Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenue	$ 5,801,401	$ 10,331,168
Operating expenses
Research and development	17,765,553	18,459,310
General and administrative	8,500,783	9,765,581
Impairment charges	1,000,000	24,940,687
Total operating expenses	27,266,336	53,165,578
Loss from operations	(21,464,935)	(42,834,410)
Other income (expense)
Changes in fair value of warrant liability, including loss on exchange	30,000	(2,878,484)
Changes in fair value of embedded derivative		184,555
Interest expense	(2,244)	(297,090)
Interest income	843,409	226,597
Other income, net	15,139	277,886
Total other income (expense)	886,304	(2,486,536)
Net loss before income tax benefit	(20,578,631)	(45,320,946)
Income tax benefit	58,500	6,149,794
Net loss	(20,520,131)	(39,171,152)
Other comprehensive loss — foreign currency translation adjustment		(463,177)
Other comprehensive income — unrealized gains on investments	20,007
Comprehensive loss	(20,500,124)	(39,634,329)
Net loss	(20,520,131)	(39,171,152)
Preferred stock accretion and other deemed dividends	(452,925)	(3,307,800)
Net loss attributable to common stockholders	$ (20,973,056)	$ (42,478,952)
Weighted-average common shares outstanding, basic and diluted	13,124,951	2,802,382
Net loss per share attributable to common stockholders, basic and diluted	$ (1.60)	$ (15.16)