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Stock-Based Compensation Plans - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock option compensation $ 1.0 $ 0.9
Stock Options Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number exercisable and fully vested 51,265  
Fully vested stock options with performance conditions attached 11,695  
Stock option compensation $ 1.0 0.9
Total intrinsic value exercised 1.8 1.5
Total compensation cost related to non-vested stock options not yet recognized $ 9.1  
Expected compensation cost recognized over the weighted-average period 2 years 4 months 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 54,256  
Total intrinsic value exercised $ 0.9 1.1
Expected compensation cost recognized over the weighted-average period 2 years 15 days  
Number of exercisable SEUs 59,624  
Compensation cost $ 0.9 $ 1.0