Other Comprehensive Income (Details 3) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassifications out of accumulated other comprehensive income (loss)
Other realized investment (gains) losses, net	$ (33,374)	$ (22,914)	$ (107,193)	$ (57,423)
Net investment income	(291,539)	(363,057)	(979,080)	(942,082)
Interest expense	(7,648)	(9,646)	(26,051)	(28,928)
Amortization of unrecognized prior service costs (benefits)	(150)	(159)	(452)	(520)
Actuarial (gains)	2,644	3,268	7,414	9,497
Tax expense or benefit	(3,599)	(2,813)	(21,481)	(15,229)
Net of tax	(5,064)	(3,202)	(35,369)	(22,447)
Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	(5,064)	(3,202)	(35,369)	(22,447)
Unrealized holding (gains) losses, net, arising on fixed maturities, available-for-sale
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	(5,503)	(3,859)	(35,820)	(24,091)
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	(8,465)	(5,937)	(55,107)	(37,063)
Total before tax	(8,465)	(5,937)	(55,107)	(37,063)
Tax expense or benefit	(2,962)	(2,078)	(19,287)	(12,972)
Net of tax	(5,503)	(3,859)	(35,820)	(24,091)
Unrealized holding (gains) losses, net, arising on cash flow hedges
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	(1,182)	(1,364)	(4,074)	(4,191)
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	(2,911)	(2,099)	(7,943)	(6,448)
Interest expense	1,092	0	1,675	0
Total before tax	(1,819)	(2,099)	(6,268)	(6,448)
Tax expense or benefit	(637)	(735)	(2,194)	(2,257)
Net of tax	(1,182)	(1,364)	(4,074)	(4,191)
Amortization of employee benefit plan items
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	1,621	2,021	4,525	5,835
Amortization of employee benefit plan items | Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Amortization of unrecognized prior service costs (benefits)	(150)	(159)	(452)	(520)
Actuarial (gains)	2,644	3,268	7,414	9,497
Total before tax	2,494	3,109	6,962	8,977
Tax expense or benefit	873	1,088	2,437	3,142
Net of tax	$ 1,621	$ 2,021	$ 4,525	$ 5,835