SEGMENT REPORTING - Assets by Reportable Segment (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,547,119	$ 1,588,151
Goodwill	519,627	525,013
Permits and other intangibles, net	406,881	419,066
Goodwill and permits and other intangibles, net	926,508	944,079
Environmental Services
Segment Reporting Information [Line Items]
Goodwill	209,713	212,531
Safety-Kleen
Segment Reporting Information [Line Items]
Goodwill	309,914	312,482
Operating segments \| Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	909,207	939,352
Goodwill	209,713	212,531
Permits and other intangibles, net	85,165	89,722
Goodwill and permits and other intangibles, net	294,878	302,253
Operating segments \| Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	552,879	555,310
Goodwill	309,914	312,482
Permits and other intangibles, net	321,716	329,344
Goodwill and permits and other intangibles, net	631,630	641,826
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 85,033	$ 93,489

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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