Stock Purchase Warrants (Tables)

3 Months Ended

Mar. 31, 2013

Stock Purchase Warrants

Schedule of assumptions used in calculating estimated fair value of warrants

	January 21, 2010 Class A Warrants		December 15, 2010 Warrants
Exercise price	$	2.44	$	1.25
Expiration date	July 21, 2015		December 15, 2015
Warrants outstanding	6,034,637		308,100
Total shares issuable on exercise	4,525,978		308,100

	December 31, 2012			March 31, 2013
January 2010 Class A Warrants
Closing stock price	$	1.26		$	0.70
Expected dividend rate	0		%	0		%
Expected stock price volatility	74.0		%	59.3		%
Risk-free interest rate	0.4		%	0.3		%
Expected life (years)	2.50			2.25

	December 31, 2012			March 31, 2013
December 2010 Warrants
Closing stock price	$	1.26		$	0.70
Expected dividend rate	0		%	0		%
Expected stock price volatility	70.1		%	77.9		%
Risk-free interest rate	0.4		%	0.3		%
Expected life (years)	2.96			2.71

Summary of change in estimated fair value of warrant liabilities

The following table summarizes the change in the estimated fair value of the Company’s warrant liabilities (in thousands):

Warrant Liabilities
Balance at December 31, 2012	$	1,995
Decrease in fair value	(1,619		)
Balance at March 31, 2013	$	376