Derivative Instruments (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net	$ 84,571	$ 94,371
Total benefits and expenses	2,457,733	2,322,275
Net income	136,664	185,535
Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net	77,241	90,257
Net income	18,079	21,624
Embedded Derivatives In Equity Indexed Annuities [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total benefits and expenses	(23,840)	(32,996)
Net income	(18,375)	(29,550)
Embedded Derivatives In Variable Annuity Contracts [Member]
Changes In Estimated Fair Value Related To Embedded Derivatives [Line Items]
Total investment related gains (losses), net	(23,661)	51,314
Net income	$ (13,669)	$ 12,192