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Assumptions to Estimate Fair Value for Stock Options at Grant Date (Detail) - Time Vested Stock Options
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Risk-free interest rate, minimum 1.01% 1.15% 0.86% 1.13%
Risk-free interest rate, maximum   1.56% 1.15% 1.56%
Expected volatility, minimum 57.00% 59.00% 57.00% 59.00%
Expected volatility, maximum   60.00% 58.00% 65.00%
Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected life (in years) 4 years 4 years 4 years 4 years
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected life (in years)   6 years 3 months 6 years 3 months 6 years 3 months
Expected dividend yield       0.36%