Investments (Details 5) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Available For Sale Securities Debt Maturities Amortized Cost
Due in one year or less	$ 179,357
Due after one year through five years	2,659,446
Due after five year through ten years	4,094,202
Due after ten years	5,055,359
Asset and mortgage-backed securities	2,826,495
Total	14,814,859	14,182,880
Available For Sale Securities Debt Maturities Fair Value
Due in one year or less	180,864
Due after one year through five years	2,770,954
Due after five year through ten years	4,447,320
Due after ten years	6,499,742
Asset and mortgage-backed securities	2,895,177
Total	$ 16,794,057	$ 16,200,950