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COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($)
1 Months Ended 12 Months Ended
Jan. 31, 2017
Jun. 30, 2015
Dec. 31, 2016
Dec. 31, 2015
Meadowland Midstream Gathering System | Principal Owner | North Dakota Industrial Commission Case        
Accrual for Environmental Loss Contingencies [Roll Forward]        
Fines and other fees sought   $ 2,500,000    
Maximum | Meadowland Midstream Gathering System | Principal Owner        
Loss Contingencies [Line Items]        
Coverage from pollution liability insurance policy     $ 25,000,000 $ 25,000,000
Coverage from property and business interruption insurance policy     $ 200,000,000  
Forecast | Business Interruption        
Loss Contingencies [Line Items]        
Recoveries recognized $ 2,600,000      
Forecast | Property Recoveries        
Loss Contingencies [Line Items]        
Recoveries recognized $ 400,000