GOODWILL AND OTHER INTANGIBLE ASSETS (Rollforward of Goodwill) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
Goodwill [Roll Forward]
Balance at beginning of year	$ 465,154
Increase from current period acquisitions	4,938
Measurement period adjustments from prior period acquisitions	(731)
Foreign currency translation and other	499
Balance at end of year	469,860
Technical Services
Goodwill [Roll Forward]
Balance at beginning of year	61,116
Balance at end of year	61,158
Industrial and Field Services
Goodwill [Roll Forward]
Balance at beginning of year	107,968
Balance at end of year	108,131
Safety-Kleen
Goodwill [Roll Forward]
Balance at beginning of year	296,070
Balance at end of year	300,571
Oil, Gas and Lodging Services
Goodwill [Roll Forward]
Balance at beginning of year	0
Balance at end of year	0
Operating Segments | 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
Foreign currency translation and other	42
Balance at end of year	61,158
Operating Segments | Industrial and Field Services
Goodwill [Roll Forward]
Balance at beginning of year	107,968
Increase from current period acquisitions	0
Measurement period adjustments from prior period acquisitions	0
Foreign currency translation and other	163
Balance at end of year	108,131
Operating Segments | Safety-Kleen
Goodwill [Roll Forward]
Balance at beginning of year	296,070
Increase from current period acquisitions	4,938
Measurement period adjustments from prior period acquisitions	(731)
Foreign currency translation and other	294
Balance at end of year	300,571
Operating Segments | 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
Foreign currency translation and other	0
Balance at end of year	$ 0