XML 57 R46.htm IDEA: XBRL DOCUMENT v3.19.1
Share-Based Compensation - Fair Value Assumption for Stock Options (Details) - Options to purchase Common Stock - $ / shares
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term, in years 6 years 4 months 10 days 6 years 4 months 2 days
Expected volatility 98.50% 84.40%
Risk-free interest rate 2.60% 2.60%
Expected dividend yield 0.00% 0.00%
Weighted-average exercise price (in usd per share) $ 2.95 $ 7.67