Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Before-tax amount
Unrealized holding gains arising during the year on available-for-sale fixed maturity investments	$ 534,028	[1]	$ 511,663	[1]	$ 724,296	[1]
Net changes during the year related to cash flow hedges	(18,881)		21,014		17,293
Reclassification adjustment for gains realized in net income	(107,713)		(74,165)		23,198
Net unrealized gains related to investments	407,434		458,512		764,787
Future policy benefits, deferred acquisition costs and value of business acquired adjustments	(83,835)		(100,216)		(129,715)
Net unrealized gains	323,599		358,296		635,072
Employee benefit plan adjustment	(68,650)		(49,566)		(5,142)
Other comprehensive income before income taxes	254,949		308,730		629,930
Tax (expense) benefit
Unrealized holding gains arising during the year on available-for-sale fixed maturity investments	(186,910)		(179,082)		(253,504)
Net changes during the year related to cash flow hedges	6,608		(7,355)		(6,053)
Reclassification adjustment for gains realized in net income	37,700		25,958		(8,119)
Net unrealized gains	(142,602)		(160,479)		(267,676)
Future policy benefits, deferred acquisition costs and value of business acquired adjustments	29,343		35,075		45,400
Net unrealized gains	(113,259)		(125,404)		(222,276)
Employee benefit plan adjustment	24,027		17,348		1,800
Other comprehensive income (loss)	(89,232)		(108,056)		(220,476)
Net-of-tax amount
Unrealized holding gains arising during the year on available-for-sale fixed maturity investments	347,118		332,581		470,792
Net changes during the year related to cash flow hedges	(12,273)		13,659		11,240
Reclassification adjustment for gains realized in net income	(70,013)		(48,207)		15,079
Net unrealized gains	264,832		298,033		497,111
Future policy benefits, deferred acquisition costs and value of business acquired adjustments	(54,492)		(65,141)		(84,315)
Net unrealized gains	210,340		232,892		412,796
Employee benefit plan adjustment	(44,623)		(32,218)		(3,342)
Other comprehensive income	$ 165,717		$ 200,674	[2]	$ 409,454	[2]

[1] Other comprehensive income includes the non-credit component of impaired losses on fixed maturities available-for-sale in the amounts of $26,583, $13,590 and $6,346 for the years ended December 31, 2012, 2011 and 2010, respectively.

[2] As adjusted; See Note 1