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REGULATORY LIABILITIES (Details) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2020
Dec. 31, 2018
Dec. 31, 2019
Jan. 31, 2019
REGULATORY LIABILITIES [Abstract]        
Contributions to postretirement benefit plan $ 17,400      
Federal corporate tax rate 21.00% 34.00%    
Decrease in the net deferred income tax liability $ 24,300,000      
Regulatory Liabilities [Abstract]        
Regulatory liabilities $ 21,821,000 $ 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 155,000   247,000  
Deferred Income Taxes [Member]        
Regulatory Liabilities [Abstract]        
Regulatory liabilities $ 21,666,000   $ 21,999,000