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Stock-Based Compensation - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Mar. 31, 2020
Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Common stock reserved for issuance stock awards (in shares) 5,810,640   5,810,640  
Stock-based compensation expense $ 7.2 $ 8.3 $ 17.9 $ 15.9
Stock-based compensation expense, net of tax $ 6.4 $ 6.7 $ 15.7 $ 13.2