SEGMENT REPORTING - Schedule of Certain Assets by Reportable Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,531,289	$ 1,525,298
Goodwill	544,639	527,023
Permits and other intangibles, net	374,230	386,620
Goodwill and Permits and other intangibles, net	918,869	913,643
Environmental Services
Segment Reporting Information [Line Items]
Goodwill	403,136	401,918
Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Goodwill	141,503	125,105
Operating Segments [Member] \| Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,068,270	1,068,910
Goodwill	403,136	401,918
Permits and other intangibles, net	221,437	228,237
Goodwill and Permits and other intangibles, net	624,573	630,155
Operating Segments [Member] \| Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Property, plant and equipment, net	371,056	366,160
Goodwill	141,503	125,105
Permits and other intangibles, net	152,793	158,383
Goodwill and Permits and other intangibles, net	294,296	283,488
Corporate, non-Segment
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 91,963	$ 90,228

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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Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

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Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance.

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Amount, after accumulated depreciation and amortization, of property, plant, and equipment and finance lease right-of-use asset.

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