GOODWILL AND OTHER INTANGIBLE ASSETS (Rollforward of Goodwill) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill [Roll Forward]
Balance at beginning of year	$ 478,523
Increase from current period acquisition	15,908
Measurement period adjustments from prior period acquisitions	(9)
Foreign currency translation	(1,717)
Balance at end of year	492,705
Environmental Services
Goodwill [Roll Forward]
Balance at beginning of year	172,386
Increase from current period acquisition	15,908
Measurement period adjustments from prior period acquisitions	(9)
Foreign currency translation	(795)
Balance at end of year	187,490
Safety-Kleen
Goodwill [Roll Forward]
Balance at beginning of year	306,137
Increase from current period acquisition	0
Measurement period adjustments from prior period acquisitions	0
Foreign currency translation	(922)
Balance at end of year	$ 305,215