Stock-Based Compensation - Stock-Settled RSUs (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
PHI Stock-Settled Restricted Stock Unit
Share-based Payment Award [Line Items]
RSUs nonvested, beginning balance	59,760
RSUs granted in period	0
RSUs vested in period	(34,151)
RSUs forfeited in period	(4,493)
RSUs nonvested, ending balance	21,116	59,760
RSUs nonvested, weighted average grant date fair value	$ 104.26	$ 99.83	$ 96.64
RSUs granted in period, weighted average grant date fair value	0
RSUs vested in period, weighted average grant date fair value	96.32
RSUs forfeited in period, weighted average grant date fair value	$ 105.70
RSUs vested in period, fair value	$ 3.0	$ 4.5	$ 2.1
BRBR Stock-Settled Restricted Stock Units
Share-based Payment Award [Line Items]
RSUs nonvested, beginning balance	385,232
RSUs granted in period	261,808
RSUs vested in period	(138,122)
RSUs forfeited in period	(41,255)
RSUs nonvested, ending balance	467,663	385,232
RSUs nonvested, weighted average grant date fair value	$ 19.85	$ 19.39
RSUs granted in period, weighted average grant date fair value	20.34
RSUs vested in period, weighted average grant date fair value	19.61
RSUs forfeited in period, weighted average grant date fair value	$ 19.47
RSUs vested in period, fair value	$ 3.0

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-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

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-Publisher FASB
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- Definition

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

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-Publisher FASB
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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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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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- Definition

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

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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.

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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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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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