Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
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]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ 13,611	$ 68,702
Derivative, Gain (Loss) on Derivative, Net	6,850	25,844
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	25,351	(16,402)
Derivative, Gain (Loss) on Derivative, Net	6,537	(21,396)
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	14,785	22,363
Derivative, Gain (Loss) on Derivative, Net	$ 11,126	$ 28,836