Annual report pursuant to Section 13 and 15(d)

Stock and Employee Benefit Plans - Fair Value Assumptions (Details)

v3.19.1
Stock and Employee Benefit Plans - Fair Value Assumptions (Details)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Stock Options    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk free interest rate, minimum (as a percent) 2.40% 1.77%
Risk free interest rate, maximum (as a percent) 3.06% 2.22%
Dividend yield (as a percent) 0.00% 0.00%
Expected volatility, minimum (as a percent) 77.10% 75.10%
Expected volatility, maximum (as a percent) 80.50% 78.90%
Stock Options | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term (in years) 4 years 9 months 5 years
Stock Options | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term (in years) 5 years 8 months 23 days 5 years 8 months 23 days
Employee Stock    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk free interest rate (as a percent) 2.48%  
Expected term (in years) 6 months  
Dividend yield (as a percent) 0.00%  
Expected volatility (as a percent) 57.57%