Condensed Consolidated Statements of Operations (Unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Grant		$ 2,378,000	$ 0	$ 3,888,000
Type of revenue [extensible list]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 14,806,000	$ 9,122,000	$ 29,195,000	$ 15,992,000
General and administrative	3,816,000	2,926,000	7,084,000	5,811,000
Total operating expenses	18,622,000	12,048,000	36,279,000	21,803,000
Loss from operations	(18,622,000)	(9,670,000)	(36,279,000)	(17,915,000)
Other income (expense):
Interest income	619,000	263,000	1,126,000	406,000
Other expense, net	(16,000)	(7,000)	(33,000)	(24,000)
Total other income	603,000	256,000	1,093,000	382,000
Net loss	$ (18,019,000)	$ (9,414,000)	$ (35,186,000)	$ (17,533,000)
Net loss per share, basic and diluted	$ (0.55)	$ (0.46)	$ (1.14)	$ (0.94)
Weighted-average common shares outstanding, basic and diluted	32,840,357	20,598,711	30,936,623	18,646,265