Business Segment Data (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments			2
Operating Revenues	$ 33,014	$ 32,725	$ 63,145	$ 63,304
Operating Income	9,563	10,328	17,343	18,630
Net Income	5,381	5,919	9,822	10,709
Capital Expenditures	1,588	13,439	21,165	20,111
Assets	638,730		638,730		$ 620,161
Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenues	29,278	28,859	55,771	55,808
Operating Income	8,877	9,694	16,097	17,426
Net Income	4,972	5,583	9,111	10,073
Capital Expenditures	11,588	13,290	21,160	19,950
Assets	642,726		642,726		619,915
Non - Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenues	3,863	4,002	7,613	7,736
Operating Income	686	634	1,246	1,204
Net Income	409	336	711	636
Capital Expenditures		149	5	161
Assets	6,681		6,681		6,245
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(127)	$ (136)	(239)	$ (240)
Assets	$ (10,677)		$ (10,677)		$ (5,999)