SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Part 2 (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 03, 2020	Jan. 31, 2019
Regulatory Assets [Abstract]
Cash received for bond issuance		$ 30,000
Amortization period of other regulatory expense [Abstract]
Rate case studies		5 years
Goodwill		50 years
Deferred acquisition costs		20 years
Franchise costs		80 years
Regulatory assets net of amortization, comprise [Abstract]
Regulatory assets, net		$ 6,473	$ 6,891
Summary of other deferred assets net of amortization [Abstract]
Investment in Co Bank		4,374	3,968
Goodwill		623	0	$ 0	$ 623
Other		312	289
Other deferred assets		5,309	4,257
Impairment or Disposal of Long-Lived Assets [Abstract]
Impairment		0	0
Regulatory Liabilities [Line Items]
Decrease in the net deferred income tax liability			24,300	24,300
Net regulatory liability amount			22,800	$ 22,800
Regulatory Liabilities		$ 21,681	22,246
Minimum [Member]
Amortization period of other regulatory expense [Abstract]
Amortization period of debt related cost	15 years
Maximum [Member]
Amortization period of other regulatory expense [Abstract]
Amortization period of debt related cost	30 years
Maryland [Member]
Amortization period of other regulatory expense [Abstract]
Rate proceedings		5 years
Delaware [Member]
Amortization period of other regulatory expense [Abstract]
Rate proceedings		2 years 6 months
DEPSC [Member]
Regulatory Liabilities [Line Items]
Net regulatory liability amount						$ 22,200
Regulatory liabilities, amortization period		49 years 6 months
MDPSC [Member]
Regulatory Liabilities [Line Items]
Net regulatory liability amount		$ 600	600
Utility Plant Retirement Cost Obligation [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		126	247
Deferred Income Taxes [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		21,555	21,999
Deferred Income Taxes [Member]
Regulatory assets net of amortization, comprise [Abstract]
Regulatory assets, net		370	386
Expense Of Rate Case Studies [Member]
Regulatory assets net of amortization, comprise [Abstract]
Regulatory assets, net		46	78
Debt Related Costs [Member]
Regulatory assets net of amortization, comprise [Abstract]
Regulatory assets, net		5,233	5,556
Goodwill [Member]
Regulatory assets net of amortization, comprise [Abstract]
Regulatory assets, net		281	288
Deferred Acquisition and Franchise Costs [Member]
Regulatory assets net of amortization, comprise [Abstract]
Regulatory assets, net		543	$ 583
Mountain Hill [Member]
Summary of other deferred assets net of amortization [Abstract]
Other		$ 200