SEGMENT REPORTING (Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,588,613	$ 1,561,978
Goodwill	517,910	514,189
Permits and other intangibles, net	438,958	441,875
Total assets	3,882,054	3,738,321
Intangible Assets, Net (Including Goodwill)	956,868	956,064
Environmental Services
Segment Reporting Information [Line Items]
Goodwill	204,860	207,019
Safety-Kleen
Segment Reporting Information [Line Items]
Goodwill	313,050	307,170
Direct revenues | Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	953,960	951,867
Goodwill	204,860	207,019
Permits and other intangibles, net	95,040	93,313
Total assets	1,724,208	1,640,706
Intangible Assets, Net (Including Goodwill)	299,900	300,332
Direct revenues | Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	561,041	553,220
Goodwill	313,050	307,170
Permits and other intangibles, net	343,918	348,562
Total assets	1,518,723	1,431,381
Intangible Assets, Net (Including Goodwill)	656,968	655,732
Corporate Items, net
Segment Reporting Information [Line Items]
Property, plant and equipment, net	73,612	56,891
Total assets	$ 639,123	$ 666,234