SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 82,497	$ 82,012	$ 163,429	$ 163,515
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	9,223	9,533	17,938	17,445
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	8,935	9,606	19,412	18,679
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	19,030	17,155	35,000	34,964
Piceance/DJ Basins
Segment Reporting Information [Line Items]
Adjusted EBITDA	27,673	27,274	56,908	56,248
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	11,093	12,998	20,952	25,086
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 6,543	$ 5,446	$ 13,219	$ 11,093