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Stock-Based Compensation (Detail) - (Table 3) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Dividend yield 0.00% 0.00% 0.00%  
Weighted average fair value $ 8.91 $ 7.11 $ 8.81  
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Volatility 23.00% 22.00% 22.00% 27.00%
Risk free interest rate 1.48% 0.86% 0.99% 1.06%
Expected life in years 3 years 3 years 3 years 3 years
Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Volatility 26.00% 26.00% 28.00% 32.00%
Risk free interest rate 1.99% 1.90% 1.60% 1.80%
Expected life in years 5 years 5 years 5 years 5 years