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Stock-Based Compensation (Stock Options) - Additional Information (Detail)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
USD ($)
shares
Sep. 30, 2017
USD ($)
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total pre-tax intrinsic value of options exercised $ 1.1 $ 1.6
Number of Stock options, granted | shares 0 0
Unvested Stock Options [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unrecognized compensation expense related to stock options $ 4.0 $ 4.0
Recognition period of unvested compensation expense   1 year 8 months 13 days