Reinsurance - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Paid losses recoverable outstanding due date	90 days
Paid losses recoverable past due	$ 0
Received reinsurance recoveries	$ 1,300,000	$ 1,600,000	$ 500,000
Unsecured reinsurance recoverable by reinsurer reporting threshold	1.50%