Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net									$ (164,750)	$ 186,193	$ 63,990
Total benefits and expenses	$ (2,621,848)	$ (2,298,497)	$ (2,416,550)	$ (2,336,488)	$ (2,420,670)	$ (2,484,773)	$ (2,532,485)	$ (2,457,733)	(9,673,383)	(9,895,661)	(9,683,099)
Net Income (Loss) Attributable to Parent	$ 163,127	$ 83,534	$ 130,391	$ 125,114	$ 191,091	$ 157,996	$ 198,296	$ 136,664	502,166	684,047	418,837
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									98,792	198,365	70,177
Net Income (Loss) Attributable to Parent									(26,025)	45,171	18,920
Embedded Derivatives In Variable Annuity Contracts [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net									(33,192)	(129,224)	142,050
Net Income (Loss) Attributable to Parent									(29,008)	27,601	70,123
Embedded Derivatives In Equity Indexed Annuities [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total benefits and expenses									(19,440)	(104,844)	(115,409)
Net Income (Loss) Attributable to Parent									$ 6,204	$ (69,963)	$ (106,792)