Deferred Reinsurance Ceding Commission - Schedule of Activity with Regard to Deferred Reinsurance Ceding Commission (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Insurance [Abstract]
Beginning balance of deferred ceding commission income	$ 34,562	$ 34,705	$ 37,464	$ 44,996
Ceding commission deferred	17,294	15,542	43,213	39,017
Less: ceding commission earned	(14,129)	(15,062)	(42,950)	(48,828)
Ending balance of deferred ceding commission income	$ 37,727	$ 35,185	$ 37,727	$ 35,185