SEGMENT REPORTING (Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,631,648	$ 1,587,365
Goodwill	492,705	478,523
Permits and other intangibles, net	464,635	469,128
Total assets	3,684,816	3,706,570
Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	998,340	927,139
Goodwill	187,490	172,386
Permits and other intangibles, net	99,401	97,519
Total assets	1,685,168	1,541,241
Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	553,308	582,162
Goodwill	305,215	306,137
Permits and other intangibles, net	365,234	371,609
Total assets	1,437,026	1,471,291
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	80,000	78,064
Goodwill	0	0
Permits and other intangibles, net	0	0
Total assets	$ 562,622	$ 694,038