Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	$ 345,754		$ 635,699		$ 469,982
Other comprehensive income (loss) before reclassifications	288,713		(272,593)		229,582
Amounts reclassified from AOCI	(31,449)		(17,352)		(63,865)
Net current period other comprehensive income (loss)	257,264	[1]	(289,945)	[1]	165,717	[1]
Balance at the end of the period	603,018		345,754		635,699
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	434,023		927,678		646,805
Other comprehensive income (loss) before reclassifications	381,198		(467,178)		347,118
Amounts reclassified from AOCI	(31,038)		(26,477)		(66,245)
Net current period other comprehensive income (loss)	350,160		(493,655)		280,873
Balance at the end of the period	784,183		434,023		927,678
Unrealized holding gains / losses arising on cash flow hedged
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	25,517		24,962		41,003
Other comprehensive income (loss) before reclassifications	13,089		2,016		(12,273)
Amounts reclassified from AOCI	(5,465)		(1,461)		(3,768)
Net current period other comprehensive income (loss)	7,624		555		(16,041)
Balance at the end of the period	33,141		25,517		24,962
Future policy benefits, DAC and VOBA adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	(70,000)		(194,147)		(139,655)
Other comprehensive income (loss) before reclassifications	(38,194)		124,147		(54,492)
Net current period other comprehensive income (loss)	(38,194)		124,147		(54,492)
Balance at the end of the period	(108,194)		(70,000)		(194,147)
Employee benefit plan adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	(43,786)		(122,794)		(78,171)
Other comprehensive income (loss) before reclassifications	(67,380)		68,422		(50,771)
Amounts reclassified from AOCI	5,054		10,586		6,148
Net current period other comprehensive income (loss)	(62,326)		79,008		(44,623)
Balance at the end of the period	$ (106,112)		$ (43,786)		$ (122,794)

[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 $177, $18,388 and $26,583 for the years ended December 31, 2014, 2013 and 2012, respectively.