Business Segment Data (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments									2
Revenues	$ 32,738	$ 37,769	$ 33,393	$ 30,698	$ 33,268	$ 38,713	$ 34,919	$ 31,177	$ 134,598	$ 138,077	$ 130,775
Operating Income	7,559	11,983	8,950	7,028	7,153	12,918	10,721	6,350	35,520	37,142	37,798
Depreciation									16,716	15,037	13,922
Other Income (Expense), Net									2,492	2,992	1,617
Interest Expense									7,264	6,758	5,506
Income Taxes									(3,140)	924	11,100
Net Income	8,071	$ 11,119	$ 8,146	$ 6,552	6,993	$ 12,290	$ 8,675	$ 4,494	33,888	32,452	22,809
Capital Expenditures									89,125	72,094	50,301
Assets	909,878				767,830				909,878	767,830
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues									(657)	(602)	(591)
Other Income (Expense), Net									(273)	(411)	(467)
Interest Expense									(273)	(411)	(467)
Assets	(9,889)				(5,913)				(9,889)	(5,913)
Regulated [Member]
Segment Reporting Information [Line Items]
Revenues									123,078	121,901	115,454
Operating Income									31,805	34,127	35,130
Depreciation									16,481	14,846	13,732
Other Income (Expense), Net									3,018	3,284	2,020
Interest Expense									7,456	7,060	5,855
Income Taxes									(4,317)	(54)	9,848
Net Income									31,602	30,405	21,447
Capital Expenditures									88,858	71,493	50,078
Assets	910,081				764,749				910,081	764,749
Non - Regulated [Member]
Segment Reporting Information [Line Items]
Revenues									12,177	16,778	15,912
Operating Income									3,715	3,015	2,668
Depreciation									235	191	190
Other Income (Expense), Net									(253)	119	64
Interest Expense									81	109	118
Income Taxes									1,177	978	1,252
Net Income									2,286	2,047	1,362
Capital Expenditures									267	601	$ 223
Assets	$ 9,686				$ 8,994				$ 9,686	$ 8,994