GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Changes in goodwill
Balance at the beginning of the period			$ 191,823
ESI acquisition			1,011
Foreign currency translation			821
Balance at the end of the period	$ 193,655		193,655
Intangible Assets
Amortizing intangible assets, Cost	213,245		213,245		$ 210,759
Accumulated amortization	(29,267)		(29,267)		(21,061)
Amortizing intangible assets, Net	183,978		183,978		189,698
Total intangible assets, cost	263,733		263,733		260,632
Total intangible assets, net	234,466		234,466		239,571
Amortization expense	2,651	$ 2,952	7,907	$ 9,558
Permits and licenses
Intangible Assets
Nonamortizing intangible assets	50,359		50,359		49,750
Tradename
Intangible Assets
Nonamortizing intangible assets	129		129		123
Permits, licenses and lease
Intangible Assets
Amortizing intangible assets, Cost	110,816		110,816		109,652
Accumulated amortization	(8,877)		(8,877)		(6,682)
Amortizing intangible assets, Net	101,939		101,939		102,970
Customer relationships
Intangible Assets
Amortizing intangible assets, Cost	82,945		82,945		82,021
Accumulated amortization	(13,149)		(13,149)		(9,015)
Amortizing intangible assets, Net	69,796		69,796		73,006
Technology - formulae and processes
Intangible Assets
Amortizing intangible assets, Cost	6,924		6,924		6,560
Accumulated amortization	(1,279)		(1,279)		(1,054)
Amortizing intangible assets, Net	5,645		5,645		5,506
Customer backlog
Intangible Assets
Amortizing intangible assets, Cost	3,652		3,652		3,652
Accumulated amortization	(835)		(835)		(561)
Amortizing intangible assets, Net	2,817		2,817		3,091
Tradename
Intangible Assets
Amortizing intangible assets, Cost	4,318		4,318		4,318
Accumulated amortization	(3,290)		(3,290)		(2,210)
Amortizing intangible assets, Net	1,028		1,028		2,108
Developed software
Intangible Assets
Amortizing intangible assets, Cost	2,914		2,914		2,899
Accumulated amortization	(922)		(922)		(678)
Amortizing intangible assets, Net	1,992		1,992		2,221
Non-compete agreements
Intangible Assets
Amortizing intangible assets, Cost	747		747		732
Accumulated amortization	(738)		(738)		(732)
Amortizing intangible assets, Net	9		9
Internet domain and website
Intangible Assets
Amortizing intangible assets, Cost	540		540		540
Accumulated amortization	(65)		(65)		(44)
Amortizing intangible assets, Net	475		475		496
Database
Intangible Assets
Amortizing intangible assets, Cost	389		389		385
Accumulated amortization	(112)		(112)		(85)
Amortizing intangible assets, Net	277		277		$ 300
Environmental Services
Changes in goodwill
Balance at the beginning of the period			147,692
ESI acquisition			1,011
Foreign currency translation			821
Balance at the end of the period	149,524		149,524
Field & Industrial Services
Changes in goodwill
Balance at the beginning of the period			44,131
Balance at the end of the period	$ 44,131		$ 44,131