Reinsurance (Details)		3 Months Ended
	Jun. 01, 2016 USD ($) catastrophic_event layer reinsurer Rate	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Reinsurance Retention Policy [Line Items]
Prepaid reinsurance premiums		$ 92,745,000		$ 132,564,000
Cash recoveries under reinsurance agreements		$ 2,484,000	$ 266,000
Flood premiums ceded (percentage)		100.00%
Insurance commissions and fees under Flood Program		$ 294,000	$ 246,000
Minimum
Reinsurance Retention Policy [Line Items]
ISO Catastrophe Definition	$ 25,000,000
Maximum
Reinsurance Retention Policy [Line Items]
Stated amount of upper retention limit per policy	10,000,000
Second And Subsequent Catastrophic Events
Reinsurance Retention Policy [Line Items]
Amount of risk reinsured in excess of stated retention	100,000,000
Second And Subsequent Catastrophic Events | Maximum
Reinsurance Retention Policy [Line Items]
Amount of risk reinsured in excess of stated retention	$ 1,515,197,000
Catastrophe
Reinsurance Retention Policy [Line Items]
Percentage of losses covered | Rate	100.00%
Prepaid reinsurance premiums	$ 191,500,000
Catastrophe | First Catastrophic Event
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Coverage Percentage Hurricane Event | catastrophic_event	0.010
Percentage of losses covered | Rate	100.00%
Catastrophe | First Catastrophic Event | Maximum
Reinsurance Retention Policy [Line Items]
Amount of risk reinsured in excess of stated retention	$ 1,415,197,000
Stated amount of upper retention limit per policy	$ 30,000,000
Catastrophe | Second Catastrophic Event
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Coverage Percentage Hurricane Event | catastrophic_event	0.020
Catastrophe | Florida Hurricane Catastrophe Fund [Member] | FLORIDA
Reinsurance Retention Policy [Line Items]
Reimbursement percentage	45.00%
Reinsurance, Aggregate Value of Property Covered Under Contracts	$ 786,700,000
Reinsurance, Losses Not Covered Prior to Coverage Beginning	246,002,000
Aggregate Coverage for Covered Losses Under Reinsurance Contract	$ 354,015,000
Catastrophe | Unaffiliated Private Reinsurers [Member]
Reinsurance Retention Policy [Line Items]
Number of private reinsurers | reinsurer	55
Number of cascading insurance layers | layer	5
Catastrophe | Unaffiliated Private Reinsurers [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Stated amount of upper retention limit per policy	$ 10,000,000
Aggregate Coverage for Covered Losses Under Reinsurance Contract	$ 685,000,000
Catastrophe | Unaffiliated Private Reinsurers [Member] | FLORIDA
Reinsurance Retention Policy [Line Items]
Reimbursement percentage	45.00%
Reinsurance, Aggregate Value of Property Covered Under Contracts	$ 769,293,000
Reinsurance, Losses Not Covered Prior to Coverage Beginning	244,206,000
Aggregate Coverage for Covered Losses Under Reinsurance Contract	346,182,000
UPC Re | Catastrophe | Maximum
Reinsurance Retention Policy [Line Items]
Stated amount of upper retention limit per policy	$ 20,000,000