Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Income Statement) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Income Statements, Captions [Line Items]
Net premiums earned	$ 524,561	$ 510,773	$ 507,271	$ 463,228	$ 476,244	$ 441,017	$ 429,747	$ 401,890	$ 2,005,833	$ 1,748,898	$ 1,456,992
Net investment income	47,270	39,271	37,635	33,388	38,360	39,121	42,451	47,209	157,564	167,141	195,948
Net realized investment gains (losses)	67,599	27,487	(115,198)	79,637	14,379	149,813	8,663	133,581	59,525	306,436	10,077
Other income									0	0	101,744
Net losses and loss expenses	(315,966)	(276,970)	(275,128)	(255,178)	(414,734)	(258,948)	(240,380)	(225,202)	(1,123,242)	(1,139,264)	(959,156)
Acquisition costs	(66,257)	(65,114)	(64,617)	(56,685)	(55,910)	(51,086)	(51,588)	(47,138)	(252,673)	(205,722)	(167,295)
General and administrative expenses	(100,467)	(88,553)	(80,585)	(82,680)	(84,404)	(78,572)	(73,979)	(70,366)	(352,285)	(307,321)	(271,656)
Amortization of intangible assets	(633)	(633)	(634)	(633)	(633)	(633)	(634)	(633)	(2,533)	(2,533)	(2,978)
Interest expense	(14,094)	(14,094)	(14,188)	(14,134)	(13,826)	(13,822)	(14,001)	(13,756)	(56,510)	(55,405)	(54,989)
Foreign exchange (loss) gain	(658)	(4,353)	(490)	(2,518)	(860)	(1,023)	1,019	81	(8,019)	(783)	(3,159)
Income tax (expense) benefit	(3,448)	(4,971)	4,072	(5,433)	237	(6,220)	(4,947)	(7,510)	(9,780)	(18,440)	(30,980)
Equity in earnings of consolidated subsidiaries									0	0	0
NET INCOME	137,907	122,843	(1,862)	158,992	(41,147)	219,647	96,351	218,156	417,880	493,007	274,548
Unrealized (losses) gains on investments arising during the year net of applicable deferred income tax (benefit) expense 2013: $0; 2012: $(265); 2011: $3,035									0	(493)	5,243
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax										(13,991)	(47,894)
Other comprehensive loss									0	(14,484)	(42,651)
COMPREHENSIVE INCOME (LOSS)									417,880	478,523	231,897
Parenthetical disclosures:
Deferred income tax (benefit) expense for unrealized gains on investments arising during the period									0	(265)	3,035
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned									0	0	0
Net investment income									0	0	0
Net realized investment gains (losses)									0	0	53,620
Other income											0
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									0	0	0
Amortization of intangible assets									0	0	0
Interest expense									0	0	0
Foreign exchange (loss) gain									0	0	0
Income tax (expense) benefit									0	0	0
Equity in earnings of consolidated subsidiaries									(974,784)	(1,100,978)	(503,945)
NET INCOME									(974,784)	(1,100,978)	(450,325)
Unrealized (losses) gains on investments arising during the year net of applicable deferred income tax (benefit) expense 2013: $0; 2012: $(265); 2011: $3,035										493	(5,243)
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax										13,991	47,894
Other comprehensive loss									0	14,484	42,651
COMPREHENSIVE INCOME (LOSS)									(974,784)	(1,086,494)	(407,674)
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned									0	0	0
Net investment income									13	26	64
Net realized investment gains (losses)									0	0	0
Other income											101,744
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									(42,122)	(35,258)	(13,354)
Amortization of intangible assets									0	0	0
Interest expense									0	0	0
Foreign exchange (loss) gain									263	159	9
Income tax (expense) benefit									98	358	(7,940)
Equity in earnings of consolidated subsidiaries									459,628	527,722	194,025
NET INCOME									417,880	493,007	274,548
Unrealized (losses) gains on investments arising during the year net of applicable deferred income tax (benefit) expense 2013: $0; 2012: $(265); 2011: $3,035										(493)	5,243
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax										(13,991)	(47,894)
Other comprehensive loss									0	(14,484)	(42,651)
COMPREHENSIVE INCOME (LOSS)									417,880	478,523	231,897
Allied World Bermuda (Subsidiary Issuer) [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned									0	0	0
Net investment income									4	20	26
Net realized investment gains (losses)									0	0	(53,620)
Other income											0
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									(1,320)	(2,973)	(5,823)
Amortization of intangible assets									0	0	0
Interest expense									(55,347)	(55,405)	(54,989)
Foreign exchange (loss) gain									(1,045)	(319)	(978)
Income tax (expense) benefit									0	0	0
Equity in earnings of consolidated subsidiaries									515,156	573,256	309,920
NET INCOME									457,448	514,579	194,536
Unrealized (losses) gains on investments arising during the year net of applicable deferred income tax (benefit) expense 2013: $0; 2012: $(265); 2011: $3,035										0	0
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax										0	0
Other comprehensive loss									0	0	0
COMPREHENSIVE INCOME (LOSS)									457,448	514,579	194,536
Other Allied World Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned									2,005,833	1,748,898	1,456,992
Net investment income									157,547	167,095	195,858
Net realized investment gains (losses)									59,525	306,436	10,077
Other income											0
Net losses and loss expenses									(1,123,242)	(1,139,264)	(959,156)
Acquisition costs									(252,673)	(205,722)	(167,295)
General and administrative expenses									(308,843)	(269,090)	(252,479)
Amortization of intangible assets									(2,533)	(2,533)	(2,978)
Interest expense									(1,163)	0	0
Foreign exchange (loss) gain									(7,237)	(623)	(2,190)
Income tax (expense) benefit									(9,878)	(18,798)	(23,040)
Equity in earnings of consolidated subsidiaries									0	0	0
NET INCOME									517,336	586,399	255,789
Unrealized (losses) gains on investments arising during the year net of applicable deferred income tax (benefit) expense 2013: $0; 2012: $(265); 2011: $3,035										(493)	5,243
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax										(13,991)	(47,894)
Other comprehensive loss									0	(14,484)	(42,651)
COMPREHENSIVE INCOME (LOSS)									$ 517,336	$ 571,915	$ 213,138