Reinsurance - Schedule of the Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Premiums Written and Earned [Abstract]
Gross Written									$ 333,460	$ 351,696	$ 350,267
Ceded Written									(8,995)	(9,344)	(8,869)
Net premiums Written									324,465	342,352	341,398
Gross Earned									341,883	359,670	355,025
Ceded Earned									(8,995)	(9,344)	(8,869)
Net premiums Earned	$ 82,277	$ 82,712	$ 82,951	$ 84,948	$ 88,837	$ 85,184	$ 88,995	$ 87,310	$ 332,888	$ 350,326	$ 346,156