Stock-based Compensation - Schedule Of Restricted Stock Units Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted-average fair value of RSUs granted	$ 36.98	$ 33.59
Total grant date fair value of RSUs vested	$ 16.3	$ 13.4
Total intrinsic value of RSUs released	$ 14.4	$ 9.1

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

+ References

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 (d)(2)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

Intrinsic value of vested award under share-based payment arrangement. Excludes share and unit options.

+ References

No definition available.

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