XML 67 R56.htm IDEA: XBRL DOCUMENT v3.8.0.1
Stock-Based Compensation Plans - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock option compensation $ 0.8 $ 1.0
Stock Options Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number exercisable and fully vested 49,272  
Fully vested stock options with performance conditions attached 2,672  
Stock option compensation $ 0.8 1.0
Total intrinsic value exercised 1.9 1.8
Total compensation cost related to non-vested stock options not yet recognized $ 8.9  
Expected compensation cost recognized over the weighted-average period 2 years 3 months 11 days  
Stock Equivalent Units [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Fully vested stock options with performance conditions attached 43,834  
Total intrinsic value exercised $ 1.6 0.9
Expected compensation cost recognized over the weighted-average period 2 years 1 month 13 days  
Number of exercisable SEUs 51,863  
Compensation cost $ 1.2 $ 0.9