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Stock-Based Compensation (Detail) - (Table 4) - $ / shares
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 0.00% 0.00%
Weighted average fair value $ 9.22 $ 8.97
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Volatility 26.00% 23.20%
Risk free interest rate 2.13% 1.50%
Expected life in years 3 years 9 months 3 years 5 months
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Volatility 26.30% 26.40%
Risk free interest rate 2.53% 1.99%
Expected life in years 4 years 5 months 5 years