GOODWILL AND OTHER INTANGIBLE ASSETS (Changes to Goodwill) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill, beginning of period		$ 465,154	$ 453,105
Increase from current period acquisitions		8,687	45,791
Measurement period adjustments from prior period acquisitions		2,186	2,095
Decrease from disposition of business		(1,300)	(4,994)
Goodwill impairment charge	$ (34,000)	0	(34,013)	$ (31,992)
Foreign currency translation		3,796	3,170
Goodwill, end of period		478,523	465,154	453,105
Technical Services
Goodwill [Roll Forward]
Goodwill, beginning of period		61,116	49,267
Increase from current period acquisitions		0	12,572
Measurement period adjustments from prior period acquisitions		0	0
Decrease from disposition of business		(1,300)	0
Goodwill impairment charge			0
Foreign currency translation		317	(723)
Goodwill, end of period		60,133	61,116	49,267
Industrial and Field Services
Goodwill [Roll Forward]
Goodwill, beginning of period		107,968	105,286
Increase from current period acquisitions		3,000	6,953
Measurement period adjustments from prior period acquisitions		0	0
Decrease from disposition of business		0	(4,994)
Goodwill impairment charge			0
Foreign currency translation		1,285	723
Goodwill, end of period		112,253	107,968	105,286
Safety-Kleen
Goodwill [Roll Forward]
Goodwill, beginning of period		296,070	266,344
Increase from current period acquisitions		5,687	26,266
Measurement period adjustments from prior period acquisitions		2,186	2,095
Decrease from disposition of business		0	0
Goodwill impairment charge			0
Foreign currency translation		2,194	1,365
Goodwill, end of period		306,137	296,070	266,344
Oil, Gas and Lodging Services
Goodwill [Roll Forward]
Goodwill, beginning of period		0	32,208
Increase from current period acquisitions		0	0
Measurement period adjustments from prior period acquisitions		0	0
Decrease from disposition of business		0	0
Goodwill impairment charge			(34,013)
Foreign currency translation		0	1,805
Goodwill, end of period		$ 0	$ 0	$ 32,208

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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