Net Loss Per Share of Common Stock - Antidilutive Securities Excluding from Computation of Earnings Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	3,838,635	15,316,586	3,838,635	15,316,586
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	3,024,743	2,900,842	3,024,743	2,900,842
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	564,638	0	564,638	0
Shares subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	46,811	64,107	46,811	64,107
ESPP purchase rights
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	84,321	0	84,321	0
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	0	12,066,654	0	12,066,654
Redeemable convertible preferred stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	0	160,657	0	160,657
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	118,122	124,326	118,122	124,326