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SEGMENT INFORMATION - Concentration Risk (Details) - Revenue - Customer concentration
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Counterparty A - Piceance/DJ Basins      
Segment Reporting Information [Line Items]      
Concentration risk, percentage 14.00% 16.00% 18.00%
Counterparty B - Piceance/DJ Basins      
Segment Reporting Information [Line Items]      
Concentration risk, percentage   14.00%