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Share Based Awards - Options assumptions (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award      
Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Period1 4 years    
Incentive Stock Options      
Share Based Compensation Arrangement By Share Based Payment Award      
Risk-free interest rate (as a percent) 2.50% 2.70% 2.10%
Expected volatility (as a percent) 50.00% 51.00% 40.00%
Expected life (in years) 6 years 1 month 6 days 6 years 1 month 6 days 6 years 1 month 6 days
Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Period1 48 months    
Minimum | ESPP      
Share Based Compensation Arrangement By Share Based Payment Award      
Risk-free interest rate (as a percent) 1.50% 1.80% 0.90%
Expected volatility (as a percent) 39.00% 34.00% 34.00%
Expected life (in years) 6 months 6 months 6 months
Maximum | ESPP      
Share Based Compensation Arrangement By Share Based Payment Award      
Risk-free interest rate (as a percent) 2.50% 2.60% 1.30%
Expected volatility (as a percent) 45.00% 54.00% 54.00%
Expected life (in years) 2 years 2 years 2 years