Loss Reserves - Change in Allowance for Credit Losses on Amounts Recoverable from Reinsurers (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Insurance [Abstract]
Balance, beginning of period	$ 338	$ 369	$ 372	$ 440
Provision for credit loss expense (benefit)	5	35	(29)	(36)
Balance, end of period	$ 343	$ 404	$ 343	$ 404