Income Taxes - Unrecognized Tax Benefits - General Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Uncertainties [Abstract]
Unrecognized tax benefits	$ 2,006	$ 16,722	$ 16,860	$ 2,655
Unrecognized tax benefits, tax benefits that if recognized would impact the effective tax rate	2,006
Unrecognized tax benefits, tax benefits that if recognized would impact the effective tax rate, long-term liability held for sale	2,300
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense [Abstract]
Interest related to unrecognized benefits	$ 1,100	$ 1,100	$ 1,100