Fair value measurement - Summary of Company's Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Sep. 30, 2022
Assets
Total financial assets	$ 316,681	$ 378,687
Total financial assets	376,225	443,086
Liabilities
Holdback	7,557	11,692
Total financial liabilities	7,557	11,692
U.S. government treasury bills
Assets
Short term investments, fair value	99,382	111,284
Commercial paper
Assets
Short term investments, fair value		14,997
Money market funds
Assets
Total financial assets	254,196	316,805
Corporate bonds
Assets
Total financial assets	22,647
Level 1
Assets
Total financial assets	353,578	428,089
Liabilities
Holdback	0	0
Total financial liabilities	0	0
Level 1 | U.S. government treasury bills
Assets
Short term investments, fair value	99,382	111,284
Level 1 | Commercial paper
Assets
Short term investments, fair value		0
Level 1 | Money market funds
Assets
Total financial assets	254,196	316,805
Level 1 | Corporate bonds
Assets
Total financial assets	0
Level 2
Assets
Total financial assets	22,647	14,997
Liabilities
Holdback	7,557	9,592
Total financial liabilities	7,557	9,592
Level 2 | U.S. government treasury bills
Assets
Short term investments, fair value	0	0
Level 2 | Commercial paper
Assets
Short term investments, fair value		14,997
Level 2 | Money market funds
Assets
Total financial assets	0	0
Level 2 | Corporate bonds
Assets
Total financial assets	22,647
Level 3
Assets
Total financial assets	0	0
Liabilities
Holdback	0	2,100
Total financial liabilities	0	2,100
Level 3 | U.S. government treasury bills
Assets
Short term investments, fair value	0	0
Level 3 | Commercial paper
Assets
Short term investments, fair value		0
Level 3 | Money market funds
Assets
Total financial assets	0	$ 0
Level 3 | Corporate bonds
Assets
Total financial assets	$ 0