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Stock-Based Compensation - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Common stock reserved for issuance stock awards (in shares) 6,025,328  
Stock-based compensation expense $ 10.7 $ 7.6
Stock-based compensation expense, net of tax $ 8.9 $ 6.5