Stock-Based Compensation - Assumptions Used to Value Stock Options (Detail) - $ / shares	9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Risk-free interest rate, minimum	0.40%	0.40%
Risk-free interest rate, maximum	1.10%	1.80%
Volatility, minimum	86.20%	90.50%
Volatility, maximum	90.40%	91.90%
Expected life (in years)	6 years 3 months	6 years 3 months
Weighted average grant date fair value per share of options granted	$ 48.64	$ 38.12