Summarized Activity in Liability for Unpaid Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Insurance [Abstract]
Balance at beginning of period	$ 662,811	$ 630,181
Less: Ceded reinsurance receivables	82,158	76,273
Net balance at beginning of period	580,653	553,908
Incurred losses and loss adjustment expenses related to:
Current year	94,194	78,247
Prior years	(3,411)	(600)
Total incurred losses and loss adjustment expenses	90,783	77,647
Paid losses and loss adjustment expenses related to:
Current year	21,719	22,034
Prior years	53,230	48,806
Total paid losses and loss adjustment expenses	74,949	70,840
Net balance at end of period	596,487	560,715
Plus: Ceded reinsurance receivables	79,421	78,753
Balance at end of period	$ 675,908	$ 639,468