SEGMENT REPORTING (Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,609,490	$ 1,611,827
Goodwill	469,860	465,154
Permits and other intangibles, net	490,952	498,721
Total assets	3,645,653	3,681,920
Technical Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	521,726	521,134
Goodwill	61,158	61,116
Permits and other intangibles, net	77,131	78,625
Total assets	856,324	862,957
Industrial and Field Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	245,250	245,143
Goodwill	108,131	107,968
Permits and other intangibles, net	17,973	17,817
Total assets	446,757	446,826
Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	589,782	584,647
Goodwill	300,571	296,070
Permits and other intangibles, net	386,125	391,390
Total assets	1,477,851	1,474,755
Oil, Gas and Lodging Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	173,347	182,038
Goodwill	0	0
Permits and other intangibles, net	9,723	10,889
Total assets	246,910	253,242
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	79,385	78,865
Goodwill	0	0
Permits and other intangibles, net	0	0
Total assets	$ 617,811	$ 644,140