Stock Options and Equity-Classified Warrants (Tables)

12 Months Ended

Dec. 31, 2016

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Total Stock-Based Compensation Expense from Stock Options and Warrants

The following table sets forth the total stock-based compensation expense resulting from stock options and warrants included in the Company's Statements of Operations:

	Years Ended December 31,
	2016		2015		2014
Research and development - employee	$	1,822,508	$	1,590,267	$	932,482
General and administrative - employee		4,661,795		5,568,537		2,383,624
Total employee stock-based compensation	$	6,484,303	$	7,158,804	$	3,316,106
Research and development – non-employee	$	—	$	—	$	86,539
General and administrative – non-employee		235,764		225,852		1,736,703
Total non-employee stock-based compensation	$	235,764	$	225,852	$	1,823,242

Significant Ranges of Outstanding Stock Options and Warrants

The following table summarizes significant ranges of outstanding stock options under the two plans at December 31, 2016:

Range of Exercise Prices		Number of Options		Weighted Average Remaining Contractual Life (years)		Weighted Average Exercise Price		Number of Options Exercisable		Weighted Average Contractual Life		Weighted Average Exercise Price
$	0.43 — 1.50		4,432,498		9.95	$	0.44		1,086,696		9.95	$	0.45
$	1.51 — 2.50		8,932,606		7.85		2.26		6,293,224		7.49		2.22
$	2.51 — 4.00		960,670		7.13		2.88		934,004		7.10		2.87
$	4.01 — 32.55		3,153,996		6.17		5.24		3,153,996		6.17		5.24
			17,479,770		8.04	$	2.37		11,467,920		7.33	$	2.93

Stock Options [Member] | Employees [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Fair Value Assumptions of Stock Options

The fair value of the stock options at the date of grant was estimated using the Black-Scholes option-pricing model, based on the following assumptions:

	2016			2015			2014
Risk-free interest rate		1.20% - 2.26	%		1.74% - 2.42	%		1.74% - 2.12	%
Expected volatility		74% - 88	%		74% - 85	%		82% - 90	%
Expected lives (years)		6 - 10			6 - 10			6 - 10
Expected dividend yield		0.00	%		0.00	%		0.00	%

Stock Options [Member] | Non-employees [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Fair Value Assumptions of Stock Options

The fair value of the stock options at the date of grant was estimated using the Black-Scholes option-pricing model, based on the following assumptions:

	2016		2015		2014
Risk-free interest rate		—		—		2.23	%
Expected volatility		—		—		85.0	%
Expected lives (years)		—		—		10
Expected dividend yield		—		—		0	%

Stock Options and Warrants Activity

Presented below is the Company's non-employee stock option activity:

	Stock Options									Weighted Average Exercise Price
	2016			2015			2014			2016		2015		2014
Outstanding — beginning of year		635,714			692,143			167,143		$	3.02	$	3.47	$	5.69
Granted		—			—			550,000			—		—		2.76
Exercised		—			—			—			—		—		—
Expired/Forfeited		(35,714	)		(56,429	)		(25,000	)		7.77		8.54		2.79
Outstanding — end of year		600,000			635,714			692,143			2.73		3.02		3.47
Exercisable at end of year		600,000			635,714			692,143		$	2.73	$	3.02	$	3.47
Weighted average fair value of stock options granted during the year:	$	—		$	—		$	1.98

Stock Options [Member] | Employees and Directors [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Stock Options and Warrants Activity

Presented below is the Company's stock option activity for employees and directors:

	Stock Options									Weighted Average Exercise Price
	2016			2015			2014			2016		2015		2014
Outstanding — beginning of year		13,583,862			9,358,592			6,228,593		$	3.11	$	2.83	$	3.11
Granted		4,857,500			4,590,000			3,190,000			0.59		2.61		2.47
Exercised		(330,000	)		(287,143	)		(1,667	)		2.14		2.05		1.83
Forfeited		(1,176,737	)		—			(24,333	)		3.49		—		2.81
Expired		(54,855	)		(77,587	)		(34,001	)		8.03		5.58		8.18
Outstanding — end of year		16,879,770			13,583,862			9,358,592			2.36		3.11		2.83
Exercisable at end of year		10,867,920			8,020,162			4,901,511		$	2.95	$	3.45	$	3.22
Weighted average fair value of stock options granted during the year:	$	0.43		$	1.88		$	1.80

Warrants [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Stock Options and Warrants Activity

A summary of the Company's warrant activity and related information for the years ended December 31 are shown below.

	Warrants									Weighted Average Exercise Price
	2016			2015			2014			2016		2015		2014
Outstanding — beginning of year		7,225,472			7,349,760			8,324,609		$	4.28	$	4.27	$	4.86
Granted		31,705,575			—			25,000			0.62		—		5.60
Exercised		(56,358	)		(10,000	)		(340,527	)		0.70		2.50		2.56
Forfeited		—			—			—			—		—		—
Expired		(6,371,899	)		(114,288	)		(659,322	)		4.48		3.82		12.66
Outstanding — end of year		32,502,790			7,225,472			7,349,760			0.68		4.28		4.27
Exercisable at end of year		30,190,290			7,225,472			7,149,760		$	0.67	$	4.28	$	4.32
Weighted average fair value of warrants granted during the year:	$	0.26		$	—		$	3.46

Significant Ranges of Outstanding Stock Options and Warrants

The following table summarizes additional information concerning warrants outstanding and exercisable at December 31, 2016:

						Warrants Outstanding
Range of Exercise Prices		Number of Shares		Weighted Average Remaining Contractual Life (years)		Weighted Average Exercise Price		Number of Warrants Exercisable		Weighted Average Contractual Life		Weighted Average Exercise Price
$	0.43 — 1.50		31,015,071		1.29	$	0.60		28,702,571		1.25	$	0.58
$	1.51 — 2.50		1,337,719		2.69		2.30		1,337,719		2.30		2.30
$	2.51 — 4.00		125,000		1.86		3.75		125,000		1.86		3.75
$	4.01 — 32.55		25,000		7.21		5.60		25,000		7.21		5.60
			32,502,790		1.35	$	0.68		30,190,290		1.35	$	0.67