Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Payments - Stock-Based Compensation Expense (Details)

v3.8.0.1
Stock-Based Payments - Stock-Based Compensation Expense (Details) - USD ($)
$ in Thousands
 1 Months Ended 3 Months Ended
May 09, 2018
Mar. 31, 2018
Mar. 31, 2017
Stock-based compensation expense for stock options and restricted common stock granted      
Stock-based compensation expense   $ 1,696 $ 884
Proceeds from issuance of common stock in public offerings and private placements, net of issuance costs   51,969  
Common Stock | Sales Agreement | Cowen and Company LLC      
Stock-based compensation expense for stock options and restricted common stock granted      
Shares issued 437,856    
Proceeds from issuance of common stock in public offerings and private placements, net of issuance costs $ 5,400    
Employee Stock options      
Stock-based compensation expense for stock options and restricted common stock granted      
Unrecognized compensation cost related to non-vested stock options granted to employees   $ 17,900  
Weighted average period over which future compensation cost is expected to be recognized for awards granted to employees   3 years 1 month 6 days  
Unrecognized compensation cost related to non-vested stock options granted to non-employees   $ 100  
Weighted average period over which future compensation cost is expected to be recognized for awards granted to non-employees   10 months 24 days  
Performance-based stock options      
Stock-based compensation expense for stock options and restricted common stock granted      
Unrecognized compensation cost related to non-vested stock options granted to employees   $ 1,200  
Weighted average period over which future compensation cost is expected to be recognized for awards granted to employees   3 years 6 months 26 days  
Research and development      
Stock-based compensation expense for stock options and restricted common stock granted      
Stock-based compensation expense   $ 565 330
General and administrative      
Stock-based compensation expense for stock options and restricted common stock granted      
Stock-based compensation expense   $ 1,131 $ 554