Stock-Based Employee Benefit Plans - Summary of Restricted Stock Unit and Performance Stock Unit Activity (Details) - $ / shares shares in Thousands	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restricted stock units (RSUs)
Shares
Outstanding at September 30, 2019 (in shares)	998
Granted (in shares)	218
Released (in shares)	(434)
Forfeited (in shares)	(61)
Outstanding at September 30, 2020 (in shares)	721	998
Weighted-average Grant-date Fair Value
Outstanding at September 30, 2019 (in dollars per share)	$ 159.99
Granted (in dollars per share)	356.66	$ 206.29	$ 161.85
Released (in dollars per share)	138.04
Forfeited (in dollars per share)	200.38
Outstanding at September 30, 2020 (in dollars per share)	$ 229.10	$ 159.99
Performance stock units (PSUs)
Shares
Outstanding at September 30, 2019 (in shares)	195
Granted (in shares)	53
Released (in shares)	(101)
Forfeited (in shares)	(20)
Outstanding at September 30, 2020 (in shares)	127	195
Weighted-average Grant-date Fair Value
Outstanding at September 30, 2019 (in dollars per share)	$ 163.38
Granted (in dollars per share)	354.18	$ 185.05	157.17
Released (in dollars per share)	152.45
Forfeited (in dollars per share)	175.50
Outstanding at September 30, 2020 (in dollars per share)	$ 248.97	$ 163.38
Market stock units (MSUs)
Shares
Outstanding at September 30, 2019 (in shares)	100
Granted (in shares)	96
Released (in shares)	(123)
Forfeited (in shares)	(10)
Outstanding at September 30, 2020 (in shares)	63	100
Weighted-average Grant-date Fair Value
Outstanding at September 30, 2019 (in dollars per share)	$ 188.63
Granted (in dollars per share)	249.13	$ 169.46	$ 151.78
Released (in dollars per share)	171.42
Forfeited (in dollars per share)	202.48
Outstanding at September 30, 2020 (in dollars per share)	$ 311.91	$ 188.63

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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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

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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).

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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

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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.

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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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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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