Stockholders' Equity

6 Months Ended

Jun. 30, 2016

Equity [Abstract]

Stockholders' Equity

4. Stockholders’ Equity

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

	Exercise Price		June 30, 2016		December 31, 2015
Expiration Date			(in thousands)
04/16/18	$	3.40		1,460		1,460
09/23/18	$	2.80		147		147
02/18/19	$	2.75		1,872		1,872
02/11/19	$	2.56		293		293
08/28/19	$	2.90		2,700		2,700
06/14/17	$	3.70		216		216
03/25/20	$	1.71		2,920		2,920
03/20/20	$	2.13		234		234
Total Warrants Outstanding				9,842		9,842

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 Price		Weighted Average Remaining Contractual Life		Aggregate Intrinsic Value
	(in thousands)								(years)		(in thousands)
Balance at December 31, 2015		2,695			2,031		$	2.01		8.44
Options granted		(2,223	)		2,223		$	0.72
Options forfeited		115			(115	)	$	3.27
Balance at June 30, 2016		587			4,139		$	1.53		8.55	$	14
Vested and exercisable at June 30, 2016					864		$	2.40		6.79	$	—
Vested and expected to vest at June 30, 2016					2,973		$	1.41		8.30	$	11
Unvested at June 30, 2016					3,275		$	1.30

As of June 30, 2016, there was approximately $1.4 million of unrecognized compensation cost related to stock option awards that is expected to be recognized as expense over a weighted average period of approximately 2.8 years.

The fair values for the stock options granted were estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions for the periods indicated:

	Six months ended June 30,
	2016			2015
Risk-free interest rate		1.5	%		1.7	%
Expected life (years)		6.0			6.0
Expected volatility		89	%		92	%
Dividend yield		0	%		0	%