Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Assumptions (Details)

v3.8.0.1
Stockholders' Equity - Assumptions (Details)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term     6 years 6 months
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate (percent) 2.00% 1.30% 1.70%
Expected volatility (percent) 43.00% 48.00% 50.00%
Expected term 6 years 6 months 6 years 7 months 6 days  
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate (percent) 2.20% 1.90% 2.00%
Expected volatility (percent) 47.00% 50.00% 58.00%
Expected term 6 years 9 months 18 days 6 years 8 months 12 days