Annual report pursuant to Section 13 and 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
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock-based compensation expense for stock options and restricted common stock granted      
Stock-based compensation expense $ 4,419 $ 4,234 $ 3,233
Unrecognized compensation cost related to non-vested stock options granted to non-employees 100    
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 $ 11,900    
Weighted average period over which future compensation cost is expected to be recognized for awards granted to employees 2 years 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 $ 1,000    
Weighted average period over which future compensation cost is expected to be recognized for awards granted to non-employees 3 years 2 months 12 days    
Research and development      
Stock-based compensation expense for stock options and restricted common stock granted      
Stock-based compensation expense $ 1,666 2,980 2,733
General and administrative      
Stock-based compensation expense for stock options and restricted common stock granted      
Stock-based compensation expense $ 2,753 $ 1,254 $ 500