Net Loss Per Share - Schedule of Anti-dilutive Effect Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	3,354,411	26,405,465
Convertible Preferred Shares (as Converted to Common Stock)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share		24,168,656
Unvested Common Stock from Early Exercise of Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	151,289	265,098
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	3,203,122	1,971,711