Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net	$ (16,178)	$ 118,527	$ (8,595)	$ 203,098
Gain Loss On Investments Related To Change In Fair Value Of Derivatives Excluding Embedded Derivatives	(46,537)	13,846	(25,607)	33,625
Total benefits and expenses	2,416,550	2,532,485	4,753,038	4,990,218
Net income	130,391	198,296	255,505	334,960
Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net	(23,098)	78,835	(25,423)	156,076
Net income	(3,917)	17,962	(6,504)	36,042
Embedded Derivatives In Equity Indexed Annuities [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total benefits and expenses	8,080	(27,285)	(21,246)	(51,125)
Net income	1,233	(15,600)	(14,766)	(33,976)
Embedded Derivatives In Variable Annuity Contracts [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net	50,878	(5,183)	25,745	(28,844)
Net income	$ 19,608	$ (6,486)	$ 10,198	$ (20,154)