GOODWILL AND INTANGIBLE ASSETS, NET - Intangible assets, net (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Intangible Assets, Net
Gross carrying amount	$ 262,712		$ 262,712		$ 264,957
Accumulated amortization	(208,715)		(208,715)		(203,911)
Net book value	53,997		53,997		61,046
Amortization expense for definite lived intangible assets	2,840	$ 3,544	7,049	$ 12,191
2020	13,700		13,700
2021	10,500		10,500
2022	5,100		5,100
2023	5,100		5,100
2024	5,100		5,100
Customer related intangible assets
Intangible Assets, Net
Gross carrying amount	214,973		214,973		214,973
Accumulated amortization	(181,367)		(181,367)		(176,043)
Net book value	33,606		33,606		38,930
Operating agreement
Intangible Assets, Net
Gross carrying amount	35,000		35,000		35,000
Accumulated amortization	(18,251)		(18,251)		(17,376)
Net book value	16,749		16,749		17,624
Trademarks and trade names
Intangible Assets, Net
Gross carrying amount	9,709		9,709		9,709
Accumulated amortization	(6,099)		(6,099)		(5,893)
Net book value	3,610		3,610		3,816
Non-compete agreements
Intangible Assets, Net
Gross carrying amount	1,230		1,230		1,230
Accumulated amortization	(1,228)		(1,228)		(1,215)
Net book value	2		2		15
Intellectual property
Intangible Assets, Net
Gross carrying amount	0		0		300
Accumulated amortization	0		0		(175)
Net book value	0		0		125
Other intangible assets
Intangible Assets, Net
Gross carrying amount	1,800		1,800		3,745
Accumulated amortization	(1,770)		(1,770)		(3,209)
Net book value	$ 30		$ 30		$ 536
Weighted Average | Customer related intangible assets
Intangible Assets, Net
Weighted average estimated useful life (in years)			9 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)			16 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)			0 years
Weighted Average | Other intangible assets
Intangible Assets, Net
Weighted average estimated useful life (in years)			5 years