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Stock-Based Compensation - Fair Value Assumptions (Details)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.00%    
2018 Equity Incentive Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.00% 0.00% 0.00%
Expected term (in years)     6 years 29 days
2018 Equity Incentive Plan | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 5 years 2 months 12 days 5 years 3 months 18 days  
Risk-free interest rates 2.50% 1.90% 1.20%
Expected volatility 38.00% 39.00% 42.00%
2018 Equity Incentive Plan | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 6 years 1 month 6 days 6 years 3 months 18 days  
Risk-free interest rates 2.90% 2.20% 2.10%
Expected volatility 45.00% 43.00% 45.00%
2018 Employee Stock Purchase Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.00%    
Expected volatility 37.00%    
2018 Employee Stock Purchase Plan | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 6 months    
Risk-free interest rates 2.40%    
2018 Employee Stock Purchase Plan | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 2 years    
Risk-free interest rates 2.90%