Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax liabilities [Abstract]
Unrealized gain on fixed income and equity security investments	$ 20,959	$ 27,914
Deferred acquisition costs	877	1,341
Loss and loss expense reserves	2,305	2,373
Limited partnership investments	1,771	4,636
Accelerated depreciation	897	601
Other	1,024	628
Total deferred tax liabilities	27,833	37,493
Deferred tax assets [Abstract]
Loss and loss expense reserves	9,349	10,973
Unearned premiums discount	1,593	2,201
Other-than-temporary investment declines	3,437	2,049
Deferred ceding commission	371	549
Deferred compensation	1,699	1,565
Other	186	183
Total deferred tax assets	16,635	17,520
Net deferred tax liabilities	(11,198)	(19,973)
Summary of the difference between federal income tax expense computed at statutory rate [Abstract]
Statutory federal income rate applied to pretax income	11,883	15,539	$ 19,218
Tax effect of (deduction) [Abstract]
Tax-exempt investment income	(919)	(924)	(811)
Other	(295)	66	(85)
Federal income tax expense	10,669	14,681	18,322
Taxes on pre-tax income [Abstract]
Current	12,488	13,041	17,383
Deferred	(1,819)	1,640	939
Federal income tax expense	10,669	14,681	18,322
Components of the provisions for deferred federal income taxes (credits) [Abstract]
Limited partnerships	(2,865)	2,025	1,058
Discounts of loss and loss expense reserves	1,526	113	313
Unearned premium discount	608	(38)	(65)
Deferred compensation	(127)	(685)	(146)
Other-than-temporary investment declines	(1,416)	(19)	680
Deferred acquisitions costs and ceding commission	(287)	(20)	(271)
Other	742	264	(630)
Provision for deferred federal income tax	(1,819)	1,640	939
Cash flows related to federal income taxes paid, net of refunds received	$ 14,500	$ 11,619	$ 17,250