Derivative Instruments (Details 6) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net									$ 254,136,000	$ (36,056,000)	$ 212,030,000
Total benefits and expenses	2,402,013,000	2,247,602,000	2,159,861,000	2,112,212,000	2,154,968,000	1,838,511,000	2,016,808,000	2,055,680,000	8,921,688,000	8,065,967,000	7,455,549,000
Net income	222,989,000	144,475,000	141,111,000	123,318,000	138,579,000	134,602,000	123,944,000	148,920,000	631,893,000	546,045,000	535,742,000
Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements And Variable Annuity Contracts [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net									115,009,000	(87,236,000)	160,274,000
Net income									25,454,000	(7,599,000)	28,831,000
Embedded Derivatives In Equity Indexed Annuities [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total benefits and expenses									(30,434,000)	(114,921,000)	(44,988,000)
Net income									6,110,000	(55,915,000)	(26,265,000)
Embedded Derivatives In Variable Annuity Contracts [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net									104,613,000	(224,184,000)	(28,786,000)
Net income									$ 6,367,000	$ (30,230,000)	$ (5,045,000)