Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Corporate income tax rate	21.00%	35.00%
Tax benefit related to remeasurement of deferred tax assets and liabilities		$ 9,572
Tax Cuts and Jobs Act of 2017, change in methodology, provisional income tax impact		1,696
Tax Cuts and Jobs Act of 2017, offsetting deferred tax liability	$ 2,262
Deferred tax liabilities amortized amount into income	323
Deferred tax liabilities [Abstract]
Unrealized gain on fixed income and equity security investments	4,572	15,086
Deferred acquisition costs	2,552	1,804
Loss and loss expense reserves	3,583	2,623
Limited partnership investments	0	3,826
Accelerated depreciation	690	492
Other	1,509	1,791
Total deferred tax liabilities	12,906	25,622
Deferred tax assets [Abstract]
Loss and loss expense reserves	9,999	6,761
Limited partnership investments	3,498	0
Unearned premiums discount	2,321	1,837
Other-than-temporary investment declines	625	815
Deferred compensation	580	885
Deferred ceding commission	1,173	627
Other	972	339
Total deferred tax assets	19,168	11,264
Net deferred tax liabilities	0	14,358
Net deferred tax assets	(6,262)	0
Summary of the difference between federal income tax expense computed at statutory rate [Abstract]
Statutory federal income rate applied to pre-tax income (loss)	(9,213)	3,543	$ 15,069
Tax effect of (deduction) [Abstract]
Tax-exempt investment income	(253)	(968)	(938)
Change in enacted tax rates	0	(9,572)	0
Other	(331)	(1,204)	(22)
Federal income tax expense (benefit)	(9,797)	(8,201)	14,109
Taxes (benefit) on pre-tax income (loss) [Abstract]
Current	8,997	(4,335)	11,271
Deferred	(18,794)	(3,866)	2,838
Federal income tax expense (benefit)	(9,797)	(8,201)	14,109
Provisions for deferred federal income taxes [Abstract]
Limited partnerships	(2,383)	4,099	503
Discounts of loss and loss expense reserves	(2,704)	1,315	(114)
Reserves - salvage and subrogation and other	427	56	(1,110)
Unearned premium discount	(484)	(1,767)	298
Deferred compensation	305	(168)	595
Other-than-temporary investment declines	695	(127)	2,320
Deferred acquisitions costs and ceding commission	201	1,553	(95)
Change in enacted tax rates	0	(9,572)	0
Unrealized gains / losses	(13,876)	0	0
Other	(975)	745	441
Provision for deferred federal income taxes	(18,794)	(3,866)	2,838
Deferred tax assets, valuation allowance	0	0
Uncertain tax positions	0	0
Accrued interest	$ 0	$ 0	$ 0