SEGMENT REPORTING (Adjusted EBITDA Information) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 120,691	$ 110,445	$ 200,826	$ 177,765
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities	2,416	2,548	4,706	5,053
Depreciation and amortization	71,531	73,393	143,943	142,295
Income from operations	46,744	34,504	52,177	30,417
Other expense	833	189	2,382	539
Loss on early extinguishment of debt	6,045	0	6,045	0
Gain on sale of business	(31,722)	0	(31,722)	0
Interest expense, net of interest income	22,492	21,647	45,068	40,627
Income (loss) before (benefit) provision for income taxes	49,096	12,668	30,404	(10,749)
Technical Services
Segment Reporting Information [Line Items]
Adjusted EBITDA	73,080	68,891	131,567	129,289
Industrial and Field Services
Segment Reporting Information [Line Items]
Adjusted EBITDA	21,484	19,960	23,397	20,393
Safety-Kleen
Segment Reporting Information [Line Items]
Adjusted EBITDA	60,281	55,234	112,649	95,289
Oil, Gas and Lodging Services
Segment Reporting Information [Line Items]
Adjusted EBITDA	268	(1,199)	58	111
Corporate Items
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ (34,422)	$ (32,441)	$ (66,845)	$ (67,317)