Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue
Total revenue	$ 10,331,168	$ 10,738,322
Operating expenses
Research and development	18,459,310	18,406,329
General and administrative	9,765,581	8,457,557
Impairment charges	24,940,687	35,919,695
Total operating expenses	53,165,578	62,783,581
Loss from operations	(42,834,410)	(52,045,259)
Other income (expense)
Changes in fair value of warrant liability, including loss on exchange	(2,878,484)	97,763
Changes in fair value of embedded derivative	184,555	(7,379)
Interest expense	(297,090)	(162,139)
Interest income	226,597	47,579
Other income, net	277,886	5,670
Total other income (expense)	(2,486,536)	(18,506)
Net loss before income tax benefit	(45,320,946)	(52,063,765)
Income tax benefit	6,149,794	5,638,375
Net loss	(39,171,152)	(46,425,390)
Other comprehensive income (loss) — foreign currency translation adjustments	(463,177)	2,997,826
Comprehensive loss	(39,634,329)	(43,427,564)
Net loss	(39,171,152)	(46,425,390)
Preferred stock accretion and other deemed dividends	(3,307,800)	(4,930,010)
Net loss attributable to common stockholders	$ (42,478,952)	$ (51,355,400)
Weighted-average common shares outstanding, basic and diluted	2,802,382	431,878
Net loss per share attributable to common stockholders, basic and diluted	$ (15.16)	$ (118.91)
Research Grants and Contracts [Member]
Revenue
Total revenue	$ 10,311,388	$ 10,696,819
License Revenue [Member]
Revenue
Total revenue	$ 19,780	$ 41,503