CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Total revenues	$ 0	$ 18	$ 6	$ 6,796
Operating expenses:
Research and development	4,242	1,836	7,360	7,819
General and administrative	2,254	2,850	4,676	6,383
Total operating expenses	6,496	4,686	12,036	14,202
Loss from operations	(6,496)	(4,668)	(12,030)	(7,406)
Other income (expense):
Interest and other income	10	191	89	205
Interest and other expense	(461)	(538)	(951)	(1,074)
Loss before income taxes	(6,947)	(5,015)	(12,892)	(8,275)
Income tax (expense) benefit	0	(1)	8	(1)
Net loss and comprehensive loss	$ (6,947)	$ (5,016)	$ (12,884)	$ (8,276)
Net loss per share, basic and diluted (in dollars per share)	$ (0.23)	$ (0.30)	$ (0.48)	$ (0.61)
Weighted average shares used to compute basic and diluted net loss per share (in shares)	29,801,974	16,705,587	26,933,173	13,560,183
Revenue, Product and Service [Extensible List]			us-gaap:RevenueUnderCollaborationsMember