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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Part 2 (Details) - USD ($) $ in Thousands | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jan. 31, 2017 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Aug. 03, 2020 | Jan. 31, 2019
Regulatory Assets [Abstract] |  |  |  |  |  |
Cash received for bond issuance |  | $ 30,000 |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |
Rate case studies |  | 5 years |  |  |  |
Goodwill |  | 50 years |  |  |  |
Deferred acquisition costs |  | 20 years |  |  |  |
Franchise costs |  | 80 years |  |  |  |
Regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |
Regulatory assets, net |  | $ 6,473 | $ 6,891 |  |  |
Summary of other deferred assets net of amortization [Abstract] |  |  |  |  |  |
Investment in Co Bank |  | 4,374 | 3,968 |  |  |
Goodwill |  | 623 | 0 | $ 0 | $ 623 |
Other |  | 312 | 289 |  |  |
Other deferred assets |  | 5,309 | 4,257 |  |  |
Impairment or Disposal of Long-Lived Assets [Abstract] |  |  |  |  |  |
Impairment |  | 0 | 0 |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Decrease in the net deferred income tax liability |  |  | 24,300 | 24,300 |  |
Net regulatory liability amount |  |  | 22,800 | $ 22,800 |  |
Regulatory Liabilities |  | $ 21,681 | 22,246 |  |  |
Minimum [Member] |  |  |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |
Amortization period of debt related cost | 15 years |  |  |  |  |
Maximum [Member] |  |  |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |
Amortization period of debt related cost | 30 years |  |  |  |  |
Maryland [Member] |  |  |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |
Rate proceedings |  | 5 years |  |  |  |
Delaware [Member] |  |  |  |  |  |
Amortization period of other regulatory expense [Abstract] |  |  |  |  |  |
Rate proceedings |  | 2 years 6 months |  |  |  |
DEPSC [Member] |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Net regulatory liability amount |  |  |  |  |  | $ 22,200
Regulatory liabilities, amortization period |  | 49 years 6 months |  |  |  |
MDPSC [Member] |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Net regulatory liability amount |  | $ 600 | 600 |  |  |
Utility Plant Retirement Cost Obligation [Member] |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Regulatory Liabilities |  | 126 | 247 |  |  |
Deferred Income Taxes [Member] |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Regulatory Liabilities |  | 21,555 | 21,999 |  |  |
Deferred Income Taxes [Member] |  |  |  |  |  |
Regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |
Regulatory assets, net |  | 370 | 386 |  |  |
Expense Of Rate Case Studies [Member] |  |  |  |  |  |
Regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |
Regulatory assets, net |  | 46 | 78 |  |  |
Debt Related Costs [Member] |  |  |  |  |  |
Regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |
Regulatory assets, net |  | 5,233 | 5,556 |  |  |
Goodwill [Member] |  |  |  |  |  |
Regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |
Regulatory assets, net |  | 281 | 288 |  |  |
Deferred Acquisition and Franchise Costs [Member] |  |  |  |  |  |
Regulatory assets net of amortization, comprise [Abstract] |  |  |  |  |  |
Regulatory assets, net |  | 543 | $ 583 |  |  |
Mountain Hill [Member] |  |  |  |  |  |
Summary of other deferred assets net of amortization [Abstract] |  |  |  |  |  |
Other |  | $ 200 |  |  |  |

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