Stock-based compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 50,925	$ 30,278	$ 79,033
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	4,012	4,562	4,587
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	11,199	13,944	19,541
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 35,714	$ 11,772	$ 54,905