Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Lease right-of-use assets	$ 29,302	$ 30,999
Current portion of operating lease liability	7,646	6,513
Lease liabilities - non-current	23,089	25,967
Operating lease liability	$ 30,735	$ 32,480
Weighted-average remaining lease term (in years)	6 years	7 years
Weighted-average discount rate	2.55%	3.06%
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current	Other Liabilities, Current
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other long-term liabilities	Other long-term liabilities
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]