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Equity Incentive Plans - Schedule of Fair Value of Option Award and ESPP on Grant Date (Detail)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Stock options [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 1.50% 1.60% 1.90%
Expected term (in years) 6 years 2 months 12 days 5 years 4 months 24 days 6 years
Expected volatility 47.00% 48.00% 55.00%
Dividend yield 0.00% 0.00% 0.00%
Employee stock purchase plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 0.60% 0.30% 0.10%
Expected term (in years) 6 months 6 months 6 months
Expected volatility 41.00% 42.00% 46.00%
Dividend yield 0.00% 0.00% 0.00%