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.

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GOODWILL AND INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Intangible Assets
Amortizing intangible assets, Cost	$ 214,959		$ 214,959		$ 216,622
Accumulated amortization	(46,359)		(46,359)		(42,186)
Amortizing intangible assets, Net	168,600		168,600		174,436
Total intangible assets, cost	263,298		263,298		264,998
Total intangible assets, net	216,939		216,939		222,812
Amortization of intangible assets	2,296	$ 2,615	4,598	$ 5,286
Permits and licenses
Intangible Assets
Nonamortizing intangible assets	48,210		48,210		48,241
Tradename
Intangible Assets
Nonamortizing intangible assets	129		129		135
Permits, licenses and lease
Intangible Assets
Amortizing intangible assets, Cost	110,726		110,726		111,818
Accumulated amortization	(13,540)		(13,540)		(12,459)
Amortizing intangible assets, Net	97,186		97,186		99,359
Customer relationships
Intangible Assets
Amortizing intangible assets, Cost	84,780		84,780		84,977
Accumulated amortization	(22,892)		(22,892)		(20,168)
Amortizing intangible assets, Net	61,888		61,888		64,809
Technology - formulae and processes
Intangible Assets
Amortizing intangible assets, Cost	6,895		6,895		7,250
Accumulated amortization	(1,661)		(1,661)		(1,630)
Amortizing intangible assets, Net	5,234		5,234		5,620
Customer backlog
Intangible Assets
Amortizing intangible assets, Cost	3,652		3,652		3,652
Accumulated amortization	(1,474)		(1,474)		(1,291)
Amortizing intangible assets, Net	2,178		2,178		2,361
Tradename
Intangible Assets
Amortizing intangible assets, Cost	4,318		4,318		4,318
Accumulated amortization	(4,318)		(4,318)		(4,318)
Developed software
Intangible Assets
Amortizing intangible assets, Cost	2,912		2,912		2,926
Accumulated amortization	(1,452)		(1,452)		(1,319)
Amortizing intangible assets, Net	1,460		1,460		1,607
Non-compete agreements
Intangible Assets
Amortizing intangible assets, Cost	747		747		748
Accumulated amortization	(747)		(747)		(748)
Internet domain and website
Intangible Assets
Amortizing intangible assets, Cost	540		540		540
Accumulated amortization	(115)		(115)		(100)
Amortizing intangible assets, Net	425		425		440
Database
Intangible Assets
Amortizing intangible assets, Cost	389		389		393
Accumulated amortization	(160)		(160)		(153)
Amortizing intangible assets, Net	$ 229		$ 229		$ 240