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Stock-Based Compensation - Assumptions in Computation of Fair Value (Detail)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.00%    
Employee stock purchase plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield     0.00%
Expected volatility 23.00% 31.00% 34.00%
Risk-free interest rate 0.36% 0.26% 0.19%
Expected life (in years) 1 year 15 days 1 year 3 months 1 year 3 months
Employee stock purchase plan | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 2.38% 2.65%  
Employee stock purchase plan | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 2.53% 2.81%