Summary of Significant Accounting Policies (Details 8) - USD ($) $ in Thousands		3 Months Ended												12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income		$ 21,040	$ 21,984	$ 16,183	$ 34,275	$ 30,068	$ 25,357	$ 20,452	$ 28,366	$ 34,287	$ 23,599	$ 25,995	$ 27,012	$ 93,482	$ 104,243	$ 110,893
Change in net unrealized gains and losses on fixed maturities and equity securities
Net unrealized holding gains and losses on fixed maturities and equity securities arising during the period														(178,035)	264,136	(363,350)
Less: reclassification adjustment for net gains included in income before income tax														11,667	10,943	22,245
Total, before tax														(189,702)	253,193	(385,595)
Income tax expense (benefit)														(67,315)	89,629	(137,185)
Total, net of tax	[1],[2]													(122,387)	163,564	(248,410)
Change in net funded status of pension and other postretirement benefit obligations
Before tax														1,815	(1,810)	5,645
Income tax expense (benefit)														656	(633)	2,110
Total, net of tax	[1]													1,159	(1,177)	3,535
Total comprehensive income (loss)														$ (27,746)	$ 266,630	$ (133,982)

[1] All amounts are net of tax.

[2] The pretax amounts reclassified from accumulated other comprehensive income, $11,667, $10,943 and $22,245, are included in net realized investment gains and losses and the related tax expenses, $4,083, $3,830 and $7,786, are included in income tax expense in the Consolidated Statements of Operations for the years ended December 31, 2015, 2014 and 2013, respectively.