Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Accounting Policies [Abstract]
Foreign currency translation adjustments	$ (25,932)	$ (28,275)
Net unrealized (losses) gains on post-retirement benefits	(11)	528
Net unrealized gains (losses) on available-for-sale securities	31	(219)
Accumulated other comprehensive loss	$ (25,912)	$ (27,966)