Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation - Estimated Fair Value of Stock Options (Details)

v3.8.0.1
Stock-Based Compensation - Estimated Fair Value of Stock Options (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 dividend yield 0.00% 0.00% 0.00%
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 1.18% 1.18% 1.55%
Volatility 45.95% 36.00% 36.30%
Expected term (in years) 5 years 11 months 9 days 5 years 5 years 6 months
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 2.22% 2.23% 1.95%
Volatility 50.52% 49.64% 39.63%
Expected term (in years) 6 years 29 days 6 years 3 months 4 days 6 years 2 months 23 days