Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Grant	$ 3,888	$ 5,205	$ 4,628
Type of revenue [extensible list]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 36,719	$ 22,815	$ 18,143
General and administrative	12,632	10,066	8,391
Total operating expenses	49,351	32,881	26,534
Loss from operations	(45,463)	(27,676)	(21,906)
Other income (expense):
Interest income	1,172	482	244
Other expense	(57)	(42)	(36)
Total other income	1,115	440	208
Net loss	$ (44,348)	$ (27,236)	$ (21,698)
Net loss per share, basic and diluted	$ (2.13)	$ (1.80)	$ (2.22)
Weighted-average common shares outstanding, basic and diluted	20,822,560	15,128,192	9,791,728