Other Comprehensive Income (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reclassifications out of accumulated other comprehensive income (loss)
Other realized investment (gains) losses, net	$ (151,705)		$ 13,330		$ (121,916)
Net investment income	(1,228,388)		(1,091,389)		(1,191,551)
Net of tax	31,449		17,352		63,865
Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	(31,449)		(17,352)
Unrealized holdings (gains) losses arising on fixed maturities, available-for-sale
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	31,038		26,477		66,245
Unrealized holdings (gains) losses arising on fixed maturities, available-for-sale | Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Other realized investment (gains) losses, net	(47,751)		(40,734)
Total before tax	(47,751)		(40,734)
Tax expense or benefit	(16,713)		(14,257)
Net of tax	(31,038)		(26,477)
Unrealized holdings (gains) losses arising on cash flow hedges
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	5,465		1,461		3,768
Unrealized holdings (gains) losses arising on cash flow hedges | Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Net investment income	(8,408)		(2,248)
Total before tax	(8,408)		(2,248)
Tax expense or benefit	(2,943)		(787)
Net of tax	(5,465)		(1,461)
Amortization of employee benefit plan items
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	(5,054)		(10,586)		(6,148)
Amortization of employee benefit plan items | Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Total before tax	7,776		16,286
Tax expense or benefit	2,722		5,700
Net of tax	5,054		10,586
Prior service costs (benefits)	3,189	[1]	(666)	[1]
Actuarial gains (losses)	2,730	[1]	16,952	[1]
Settlement	$ 1,857	[1]	$ 0	[1]

[1] These accumulated other comprehensive income components are included in the computation of net periodic (benefit) cost of employee benefit plans (see Note 17 for additional details).