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Stock-Based Compensation - Schedule of Fair Value of Employee Stock Options (Details)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Options to Purchase Common Stock    
Share-based Compensation    
Expected volatility, Minimum 51.90% 47.20%
Expected volatility, Maximum 52.00% 47.30%
Risk-free interest rate, Minimum 2.70% 2.00%
Risk-free interest rate, Maximum 2.72% 2.10%
Expected term (in years) 6 years 29 days  
Minimum | Options to Purchase Common Stock    
Share-based Compensation    
Expected term (in years)   5 years 9 months 18 days
Maximum | Options to Purchase Common Stock    
Share-based Compensation    
Expected term (in years)   6 years
2016 Employee Stock Purchase Plan    
Share-based Compensation    
Expected volatility, Minimum 66.20%  
Expected volatility, Maximum 72.70%  
Risk-free interest rate 0.94%  
Expected term (in years) 6 months