Annual report pursuant to Section 13 and 15(d)

Stock-based Compensation - Option Valuation Method (Details)

v3.19.1
Stock-based Compensation - Option Valuation Method (Details)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Weighted average expected volatility, employees 52.31% 51.38%
Weighted average expected volatility, non-employees directors 58.65% 53.86%
Weighted average risk-free interest rate, employees 2.64% 2.07%
Weighted average risk-free interest rate, non-employees directors 2.44% 2.01%
Weighted average expected term (in years), employees 6 years 7 days 6 years 14 days
Weighted average expected term (in years), non-employees directors 5 years 3 months 10 days 5 years 4 months 13 days