Business Segment Data (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments			2	2
Operating Revenues	$ 34,919	$ 33,014	$ 66,096	$ 63,145
Operating Income	10,721	9,358	17,071	16,933
Net Income	8,675	5,381	13,169	9,822
Capital Expenditures	18,366	11,588	28,377	21,165
Assets	729,744		729,744		$ 661,140
Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenues	31,168	29,278	58,374	55,771
Operating Income	9,988	8,672	15,613	15,687
Net Income	8,151	4,972	12,134	9,111
Capital Expenditures	18,350	11,588	28,328	21,160
Assets	732,592		732,592		661,816
Non - Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenues	3,882	3,863	7,982	7,613
Operating Income	733	686	1,458	1,246
Net Income	524	409	1,035	711
Capital Expenditures	16		49	5
Assets	6,819		6,819		7,093
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(131)	$ (127)	(260)	$ (239)
Assets	$ (9,667)		$ (9,667)		$ (7,769)