Income Taxes - Reconciliation of Income Tax Provision at Federal Statutory Income Tax Rate and Effective Tax Rate (Detail)	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)	(21.00%)
State taxes, net of federal benefit	(2.90%)	(2.30%)	(2.80%)
Change in valuation allowance	30.80%	9.90%	52.10%
Federal research and development tax credit	(4.60%)	(5.30%)	(13.30%)
Share-based compensation	(0.80%)	2.40%	2.80%
State research and development tax credit	(1.50%)	(0.80%)	(2.60%)
Change in deferred tax rate	(0.10%)	(9.50%)	(10.20%)
Other	(0.30%)	(0.00%)	(1.70%)
Effective income tax rate	(0.40%)	(26.60%)	3.30%