Income Taxes - Deferred Tax Assets (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 31,902,006	$ 45,759,780
Research and development credit carryforwards	2,432,058	2,180,700
Accrued expenses	748,334	752,866
Stock-based compensation	229,676	566,487
Other	19,240	14,321
Total gross deferred tax assets	35,331,314	49,274,154
Valuation allowance	(35,331,314)	(49,274,154)
Net deferred tax assets	$ 0	$ 0