Fair Value Of Financial Instruments (Narrative) (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
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net realized investment gains (losses)	$ 31,632	$ (130,809)	$ 58,878	$ 50,376	$ (3,738)	$ 116,930	$ 94,933	$ 77,487	$ 10,077	$ 285,612	$ 126,352
Hedge Funds [Member] | Unrealized Gains And Losses [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net realized investment gains (losses)									(5,302)	15,372
Mortgage-Backed [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Transfers of securities from Level 3 to Level 2									41,694
Mortgage-Backed [Member] | Unrealized Gains And Losses [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net realized investment gains (losses)									(353)	9,282
Asset-Backed [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Transfers of securities from Level 3 to Level 2									4,988	155,158
Asset-Backed [Member] | Unrealized Gains And Losses [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net realized investment gains (losses)									$ (2,902)	$ (145)
Senior Notes [Member] | 7.50% Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes, interest rate	7.50%								7.50%
Debt instrument interest rate traded percentage									114.30%
Debt instrument interest rate effective yield percentage									4.00%
Senior Notes [Member] | 5.50% Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes, interest rate	5.50%								5.50%
Debt instrument interest rate traded percentage									100.40%
Debt instrument interest rate effective yield percentage									5.40%