Summary of significant accounting policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2024 USD ($) segment	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jan. 01, 2024 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tangible asset impairment charges	$ 9,066	$ 6,785	$ 0
Credit period granted to customers	30 days
Accounts receivable, allowance for credit loss	$ 700	200
Number of reportable segments | segment	1
Number of operating segments | segment	1
Advertising and promotion expenses	$ 5,200	2,900	$ 2,400
Accumulated deficit	(1,241,908)	$ (1,033,034)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit				$ (100)
Revision of Prior Period, Reclassification, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tangible asset impairment charges	$ 6,800