GOODWILL AND INTANGIBLE ASSETS, NET - Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Intangible Assets, Net
Gross carrying amount	$ 264,957	$ 324,796
Accumulated amortization	(203,911)	(233,143)
Net book value	61,046	91,653
Amortization expense for definite lived intangible assets	19,021	28,412	$ 35,367
Amortization expense, 2020	13,500
Amortization expense, 2021	10,600
Amortization expense, 2022	5,200
Amortization expense, 2023	5,100
Amortization expense, 2024	5,100
Customer related intangible assets
Intangible Assets, Net
Gross carrying amount	214,973	273,172
Accumulated amortization	(176,043)	(207,639)
Net book value	$ 38,930	65,533
Customer related intangible assets | Weighted average
Intangible Assets, Net
Estimated useful life	9 years
Operating agreement
Intangible Assets, Net
Gross carrying amount	$ 35,000	35,000
Accumulated amortization	(17,376)	(15,632)
Net book value	$ 17,624	19,368
Operating agreement | Weighted average
Intangible Assets, Net
Estimated useful life	20 years
Trademarks and trade names
Intangible Assets, Net
Gross carrying amount	$ 9,709	11,349
Accumulated amortization	(5,893)	(6,244)
Net book value	$ 3,816	5,105
Trademarks and trade names | Weighted average
Intangible Assets, Net
Estimated useful life	16 years
Non-compete agreements
Intangible Assets, Net
Gross carrying amount	$ 1,230	1,230
Accumulated amortization	(1,215)	(1,026)
Net book value	$ 15	204
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	(175)	(145)
Net book value	$ 125	155
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	(3,209)	(2,457)
Net book value	$ 536	$ 1,288
Other intangible assets | Weighted average
Intangible Assets, Net
Estimated useful life	5 years