Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans - Schedule of Fair Value of Stock Option Grants Valuation Assumptions by Block-Scholes Option Pricing Model (Details)

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Equity Incentive Plans - Schedule of Fair Value of Stock Option Grants Valuation Assumptions by Block-Scholes Option Pricing Model (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term (in years) 6 years    
Expected volatility   55.00% 55.00%
Expected dividend yield 0.00%    
Risk-free interest rate, minimum 2.60% 1.85% 0.75%
Risk-free interest rate, maximum 3.00% 2.29% 1.77%
Minimum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Fair value of common stock $ 23.72 $ 3.06 $ 0.85
Expected term (in years)   5 years 2 years
Expected volatility 64.00%    
Maximum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Fair value of common stock $ 47.39 $ 19.56 $ 3.06
Expected term (in years)   6 years 10 years
Expected volatility 67.00%