v3.23.1
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%