Other Comprehensive Income (Details 3) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassifications out of accumulated other comprehensive income (loss)
Other realized investment (gains) losses, net		$ (22,914)	$ (25,935)	$ (57,423)	$ (91,829)
Net investment income		(363,057)	(292,061)	(942,082)	(911,694)
Prior service costs (benefits)		(159)	(181)	(520)	(542)
Actuarial losses (gains)		3,268	973	9,497	2,187
Settlement		0	2,666	0	2,666
Tax expense or benefit		(2,813)	(2,358)	(15,229)	(12,422)
Net of tax		(3,202)	(1,578)	(22,447)	(20,268)
Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax		(3,202)	(1,578)	(22,447)	(20,268)
Unrealized holding (gains) losses, net, arising on fixed maturities, available-for-sale
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax		(3,859)	(2,664)	(24,091)	(18,374)
Unrealized holding (gains) losses, net, 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		(5,937)	(4,099)	(37,063)	(28,268)
Total before tax		5,937	4,099	37,063	28,268
Tax expense or benefit		(2,078)	(1,435)	(12,972)	(9,894)
Net of tax		(3,859)	(2,664)	(24,091)	(18,374)
Unrealized holding (gains) losses, net, arising on cash flow hedges
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax		(1,364)	(1,716)	(4,191)	(4,696)
Unrealized holding (gains) losses, net, arising on cash flow hedges | Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Net investment income		(2,099)	(2,639)	(6,448)	(7,224)
Total before tax		2,099	2,639	6,448	7,224
Tax expense or benefit		(735)	(923)	(2,257)	(2,528)
Net of tax		(1,364)	(1,716)	(4,191)	(4,696)
Amortization of employee benefit plan items
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax		2,021	2,802	5,835	2,802
Amortization of employee benefit plan items | Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Prior service costs (benefits)	[1]	(159)	(542)	(520)	(542)
Actuarial losses (gains)	[1]	3,268	2,187	9,497	2,187
Settlement	[1]	0	2,666	0	2,666
Total before tax		(3,109)	(4,311)	(8,977)	(4,311)
Tax expense or benefit		1,088	1,509	3,142	1,509
Net of tax		$ 2,021	$ 2,802	$ 5,835	$ 2,802

[1] These accumulated other comprehensive income components are included in the computation of net periodic (benefit) cost of employee benefit plans (see Note 10 for additional details).