SEGMENT INFORMATION - Total Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Assets	$ 1,376,857	$ 1,360,605
Operating segment | Water services
Segment Reporting Information [Line Items]
Assets	862,342	865,992
Operating segment | Water infrastructure
Segment Reporting Information [Line Items]
Assets	320,721	250,207
Operating segment | Oilfield chemicals
Segment Reporting Information [Line Items]
Assets	184,882	173,762
Operating segment | Other
Segment Reporting Information [Line Items]
Assets	$ 8,912	$ 70,644