Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income		$ 49,824	$ 73,799	$ 84,652	$ 172,421
Components of other comprehensive income
Unrealized holding gains (losses), net, arising on available-for-sale fixed maturity investments		236,996	393,130	367,225	839,740
Unrealized holding gains (losses), net, arising on cash flow hedges		(18,245)	6,102	(25,200)	4,498
Reclassification adjustment for (gains) losses, net, realized in net income		(1,832)	(28,635)	(357)	(51,091)
Net unrealized gains (losses) related to investments		216,919	370,597	341,668	793,147
Future policy benefits, DAC and VOBA adjustments		(55,549)	(96,531)	(84,015)	(172,771)
Employee benefit plan adjustment		2,146	2,234	4,292	4,468
Other comprehensive income before income taxes		163,516	276,300	261,945	624,844
Income tax expense related to items of other comprehensive income		57,231	96,704	91,681	218,695
Other comprehensive income (loss)	[1]	106,285	179,596	170,264	406,149
Total comprehensive income		$ 156,109	$ 253,395	$ 254,916	$ 578,570

[1] Other comprehensive income includes the non-credit component of impaired gains (losses), net, on fixed maturities available-for-sale in the amounts of $(520) and $(2,472) for the three months ended June 30, 2017, and 2016, respectively and $(1,609) and $(4,367) for the six months ended June 30, 2017, and 2016, respectively.