Segment and Geographic Information - Reconciliation of Reportable Segment Assets to Corresponding Consolidated Amounts (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Cash and cash equivalents, restricted cash, and marketable securities	$ 975,358	$ 1,134,256
Deferred tax asset	925	571
Other assets	30,009	29,108
Assets	2,563,497	2,885,720
Operating Segments
Segment Reporting Information [Line Items]
Assets	$ 1,557,205	$ 1,721,785