Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue:
Collaboration revenue - related party	$ 5,186,000	$ 10,454,000	$ 10,648,000	$ 17,069,000
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Grant revenue	$ 831,000	$ 260,000	$ 1,570,000	$ 706,000
Collaboration revenue	28,000	1,817,000	2,016,000	2,077,000
Total revenue	6,045,000	12,531,000	14,234,000	19,852,000
Operating expenses:
Research and development expenses	20,099,000	17,905,000	41,842,000	40,792,000
General and administrative expenses	6,491,000	5,574,000	12,629,000	13,069,000
Restructuring expenses	0		0	1,492,000
Total operating expenses	26,590,000	23,479,000	54,471,000	55,353,000
Loss from operations	(20,545,000)	(10,948,000)	(40,237,000)	(35,501,000)
Other (expense) income:
Interest income	74,000	189,000	233,000	409,000
Interest expense	(719,000)		(1,435,000)
Other income	476,000		844,000
Total other (expense) income, net	(169,000)	189,000	(358,000)	409,000
Net loss	$ (20,714,000)	$ (10,759,000)	$ (40,595,000)	$ (35,092,000)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.28)	$ (0.24)	$ (0.56)	$ (0.81)
Weighted average common shares outstanding, basic and diluted	73,306,248	45,140,830	72,063,881	43,095,686
Net loss	$ (20,714,000)	$ (10,759,000)	$ (40,595,000)	$ (35,092,000)
Other comprehensive loss:
Unrealized gain on investments, net of tax of $0	11,000		1,000
Total other comprehensive gain	11,000		1,000
Comprehensive loss	$ (20,703,000)	$ (10,759,000)	$ (40,594,000)	$ (35,092,000)