Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Deferred tax liabilities:
Unrealized gain on fixed income and equity security investments	$ 26,432	$ 19,098
Deferred acquisition costs	1,829	2,782
Salvage and subrogation	2,638	2,555
Limited partnership investments	2,612	1,554
Other	866	1,562
Total deferred tax liabilities	34,377	27,551
Deferred tax assets:
Loss and loss expense reserves	11,071	11,384
Unearned premiums discount	2,162	2,097
Other-than-temporary investment declines	2,053	2,733
Deferred ceding commission	1,018	1,700
Deferred compensation	880	734
Other	342	325
Total deferred tax assets	17,526	18,973
Net deferred tax liabilities	(16,851)	(8,578)
Summary of the Difference Between Federal Income Tax Expense computed at Statutory Rate [Abstract]
Statutory federal income rate applied to pretax income (loss)	19,218	16,312	(15,851)
Tax effect of (deduction):
Tax-exempt investment income	(811)	(933)	(1,145)
Net reduction of tax positions	(116)	(693)	(174)
Other	31	1	56
Federal income tax expense (benefit)	18,322	14,687	(17,114)
Taxes (credits) on pre-tax income (loss) [Abstract]
Current	17,383	10,819	(8,205)
Deferred	939	3,868	(8,909)
Federal income tax expense (benefit)	18,322	14,687	(17,114)
Components of the provisions for deferred federal income taxes (credits) [Abstract]
Limited partnerships	1,058	3,013	(7,196)
Discounts of loss and loss expense reserves	298	(57)	(2,546)
Unearned premium discount	(66)	265	(30)
Deferred compensation	(146)	112	499
Other-than-temporary investment declines	680	169	(240)
Deferred acquisitions costs and ceding commission	(270)	(520)	(87)
Other	(615)	886	691
Provision for deferred federal income tax (credits)	939	3,868	(8,909)
Cash flows related to federal income taxes paid, net of refunds received	17,250	3,661	2,859
Reconciliation of the beginning and ending amounts of unrecognized federal income taxes (credits) [Roll Forward]
Balance at beginning of period	0	6,000
Reductions for tax positions of the current year	0	0
Reductions for tax positions of prior years	0	(6,000)
Balance at end of period	$ 0	$ 0	$ 6,000