Other Comprehensive Income - Accum Balances for each classification (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period		$ 603,018	$ 345,754	$ 635,699
Other comprehensive income (loss) before reclassifications		(343,098)	288,713	(272,593)
Amounts reclassified from AOCI		(26,482)	(31,449)	(17,352)
Net current period other comprehensive income (loss)	[1]	(369,580)	257,264	(289,945)
Balance at the end of the period		233,438	603,018	345,754
Unrealized holding gains / losses arising on fixed maturities, available-for-sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period		784,183	434,023	927,678
Other comprehensive income (loss) before reclassifications		(418,522)	381,198	(467,178)
Amounts reclassified from AOCI		(26,141)	(31,038)	(26,477)
Net current period other comprehensive income (loss)		(444,663)	350,160	(493,655)
Balance at the end of the period		339,520	784,183	434,023
Unrealized holding gains / losses arising on cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period		33,141	25,517	24,962
Other comprehensive income (loss) before reclassifications		20,190	13,089	2,016
Amounts reclassified from AOCI		(8,047)	(5,465)	(1,461)
Net current period other comprehensive income (loss)		12,143	7,624	555
Balance at the end of the period		45,284	33,141	25,517
Future policy benefits, DAC and VOBA adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period		(108,194)	(70,000)	(194,147)
Other comprehensive income (loss) before reclassifications		42,409	(38,194)	124,147
Net current period other comprehensive income (loss)		42,409	(38,194)	124,147
Balance at the end of the period		(65,785)	(108,194)	(70,000)
Employee benefit plan adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period		(106,112)	(43,786)	(122,794)
Other comprehensive income (loss) before reclassifications		12,825	(67,380)	68,422
Amounts reclassified from AOCI		7,706	5,054	10,586
Net current period other comprehensive income (loss)		20,531	(62,326)	79,008
Balance at the end of the period		$ (85,581)	$ (106,112)	$ (43,786)

[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 $(6,596), $177, and $18,388 for the years ended December 31, 2015, 2014, and 2013, respectively.