Income Taxes (Schedule Of Income Sources) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Tax Contingency [Line Items]
Income before income taxes	$ 195,052	$ (5,300)	$ 104,873	$ 10,903	$ 92,579	$ 268,089	$ 194,337	$ 136,945	$ 305,528	$ 691,950	$ 643,531
Europe [Member]
Income Tax Contingency [Line Items]
Income before income taxes									108,800	5,986	10,567
Bermuda [Member]
Income Tax Contingency [Line Items]
Income before income taxes									133,553	609,880	537,333
United States [Member]
Income Tax Contingency [Line Items]
Income before income taxes									$ 63,175	$ 76,084	$ 95,631