Financial Statements Schedules Schedule III. Supplementary Insurance Information - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred acquisition costs, net	$ 13,045				$ 13,609				$ 13,045	$ 13,609	$ 12,143	$ 12,197
Property and casualty	63,652				53,795				63,652	53,795	55,471
Unearned premiums	36,686				40,176				36,686	40,176	35,234
Net premiums earned	31,447	$ 32,556	$ 33,518	$ 32,922	33,419	$ 32,949	$ 31,813	$ 29,427	130,443	127,608	117,433
Amortization									28,428	27,822	26,361
Other Cost and Expense, Operating										17,543	17,130
Supplemental Information for Property, Casualty Insurance Underwriters, Premiums Written									126,959	132,550	116,239
Property, Liability and Casualty Insurance Product Line [Member]
Deferred acquisition costs, net	6,720				7,782				6,720	7,782	6,696
Property and casualty	63,652				53,795				63,652	53,795	55,471	$ 63,895
Unearned premiums					40,176					40,176	35,234
Net premiums earned									130,443	127,608	117,433
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									120,791	104,384	87,055
Amortization									24,203	24,154	23,333
Other Cost and Expense, Operating									15,956	17,543	17,130
Supplemental Information for Property, Casualty Insurance Underwriters, Premiums Written									126,959	132,550	116,239
Corporation [Member]
Deferred acquisition costs, net	$ 6,720				7,782				6,720	7,782	6,696
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									120,791	104,384	87,055
Amortization									$ 24,203	24,154	23,333
Segment Reconciling Items [Member]
Deferred acquisition costs, net					0					0	0
Property and casualty					0					0	0
Unearned premiums					$ 0					0	0
Net premiums earned										0	0
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims										0	0
Amortization										0	0
Other Cost and Expense, Operating										0	0
Supplemental Information for Property, Casualty Insurance Underwriters, Premiums Written										$ 0	$ 0