Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Weighted Average Assumptions) (Details)

v3.10.0.1
Stock-Based Compensation (Weighted Average Assumptions) (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Summary of weighted average assumptions used to value options granted      
Grant date fair value of options (in dollars per share) $ 0.00 $ 14.51 $ 9.56
Volatility (as a percent) 0.00% 43.80% 42.20%
Risk-free interest rate (as a percent) 0.00% 2.10% 1.40%
Dividend yield (as a percent) 0.00% 0.00% 0.00%
Expected term (in years) 0 years 6 years 3 months 18 days 6 years 3 months 18 days