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REGULATORY LIABILITIES (Details) - USD ($) | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2020 | Dec. 31, 2018 | Dec. 31, 2019 | Jan. 31, 2019
REGULATORY LIABILITIES [Abstract] |  |  |  |
Contributions to postretirement benefit plan | $ 17,400 |  |  |
Federal corporate tax rate | 21.00% | 34.00% |  |
Decrease in the net deferred income tax liability | $ 24,300,000 |  |  |
Regulatory Liabilities [Abstract] |  |  |  |
Regulatory liabilities | $ 21,821,000 | $ 22,800,000 | $ 22,246,000 |
DEPSC [Member] |  |  |  |
Regulatory Liabilities [Abstract] |  |  |  |
Regulatory liabilities |  |  |  | $ 22,200,000
Regulatory liabilities, amortization period | 49 years 6 months |  |  |
MDPSC [Member] |  |  |  |
Regulatory Liabilities [Abstract] |  |  |  |
Regulatory liabilities | $ 600,000 |  |  |
Utility Plant Retirement Cost Obligation [Member] |  |  |  |
Regulatory Liabilities [Abstract] |  |  |  |
Regulatory liabilities | 155,000 |  | 247,000 |
Deferred Income Taxes [Member] |  |  |  |
Regulatory Liabilities [Abstract] |  |  |  |
Regulatory liabilities | $ 21,666,000 |  | $ 21,999,000 |

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- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 6.I.Fact.4) -URI http://asc.fasb.org/extlink&oid=116825942&loc=d3e330036-122817 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
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