Income taxes - Components of pre-tax loss (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
US	$ (209,545)	$ (205,389)	$ (231,659)
Foreign	1,379	1,923	3,385
Loss before income taxes	$ (208,166)	$ (203,466)	$ (228,274)

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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+ Details