Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplementary Insurance Information, by Segment [Line Items]
Deferred Policy Acquisition Costs	$ 16,002	$ 19,193	$ 20,366
Future Policy Benefits, Losses, Claims and Loss Adjustment Expenses	527,100	481,567	450,878
Unearned Premiums	276,642	241,254	216,407
Premium Revenue	361,037	353,370	349,081
Net Investment Income	18,874	16,342	13,969
Benefits Claims, Losses and Settlement Expenses	288,308	253,688	230,149
Amortization of Deferred Policy Acquisition Costs	34,265	39,076	32,674
Other Operating Expenses	103,615	105,596	103,614
Net Premiums Written	365,583	361,829	356,944
Specialty Commercial Segment [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred Policy Acquisition Costs	8,668	11,961	13,501
Future Policy Benefits, Losses, Claims and Loss Adjustment Expenses	416,788	358,961	314,975
Unearned Premiums	224,903	185,634	161,730
Premium Revenue	259,086	241,890	237,640
Net Investment Income	16,809	12,962	11,524
Benefits Claims, Losses and Settlement Expenses	213,050	169,125	148,664
Amortization of Deferred Policy Acquisition Costs	21,600	27,474	23,371
Other Operating Expenses	57,458	58,678	58,212
Net Premiums Written	265,022	249,072	241,775
Standard Commercial Segment [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred Policy Acquisition Costs	6,421	5,849	5,633
Future Policy Benefits, Losses, Claims and Loss Adjustment Expenses	87,323	93,793	105,971
Unearned Premiums	37,574	34,334	33,701
Premium Revenue	66,218	67,510	72,613
Net Investment Income	3,855	3,471	3,623
Benefits Claims, Losses and Settlement Expenses	45,227	41,173	47,071
Amortization of Deferred Policy Acquisition Costs	10,890	12,199	4,237
Other Operating Expenses	23,180	22,117	22,820
Net Premiums Written	69,288	68,490	71,097
Personal Segment [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred Policy Acquisition Costs	913	1,383	1,232
Future Policy Benefits, Losses, Claims and Loss Adjustment Expenses	22,989	28,813	29,932
Unearned Premiums	14,165	21,286	20,976
Premium Revenue	35,733	43,970	38,828
Net Investment Income	1,194	1,276	1,235
Benefits Claims, Losses and Settlement Expenses	30,031	43,390	34,414
Amortization of Deferred Policy Acquisition Costs	1,775	(597)	5,066
Other Operating Expenses	12,712	13,119	12,205
Net Premiums Written	31,273	44,267	44,072
Corporate [Member]
Supplementary Insurance Information, by Segment [Line Items]
Net Investment Income, Corporate	(2,984)	(1,367)	(2,413)
Other Operating Expenses	$ 10,265	$ 11,682	$ 10,377