SEGMENT REPORTING - Assets by Reportable Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,596,917	$ 1,561,978
Goodwill	525,044	514,189
Permits and other intangibles, net	433,853	441,875
Intangible Assets, Net (Including Goodwill)	958,897	956,064
Total assets	3,955,321	3,738,321
Environmental Services
Segment Reporting Information [Line Items]
Goodwill	212,808	207,019
Safety-Kleen
Segment Reporting Information [Line Items]
Goodwill	312,236	307,170
Direct revenues | Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	956,381	951,867
Goodwill	212,808	207,019
Permits and other intangibles, net	93,303	93,313
Intangible Assets, Net (Including Goodwill)	306,111	300,332
Total assets	1,756,818	1,640,706
Direct revenues | Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	559,510	553,220
Goodwill	312,236	307,170
Permits and other intangibles, net	340,550	348,562
Intangible Assets, Net (Including Goodwill)	652,786	655,732
Total assets	1,513,920	1,431,381
Corporate Items, net
Segment Reporting Information [Line Items]
Property, plant and equipment, net	81,026	56,891
Total assets	$ 684,583	$ 666,234