Stock Awards (Details) (USD $)	9 Months Ended
	Sep. 30, 2012
Summary of stock option activity
Number of Shares, Outstanding at December 31, 2011	39,601,640
Number of Shares, Granted	7,085,680
Number of Shares, Exercised	(5,523,840)
Number of Shares, Forfeited	(3,543,871)
Number of shares, Cancelled	(340,167)
Number of Shares, Outstanding at September 30, 2012	37,279,442
Number of Shares, Vested and expected to vest as of September 30, 2012	36,593,833
Number of Shares, Vested and exercisable as of September 30, 2012	11,607,655
Weighted-Average Exercise Price, Outstanding at December 31, 2011	$ 2.20
Weighted-Average Exercise Price, Granted	$ 13.48
Weighted-Average Exercise Price, Exercised	$ 0.61
Weighted-Average Exercise Price, Forfeited	$ 3.22
Weighted-Average Exercise Price Cancelled	$ 1.90
Weighted-Average Exercise Price, Outstanding at September 30, 2012	$ 4.48
Weighted-Average Exercise Price, Vested and expected to vest as of September 30, 2012	$ 4.43
Weighted-Average Exercise Price, Vested and exercisable as of September 30, 2012	$ 1.77
Weighted-Average Remaining Contractual Term, Outstanding at September 30, 2012	8 years 6 months 4 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest as of September 30, 2012	8 years 6 months
Weighted-Average Remaining Contractual Term, Vested and exercisable as of September 30, 2012	7 years 6 months 29 days
Aggregate Intrinsic Value, Outstanding at September 30, 2012	$ 1,274,895,101
Aggregate Intrinsic Value, Vested and expected to vest as of September 30, 2012	1,253,278,350
Aggregate Intrinsic Value, Vested and exercisable as of September 30, 2012	$ 428,488,416