Unpaid Losses and Loss Adjustment Expenses - Narrative (Details) - USD ($)		3 Months Ended
	Sep. 28, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid losses and loss adjustment expenses		$ 85,491,000	$ 62,135,000	$ 87,896,000		$ 54,651,000
Deferred gain on ADC		1,431,000	0
Prior-year adverse (favorable) reserve development		16,000	(3,079,000)
Offset amount by favorable development		278,000	456,000
Liability line of business
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior-year adverse (favorable) reserve development		(104,000)	(1,300,000)
Florida homeowners line
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior-year adverse (favorable) reserve development			(325,000)
Commercial property line
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior-year adverse (favorable) reserve development			(1,600,000)
Personal automobile line
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior-year adverse (favorable) reserve development		(366,000)	$ (201,000)
Adverse development cover reinsurance agreement (ADC)
Liability for Claims and Claims Adjustment Expense [Line Items]
ADC loss development cover, maximum amount	$ 17,500,000.0	1,700,000.0
Reinsurance retention policy, co-participation (percentage)	10.00%
Increase in reinsurance recoverable		8,900,000
Reinsurance recoverable		8,600,000
Deferred gain on ADC		1,400,000
Hurricane
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior-year adverse (favorable) reserve development		$ (266,000)
Minimum | Adverse development cover reinsurance agreement (ADC)
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance retention policy carried reserves threshold	$ 1,400,000
Unpaid losses and loss adjustment expenses					$ 36,600,000
Maximum | Adverse development cover reinsurance agreement (ADC)
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance retention policy carried reserves threshold	$ 19,500,000
Unpaid losses and loss adjustment expenses					$ 57,500,000