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Assumptions Used to Estimate Fair Value of Employee Stock Purchase Plan (Detail)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected dividend yield 0.00% 0.00% 0.00%
Expected volatility, Minimum 33.00% 33.00% 38.00%
Expected volatility, Maximum 49.00% 52.00% 54.00%
Risk-free interest rate, Minimum 0.20% 0.10% 0.10%
Risk-free interest rate, Maximum 2.40% 2.50% 2.50%
Expected forfeiture 10.00% 10.00% 10.00%
Contractual term of up to 10 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%
Expected volatility, Minimum 35.00% 29.00% 34.00%
Expected volatility, Maximum 36.00% 52.00% 53.00%
Risk-free interest rate, Minimum 0.10% 0.10% 0.10%
Risk-free interest rate, Maximum 0.30% 0.20% 0.20%
Expected forfeiture 0.00% 0.00% 0.00%
Contractual term of up to 24 months 24 months 24 months