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Stock-Based Compensation - Fair Value Assumptions (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Stock-based compensation      
Unamortized stock-based compensation expense not yet recognized $ 65.3    
RSU      
Stock-based compensation      
Unamortized stock-based compensation expense not yet recognized $ 28.6    
Options remaining vesting period 4 years    
Weighted average period of recognition 1 year 6 months    
Stock options      
Stock-based compensation      
Weighted average estimated grant date fair value (per share) $ 32.07 $ 14.98 $ 20.62
Unamortized stock-based compensation expense not yet recognized $ 36.7    
Options remaining vesting period 4 years    
Weighted average period of recognition 2 years 1 month 6 days    
Stock-based awards - weighted average assumptions used to estimate fair value of options granted      
Risk-free interest rate (as a percent) 2.17% 2.67% 2.13%
Expected dividend yield (as a percent) 0.00% 0.00% 0.00%
Expected volatility rate (as a percent) 46.80% 44.90% 46.50%
Expected term 6 years 3 days 6 years 1 month 6 days 6 years 14 days