REVENUES - Geography (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of revenue
Revenue	$ 120,059
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		$ 110,234
United States
Disaggregation of revenue
Revenue	108,574
United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		96,192
Canada
Disaggregation of revenue
Revenue	11,485
Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		14,042
Operating Segment | Environmental Services
Disaggregation of revenue
Revenue	86,471
Operating Segment | Environmental Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		81,303
Operating Segment | Environmental Services | United States
Disaggregation of revenue
Revenue	74,986
Operating Segment | Environmental Services | United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		67,261
Operating Segment | Environmental Services | Canada
Disaggregation of revenue
Revenue	11,485
Operating Segment | Environmental Services | Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		14,042
Operating Segment | Field and Industrial Services
Disaggregation of revenue
Revenue	33,588
Operating Segment | Field and Industrial Services | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		28,931
Operating Segment | Field and Industrial Services | United States
Disaggregation of revenue
Revenue	$ 33,588
Operating Segment | Field and Industrial Services | United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of revenue
Revenue		$ 28,931