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Income Taxes - Additional Information (Details) - 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]          
Income tax expense $ 9.2 $ 3.3 $ 16.3 $ 8.7  
Effective income tax rate, percent 24.50% 24.10% 24.40% 24.30%  
Valuation allowance, deferred tax asset, amount $ 1.3   $ 1.3   $ 1.5
Deferred Income Tax Liabilities, Net (7.4)   (7.4)   (5.7)
Deferred Income Tax Liabilities, Net of Deferred Income Tax Assets $ (6.1)   $ (6.1)   $ (4.2)