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REGULATORY LIABILITIES (Details) - USD ($) | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2019 | Dec. 31, 2018 | Jan. 31, 2019
REGULATORY LIABILITIES [Abstract] |  |  |
Contributions to postretirement benefit plan | $ 17,000 |  |
Federal corporate tax rate | 21.00% | 34.00% |
Decrease in the net deferred income tax liability | $ 24,300,000 |  |
Regulatory Liabilities [Abstract] |  |  |
Regulatory liabilities | $ 22,452,000 | $ 22,813,000 |
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 |  |
Postretirement Benefit Obligation [Member] |  |  |
Regulatory Liabilities [Abstract] |  |  |
Regulatory liabilities | 52,000 | 52,000 |
Utility Plant Retirement Cost Obligation [Member] |  |  |
Regulatory Liabilities [Abstract] |  |  |
Regulatory liabilities | 291,000 | 319,000 |
Deferred Income Taxes [Member] |  |  |
Regulatory Liabilities [Abstract] |  |  |
Regulatory liabilities | $ 22,109,000 | $ 22,442,000 |

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