CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($)
$ in Thousands
Common stock
Additional paid-in capital
Accumulated other comprehensive loss
Accumulated deficit
Convertible preferred stock
Series B convertible preferred stock
Series C convertible preferred stock
Total
Balances at Beginning of period (in shares) at Dec. 31, 2016 7,886,292              
Balances at Beginning of period at Dec. 31, 2016 $ 8     $ (17,132)       $ (17,124)
Issuance of common stock upon exercise of stock options (in shares) 250,572              
Issuance of common stock upon exercise of stock options   $ 37           37
Issuance of common stock for one‑time bonus payment (in shares) 213,439              
Issuance of restricted common stock upon early exercise of stock options (in shares) 1,400,000              
Issuance of restricted common stock upon early exercise of stock options $ 1 (1)            
Issuance of restricted common stock (in shares) 5,227,014              
Issuance of restricted common stock $ 6 (6)            
Stock-based compensation expense   17,903           17,903
Accretion of Series A redeemable convertible preferred stock to redemption value   (656)           (656)
Net loss       (43,847)       (43,847)
Balances at End of period (in shares) at Dec. 31, 2017 14,977,317              
Balances at End of period at Dec. 31, 2017 $ 15 17,277   (60,979)       (43,687)
Balances at Beginning of period (in shares) at Dec. 31, 2016         29,570,662      
Balances at Beginning of period at Dec. 31, 2016         $ 19,067      
Convertible preferred stock                
Issuance of stock, net of issuance costs (in shares)           14,362,344    
Issuance of stock, net of issuance costs           $ 120,067    
Accretion of Series A redeemable convertible preferred stock to redemption value         $ 656      
Balances at End of period (in shares) at Dec. 31, 2017         43,933,006      
Balances at End of period at Dec. 31, 2017         $ 139,790      
Shares issued 12,055,450              
Issuance of common stock, initial public offering, net of issuance cost $3,548 $ 12 254,306           254,318
Cashless exercise of warrants 131,273              
Issuance of common stock upon exercise of stock options (in shares) 225,375              
Issuance of common stock upon exercise of stock options   64           64
Stock-based compensation expense   27,528           27,528
Vesting of restricted common stock   180           180
Conversion of preferred stock warrant to common stock warrant upon closing of initial public offering   3,053           3,053
Conversion of redeemable convertible preferred stock to common stock (in shares) 51,845,438              
Conversion of redeemable convertible preferred stock to common stock $ 52 240,724           240,776
Unrealized gains (losses) on investments     $ (29)         (29)
Net loss       (89,195)       (89,195)
Balances at End of period (in shares) at Dec. 31, 2018 79,234,853              
Balances at End of period at Dec. 31, 2018 $ 79 543,040 (29) (150,082)       $ 393,008
Convertible preferred stock                
Issuance of stock, net of issuance costs (in shares)             7,912,432  
Issuance of stock, net of issuance costs             $ 100,986  
Conversion of redeemable convertible preferred stock to common stock (in shares)         (51,845,438)      
Conversion of redeemable convertible preferred stock to common stock         $ (240,776)      
Balances at End of period (in shares) at Dec. 31, 2018               0
Cumulative effect adjustment for adoption   (92)   92        
Issuance of common stock upon exercise of stock options (in shares) 1,449,309              
Issuance of common stock upon exercise of stock options $ 2 2,443           $ 2,445
Stock-based compensation expense   41,271           41,271
Repurchase of unvested restricted common stock (in shares) (667,917)              
Repurchase of unvested restricted common stock $ (1)             (1)
Vesting of restricted common stock   44           44
Unrealized gains (losses) on investments     104         104
Net loss       (163,458)       (163,458)
Balances at End of period (in shares) at Dec. 31, 2019 80,016,245              
Balances at End of period at Dec. 31, 2019 $ 80 $ 586,798 $ 75 (312,740)       $ 274,213
Balances at End of period (in shares) at Dec. 31, 2019               0
Cumulative effect adjustment for adoption       $ 800       $ 800