Investments in Fixed Maturity Securities (The Amortized Cost and Fair Value of Fixed Maturity Securities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 926,865
Amortized Cost, Due after one year through five years	3,411,033
Amortized Cost, Due after five years through ten years	3,046,756
Amortized Cost, Due after ten years	2,554,437
Amortized Cost, Mortgage-backed securities	1,352,540
Total investment in fixed maturity securities, Amortized Cost	11,291,631	11,217,954
Fair Value, Due in one year or less	935,322
Fair Value, Due after one year through five years	3,548,043
Fair Value, Due after five years through ten years	3,191,387
Fair Value, Due after ten years	2,596,505
Fair Value, Mortgage-backed securities	1,360,487
Total investments in fixed maturity securities, Fair Value	$ 11,631,744	$ 11,968,376