Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 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	$ 3,684	$ 40,733	$ (19,164)	$ 94,835
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	15,108	76,966	83,810	(15,283)
Derivative, Gain (Loss) on Derivative, Net	2,941	18,807	28,785	(7,970)
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	(5,955)	(2,019)	(22,357)	(626)
Derivative, Gain (Loss) on Derivative, Net	(6,925)	(7,816)	(28,322)	3,418
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	360	(28,137)	22,723	(91,077)
Derivative, Gain (Loss) on Derivative, Net	$ 3,023	$ (40,167)	$ 31,859	$ (66,010)