Common Stock (Details)		12 Months Ended
	Nov. 08, 2019 shares	Dec. 31, 2019 USD ($) Vote shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Common Stock
Common stock, shares authorized for issuance		290,000,000	290,000,000
Preferred stock, shares authorized for issuance		10,000,000	10,000,000
Number of votes per share of common stock | Vote		1
Dividends on common stock | $		$ 0
Proceeds from sale of stock | $			$ 64,877,000	$ 711,000
Shares of common stock reserved for issuance, on an as-converted basis
Shares available for future option grants		1,704,183	2,486,637	2,576,535
Outstanding options		5,643,410	3,778,259	3,013,394
Unvested restricted common stock (founders and early exercise of stock options)			43,076	319,203
Shares reserved for employee stock purchase plan		400,000	400,000	400,000
Total		9,205,593	6,707,972	6,309,132
Exchange Warrants
Shares of common stock reserved for issuance, on an as-converted basis
Exchange warrants	1,458,000	1,458,000