Loss Reserves - Change in Allowance for Credit Losses on Amounts Recoverable from Reinsurers (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Insurance [Abstract]
Balance, beginning of period	$ 449	$ 444
Provision for credit loss benefit	(61)	(56)
Balance, end of period	$ 388	$ 388