Income Taxes - Components of Pre-tax Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
US	$ (78,490)	$ (209,545)	$ (205,389)
Foreign	1,539	1,379	1,923
Loss before income taxes	$ (76,951)	$ (208,166)	$ (203,466)