Income Taxes - Difference in Actual Income Tax Expense Computed by Applying the Statutory Federal Income Tax Rate to Loss Before Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Computed tax (benefit) at statutory rate (2018: 21%, 2017: 34%)	$ (3,454,582)	$ (6,445,413)
State taxes, net of federal benefit	(384,035)	(532,952)
Stock-based compensation	82,024	231,396
Foreign tax rate differential	(3,158)
Return to provision	(31,111)	(15,375)
Other	51,598	20,292
Federal rate change on deferred items as of enactment date		16,232,211
Uncertain tax position adjustment for prior periods	1,029,115
Increase (decrease) in valuation allowance	3,731,884	(8,470,655)
Total income tax expense	3,526	2,921
State
Income Tax Disclosure [Line Items]
Research and development tax credit	(511,845)	(576,525)
Federal
Income Tax Disclosure [Line Items]
Research and development tax credit	$ (506,364)	$ (440,058)