Fair Value Measurement - Additional Information (Details) - EUR (€) |
12 Months Ended | |
|---|---|---|
Sep. 30, 2025 |
Sep. 30, 2024 |
|
| Disclosure of fair value measurement [abstract] | ||
| Transfers out of level 1 into level 2 of fair value hierarchy, liabilities held at end of reporting period | € 0 | € 0 |
| Transfers out of level 2 into level 1 of fair value hierarchy, liabilities held at end of reporting period | 0 | 0 |
| Tax receivable agreement liability | 302,400,000 | 344,590,000 |
| Increase (decrease) in fair value recorded through Finance cost, net | € (9,800,000) | € 3,800,000 |
| Percentage of yield volatility | 35.00% | 40.00% |
| Percentage of credit spread | 1.24% | 1.13% |
| Percentge of increase decrease in yield volatility | 2.50% | 2.50% |
| Increase/decrease in fair value | € 900,000 | € 1,200,000 |
| Cash flow hedge reserve of a cumulative loss | € 300,000 | |