Condensed Consolidated Guarantor Financial Statements (Schedule of Condensed Consolidating Balance Sheet) (Details) (USD $) In Thousands	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009
Investments	$ 7,502,765		$ 7,183,554
Cash and cash equivalents	740,804		756,995	442,689		292,188
Insurance balances receivable	653,002		529,927
Prepaid reinsurance	223,269		187,287
Reinsurance recoverable	1,013,951	975,523	927,588	932,435	920,480	919,991
Net deferred acquisition costs	112,083		96,803
Goodwill	268,376		268,376
Intangible assets	55,342		56,876
Balances receivable on sale of investments	106,486		188,408
Investments in subsidiaries
Due (to) from subsidiaries
Other assets	181,021		231,817
Total assets	10,857,099		10,427,631
Reserve for losses and loss expenses	5,251,304	5,100,643	4,879,188	4,920,435	4,853,359	4,761,772
Unearned premiums	1,184,676		962,203
Reinsurance balances payable	132,661		99,732
Balances due on purchases of investments	358,837		506,978
Senior notes	797,823		797,700
Accounts payable and accrued liabilities	87,381		106,010
Total liabilities	7,812,682		7,351,811
Total shareholders' equity	3,044,417		3,075,820
Total liabilities and shareholders' equity	10,857,099		10,427,631
Allied World Switzerland (Parent Guarantor) [Member]
Investments
Cash and cash equivalents	70,587		138,488
Insurance balances receivable
Prepaid reinsurance
Reinsurance recoverable
Net deferred acquisition costs
Goodwill
Intangible assets
Balances receivable on sale of investments
Investments in subsidiaries	2,978,767		2,944,975
Due (to) from subsidiaries	(1,771)		(7,143)
Other assets	216
Total assets	3,047,799		3,076,320
Reserve for losses and loss expenses
Unearned premiums
Reinsurance balances payable
Balances due on purchases of investments
Senior notes
Accounts payable and accrued liabilities	3,382		500
Total liabilities	3,382		500
Total shareholders' equity	3,044,417		3,075,820
Total liabilities and shareholders' equity	3,047,799		3,076,320
Allied World Bermuda (Subsidiary Issuer) [Member]
Investments
Cash and cash equivalents	38,402		125,663	43,479		53,849
Insurance balances receivable
Prepaid reinsurance
Reinsurance recoverable
Net deferred acquisition costs
Goodwill
Intangible assets
Balances receivable on sale of investments
Investments in subsidiaries	1,990,580		1,981,158
Due (to) from subsidiaries	(7,421)		(9,419)
Other assets	61,229		8,801
Total assets	2,082,790		2,106,203
Reserve for losses and loss expenses
Unearned premiums
Reinsurance balances payable
Balances due on purchases of investments
Senior notes	797,823		797,700
Accounts payable and accrued liabilities	18,074		18,111
Total liabilities	815,897		815,811
Total shareholders' equity	1,266,893		1,290,392
Total liabilities and shareholders' equity	2,082,790		2,106,203
Other Allied World Subsidiaries [Member]
Investments	7,502,765		7,183,554
Cash and cash equivalents	631,815		492,844	399,210		238,339
Insurance balances receivable	653,002		529,927
Prepaid reinsurance	223,269		187,287
Reinsurance recoverable	1,013,951		927,588
Net deferred acquisition costs	112,083		96,803
Goodwill	268,376		268,376
Intangible assets	55,342		56,876
Balances receivable on sale of investments	106,486		188,408
Investments in subsidiaries
Due (to) from subsidiaries	9,192		16,562
Other assets	173,196		223,016
Total assets	10,749,477		10,171,241
Reserve for losses and loss expenses	5,251,304		4,879,188
Unearned premiums	1,184,676		962,203
Reinsurance balances payable	132,661		99,732
Balances due on purchases of investments	358,837		506,978
Senior notes
Accounts payable and accrued liabilities	65,925		87,399
Total liabilities	6,993,403		6,535,500
Total shareholders' equity	3,756,074		3,635,741
Total liabilities and shareholders' equity	10,749,477		10,171,241
Consolidating Adjustments [Member]
Investments
Cash and cash equivalents
Insurance balances receivable
Prepaid reinsurance
Reinsurance recoverable
Net deferred acquisition costs
Goodwill
Intangible assets
Balances receivable on sale of investments
Investments in subsidiaries	(4,969,347)		(4,926,133)
Due (to) from subsidiaries
Other assets	(53,620)
Total assets	(5,022,967)		(4,926,133)
Reserve for losses and loss expenses
Unearned premiums
Reinsurance balances payable
Balances due on purchases of investments
Senior notes
Accounts payable and accrued liabilities
Total liabilities
Total shareholders' equity	(5,022,967)		(4,926,133)
Total liabilities and shareholders' equity	$ (5,022,967)		$ (4,926,133)