REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 843,181	$ 755,846	$ 2,442,099	$ 2,197,575
United States
Disaggregation of Revenue [Line Items]
Total third party revenues	718,223	625,746	2,064,531	1,835,828
Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	124,958	130,100	377,568	361,747
Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	264,769	246,323	758,081	731,028
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	77,025	76,446	223,052	208,172
Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	134,323	90,894	399,132	265,695
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	33,163	27,155	89,300	81,795
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	200,681	191,420	594,876	575,964
Kleen Performance Products
Disaggregation of Revenue [Line Items]
Total third party revenues	133,220	123,608	377,658	334,921
Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	508,813	440,163	1,468,417	1,285,701
Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	410,792	334,625	1,162,891	991,731
Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	98,021	105,538	305,526	293,970
Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	264,769	246,323	758,081	731,028
Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	77,025	76,446	223,052	208,172
Environmental Services | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	134,323	90,894	399,132	265,695
Environmental Services | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	32,696	26,500	88,152	80,806
Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Environmental Services | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen
Disaggregation of Revenue [Line Items]
Total third party revenues	333,901	315,028	972,534	910,885
Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	307,497	290,653	901,198	843,341
Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	26,404	24,375	71,336	67,544
Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	200,681	191,420	594,876	575,964
Safety-Kleen | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Total third party revenues	133,220	123,608	377,658	334,921
Corporate
Disaggregation of Revenue [Line Items]
Total third party revenues	467	655	1,148	989
Corporate | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	(66)	468	442	756
Corporate | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	533	187	706	233
Corporate | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	467	655	1,148	989
Corporate | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 0	$ 0	$ 0	$ 0