Losses and Loss Adjustment Expenses Incurred and Paid - Information Regarding the Reserve for Unpaid Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Insurance [Abstract]
Liability for unpaid losses and LAE at beginning of period, gross	$ 162,232	$ 166,012	$ 161,079	$ 122,071
Reinsurance balances receivable, beginning balance	(794)	(674)	(769)	(464)
Liability for unpaid losses and LAE at beginning of period, net	161,438	165,338	160,310	121,607
Add: Provision for losses and LAE:
Current period	56,660	71,140	172,856	217,802
Prior periods	(3,583)	(61)	(693)	27,460
Net losses and LAE incurred	53,077	71,079	172,163	245,262
Less: Losses and LAE paid:
Current period	35,008	52,558	81,327	111,307
Prior periods	17,588	20,000	89,227	91,703
Net losses and LAE paid	52,596	72,558	170,554	203,010
Liability for unpaid losses and LAE at end of period, net	161,919	163,859	161,919	163,859
Reinsurance balances receivable, ending balance	837	841	837	841
Liability for unpaid losses and LAE at end of period, gross	$ 162,756	$ 164,700	$ 162,756	$ 164,700