Summary of Significant Accounting Policies (Details 8) - USD ($) $ in Thousands		3 Months Ended												12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	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, 2016	Dec. 31, 2015	Dec. 31, 2014
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income		$ 19,823	$ 26,923	$ 11,866	$ 25,153	$ 21,040	$ 21,984	$ 16,183	$ 34,275	$ 30,068	$ 25,357	$ 20,452	$ 28,366	$ 83,765	$ 93,482	$ 104,243
Change in net unrealized investment gains and losses on fixed maturities and equity securities:
Net unrealized investment gains and losses on fixed maturities and equity securities arising during the period														6,144	(178,035)	264,136
Less: reclassification adjustment for net gains included in income before income tax														5,176	11,667	10,943
Total, before tax														968	(189,702)	253,193
Income tax expense (benefit)														397	(67,315)	89,629
Total, net of tax	[1],[2]													571	(122,387)	163,564
Change in net funded status of pension and other postretirement benefit obligations:
Before tax														(37)	1,815	(1,810)
Income tax expense (benefit)														(14)	656	(633)
Total, net of tax	[1]													(23)	1,159	(1,177)
Total comprehensive income (loss)														$ 84,313	$ (27,746)	$ 266,630

[1] All amounts are net of tax.

[2] The pretax amounts reclassified from accumulated other comprehensive income, $5,176, $11,667 and $10,943, are included in net realized investment gains and losses and the related tax expenses, $1,812, $4,083 and $3,830, are included in income tax expense in the Consolidated Statements of Operations for the years ended December 31, 2016, 2015 and 2014, respectively.