Stock Purchase Warrants (Tables)

12 Months Ended

Dec. 31, 2013

	January 21, 2010 Class A Warrants		December 15, 2010 Warrants		August 16, 2013 Warrants
Exercise price	$	23.46	$	3.30	$	4.80
Expiration date	July 21, 2015		December 15, 2015		August 16, 2018
Total shares issuable on exercise	226,299		15,405		1,133,350

Schedule of assumptions used in calculating estimated fair value of warrants

January 2010 Class A Warrants	December 31, 2012			December 31, 2013
Closing stock price	$	25.20		$	3.23
Expected dividend rate	0		%	0		%
Expected stock price volatility	74.0		%	84.6		%
Risk-free interest rate	0.4		%	0.3		%
Expected life (years)	2.50			1.50

December 2010 Warrants	December 31, 2012			December 31, 2013
Closing stock price	$	25.20		$	3.23
Expected dividend rate	0		%	0		%
Expected stock price volatility	70.1		%	80.4		%
Risk-free interest rate	0.4		%	0.4		%
Expected life (years)	2.96			1.96

August 2013 Warrants	December 31, 2012		December 31, 2013
Closing stock price	$	—	$	3.23
Expected dividend rate	—		0		%
Expected stock price volatility	—		77.5		%
Risk-free interest rate	—		1.6		%
Expected life (years)	—		4.63

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, 2011	$	16,625
Warrants exchanged for common stock	(10,382		)
Decrease in fair value	(4,248		)
Balance at December 31, 2012	1,995
Warrant issuance	5,874
Warrant exercises	(513		)
Decrease in fair value	(5,337		)
Balance at December 31, 2013	$	2,019

- 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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