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Stock Incentive Plans - Summary of Unvested Common Stock from Early Exercises Subject to Repurchase (Details)
 12 Months Ended
Dec. 31, 2019
shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Unvested shares—Beginning Balance 151,289
Vested (94,816)
Repurchased (34,807)
Unvested shares—Ending Balance 21,666