Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Gross unrecognized tax benefits at the beginning of the year	$ 1,810	$ 1,607	$ 1,321
Additions from tax positions taken in the current year	268	203	213
Additions from tax positions taken in prior years	36	0	73
Gross unrecognized tax benefits at end of the year	$ 2,114	$ 1,810	$ 1,607