Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue:
Collaboration revenue - related party	$ 80,000	$ 4,840,000	$ 10,728,000	$ 21,909,000
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Grant revenue	$ 1,337,000	$ 85,000	$ 2,907,000	$ 791,000
Collaboration revenue		2,106,000	2,016,000	4,183,000
Total revenue	1,417,000	7,031,000	15,651,000	26,883,000
Operating expenses:
Research and development expenses	23,861,000	18,317,000	65,703,000	59,109,000
General and administrative expenses	7,551,000	5,897,000	20,180,000	18,966,000
Restructuring expenses	0		0	1,492,000
Total operating expenses	31,412,000	24,214,000	85,883,000	79,567,000
Loss from operations	(29,995,000)	(17,183,000)	(70,232,000)	(52,684,000)
Other (expense) income:
Interest income	100,000	335,000	333,000	744,000
Interest expense	(730,000)		(2,165,000)
Other income	345,000	439,000	1,189,000	439,000
Total other (expense) income, net	(285,000)	774,000	(643,000)	1,183,000
Net loss	$ (30,280,000)	$ (16,409,000)	$ (70,875,000)	$ (51,501,000)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.36)	$ (0.23)	$ (0.93)	$ (0.99)
Weighted average common shares outstanding, basic and diluted	83,531,617	69,944,068	75,914,361	52,143,492
Net loss	$ (30,280,000)	$ (16,409,000)	$ (70,875,000)	$ (51,501,000)
Other comprehensive loss:
Unrealized gain on investments, net of tax of $0	1,000	7,000	2,000	7,000
Total other comprehensive gain	1,000	7,000	2,000	7,000
Comprehensive loss	$ (30,279,000)	$ (16,402,000)	$ (70,873,000)	$ (51,494,000)