Fair value measurement - Summary of Company's Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Assets
Short term investments, fair value	$ 50,083	$ 49,943
Total financial assets	249,941	295,597
Corporate bonds
Assets
Short term investments, fair value		14,889
U.S. government treasury bills
Assets
Short term investments, fair value	50,083	35,054
Money market funds
Assets
Money market funds	199,858	245,654
Level 1
Assets
Total financial assets	249,941	280,708
Level 1 | Corporate bonds
Assets
Short term investments, fair value		0
Level 1 | U.S. government treasury bills
Assets
Short term investments, fair value	50,083	35,054
Level 1 | Money market funds
Assets
Money market funds	199,858	245,654
Level 2
Assets
Total financial assets	0	14,889
Level 2 | Corporate bonds
Assets
Short term investments, fair value		14,889
Level 2 | U.S. government treasury bills
Assets
Short term investments, fair value	0	0
Level 2 | Money market funds
Assets
Money market funds	0	0
Level 3
Assets
Total financial assets	0	0
Level 3 | Corporate bonds
Assets
Short term investments, fair value		0
Level 3 | U.S. government treasury bills
Assets
Short term investments, fair value	0	0
Level 3 | Money market funds
Assets
Money market funds	$ 0	$ 0