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REGULATORY LIABILITIES (Details) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Jan. 31, 2019
REGULATORY LIABILITIES [Abstract]      
Contributions to postretirement benefit plan $ 11,000    
Federal corporate tax rate 21.00% 34.00%  
Decrease in the net deferred income tax liability $ 24,300,000    
Regulatory Liabilities [Abstract]      
Regulatory liabilities $ 22,603,000 $ 22,813,000  
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    
Postretirement Benefit Obligation [Member]      
Regulatory Liabilities [Abstract]      
Regulatory liabilities 52,000 52,000  
Utility Plant Retirement Cost Obligation [Member]      
Regulatory Liabilities [Abstract]      
Regulatory liabilities 331,000 319,000  
Deferred Income Taxes [Member]      
Regulatory Liabilities [Abstract]      
Regulatory liabilities $ 22,220,000 $ 22,442,000