Loss Reserves - Liability for Unpaid Loss and Loss Adjustment Expenses, Net of Related Amounts Recoverable from Reinsurers (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Liability for Unpaid Claims and Claims Adjustment Expense, Activity in Liability [Abstract]
Balance, beginning of period	$ 696,037	$ 745,278
Less amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	112,555	119,266
Net balance, beginning of period	583,482	626,012
Add incurred related to:
Current accident year	95,693	97,863
Prior accident years	(21,039)	(19,796)
Total incurred	74,654	78,067
Less paid related to:
Current accident year	12,938	14,063
Prior accident years	75,252	82,473
Total paid	88,190	96,536
Net balance, end of period	569,946	607,543
Add amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	114,667	117,348
Balance, end of period	$ 684,613	$ 724,891