Income Taxes - Gross Unrecognized Tax Benefits (Details) - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Sep. 30, 2022 |
Sep. 30, 2021 |
Sep. 30, 2020 |
|
| Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] | |||
| Beginning balance of unrecognized tax benefits | $ 0 | $ 0 | $ 0 |
| Increase for prior period tax positions | 3,481,000 | 0 | 0 |
| Ending balance of unrecognized tax benefits | $ 3,481,000 | $ 0 | $ 0 |