Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Condensed Income Statements, Captions [Line Items]
Net premiums earned	$ 646,376	$ 537,247	$ 1,214,924	$ 1,067,532
Net investment income	42,760	36,793	87,311	84,412
Net realized investment gains (losses)	(20,182)	85,217	24,843	139,422
Other insurance-related income	924	0	1,778	0
Net losses and loss expenses	(431,521)	(314,855)	(756,697)	(590,141)
Acquisition costs	(100,618)	(74,279)	(179,317)	(142,001)
General and administrative expenses	(108,363)	(96,188)	(205,501)	(176,528)
Other insurance-related expenses	(1,235)	0	(3,058)	0
Amortization of intangible assets	(2,819)	(634)	(3,452)	(1,267)
Interest expense	(14,466)	(14,592)	(28,803)	(29,126)
Foreign exchange loss	(1,265)	(651)	(11,162)	(700)
Income tax (expense) benefit	(133)	(6,195)	(7,052)	(22,768)
Equity in earnings of consolidated subsidiaries	0	0	0	0
NET INCOME	9,458	151,863	133,814	328,835
Other comprehensive loss	(3,272)	0	(3,272)	0
COMPREHENSIVE INCOME (LOSS)	6,186	151,863	130,542	328,835
Consolidating Adjustments [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 insurance-related 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 insurance-related expenses	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	0	0	0	0
Foreign exchange loss	0	0	0	0
Income tax (expense) benefit	0	0	0	0
Equity in earnings of consolidated subsidiaries	(50,976)	(333,149)	(329,122)	(718,451)
NET INCOME	(50,976)	(333,149)	(329,122)	(718,451)
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	(50,976)	(333,149)	(329,122)	(718,451)
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	0	0	0	0
Net investment income	3	2	5	4
Net realized investment gains (losses)	0	0	0	0
Other insurance-related income	0	0	0	0
Net losses and loss expenses	0	0	0	0
Acquisition costs	0	0	0	0
General and administrative expenses	(10,153)	(10,813)	(19,615)	(19,727)
Other insurance-related expenses	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	0	0	0	0
Foreign exchange loss	2	(2)	7	(4)
Income tax (expense) benefit	558	323	(81)	(86)
Equity in earnings of consolidated subsidiaries	19,048	162,353	153,498	348,648
NET INCOME	9,458	151,863	133,814	328,835
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	9,458	151,863	133,814	328,835
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 insurance-related income	0	0	0	0
Net losses and loss expenses	0	0	0	0
Acquisition costs	0	0	0	0
General and administrative expenses	(425)	1,654	(185)	(737)
Other insurance-related expenses	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	(13,871)	(13,853)	(27,737)	(27,700)
Foreign exchange loss	3	(12)	13	21
Income tax (expense) benefit	0	0	0	0
Equity in earnings of consolidated subsidiaries	31,928	170,796	175,624	369,803
NET INCOME	17,635	158,585	147,715	341,387
Other comprehensive loss	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	17,635	158,585	147,715	341,387
Other Allied World Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	646,376	537,247	1,214,924	1,067,532
Net investment income	42,757	36,791	87,306	84,408
Net realized investment gains (losses)	(20,182)	85,217	24,843	139,422
Other insurance-related income	924	0	1,778	0
Net losses and loss expenses	(431,521)	(314,855)	(756,697)	(590,141)
Acquisition costs	(100,618)	(74,279)	(179,317)	(142,001)
General and administrative expenses	(97,785)	(87,029)	(185,701)	(156,064)
Other insurance-related expenses	(1,235)	0	(3,058)	0
Amortization of intangible assets	(2,819)	(634)	(3,452)	(1,267)
Interest expense	(595)	(739)	(1,066)	(1,426)
Foreign exchange loss	(1,270)	(637)	(11,182)	(717)
Income tax (expense) benefit	(691)	(6,518)	(6,971)	(22,682)
Equity in earnings of consolidated subsidiaries	0	0	0	0
NET INCOME	33,341	174,564	181,407	377,064
Other comprehensive loss	(3,272)	0	(3,272)	0
COMPREHENSIVE INCOME (LOSS)	$ 30,069	$ 174,564	$ 178,135	$ 377,064