SEGMENT REPORTING (Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,614,429	$ 1,587,365
Goodwill	514,102	478,523
Permits and other intangibles, net	451,355	469,128
Total assets	3,774,329	3,706,570
Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	997,708	927,139
Goodwill	204,760	172,386
Permits and other intangibles, net	96,175	97,519
Total assets	1,714,209	1,541,241
Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	558,550	582,162
Goodwill	309,342	306,137
Permits and other intangibles, net	355,180	371,609
Total assets	1,445,995	1,471,291
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	58,171	78,064
Goodwill	0	0
Permits and other intangibles, net	0	0
Total assets	$ 614,125	$ 694,038