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Stock Plans - Additional Information (Detail) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Compensation cost on stock-based compensation plans $ 1.6 $ 1.5 $ 3.2 $ 3.1  
Restricted Stock Units [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock award granted by Company     0.1    
Weighted-average grant-date fair value of restricted stock awards granted     $ 66.65    
Restricted stock award, outstanding 0.4   0.4   0.5