Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Available For Sale Securities Debt Maturities Amortized Cost
Due in one year or less	$ 686,582
Due after one year through five years	4,882,381
Due after five year through ten years	7,920,478
Due after ten years	9,138,647
Asset and mortgage-backed securities	3,677,244
Total	26,305,332	$ 23,105,597
Available For Sale Securities Debt Maturities Fair Value
Due in one year or less	696,191
Due after one year through five years	5,118,186
Due after five year through ten years	8,213,365
Due after ten years	10,257,261
Asset and mortgage-backed securities	3,778,972
Total	$ 28,063,975	$ 25,480,972