Income Taxes - Components of Deferred Tax Asset (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets
Net federal operating loss carryforwards	$ 12,844,032	$ 12,747,837
Net foreign operating loss carryforwards	49,846	23,293
Net state operating loss carryforwards	7,981,812	4,068,086
Non-cash compensation	1,719,315	1,450,620
Research and development credits	5,713,709	3,491,251
Deferred finance costs	44,042
Fixed assets	2,597
Accrued expenses	472,004	308,007
Deferred tax asset, excluding valuation allowance	28,827,357	22,089,094
Fixed Assets		(19,985)
Less valuation allowance	$ (28,827,357)	$ (22,069,109)	$ (7,756,147)