LONG-TERM DEBT - Summary of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Sep. 30, 2022	Jun. 22, 2020
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 1,565,319	$ 1,595,560
less: Current portion, Outstanding Balance	(10,043)	(12,653)
Long-term debt, Outstanding Balance, Non-current	1,555,276	1,582,907
Original Issuer Premium/(Discount)	(786)	(878)
Capitalized Fees & Expenses	(18,075)	(21,031)
Long-term debt, Balance Sheet	1,546,458	1,573,651
less: Current portion, Balance Sheet	(10,043)	(12,653)
Long-term debt, Balance Sheet, Non-current	1,536,415	1,560,998
Senior notes due 2028
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	974,775	974,775
Original Issuer Premium/(Discount)	230	266
Capitalized Fees & Expenses	(9,425)	(10,939)
Long-term debt, Balance Sheet	$ 965,580	$ 964,102
Coupon Interest Rate	5.75%	5.75%	5.75%
Term Loan B due 2029
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 490,000	$ 496,000
Original Issuer Premium/(Discount)	(1,016)	(1,144)
Capitalized Fees & Expenses	(7,769)	(8,823)
Long-term debt, Balance Sheet	481,215	486,033
Revolver due 2025
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	86,705	97,328
Original Issuer Premium/(Discount)	0	0
Capitalized Fees & Expenses	(859)	(1,227)
Long-term debt, Balance Sheet	85,846	96,101
Finance lease - real estate
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	12,056	13,091
Original Issuer Premium/(Discount)	0	0
Capitalized Fees & Expenses	0	0
Long-term debt, Balance Sheet	12,056	13,091
Non US lines of credit
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	0	0
Original Issuer Premium/(Discount)	0	0
Capitalized Fees & Expenses	(7)	(2)
Long-term debt, Balance Sheet	(7)	(2)
Non US term loans
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	0	12,090
Original Issuer Premium/(Discount)	0	0
Capitalized Fees & Expenses	0	(27)
Long-term debt, Balance Sheet	0	12,063
Other long term debt
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	1,783	2,276
Original Issuer Premium/(Discount)	0	0
Capitalized Fees & Expenses	(15)	(13)
Long-term debt, Balance Sheet	$ 1,768	$ 2,263