Summary of Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Amortized cost
Maturing in one year or less	$ 548,021
Maturing after one year through five years	3,643,813
Maturing after five years through ten years	3,852,033
Maturing after ten years	5,110,752
Mortgage-backed and asset-backed securities	3,027,578
Amortized cost	16,182,197	17,807,359
Estimated fair value
Maturing in one year or less	578,347
Maturing after one year through five years	3,968,142
Maturing after five years through ten years	4,085,469
Maturing after ten years	5,453,109
Mortgage-backed and asset-backed securities	3,207,999
Estimated fair value and carrying value	$ 17,293,066	$ 18,469,544