Schedule VI. Supplemental Information Concerning Property-Casualty Insurance Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Information For Property Casualty Insurance Underwriters [Abstract]
Deferred Policy Acquisition Costs	$ 17,810	$ 19,048	$ 19,734
Reserves for Unpaid Loss and Loss Adjustment Expense	760,561	772,887	798,409
Unearned Premium	129,260	140,873	149,296
Net Premiums Earned	304,427	332,888	350,326
Net Investment Income	29,364	32,483	30,452
Loss and LAE Related to Current Period	220,710	241,344	250,487
Loss and LAE Related to Prior Periods	(63,484)	(65,002)	(45,596)
Amortization of Deferred Policy Acquisition Costs	(41,583)	(44,558)	(45,769)
Paid Claims and Claim Adjustment Expenses	179,916	189,991	200,654
Net Premiums Written	$ 292,814	$ 324,465	$ 342,352