Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$ 304,782	$ 11,514
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of trading securities	(1,568,993)	(1,330,735)
Purchases of other invested assets	(779,934)	(54,026)
Sales of trading securities	1,494,648	1,188,307
Sales of other invested assets	663,237	97,989
Other	2,487	114,407
Net cash (used in) provided by investing activities	(188,555)	15,942
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	(16,732)	0
Dividends paid - par value reduction	0	(12,981)
Proceeds from the exercise of stock options	3,030	2,472
Share repurchases	(68,659)	(36,245)
Net cash used in financing activities	(82,361)	(46,754)
NET INCREASE IN CASH AND CASH EQUIVALENTS	33,866	(19,298)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	531,936	681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	565,802	662,581
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	0	0
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash (used in) provided by investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	0
Dividends paid - par value reduction		0
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	0	0
NET INCREASE IN CASH AND CASH EQUIVALENTS	0	0
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	0	0
CASH AND CASH EQUIVALENTS, END OF PERIOD	0	0
Allied World Switzerland (Parent Guarantor) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	94,128	59,772
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash (used in) provided by investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	(16,732)
Dividends paid - par value reduction		(12,981)
Proceeds from the exercise of stock options	3,030	2,472
Share repurchases	(68,659)	(36,245)
Net cash used in financing activities	(82,361)	(46,754)
NET INCREASE IN CASH AND CASH EQUIVALENTS	11,767	13,018
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790	19,997
CASH AND CASH EQUIVALENTS, END OF PERIOD	22,557	33,015
Allied World Bermuda (Subsidiary Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	(1,728)	5,859
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of trading securities	0	0
Purchases of other invested assets	0	0
Sales of trading securities	0	0
Sales of other invested assets	0	0
Other	0	0
Net cash (used in) provided by investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	0
Dividends paid - par value reduction		0
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	0	0
NET INCREASE IN CASH AND CASH EQUIVALENTS	(1,728)	5,859
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	2,775	11,324
CASH AND CASH EQUIVALENTS, END OF PERIOD	1,047	17,183
Other Allied World Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	212,382	(54,117)
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of trading securities	(1,568,993)	(1,330,735)
Purchases of other invested assets	(779,934)	(54,026)
Sales of trading securities	1,494,648	1,188,307
Sales of other invested assets	663,237	97,989
Other	2,487	114,407
Net cash (used in) provided by investing activities	(188,555)	15,942
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	0
Dividends paid - par value reduction		0
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	0	0
NET INCREASE IN CASH AND CASH EQUIVALENTS	23,827	(38,175)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	518,371	650,558
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 542,198	$ 612,383