GOODWILL AND OTHER INTANGIBLE ASSETS - Changes to Goodwill (Details) $ in Thousands	6 Months Ended
Jun. 30, 2021 USD ($)
Goodwill [Roll Forward]
Balance at January 1, 2021	$ 527,023
Increase from current period acquisition	15,958
Foreign currency translation	1,658
Balance at June 30, 2021	544,639
Environmental Services
Goodwill [Roll Forward]
Balance at January 1, 2021	401,918
Increase from current period acquisition	0
Foreign currency translation	1,218
Balance at June 30, 2021	403,136
Safety-Kleen Sustainability Solutions
Goodwill [Roll Forward]
Balance at January 1, 2021	125,105
Increase from current period acquisition	15,958
Foreign currency translation	440
Balance at June 30, 2021	$ 141,503

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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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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