REVENUES (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)	Dec. 31, 2018 item
Disaggregation of revenue
Number of reportable segments | segment			2
Revenue	$ 155,802	$ 136,912	$ 286,839	$ 256,971
Field and Industrial Services
Disaggregation of revenue
Number of service lines | item					2
Treatment and disposal
Disaggregation of revenue
Revenue	93,512	80,995	174,021	156,351
Transportation and Logistics
Disaggregation of revenue
Revenue	35,225	28,465	56,937	47,877
Industrial Services
Disaggregation of revenue
Revenue	4,963	4,506	10,980	8,385
Small Quantity Generation
Disaggregation of revenue
Revenue	9,326	9,138	17,515	17,465
Total Waste Management
Disaggregation of revenue
Revenue	8,004	9,019	16,719	19,241
Remediation
Disaggregation of revenue
Revenue	889	3,968	2,616	6,158
Emergency Response
Disaggregation of revenue
Revenue	3,180	749	6,226	1,391
Other
Disaggregation of revenue
Revenue	703	72	1,825	103
Operating Segment | Environmental Services
Disaggregation of revenue
Revenue	112,844	98,960	205,177	185,431
Operating Segment | Field and Industrial Services
Disaggregation of revenue
Revenue	42,958	37,952	81,662	71,540
Operating Segment | Treatment and disposal | Environmental Services
Disaggregation of revenue
Revenue	90,379	78,093	168,092	150,802
Operating Segment | Treatment and disposal | Field and Industrial Services
Disaggregation of revenue
Revenue	3,133	2,902	5,929	5,549
Operating Segment | Transportation and Logistics | Environmental Services
Disaggregation of revenue
Revenue	22,465	20,867	37,085	34,629
Operating Segment | Transportation and Logistics | Field and Industrial Services
Disaggregation of revenue
Revenue	12,760	7,598	19,852	13,248
Operating Segment | Industrial Services | Field and Industrial Services
Disaggregation of revenue
Revenue	4,963	4,506	10,980	8,385
Operating Segment | Small Quantity Generation | Field and Industrial Services
Disaggregation of revenue
Revenue	9,326	9,138	17,515	17,465
Operating Segment | Total Waste Management | Field and Industrial Services
Disaggregation of revenue
Revenue	8,004	9,019	16,719	19,241
Operating Segment | Remediation | Field and Industrial Services
Disaggregation of revenue
Revenue	889	3,968	2,616	6,158
Operating Segment | Emergency Response | Field and Industrial Services
Disaggregation of revenue
Revenue	3,180	749	6,226	1,391
Operating Segment | Other | Field and Industrial Services
Disaggregation of revenue
Revenue	$ 703	$ 72	$ 1,825	$ 103