Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	$ 645,085		$ 311,682		$ 345,754		$ 635,699
Other comprehensive income (loss) before reclassifications	(62,601)		(28,619)		255,420		(338,300)
Amounts reclassified from AOCI	(1,578)		(8,745)		(20,268)		(23,081)
Other comprehensive income (loss)	(64,179)	[1]	(37,364)	[1]	235,152	[1]	(361,381)	[1]
Balance at the end of the period	580,906		274,318		580,906		274,318
Unrealized holding gains / losses arising on fixed maturities, available-for- sale
Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	790,332		506,490		434,023		927,678
Other comprehensive income (loss) before reclassifications	(65,520)		(13,373)		306,499		(422,791)
Amounts reclassified from AOCI	(2,664)		(8,361)		(18,374)		(20,131)
Other comprehensive income (loss)	(68,184)		(21,734)		288,125		(442,922)
Balance at the end of the period	722,148		484,756		722,148		484,756
Unrealized holding gains / losses arising on cash flow hedges
Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	25,068		33,386		25,517		24,962
Other comprehensive income (loss) before reclassifications	4,815		(32,440)		7,346		(21,450)
Amounts reclassified from AOCI	(1,716)		(384)		(4,696)		(2,950)
Other comprehensive income (loss)	3,099		(32,824)		2,650		(24,400)
Balance at the end of the period	28,167		562		28,167		562
Future policy benefits, DAC and VOBA adjustments
Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	(126,529)		(105,399)		(70,000)		(194,146)
Other comprehensive income (loss) before reclassifications	263		17,194		(56,266)		105,941
Amounts reclassified from AOCI	0		0		0		0
Other comprehensive income (loss)	263		17,194		(56,266)		105,941
Balance at the end of the period	(126,266)		(88,205)		(126,266)		(88,205)
Employee benefit plan adjustment
Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	(43,786)		(122,795)		(43,786)		(122,795)
Other comprehensive income (loss) before reclassifications	(2,159)		0		(2,159)		0
Amounts reclassified from AOCI	2,802		0		2,802		0
Other comprehensive income (loss)	643		0		643		0
Balance at the end of the period	$ (43,143)		$ (122,795)		$ (43,143)		$ (122,795)

[1] Other comprehensive income (loss) includes the non-credit component of impaired gains (losses) on fixed maturities available-for-sale in the amounts of $(996) and $3,173 for the three months ended September 30, 2014 and 2013, respectively, and $(3,812) and $9,818 for the nine months ended September 30, 2014 and 2013, respectively.