Business Segment Data (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments	2	2	2	2
Operating Revenues	$ 33,393	$ 34,919	$ 64,090	$ 66,096
Operating Income	8,950	10,721	15,977	17,071
Net Income	8,146	8,675	14,696	13,169
Capital Expenditures	23,374	18,366	35,698	28,377
Assets	807,571		807,571		$ 767,830
Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenues	30,444	31,168	58,342	58,374
Operating Income	7,903	9,988	13,936	15,613
Net Income	7,423	8,151	13,290	12,134
Capital Expenditures	23,268	18,350	35,561	28,328
Assets	807,021		807,021		764,749
Non - Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenues	3,087	3,882	6,012	7,982
Operating Income	1,047	733	2,041	1,458
Net Income	723	524	1,406	1,035
Capital Expenditures	106	16	137	49
Assets	9,093		9,093		8,994
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(138)	$ (131)	(264)	$ (260)
Assets	$ (8,543)		$ (8,543)		$ (5,913)