OPERATING SEGMENTS - Reconciliation of EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reconciliation of Net Income to adjusted EBITDA
Net income	$ 10,114	$ 9,904	$ 26,569	$ 17,907
Income tax expense	6,278	6,858	16,828	14,815
Interest expense	4,288	5,081	13,150	16,208
Interest income	(8)	(17)	(90)	(64)
Foreign currency (gain) loss	224	994	(192)	1,769
Other (income) expense	19	(387)	(2,480)	(1,156)
Depreciation and amortization of property and equipment	6,454	6,591	18,561	21,726
Amortization of intangible assets	2,651	2,952	7,907	9,558
Stock-based compensation	605	646	2,182	1,736
Accretion and non-cash adjustment of closure & post-closure liabilities	1,031	1,132	3,081	3,208
Impairment charges				6,700
Adjusted EBITDA	31,656	33,754	85,516	92,407
Operating Segment | Environmental Services
Reconciliation of Net Income to adjusted EBITDA
Adjusted EBITDA	37,747	38,420	104,352	110,778
Operating Segment | Field & Industrial Services
Reconciliation of Net Income to adjusted EBITDA
Adjusted EBITDA	4,466	6,435	13,267	15,790
Corporate
Reconciliation of Net Income to adjusted EBITDA
Adjusted EBITDA	$ (10,557)	$ (11,101)	$ (32,103)	$ (34,161)