SEGMENT INFORMATION - Adjusted EBITDA by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 82,740	$ 82,674	$ 246,169	$ 246,189
Utica Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	6,521	8,412	24,459	25,857
Ohio Gathering
Segment Reporting Information [Line Items]
Adjusted EBITDA	10,171	10,522	29,583	29,201
Williston Basin
Segment Reporting Information [Line Items]
Adjusted EBITDA	19,849	16,212	54,849	51,176
Piceance/DJ Basins
Segment Reporting Information [Line Items]
Adjusted EBITDA	29,831	30,008	86,739	86,256
Barnett Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	10,818	10,838	31,770	35,924
Marcellus Shale
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 5,550	$ 6,682	$ 18,769	$ 17,775