GOODWILL AND INTANGIBLE ASSETS, NET - Intangible Assets, Net (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets, Net
Gross carrying amount	$ 324,796	$ 333,787
Accumulated amortization	(233,143)	(213,722)
Net book value	91,653	120,065
Amortization expense for definite lived intangible assets	28,412	35,367	$ 47,576
Amortization expense, 2019	20,400
Amortization expense, 2020	17,700
Amortization expense, 2021	11,600
Amortization expense, 2022	7,300
Amortization expense, 2023	6,300
Trademarks and trade names
Intangible Assets, Net
Gross carrying amount	11,349	15,354
Accumulated amortization	(6,244)	(8,881)
Net book value	$ 5,105	6,473
Trademarks and trade names | Weighted average
Intangible Assets, Net
Estimated useful life	15 years
Customer related intangible assets
Intangible Assets, Net
Gross carrying amount	$ 273,172	277,828
Accumulated amortization	(207,639)	(188,258)
Net book value	$ 65,533	89,570
Customer related intangible assets | Weighted average
Intangible Assets, Net
Estimated useful life	10 years
Operating agreement
Intangible Assets, Net
Gross carrying amount	$ 35,000	35,000
Accumulated amortization	(15,632)	(13,865)
Net book value	$ 19,368	21,135
Operating agreement | Weighted average
Intangible Assets, Net
Estimated useful life	20 years
Non-compete agreements
Intangible Assets, Net
Gross carrying amount	$ 1,230	1,560
Accumulated amortization	(1,026)	(897)
Net book value	$ 204	663
Non-compete agreements | Weighted average
Intangible Assets, Net
Estimated useful life	4 years
Intellectual property
Intangible Assets, Net
Gross carrying amount	$ 300	300
Accumulated amortization	(145)	(115)
Net book value	$ 155	185
Intellectual property | Weighted average
Intangible Assets, Net
Estimated useful life	10 years
Other intangible assets
Intangible Assets, Net
Gross carrying amount	$ 3,745	3,745
Accumulated amortization	(2,457)	(1,706)
Net book value	$ 1,288	$ 2,039
Other intangible assets | Weighted average
Intangible Assets, Net
Estimated useful life	5 years