Significant Accounting Policies, Regulatory Assets and Liabilities (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) ServiceLine	Dec. 31, 2018 USD ($)
Assets [Abstract]
Regulatory assets	$ 34,189	$ 32,353
Liabilities [Abstract]
Regulatory liabilities	25,399	26,814
Excess Accumulated Deferred Income Taxes on Accelerated Depreciation [Member]
Liabilities [Abstract]
Regulatory liabilities	14,008	14,184
Income Taxes [Member]
Liabilities [Abstract]
Regulatory liabilities	$ 7,494	6,979
Income Taxes [Member] \| Minimum [Member]
Liabilities [Abstract]
Remaining recovery period	1 year
Income Taxes [Member] \| Maximum [Member]
Liabilities [Abstract]
Remaining recovery period	50 years
IRS TPR Catch-Up Deduction [Member]
Liabilities [Abstract]
Regulatory liabilities	$ 3,671	3,887
Remaining recovery period	14 years
Revenue Reduction For Tax Rate Change [Member]
Liabilities [Abstract]
Regulatory liabilities	$ 226	1,764
Remaining recovery period	1 year
Term for negative surcharge on bills to customers	1 year
Income Taxes [Member]
Assets [Abstract]
Regulatory assets	$ 24,405	21,432
Postretirement Benefits [Member]
Assets [Abstract]
Regulatory assets	$ 365	3,071
Postretirement Benefits [Member] \| Minimum [Member]
Assets [Abstract]
Remaining recovery period	5 years
Postretirement Benefits [Member] \| Maximum [Member]
Assets [Abstract]
Remaining recovery period	10 years
Unrealized Swap Losses [Member]
Assets [Abstract]
Regulatory assets	$ 2,227	1,799
Unrealized Swap Losses [Member] \| Minimum [Member]
Assets [Abstract]
Remaining recovery period	1 year
Unrealized Swap Losses [Member] \| Maximum [Member]
Assets [Abstract]
Remaining recovery period	10 years
Utility Plant Retirement Costs [Member]
Assets [Abstract]
Regulatory assets	$ 5,012	4,841
Remaining recovery period	5 years
Customer-Owned Lead Service Line Replacements [Member]
Assets [Abstract]
Regulatory assets	$ 944	304
Remaining recovery period	4 years
Term of tariff modification to replace customer-owned lead service lines connected to company-owned lead service lines	3 years
Number of lead customer-owned service lines to be replaced annually \| ServiceLine	400
Term of tariff modification to replace customer-owned lead service lines	9 years
Income Taxes on Customers' Advances for Construction and Contributions in Aid of Construction [Member]
Assets [Abstract]
Regulatory assets	$ 998	577
Service Life Study Expenses [Member]
Assets [Abstract]
Regulatory assets	$ 13	18
Remaining recovery period	3 years
Rate Case Filing Expenses [Member]
Assets [Abstract]
Regulatory assets	$ 225	$ 311
Remaining recovery period	2 years

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 405
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

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Amortization period for the recovery of regulatory liability, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Remaining recovery period of regulatory assets for which no return on investment during recovery period is provided, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 980
-SubTopic 340
-Section 55
-Paragraph 2
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Number of lead customer-owned service lines to be replaced annually whenever they are discovered.

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Term to return the 2018 income tax savings pursuant to the 2017 Tax Act, the associated tax gross-up, and the excess accumulated deferred income taxes on accelerated depreciation to customers as a reconcilable negative surcharge on bills pursuant to a rate order approved by the Pennsylvania Public Utility Commission (PPUC), in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Term of consent order agreement with the Pennsylvania Department of Environmental Protection involving the replacement of lead customer-owned service lines regardless of material used for company-owned service lines, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Term of tariff modification involving the replacement of lead customer-owned service lines that are discovered when the Company replaces its lead service lines, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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