Fair Value Measurements (Details 3) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 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	$ 16,249,035	$ 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	257,173	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)	3.00%	5.00%
Adjusted ABX Index spread assumption	4.95%	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	$ 255,293	$ 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)	1.00%	1.20%
Overall discount rate (as a percent)	3.03%	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)	5.70%	7.90%
Overall discount rate (as a percent)	6.23%	9.18%