Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Stock-Based Payments - Weighted-Average Assumptions to Estimate Fair Value of Stock Options (Details) - Stock options - $ / shares
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Weighted-average assumptions used in Black-Scholes option-pricing model to estimate fair value        
Weighted-average risk-free interest rate (as a percent) 2.79% 1.86% 2.47% 2.03%
Expected option term (in years) 5 years 8 months 27 days 5 years 8 months 19 days 6 years 11 days 6 years
Volatility (as a percent) 91.16% 91.42% 90.37% 87.05%
Weighted-average grant date fair value of options granted (in dollars per share)     $ 8.13 $ 8.52