Loss Reserves - Liability for Unpaid Loss and Loss Adjustment Expenses, Net of Related Amounts Recoverable from Reinsurers (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Roll Forward In Liability For Unpaid Claims And Claims Adjustment Expense [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	49,119	47,965
Prior accident years	(10,110)	(10,224)
Total incurred	39,009	37,741
Less paid related to:
Current accident year	2,603	2,850
Prior accident years	44,249	47,063
Total paid	46,852	49,913
Net balance, end of period	575,639	613,840
Add amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	111,013	114,718
Balance, end of period	$ 686,652	$ 728,558