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REGULATORY LIABILITIES (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
REGULATORY LIABILITIES [Abstract]
Contributions to postretirement benefit plan	$ 28,100
Federal corporate tax rate	21.00%	34.00%
Decrease in the net deferred income tax liability	$ 24,300,000
Regulatory Liabilities [Abstract]
Regulatory liabilities	23,927,000	$ 23,201,000
Postretirement Benefit Obligation [Member]
Regulatory Liabilities [Abstract]
Regulatory liabilities	112,000	112,000
Utility Plant Retirement Cost Obligation [Member]
Regulatory Liabilities [Abstract]
Regulatory liabilities	461,000	549,000
Deferred Income Taxes [Member]
Regulatory Liabilities [Abstract]
Regulatory liabilities	$ 23,354,000	$ 22,540,000

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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 of 2017.

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

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-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
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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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