INDEBTEDNESS - Estimated Fair Values of Debt Obligations (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2021	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Principal prepayment		$ (8,832)	$ (6,937)
Second lien notes
Debt Instrument [Line Items]
Total debt instruments	$ 0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, beginning of period	266,438	266,438
Principal prepayment	(245,781)
Change in fair value	(20,657)
Second lien notes fair value, end of period	$ 0
Senior Notes
Debt Instrument [Line Items]
Total debt instruments		1,129,598
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		1,129,598
Senior Notes | First lien term loan
Debt Instrument [Line Items]
Total debt instruments		1,129,598
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		1,129,598
Senior Notes | Second lien notes
Debt Instrument [Line Items]
Total debt instruments		0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		0
Senior Notes | Markets for Identical Item (Level 1)
Debt Instrument [Line Items]
Total debt instruments		0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		0
Senior Notes | Markets for Identical Item (Level 1) | First lien term loan
Debt Instrument [Line Items]
Total debt instruments		0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		0
Senior Notes | Markets for Identical Item (Level 1) | Second lien notes
Debt Instrument [Line Items]
Total debt instruments		0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		0
Senior Notes | Significant Other Observable Inputs (Level 2)
Debt Instrument [Line Items]
Total debt instruments		1,156,919
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		1,156,919
Senior Notes | Significant Other Observable Inputs (Level 2) | First lien term loan
Debt Instrument [Line Items]
Total debt instruments		1,156,919
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		1,156,919
Senior Notes | Significant Other Observable Inputs (Level 2) | Second lien notes
Debt Instrument [Line Items]
Total debt instruments		0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		0
Senior Notes | Significant Unobservable Inputs (Level 3)
Debt Instrument [Line Items]
Total debt instruments		0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		0
Senior Notes | Significant Unobservable Inputs (Level 3) | First lien term loan
Debt Instrument [Line Items]
Total debt instruments		0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		0
Senior Notes | Significant Unobservable Inputs (Level 3) | Second lien notes
Debt Instrument [Line Items]
Total debt instruments		0
Debt Instrument, Changes In Long-Term Debt [Roll Forward]
Second lien notes fair value, end of period		$ 0