Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Grant revenues		$ 657	$ 367	$ 1,099
Type of Revenue Extensible List	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 10,285	$ 5,222	$ 17,540	$ 9,942
General and administrative	3,060	1,118	6,216	2,366
Total operating expenses	13,345	6,340	23,756	12,308
Loss from operations	(13,345)	(5,683)	(23,389)	(11,209)
Other income (expense):
Interest income	960	151	1,970	215
Other income (expense)	(42)	(36)	(24)	(38)
Total other income (expense), net	918	115	1,946	177
Net loss	(12,427)	(5,568)	(21,443)	(11,032)
Other comprehensive income (loss):
Unrealized gain on investment securities	89		173
Comprehensive loss	$ (12,338)	$ (5,568)	$ (21,270)	$ (11,032)
Net loss per share:
Net loss per share – basic and diluted	$ (0.51)	$ (2.41)	$ (0.89)	$ (5.28)
Weighted-average shares outstanding – basic and diluted	24,161	2,307	24,128	2,089