Reinsurance - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance [Abstract]
Paid losses recoverable outstanding due date	90 days
Received reinsurance recoveries	$ 4.4	$ 2.0	$ 1.3
Unsecured reinsurance recoverable by reinsurer reporting threshold	1.50%