Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 2,703	$ 1,854	$ 1,219
Increases related to tax positions taken during the current period	220	240	180
Increases related to tax positions taken during a prior period	97	609	455
Decreases related to expiration of statute of limitations	(545)	0	0
Decreases related to settlement with taxing authorities	(1,223)	0	0
Balance at end of period	$ 1,252	$ 2,703	$ 1,854