Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Cash Flows) (Details) (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Condensed Consolidated Financial Statements Cash Flow [Line Items]
Net income	$ 91,448	$ 572,219
Stock compensation expense	16,917	25,177
Amortization of discount on senior notes	185	98
Other assets	(182,658)	(362,283)
Accounts payable and accrued liabilities	571,548	174,344
Interest payable	(5,250)	9,375
Net cash provided by (used in) operating activities	492,190	418,930
Purchases of fixed maturity investments - available for sale	(727)	(138,918)
Purchases of fixed maturity investments - trading	(5,209,039)	(8,739,173)
Purchases of equity securities and other invested assets	(611,930)	(261,178)
Sales of fixed maturity investments - available for sale	627,392	2,057,431
Sales of fixed maturity investments - trading	4,772,552	7,583,380
Sale of equity securities and other invested assets	109,157	8,579
Other	55,328	(290,404)
Net cash used in investing activities	(257,267)	219,717
Dividends paid		(28,774)
Dividends paid - par value reduction	(14,295)
Proceeds from the exercise of stock options	5,317	7,053
Share repurchases	(60,000)	(415,009)
Repurchase of founder warrants	(53,620)	(32,819)
Other		(32,819)
Net cash (used in) provided by financing activities	(122,598)	(469,549)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	112,325	169,098
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	756,995	292,188
CASH AND CASH EQUIVALENTS, END OF PERIOD	869,320	461,286
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Consolidated Financial Statements Cash Flow [Line Items]
Net income	91,448
Equity in earnings of consolidated subsidiaries	(67,035)
Stock compensation expense	650
Other assets	(1,673)
Accounts payable and accrued liabilities	10,928
Interest payable
Net cash provided by (used in) operating activities	34,318
Other	(4,496)
Net cash used in investing activities	(4,496)
Dividends paid - par value reduction	(14,295)
Proceeds from the exercise of stock options	5,317
Share repurchases	(60,000)
Other	(391)
Net cash (used in) provided by financing activities	(69,369)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(39,547)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	138,488
CASH AND CASH EQUIVALENTS, END OF PERIOD	98,941
Allied World Bermuda (Subsidiary Issuer) [Member]
Condensed Consolidated Financial Statements Cash Flow [Line Items]
Net income	66,761	572,219
Equity in earnings of consolidated subsidiaries	(114,243)	(613,996)
Dividends received from subsidiaries		540,000
Stock compensation expense		428
Amortization of discount on senior notes	185	98
Other assets	(871)	(443)
Accounts payable and accrued liabilities	740	(16,615)
Interest payable	(5,250)	9,375
Net cash provided by (used in) operating activities	(52,678)	491,066
Other		(2,097)
Net cash used in investing activities		(2,097)
Dividends paid		(28,774)
Proceeds from the exercise of stock options		7,053
Share repurchases		(415,009)
Repurchase of founder warrants	(53,620)
Other	(820)	(32,819)
Net cash (used in) provided by financing activities	(54,440)	(469,549)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(107,118)	19,420
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	125,663	53,849
CASH AND CASH EQUIVALENTS, END OF PERIOD	18,545	73,269
Other Allied World Subsidiaries [Member]
Condensed Consolidated Financial Statements Cash Flow [Line Items]
Net income	114,517	613,996
Stock compensation expense	16,267	24,749
Other assets	(180,114)	(361,840)
Accounts payable and accrued liabilities	559,880	190,959
Interest payable
Net cash provided by (used in) operating activities	510,550	467,864
Purchases of fixed maturity investments - available for sale	(727)	(138,918)
Purchases of fixed maturity investments - trading	(5,209,039)	(8,739,173)
Purchases of equity securities and other invested assets	(611,930)	(261,178)
Sales of fixed maturity investments - available for sale	627,392	2,057,431
Sales of fixed maturity investments - trading	4,772,552	7,583,380
Sale of equity securities and other invested assets	109,157	8,579
Other	59,824	(288,307)
Net cash used in investing activities	(252,771)	221,814
Dividends paid		(540,000)
Other	1,211
Net cash (used in) provided by financing activities	1,211	(540,000)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	258,990	149,678
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	492,844	238,339
CASH AND CASH EQUIVALENTS, END OF PERIOD	751,834	388,017
Consolidating Adjustments [Member]
Condensed Consolidated Financial Statements Cash Flow [Line Items]
Net income	(181,278)	(613,996)
Equity in earnings of consolidated subsidiaries	181,278	613,996
Dividends received from subsidiaries		(540,000)
Interest payable
Net cash provided by (used in) operating activities		(540,000)
Dividends paid		540,000
Net cash (used in) provided by financing activities		$ 540,000