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Stock-Based Compensation - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Mar. 31, 2018
Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Stock options, grants in period, shares 210,808 190,145 1,396,989 866,582    
Stock options, grants in period, weighted average grant date fair value per share $ 11.23 $ 1.76 $ 7.29 $ 1.75    
Common stock issued under equity compensation plans 5,171 240,407 713,931 519,059    
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 1,181,717   1,181,717     812,769
Cash received from early exercise of unvested options $ 3.5   $ 3.5     $ 0.9
Award vesting period     48 months