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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Income Statements, Captions [Line Items]
Net premiums earned	$ 573,489	$ 541,737	$ 537,247	$ 530,285	$ 524,561	$ 510,773	$ 507,271	$ 463,228	$ 2,182,758	$ 2,005,833	$ 1,748,898
Net investment income	49,050	43,412	36,793	47,619	47,270	39,271	37,635	33,388	176,874	157,564	167,141
Net realized investment gains (losses)	(15,329)	(35,136)	85,217	54,205	67,599	27,487	(115,198)	79,637	88,957	59,525	306,436
Other income	1,032	1,032	0	0					2,064	0	0
Net losses and loss expenses	(272,959)	(336,090)	(314,855)	(275,286)	(315,966)	(276,970)	(275,128)	(255,178)	(1,199,190)	(1,123,242)	(1,139,264)
Acquisition costs	(80,718)	(72,403)	(74,279)	(67,722)	(66,257)	(65,114)	(64,617)	(56,685)	(295,122)	(252,673)	(205,722)
General and administrative expenses	(100,914)	(88,294)	(96,188)	(80,340)	(100,467)	(88,553)	(80,585)	(82,680)	(365,736)	(352,285)	(307,321)
Other expense	(2,003)	(6,575)	0	0					(8,578)	0	0
Amortization of intangible assets	(633)	(633)	(634)	(633)	(633)	(633)	(634)	(633)	(2,533)	(2,533)	(2,533)
Interest expense	(14,304)	(14,325)	(14,592)	(14,534)	(14,094)	(14,094)	(14,188)	(14,134)	(57,755)	(56,510)	(55,405)
Foreign exchange (loss) gain	21	(278)	(651)	(49)	(658)	(4,353)	(490)	(2,518)	(957)	(8,019)	(783)
Income tax (expense) benefit	(6,223)	(1,532)	(6,195)	(16,573)	(3,448)	(4,971)	4,072	(5,433)	(30,523)	(9,780)	(18,440)
Equity in earnings of consolidated subsidiaries									0	0	0
NET INCOME	130,509	30,915	151,863	176,972	137,907	122,843	(1,862)	158,992	490,259	417,880	493,007
Unrealized losses on investments arising during the year net of applicable deferred income tax benefit 2014: $0; 2013: $0; 2012: $(265)									0	0	(493)
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax											(13,991)
Other comprehensive loss									0	0	(14,484)
COMPREHENSIVE INCOME (LOSS)									490,259	417,880	478,523
Parenthetical disclosures:
Deferred income tax (benefit) expense for unrealized gains on investments arising during the period									0	0	(265)
Consolidating Adjustments
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	0
Other income									0	0	0
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									0	0	0
Other expense									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									(1,090,522)	(974,784)	(1,100,978)
NET INCOME									(1,090,522)	(974,784)	(1,100,978)
Unrealized losses on investments arising during the year net of applicable deferred income tax benefit 2014: $0; 2013: $0; 2012: $(265)											493
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax											13,991
Other comprehensive loss									0	0	14,484
COMPREHENSIVE INCOME (LOSS)									(1,090,522)	(974,784)	(1,086,494)
Allied World Switzerland (Parent Guarantor)
Condensed Income Statements, Captions [Line Items]
Net premiums earned									0	0	0
Net investment income									50	13	26
Net realized investment gains (losses)									0	0	0
Other income									0	0	0
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									(35,596)	(42,122)	(35,258)
Other expense									0	0	0
Amortization of intangible assets									0	0	0
Interest expense									0	0	0
Foreign exchange (loss) gain									20	263	159
Income tax (expense) benefit									(89)	98	358
Equity in earnings of consolidated subsidiaries									525,874	459,628	527,722
NET INCOME									490,259	417,880	493,007
Unrealized losses on investments arising during the year net of applicable deferred income tax benefit 2014: $0; 2013: $0; 2012: $(265)											(493)
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax											(13,991)
Other comprehensive loss									0	0	(14,484)
COMPREHENSIVE INCOME (LOSS)									490,259	417,880	478,523
Allied World Bermuda (Subsidiary Issuer)
Condensed Income Statements, Captions [Line Items]
Net premiums earned									0	0	0
Net investment income									0	4	20
Net realized investment gains (losses)									0	0	0
Other income									0	0	0
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									(3,088)	(1,320)	(2,973)
Other expense									0	0	0
Amortization of intangible assets									0	0	0
Interest expense									(55,418)	(55,347)	(55,405)
Foreign exchange (loss) gain									104	(1,045)	(319)
Income tax (expense) benefit									0	0	0
Equity in earnings of consolidated subsidiaries									564,648	515,156	573,256
NET INCOME									506,246	457,448	514,579
Unrealized losses on investments arising during the year net of applicable deferred income tax benefit 2014: $0; 2013: $0; 2012: $(265)											0
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax											0
Other comprehensive loss									0	0	0
COMPREHENSIVE INCOME (LOSS)									506,246	457,448	514,579
Other Allied World Subsidiaries
Condensed Income Statements, Captions [Line Items]
Net premiums earned									2,182,758	2,005,833	1,748,898
Net investment income									176,824	157,547	167,095
Net realized investment gains (losses)									88,957	59,525	306,436
Other income									2,064	0	0
Net losses and loss expenses									(1,199,190)	(1,123,242)	(1,139,264)
Acquisition costs									(295,122)	(252,673)	(205,722)
General and administrative expenses									(327,052)	(308,843)	(269,090)
Other expense									(8,578)	0	0
Amortization of intangible assets									(2,533)	(2,533)	(2,533)
Interest expense									(2,337)	(1,163)	0
Foreign exchange (loss) gain									(1,081)	(7,237)	(623)
Income tax (expense) benefit									(30,434)	(9,878)	(18,798)
Equity in earnings of consolidated subsidiaries									0	0	0
NET INCOME									584,276	517,336	586,399
Unrealized losses on investments arising during the year net of applicable deferred income tax benefit 2014: $0; 2013: $0; 2012: $(265)											(493)
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax											(13,991)
Other comprehensive loss									0	0	(14,484)
COMPREHENSIVE INCOME (LOSS)									$ 584,276	$ 517,336	$ 571,915