Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Type of revenue [extensible list]	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 14,562	$ 14,389
General and administrative	4,460	3,268
Total operating expenses	19,022	17,657
Loss from operations	(19,022)	(17,657)
Other income (expense):
Interest income	300	507
Other expense, net	(6)	(17)
Total other income	294	490
Net loss	$ (18,728)	$ (17,167)
Net loss per share, basic and diluted	$ (0.57)	$ (0.59)
Weighted-average common shares outstanding, basic and diluted	33,097,736	29,011,737