Income Taxes - Schedule of Company's Deferred Income Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax assets:
Discounting of net unpaid loss and loss adjustment expenses	$ 21,377	$ 8,830
Unearned premiums	8,069	8,466
Accrued expenses and other	2,636	2,359
State income tax	855	782
Accrued policyholder dividends	2,188	1,918
Impaired securities	21	42
Capital loss carryforward		190
Accrued insurance-related assessments	3,139	3,256
Net unrealized loss on securities	496
Total deferred tax assets	38,781	25,843
Deferred income tax liabilities:
Deferred policy acquisition costs	(5,207)	(5,317)
Callable bond amortization	(5)	(8)
Unrealized gain on securities available-for-sale		(1,070)
Property and equipment and other	(178)	(3)
Salvage and subrogation	(719)	(183)
Loss reserves adjustment due to the Tax Act	(10,820)
Total deferred income tax liabilities	(16,929)	(6,581)
Net deferred income taxes	$ 21,852	$ 19,262