Loss and Loss Adjustment Expense Reserves - Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses
Net outstanding liabilities	$ 458,014
Reinsurance recoverable on unpaid claims	122,372	$ 108,398	$ 83,085
Unallocated claims adjustment expenses	30,180
Total gross liability for unpaid claims and claim adjustment expenses	610,566	$ 584,719	$ 574,054	$ 560,321
Private Passenger Automobile Liability
Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses
Net outstanding liabilities	206,964
Reinsurance recoverable on unpaid claims	238
Private Passenger Automobile Physical Damage
Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses
Net outstanding liabilities	(8,509)
Commercial Automobile Liability
Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses
Net outstanding liabilities	96,567
Reinsurance recoverable on unpaid claims	116,756
Commercial Automobile Physical Damage
Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses
Net outstanding liabilities	2,318
Reinsurance recoverable on unpaid claims	2,255
Homeowners Liability
Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses
Net outstanding liabilities	35,968
Homeowners Property Damage
Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses
Net outstanding liabilities	49,251
Reinsurance recoverable on unpaid claims	1
Other short-Duration Insurance Lines
Reconciliation of the Disclosure of Incurred and Paid Claims Development to the Liability for Unpaid claims and Claim Adjustment Expenses
Net outstanding liabilities	75,455
Reinsurance recoverable on unpaid claims	$ 3,122