Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Unrealized gains losses arising on fixed maturities, available-for sale	Jun. 30, 2012 Unrealized gains losses arising on fixed maturities, available-for sale	Jun. 30, 2013 Unrealized gains losses arising on fixed maturities, available-for sale	Jun. 30, 2012 Unrealized gains losses arising on fixed maturities, available-for sale	Jun. 30, 2013 Gains / losses on cash flow hedged	Jun. 30, 2012 Gains / losses on cash flow hedged	Jun. 30, 2013 Gains / losses on cash flow hedged	Jun. 30, 2012 Gains / losses on cash flow hedged	Jun. 30, 2013 Future policy benefits, DAC and VOBA adjustments	Jun. 30, 2012 Future policy benefits, DAC and VOBA adjustments	Jun. 30, 2013 Future policy benefits, DAC and VOBA adjustments	Jun. 30, 2012 Future policy benefits, DAC and VOBA adjustments	Jun. 30, 2013 Employee benefit plan adjustments	Mar. 31, 2013 Employee benefit plan adjustments	Dec. 31, 2012 Employee benefit plan adjustments	Jun. 30, 2012 Employee benefit plan adjustments	Mar. 31, 2012 Employee benefit plan adjustments	Dec. 31, 2011 Employee benefit plan adjustments
Accumulated balances for each classification of other comprehensive income (loss)
Balance at the beginning of the period	$ 618,504	$ 485,845	$ 635,699	$ 469,982	$ 885,393	$ 658,245	$ 927,678	$ 646,805	$ 40,068	$ 37,555	$ 24,962	$ 41,003	$ (184,162)	$ (131,784)	$ (194,146)	$ (139,655)	$ (122,795)	$ (122,795)	$ (122,795)	$ (78,171)	$ (78,171)	$ (78,171)
Other comprehensive income (loss) before reclassifications	(308,463)	93,064	(309,681)	120,557	(382,650)	112,011	(409,418)	134,588	(4,576)	7,530	10,990	4,575	78,763	(26,477)	88,747	(18,606)
Amounts reclassified from AOCI	1,641	(16,168)	(14,336)	(27,798)	3,747	(15,703)	(11,770)	(26,840)	(2,106)	(465)	(2,566)	(958)
Net current period other comprehensive income (loss)	(306,822)	76,896	(324,017)	92,759	(378,903)	96,308	(421,188)	107,748	(6,682)	7,065	8,424	3,617	78,763	(26,477)	88,747	(18,606)
Balance at the end of the period	$ 311,682	$ 562,741	$ 311,682	$ 562,741	$ 506,490	$ 754,553	$ 506,490	$ 754,553	$ 33,386	$ 44,620	$ 33,386	$ 44,620	$ (105,399)	$ (158,261)	$ (105,399)	$ (158,261)	$ (122,795)	$ (122,795)	$ (122,795)	$ (78,171)	$ (78,171)	$ (78,171)