REVENUES - Geography (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of revenue
Revenue	$ 136,912		$ 256,971
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		$ 126,057		$ 236,291
United States
Disaggregation of revenue
Revenue	122,869		231,443
United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		110,763		206,955
Canada
Disaggregation of revenue
Revenue	14,043		25,528
Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		15,294		29,336
Operating Segment | Environmental Services
Disaggregation of revenue
Revenue	98,960		185,431
Operating Segment | Environmental Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		89,591		170,894
Operating Segment | Environmental Services | United States
Disaggregation of revenue
Revenue	84,917		159,903
Operating Segment | Environmental Services | United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		74,297		141,558
Operating Segment | Environmental Services | Canada
Disaggregation of revenue
Revenue	14,043		25,528
Operating Segment | Environmental Services | Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		15,294		29,336
Operating Segment | Field and Industrial Services
Disaggregation of revenue
Revenue	37,952		71,540
Operating Segment | Field and Industrial Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		36,466		65,397
Operating Segment | Field and Industrial Services | United States
Disaggregation of revenue
Revenue	$ 37,952		$ 71,540
Operating Segment | Field and Industrial Services | United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		$ 36,466		$ 65,397