Income taxes - Schedule of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 226,959	$ 209,338
Research and development credit carryforwards	59,578	49,454
Capitalized research and development	43,232	30,599
Operating lease liability	21,377	22,921
Stock-based compensation	13,384	13,858
Other	14,310	8,107
Gross deferred tax assets	378,840	334,277
Less: Valuation allowance	(360,594)	(302,381)
Net deferred tax assets	18,246	31,896
Fixed assets	0	(1,363)
Operating lease right-of-use asset	(14,786)	(17,417)
Intangible assets	(3,460)	(13,116)
Gross deferred tax liabilities	(18,246)	(31,896)
Total net deferred tax asset	$ 0	$ 0