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Stock-Based Compensation Plans - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock option compensation $ 1.6 $ 0.8
Stock Options Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number exercisable and fully vested 45,170  
Fully vested stock options with performance conditions attached 6,592  
Stock option compensation $ 1.6 0.8
Total intrinsic value exercised 2.1 1.9
Total compensation cost related to non-vested stock options not yet recognized $ 14.1  
Expected compensation cost recognized over the weighted-average period 2 years 3 months 25 days  
Stock Equivalent Units [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number exercisable and fully vested 41,312  
Fully vested stock options with performance conditions attached 37,920  
Total intrinsic value exercised $ 6.2 1.6
Expected compensation cost recognized over the weighted-average period 2 years 4 months 20 days  
Compensation cost $ 7.5 $ 1.2