Stock-Based Compensation (Details 3) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Number of shares
Outstanding at the beginning of the period (in shares)	17,617
Granted (in shares)	294
Exercised (in shares)	(378)
Forfeited (in shares)	(78)
Outstanding at the end of the period (in shares)	17,455
Exercisable at the end of the period (in shares)	14,529
Vested and expected to vest at the end of the period (in shares)	17,304
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 2.56
Granted (in dollars per share)	$ 6.73
Exercised (in dollars per share)	$ 2.24
Forfeited (in dollars per share)	$ 3.42
Outstanding at the end of the period (in dollars per share)	$ 2.63
Exercisable at the end of the period (in dollars per share)	$ 2.27
Vested and expected to vest at the end of the period (in dollars per share)	$ 2.61
Aggregate intrinsic value
Outstanding at the beginning of the period (in dollars)	$ 74,329
Outstanding at the end of the period (in dollars)	81,093
Exercisable at the end of the period (in dollars)	72,740
Vested and expected to vest at the end of the period (in dollars)	$ 80,782