Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net									$ 94,195	$ (164,750)	$ 186,193
Total benefits and expenses	$ 2,773,755	$ 2,612,977	$ 2,685,845	$ 2,404,988	$ 2,621,848	$ 2,298,497	$ 2,416,550	$ 2,336,488	10,477,565	9,673,383	9,895,661
Net Income (Loss) Attributable to Parent	$ 190,149	$ 198,719	$ 236,103	$ 76,472	$ 163,127	$ 83,534	$ 130,391	$ 125,114	701,443	502,166	684,047
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									54,169	98,792	198,365
Net Income (Loss) Attributable to Parent									9,160	(26,025)	45,171
Embedded Derivatives In Variable Annuity Contracts [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net									7,835	(33,192)	(129,224)
Net Income (Loss) Attributable to Parent									(41,201)	(29,008)	27,601
Embedded Derivatives In Equity Indexed Annuities [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total benefits and expenses									10,708	19,440	(104,844)
Net Income (Loss) Attributable to Parent									$ (4,148)	$ 6,204	$ (69,963)