Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Grant	$ 2,378	$ 1,479	$ 3,888	$ 2,462
Type of revenue [extensible list]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 9,122	$ 5,835	$ 15,992	$ 10,784
General and administrative	2,926	2,364	5,811	4,729
Total operating expenses	12,048	8,199	21,803	15,513
Loss from operations	(9,670)	(6,720)	(17,915)	(13,051)
Other income (expense):
Interest income	263	100	406	195
Other expense, net	(7)	(12)	(24)	(23)
Total other income	256	88	382	172
Net loss	$ (9,414)	$ (6,632)	$ (17,533)	$ (12,879)
Net loss per share, basic and diluted	$ (0.46)	$ (0.47)	$ (0.94)	$ (0.94)
Weighted-average common shares outstanding, basic and diluted	20,598,711	14,114,101	18,646,265	13,742,029