INCOME TAXES (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) Reserve	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 31, 2019 USD ($)
Income Taxes [Abstract]
Federal corporate tax rate	21.00%	21.00%	34.00%
Decrease in the net deferred income tax liability		$ 24,300	$ 23,500
Net benefit to continuing operations		500	1,000
Net regulatory liability amount		22,800	22,500
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Valuation allowance	$ 335	396	360
Number of reserves established for uncertain tax positions | Reserve	2
State income taxes [Abstract]
Current	$ 2,405	1,768	489
Deferred	(610)	71	1,368
Total state income tax expense	1,795	1,839	1,857
Federal income taxes [Abstract]
Current	6,015	2,404	(1,418)
Deferred	(2,629)	748	6,856
Total federal income tax expense	3,386	3,152	5,438
Reconciliation of effective tax rate [Abstract]
Income before federal and state income taxes	$ 20,106	$ 19,270	$ 21,278
Income before federal and state income taxes	100.00%	100.00%	100.00%
Amount computed at statutory rate	$ 4,222	$ 4,047	$ 7,234
Amount computed at statutory rate	21.00%	21.00%	34.00%
Reconciling Items [Abstract]
State income tax-net of federal tax benefit	$ 1,414	$ 1,350	$ 1,297
State income tax-net of federal tax benefit	7.00%	7.00%	6.10%
Regulatory liability adjustment	$ (451)	$ (920)	$ 0
Regulatory liability adjustment	(2.20%)	(4.80%)	0.00%
Federal rate change and TCJA effects	$ 0	$ 325	$ (957)
Federal rate change and TCJA effects	0.000	0.017	(0.045)
Other	$ (4)	$ 189	$ (279)
Other	0.00%	1.00%	(1.30%)
Total income tax expense	$ 5,181	$ 4,991	$ 7,295
Total effective income tax rate	25.80%	25.90%	34.30%
Deferred tax assets related to [Abstract]
Federal and state operating loss carry-forwards	$ 725	$ 1,050	$ 1,094
Valuation allowance	(335)	(396)	(360)
Bad debt allowance	73	65	80
Stock options	185	202	207
Other	70	85	161
Total deferred tax assets	718	1,006	1,182
Deferred tax liabilities related to [Abstract]
Property plant and equipment basis differences	(50,219)	(53,296)	(52,629)
Bond retirement costs	(1,286)	(1,361)	(1,437)
Uncertain tax position	(271)	(283)	(145)
Expenses of rate proceedings	0	(2)	(8)
Property taxes	(544)	(521)	(500)
Other	(657)	(597)	(600)
Total deferred tax liabilities	(52,977)	(56,060)	(55,319)
Net deferred tax liability	(52,259)	(55,054)	(54,137)
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense [Abstract]
Balance at beginning of year	283	145
Additions based on tax positions related to the current year	37	130
Additions based on tax positions related to prior years	24	13
Reductions for tax positions of prior years	0	0
Settlements	0	0
Federal tax rate change	0	(5)
Lapses in statutes of limitations	(73)	0
Balance at end of year	$ 271	283	145
Minimum [Member]
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Operating Loss Carryforwards Expiration Period	2020
Maximum [Member]
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Operating Loss Carryforwards Expiration Period	2040
Valuation Allowance for Deferred Tax Assets [Member]
Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning Of Period	$ 396	360	286
Additions Charged to Costs and Expenses	41	36	74
Deductions	(102)	0	0
Balance at End of Period	335	396	360
DEPSC [Member]
Income Taxes [Abstract]
Net regulatory liability amount				$ 22,200
Amortization of regulatory liability		$ 22,200
Amortization period of regulatory liability		49 years 6 months
MDPSC [Member]
Income Taxes [Abstract]
Net regulatory liability amount	600	$ 600
Federal Authorities [Member]
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Federal alternative minimum tax credit carry-forwards			$ 2,700
State Authorities [Member]
Income Tax Examination, Operating Loss Carryforwards [Abstract]
Net operating loss carry-forwards	$ 10,900