Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Income Statement) (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Gross premiums written	$ 442,698	$ 378,445	$ 1,522,984	$ 1,376,455
Premiums ceded	(92,438)	(76,276)	(296,050)	(271,199)
Net premiums written	350,260	302,169	1,226,934	1,105,256
Change in unearned premiums	21,080	37,327	(165,411)	(88,512)
Net premiums earned	371,340	339,496	1,061,523	1,016,744
Net investment income	47,883	59,479	150,459	193,975
Net realized investment gains (losses)	(130,809)	116,930	(21,555)	289,350
Net impairment charges recognized in earnings				(168)
Other income	35,000		35,000	913
Total revenues	323,414	515,905	1,225,427	1,500,814
Net losses and loss expenses	205,546	126,988	745,811	547,864
Acquisition costs	39,680	41,919	120,733	120,641
General and administrative expenses	66,007	69,871	201,164	201,423
Amortization and impairment of intangible assets	767	892	2,300	2,675
Interest expense	13,748	9,533	41,235	28,592
Foreign exchange loss (gain)	2,966	(1,387)	3,708	248
Income tax expense	5,672	13,569	19,028	27,152
Total Expenses	334,386	261,385	1,133,979	928,595
Income (loss) before equity in earnings of consolidated subsidiaries	(10,972)	254,520	91,448	572,219
NET INCOME (LOSS)	(10,972)	254,520	91,448	572,219
Allied World Switzerland (Parent Guarantor) [Member]
Net investment income	7		51
Other income	35,000		35,000
Total revenues	35,007		35,051
General and administrative expenses	2,110		7,919
Foreign exchange loss (gain)	(10)		(11)
Income tax expense	2,730		2,730
Total Expenses	4,830		10,638
Income (loss) before equity in earnings of consolidated subsidiaries	30,177		24,413
Equity in earnings of consolidated subsidiaries	(41,148)		67,035
NET INCOME (LOSS)	(10,971)		91,448
Allied World Bermuda (Subsidiary Issuer) [Member]
Net investment income	3	22	25	43
Net realized investment gains (losses)				(3,958)
Total revenues	3	22	25	(3,915)
General and administrative expenses	913	3,174	5,141	9,825
Interest expense	13,748	9,533	41,235	28,592
Foreign exchange loss (gain)	907	(555)	1,131	(555)
Total Expenses	15,568	12,152	47,507	37,862
Income (loss) before equity in earnings of consolidated subsidiaries	(15,565)	(12,130)	(47,482)	(41,777)
Equity in earnings of consolidated subsidiaries	(26,615)	266,650	114,243	613,996
NET INCOME (LOSS)	(42,180)	254,520	66,761	572,219
Other Allied World Subsidiaries [Member]
Gross premiums written	442,698	378,445	1,522,984	1,376,455
Premiums ceded	(92,438)	(76,276)	(296,050)	(271,199)
Net premiums written	350,260	302,169	1,226,934	1,105,256
Change in unearned premiums	21,080	37,327	(165,411)	(88,512)
Net premiums earned	371,340	339,496	1,061,523	1,016,744
Net investment income	47,873	59,457	150,383	193,932
Net realized investment gains (losses)	(130,809)	116,930	(21,555)	293,308
Net impairment charges recognized in earnings				(168)
Other income				913
Total revenues	288,404	515,883	1,190,351	1,504,729
Net losses and loss expenses	205,546	126,988	745,811	547,864
Acquisition costs	39,680	41,919	120,733	120,641
General and administrative expenses	62,984	66,697	188,104	191,598
Amortization and impairment of intangible assets	767	892	2,300	2,675
Foreign exchange loss (gain)	2,069	(832)	2,588	803
Income tax expense	2,942	13,569	16,298	27,152
Total Expenses	313,988	249,233	1,075,834	890,733
Income (loss) before equity in earnings of consolidated subsidiaries	(25,584)	266,650	114,517	613,996
NET INCOME (LOSS)	(25,584)	266,650	114,517	613,996
Consolidating Adjustments [Member]
Equity in earnings of consolidated subsidiaries	67,763	(266,650)	(181,278)	(613,996)
NET INCOME (LOSS)	$ 67,763	$ (266,650)	$ (181,278)	$ (613,996)