Stock-Based Compensation (Total Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | |||
Stock-based compensation expense | $ 31.7 | $ 24.1 | $ 14.5 |
Cost of revenue [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | |||
Stock-based compensation expense | 11.7 | 9.6 | 7.5 |
Selling and marketing expense [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | |||
Stock-based compensation expense | 3.5 | 3.0 | 1.9 |
General and administrative expense [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | |||
Stock-based compensation expense | $ 16.5 | $ 11.5 | $ 5.1 |