Summarized Activity in Liability for Unpaid Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance [Abstract]
Balance at beginning of period	$ 630,181	$ 680,031	$ 634,664
Less: Ceded reinsurance receivables	76,273	109,342	97,243
Net balance at beginning of period	553,908	570,689	537,421
Incurred losses and loss adjustment expenses related to:
Current year	367,739	308,211	363,423
Prior years	(31,538)	(32,809)	(28,798)
Total incurred losses and loss adjustment expenses	336,201	275,402	334,625
Paid losses and loss adjustment expenses related to:
Current year	183,109	146,128	173,545
Prior years	126,347	146,055	127,812
Total paid losses and loss adjustment expenses	309,456	292,183	301,357
Net balance at end of period	580,653	553,908	570,689
Plus: Ceded reinsurance receivables	82,158	76,273	109,342
Balance at end of period	$ 662,811	$ 630,181	$ 680,031