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Stock-Based Compensation (Detail) - (Table 4) - $ / shares
9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 0.00% 0.00%
Weighted average fair value $ 6.52 $ 5.94
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Volatility 25.10% 23.00%
Risk free interest rate 2.10% 1.50%
Expected life in years 3 years 4 months 24 days 3 years 4 months 24 days
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Volatility 27.20% 26.40%
Risk free interest rate 2.70% 2.00%
Expected life in years 4 years 10 months 24 days 5 years