Income taxes - Schedule of unrecognized tax benefits roll forward (Details) - USD ($) $ in Thousands |
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] | |||
| Balance beginning of the year | $ 7,437 | $ 4,700 | $ 3,291 |
| Increases related to tax positions during the year | 5,082 | 2,737 | 1,409 |
| Increases related to tax positions taken in the prior year | 864 | ||
| Balance end of the year | $ 13,383 | $ 7,437 | $ 4,700 |