GOODWILL AND INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Intangible Assets
Amortizing intangible assets, Cost	$ 215,494		$ 215,494		$ 214,373
Accumulated amortization	(37,324)		(37,324)		(31,788)
Amortizing intangible assets, Net	178,170		178,170		182,585
Total intangible assets, cost	267,291		267,291		266,144
Total intangible assets, net	229,967		229,967		234,356
Amortization of intangibles	2,615	$ 2,646	5,286	$ 5,256
Permits and licenses
Intangible Assets
Nonamortizing intangible assets	51,666		51,666		51,645
Tradename
Intangible Assets
Nonamortizing intangible assets	131		131		126
Permits, licenses and lease
Intangible Assets
Amortizing intangible assets, Cost	111,078		111,078		110,341
Accumulated amortization	(10,966)		(10,966)		(9,462)
Amortizing intangible assets, Net	100,112		100,112		100,879
Customer relationships
Intangible Assets
Amortizing intangible assets, Cost	84,843		84,843		84,711
Accumulated amortization	(17,340)		(17,340)		(14,519)
Amortizing intangible assets, Net	67,503		67,503		70,192
Technology - Formulae and processes
Intangible Assets
Amortizing intangible assets, Cost	7,009		7,009		6,770
Accumulated amortization	(1,464)		(1,464)		(1,305)
Amortizing intangible assets, Net	5,545		5,545		5,465
Customer backlog
Intangible Assets
Amortizing intangible assets, Cost	3,652		3,652		3,652
Accumulated amortization	(1,109)		(1,109)		(926)
Amortizing intangible assets, Net	2,543		2,543		2,726
Tradename
Intangible Assets
Amortizing intangible assets, Cost	4,318		4,318		4,318
Accumulated amortization	(4,318)		(4,318)		(3,650)
Amortizing intangible assets, Net					668
Developed software
Intangible Assets
Amortizing intangible assets, Cost	2,917		2,917		2,907
Accumulated amortization	(1,157)		(1,157)		(994)
Amortizing intangible assets, Net	1,760		1,760		1,913
Non-compete agreements
Intangible Assets
Amortizing intangible assets, Cost	747		747		747
Accumulated amortization	(747)		(747)		(742)
Amortizing intangible assets, Net					5
Internet domain and website
Intangible Assets
Amortizing intangible assets, Cost	540		540		540
Accumulated amortization	(86)		(86)		(72)
Amortizing intangible assets, Net	454		454		468
Database
Intangible Assets
Amortizing intangible assets, Cost	390		390		387
Accumulated amortization	(137)		(137)		(118)
Amortizing intangible assets, Net	$ 253		$ 253		$ 269