Investments in Fixed Maturity Securities (The Amortized Cost and Fair Value of Fixed Maturity Securities) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Investments in Fixed Maturity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 707,725
Amortized Cost, Due after one year through five years	3,220,365
Amortized Cost, Due after five years through ten years	2,552,147
Amortized Cost, Due after ten years	2,739,124
Amortized Cost, Mortgage-backed securities	1,473,880
Total investment in fixed maturity securities, Amortized Cost	10,693,241	10,853,193
Fair Value, Due in one year or less	718,688
Fair Value, Due after one year through five years	3,373,391
Fair Value, Due after five years through ten years	2,748,995
Fair Value, Due after ten years	2,862,575
Fair Value, Mortgage-backed securities	1,544,848
Total investments in fixed maturity securities, Fair Value	$ 11,248,497	$ 11,215,317