Business Segment Data (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments	2
Operating Revenues	$ 30,131	$ 30,579
Operating Income	7,780	8,302
Net Income	4,441	4,790
Capital Expenditures	9,577	6,672
Assets	627,261		$ 620,161
Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenues	26,493	26,949
Operating Income	7,220	7,733
Net Income	4,139	4,492
Capital Expenditures	9,572	6,660
Assets	629,668		619,915
Non - Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenues	3,750	3,734
Operating Income	560	569
Net Income	302	298
Capital Expenditures	5	12
Assets	6,850		6,245
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(112)	$ (104)
Assets	$ (9,257)		$ (5,999)