SEGMENT REPORTING - Assets by Reportable Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,553,808	$ 1,588,151
Goodwill	523,154	525,013
Permits and other intangibles, net	400,448	419,066
Goodwill and permits and other intangibles, net	923,602	944,079
Environmental Services
Segment Reporting Information [Line Items]
Goodwill	210,617	212,531
Safety-Kleen
Segment Reporting Information [Line Items]
Goodwill	312,537	312,482
Operating segments \| Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	904,626	939,352
Goodwill	210,617	212,531
Permits and other intangibles, net	83,465	89,722
Goodwill and permits and other intangibles, net	294,082	302,253
Operating segments \| Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	558,597	555,310
Goodwill	312,537	312,482
Permits and other intangibles, net	316,983	329,344
Goodwill and permits and other intangibles, net	629,520	641,826
Corporate
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 90,585	$ 93,489

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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