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Stock-based Compensation - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Feb. 11, 2020
Mar. 31, 2021
Mar. 31, 2020
Mar. 31, 2021
Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based compensation number of additional shares authorized 4,850,000        
Stock-based compensation number of shares authorized   5,302,025   5,302,025  
Restricted Stock Awards [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of shares that will vest       100.00%  
Stock Options [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Non-qualified options granted expiration period       10 years  
Vesting period       3 years  
Allocated stock-based compensation expense   $ 1.2 $ 1.0 $ 2.2 $ 2.1
Unrecognized compensation cost related to unvested stock   6.3   $ 6.3  
Unrecognized compensation cost related to unvested stock, expected weighted-average period of recognition       2 years 1 month 6 days  
Restricted Stock Units (RSUs) [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Allocated stock-based compensation expense   3.0 $ 3.3 $ 5.8 $ 7.0
Unrecognized compensation cost related to unvested stock   $ 16.8   $ 16.8  
Unrecognized compensation cost related to unvested stock, expected weighted-average period of recognition       2 years  
Restricted Stock Units (RSUs) [Member] | Minimum [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of shares that will vest       0.00%  
Restricted Stock Units (RSUs) [Member] | Maximum [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of shares that will vest       200.00%