LONG-TERM DEBT - Summary of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020	Jun. 22, 2020	Feb. 19, 2020
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 1,071,121	$ 1,064,422
less: Current portion, Outstanding Balance	(13,024)	(9,922)
Long-term debt, Outstanding Balance, Non-current	1,058,097	1,054,500
Original Issuer Premium	327	363
less: Current portion, Original Issuer Premium	0	0
Long-term debt, Original Issuer Premium, Non-current	327	363
Capitalized Fees & Expenses	(15,812)	(17,821)
Long-term debt, Balance Sheet	1,055,636	1,046,964
less: Current portion, Balance Sheet	(13,024)	(9,922)
Long-term debt, Balance Sheet, Non-current	1,042,612	1,037,042
Senior notes due 2028
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	1,000,000	1,000,000
Original Issuer Premium	327	363
Capitalized Fees & Expenses	(13,811)	(15,376)
Long-term debt, Balance Sheet	$ 986,516	$ 984,987
Coupon Interest Rate	5.75%	5.75%	5.75%	5.75%
Revolver due 2025
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 20,775	$ 12,858
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(1,841)	(2,209)
Long-term debt, Balance Sheet	18,934	10,649
Finance lease - real estate
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	15,265	17,218
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(11)	(30)
Long-term debt, Balance Sheet	$ 15,254	$ 17,188
Coupon Interest Rate	5.60%	5.60%
Non US lines of credit
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 2,871	$ 0
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(21)	(30)
Long-term debt, Balance Sheet	2,850	(30)
Non US term loans
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	28,204	31,086
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(113)	(160)
Long-term debt, Balance Sheet	28,091	30,926
Other long term debt
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	4,006	3,260
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(15)	(16)
Long-term debt, Balance Sheet	$ 3,991	$ 3,244

Amount of long term capitalized fees and expenses.

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The current portion of long term debt gross value.

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The carrying amount of long-term debt, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities).

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after accumulated amortization, of debt premium.

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Amount of debt premium to be amortized within one year or the normal operating cycle, if longer.

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Amount of debt premium to be amortized after one year or the normal operating cycle, if longer.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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