Other Comprehensive Income - Accum Balances for each classification (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		$ 1,882,266	$ 2,137,513	$ 1,875,732
Other comprehensive income (loss) before reclassifications		44,680	(343,098)	288,713
Amounts reclassified from AOCI		(42,243)	(26,482)	(31,449)
Net current period other comprehensive income (loss)	[1]	2,437	(369,580)	257,264
Balances		2,012,321	1,882,266	2,137,513
Unrealized holding gains / losses arising on fixed maturities, available-for-sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		339,520	784,183	434,023
Other comprehensive income (loss) before reclassifications		13,192	(418,522)	381,198
Amounts reclassified from AOCI		(40,964)	(26,141)	(31,038)
Net current period other comprehensive income (loss)		(27,772)	(444,663)	350,160
Balances		311,748	339,520	784,183
Unrealized holding gains / losses arising on cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		45,284	33,141	25,517
Other comprehensive income (loss) before reclassifications		29,104	20,190	13,089
Amounts reclassified from AOCI		(7,312)	(8,047)	(5,465)
Net current period other comprehensive income (loss)		21,792	12,143	7,624
Balances		67,076	45,284	33,141
Future policy benefits, DAC and VOBA adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		(65,785)	(108,194)	(70,000)
Other comprehensive income (loss) before reclassifications		7,139	42,409	(38,194)
Net current period other comprehensive income (loss)		7,139	42,409	(38,194)
Balances		(58,646)	(65,785)	(108,194)
Employee benefit plan adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		(85,581)	(106,112)	(43,786)
Other comprehensive income (loss) before reclassifications		(4,755)	12,825	(67,380)
Amounts reclassified from AOCI		6,033	7,706	5,054
Net current period other comprehensive income (loss)		1,278	20,531	(62,326)
Balances		(84,303)	(85,581)	(106,112)
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances		233,438	603,018	345,754
Net current period other comprehensive income (loss)		2,437	(369,580)	257,264
Balances		$ 235,875	$ 233,438	$ 603,018

[1] Other comprehensive income (loss) includes the non-credit component of impaired losses on fixed maturities available-for-sale, net of future policy benefits, DAC and VOBA adjustments and income taxes, in the amounts of $(6,520), $(6,596), and $177 for the years ended December 31, 2016, 2015, and 2014, respectively.