REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 849,140	$ 752,788	$ 1,598,918	$ 1,441,729
United States
Disaggregation of Revenue [Line Items]
Revenues	714,549	624,095	1,346,308	1,210,082
Canada
Disaggregation of Revenue [Line Items]
Revenues	134,591	128,693	252,610	231,647
Technical Services
Disaggregation of Revenue [Line Items]
Revenues	257,006	254,487	493,312	484,705
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	76,092	70,707	146,027	131,726
Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	161,046	99,733	264,809	174,801
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	26,281	24,905	56,137	54,640
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	200,034	192,817	394,195	384,544
Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	128,681	110,139	244,438	211,313
Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	519,916	449,631	959,604	845,538
Environmental Services | United States
Disaggregation of Revenue [Line Items]
Revenues	408,127	343,323	752,099	657,106
Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Revenues	111,789	106,308	207,505	188,432
Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Revenues	257,006	254,487	493,312	484,705
Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	76,092	70,707	146,027	131,726
Environmental Services | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	161,046	99,733	264,809	174,801
Environmental Services | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	25,772	24,704	55,456	54,306
Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Environmental Services | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Safety-Kleen
Disaggregation of Revenue [Line Items]
Revenues	328,715	302,956	638,633	595,857
Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Revenues	306,059	280,617	593,701	552,688
Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Revenues	22,656	22,339	44,932	43,169
Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Safety-Kleen | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Safety-Kleen | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	200,034	192,817	394,195	384,544
Safety-Kleen | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	128,681	110,139	244,438	211,313
Corporate
Disaggregation of Revenue [Line Items]
Revenues	509	201	681	334
Corporate | United States
Disaggregation of Revenue [Line Items]
Revenues	363	155	508	288
Corporate | Canada
Disaggregation of Revenue [Line Items]
Revenues	146	46	173	46
Corporate | Technical Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Corporate | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Corporate | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Corporate | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	509	201	681	334
Corporate | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Corporate | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0	$ 0	$ 0