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, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 340,997	$ 299,068
Reinsurance recoverable on unpaid claims	272,604	221,716
Unallocated claims adjustment expenses	6,754	6,463
Total gross liability for unpaid claims and claim adjustment expenses	620,355	527,247	$ 527,100
Commercial Auto business units [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	189,896	150,288
Reinsurance recoverable on unpaid claims	112,931	23,262
Unallocated claims adjustment expenses	1,383	1,264
E&S Casualty business unit [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	63,528	61,014
Reinsurance recoverable on unpaid claims	91,900	139,928
Unallocated claims adjustment expenses	760	707
Commercial Accounts business unit [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	51,200	56,865
Reinsurance recoverable on unpaid claims	13,671	8,255
Unallocated claims adjustment expenses	2,732	2,788
Aviation [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	2,514	2,185
Reinsurance recoverable on unpaid claims	9,469	9,114
Unallocated claims adjustment expenses	85	383
Runoff [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	3,109	5,070
Reinsurance recoverable on unpaid claims	1,326	1,528
Unallocated claims adjustment expenses	170	170
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	4,234	2,164
Reinsurance recoverable on unpaid claims	3,618	421
Unallocated claims adjustment expenses	63	31
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	15,027	8,743
Reinsurance recoverable on unpaid claims	11,752	13,131
Unallocated claims adjustment expenses	1,250	955
Property [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	11,489	12,739
Reinsurance recoverable on unpaid claims	27,937	26,077
Unallocated claims adjustment expenses	$ 311	$ 165