INCOME TAXES - Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Price concessions	$ 6,907	$ 12,302
Compensation and benefits	4,058	3,672
Interest limitation carryforward	39,094	38,623
Operating lease liability	22,644	19,462
Net operating losses	155,922	147,749
Other	8,682	5,506
Deferred tax assets before valuation allowance	237,307	227,314
Valuation allowance	(112,085)	(109,531)	$ (1,373)	$ (1,263)
Deferred tax assets net of valuation allowance	125,222	117,783
Deferred tax liabilities:
Accelerated depreciation	(12,593)	(10,376)
Operating lease right-of-use asset	(17,186)	(15,442)
Intangible assets	(67,127)	(71,204)
Goodwill	(28,976)	(20,250)
Other	(2,679)	(2,654)
Deferred tax liabilities	(128,561)	(119,926)
Net deferred tax liabilities	$ (3,339)	$ (2,143)