DEBT - Total Debt (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Jun. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Long-term debt	$ 1,091,688	$ 959,676
Less: Unamortized debt issuance costs	(15,684)	(17,900)
Total debt, excluding unamortized debt issuance costs	1,076,004	941,776
Less: Current maturities and short-term debt	(163,313)	(13,313)
Total long-term debt excluding current maturities	912,691	928,463
Senior secured term loan facility
Debt Instrument [Line Items]
Long-term debt	941,688	959,676
Term loan facility
Debt Instrument [Line Items]
Total debt, excluding unamortized debt issuance costs	941,688
Term loan facility \| Revolving credit facility \| Credit Agreement
Debt Instrument [Line Items]
Long-term debt	$ 150,000	$ 0
Term loan facility \| Revolving credit facility \| Credit Agreement \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Term loan facility \| Senior secured term loan facility \| Credit Agreement \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%	2.25%

Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
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- Definition

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.

+ References

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- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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