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Stockholders' Equity - Summary of Fair Value of Option Grant and ESPP Purchase Right on Grant Date Using Black-Scholes Option Pricing Model (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Payment Arrangement, Option      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 1.80% 2.80% 2.10%
Dividend yield 0.00% 0.00% 0.00%
Volatility 66.50% 70.40% 74.00%
Expected life 6 years 6 years 6 years
Employee Stock Purchase Plan      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 1.90% 2.40% 1.20%
Dividend yield 0.00% 0.00% 0.00%
Volatility 52.10% 59.70% 50.00%
Expected life 6 months 6 months 6 months