Stockholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Summary of stock option activity
Number of Shares, Outstanding-December 31, 2012	8,251,850
Number of Shares, Granted	698,576
Number of Shares, Exercised	(1,291,004)
Number of Shares, Canceled or expired	(115,766)
Number of Shares, Outstanding-March 31, 2013	7,543,656
Number of Shares, Options vested and expected to vest as of March 31, 2013	7,131,220
Number of Shares, Options vested and exercisable as of March 31, 2013	3,483,625
Weighted- Average Exercise Price, Outstanding-December 31, 2012	$ 10.50
Weighted- Average Exercise Price, Granted	$ 169.94
Weighted- Average Exercise Price, Exercised	$ 9.35
Weighted- Average Exercise Price, Canceled or expired	$ 12.94
Weighted- Average Exercise Price, Outstanding-March 31, 2013	$ 25.43
Weighted- Average Exercise Price, Options vested and expected to vest as of March 31, 2013	$ 22.48
Weighted- Average Exercise Price, Options vested and exercisable as of March 31, 2013	$ 5.38
Weighted average remaining contractual term, outstanding	7 years 1 month 24 days
Weighted average remaining contractual term, options vested and expected to vest	7 years 0 months 25 days
Weighted average remaining contractual, options vested and exercisable	6 years 2 months 19 days
Aggregate Intrinsic Value, Outstanding-March 31, 2013	$ 1,136,374
Aggregate Intrinsic Value, Options vested and expected to vest as of March 31, 2013	1,095,246
Aggregate Intrinsic Value, Options vested and exercisable as of March 31, 2013	$ 594,569