Deferred Reinsurance Ceding Commission - Schedule of Activity with Regard to Deferred Reinsurance Ceding Commission (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Insurance [Abstract]
Beginning balance of deferred ceding commission income	$ 39,995	$ 37,464
Ceding commission deferred	13,029	10,845
Less: ceding commission earned	(15,033)	(13,929)
Ending balance of deferred ceding commission income	$ 37,991	$ 34,380