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NDPSC (Details 3) - NDPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($)
Feb. 01, 2021
Jan. 01, 2021
Aug. 26, 2020
Electricity [Member] | Subsequent Event [Member]      
Public Utilities, General Disclosures [Line Items]      
Renewable Resource Cost Adjustment Rate Tariff $ 14,400,000    
Public Utilities, Approved Rate Increase (Decrease), Amount $ (300,000)    
Pending Rate Case [Member] | Gas Distribution [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Requested Rate Increase (Decrease), Amount     $ 9,000,000.0
Public Utilities, Requested Rate Increase (Decrease), Percentage     7.80%
Pending Rate Case [Member] | Gas Distribution [Member] | Subsequent Event [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Interim Rate Increase (Decrease), Amount   $ 6,900,000  
Public Utilities, Interim Rate Increase (Decrease), Percentage   6.00%