GOODWILL AND INTANGIBLE ASSETS, NET - Intangible assets, net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Intangible Assets, Net
Gross carrying amount	$ 333,787		$ 333,787
Accumulated amortization	(220,869)		(213,722)
Net book value	112,918		120,065
Amortization expense for definite lived intangible assets	7,147	$ 9,146
2018	26,400
2019	21,800
2020	18,200
2021	11,400
2022	7,300
Customer related intangible assets
Intangible Assets, Net
Gross carrying amount	277,828		277,828
Accumulated amortization	(194,470)		(188,258)
Net book value	83,358		89,570
Operating agreement
Intangible Assets, Net
Gross carrying amount	35,000		35,000
Accumulated amortization	(14,307)		(13,865)
Net book value	20,693		21,135
Trademarks and trade names
Intangible Assets, Net
Gross carrying amount	15,354		15,354
Accumulated amortization	(9,080)		(8,881)
Net book value	6,274		6,473
Non-compete agreements
Intangible Assets, Net
Gross carrying amount	1,560		1,560
Accumulated amortization	(995)		(897)
Net book value	565		663
Intellectual property
Intangible Assets, Net
Gross carrying amount	300		300
Accumulated amortization	(123)		(115)
Net book value	177		185
Other intangible assets
Intangible Assets, Net
Gross carrying amount	3,745		3,745
Accumulated amortization	(1,894)		(1,706)
Net book value	$ 1,851		$ 2,039
Weighted Average | Customer related intangible assets
Intangible Assets, Net
Weighted average estimated useful life (in years)	10 years
Weighted Average | Operating agreement
Intangible Assets, Net
Weighted average estimated useful life (in years)	20 years
Weighted Average | Trademarks and trade names
Intangible Assets, Net
Weighted average estimated useful life (in years)	13 years
Weighted Average | Non-compete agreements
Intangible Assets, Net
Weighted average estimated useful life (in years)	4 years
Weighted Average | Intellectual property
Intangible Assets, Net
Weighted average estimated useful life (in years)	10 years
Weighted Average | Other intangible assets
Intangible Assets, Net
Weighted average estimated useful life (in years)	5 years