GOODWILL AND OTHER INTANGIBLE ASSETS - Rollforward of Goodwill (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Goodwill [Roll Forward]
Balance at January 1, 2020	$ 525,013
Measurement period adjustments from prior period acquisitions	54
Decrease from disposition of businesses	(649)
Foreign currency translation	(4,791)
Balance at March 31, 2020	519,627
Environmental Services
Goodwill [Roll Forward]
Balance at January 1, 2020	212,531
Measurement period adjustments from prior period acquisitions	54
Decrease from disposition of businesses	(649)
Foreign currency translation	(2,223)
Balance at March 31, 2020	209,713
Safety-Kleen
Goodwill [Roll Forward]
Balance at January 1, 2020	312,482
Measurement period adjustments from prior period acquisitions	0
Decrease from disposition of businesses	0
Foreign currency translation	(2,568)
Balance at March 31, 2020	$ 309,914