Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reconciliation of Unrecognized Tax Benefits
Beginning balance	$ 1,435	$ 3,091	$ 6,530
Increase for tax positions taken during a prior period	1,401	0	963
Increase for tax positions taken during the current period	249	0	0
Decrease for tax positions as a result of the lapse of the statute of limitations	0	(1,656)	(4,402)
Ending balance	$ 3,085	$ 1,435	$ 3,091