Loss Reserves - Liability for Unpaid Loss and Loss Adjustment Expenses, Net of Related Amounts Recoverable from Reinsurers (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 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	28,074	30,566
Prior accident years	(31,195)	(30,201)
Total incurred	111,808	115,792
Less paid related to:
Current accident year	143,003	145,993
Prior accident years	104,602	111,968
Total paid	132,676	142,534
Net balance, end of period	562,614	599,270
Add amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	121,734	116,926
Balance, end of period	$ 684,348	$ 716,196