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, 2022	Jun. 30, 2021
Roll Forward In Liability For Unpaid Claims And Claims Adjustment Expense [Abstract]
Balance, beginning of period	$ 745,278	$ 760,561
Less amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	119,266	105,707
Net balance, beginning of period	626,012	654,854
Add incurred related to:
Current accident year	97,863	101,257
Prior accident years	(19,796)	(29,317)
Total incurred	78,067	71,940
Less paid related to:
Current accident year	14,063	12,786
Prior accident years	82,473	79,814
Total paid	96,536	92,600
Net balance, end of period	607,543	634,194
Add amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	117,348	110,775
Balance, end of period	$ 724,891	$ 744,969