SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 80,932	$ 81,503
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	8,715	7,912
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	10,477	9,073
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	15,970	17,809
Piceance/DJ Basins
Segment Reporting Information [Line Items]
Adjusted EBITDA	29,235	28,974
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	9,859	12,088
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 6,676	$ 5,647