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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Intangible Assets
Amortizing intangible assets, Cost	$ 280,958		$ 280,958		$ 279,751
Accumulated amortization	(52,637)		(52,637)		(46,601)
Amortizing intangible assets, Net	228,321		228,321		233,150
Total intangible assets, cost	327,503		327,503		326,267
Total intangible assets, net	274,866		274,866		279,666
Amortization of intangible assets	2,863	$ 2,296	5,674	$ 4,598
Permits and licenses
Intangible Assets
Non-amortizing intangible assets	46,415		46,415		46,391
Tradename
Intangible Assets
Non-amortizing intangible assets	130		130		125
Permits, licenses and lease
Intangible Assets
Amortizing intangible assets, Cost	165,600		165,600		164,840
Accumulated amortization	(16,817)		(16,817)		(14,804)
Amortizing intangible assets, Net	148,783		148,783		150,036
Customer relationships
Intangible Assets
Amortizing intangible assets, Cost	99,396		99,396		99,241
Accumulated amortization	(28,948)		(28,948)		(25,676)
Amortizing intangible assets, Net	70,448		70,448		73,565
Technology - formulae and processes
Intangible Assets
Amortizing intangible assets, Cost	6,951		6,951		6,672
Accumulated amortization	(1,897)		(1,897)		(1,714)
Amortizing intangible assets, Net	5,054		5,054		4,958
Customer backlog
Intangible Assets
Amortizing intangible assets, Cost	3,652		3,652		3,652
Accumulated amortization	(1,839)		(1,839)		(1,656)
Amortizing intangible assets, Net	1,813		1,813		1,996
Developed software
Intangible Assets
Amortizing intangible assets, Cost	2,894		2,894		2,884
Accumulated amortization	(1,737)		(1,737)		(1,581)
Amortizing intangible assets, Net	1,157		1,157		1,303
Non-compete agreements
Intangible Assets
Amortizing intangible assets, Cost	1,542		1,542		1,542
Accumulated amortization	(1,076)		(1,076)		(875)
Amortizing intangible assets, Net	466		466		667
Internet domain and website
Intangible Assets
Amortizing intangible assets, Cost	536		536		536
Accumulated amortization	(142)		(142)		(128)
Amortizing intangible assets, Net	394		394		408
Database
Intangible Assets
Amortizing intangible assets, Cost	387		387		384
Accumulated amortization	(181)		(181)		(167)
Amortizing intangible assets, Net	$ 206		$ 206		$ 217