Losses and Loss Adjustment Reserve - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) Reinsurer	Dec. 31, 2018 USD ($)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded rate of premiums under insurance program	100.00%
Document Period End Date	Jun. 30, 2019
Premiums written net	$ 326,901
Ceded unpaid loss	77,300
Prepaid reinsurance premiums	343,594	$ 337,920
Reserve for losses and loss adjustment expense	$ 77,300
Number of reinsurers | Reinsurer	2
Wright National Flood Insurance Company [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded rate of premiums under insurance program	100.00%
Expenses and allowance rate received in premiums	30.00%
Premiums written net	$ 326,000
Wright National Flood Insurance Company [Member] | Quota Share Agreement
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Effective cedes rate under quota share agreement	100.00%
Commission rate, percent of ceded written premiums	30.50%
Ceded amount	$ 900