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OPERATING SEGMENTS - Summarized Financial Information (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 USD ($)
OPERATING SEGMENTS
Number of reportable segments \| segment			2
Revenue	$ 155,802	$ 136,912	$ 286,839	$ 256,971
Depreciation, amortization and accretion	13,125	10,421	25,186	20,402
Capital expenditures	17,434	7,402	24,657	14,960
Total assets	961,416	824,663	961,416	824,663	$ 947,898
Treatment and disposal
OPERATING SEGMENTS
Revenue	93,512	80,995	174,021	156,351
Transportation and Logistics
OPERATING SEGMENTS
Revenue	35,225	28,465	56,937	47,877
Remediation
OPERATING SEGMENTS
Revenue	889	3,968	2,616	6,158
Other
OPERATING SEGMENTS
Revenue	703	72	1,825	103
Corporate
OPERATING SEGMENTS
Depreciation, amortization and accretion	597	330	901	446
Capital expenditures	920	618	1,253	1,134
Total assets	68,120	98,160	68,120	98,160
Environmental Services \| Operating Segment
OPERATING SEGMENTS
Revenue	112,844	98,960	205,177	185,431
Depreciation, amortization and accretion	10,377	8,676	20,003	17,186
Capital expenditures	14,455	4,935	21,296	10,939
Total assets	725,311	599,706	725,311	599,706
Environmental Services \| Operating Segment \| Treatment and disposal
OPERATING SEGMENTS
Revenue	90,379	78,093	168,092	150,802
Environmental Services \| Operating Segment \| Transportation and Logistics
OPERATING SEGMENTS
Revenue	22,465	20,867	37,085	34,629
Field and Industrial Services \| Operating Segment
OPERATING SEGMENTS
Revenue	42,958	37,952	81,662	71,540
Depreciation, amortization and accretion	2,151	1,415	4,282	2,770
Capital expenditures	2,059	1,849	2,108	2,887
Total assets	167,985	126,797	167,985	126,797
Field and Industrial Services \| Operating Segment \| Treatment and disposal
OPERATING SEGMENTS
Revenue	3,133	2,902	5,929	5,549
Field and Industrial Services \| Operating Segment \| Transportation and Logistics
OPERATING SEGMENTS
Revenue	12,760	7,598	19,852	13,248
Field and Industrial Services \| Operating Segment \| Remediation
OPERATING SEGMENTS
Revenue	889	3,968	2,616	6,158
Field and Industrial Services \| Operating Segment \| Other
OPERATING SEGMENTS
Revenue	$ 703	$ 72	$ 1,825	$ 103