Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$ 452,108	$ 125,906
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	(3,905,650)	(3,186,162)
Purchases of other invested assets	(181,419)	(141,805)
Sales of trading securities	3,705,229	3,171,977
Sales of other invested assets	184,166	126,491
Other	13,472	(13,924)
Net cash used in investing activities	(184,202)	(43,423)
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	(33,207)	0
Dividends paid - par value reduction	0	(12,981)
Proceeds from the exercise of stock options	6,313	5,293
Share repurchases	(137,810)	(82,571)
Net cash used in financing activities	(164,704)	(90,259)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	103,202	(7,776)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	531,936	681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	635,138	674,103
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	0	0
CASH FLOWS USED IN 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 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 (DECREASE) 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:	194,890	73,938
CASH FLOWS USED IN 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 investing activities	0	0
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid	(33,207)
Dividends paid - par value reduction		(12,981)
Proceeds from the exercise of stock options	6,313	5,293
Share repurchases	(137,810)	(82,571)
Net cash used in financing activities	(164,704)	(90,259)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	30,186	(16,321)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790	19,997
CASH AND CASH EQUIVALENTS, END OF PERIOD	40,976	3,676
Allied World Bermuda (Subsidiary Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	(1,489)	(3,025)
CASH FLOWS USED IN 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 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 (DECREASE) IN CASH AND CASH EQUIVALENTS	(1,489)	(3,025)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	2,775	11,324
CASH AND CASH EQUIVALENTS, END OF PERIOD	1,286	8,299
Other Allied World Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	258,707	54,993
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	(3,905,650)	(3,186,162)
Purchases of other invested assets	(181,419)	(141,805)
Sales of trading securities	3,705,229	3,171,977
Sales of other invested assets	184,166	126,491
Other	13,472	(13,924)
Net cash used in investing activities	(184,202)	(43,423)
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 (DECREASE) IN CASH AND CASH EQUIVALENTS	74,505	11,570
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	518,371	650,558
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 592,876	$ 662,128