Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2019

Summary of the Company's Outstanding Common Stock Warrants

The following is a summary of the Company’s outstanding common stock warrants:

			March 31, 2019		December 31, 2018
Expiration Date	Exercise Price		(number of shares in thousands)
02/11/19	$	2.56		—		293
02/18/19	$	2.75		—		1,872
08/28/19	$	2.90		2,700		2,700
03/20/20	$	2.13		234		234
03/25/20	$	1.71		2,920		2,920
04/12/20	$	0.40		7,437		7,437
06/20/20	$	0.40		7,437		7,437
04/30/23	$	0.20		1,488		1,488
Total Warrants Outstanding				22,216		24,381

Summary of the Company's Stock Option Activity under 2017,2015 and 2005 Plans

The following is a summary of the Company’s stock option activity under its equity incentive plans:

	Options Available for Grant		Options Outstanding			Weighted Average Exercise		Weighted Average Remaining Contractual Life		Aggregate Intrinsic Value
	(in thousands)					Price		(years)		(in thousands)
Balance at December 31, 2018		2,465		6,785		$	0.75		7.1
Options forfeited		11		(11	)	$	4.78
Balance at March 31, 2019		2,476		6,774		$	0.74		6.9	$	—
Vested and exercisable at March 31, 2019				4,335		$	0.72		6.9	$	—
Vested and expected to vest at March 31, 2019				6,461		$	0.59		6.9	$	—
Unvested at March 31, 2019				2,439		$	0.78

- Definition

Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable.

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