Investments In Fixed Maturity Securities Investments in Fixed Maturity Securities (Amortized cost and fair value of fixed maturity securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 803,520
Amortized Cost, Due after one year through five years	5,237,765
Amortized Cost, Due after five years through ten years	3,169,976
Amortized Cost, Due after ten years	2,773,270
Amortized Cost, Mortgaged-backed securities	1,202,992
Total investments in fixed maturity securities, Amortized Value	13,187,523	$ 12,958,335
Fair Value, Due in one year or less	819,242
Fair Value, Due after one year through five years	5,368,120
Fair Value, Due after five years through ten years	3,311,894
Fair Value, Due after ten years	2,823,111
Fair Value, Mortgage-backed securities	1,208,239
Total investments in fixed maturity securities, Fair Value	$ 13,530,606	$ 13,204,814