Common Stock (Tables)

6 Months Ended

Jun. 30, 2012

Common Stock [Abstract]

Common stock outstanding and reserved shares of common stock for future issuance

A summary of the stock option activity for the six months ended June 30, 2012 is as follows:

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at December 31, 2011		39,601,640		$	2.20
Granted		6,547,060			11.93
Exercised		(5,192,303	)		0.61
Forfeited		(2,532,977	)		2.62
Cancelled		(288,500	)		1.82
Outstanding at June 30, 2012		38,134,900		$	4.06		8.73 years	$	783,334,667
Vested and expected to vest as of June 30, 2012		37,328,778		$	4.02		8.72 years	$	768,157,382
Vested and exercisable as of June 30, 2012		8,792,753		$	1.37		7.37 years	$	204,228,567