GOODWILL AND OTHER INTANGIBLE ASSETS (Rollforward of Goodwill) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Goodwill [Roll Forward]
Balance at beginning of year	$ 465,154
Increase from current period acquisitions	4,916
Measurement period adjustments from prior period acquisitions	2,186
Decrease from disposition of business	(1,300)
Foreign currency translation and other	1,863
Balance at end of year	472,819
Technical Services
Goodwill [Roll Forward]
Balance at beginning of year	61,116
Balance at end of year	59,973
Industrial and Field Services
Goodwill [Roll Forward]
Balance at beginning of year	107,968
Balance at end of year	108,583
Safety-Kleen
Goodwill [Roll Forward]
Balance at beginning of year	296,070
Balance at end of year	304,263
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
Decrease from disposition of business	(1,300)
Foreign currency translation and other	157
Balance at end of year	59,973
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
Decrease from disposition of business	0
Foreign currency translation and other	615
Balance at end of year	108,583
Operating Segments | Safety-Kleen
Goodwill [Roll Forward]
Balance at beginning of year	296,070
Increase from current period acquisitions	4,916
Measurement period adjustments from prior period acquisitions	2,186
Decrease from disposition of business	0
Foreign currency translation and other	1,091
Balance at end of year	304,263
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
Decrease from disposition of business
Foreign currency translation and other	0
Balance at end of year	$ 0