Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation - Fair Value of Employee Stock Options Granted and ESPP Rights to Purchase Common Stock Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details)

v3.20.1
Stock-Based Compensation - Fair Value of Employee Stock Options Granted and ESPP Rights to Purchase Common Stock Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected dividend yield 0.00%    
Employee options      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term (years)     6 years 1 month 6 days
Expected volatility     89.80%
Risk-free interest rate     2.00%
ESPP Rights      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term (years) 6 months 6 months  
Expected volatility   74.30%  
Risk-free interest rate   2.50%  
Minimum | Employee options      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term (years) 5 years 9 months 18 days 5 years 6 months  
Expected volatility, Minimum 78.70% 82.00%  
Risk-free interest rate, Minimum 1.50% 2.60%  
Minimum | ESPP Rights      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility, Minimum 73.70%    
Risk-free interest rate, Minimum 1.60%    
Maximum | Employee options      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term (years) 5 years 10 months 24 days 6 years 1 month 6 days  
Expected volatility, Maximum 83.70% 83.20%  
Risk-free interest rate, Maximum 2.60% 3.10%  
Maximum | ESPP Rights      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility, Maximum 109.90%    
Risk-free interest rate, Maximum 2.40%