Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue
Grant revenue		$ 3,054,000		$ 4,753,000
Type of Revenue [Extensible List]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses
Research and development	$ 2,522,000	$ 3,637,000	$ 6,014,000	$ 6,485,000
General and administrative	3,201,000	3,291,000	7,151,000	7,881,000
Loss on impairment of long-lived assets			2,870,000
Total operating expenses	5,723,000	6,928,000	16,035,000	14,366,000
Loss from operations	(5,723,000)	(3,874,000)	(16,035,000)	(9,613,000)
Interest income	26,000	233,000	243,000	579,000
Other income (expense), net	656,000	597,000	(45,000)	1,286,000
Net loss	$ (5,041,000)	$ (3,044,000)	$ (15,837,000)	$ (7,748,000)
Net loss per share - basic and diluted	$ (0.32)	$ (0.27)	$ (1.02)	$ (0.69)
Weighted-average common shares used to compute basic and diluted net loss per share	15,902	11,280	15,457	11,277