Reinsurance - Schedule of the Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Premiums Written and Earned [Abstract]
Gross Written									$ 303,090	$ 333,460	$ 351,696
Ceded Written									(10,276)	(8,995)	(9,344)
Net premiums Written									292,814	324,465	342,352
Gross Earned									314,703	341,883	359,670
Ceded Earned									(10,276)	(8,995)	(9,344)
Net premiums Earned	$ 74,702	$ 74,771	$ 75,964	$ 78,990	$ 82,277	$ 82,712	$ 82,951	$ 84,948	$ 304,427	$ 332,888	$ 350,326