Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

Stock-based compensation cost that has been expensed in the statements of operations amounted to $1.5 million, $2.7 million and $2.4 million for the years ended December 31, 2018, 2017 and 2016, allocated as follows:

	Year Ended
	2018		2017		2016
Research and development	$	587,437	$	794,367	$	629,400
General and administrative		870,283		1,921,775		1,691,949
Restructuring costs		-		-		51,266
	$	1,457,720	$	2,716,142	$	2,372,615

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

For options granted in 2018, 2017 and 2016, the Company calculated the fair value of each option grant on the respective dates of grant using the following weighted average assumptions:

	2018			2017			2016
Expected term		5.78 years			5.85 years			5.84 years
Risk-free interest rate		2.80	%		2.13	%		1.76	%
Expected dividend yield		—			—			—
Expected volatility		83.56	%		80.54	%		84.26	%

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

The following table presents the placement in the fair value hierarchy of assets and liabilities that are measured at fair value on a recurring basis at December 31, 2018 and 2017:

			Fair value measurements at reporting date using
	December 31, 2018		Level 1 inputs		Level 2 inputs		Level 3 inputs
Assets:
Cash equivalents - money market funds and corporate bonds	$	7,331,005	$	4,835,433	$	2,495,572	$	-
Government treasury bills		897,381		897,381		-		-
Corporate bonds, notes and commercial paper		6,275,656		-		6,275,656		-
	$	14,504,042	$	5,732,814	$	8,771,228	$	-

			Fair value measurements at reporting date using
	December 31, 2017		Level 1 inputs		Level 2 inputs		Level 3 inputs
Assets:
Cash equivalents - money market funds	$	2,171,814	$	2,171,814	$	-	$	-
Government bonds and notes		4,741,690		4,741,690		-		-
Corporate bonds, notes and commercial paper		13,515,631		-		13,515,631		-
	$	20,429,135	$	6,913,504	$	13,515,631	$	-

Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]

	Year Ended December 31,
	2018			2017			2016
Basic loss per share attributable to common stock:
Numerator
Net loss	$	(11,660,022	)	$	(20,982,860	)	$	(18,971,508	)
Denominator
Weighted avg. common shares outstanding		21,352,339			20,051,934			18,258,149
Basic loss per share attributable to common stock	$	(0.55	)	$	(1.05	)	$	(1.04	)
Diluted loss per share attributable to common stock:
Numerator
Net loss	$	(11,660,022	)	$	(20,982,860	)	$	(18,971,508	)
Denominator
Weighted avg. common shares outstanding		21,352,339			20,051,934			18,258,149
Diluted loss per share attributable to common stock	$	(0.55	)	$	(1.05	)	$	(1.04	)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

The computation of diluted earnings per share for the years ended December 31, 2018, 2017 and 2016 does not include stock options and unvested restricted stock units to purchase shares in the computation of diluted earnings per share because these instruments were antidilutive:

	December 31,
	2018		2017		2016
Stock options		2,424,617		2,374,449		2,225,850
Unvested restricted stock awards		—		—		—
Unvested restricted stock units		682,124		203,998		—