Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$ 106,109	$ 628,856	$ 548,208
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of available for sale securities	0	0	(727)
Purchases of trading securities	(7,527,670)	(8,006,237)	(7,854,053)
Purchases of other invested assets	(276,926)	(333,031)	(281,957)
Sales of available for sale securities	0	236,978	609,833
Sales of trading securities	7,540,194	7,892,907	6,942,291
Sales of other invested assets	187,477	53,741	71,543
Capital contribution to subsidiary		0
Other	28,782	(104,091)	3,946
Net cash used in investing activities	(48,143)	(259,733)	(509,124)
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid - par value reduction	(12,981)	(67,825)	(28,600)
Dividends paid	(34,059)	0	0
Proceeds from the exercise of stock options	12,137	10,527	6,837
Share repurchases	(173,006)	(263,942)	(86,700)
Repurchase of founder warrants	0	0	(53,620)
Proceeds from Contributed Capital		0
Other			0
Net cash used in financing activities	(207,909)	(321,240)	(162,083)
NET(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(149,943)	47,883	(122,999)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	681,879	633,996	756,995
CASH AND CASH EQUIVALENTS, END OF PERIOD	531,936	681,879	633,996
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	0	0	0
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of available for sale securities			0
Purchases of trading securities	0	0	0
Purchases of other invested assets	0	0	0
Sales of available for sale securities		0	0
Sales of trading securities	0	0	0
Sales of other invested assets	0	0	0
Capital contribution to subsidiary		110,000
Other	0	0	0
Net cash used in investing activities	0	110,000	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid - par value reduction	0	0	0
Dividends paid	0
Proceeds from the exercise of stock options	0	0	0
Share repurchases	0	0	0
Repurchase of founder warrants			0
Proceeds from Contributed Capital		(110,000)
Other			0
Net cash used in financing activities	0	(110,000)	0
NET(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	0	0	0
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	0	0	0
CASH AND CASH EQUIVALENTS, END OF PERIOD	0	0	0
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	198,702	338,565	87,592
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of available for sale securities			0
Purchases of trading securities	0	0	0
Purchases of other invested assets	0	0	0
Sales of available for sale securities		0	0
Sales of trading securities	0	0	0
Sales of other invested assets	0	0	0
Capital contribution to subsidiary		(110,000)
Other	0	0	(4,496)
Net cash used in investing activities	0	(110,000)	(4,496)
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid - par value reduction	(12,981)	(67,825)	(28,600)
Dividends paid	(34,059)
Proceeds from the exercise of stock options	12,137	10,527	6,837
Share repurchases	(173,006)	(263,942)	(86,700)
Repurchase of founder warrants			0
Proceeds from Contributed Capital		0
Other			(449)
Net cash used in financing activities	(207,909)	(321,240)	(108,912)
NET(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(9,207)	(92,675)	(25,816)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	19,997	112,672	138,488
CASH AND CASH EQUIVALENTS, END OF PERIOD	10,790	19,997	112,672
Allied World Bermuda (Subsidiary Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	(8,549)	2,438	(62,404)
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of available for sale securities			0
Purchases of trading securities	0	0	0
Purchases of other invested assets	0	0	0
Sales of available for sale securities		0	0
Sales of trading securities	0	0	0
Sales of other invested assets	0	0	0
Capital contribution to subsidiary		0
Other	0	0	0
Net cash used in investing activities	0	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid - par value reduction	0	0	0
Dividends paid	0
Proceeds from the exercise of stock options	0	0	0
Share repurchases	0	0	0
Repurchase of founder warrants			(53,620)
Proceeds from Contributed Capital		0
Other			(753)
Net cash used in financing activities	0	0	(54,373)
NET(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(8,549)	2,438	(116,777)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	11,324	8,886	125,663
CASH AND CASH EQUIVALENTS, END OF PERIOD	2,775	11,324	8,886
Other Allied World Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	(84,044)	287,853	523,020
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of available for sale securities			(727)
Purchases of trading securities	(7,527,670)	(8,006,237)	(7,854,053)
Purchases of other invested assets	(276,926)	(333,031)	(281,957)
Sales of available for sale securities		236,978	609,833
Sales of trading securities	7,540,194	7,892,907	6,942,291
Sales of other invested assets	187,477	53,741	71,543
Capital contribution to subsidiary		0
Other	28,782	(104,091)	8,442
Net cash used in investing activities	(48,143)	(259,733)	(504,628)
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid - par value reduction	0	0	0
Dividends paid	0
Proceeds from the exercise of stock options	0	0	0
Share repurchases	0	0	0
Repurchase of founder warrants			0
Proceeds from Contributed Capital		110,000
Other			1,202
Net cash used in financing activities	0	110,000	1,202
NET(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(132,187)	138,120	19,594
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	650,558	512,438	492,844
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 518,371	$ 650,558	$ 512,438