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Investments (Schedule Of Contractual Maturities Of Fixed Maturity Investments) (Details) (USD $)
In Thousands
Sep. 30, 2011
Dec. 31, 2010
Investments  
Trading, Amortized Cost, Due in less than one year$ 167,947 
Trading, Amortized Cost, Due after one through five years1,876,919 
Trading, Amortized Cost, Due after five through ten years815,283 
Trading, Amortized Cost, Due after ten years127,583 
Trading, Amortized Cost, Mortgage backed669,592 
Trading, Amortized Cost, Asset backed14,404 
Trading, Amortized Cost3,671,7283,859,442
Trading, Fair Value, Due in less than one year168,432 
Trading, Fair Value, Due after one through five years1,880,559 
Trading, Fair Value, Due after five through ten years817,714 
Trading, Fair Value, Due after ten years131,180 
Trading, Fair Value, Mortgage backed675,399 
Trading, Fair Value, Asset backed14,385 
Trading, Fair Value3,687,6693,871,780
Available for Sale, Amortized Cost, Due in less than one year174 
Available for Sale, Amortized Cost, Due after one through five years11,869 
Available for Sale, Amortized Cost, Due after five through ten years13,172 
Available for Sale, Amortized Cost, Due after ten years6,090 
Available for Sale, Amortized Cost, Mortgage-backed102,985 
Available for Sale, Amortized Cost, Asset-backed4,993 
Available for Sale, Amortized Cost139,283225,549
Available for Sale, Fair Value, Due in less than one year125 
Available for Sale, Fair Value, Due after one through five years12,857 
Available for Sale, Fair Value, Due after five through ten years13,482 
Available for Sale, Fair Value, Due after ten years6,520 
Available for Sale, Fair Value, Mortgage-backed111,761 
Available for Sale, Fair Value, Asset-backed5,224 
Available for Sale, Fair Value149,969244,917
Debt Securities, Amortized Cost, Due in less than one year168,121 
Debt Securities, Amortized Cost, Due after one through five years1,888,788 
Debt Securities, Amortized Cost, Due after five through ten years828,455 
Debt Securities, Amortized Cost, Due after ten years133,673 
Debt Securities, Amortized Cost, Mortgage backed772,577 
Debt Securities, Amortized Cost, Asset backed19,397 
Debt Securities, Amortized Cost3,811,011 
Debt Securities, Fair Value, Due in less than one year168,557 
Debt Securities, Fair Value, Due after one through five years1,893,416 
Debt Securities, Fair Value, Due after five through ten years831,196 
Debt Securities, Fair Value, Due after ten years137,700 
Debt Securities, Fair Value, Mortgage backed787,160 
Debt Securities, Fair Value, Asset backed19,609 
Debt Securities, Fair Value$ 3,837,638