Stock Options and Equity-Classified Warrants (Tables)

12 Months Ended

Dec. 31, 2017

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

Schedule of Total Stock-Based Compensation Expense from Stock Options

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

	Years Ended December 31,
	2017		2016		2015
Research and development - employee	$	549,315	$	1,822,508	$	1,590,267
General and administrative - employee		1,909,729		4,661,795		5,568,537
Total employee stock-based compensation	$	2,459,044	$	6,484,303	$	7,158,804
Research and development – non-employee	$	11,600	$	—	$	—
General and administrative – non-employee		410,400		235,764		225,852
Total non-employee stock-based compensation	$	422,000	$	235,764	$	225,852

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, 2017:

Range of Exercise Prices		Number of Options		Weighted Average RemainingContractual Life (years)		Weighted Average Exercise Price		Number of Options Exercisable		Weighted Average Contractual Life		Weighted Average Exercise Price
$	1.50 — 1.75		829,702		9.96	$	1.75		400,000		9.96	$	1.75
$	1.76 —11.00		720,970		7.98		4.76		469,910		7.47		5.92
$	11.01 — 15.00		776,290		7.20		13.92		667,290		7.07		13.80
$	15.01 — 195.30		538,550		5.44		27.36		537,578		5.43		27.36
			2,865,512		7.86	$	10.62		2,074,778		7.29	$	13.21

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:

	2017			2016			2015
Risk-free interest rate		2.04% - 2.35	%		1.20% - 2.26	%		1.74% - 2.12	%
Expected volatility		86% - 92	%		74% - 88	%		74% - 85	%
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:

	2017			2016		2015
Risk-free interest rate		2.30% - 2.35	%		—		—
Expected volatility		92.00	%		—		—
Expected lives (years)		10			—		—
Expected dividend yield		—			—		—

Stock Options and Warrants Activity

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

	Stock Options								Weighted Average Exercise Price
	2017		2016			2015			2017		2016		2015
Outstanding — beginning of year		100,000		105,952			115,357		$	16.41	$	18.12	$	20.82
Granted		273,333		—			—			1.78		—		—
Exercised		—		—			—			—		—		—
Expired/Forfeited		—		(5,952	)		(9,405	)		—		46.62		51.24
Outstanding — end of year		373,333		100,000			105,952			5.70		16.41		18.12
Exercisable at end of year		373,333		100,000			105,952		$	5.70	$	16.41	$	18.12
Weighted average fair value of stock options granted during the year:	$	1.54	$	—		$	—

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
	2017			2016			2015			2017		2016		2015
Outstanding — beginning of year		2,813,280			2,263,977			1,559,765		$	14.14	$	18.66	$	16.98
Granted		591,369			809,500			765,000			1.87		3.54		15.66
Exercised		(19,213	)		(55,000	)		(47,857	)		2.58		12.84		12.30
Forfeited		(874,210	)		(196,054	)		—			13.11		20.94		—
Expired		(19,047	)		(9,143	)		(12,931	)		56.88		48.18		33.48
Outstanding — end of year		2,492,179			2,813,280			2,263,977			11.35		14.14		18.66
Exercisable at end of year		1,701,445			1,811,320			1,336,694		$	14.85	$	17.70	$	20.70
Weighted average fair value of stock options granted during the year:	$	1.47		$	2.58		$	11.28

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
	2017			2016			2015			2017		2016		2015
Outstanding — beginning of year		5,417,155			1,204,245			1,224,960		$	4.08	$	25.68	$	25.62
Granted		584,554			5,284,263			—			6.31		3.72		—
Exercised		(861,581	)		(9,393	)		(1,667	)		3.66		4.20		15.00
Forfeited		—			—			—			—		—		—
Expired		(1,159,347	)		(1,061,960	)		(19,048	)		4.92		26.88		22.92
Outstanding — end of year		3,980,781			5,417,155			1,204,245			4.26		4.08		25.68
Exercisable at end of year		3,626,613			5,031,715			1,204,245		$	4.23	$	4.02	$	25.68
Weighted average fair value of warrants granted during the year:	$	1.65		$	1.56		$	—

Significant Ranges of Outstanding Stock Options and Warrants

The following table summarizes additional information concerning warrants outstanding and exercisable at December 31, 2017:

						Warrants Outstanding
Range of Exercise Prices		Number of Shares		Weighted Average RemainingContractual Life (years)		Weighted Average Exercise Price		Number of Warrants Exercisable		Weighted Average Contractual Life		Weighted Average Exercise Price
$	3.00 — 6.00		3,252,137		0.60	$	3.19		2,918,803		0.62	$	3.08
$	6.01 — 9.00		500,000		1.07		6.60		500,000		1.07		6.60
$	9.01 — 12.00		83,335		3.11		10.44		62,501		3.11		10.44
$	12.01 — 33.60		145,309		1.19		16.65		145,309		1.19		16.65
			3,980,781		0.74	$	4.26		3,626,613		0.75	$	4.23