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	$ 1,836	$ 18	$ 3,049	$ 18
Operating expenses:
Cost of revenue	141		141
Research and development	18,864	19,475	34,708	39,856
General and administrative	7,038	5,371	14,176	10,488
Total operating expenses	26,043	24,846	49,025	50,344
Loss from operations	(24,207)	(24,828)	(45,976)	(50,326)
Interest expense	(1,226)	(1,451)	(2,583)	(2,885)
Other income, net	477	812	1,230	1,602
Loss before provision for income taxes	(24,956)	(25,467)	(47,329)	(51,609)
Provision for income taxes				2
Net loss	$ (24,956)	$ (25,467)	$ (47,329)	$ (51,611)
Net loss per common share, basic and diluted	$ (0.28)	$ (0.41)	$ (0.53)	$ (0.82)
Shares used in computing net loss per share - basic and diluted	89,080,046	62,651,863	88,980,353	62,599,371
Comprehensive loss:
Net loss	$ (24,956)	$ (25,467)	$ (47,329)	$ (51,611)
Unrealized gains on available-for-sale securities	361	4	297	54
Comprehensive loss	(24,595)	(25,463)	(47,032)	(51,557)
Licensing
Revenues:
Total revenues	706		706
Collaborative development
Revenues:
Total revenues	1,125		2,300
Other
Revenues:
Total revenues	$ 5	$ 18	$ 43	$ 18