Stock-based compensation expense - Valuation Assumptions (Detail) |
12 Months Ended | ||
---|---|---|---|
Sep. 30, 2022 |
Sep. 30, 2021 |
Sep. 30, 2020 |
|
Option | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Expected term (years) | 6 years | ||
Expected volatility | 70.70% | ||
Risk-free interest rate | 1.40% | ||
Dividend yield | 0.00% | ||
Performance Stock Options | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Expected term (years) | 5 years 10 months 24 days | 6 years 1 month 6 days | 6 years 2 months 12 days |
Expected volatility | 70.90% | 64.40% | 62.10% |
Risk-free interest rate | 2.80% | 1.00% | 1.30% |
Dividend yield | 0.00% | 0.00% | 0.00% |