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Stock-Based Compensation - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Mar. 31, 2021
Mar. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Common stock reserved for issuance stock awards (in shares) 4,664,003   4,664,003  
Stock-based compensation expense $ 9.9 $ 7.2 $ 17.3 $ 17.9
Stock-based compensation expense, net of tax $ 8.3 $ 6.4 $ 14.7 $ 15.7