SEGMENT REPORTING (Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,602,453	$ 1,611,827
Goodwill	472,819	465,154
Permits and other intangibles, net	482,828	498,721
Total assets	3,806,282	3,681,920
Technical Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	512,058	521,134
Goodwill	59,973	61,116
Permits and other intangibles, net	76,022	78,625
Total assets	851,852	862,957
Industrial and Field Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	243,195	245,143
Goodwill	108,583	107,968
Permits and other intangibles, net	17,135	17,817
Total assets	457,253	446,826
Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	590,282	584,647
Goodwill	304,263	296,070
Permits and other intangibles, net	381,020	391,390
Total assets	1,477,660	1,474,755
Oil, Gas and Lodging Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	181,001	182,038
Goodwill	0	0
Permits and other intangibles, net	8,651	10,889
Total assets	246,195	253,242
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	75,917	78,865
Goodwill	0	0
Permits and other intangibles, net	0	0
Total assets	$ 773,322	$ 644,140