STOCK-BASED COMPENSATION - Restricted Stock (Details) - Restricted stock - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Stock based award plan
Unrecognized compensation cost (in dollars)	$ 34.4
Weighted-average period over which unrecognized compensation cost is expected to be recognized	2 years 4 months 24 days
Restricted stock awards activity, shares
Unvested at the beginning of the period (in shares)	659	648	668
Granted (in shares)	626	292	294
Vested (in shares)	(258)	(271)	(256)
Forfeited (in shares)	(26)	(10)	(58)
Unvested at the end of the period (in shares)	1,001	659	648
Restricted stock awards activity, weighted average grant date fair value
Unvested at the beginning of the period (in dollars per share)	$ 70.76	$ 64.24	$ 67.03
Granted (in dollars per share)	59.53	78.69	58.25
Vested (in dollars per share)	70.60	63.81	64.75
Forfeited (in dollars per share)	66.73	68.09	63.65
Unvested at the end of the period (in dollars per share)	$ 63.74	$ 70.76	$ 64.24
Minimum
Stock based award plan
Vesting period	3 years
Maximum
Stock based award plan
Vesting period	6 years

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(3)
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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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-Subparagraph (c)(2)(iii)(1)
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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Name Accounting Standards Codification
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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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-Publisher FASB
-Name Accounting Standards Codification
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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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