Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Gain Loss On Investments Related To Change In Fair Value Of Derivatives Excluding Embedded Derivatives	$ (8,961)	$ (5,427)	$ (28,125)	$ 89,408
Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	23,044	49,078	106,854	33,795
Derivative, Gain (Loss) on Derivative, Net	7,515	9,653	36,300	1,683
Embedded Derivatives In Equity Indexed Annuities [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(13,133)	(20,104)	(35,490)	(20,730)
Derivative, Gain (Loss) on Derivative, Net	(9,737)	(13,397)	(38,059)	(9,979)
Embedded Derivatives In Variable Annuity Contracts [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(6,205)	7,988	16,518	(83,089)
Derivative, Gain (Loss) on Derivative, Net	$ (1,074)	$ 2,595	$ 30,785	$ (63,415)