Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Income Statements, Captions [Line Items]
Net premiums earned	$ 650,653	$ 541,737	$ 1,865,577	$ 1,609,269
Net investment income	45,667	43,412	132,978	127,824
Net realized investment gains (losses)	(113,626)	(35,136)	(88,783)	104,286
Other income	735	1,032	2,513	1,032
Net losses and loss expenses	(416,881)	(336,090)	(1,173,578)	(926,231)
Acquisition costs	(100,101)	(72,403)	(279,418)	(214,404)
General and administrative expenses	(105,798)	(88,294)	(311,299)	(264,822)
Other expense	(1,245)	(6,575)	(4,303)	(6,575)
Amortization of intangible assets	(2,639)	(633)	(6,091)	(1,900)
Interest expense	(14,469)	(14,325)	(43,272)	(43,451)
Foreign exchange gain (loss)	793	(278)	(10,369)	(978)
Income tax (expense) benefit	5,281	(1,532)	(1,771)	(24,300)
Equity in earnings of consolidated subsidiaries	0	0	0	0
NET (LOSS) INCOME	(51,630)	30,915	82,184	359,750
Other comprehensive loss: foreign currency translation adjustment, net of tax	(993)	0	(4,265)	0
COMPREHENSIVE INCOME (LOSS)	(52,623)	30,915	77,919	359,750
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
Other income	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
Other expense	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	0	0	0	0
Foreign exchange gain (loss)	0	0	0	0
Income tax (expense) benefit	0	0	0	0
Equity in earnings of consolidated subsidiaries	80,743	(88,673)	(248,379)	(807,124)
NET (LOSS) INCOME	80,743	(88,673)	(248,379)	(807,124)
Other comprehensive loss: foreign currency translation adjustment, net of tax	993	0	4,265	0
COMPREHENSIVE INCOME (LOSS)	81,736	(88,673)	(244,114)	(807,124)
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	0	0	0	0
Net investment income	0	2	5	6
Net realized investment gains (losses)	0	0	0	0
Other income	0	0	0	0
Net losses and loss expenses	0	0	0	0
Acquisition costs	0	0	0	0
General and administrative expenses	(7,438)	(8,285)	(27,053)	(28,012)
Other expense	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	0	0	0	0
Foreign exchange gain (loss)	2	16	9	12
Income tax (expense) benefit	(472)	0	(553)	(86)
Equity in earnings of consolidated subsidiaries	(43,722)	39,182	109,776	387,830
NET (LOSS) INCOME	(51,630)	30,915	82,184	359,750
Other comprehensive loss: foreign currency translation adjustment, net of tax	(993)	0	(4,265)	0
COMPREHENSIVE INCOME (LOSS)	(52,623)	30,915	77,919	359,750
Allied World Bermuda (Subsidiary Issuer) [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
Other income	0	0	0	0
Net losses and loss expenses	0	0	0	0
Acquisition costs	0	0	0	0
General and administrative expenses	590	(182)	405	(919)
Other expense	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	(13,876)	(13,855)	(41,613)	(41,556)
Foreign exchange gain (loss)	0	47	13	68
Income tax (expense) benefit	0	0	0	0
Equity in earnings of consolidated subsidiaries	(37,021)	49,491	138,603	419,294
NET (LOSS) INCOME	(50,307)	35,501	97,408	376,887
Other comprehensive loss: foreign currency translation adjustment, net of tax	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	(50,307)	35,501	97,408	376,887
Other Allied World Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	650,653	541,737	1,865,577	1,609,269
Net investment income	45,667	43,410	132,973	127,818
Net realized investment gains (losses)	(113,626)	(35,136)	(88,783)	104,286
Other income	735	1,032	2,513	1,032
Net losses and loss expenses	(416,881)	(336,090)	(1,173,578)	(926,231)
Acquisition costs	(100,101)	(72,403)	(279,418)	(214,404)
General and administrative expenses	(98,950)	(79,827)	(284,651)	(235,891)
Other expense	(1,245)	(6,575)	(4,303)	(6,575)
Amortization of intangible assets	(2,639)	(633)	(6,091)	(1,900)
Interest expense	(593)	(470)	(1,659)	(1,895)
Foreign exchange gain (loss)	791	(341)	(10,391)	(1,058)
Income tax (expense) benefit	5,753	(1,532)	(1,218)	(24,214)
Equity in earnings of consolidated subsidiaries	0	0	0	0
NET (LOSS) INCOME	(30,436)	53,172	150,971	430,237
Other comprehensive loss: foreign currency translation adjustment, net of tax	(993)	0	(4,265)	0
COMPREHENSIVE INCOME (LOSS)	$ (31,429)	$ 53,172	$ 146,706	$ 430,237