Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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	$ (25,258)	$ (8,961)	$ (58,883)	$ (28,125)
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	(2,081)	23,044	20,335	106,854
Derivative, Gain (Loss) on Derivative, Net	(1,320)	7,515	11,517	36,300
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	(25,347)	(13,133)	6,523	(35,490)
Derivative, Gain (Loss) on Derivative, Net	(17,311)	(9,737)	(6,808)	(38,059)
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	32,133	(6,205)	62,242	16,518
Derivative, Gain (Loss) on Derivative, Net	$ 9,463	$ (1,074)	$ 33,061	$ 30,785