SEGMENT REPORTING - Assets by Reportable Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,593,993	$ 1,561,978
Goodwill	524,581	514,189
Permits and other intangibles, net	425,863	441,875
Intangible Assets, Net (Including Goodwill)	950,444	956,064
Total assets	4,021,862	3,738,321
Environmental Services
Segment Reporting Information [Line Items]
Goodwill	212,638	207,019
Safety-Kleen
Segment Reporting Information [Line Items]
Goodwill	311,943	307,170
Operating segments | Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	946,367	951,867
Goodwill	212,638	207,019
Permits and other intangibles, net	91,292	93,313
Intangible Assets, Net (Including Goodwill)	303,930	300,332
Total assets	1,750,343	1,640,706
Operating segments | Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	556,247	553,220
Goodwill	311,943	307,170
Permits and other intangibles, net	334,571	348,562
Intangible Assets, Net (Including Goodwill)	646,514	655,732
Total assets	1,501,838	1,431,381
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	91,379	56,891
Total assets	$ 769,681	$ 666,234