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
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	2,488	4,304	6,557	8,478
General and administrative	1,912	3,075	4,719	6,214
Total operating expenses	4,400	7,379	11,276	14,692
Loss from operations	(4,400)	(7,379)	(11,276)	(14,692)
Gain on sale of property and equipment			66
Interest income	10	207	72	307
Net loss	$ (4,390)	$ (7,172)	$ (11,138)	$ (14,385)
Net loss per share — basic and diluted	$ (0.14)	$ (0.26)	$ (0.38)	$ (0.68)
Weighted average common shares outstanding—basic and diluted	31,221,139	27,526,065	29,515,749	21,206,269
Comprehensive loss:
Net loss	$ (4,390)	$ (7,172)	$ (11,138)	$ (14,385)
Other comprehensive gain (loss):
Unrealized gain (loss) on investments, net of tax of $0	(1)	24	(9)	29
Total other comprehensive gain (loss)	(1)	24	(9)	29
Total comprehensive loss	$ (4,391)	$ (7,148)	$ (11,147)	$ (14,356)