XML 24 R41.htm IDEA: XBRL DOCUMENT v3.19.3
Stock-Based Compensation - Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2019
Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term (years) 5 years 10 months 24 days 5 years 10 months 24 days  
Expected volatility, Minimum 80.60% 78.70% 82.00%
Expected volatility, Maximum 81.00% 81.90% 82.80%
Risk-free interest rate, Minimum 1.50% 1.50% 2.60%
Risk-free interest rate, Maximum 1.90% 2.60% 2.80%
Minimum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term (years)     5 years 6 months
Maximum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term (years)     6 years 1 month 6 days