Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Other Comprehensive Income [Roll Forward]
Beginning balance		$ 459,991	$ 691,137	$ 233,438	$ 603,018
Other comprehensive income (loss) before reclassifications		196,757	(280,398)	436,454	(174,402)
Amounts reclassified from AOCI		(17,161)	(1,368)	(30,305)	(19,245)
Other comprehensive income (loss)	[1]	179,596	(281,766)	406,149	(193,647)
Ending balance		639,587	409,371	639,587	409,371
Unrealized holding gains / losses arising on fixed maturities, available-for- sale
Other Comprehensive Income [Roll Forward]
Beginning balance		616,836	883,761	339,520	784,183
Other comprehensive income (loss) before reclassifications		255,535	(321,318)	545,831	(203,424)
Amounts reclassified from AOCI		(17,337)	(1,916)	(30,317)	(20,232)
Other comprehensive income (loss)		238,198	(323,234)	515,514	(223,656)
Ending balance		855,034	560,527	855,034	560,527
Unrealized holding gains / losses arising on cash flow hedges
Other Comprehensive Income [Roll Forward]
Beginning balance		42,625	42,824	45,284	33,141
Other comprehensive income (loss) before reclassifications		3,967	(10,812)	2,924	339
Amounts reclassified from AOCI		(1,276)	(1,359)	(2,892)	(2,827)
Other comprehensive income (loss)		2,691	(12,171)	32	(2,488)
Ending balance		45,316	30,653	45,316	30,653
Future policy benefits, DAC and VOBA adjustments
Other Comprehensive Income [Roll Forward]
Beginning balance		(115,341)	(131,028)	(65,785)	(108,194)
Other comprehensive income (loss) before reclassifications		(62,745)	51,732	(112,301)	28,898
Amounts reclassified from AOCI		0	0	0	0
Other comprehensive income (loss)		(62,745)	51,732	(112,301)	28,898
Ending balance		(178,086)	(79,296)	(178,086)	(79,296)
Employee benefit plan adjustment
Other Comprehensive Income [Roll Forward]
Beginning balance		(84,129)	(104,420)	(85,581)	(106,112)
Other comprehensive income (loss) before reclassifications		0	0	0	(215)
Amounts reclassified from AOCI		1,452	1,907	2,904	3,814
Other comprehensive income (loss)		1,452	1,907	2,904	3,599
Ending balance		$ (82,677)	$ (102,513)	$ (82,677)	$ (102,513)

[1] Other comprehensive income (loss) includes the non-credit component of impaired gains (losses), net, on fixed maturities available-for-sale in the amounts of $(2,472) and $1,314 for the three months ended June 30, 2016, and 2015, respectively, and $(4,367) and $(1,229) for the six months ended June 30, 2016, and 2015, respectively.