GOODWILL AND OTHER INTANGIBLE ASSETS (Rollforward of Goodwill) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
Goodwill [Roll Forward]
Balance at beginning of year	$ 465,154
Increase from current period acquisitions	8,612
Measurement period adjustments from prior period acquisitions	2,186
Decrease from disposition of business	(1,300)
Foreign currency translation and other	4,076
Balance at end of year	478,728
Technical Services
Goodwill [Roll Forward]
Balance at beginning of year	61,116
Increase from current period acquisitions	0
Measurement period adjustments from prior period acquisitions	0
Decrease from disposition of business	(1,300)
Foreign currency translation and other	338
Balance at end of year	60,154
Industrial and Field Services
Goodwill [Roll Forward]
Balance at beginning of year	107,968
Increase from current period acquisitions	2,999
Measurement period adjustments from prior period acquisitions	0
Decrease from disposition of business	0
Foreign currency translation and other	1,398
Balance at end of year	112,365
Safety-Kleen
Goodwill [Roll Forward]
Balance at beginning of year	296,070
Increase from current period acquisitions	5,613
Measurement period adjustments from prior period acquisitions	2,186
Decrease from disposition of business	0
Foreign currency translation and other	2,340
Balance at end of year	306,209
Oil, Gas and Lodging Services
Goodwill [Roll Forward]
Balance at beginning of year	0
Increase from current period acquisitions	0
Measurement period adjustments from prior period acquisitions	0
Decrease from disposition of business	0
Foreign currency translation and other	0
Balance at end of year	$ 0