Reserves for Unpaid Losses and Loss Adjustment Expenses (Reconciliation of Incurred and Paid Claims to Liability for Unpaid Losses and LAE) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Liabilities for unpaid losses and allocated loss adjustment expense, net of reinsurance	$ 365,060	$ 350,368
Reinsurance recoverable on unpaid claims	154,612	123,237
Unallocated claims adjustment expenses	7,428	7,962
Total gross liability for unpaid claims and claim adjustment expenses	527,100	481,567	$ 450,878	$ 415,135
Specialty Commercial Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Liabilities for unpaid losses and allocated loss adjustment expense, net of reinsurance	275,436	252,602
Reinsurance recoverable on unpaid claims	137,975	102,597
Unallocated claims adjustment expenses	3,377	3,831
Standard Commercial Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Liabilities for unpaid losses and allocated loss adjustment expense, net of reinsurance	78,119	82,222
Reinsurance recoverable on unpaid claims	6,051	8,540
Unallocated claims adjustment expenses	3,153	3,031
Personal Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Liabilities for unpaid losses and allocated loss adjustment expense, net of reinsurance	11,505	15,544
Reinsurance recoverable on unpaid claims	10,586	12,100
Unallocated claims adjustment expenses	$ 898	$ 1,100