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Stock-Based Compensation (Stock Options) - Additional Information (Detail) - USD ($)
shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Recognition period of unvested compensation expense 2 years 10 months 24 days    
Number of shares available for grant 2.5    
Total pre-tax intrinsic value of options exercised $ 0.2 $ 3.4 $ 1.1
Fair value of options fully vested 2.5 $ 4.3 $ 5.7
Non Vested Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation expense related to non-vested stock options $ 0.8    
Recognition period of unvested compensation expense 1 year