-14	Apr. 03, 2014	Jan. 02, 2014	Oct. 31, 2013	Jul. 31, 2013	Jul. 02, 2014
					Common shares	Common shares	Common shares	Common shares	Common shares	Subsequent event
										Common shares
Dividends, Common Stock [Abstract]	'	'	'	'	'	'	'	'	'	'
Dividends paid per common share	$0.17	$0	$0.33	$0.13	'	$0.17	$0.17	$0.17	$0.17	$0.23
Payment of quarterly dividends	'	'	'	'	'	$16,495	$16,732	'	'	'
Dividends declared per share	'	'	'	'	$0.23	'	'	'	'	'

Shareholders_Equity_Schedule_O2

Shareholders' Equity (Schedule Of Share Repurchases) (Details) (USD $)	0 Months Ended	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	1-May-14	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Stockholders' Equity Note [Abstract]	'	'	'	'	'
Stock Repurchase Program, Authorized Amount	$500,000	'	'	'	'
Shares repurchased, shares	'	1,949,496	1,524,984	3,961,692	2,821,335
Cost of shares repurchased	'	$70,874	$46,326	$139,532	$82,571
Shares repurchased, average price per share	'	$36.36	$30.38	$35.22	$29.27
Treasury shares held for issuance pursuant to equity-based compensation plans	3,000,000	'	'	'	'

Employee_Benefit_Plans_Restric

Employee Benefit Plans (Restricted Stock Units) (Details) (USD $)	12 Months Ended	6 Months Ended
	Dec. 31, 2013	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 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	'	143,697	804,519	'	'	'
Granted, shares	'	454,176	166,302	'	'	'
Additional awards granted due to achievement of performance criteria, shares	'	'	104,895	'	'	'
Forfeited, shares	'	-5,097	-1,848	'	'	'
Fully vested, shares	'	-76,230	-454,440	'	'	'
Outstanding, end of year, shares	'	516,546	619,428	'	'	'
Weighted average grant date fair value:	'	'	'	'	'	'
Outstanding, beginning of year - weighted average grant date fair value	'	$21.69	$23.21	'	'	'
Granted - weighted average grant date fair value	'	$33.56	$33.56	'	'	'
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	'	'	($20.50)	'	'	'
Forfeited - weighted average grant date fair value	'	($30.64)	($25.28)	'	'	'
Vested - weighted average grant date fair value	'	($21.75)	($20.50)	'	'	'
Outstanding, end of year - weighted average grant date fair value	'	$32.03	$27.51	'	'	'
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%	135.00%

Employee_Benefit_Plans_CashEqu

Employee Benefit Plans (Cash-Equivalent Stock Awards) (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Cash Equivalent Stock Awards Rsus [Member]	'	'
Activity:	'	'
Outstanding, beginning of year, shares	2,049,084	'
Granted, shares	438,162	'
Additional awards granted due to achievement of performance criteria, shares	0	'
Forfeited, shares	-38,886	'
Fully vested, shares	-751,920	'
Outstanding, end of year, shares	1,696,440	2,049,084
Weighted average grant date fair value:	'	'
Outstanding, beginning of year - weighted average grant date fair value	$24.69	'
Granted - weighted average grant date fair value	$33.56	'
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	$0	'
Forfeited - weighted average grant date fair value	($26.36)	'
Vested - weighted average grant date fair value	($22.47)	'
Outstanding, end of year - weighted average grant date fair value	$27.93	$24.69
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]	'	'
Vesting period	'	'4 years
Cash Equivalent Stock Awards Performance Based [Member]	'	'
Activity:	'	'
Outstanding, beginning of year, shares	1,031,961	'
Granted, shares	249,438	'
Additional awards granted due to achievement of performance criteria, shares	104,895	'
Forfeited, shares	-2,769	'
Fully vested, shares	-454,440	'
Outstanding, end of year, shares	929,085	1,031,961
Weighted average grant date fair value:	'	'
Outstanding, beginning of year - weighted average grant date fair value	$23.67	'
Granted - weighted average grant date fair value	$33.56	'
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	$20.50	'
Forfeited - weighted average grant date fair value	($25.28)	'
Vested - weighted average grant date fair value	($20.50)	'
Outstanding, end of year - weighted average grant date fair value	$27.51	$23.67
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]	'	'
Vesting period	'	'3 years

Employee_Benefit_Plans_Other_D

Employee Benefit Plans (Other Details) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Share-based compensation expense	$16,258	$10,782	$25,127	$27,533
Employee Stock Option [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Share-based compensation expense	413	679	1,140	2,014
Restricted Stock Units (RSUs) [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Share-based compensation expense	2,977	1,891	6,490	4,551
Cash Equivalent Stock Awards [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Share-based compensation expense	$12,868	$8,212	$17,497	$20,968

Earnings_Per_Share_Narrative_D

Earnings Per Share (Narrative) (Details) (Stock Compensation Plan [Member])	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 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	0	0	0	0

Earnings_Per_Share_Comparison_

Earnings Per Share (Comparison Of Basic And Diluted Earnings Per Share) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share, Basic [Abstract]	'	'	'	'
Net income	$151,863	($1,862)	$328,835	$157,130
Weighted average common shares outstanding	97,809,639	103,267,659	98,672,618	103,552,656
Basic earnings per share	$1.55	($0.02)	$3.33	$1.52
Earnings Per Share, Diluted [Abstract]	'	'	'	'
Net income	$151,863	($1,862)	$328,835	$157,130
Weighted average common shares outstanding	97,809,639	103,267,659	98,672,618	103,552,656
Share equivalents:	'	'	'	'
Warrants and options	1,448,071	0	1,456,439	1,479,675
RSUs and LTIP awards	455,744	0	550,224	913,587
Employee share purchase plan	11,348	0	12,287	3,867
Weighted average common shares and common share equivalents outstanding - diluted	99,724,802	103,267,659	100,691,568	105,949,785
Diluted earnings per share	$1.52	($0.02)	$3.27	$1.48

Segment_Information_Summary_Of

Segment Information (Summary Of Segment Results) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
			segments
Segment Reporting Information [Line Items]	'	'	'	'
Gross premiums written	$760,405	$765,200	$1,661,798	$1,602,281
Net premiums written	553,924	581,222	1,325,538	1,276,274
Net premiums earned	537,247	507,271	1,067,532	970,499
Net losses and loss expenses	-314,855	-275,128	-590,141	-530,306
Acquisition costs	-74,279	-64,617	-142,001	-121,302
General and administrative expenses	-96,188	-80,585	-176,528	-163,265
Underwriting income (loss)	51,925	86,941	158,862	155,626
Net investment income	36,793	37,635	84,412	71,023
Net realized investment gains	85,217	-115,198	139,422	-35,561
Amortization of intangible assets	-634	-634	-1,267	-1,267
Interest expense	-14,592	-14,188	-29,126	-28,322
Foreign exchange loss	-651	-490	-700	-3,008
Income before income taxes	158,058	-5,934	351,603	158,491
Loss and loss expense ratio	58.60%	54.20%	55.30%	54.60%
Acquisition cost ratio	13.80%	12.70%	13.30%	12.50%
General and administrative expense ratio	17.90%	15.90%	16.50%	16.80%
Expense ratio	31.70%	28.60%	29.80%	29.30%
Combined ratio	90.30%	82.80%	85.10%	83.90%
Number of operating segments	'	'	3	'
Operating Segments [Member] | U S Insurance [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Gross premiums written	341,426	307,297	611,371	563,315
Net premiums written	221,950	221,419	424,690	413,672
Net premiums earned	214,593	197,436	426,716	385,875
Net losses and loss expenses	-145,485	-124,364	-287,480	-257,688
Acquisition costs	-29,677	-27,270	-57,180	-50,398
General and administrative expenses	-46,593	-38,302	-84,030	-77,898
Underwriting income (loss)	-7,162	7,500	-1,974	-109
Loss and loss expense ratio	67.80%	63.00%	67.40%	66.80%
Acquisition cost ratio	13.80%	13.80%	13.40%	13.10%
General and administrative expense ratio	21.70%	19.40%	19.70%	20.20%
Expense ratio	35.50%	33.20%	33.10%	33.30%
Combined ratio	103.30%	96.20%	100.50%	100.10%
Operating Segments [Member] | International Insurance [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Gross premiums written	204,478	192,593	338,842	321,109
Net premiums written	122,171	106,394	197,630	184,139
Net premiums earned	89,205	87,041	177,544	171,255
Net losses and loss expenses	-35,920	-30,968	-59,486	-59,903
Acquisition costs	-575	358	374	1,207
General and administrative expenses	-29,411	-24,135	-54,171	-48,924
Underwriting income (loss)	23,299	32,296	64,261	63,635
Loss and loss expense ratio	40.30%	35.60%	33.50%	35.00%
Acquisition cost ratio	0.60%	-0.40%	-0.20%	-0.70%
General and administrative expense ratio	33.00%	27.70%	30.50%	28.60%
Expense ratio	33.60%	27.30%	30.30%	27.90%
Combined ratio	73.90%	62.90%	63.80%	62.90%
Operating Segments [Member] | Reinsurance [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Gross premiums written	214,501	265,310	711,585	717,857
Net premiums written	209,803	253,409	703,218	678,463
Net premiums earned	233,449	222,794	463,272	413,369
Net losses and loss expenses	-133,450	-119,796	-243,175	-212,715
Acquisition costs	-44,027	-37,705	-85,195	-72,111
General and administrative expenses	-20,184	-18,148	-38,327	-36,443
Underwriting income (loss)	$35,788	$47,145	$96,575	$92,100
Loss and loss expense ratio	57.20%	53.80%	52.50%	51.50%
Acquisition cost ratio	18.90%	16.90%	18.40%	17.40%
General and administrative expense ratio	8.60%	8.10%	8.30%	8.80%
Expense ratio	27.50%	25.00%	26.70%	26.20%
Combined ratio	84.70%	78.80%	79.20%	77.70%

Segment_Information_Gross_Prem

Segment Information (Gross Premiums Written By Geographic Location) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	$760,405	$765,200	$1,661,798	$1,602,281
United States	'	'	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	442,549	440,151	963,321	918,594
Bermuda	'	'	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	185,872	211,040	415,503	439,712
Europe	'	'	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	77,985	60,234	181,321	146,743
Singapore	'	'	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	45,375	48,918	87,316	87,031
Hong Kong	'	'	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	3,756	4,857	8,639	10,201
Canada	'	'	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	3,094	0	3,924	0
Australia	'	'	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	1,774	0	1,774	0
Switzerland	'	'	'	'
Revenues from External Customers and Long-Lived Assets [Line Items]	'	'	'	'
Gross premiums written	$10,261	$5,868	$54,554	$46,674

Segment_Information_Narrative_

Segment Information (Narrative) (Details) (Operating Segments [Member], U S Insurance [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014
Operating Segments [Member] | U S Insurance [Member]	'
Segment Reporting Information [Line Items]	'
Goodwill, Acquired During Period	$9,385

Commitments_And_Contingencies_

Commitments And Contingencies (Details) (Switzerland, CHF)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 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 $)	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
ASSETS:	'	'	'	'	'	'
Investments	$8,027,840	'	$7,712,036	'	'	'
Cash and cash equivalents	635,138	'	531,936	674,103	'	681,879
Insurance balances receivable	976,441	'	664,731	'	'	'
Funds held	414,445	'	632,430	'	'	'
Reinsurance recoverable	1,301,742	1,280,525	1,234,504	1,179,525	1,163,503	1,141,110
Net deferred acquisition costs	163,259	'	126,661	'	'	'
Goodwill and intangible assets	325,325	'	317,207	'	'	'
Balances receivable on sale of investments	164,713	'	76,544	'	'	'
Investments in subsidiaries	0	'	0	'	'	'
Due from subsidiaries	0	'	0	'	'	'
Other assets	660,744	'	649,781	'	'	'
Total assets	12,669,647	'	11,945,830	'	'	'
LIABILITIES:	'	'	'	'	'	'
Reserve for losses and loss expenses	5,935,678	5,856,798	5,766,529	5,696,865	5,673,220	5,645,549
Unearned premiums	1,703,684	'	1,396,256	'	'	'
Reinsurance balances payable	224,182	'	173,023	'	'	'
Balances due on purchases of investments	180,378	'	104,740	'	'	'
Senior notes	798,648	'	798,499	'	'	'
Due to subsidiaries	0	'	0	'	'	'
Other liabilities	144,315	'	186,957	'	'	'
Total liabilities	8,986,885	'	8,426,004	'	'	'
Total shareholders’ equity	3,682,762	'	3,519,826	3,373,229	'	3,326,335
Total liabilities and shareholders’ equity	12,669,647	'	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	-7,801,785	'	-7,431,620	'	'	'
Due from subsidiaries	-110,208	'	-357,497	'	'	'
Other assets	0	'	0	'	'	'
Total assets	-7,911,993	'	-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	-110,208	'	-357,497	'	'	'
Other liabilities	0	'	0	'	'	'
Total liabilities	-110,208	'	-357,497	'	'	'
Total shareholders’ equity	-7,801,785	'	-7,431,620	'	'	'
Total liabilities and shareholders’ equity	-7,911,993	'	-7,789,117	'	'	'
Allied World Switzerland (Parent Guarantor) [Member]	'	'	'	'	'	'
ASSETS:	'	'	'	'	'	'
Investments	0	'	0	'	'	'
Cash and cash equivalents	40,976	'	10,790	3,676	'	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	3,600,731	'	3,413,001	'	'	'
Due from subsidiaries	75,813	'	111,172	'	'	'
Other assets	1,090	'	1,757	'	'	'
Total assets	3,718,610	'	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	8,373	'	12,945	'	'	'
Other liabilities	27,475	'	3,949	'	'	'
Total liabilities	35,848	'	16,894	'	'	'
Total shareholders’ equity	3,682,762	'	3,519,826	'	'	'
Total liabilities and shareholders’ equity	3,718,610	'	3,536,720	'	'	'
Allied World Bermuda (Subsidiary Issuer) [Member]	'	'	'	'	'	'
ASSETS:	'	'	'	'	'	'
Investments	0	'	0	'	'	'
Cash and cash equivalents	1,286	'	2,775	8,299	'	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	4,201,054	'	4,018,619	'	'	'
Due from subsidiaries	18,859	'	122,846	'	'	'
Other assets	4,026	'	4,671	'	'	'
Total assets	4,225,225	'	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	798,648	'	798,499	'	'	'
Due to subsidiaries	7,163	'	110,534	'	'	'
Other liabilities	17,976	'	17,797	'	'	'
Total liabilities	823,787	'	926,830	'	'	'
Total shareholders’ equity	3,401,438	'	3,222,081	'	'	'
Total liabilities and shareholders’ equity	4,225,225	'	4,148,911	'	'	'
Other Allied World Subsidiaries [Member]	'	'	'	'	'	'
ASSETS:	'	'	'	'	'	'
Investments	8,027,840	'	7,712,036	'	'	'
Cash and cash equivalents	592,876	'	518,371	662,128	'	650,558
Insurance balances receivable	976,441	'	664,731	'	'	'
Funds held	414,445	'	632,430	'	'	'
Reinsurance recoverable	1,301,742	'	1,234,504	'	'	'
Net deferred acquisition costs	163,259	'	126,661	'	'	'
Goodwill and intangible assets	325,325	'	317,207	'	'	'
Balances receivable on sale of investments	164,713	'	76,544	'	'	'
Investments in subsidiaries	0	'	0	'	'	'
Due from subsidiaries	15,536	'	123,479	'	'	'
Other assets	655,628	'	643,353	'	'	'
Total assets	12,637,805	'	12,049,316	'	'	'
LIABILITIES:	'	'	'	'	'	'
Reserve for losses and loss expenses	5,935,678	'	5,766,529	'	'	'
Unearned premiums	1,703,684	'	1,396,256	'	'	'
Reinsurance balances payable	224,182	'	173,023	'	'	'
Balances due on purchases of investments	180,378	'	104,740	'	'	'
Senior notes	0	'	0	'	'	'
Due to subsidiaries	94,672	'	234,018	'	'	'
Other liabilities	98,864	'	165,211	'	'	'
Total liabilities	8,237,458	'	7,839,777	'	'	'
Total shareholders’ equity	4,400,347	'	4,209,539	'	'	'
Total liabilities and shareholders’ equity	$12,637,805	'	$12,049,316	'	'	'

Condensed_Consolidated_Guarant3

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Income Statement) (Details) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Condensed Income Statements, Captions [Line Items]	'	'	'	'
Net premiums earned	$537,247	$507,271	$1,067,532	$970,499
Net investment income	36,793	37,635	84,412	71,023
Net realized investment gains (losses)	85,217	-115,198	139,422	-35,561
Net losses and loss expenses	-314,855	-275,128	-590,141	-530,306
Acquisition costs	-74,279	-64,617	-142,001	-121,302
General and administrative expenses	-96,188	-80,585	-176,528	-163,265
Amortization of intangible assets	-634	-634	-1,267	-1,267
Interest expense	-14,592	-14,188	-29,126	-28,322
Foreign exchange loss	-651	-490	-700	-3,008
Income tax (expense) benefit	-6,195	4,072	-22,768	-1,361
Equity in earnings of consolidated subsidiaries	0	0	0	0
NET INCOME	151,863	-1,862	328,835	157,130
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	151,863	-1,862	328,835	157,130
Consolidation, Eliminations [Member]	'	'	'	'
Condensed Income Statements, Captions [Line Items]	'	'	'	'
Net premiums earned	0	0	0	0
Net investment income	0	0	0	0
Net realized investment gains (losses)	0	0	0	0
Net losses and loss expenses	0	0	0	0
Acquisition costs	0	0	0	0
General and administrative expenses	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	0	0	0	0
Foreign exchange loss	0	0	0	0
Income tax (expense) benefit	0	0	0	0
Equity in earnings of consolidated subsidiaries	-333,149	-27,848	-718,451	-379,027
NET INCOME	-333,149	-27,848	-718,451	-379,027
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	-333,149	-27,848	-718,451	-379,027
Allied World Switzerland (Parent Guarantor) [Member]	'	'	'	'
Condensed Income Statements, Captions [Line Items]	'	'	'	'
Net premiums earned	0	0	0	0
Net investment income	2	1	4	8
Net realized investment gains (losses)	0	0	0	0
Net losses and loss expenses	0	0	0	0
Acquisition costs	0	0	0	0
General and administrative expenses	-10,813	-8,566	-19,727	-19,552
Amortization of intangible assets	0	0	0	0
Interest expense	0	0	0	0
Foreign exchange loss	-2	2	-4	274
Income tax (expense) benefit	323	0	-86	0
Equity in earnings of consolidated subsidiaries	162,353	6,701	348,648	176,400
NET INCOME	151,863	-1,862	328,835	157,130
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	151,863	-1,862	328,835	157,130
Allied World Bermuda (Subsidiary Issuer) [Member]	'	'	'	'
Condensed Income Statements, Captions [Line Items]	'	'	'	'
Net premiums earned	0	0	0	0
Net investment income	0	2	0	4
Net realized investment gains (losses)	0	0	0	0
Net losses and loss expenses	0	0	0	0
Acquisition costs	0	0	0	0
General and administrative expenses	1,654	-455	-737	-912
Amortization of intangible assets	0	0	0	0
Interest expense	-13,853	-13,835	-27,700	-27,665
Foreign exchange loss	-12	-628	21	-723
Income tax (expense) benefit	0	0	0	0
Equity in earnings of consolidated subsidiaries	170,796	21,147	369,803	202,627
NET INCOME	158,585	6,231	341,387	173,331
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	158,585	6,231	341,387	173,331
Other Allied World Subsidiaries [Member]	'	'	'	'
Condensed Income Statements, Captions [Line Items]	'	'	'	'
Net premiums earned	537,247	507,271	1,067,532	970,499
Net investment income	36,791	37,632	84,408	71,011
Net realized investment gains (losses)	85,217	-115,198	139,422	-35,561
Net losses and loss expenses	-314,855	-275,128	-590,141	-530,306
Acquisition costs	-74,279	-64,617	-142,001	-121,302
General and administrative expenses	-87,029	-71,564	-156,064	-142,801
Amortization of intangible assets	-634	-634	-1,267	-1,267
Interest expense	-739	-353	-1,426	-657
Foreign exchange loss	-637	136	-717	-2,559
Income tax (expense) benefit	-6,518	4,072	-22,682	-1,361
Equity in earnings of consolidated subsidiaries	0	0	0	0
NET INCOME	174,564	21,617	377,064	205,696
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	$174,564	$21,617	$377,064	$205,696

Condensed_Consolidated_Guarant4

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Cash Flows) (Details) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Condensed Cash Flow Statements, Captions [Line Items]	'	'
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$452,108	$125,906
CASH FLOWS USED IN INVESTING ACTIVITIES:	'	'
Purchases of trading securities	-3,905,650	-3,186,162
Purchases of other invested assets	-181,419	-141,805
Sales of trading securities	3,705,229	3,171,977
Sales of other invested assets	184,166	126,491
Other	13,472	-13,924
Net cash used in investing activities	-184,202	-43,423
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	-33,207	0
Dividends paid - par value reduction	0	-12,981
Proceeds from the exercise of stock options	6,313	5,293
Share repurchases	-137,810	-82,571
Net cash used in financing activities	-164,704	-90,259
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	103,202	-7,776
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	531,936	681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	635,138	674,103
Consolidation, Eliminations [Member]	'	'
Condensed Cash Flow Statements, Captions [Line Items]	'	'
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	0	0
CASH FLOWS USED IN INVESTING ACTIVITIES:	'	'
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash used in investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	0	'
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 (DECREASE) 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:	194,890	73,938
CASH FLOWS USED IN INVESTING ACTIVITIES:	'	'
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash used in investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	-33,207	'
Dividends paid - par value reduction	'	-12,981
Proceeds from the exercise of stock options	6,313	5,293
Share repurchases	-137,810	-82,571
Net cash used in financing activities	-164,704	-90,259
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	30,186	-16,321
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790	19,997
CASH AND CASH EQUIVALENTS, END OF PERIOD	40,976	3,676
Allied World Bermuda (Subsidiary Issuer) [Member]	'	'
Condensed Cash Flow Statements, Captions [Line Items]	'	'
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	-1,489	-3,025
CASH FLOWS USED IN INVESTING ACTIVITIES:	'	'
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash used in investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:	'	'
Dividends paid	0	'
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 (DECREASE) IN CASH AND CASH EQUIVALENTS	-1,489	-3,025
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	2,775	11,324
CASH AND CASH EQUIVALENTS, END OF PERIOD	1,286	8,299
Other Allied World Subsidiaries [Member]	'	'
Condensed Cash Flow Statements, Captions [Line Items]	'	'
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	258,707	54,993
CASH FLOWS USED IN INVESTING ACTIVITIES:	'	'
Purchases of trading securities	-3,905,650	-3,186,162
Purchases of other invested assets	-181,419	-141,805
Sales of trading securities	3,705,229	3,171,977
Sales of other invested assets	184,166	126,491
Other	13,472	-13,924
Net cash used in investing activities	-184,202	-43,423
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 (DECREASE) IN CASH AND CASH EQUIVALENTS	74,505	11,570
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	518,371	650,558
CASH AND CASH EQUIVALENTS, END OF PERIOD	$592,876	$662,128

Condensed_Consolidated_Guarant5

Condensed Consolidated Guarantor Financial Statements (Notes to Consolidated Guarantor Financial Statements) (Details) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Investments in subsidiaries	$0	'	$0	'
Total shareholders’ equity	3,682,762	3,373,229	3,519,826	3,326,335
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	205,000	155,000	'	'
Allied World Bermuda (Subsidiary Issuer) [Member]	'	'	'	'
Investments in subsidiaries	4,201,054	'	4,018,619	'
Total shareholders’ equity	3,401,438	'	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		6 Months Ended		0 Months Ended		1 Months Ended		0 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Apr. 03, 2014	Jan. 02, 2014	Oct. 31, 2013	Jul. 31, 2013	Jul. 02, 2014
					Common shares	Common shares	Common shares	Common shares	Common shares
									Subsequent event
Subsequent Event [Line Items]	'	'	'	'	'	'	'	'	'
Dividends paid per common share	$0.17	$0	$0.33	$0.13	$0.17	$0.17	$0.17	$0.17	$0.23