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Stock-Based Compensation Plans - Additional Information (Detail) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock option compensation $ 2.9 $ 2.8
Stock Options Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number exercisable and fully vested 87,136  
Fully vested stock options with performance conditions attached 65,176  
Stock option compensation $ 2.9 2.8
Total intrinsic value exercised 1.7 4.6
Total compensation cost related to non-vested stock options not yet recognized $ 10.5  
Expected compensation cost recognized over the weighted-average period 2 years 1 month 24 days  
Stock Equivalent Units [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Fully vested stock options with performance conditions attached 27,935  
Total intrinsic value exercised $ 1.3 6.1
Expected compensation cost recognized over the weighted-average period 2 years 29 days  
Number of exercisable SEUs 32,132  
Compensation cost $ 2.9 $ 3.0