Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Income Statement) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Condensed Income Statements, Captions [Line Items]
Net premiums earned	$ 541,737	$ 510,773	$ 1,609,269	$ 1,481,272
Net investment income	43,412	39,271	127,824	110,294
Net realized investment gains (losses)	(35,136)	27,487	104,286	(8,074)
Other income	1,032	0	1,032	0
Net losses and loss expenses	(336,090)	(276,970)	(926,231)	(807,276)
Acquisition costs	(72,403)	(65,114)	(214,404)	(186,416)
General and administrative expenses	(88,294)	(88,553)	(264,822)	(251,818)
Other expense	(6,575)	0	(6,575)	0
Amortization of intangible assets	(633)	(633)	(1,900)	(1,900)
Interest expense	(14,325)	(14,094)	(43,451)	(42,416)
Foreign exchange gain (loss)	(278)	(4,353)	(978)	(7,361)
Income tax (expense) benefit	(1,532)	(4,971)	(24,300)	(6,332)
Equity in earnings of consolidated subsidiaries	0	0	0	0
NET INCOME	30,915	122,843	359,750	279,973
Other comprehensive income	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	30,915	122,843	359,750	279,973
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	(88,673)	(280,829)	(807,124)	(659,856)
NET INCOME	(88,673)	(280,829)	(807,124)	(659,856)
Other comprehensive income	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	(88,673)	(280,829)	(807,124)	(659,856)
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	0	0	0	0
Net investment income	2	3	6	11
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	(8,285)	(7,323)	(28,012)	(26,875)
Other expense	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	0	0	0	0
Foreign exchange gain (loss)	16	(13)	12	261
Income tax (expense) benefit	0	0	(86)	0
Equity in earnings of consolidated subsidiaries	39,182	130,176	387,830	306,576
NET INCOME	30,915	122,843	359,750	279,973
Other comprehensive income	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	30,915	122,843	359,750	279,973
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	4
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	(182)	(4,961)	(919)	(5,873)
Other expense	0	0	0	0
Amortization of intangible assets	0	0	0	0
Interest expense	(13,855)	(13,838)	(41,556)	(41,503)
Foreign exchange gain (loss)	47	(212)	68	(935)
Income tax (expense) benefit	0	0	0	0
Equity in earnings of consolidated subsidiaries	49,491	150,653	419,294	353,280
NET INCOME	35,501	131,642	376,887	304,973
Other comprehensive income	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	35,501	131,642	376,887	304,973
Other Allied World Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net premiums earned	541,737	510,773	1,609,269	1,481,272
Net investment income	43,410	39,268	127,818	110,279
Net realized investment gains (losses)	(35,136)	27,487	104,286	(8,074)
Other income	1,032	0	1,032	0
Net losses and loss expenses	(336,090)	(276,970)	(926,231)	(807,276)
Acquisition costs	(72,403)	(65,114)	(214,404)	(186,416)
General and administrative expenses	(79,827)	(76,269)	(235,891)	(219,070)
Other expense	(6,575)	0	(6,575)	0
Amortization of intangible assets	(633)	(633)	(1,900)	(1,900)
Interest expense	(470)	(256)	(1,895)	(913)
Foreign exchange gain (loss)	(341)	(4,128)	(1,058)	(6,687)
Income tax (expense) benefit	(1,532)	(4,971)	(24,214)	(6,332)
Equity in earnings of consolidated subsidiaries	0	0	0	0
NET INCOME	53,172	149,187	430,237	354,883
Other comprehensive income	0	0	0	0
COMPREHENSIVE INCOME (LOSS)	$ 53,172	$ 149,187	$ 430,237	$ 354,883