Income Taxes - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Taxes [Line Items]
Income tax expense (benefit)	$ 4.6	$ (9.6)	$ 12.8
Unrecognized tax benefits	$ 0.0	$ 0.0
State
Income Taxes [Line Items]
Tax examination	2016
Net operating losses	$ 207.5
Net operating losses, expiration start year	2021
Net operating losses, expiration end year	2041
U.S. federal
Income Taxes [Line Items]
Tax examination	2018
Cares Act
Income Taxes [Line Items]
Income taxes receivable	$ 39.0
Income tax expense (benefit)	$ (10.1)