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North Dakota Public Service Commission (NDPSC) (Details 3) - NDPSC - USD ($)
$ in Millions
Jul. 19, 2018
Mar. 09, 2018
Mar. 01, 2018
Feb. 14, 2018
Sep. 06, 2017
Jul. 21, 2017
Natural gas rate proceeding            
Public Utilities, General Disclosures [Line Items]            
Public utilities, requested rate increase (decrease), amount           $ 5.9
Public utilities, requested rate increase (decrease), percentage           5.40%
Public utilities, interim rate increase (decrease), amount         $ 4.6  
Public utilities, interim rate increase (decrease), percentage         4.20%  
Natural gas rate proceeding | Tax Cuts and Jobs Act            
Public Utilities, General Disclosures [Line Items]            
Public utilities interm rate increase (decrese) revised       $ 2.7    
Public utilities, requested rate increase (decrease), amended, amount     $ 3.6      
Electric rate proceeding | Tax Cuts and Jobs Act            
Public Utilities, General Disclosures [Line Items]            
Public utilities, requested rate increase (decrease), amount   $ (7.2)        
Public utilities, requested rate increase (decrease), percentage   (3.90%)        
Subsequent Event | Natural gas rate proceeding | Tax Cuts and Jobs Act            
Public Utilities, General Disclosures [Line Items]            
Public utilities, requested rate increase (decrease), amended, amount $ 2.5          
Public utilities, requested rate increase (decrease), amended percentage 2.30%