The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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GOODWILL AND INTANGIBLE ASSETS, NET - Intangible Assets, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Intangible Assets, Net
Gross carrying amount	$ 259,016		$ 259,016		$ 262,712
Accumulated amortization	(220,873)		(220,873)		(216,386)
Net book value	38,143		38,143		46,326
Amortization expense for definite lived intangible assets	2,673	$ 4,295	8,183	$ 11,344
2021	9,500		9,500
2022	5,100		5,100
2023	5,100		5,100
2024	5,100		5,100
2025	5,100		5,100
Customer related intangible assets
Intangible Assets, Net
Gross carrying amount	214,307		214,307		214,973
Accumulated amortization	(193,844)		(193,844)		(187,923)
Net book value	20,463		20,463		27,050
Operating agreement
Intangible Assets, Net
Gross carrying amount	35,000		35,000		35,000
Accumulated amortization	(20,417)		(20,417)		(19,126)
Net book value	14,583		14,583		15,874
Trademarks and trade names
Intangible Assets, Net
Gross carrying amount	9,709		9,709		9,709
Accumulated amortization	(6,612)		(6,612)		(6,307)
Net book value	3,097		3,097		3,402
Non-compete agreements
Intangible Assets, Net
Gross carrying amount	0		0		1,230
Accumulated amortization	0		0		(1,230)
Net book value	0		0		0
Other intangible assets
Intangible Assets, Net
Gross carrying amount	0		0		1,800
Accumulated amortization	0		0		(1,800)
Net book value	$ 0		$ 0		$ 0
Weighted Average \| Customer related intangible assets
Intangible Assets, Net
Weighted average estimated useful life (in years)			9 months
Weighted Average \| Operating agreement
Intangible Assets, Net
Weighted average estimated useful life (in years)			20 months
Weighted Average \| Trademarks and trade names
Intangible Assets, Net
Weighted average estimated useful life (in years)			16 months
Weighted Average \| Non-compete agreements
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)			0 years