Reinsurance - Impact of the Reinsurance Treaties on Premiums Written and Earned (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Premiums Written:
Direct	$ 171,906	$ 133,441	$ 248,478	$ 201,053
Assumed	(25)		(79)	(2)
Gross written	171,881	133,441	248,399	201,051
Ceded	(34,354)	(31,317)	(65,073)	(62,730)
Net premiums written	137,527	102,124	183,326	138,321
Premiums Earned:
Direct	106,852	83,315	197,619	165,914
Assumed	951		2,549	(2)
Gross earned	107,803	83,315	200,168	165,912
Ceded	(34,354)	(31,317)	(65,073)	(62,730)
Net premiums earned	$ 73,449	$ 51,998	$ 135,095	$ 103,182