Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income		$ 46,581	$ 40,017	$ 131,237	$ 212,439
Components of other comprehensive income
Unrealized holding gains (losses), net, arising on available-for-sale fixed maturity investments		39,983	55,849	407,208	895,589
Unrealized holding gains (losses), net, arising on cash flow hedges		(23,111)	(7,805)	(48,311)	(3,307)
Reclassification adjustment for (gains) losses, net, realized in net income		(2,885)	(10,284)	(3,242)	(61,375)
Net unrealized gains (losses) related to investments		13,987	37,760	355,655	830,907
Future policy benefits, DAC and VOBA adjustments		(1,977)	(18,214)	(85,992)	(190,985)
Employee benefit plan adjustment		10,744	2,494	15,036	6,962
Other comprehensive income before income taxes		22,754	22,040	284,699	646,884
Income tax expense related to items of other comprehensive income		7,963	7,715	99,644	226,410
Other comprehensive income (loss)	[1]	14,791	14,325	185,055	420,474
Total comprehensive income		$ 61,372	$ 54,342	$ 316,292	$ 632,913

[1] Other comprehensive income includes the non-credit component of impaired gains (losses), net, on fixed maturities available-for-sale in the amounts of $(2,258) and $(959) for the three months ended September 30, 2017, and 2016, respectively and $(3,867) and $(5,326) for the nine months ended September 30, 2017, and 2016, respectively.