GOODWILL AND INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Intangible Assets
Amortizing intangible assets, Cost	$ 215,712		$ 216,622
Accumulated amortization	(44,262)		(42,186)
Amortizing intangible assets, Net	171,450		174,436
Total intangible assets, cost	264,068		264,998
Total intangible assets, net	219,806		222,812
Amortization of intangible assets	2,302	$ 2,670
Permits and licenses
Intangible Assets
Nonamortizing intangible assets	48,224		48,241
Tradename
Intangible Assets
Nonamortizing intangible assets	132		135
Permits, licenses and lease
Intangible Assets
Amortizing intangible assets, Cost	111,219		111,818
Accumulated amortization	(12,990)		(12,459)
Amortizing intangible assets, Net	98,229		99,359
Customer relationships
Intangible Assets
Amortizing intangible assets, Cost	84,871		84,977
Accumulated amortization	(21,530)		(20,168)
Amortizing intangible assets, Net	63,341		64,809
Technology - formulae and processes
Intangible Assets
Amortizing intangible assets, Cost	7,055		7,250
Accumulated amortization	(1,643)		(1,630)
Amortizing intangible assets, Net	5,412		5,620
Customer backlog
Intangible Assets
Amortizing intangible assets, Cost	3,652		3,652
Accumulated amortization	(1,383)		(1,291)
Amortizing intangible assets, Net	2,269		2,361
Tradename
Intangible Assets
Amortizing intangible assets, Cost	4,318		4,318
Accumulated amortization	(4,318)		(4,318)
Developed software
Intangible Assets
Amortizing intangible assets, Cost	2,918		2,926
Accumulated amortization	(1,385)		(1,319)
Amortizing intangible assets, Net	1,533		1,607
Non-compete agreements
Intangible Assets
Amortizing intangible assets, Cost	748		748
Accumulated amortization	(748)		(748)
Internet domain and website
Intangible Assets
Amortizing intangible assets, Cost	540		540
Accumulated amortization	(108)		(100)
Amortizing intangible assets, Net	432		440
Database
Intangible Assets
Amortizing intangible assets, Cost	391		393
Accumulated amortization	(157)		(153)
Amortizing intangible assets, Net	$ 234		$ 240

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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