REVENUES - Geography (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of revenue
Revenue	$ 151,416		$ 408,387
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		$ 134,054		$ 370,345
United States
Disaggregation of revenue
Revenue	129,402		360,845
United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		112,821		319,776
Canada
Disaggregation of revenue
Revenue	22,014		47,542
Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		21,233		50,569
Operating Segment | Environmental Services
Disaggregation of revenue
Revenue	107,197		292,628
Operating Segment | Environmental Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		97,661		268,555
Operating Segment | Environmental Services | United States
Disaggregation of revenue
Revenue	85,183		245,086
Operating Segment | Environmental Services | United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		76,428		217,986
Operating Segment | Environmental Services | Canada
Disaggregation of revenue
Revenue	22,014		47,542
Operating Segment | Environmental Services | Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		21,233		50,569
Operating Segment | Field and Industrial Services
Disaggregation of revenue
Revenue	44,219		115,759
Operating Segment | Field and Industrial Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		36,393		101,790
Operating Segment | Field and Industrial Services | United States
Disaggregation of revenue
Revenue	$ 44,219		$ 115,759
Operating Segment | Field and Industrial Services | United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		$ 36,393		$ 101,790