INDEBTEDNESS - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2021	Jan. 20, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Oct. 31, 2021
Debt Instrument [Line Items]
Repayment of debt					$ 8,832,000	$ 6,937,000
Cash outflow from financing activities					11,072,000	16,407,000
Proceeds from issuance of debt					355,200,000	0
Debt issuance costs			$ 18,590,000		18,590,000		$ 23,823,000
Loss on extinguishment of debt					12,403,000	8,349,000
Deferred financing costs					2,880,000	$ 0
Senior Notes
Debt Instrument [Line Items]
Loss on extinguishment of debt					12,400,000
Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Legal fees								$ 9,400,000
Credit Agreements Amendment
Debt Instrument [Line Items]
Prepayment penalty			2,400,000		2,400,000
Credit Agreements Amendment | Senior Notes
Debt Instrument [Line Items]
Cash outflow from financing activities					352,000,000
Proceeds from issuance of debt					356,200,000
Legal fees			7,200,000		7,200,000
Debt issuance costs			3,700,000		3,700,000
Accumulated amortization expensed			$ 900,000		900,000
Loss on extinguishment of debt					9,800,000
Deferred financing costs					1,000,000
Payments of financing costs					2,900,000
Payments of debt issuance costs in operating activities					900,000
New Senior Unsecured Notes | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Debt instrument, face amount								500,000,000
First Lien Term Loan | Credit Agreements Amendment | Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount	$ 250,000,000
Debt instrument, basis spread	3.75%						4.25%
Repayment of debt					161,200,000
Debt principal payment					2,900,000
Loss on extinguishment of debt					$ 2,600,000
Effective rate on term loans at end of period			3.83%		3.83%		4.40%
Weighted average interest rate paid on term loans during period			3.84%	4.67%	5.87%	5.29%
First Lien Term Loan | New First Lien Term Loan | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Debt instrument, face amount								$ 600,000,000
Second Lien Term Loan | Credit Agreements Amendment | Senior Notes
Debt Instrument [Line Items]
Repayment of debt					$ 122,900,000
Effective rate on term loans at end of period							8.98%
Weighted average interest rate paid on term loans during period		8.98%		9.51%		10.17%
Second Lien Term Loan | Credit Agreements Amendment | Notes Payable
Debt Instrument [Line Items]
Repayment of debt					$ 245,800,000