Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 232,380	$ 226,959
Research and development credit carryforwards	67,626	59,578
Capitalized research and development	54,438	43,232
Operating lease liability	18,657	21,377
Stock-based compensation	13,359	13,384
Other	12,333	14,310
Gross deferred tax assets	398,793	378,840
Less: Valuation allowance	(383,378)	(360,594)
Net deferred tax assets	15,415	18,246
Operating lease right-of-use asset	(12,174)	(14,786)
Intangible assets	(3,241)	(3,460)
Gross deferred tax liabilities	(15,415)	(18,246)
Total net deferred tax asset	$ 0	$ 0