Shareholders' Equity (Narrative) (Details)	0 Months Ended						3 Months Ended			12 Months Ended							0 Months Ended				2 Months Ended	3 Months Ended			1 Months Ended			1 Months Ended		0 Months Ended	12 Months Ended					12 Months Ended
	May 05, 2011 USD ($)	Nov. 26, 2010 USD ($)	Nov. 15, 2010	Sep. 09, 2010 USD ($)	Jun. 10, 2010 USD ($)	Mar. 31, 2010 USD ($)	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2010 CHF	Dec. 31, 2009 USD ($)	Dec. 31, 2011 CHF	Dec. 31, 2011 Voting Common Stock [Member]	Dec. 31, 2011 Nonvoting Common Stock [Member]	Jan. 06, 2012 Par Value Reduction [Member] USD ($)	Oct. 07, 2011 Par Value Reduction [Member] USD ($)	Aug. 05, 2011 Par Value Reduction [Member] USD ($)	Jul. 18, 2011 Par Value Reduction [Member] CHF	Sep. 19, 2011 Par Value Reduction [Member] CHF	Dec. 19, 2011 Par Value Reduction [Member] CHF	Dec. 31, 2011 Allied World Bermuda [Member] USD ($)	Dec. 31, 2010 Allied World Bermuda [Member] USD ($)	Nov. 30, 2010 The Goldman Sachs Group, Inc ("Goldman Sachs") [Member] USD ($)	Aug. 31, 2010 The Goldman Sachs Group, Inc ("Goldman Sachs") [Member] USD ($)	Nov. 05, 2010 The Goldman Sachs Group, Inc ("Goldman Sachs") [Member]	Aug. 31, 2010 The Chubb Corporation ("Chubb") [Member] USD ($)	Feb. 28, 2011 American International Group, Inc. ("AIG") [Member] USD ($)	Nov. 26, 2010 Redomestication [Member] USD ($)	Dec. 31, 2010 Redomestication [Member]	Dec. 31, 2010 Redomestication [Member] Voting Common Stock [Member] USD ($)	Dec. 31, 2010 Redomestication [Member] Voting Common Stock [Member] CHF	Dec. 31, 2010 Redomestication [Member] Nonvoting Common Stock [Member] USD ($)	Dec. 31, 2010 Redomestication [Member] Nonvoting Common Stock [Member] CHF	Dec. 31, 2010 Redomestication [Member] Treasury Shares [Member] USD ($)	Dec. 31, 2010 Allied World Switzerland (Parent Guarantor) [Member] Redomestication [Member] CHF
Class of Warrant or Right [Line Items]
Maximum percent increase in share capital										20.00%
Maximum authorized value increase of registered share capital														111,682
Maximum authorized increased voting shares										7,960,260
maximum number of conditional capital voting shares										7,200,000
Common shares, outstanding										37,742,131	38,089,226	38,089,226			37,712,891	29,240																39,801,302	39,801,302	202,340	202,340
Total share capital										557,153,000	600,055,000																						597,020,000		3,035,000
Par value per share												15		14.03										$ 0.03								$ 15.00	15.00	$ 15.00	15.00		15.00
Reduction in additional paid-in capital										78,225,000	170,239,000
Adjustment to additional paid-in capital, other												600,055,000
Exchange rate between the U.S. Dollar and Swiss Franc											one-for-one	one-for-one
Maximum percentage of registered capital in treasury shares											10.00%	10.00%
Shares cancelled, shares																															10,879,106
Shares cancelled																																				561,851,000
Warrant agreements to acquire common shares																							5,500,000		1,500,000			2,000,000	2,000,000
Warrants, exercise price per share																							$ 34.20		$ 34.20			$ 34.20	$ 34.20
Dividends paid per common share		$ 0.2		$ 0.2	$ 0.2	$ 0.20				$ 0.75	$ 1.05		$ 0.74							0.30	0.32	0.35								$ 0.25
Dividend, date of record			Nov. 15, 2010				Aug. 24, 2010	May 25, 2010	Mar. 16, 2010																						Nov. 15, 2010
Repurchase of warrant										53,620,000	70,016,000														37,197,000			32,819,000	53,620,000
Shares repurchased										1,419,163															3,159,793	5,000,000
Shares repurchased, average price per share										$ 61.09															$ 58.69	$ 50.00
Cost of shares repurchased										86,700,000	674,662,000														185,448,000	250,000,000
Percentage discount of weighted average trading price of common share																											0.50%
Common Stock, Dividends, Per Share, Cash Paid		$ 0.2		$ 0.2	$ 0.2	$ 0.20				$ 0.75	$ 1.05		$ 0.74							0.30	0.32	0.35								$ 0.25
Dividends declared per share	$ 0.375
Cash dividends for common stock																	$ 14,302,000	$ 14,305,000	$ 14,295,000