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REGULATORY MATTERS (2019 FERC Rate Case) (Details) - USD ($)
$ in Thousands
12 Months Ended
May 31, 2019
Dec. 31, 2019
Sep. 19, 2019
Dec. 31, 2018
Public Utilities, General Disclosures [Line Items]        
Regulatory Liabilities   $ 96,017   $ 95,094
Regulatory Assets   $ 465,000   $ 400,000
FERC | Transmission Services Rate        
Public Utilities, General Disclosures [Line Items]        
Return on equity (percentage)   10.40%    
Requested recovery in development, percentage 100.00%      
Requested recovery in development $ 9,000      
Allowed cost recovery in development, percentage     50.00%  
Regulatory Assets   $ 4,000    
FERC | Transmission Services Rate | Revenue Subject to Refund        
Public Utilities, General Disclosures [Line Items]        
Regulatory Liabilities   $ 4,000