Other Comprehensive Income (Details 3) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassifications out of accumulated other comprehensive income (loss)
Other realized investment (gains) losses, net	$ (22,221)	$ (42,013)	$ (10,467)	$ (73,819)
Net investment income	(297,221)	(355,755)	(610,691)	(687,540)
Interest expense	(7,646)	(8,679)	(15,276)	(18,403)
Total before tax	(75,992)	(113,509)	(127,938)	(236,169)
Tax expense or benefit	(26,168)	(39,710)	(43,286)	(63,748)
Net income	49,824	73,799	84,652	172,421
Net of tax	204	(17,161)	2,558	(30,305)
Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax			2,558	(30,305)
Unrealized holding (gains) losses, net, arising on fixed maturities, available-for-sale
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	(1,564)	(17,337)	332	(30,317)
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	(2,406)	(26,672)	511	(46,642)
Total before tax	(2,406)	(26,672)	511	(46,642)
Tax expense or benefit	(842)	(9,335)	179	(16,325)
Net income	1,564	17,337	(332)	30,317
Unrealized holding (gains) losses, net, arising on cash flow hedges
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	373	(1,276)	(564)	(2,892)
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	(213)	(2,546)	(2,535)	(5,032)
Interest expense	787	583	1,667	583
Total before tax	574	(1,963)	(868)	(4,449)
Tax expense or benefit	201	(687)	(304)	(1,557)
Net income	(373)	1,276	564	2,892
Amortization of employee benefit plan items
Reclassifications out of accumulated other comprehensive income (loss)
Net of tax	1,395	1,452	2,790	2,904
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	2,146	2,234	4,292	4,468
Tax expense or benefit	(751)	(782)	(1,502)	(1,564)
Net of tax	1,395	1,452	2,790	2,904
Prior service (benefits) | Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Total before tax	(73)	151	(146)	302
Actuarial losses | Amount reclassified from accumulated other comprehensive income (loss)
Reclassifications out of accumulated other comprehensive income (loss)
Total before tax	$ 2,073	$ 2,385	$ 4,146	$ 4,770