Reinsurance (Details) $ in Thousands		3 Months Ended
	Jun. 01, 2017 catastrophic_event	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Reinsurance Retention Policy
Prepaid reinsurance premiums | $		$ 133,304		$ 217,885
Flood premiums ceded (percentage)		100.00%
Insurance commissions and fees under Flood Program | $		$ 342	$ 388
Catastrophe | First Catastrophic Event
Reinsurance Retention Policy
Reinsurance Retention Policy, Coverage Percentage Hurricane Event | catastrophic_event	0.010
Catastrophe | Second Catastrophic Event
Reinsurance Retention Policy
Reinsurance Retention Policy, Coverage Percentage Hurricane Event | catastrophic_event	0.020