Segment and Geographic Information - Reconciliation of Reportable Segment Assets to Corresponding Consolidated Amounts (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Segment Reporting Information [Line Items]
Cash and cash equivalents, restricted cash, and marketable securities	$ 1,051,395	$ 1,134,256
Deferred tax asset	1,341	571
Other assets	30,030	29,108
Assets	2,824,314	2,885,720
Operating Segments
Segment Reporting Information [Line Items]
Assets	$ 1,741,548	$ 1,721,785