Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 13.5	$ 9.4	$ 5.7
Increase due to current year tax positions	3.1	8.9	5.0
Increase due to prior year tax positions	0.9	2.1	3.7
Decrease due to prior year tax positions	(0.9)	(6.9)	(0.3)
Decrease due to settlements with tax authorities	0.0	0.0	0.0
Decrease due to lapse of statute of limitations	0.0	0.0	(4.7)
Ending balance	16.6	13.5	9.4
Unrecognized tax benefits including interest and penalties that would affect the effective tax rate if recognized	$ 17.7	$ 13.6	$ 7.2

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

No definition available.

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

+ References

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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