Income Taxes - Valuation Allowance (Details) - USD ($) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
Sep. 30, 2024 |
Sep. 30, 2023 |
Sep. 30, 2022 |
Sep. 30, 2021 |
|
| Valuation Allowance [Line Items] | ||||
| Deferred Tax Assets, Valuation Allowance | $ 43.7 | $ 36.4 | $ 35.5 | $ 41.6 |
| Deeside acquisition | ||||
| Valuation Allowance [Line Items] | ||||
| Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount | 20.4 | 0.0 | 0.0 | |
| State carryforwards, including NOLs, Section 163(j) and credits | ||||
| Valuation Allowance [Line Items] | ||||
| Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount | (11.8) | (0.1) | (7.6) | |
| Other foreign-related changes | ||||
| Valuation Allowance [Line Items] | ||||
| Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount | $ (1.3) | $ 1.0 | $ 1.5 | |