Fair Value Measurements - Fair Value of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unamortized discounts and issuance costs	$ (5.3)	$ (5.6)
Level 2 \| Fair value \| Senior Notes \| 2031 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	457.2	478.5
Level 2 \| Carrying Value \| Senior Notes \| 2031 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	530.6	530.4
Unamortized discounts and issuance costs	$ (4.4)	$ (4.6)

Amount of unamortized debt discount (premium) and debt issuance costs.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant