Significant Accounting Policies, Utility Plant and Depreciation (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($) System County	Dec. 31, 2019 USD ($)
Significant Accounting Policies [Abstract]
Number of wastewater collection systems operated \| System	2
Number of wastewater collection and treatment systems operated \| System	5
Number of counties in which franchised territory is located \| County	3
Utility Plant and Depreciation [Abstract]
Utility plant acquisition adjustments	$ 3,707	$ 3,318
Amortization of utility plant acquisition adjustments	67	61
Utility plant	$ 438,670	$ 401,383
Effective rate of depreciation	2.33%	2.29%
Mains and Accessories [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 212,164	$ 200,954
Mains and Accessories [Member] \| Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	10 years
Mains and Accessories [Member] \| Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	86 years
Services, Meters and Hydrants [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 80,590	77,501
Services, Meters and Hydrants [Member] \| Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	17 years
Services, Meters and Hydrants [Member] \| Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	51 years
Operations Structures, Reservoirs and Water Tanks [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 65,617	63,530
Operations Structures, Reservoirs and Water Tanks [Member] \| Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	9 years
Operations Structures, Reservoirs and Water Tanks [Member] \| Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	58 years
Pumping and Treatment Equipment [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 34,163	33,124
Pumping and Treatment Equipment [Member] \| Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	6 years
Pumping and Treatment Equipment [Member] \| Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	30 years
Office, Transportation and Operating Equipment [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 15,520	14,464
Office, Transportation and Operating Equipment [Member] \| Minimum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	3 years
Office, Transportation and Operating Equipment [Member] \| Maximum [Member]
Utility Plant and Depreciation [Abstract]
Remaining life	22 years
Land and Other Non-Depreciable Assets [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 3,478	3,393
Utility Plant in Service [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	411,532	392,966
Construction Work in Progress [Member]
Utility Plant and Depreciation [Abstract]
Utility plant	$ 27,138	$ 8,417

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Amount of acquisition adjustments included in property, plant and equipment (PPE) for utilities.

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Composite depreciation rate for public utility plants in service.

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Period end amount of total gross PPE.

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Number of counties in which the Company's franchised territory is located within south-central Pennsylvania.

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The number of wastewater treatment and collection systems operated by the entity.

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The number of wastewater collection systems operated by the entity.

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Amount of amortization of utility plant acquisition adjustments.

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