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Income Taxes -Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Mar. 31, 2021
Mar. 31, 2020
Sep. 30, 2020
Income Tax Disclosure [Abstract]          
Effective income tax rate 25.20% 6.70% 13.70% (8.50%)  
Unrecognized tax benefits, uncertain tax positions $ 10.2   $ 10.2   $ 8.0
Unrecognized tax benefits, accrued interest $ 0.5   $ 0.5   $ 0.4