Consolidated Statements of Shareholders' Equity (USD $) In Thousands	Total	[CommonStockMember]	[PreferredStockMember]	[AdditionalPaidInCapitalMember]	[AccumulatedOtherComprehensiveIncomeMember]	[RetainedEarningsMember]	[TreasuryStockMember]
Balance at beginning of year at Dec. 31, 2008		$ 57,749	$ 20,800	$ 1,465,688	$ 22,808	$ 2,729,662	$ (97,599)
Net (loss) income	1,536,854					1,536,854
Dividends on common shares						(117,326)
Dividends on preferred shares	(34,525)					(34,525)
Issuance of common shares related to the acquisition of Paris Re		24,361		1,858,055
Issuance of common shares, other		476		33,261
Issuance of preferred shares			0	0
Change in currency translation adjustment	47,955				47,955
Change in other accumulated comprehensive (loss) income	14,164				14,164
Reissuance of treasury shares related to the acquisition of Paris Re						(13,883)	97,227
Repurchase of common shares							0
Balance at end of year at Dec. 31, 2009	7,645,727	82,586	20,800	3,357,004	84,927	4,100,782	(372)
Net (loss) income	852,552					852,552
Dividends on common shares						(157,631)
Dividends on preferred shares	(34,525)					(34,525)
Issuance of common shares related to the acquisition of Paris Re		0		0
Issuance of common shares, other		1,447		62,860
Issuance of preferred shares			0	0
Change in currency translation adjustment	(66,742)				(66,742)
Change in other accumulated comprehensive (loss) income	(14,129)				(14,129)
Reissuance of treasury shares related to the acquisition of Paris Re						0	0
Repurchase of common shares							(1,082,640)
Balance at end of year at Dec. 31, 2010	7,206,919	84,033	20,800	3,419,864	4,056	4,761,178	(1,083,012)
Net (loss) income	(520,291)					(520,291)
Dividends on common shares						(158,764)
Dividends on preferred shares	(47,020)					(47,020)
Issuance of common shares related to the acquisition of Paris Re		0		0
Issuance of common shares, other		734		37,160
Issuance of preferred shares			14,950	346,772
Change in currency translation adjustment	(11,834)				(11,834)
Change in other accumulated comprehensive (loss) income	(4,866)				(4,866)
Reissuance of treasury shares related to the acquisition of Paris Re						0	0
Repurchase of common shares							(396,218)
Balance at end of year at Dec. 31, 2011	$ 6,467,542	$ 84,767	$ 35,750	$ 3,803,796	$ (12,644)	$ 4,035,103	$ (1,479,230)