GOODWILL AND OTHER INTANGIBLE ASSETS (Changes to Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 478,523	$ 465,154
Increase from current period acquisitions	40,704	8,687
Measurement period adjustments from prior period acquisitions	(78)	2,186
Decrease from disposition of business		(1,300)
Goodwill impairment charge	0	0	$ (34,013)
Foreign currency translation	(4,960)	3,796
Goodwill, end of period	514,189	478,523	465,154
Environmental Services
Goodwill [Roll Forward]
Goodwill, beginning of period	172,386	169,084
Increase from current period acquisitions	37,007	3,000
Measurement period adjustments from prior period acquisitions	(78)	0
Decrease from disposition of business		(1,300)
Foreign currency translation	(2,296)	1,602
Goodwill, end of period	207,019	172,386	169,084
Safety-Kleen
Goodwill [Roll Forward]
Goodwill, beginning of period	306,137	296,070
Increase from current period acquisitions	3,697	5,687
Measurement period adjustments from prior period acquisitions	0	2,186
Decrease from disposition of business		0
Foreign currency translation	(2,664)	2,194
Goodwill, end of period	$ 307,170	$ 306,137	$ 296,070