Leases - Summary of Operating Leases (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2020 USD ($) numberOfOperatingLeases
Lessee, Lease, Description [Line Items]
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesAndOtherLiabilities
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssets
Right-of-use asset	$ 22,709
Lease liability	$ 24,114
Weighted average remaining lease term	6 years 3 months 14 days
Weighted average discount rate	1.83%
Operating lease expense	$ 7,100
Number of operating leases that had not yet commenced | numberOfOperatingLeases	0
Minimum
Lessee, Lease, Description [Line Items]
Operating lease term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Operating lease term	15 years