Unpaid Losses and Loss Adjustment Expenses - Narrative (Details) - USD ($)		3 Months Ended		9 Months Ended
	Sep. 28, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Liability for Claims and Claims Adjustment Expense [Line Items]
Unpaid losses and loss adjustment expenses		$ 97,337,000	$ 91,046,000	$ 97,337,000	$ 91,046,000	$ 97,981,000	$ 92,807,000	$ 83,662,000	$ 87,896,000
Prior-year adverse (favorable) reserve development		2,703,000	3,401,000	7,076,000	4,871,000
Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior-year adverse (favorable) reserve development, before ADC deferred gain			4,200,000		5,300,000
Personal Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior-year adverse (favorable) reserve development, before ADC deferred gain			612,000		1,900,000
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
Reinsurance retention policy, co-participation (percentage)	10.00%
Prior-year adverse (favorable) reserve development			1,500,000		2,400,000
Amortization of deferred gain on ADC		$ 481,000		$ 5,700,000
Hurricane
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior-year adverse (favorable) reserve development			$ 83,000		$ 471,000
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