LONG-TERM DEBT - Summary of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020	Jun. 22, 2020	Feb. 19, 2020
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 1,074,915	$ 1,064,422
less: Current portion, Outstanding Balance	(14,913)	(9,922)
Long-term debt, Outstanding Balance, Non-current	1,060,002	1,054,500
Original Issuer Premium	339	363
less: Current portion, Original Issuer Premium	0	0
Long-term debt, Original Issuer Premium, Non-current	339	363
Capitalized Fees & Expenses	(16,482)	(17,821)
Long-term debt, Balance Sheet	1,058,772	1,046,964
less: Current portion, Balance Sheet	(14,913)	(9,922)
Long-term debt, Balance Sheet, Non-current	1,043,859	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	339	363
Capitalized Fees & Expenses	(14,329)	(15,376)
Long-term debt, Balance Sheet	$ 986,010	$ 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	$ 20,622	$ 12,858
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(1,963)	(2,209)
Long-term debt, Balance Sheet	18,659	10,649
Finance lease - real estate
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	15,924	17,218
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(17)	(30)
Long-term debt, Balance Sheet	$ 15,907	$ 17,188
Coupon Interest Rate	5.60%	5.60%
Non US lines of credit
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	$ 4,405	$ 0
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(24)	(30)
Long-term debt, Balance Sheet	4,381	(30)
Non US term loans
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	29,870	31,086
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(133)	(160)
Long-term debt, Balance Sheet	29,737	30,926
Other long term debt
Debt Instrument [Line Items]
Long-term debt, Outstanding Balance	4,094	3,260
Original Issuer Premium	0	0
Capitalized Fees & Expenses	(16)	(16)
Long-term debt, Balance Sheet	$ 4,078	$ 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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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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