Net Loss per Share - Anti-Dilutive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Excluded from the calculation of diluted net loss per share, due to anti-dilutive effect
Shares of common stock equivalents	5,561,098	4,169,538	5,561,098	4,169,538
Common stock subject to repurchase
Excluded from the calculation of diluted net loss per share, due to anti-dilutive effect
Shares of common stock equivalents		12,384		12,384
Outstanding options
Excluded from the calculation of diluted net loss per share, due to anti-dilutive effect
Shares of common stock equivalents	5,561,098	4,157,154	5,561,098	4,157,154