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, 2025	Sep. 30, 2024
Liability for Unpaid Claims and Claims Adjustment Expense, Activity in Liability [Abstract]
Balance, beginning of period	$ 651,309	$ 673,994
Less amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	112,742	119,746
Net balance, beginning of period	538,567	554,248
Add incurred related to:
Current accident year	148,718	144,931
Prior accident years	(26,220)	(25,166)
Total incurred	122,498	119,765
Less paid related to:
Current accident year	35,765	29,872
Prior accident years	116,876	102,082
Total paid	152,641	131,954
Net balance, end of period	508,424	542,059
Add amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	109,436	121,427
Balance, end of period	$ 617,860	$ 663,486