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Stock-Based Compensation - Assumptions in Computation of Fair Value (Detail)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield (percent) 0.00%    
Employee stock purchase plans [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield (percent)   0.00% 0.00%
Expected volatility (percent) 31.00% 34.00% 41.00%
Risk-free interest rate (percent) 0.26% 0.19% 0.37%
Expected life (in years) 1 year 3 months 1 year 3 months 1 year 3 months
Employee stock purchase plans [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield (percent) 2.65%    
Employee stock purchase plans [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield (percent) 2.81%