Fair Value Measurements (Details 3) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table
Fixed maturities available-for-sale	$ 16,281,559	$ 18,188,344
Recurring basis | Level 3
Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table
Fixed maturities available-for-sale	262,596	267,392
Fixed maturities available-for-sale, Asset-backed securities | Recurring basis | Internal model pricing | Weighted average
Unobservable Input
Prepayment speed assumption (as a percent)	5.00%	5.00%
Constant default rate assumption (as a percent)	4.00%	5.00%
Adjusted ABX Index spread assumption	5.51%	6.55%
Internally calculated liquidity premium adjustment included in Adjusted ABX Index spread assumption	2.17%	2.17%
Fixed maturities available-for-sale, Asset-backed securities | Recurring basis | Level 3 | Internal model pricing
Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table
Fixed maturities available-for-sale	$ 260,709	$ 265,470
Fixed maturities available-for-sale, Asset-backed securities | Recurring basis | Level 3 | Internal model pricing | Minimum
Unobservable Input
Constant default rate assumption (as a percent)	0.80%	1.20%
Overall discount rate (as a percent)	2.89%	3.84%
Fixed maturities available-for-sale, Asset-backed securities | Recurring basis | Level 3 | Internal model pricing | Maximum
Unobservable Input
Constant default rate assumption (as a percent)	9.20%	7.90%
Overall discount rate (as a percent)	8.69%	9.18%