Income Taxes - Schedule of Company's Deferred Income Tax Assets and Liabilities (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax assets:
Discounting of net unpaid loss and loss adjustment expenses	$ 19,297,000	$ 19,985,000
Unearned premiums	6,984,000	7,638,000
Accrued expenses and other	2,947,000	2,612,000
State income tax	2,212,000	2,484,000
Accrued policyholder dividends	2,020,000	2,330,000
Capital loss carryforward		20,000
Accrued insurance-related assessments	1,963,000	2,672,000
Total deferred tax assets	35,423,000	37,741,000
Less: Valuation allowance	(2,169,000)	(2,025,000)	$ 0
Net deferred tax assets	33,254,000	35,716,000
Deferred income tax liabilities:
Deferred policy acquisition costs	(4,547,000)	(4,838,000)
Callable bond amortization		(2,000)
Unrealized gain on securities available-for-sale	(7,194,000)	(3,970,000)
Property and equipment and other	(260,000)	(271,000)
Salvage and subrogation	(516,000)	(636,000)
Loss reserves adjustment due to the Tax Act	(7,072,000)	(8,486,000)
Total deferred income tax liabilities	(19,589,000)	(18,203,000)
Net deferred income taxes	$ 13,665,000	$ 17,513,000