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Fair Value Measurements - Fair Value of Debt (Details) - USD ($) $ in Millions | Mar. 31, 2026 | Sep. 30, 2025
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Unamortized discounts and issuance costs | $ (19.3) | $ (6.6)
Level 2 | Fair value | Senior Notes | 2031 Notes |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 485.6 | 491.0
Level 2 | Carrying Value | Senior Notes | 2031 Notes |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 531.2 | 531.0
Unamortized discounts and issuance costs | $ (3.8) | $ (4.0)

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