Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net	$ 86,624	$ (111,346)	$ 84,002	$ (119,941)
Gain Loss On Investments Related To Change In Fair Value Of Derivatives Excluding Embedded Derivatives	(5,427)	67,831	89,408	42,224
Total benefits and expenses	2,612,977	2,298,497	7,703,810	7,051,535
Net income	198,719	83,534	511,294	339,039
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	49,078	(46,169)	33,795	(71,592)
Net income	9,653	(11,783)	1,683	(18,287)
Embedded Derivatives In Equity Indexed Annuities [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total benefits and expenses	(20,104)	50,246	(20,730)	28,999
Net income	(13,397)	27,861	(9,979)	13,095
Embedded Derivatives In Variable Annuity Contracts [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net	7,988	(95,372)	(83,089)	(69,628)
Net income	$ 2,595	$ (116,994)	$ (63,415)	$ (106,796)