Common Stock Warrant Liability

3 Months Ended

Mar. 31, 2013

Common Stock Warrant Liability [Abstract]

Common Stock Warrant Liability

Note 7 – Common Stock Warrant Liability

We account for common stock warrants in accordance with applicable accounting guidance provided in ASC 815, either as derivative liabilities or as equity instruments depending on the specific terms of the warrant agreement.

The registered warrants that we issued in May 2009 and February 2010 have been classified as derivative liabilities and reported, at each balance sheet date, at estimated fair value determined using the Black-Scholes option-pricing model. The February 2011 five-year warrants have been classified as derivative liabilities and reported, at each balance sheet date, at estimated fair value determined using a trinomial pricing model. (See, Note 8 in our 2012 Form 10-K for a discussion of the common stock warrant liability.)

Selected terms and estimated fair value of warrants accounted for as derivative liabilities at March 31, 2013 are as follows:

						Fair Value of Warrants (in thousands)
Issuance Date	Number of Warrant Shares		Exercise Price		Warrant Expiration Date	Issuance Date		March 31, 2013
5/13/2009		466,667	$	17.25	5/13/2014	$	3,360	$	–
2/23/2010		916,669		12.75	2/23/2015		5,701		33
2/22/2011		4,948,750		2.80	2/22/2016		8,004		6,110

Changes in the estimated fair value of warrants classified as derivative liabilities are reported in the accompanying Consolidated Statement of Operations as the "Change in fair value of common stock warrants."