Fair Value Measurement - Summary of Company's Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
Assets
Total financial assets	$ 546,095	$ 442,472
Liabilities
Total financial liabilities	17,098	9,856
Money market funds
Assets
Total financial assets	349,277	430,438
Corporate bonds
Assets
Total financial assets	29,817
Commercial paper
Assets
Total financial assets	54,945
U.S. government treasury bills
Assets
Total financial assets	112,056	12,034
Contingent consideration and indemnity holdback
Liabilities
Total financial liabilities	17,098	9,856
Level 1
Assets
Total financial assets	461,333	442,472
Liabilities
Total financial liabilities	0	0
Level 1 | Money market funds
Assets
Total financial assets	349,277	430,438
Level 1 | Corporate bonds
Assets
Total financial assets	0
Level 1 | Commercial paper
Assets
Total financial assets	0
Level 1 | U.S. government treasury bills
Assets
Total financial assets	112,056	12,034
Level 1 | Contingent consideration and indemnity holdback
Liabilities
Total financial liabilities	0	0
Level 2
Assets
Total financial assets	84,762	0
Liabilities
Total financial liabilities	11,398	9,856
Level 2 | Money market funds
Assets
Total financial assets	0	0
Level 2 | Corporate bonds
Assets
Total financial assets	29,817
Level 2 | Commercial paper
Assets
Total financial assets	54,945
Level 2 | U.S. government treasury bills
Assets
Total financial assets	0	0
Level 2 | Contingent consideration and indemnity holdback
Liabilities
Total financial liabilities	11,398	9,856
Level 3
Assets
Total financial assets	0	0
Liabilities
Total financial liabilities	5,700	0
Level 3 | Money market funds
Assets
Total financial assets	0	0
Level 3 | Corporate bonds
Assets
Total financial assets	0
Level 3 | Commercial paper
Assets
Total financial assets	0
Level 3 | U.S. government treasury bills
Assets
Total financial assets	0	0
Level 3 | Contingent consideration and indemnity holdback
Liabilities
Total financial liabilities	$ 5,700	$ 0