Summarized Activity in Liability for Unpaid Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Insurance [Abstract]
Balance at beginning of period	$ 697,618	$ 651,073	$ 662,811	$ 630,181
Less: Ceded reinsurance receivables	87,151	87,221	82,158	76,273
Net balance at beginning of period	610,467	563,852	580,653	553,908
Incurred losses and loss adjustment expenses related to:
Current year	110,644	108,859	290,247	273,709
Prior years	(1,449)	(11,711)	669	(31,617)
Total incurred losses and loss adjustment expenses	109,195	97,148	290,916	242,092
Paid losses and loss adjustment expenses related to:
Current year	46,501	60,114	106,778	119,541
Prior years	30,128	29,612	121,758	105,185
Total paid losses and loss adjustment expenses	76,629	89,726	228,536	224,726
Net balance at end of period	643,033	571,274	643,033	571,274
Plus: Ceded reinsurance receivables	88,732	98,656	88,732	98,656
Balance at end of period	$ 731,765	$ 669,930	$ 731,765	$ 669,930