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Stock-Based Compensation - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Stock options, grants in period, shares 1,186,181 676,437  
Stock options, grants in period, weighted average grant date fair value per share $ 6.66 $ 1.75  
Common stock issued under equity compensation plans 708,760 278,652  
2018 Equity Incentive Plan      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Number of shares issued or transferred 3,570,000    
2015 Stock Plan      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Shares not vested and subject to repurchase 1,329,165   812,769
Cash received for early exercise of unvested options $ 3.8   $ 0.9
Award vesting period 48 months