Condensed Consolidated Guarantor Financial Statements (Schedule of Condensed Consolidating Income Statement) (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Gross premiums written	$ 519,598	$ 493,847	$ 1,080,286	$ 998,010
Premiums ceded	(123,795)	(124,052)	(203,612)	(194,923)
Net premiums written	395,803	369,795	876,674	803,087
Change in unearned premiums	(40,496)	(30,871)	(186,491)	(125,839)
Net premiums earned	355,307	338,924	690,183	677,248
Net investment income	52,368	65,594	102,576	134,496
Net realized investment gains (losses)	58,878	94,933	109,254	172,420
Net impairment charges recognized in earnings				(168)
Other income		616		913
Total revenues	466,553	500,067	902,013	984,909
Net losses and loss expenses	235,813	188,722	540,265	420,876
Acquisition costs	42,971	37,938	81,053	78,722
General and administrative expenses	67,201	68,089	135,157	131,552
Amortization of intangible assets			1,533		3,483
Amortization and impairment of intangible assets	766	891	1,533	1,783
Interest expense	13,745	9,531	27,487	19,059
Foreign exchange (gain) loss	1,184	559	742	1,635
Income tax expense	11,073	10,378	13,356	13,583
Total Expenses	372,753	316,108	799,593	667,210
Income (loss) before equity in earnings of consolidated subsidiaries	93,800	183,959	102,420	317,699
Equity in earnings of consolidated subsidiaries
NET INCOME (LOSS)	93,800	183,959	102,420	317,699
Allied World Switzerland (Parent Guarantor) [Member]
Gross premiums written
Premiums ceded
Net premiums written
Change in unearned premiums
Net premiums earned
Net investment income	15		45
Net realized investment gains (losses)
Net impairment charges recognized in earnings
Other income
Total revenues	15		45
Net losses and loss expenses
Acquisition costs
General and administrative expenses	4,746		5,810
Amortization and impairment of intangible assets
Interest expense
Foreign exchange (gain) loss	3		(1)
Income tax expense
Total Expenses	4,749		5,809
Income (loss) before equity in earnings of consolidated subsidiaries	(4,734)		(5,764)
Equity in earnings of consolidated subsidiaries	98,534		108,184
NET INCOME (LOSS)	93,800		102,420
Allied World Bermuda (Subsidiary Issuer) [Member]
Gross premiums written
Premiums ceded
Net premiums written
Change in unearned premiums
Net premiums earned
Net investment income	8	20	22	21
Net realized investment gains (losses)		(3,958)		(3,958)
Net impairment charges recognized in earnings
Other income
Total revenues	8	(3,938)	22	(3,937)
Net losses and loss expenses
Acquisition costs
General and administrative expenses	1,483	3,168	4,229	6,651
Amortization and impairment of intangible assets
Interest expense	13,745	9,531	27,487	19,059
Foreign exchange (gain) loss	(17)		224
Income tax expense
Total Expenses	15,211	12,699	31,940	25,710
Income (loss) before equity in earnings of consolidated subsidiaries	(15,203)	(16,637)	(31,918)	(29,647)
Equity in earnings of consolidated subsidiaries		200,596		347,346
NET INCOME (LOSS)	(15,203)	183,959	(31,918)	317,699
Other Allied World Subsidiaries [Member]
Gross premiums written	519,598	493,847	1,080,286	998,010
Premiums ceded	(123,795)	(124,052)	(203,612)	(194,923)
Net premiums written	395,803	369,795	876,674	803,087
Change in unearned premiums	(40,496)	(30,871)	(186,491)	(125,839)
Net premiums earned	355,307	338,924	690,183	677,248
Net investment income	52,345	65,574	102,509	134,475
Net realized investment gains (losses)	58,878	98,891	109,254	176,378
Net impairment charges recognized in earnings				(168)
Other income		616		913
Total revenues	466,530	504,005	901,946	988,846
Net losses and loss expenses	235,813	188,722	540,265	420,876
Acquisition costs	42,971	37,938	81,053	78,722
General and administrative expenses	60,972	64,921	125,118	124,901
Amortization and impairment of intangible assets	766	891	1,533	1,783
Interest expense
Foreign exchange (gain) loss	1,198	559	519	1,635
Income tax expense	11,073	10,378	13,356	13,583
Total Expenses	352,793	303,409	761,844	641,500
Income (loss) before equity in earnings of consolidated subsidiaries	113,737	200,596	140,102	347,346
Equity in earnings of consolidated subsidiaries
NET INCOME (LOSS)	113,737	200,596	140,102	347,346
Consolidating Adjustments [Member]
Gross premiums written
Premiums ceded
Net premiums written
Change in unearned premiums
Net premiums earned
Net investment income
Net realized investment gains (losses)
Net impairment charges recognized in earnings
Other income
Total revenues
Net losses and loss expenses
Acquisition costs
General and administrative expenses
Amortization and impairment of intangible assets
Interest expense
Foreign exchange (gain) loss
Income tax expense
Total Expenses
Income (loss) before equity in earnings of consolidated subsidiaries
Equity in earnings of consolidated subsidiaries	(98,534)	(200,596)	(108,184)	(347,346)
NET INCOME (LOSS)	$ (98,534)	$ (200,596)	$ (108,184)	$ (347,346)