Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$ 667,107	$ 332,050
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of trading securities	(5,608,594)	(4,955,817)
Purchases of other invested assets	(242,227)	(211,501)
Sales of trading securities	5,500,176	5,137,280
Sales of other invested assets	243,123	189,155
Other	(46,620)	(78,203)
Net cash (used in) provided by investing activities	(154,142)	80,914
CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Dividends paid - par value reduction	0	(12,981)
Dividends paid	(55,064)	(17,117)
Intercompany dividends paid	0	0
Proceeds from the exercise of stock options	7,640	8,465
Share repurchases	(166,207)	(120,163)
Net cash used in financing activities	(213,631)	(141,796)
NET INCREASE IN CASH AND CASH EQUIVALENTS	299,334	271,168
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	531,936	681,879
CASH AND CASH EQUIVALENTS, END OF PERIOD	831,270	953,047
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	(575,000)	(503,500)
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 PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Dividends paid - par value reduction		0
Dividends paid	0	0
Intercompany dividends paid	575,000	503,500
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	575,000	503,500
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:	241,037	177,859
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 PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Dividends paid - par value reduction		(12,981)
Dividends paid	(55,064)	(17,117)
Intercompany dividends paid	0	0
Proceeds from the exercise of stock options	7,640	8,465
Share repurchases	(166,207)	(120,163)
Net cash used in financing activities	(213,631)	(141,796)
NET INCREASE IN CASH AND CASH EQUIVALENTS	27,406	36,063
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	10,790	19,997
CASH AND CASH EQUIVALENTS, END OF PERIOD	38,196	56,060
Allied World Bermuda (Subsidiary Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	263,554	226,564
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 PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Dividends paid - par value reduction		0
Dividends paid	0	0
Intercompany dividends paid	(264,000)	(229,500)
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	(264,000)	(229,500)
NET INCREASE IN CASH AND CASH EQUIVALENTS	(446)	(2,936)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	2,775	11,324
CASH AND CASH EQUIVALENTS, END OF PERIOD	2,329	8,388
Other Allied World Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	737,516	431,127
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of trading securities	(5,608,594)	(4,955,817)
Purchases of other invested assets	(242,227)	(211,501)
Sales of trading securities	5,500,176	5,137,280
Sales of other invested assets	243,123	189,155
Other	(46,620)	(78,203)
Net cash (used in) provided by investing activities	(154,142)	80,914
CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES:
Dividends paid - par value reduction		0
Dividends paid	0	0
Intercompany dividends paid	(311,000)	(274,000)
Proceeds from the exercise of stock options	0	0
Share repurchases	0	0
Net cash used in financing activities	(311,000)	(274,000)
NET INCREASE IN CASH AND CASH EQUIVALENTS	272,374	238,041
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	518,371	650,558
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 790,745	$ 888,599