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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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OPERATING SEGMENTS - Summarized Financial Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
OPERATING SEGMENTS
Number of reportable segments \| segment	2
Revenue	$ 120,059	$ 110,234
Total revenue	120,059
Depreciation, amortization and accretion	9,981	10,376
Capital expenditures	7,558	7,151
Total assets	801,085	771,726	$ 802,076
Treatment and disposal
OPERATING SEGMENTS
Total revenue	75,038
Transportation and Logistics
OPERATING SEGMENTS
Total revenue	19,867
Industrial Cleaning
OPERATING SEGMENTS
Total revenue	3,505
Technical Services
OPERATING SEGMENTS
Total revenue	20,405
Remediation
OPERATING SEGMENTS
Total revenue	353
Other
OPERATING SEGMENTS
Total revenue	891
Corporate
OPERATING SEGMENTS
Depreciation, amortization and accretion	116	128
Capital expenditures	516	899
Total assets	81,597	58,421
Environmental Services \| Operating Segment
OPERATING SEGMENTS
Revenue	86,471	81,303
Total revenue	86,471
Depreciation, amortization and accretion	8,510	8,790
Capital expenditures	6,004	4,214
Total assets	595,304	594,310
Environmental Services \| Operating Segment \| Treatment and disposal
OPERATING SEGMENTS
Total revenue	72,301
Environmental Services \| Operating Segment \| Transportation and Logistics
OPERATING SEGMENTS
Total revenue	14,170
Field and Industrial Services \| Operating Segment
OPERATING SEGMENTS
Revenue	33,588	28,931
Total revenue	33,588
Depreciation, amortization and accretion	1,355	1,458
Capital expenditures	1,038	2,038
Total assets	124,184	$ 118,995
Field and Industrial Services \| Operating Segment \| Treatment and disposal
OPERATING SEGMENTS
Total revenue	2,737
Field and Industrial Services \| Operating Segment \| Transportation and Logistics
OPERATING SEGMENTS
Total revenue	5,697
Field and Industrial Services \| Operating Segment \| Industrial Cleaning
OPERATING SEGMENTS
Total revenue	3,505
Field and Industrial Services \| Operating Segment \| Technical Services
OPERATING SEGMENTS
Total revenue	20,405
Field and Industrial Services \| Operating Segment \| Remediation
OPERATING SEGMENTS
Total revenue	353
Field and Industrial Services \| Operating Segment \| Other
OPERATING SEGMENTS
Total revenue	$ 891