Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
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	$ (14,151)	$ 3,684	$ (33,625)	$ (19,164)
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	8,805	15,108	22,416	83,810
Derivative, Gain (Loss) on Derivative, Net	5,987	2,941	12,836	28,785
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	6,519	(5,955)	31,870	(22,357)
Derivative, Gain (Loss) on Derivative, Net	3,966	(6,925)	10,503	(28,322)
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	15,324	360	30,109	22,723
Derivative, Gain (Loss) on Derivative, Net	$ 12,472	$ 3,023	$ 23,598	$ 31,859