Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities [Abstract]
Unrealized gain on fixed income and equity security investments		$ 15,086	$ 18,335
Deferred acquisition costs		1,804	874
Loss and loss expense reserves		2,623	1,198
Limited partnership investments		3,826	2,274
Accelerated depreciation		492	1,037
Other		1,791	1,251
Total deferred tax liabilities		25,622	24,969
Deferred tax assets [Abstract]
Loss and loss expense reserves		6,761	9,467
Unearned premiums discount		1,837	1,295
Other-than-temporary investment declines		815	858
Deferred compensation		885	1,097
Deferred ceding commission		627	464
Other		339	376
Total deferred tax assets		11,264	13,557
Net deferred tax liabilities		$ 14,358	11,412
Income Tax Disclosure [Line Items]
Corporate income tax rate		35.00%
Tax benefit related to remeasurement of deferred tax assets and liabilities		$ 9,600
Summary of the difference between federal income tax expense computed at statutory rate [Abstract]
Statutory federal income rate applied to pretax income		3,543	15,069	$ 11,883
Tax effect of (deduction) [Abstract]
Tax-exempt investment income		(968)	(938)	(919)
Change in enacted tax rates		(9,572)	0	0
Other		(1,204)	(22)	(295)
Federal income tax expense (benefit)		(8,201)	14,109	10,669
Taxes (benefit) on pre-tax income [Abstract]
Current		(4,335)	11,271	12,488
Deferred		(3,866)	2,838	(1,819)
Federal income tax expense (benefit)		(8,201)	14,109	10,669
Components of the provisions for deferred federal income taxes (credits) [Abstract]
Limited partnerships		4,099	503	(2,865)
Discounts of loss and loss expense reserves		1,315	(114)	1,526
Reserves - salvage and subrogation and other		56	(1,110)	29
Unearned premium discount		(1,767)	298	608
Deferred compensation		(168)	595	(127)
Other-than-temporary investment declines		(127)	2,320	(1,416)
Deferred acquisitions costs and ceding commission		1,553	(95)	(287)
Change in enacted tax rates		(9,572)	0	0
Other		745	441	713
Provision for deferred federal income tax		(3,866)	2,838	(1,819)
Deferred tax assets, valuation allowance		0	0
Uncertain tax positions		0	0
Accrued interest		$ 0	$ 0	$ 0
Plan [Member]
Income Tax Disclosure [Line Items]
Corporate income tax rate	21.00%