Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Schedule of Assumptions Used to Determine Grant Date Fair Value of Employee and Director Options Granted (Details)

v3.19.2
Share-Based Compensation - Schedule of Assumptions Used to Determine Grant Date Fair Value of Employee and Director Options Granted (Details) - $ / shares
6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Volatility   60.00%
Volatility, minimum 68.90%  
Volatility, maximum 70.20%  
Expected term in years   6 years 3 months
Dividend rate 0.00% 0.00%
Risk-free interest rate   2.16%
Risk-free interest rate, minimum 1.96%  
Risk-free interest rate, maximum 2.57%  
Minimum    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years 5 years 6 months  
Share price $ 5.80 $ 12.20
Fair value of option on grant date $ 3.74 7.03
Maximum    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years 6 years 3 months  
Share price $ 6.80 13.00
Fair value of option on grant date $ 4.41 $ 7.49