SEGMENT REPORTING (Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,609,382	$ 1,587,365
Goodwill	497,251	478,523
Permits and other intangibles, net	455,920	469,128
Total assets	3,715,461	3,706,570
Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	988,957	927,139
Goodwill	192,629	172,386
Permits and other intangibles, net	96,165	97,519
Total assets	1,681,627	1,541,241
Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	555,124	582,162
Goodwill	304,622	306,137
Permits and other intangibles, net	359,755	371,609
Total assets	1,436,014	1,471,291
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	65,301	78,064
Goodwill	0	0
Permits and other intangibles, net	0	0
Total assets	$ 597,820	$ 694,038