Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue:
Collaboration revenue - related party	$ 6,615	$ 3,766
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Grant revenue	$ 446	$ 205
Revenue	260
Total revenue	7,321	3,971
Operating expenses:
Research and development expenses	22,887	23,460
General and administrative expenses	7,495	8,777
Restructuring expenses	1,492
Total operating expenses	31,874	32,237
Loss from operations	(24,553)	(28,266)
Other income (expense):
Interest income (expense), net	220	347
Total other income (expense), net	220	347
Net loss	$ (24,333)	$ (27,919)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.59)	$ (0.69)
Weighted average common shares outstanding, basic and diluted	41,027,824	40,628,434
Net loss	$ (24,333)	$ (27,919)
Other comprehensive income:
Unrealized gain on investments, net of tax of $0		40
Total other comprehensive income		40
Comprehensive loss	$ (24,333)	$ (27,879)