OPERATING SEGMENTS - Summarized Financial Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
OPERATING SEGMENTS
Number of reportable segments | segment			2
Total revenue	$ 134,054	$ 124,824	$ 370,345	$ 360,493
Depreciation, amortization and accretion	10,776	10,136	31,838	29,549
Capital expenditures	8,802	2,956	26,354	22,550
Total assets	802,651	773,310	802,651	773,310	$ 776,400
Treatment and disposal
OPERATING SEGMENTS
Total revenue	79,666	74,456	225,145	213,738
Transportation and Logistics
OPERATING SEGMENTS
Total revenue	25,545	21,139	66,761	62,170
Industrial Cleaning
OPERATING SEGMENTS
Total revenue	4,328	5,025	13,252	16,497
Technical Services
OPERATING SEGMENTS
Total revenue	20,314	20,364	55,778	57,136
Remediation
OPERATING SEGMENTS
Total revenue	2,672	3,326	6,495	8,816
Other
OPERATING SEGMENTS
Total revenue	1,529	514	2,914	2,136
Corporate
OPERATING SEGMENTS
Depreciation, amortization and accretion	118	115	375	362
Capital expenditures	647	546	2,250	2,358
Total assets	59,442	59,118	59,442	59,118
Environmental Services | Operating Segment
OPERATING SEGMENTS
Total revenue	97,661	87,785	268,555	252,106
Depreciation, amortization and accretion	9,342	8,665	27,238	25,117
Capital expenditures	7,594	1,960	21,204	18,309
Total assets	619,156	589,841	619,156	589,841
Environmental Services | Operating Segment | Treatment and disposal
OPERATING SEGMENTS
Total revenue	77,071	70,719	217,012	204,352
Environmental Services | Operating Segment | Transportation and Logistics
OPERATING SEGMENTS
Total revenue	20,590	17,066	51,543	47,754
Field & Industrial Services | Operating Segment
OPERATING SEGMENTS
Total revenue	36,393	37,039	101,790	108,387
Depreciation, amortization and accretion	1,316	1,356	4,225	4,070
Capital expenditures	561	450	2,900	1,883
Total assets	124,053	124,351	124,053	124,351
Field & Industrial Services | Operating Segment | Treatment and disposal
OPERATING SEGMENTS
Total revenue	2,595	3,737	8,133	9,386
Field & Industrial Services | Operating Segment | Transportation and Logistics
OPERATING SEGMENTS
Total revenue	4,955	4,073	15,218	14,416
Field & Industrial Services | Operating Segment | Industrial Cleaning
OPERATING SEGMENTS
Total revenue	4,328	5,025	13,252	16,497
Field & Industrial Services | Operating Segment | Technical Services
OPERATING SEGMENTS
Total revenue	20,314	20,364	55,778	57,136
Field & Industrial Services | Operating Segment | Remediation
OPERATING SEGMENTS
Total revenue	2,672	3,326	6,495	8,816
Field & Industrial Services | Operating Segment | Other
OPERATING SEGMENTS
Total revenue	$ 1,529	$ 514	$ 2,914	$ 2,136