Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Payments - Weighted-Average Assumptions to Estimate Fair Value of Stock Options (Details)

v3.19.2
Stock-Based Payments - Weighted-Average Assumptions to Estimate Fair Value of Stock Options (Details) - Stock Option - $ / shares
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Weighted-average risk-free interest rate 1.97% 2.79% 2.47% 2.47%
Expected option term (in years) 5 years 7 months 17 days 5 years 8 months 26 days 6 years 7 days 6 years 10 days
Volatility 90.33% 91.16% 91.51% 90.37%
Weighted-average grant date fair value of options granted (in dollars per share)     $ 5.10 $ 8.13