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REGULATORY LIABILITIES (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2018	Dec. 31, 2019	Jan. 31, 2019
REGULATORY LIABILITIES [Abstract]
Contributions to postretirement benefit plan	$ 5,700
Federal corporate tax rate	21.00%	34.00%
Decrease in the net deferred income tax liability	$ 24,300,000
Regulatory Liabilities [Abstract]
Regulatory liabilities	$ 22,104,000	$ 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	216,000		247,000
Deferred Income Taxes [Member]
Regulatory Liabilities [Abstract]
Regulatory liabilities	$ 21,888,000		$ 21,999,000

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of cash outflow for pension and other postretirement benefits. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree.

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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.

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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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Amount of income tax benefit for remeasurement of deferred tax liability from change in tax rate pursuant to Tax Cuts and Jobs Act.

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