Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation - Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details)

v3.19.1
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
Mar. 31, 2019
Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Expected term (years) 5 years 10 months 24 days 6 years 1 month 6 days
Expected volatility   82.00%
Expected volatility, Minimum 79.90%  
Expected volatility, Maximum 81.90%  
Risk-free interest rate   2.60%
Risk-free interest rate, Minimum 2.40%  
Risk-free interest rate, Maximum 2.60%