SEGMENT REPORTING (Segment Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total revenues	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 692,113	$ 729,520	$ 697,510	$ 636,083	$ 2,944,978	$ 2,755,226	$ 3,275,137
Property, plant and equipment, net	1,587,365				1,611,827				1,587,365	1,611,827
Permits and other intangibles, net	469,128				498,721				469,128	498,721
Goodwill	478,523				465,154				478,523	465,154	453,105
Goodwill and Permits and other intangibles, net	947,651				963,875				947,651	963,875
Assets	3,706,570				3,681,920				3,706,570	3,681,920	3,431,428
Technical Services
Total revenues									1,144,149	1,056,735	1,139,080
Property, plant and equipment, net	504,754				521,134				504,754	521,134
Permits and other intangibles, net	73,775				78,625				73,775	78,625
Goodwill	60,133				61,116				60,133	61,116	49,267
Goodwill and Permits and other intangibles, net	133,908				139,741				133,908	139,741
Assets	847,994				862,957				847,994	862,957	800,060
Industrial and Field Services
Total revenues									593,722	582,215	989,953
Property, plant and equipment, net	254,091				245,143				254,091	245,143
Permits and other intangibles, net	17,049				17,817				17,049	17,817
Goodwill	112,253				107,968				112,253	107,968	105,286
Goodwill and Permits and other intangibles, net	129,302				125,785				129,302	125,785
Assets	464,142				446,826				464,142	446,826	461,180
Safety-Kleen
Total revenues									1,087,886	996,083	941,689
Property, plant and equipment, net	582,162				584,647				582,162	584,647
Permits and other intangibles, net	371,609				391,390				371,609	391,390
Goodwill	306,137				296,070				306,137	296,070	266,344
Goodwill and Permits and other intangibles, net	677,746				687,460				677,746	687,460
Assets	1,471,291				1,474,755				1,471,291	1,474,755	1,297,971
Oil, Gas and Lodging Services
Total revenues									119,603	119,883	207,139
Property, plant and equipment, net	168,294				182,038				168,294	182,038
Permits and other intangibles, net	6,695				10,889				6,695	10,889
Goodwill	0				0				0	0	32,208
Goodwill and Permits and other intangibles, net	6,695				10,889				6,695	10,889
Assets	229,105				253,242				229,105	253,242	333,245
Corporate Items
Property, plant and equipment, net	78,064				78,865				78,064	78,865
Assets	694,038				644,140				694,038	644,140	538,972
United States and Puerto Rico
Total revenues									$ 2,392,000	$ 2,213,400	$ 2,576,200
Percent of revenues									81.20%	80.30%	78.70%
United States
Assets	2,985,394				2,960,337				$ 2,985,394	$ 2,960,337	$ 2,575,746
Canada
Total revenues									$ 552,100	$ 538,000	$ 695,000
Percent of revenues									18.70%	19.50%	21.20%
Property, plant and equipment, net	$ 411,900				$ 400,300				$ 411,900	$ 400,300
Percent of property, plant and equipment, net	26.00%				24.80%				26.00%	24.80%
Permits and other intangibles, net	$ 60,500				$ 63,100				$ 60,500	$ 63,100
Percent of permits and other intangibles, net	12.90%				12.70%				12.90%	12.70%
Assets	$ 721,176				$ 721,583				$ 721,176	$ 721,583	$ 851,949
Other foreign
Percent of revenues									0.10%		0.10%
Assets	$ 0				$ 0				$ 0	$ 0	$ 3,733