Reinsurance - Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 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%
Premiums written net	$ 539,489
Ceded unpaid loss	309,800
Prepaid reinsurance premiums	383,565	$ 337,920
Reserve for losses and loss adjustment expense	$ 309,800
Number of reinsurers | Reinsurer	2
Wright National Flood Insurance Company
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	$ 538,000
Wright National Flood Insurance Company | 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	$ 1,500