CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues:
Total revenues	$ 1,213
Operating expenses:
Research and development	15,844	$ 20,381
General and administrative	7,138	5,117
Total operating expenses	22,982	25,498
Loss from operations	(21,769)	(25,498)
Interest expense	(1,357)	(1,434)
Other income, net	753	790
Loss before provision for income taxes	(22,373)	(26,142)
Provision for income taxes		2
Net loss	$ (22,373)	$ (26,144)
Net loss per common share, basic and diluted	$ (0.25)	$ (0.42)
Shares used in computing net loss per share - basic and diluted	88,880,658	62,546,295
Comprehensive loss:
Net loss	$ (22,373)	$ (26,144)
Unrealized (losses) gains on available-for-sale securities	(64)	50
Comprehensive loss	(22,437)	$ (26,094)
Collaborative development
Revenues:
Total revenues	1,175
Other
Revenues:
Total revenues	$ 38