INCOME TAXES (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) Reserve	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 31, 2019 USD ($)
Income Taxes [Abstract]
Federal corporate tax rate	21.00%	21.00%	21.00%	34.00%
Decrease in the net deferred income tax liability		$ 24,300,000	$ 24,300,000
Net regulatory liability amount		22,800,000	22,800,000
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Valuation allowance	$ 618,000	335,000
Number of reserves established for uncertain tax positions | Reserve	2
State income taxes [Abstract]
Current	$ 2,348,000	2,405,000	1,768,000
Deferred	(279,000)	(610,000)	71,000
Total state income tax expense	2,069,000	1,795,000	1,839,000
Federal income taxes [Abstract]
Current	5,725,000	6,015,000	2,404,000
Deferred	(2,110,000)	(2,629,000)	748,000
Total federal income tax expense	3,615,000	3,386,000	3,152,000
Reconciliation of effective tax rate [Abstract]
Income before federal and state income taxes	$ 22,501,000	$ 20,106,000	$ 19,270,000
Income before federal and state income taxes	100.00%	100.00%	100.00%
Income Tax Expense (Benefit) [Abstract]
Amount computed at statutory rate	$ 4,725,000	$ 4,222,000	$ 4,047,000
Amount computed at statutory rate	21.00%	21.00%	21.00%	34.00%
State income tax-net of federal tax benefit	$ 1,704,000	$ 1,414,000	$ 1,350,000
State income tax-net of federal tax benefit	7.60%	7.00%	7.00%
Regulatory liability adjustment	$ (451,000)	$ (451,000)	$ (920,000)
Regulatory liability adjustment	(2.00%)	(2.20%)	(4.80%)
Federal rate change and TCJA effects	$ 0	$ 0	$ 325,000
Federal rate change and TCJA effects	0	0	0.017
Other	$ (294,000)	$ (4,000)	$ 189,000
Other	(1.30%)	0.00%	1.00%
Total income tax expense	$ 5,684,000	$ 5,181,000	$ 4,991,000
Total effective income tax rate	25.30%	25.80%	25.90%
Deferred tax assets related to [Abstract]
Federal and state operating loss carry-forwards	$ 629,000	$ 725,000
Valuation allowance	(493,000)	(335,000)
Bad debt allowance	240,000	73,000
Stock options	148,000	185,000
Other	75,000	70,000
Total deferred tax assets	599,000	718,000
Deferred tax liabilities related to [Abstract]
Property plant and equipment basis differences	(48,536,000)	(50,490,000)
Bond retirement costs	(1,210,000)	(1,286,000)
Expenses of rate proceedings	0	0
Property taxes	(481,000)	(544,000)
Other	(685,000)	(657,000)
Total deferred tax liabilities	(50,912,000)	(52,977,000)
Net deferred tax liability	(50,313,000)	(52,259,000)
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense [Abstract]
Balance at beginning of year	271,000	283,000
Additions based on tax positions related to the current year	0	37,000
Additions based on tax positions related to prior years	21,000	24,000
Reductions for tax positions of prior years	(83,000)	0
Settlements	0	0
Federal tax rate change	0	0
Lapses in statutes of limitations	0	(73,000)
Balance at end of year	$ 209,000	271,000	$ 283,000
Minimum [Member]
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Operating Loss Carryforwards Expiration Period	2022
Maximum [Member]
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Operating Loss Carryforwards Expiration Period	2042
Valuation Allowance for Deferred Tax Assets [Member]
Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning Of Period	$ 335,000	396,000	360,000
Additions Charged to Costs and Expenses	158,000	41,000	36,000
Deductions	0	(102,000)	0
Balance at End of Period	493,000	335,000	$ 396,000	$ 360,000
DEPSC [Member]
Income Taxes [Abstract]
Net regulatory liability amount					$ 22,200,000
Amortization of regulatory liability		$ 22,200,000
Amortization period of regulatory liability		49 years 6 months
MDPSC [Member]
Income Taxes [Abstract]
Net regulatory liability amount	600,000	$ 600,000
State Authorities [Member]
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Net operating loss carry-forwards	$ 9,400,000