Warrants to Purchase Preferred Stock (Tables)

6 Months Ended

Jun. 30, 2013

Warrants to purchase preferred stock

Summary of the Company's outstanding warrants to purchase preferred stock

						Fair Value as of
			Exercise		Warrants	December 31,		June 30,
	Grant Date	Expiration Date	Price		Outstanding	2012		2013
								(unaudited)
Series A	June 7, 2007	June 7, 2017	$	1.27	35,520	$	299	$	277
Series B-1	December 8, 2008	December 7, 2018	$	4.86	33,930	246		198
Series C	February 8, 2010	February 8, 2020	$	3.79	31,659	245		208
Series 1	December 8, 2010	June 30, 2017	$	2.46	31,130	256		211
Series 3	December 8, 2010	February 6, 2015	$	5.75	8,694	57		32
					140,933	$	1,103	$	926

- 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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