Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	2,684	4,475	9,241	12,953
General and administrative	2,344	3,440	7,063	9,654
Total operating expenses	5,028	7,915	16,304	22,607
Loss from operations	(5,028)	(7,915)	(16,304)	(22,607)
Gain on sale of property and equipment			66
Interest income	5	166	77	473
Net loss	$ (5,023)	$ (7,749)	$ (16,161)	$ (22,134)
Net loss per share — basic and diluted	$ (0.13)	$ (0.28)	$ (0.49)	$ (0.95)
Weighted average common shares outstanding—basic and diluted	39,321,177	27,810,358	32,808,082	23,431,823
Comprehensive loss:
Net loss	$ (5,023)	$ (7,749)	$ (16,161)	$ (22,134)
Other comprehensive gain (loss):
Unrealized gain (loss) on investments, net of tax of $0	1	(7)	(8)	22
Total other comprehensive gain (loss)	1	(7)	(8)	22
Total comprehensive loss	$ (5,022)	$ (7,756)	$ (16,169)	$ (22,112)