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Assumptions Used to Estimate Fair Value of Employee Stock Purchase Plan (Detail)
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility, Minimum 35.00% 36.00% 33.00% 36.00%
Expected volatility, Maximum 49.00% 51.00% 49.00% 52.00%
Risk-free interest rate, Minimum 0.30% 0.10% 0.20% 0.10%
Risk-free interest rate, Maximum 2.40% 2.20% 2.40% 2.50%
Contractual term of up to 10 years 7 years 10 years 10 years
Employee stock purchase plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility, Minimum 35.00%   35.00% 29.00%
Expected volatility   29.00%    
Expected volatility, Maximum 36.00%   36.00% 52.00%
Risk-free interest rate, Minimum 0.20%   0.10% 0.10%
Risk-free interest rate   0.10%    
Risk-free interest rate, Maximum 0.30%   0.30% 0.20%
Expected forfeiture 0.00% 0.00% 0.00% 0.00%
Contractual term of up to 24 months 24 months 24 months 24 months