Organization and description of business (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 1,241,908	$ 1,033,034
Net loss attributable to common stockholders	208,726	204,618	$ 217,863
Cash and cash equivalents	226,316	286,470
Short-term investments	$ 50,083	$ 49,943