Impact of Recently Issued Accounting Standards - Impact of Adopting ASU 2014-09 (Details) - USD ($)	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Revenues [Abstract]
Revenue under collaborative research and development arrangements	$ 1,289,046	$ 4,288,586
Revenue under collaborative research and development arrangements with affiliated entities	148,008	233,330
Grants and miscellaneous revenue	92,590	5,240,233
Grants and miscellaneous revenue from affiliated entity	0	614,036
Total revenues	1,529,644	10,376,185
Operating Expenses [Abstract]
Research and development	24,577,751	24,542,504
General and administrative	9,698,015	7,767,589
Total operating expenses	34,275,766	$ 32,310,093
Calculated under Revenue Guidance in Effect before Topic 606
Revenues [Abstract]
Revenue under collaborative research and development arrangements	1,289,046
Revenue under collaborative research and development arrangements with affiliated entities	148,008
Grants and miscellaneous revenue	1,850,341
Grants and miscellaneous revenue from affiliated entity	464,400
Total revenues	3,751,795
Operating Expenses [Abstract]
Research and development	22,355,600
General and administrative	9,698,015
Total operating expenses	32,053,615
Accounting Standards Update 2014-09 \| Difference between Revenue Guidance in Effect before and after Topic 606
Revenues [Abstract]
Revenue under collaborative research and development arrangements	0
Revenue under collaborative research and development arrangements with affiliated entities	0
Grants and miscellaneous revenue	(1,757,751)
Grants and miscellaneous revenue from affiliated entity	(464,400)
Total revenues	(2,222,151)
Operating Expenses [Abstract]
Research and development	(2,222,151)
General and administrative	0
Total operating expenses	$ (2,222,151)

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-Publisher FASB
-Name Accounting Standards Codification
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