GOODWILL AND OTHER INTANGIBLE ASSETS (Changes to Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 525,013	$ 514,189
Increase from current period acquisitions	1,439	12,603
Measurement period adjustments from prior period acquisitions	23	(4,030)
Decrease from disposition of businesses	(674)
Foreign currency translation	1,222	2,251
Goodwill, end of period	527,023	525,013
Environmental Services
Goodwill [Roll Forward]
Goodwill, beginning of period	212,531	207,019
Increase from current period acquisitions	0	7,378
Measurement period adjustments from prior period acquisitions	23	(2,675)
Decrease from disposition of businesses	(674)
Foreign currency translation	506	809
Goodwill, end of period	212,386	212,531
Safety-Kleen
Goodwill [Roll Forward]
Goodwill, beginning of period	312,482	307,170
Increase from current period acquisitions	1,439	5,225
Measurement period adjustments from prior period acquisitions	0	(1,355)
Decrease from disposition of businesses	0
Foreign currency translation	716	1,442
Goodwill, end of period	$ 314,637	$ 312,482

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 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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Amount of divestiture 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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