STOCK-BASED COMPENSATION - Narrative (Details) $ / shares in Units, $ in Millions	12 Months Ended
Sep. 30, 2021 USD ($) tranche component $ / shares shares	Sep. 30, 2020 shares
2016 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	0	0
Stock options outstanding (in shares)	2,700,000
Exercisable (in shares)	2,500,000
Stock options outstanding (in dollars per share) \| $ / shares	$ 63.34
Exercisable at the end of the period (in dollars per share) \| $ / shares	$ 63.57
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period over which awards expire	10 years
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years	4 years
Unrecognized compensation cost related to unvested awards \| $	$ 28.0
Weighted-average compensation cost recognition period	2 years
Restricted Stock \| 2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	700,982
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Unrecognized compensation cost related to unvested awards \| $	$ 9.5
Weighted-average compensation cost recognition period	1 year 10 months 24 days
Number of components included in award units \| component	2
Performance Share Units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested	0.00%
Performance Share Units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested	200.00%
Performance Share Units \| 2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	312,600
First Component of Performance Share Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance cycle period of each tranche	3 years
Second Component of Performance Share Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period over which awards expire	3 years
Performance cycle period of each tranche	1 year
Number of tranches in component \| tranche	3

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Represents the performance cycle of each tranche in a share based payment arrangement.

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Number of tranches in a share based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Percentage of vesting of award under share-based payment arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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