LONG-TERM DEBT - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023	Sep. 30, 2020
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 1,603,554	$ 1,489,812
less: Current portion, Outstanding Balance	(8,152)	(9,625)
Long-term debt, Outstanding Balance	1,595,402	1,480,187
Original Issuer Premium/(Discount)	(643)	(704)
Capitalized Fees & Expenses	(17,551)	(19,579)
Long-term debt, Balance Sheet	1,585,360	1,469,529
less: Current portion, Balance Sheet	(8,152)	(9,625)
Long-term debt, Balance Sheet	1,577,208	1,459,904
Senior notes due 2028
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	974,775	974,775
Original Issuer Premium/(Discount)	194	218
Capitalized Fees & Expenses	(7,910)	(8,920)
Long-term debt, Balance Sheet	$ 967,059	$ 966,073
Coupon Interest Rate	5.75%	5.75%	5.75%
Term Loan B due 2029
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 459,000	$ 463,000
Original Issuer Premium/(Discount)	(837)	(922)
Capitalized Fees & Expenses	(6,378)	(7,039)
Long-term debt, Balance Sheet	451,785	455,039
Revolver due 2028
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	169,500	50,445
Original Issuer Premium/(Discount)	0	0
Capitalized Fees & Expenses	(3,232)	(3,606)
Long-term debt, Balance Sheet	166,268	46,839
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	(9)	(3)
Long-term debt, Balance Sheet	(9)	(3)
Other long term debt
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	279	1,592
Original Issuer Premium/(Discount)	0	0
Capitalized Fees & Expenses	(22)	(11)
Long-term debt, Balance Sheet	$ 257	$ 1,581