Stock-Based Compensation (Details 4) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shares
Outstanding at the beginning of the period (in shares)	17,617
Granted (in shares)	3,251
Exercised (in shares)	(2,622)
Cancelled (in shares)	(180)
Outstanding at the end of the period (in shares)	18,066	17,617
Number of shares vested and expected to vest	17,741
Number of stock option exercisable	13,616
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 2.56
Grants (in dollars per share)	$ 7.45
Exercises or releases (in dollars per share)	$ 2.06
Cancelled (in dollars per share)	$ 4.34
Outstanding at the end of the period (in dollars per share)	$ 3.50	$ 2.56
Weighted average exercise price of shares vested and expected to vest	$ 3.43
Weighted average exercise price for exercisable option	$ 2.52
Weighted Average Remaining Contractual Term
Outstanding at the end of the period	6 years 6 months 14 days
Vested and expected to vest	6 years 5 months 26 days
Exercisable	5 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 51,486,000
Options exercisable (in dollars)	49,155,000
Shares vested and expected to vest (in dollars)	51,434,000
Additional disclosures
Aggregate intrinsic value of options exercised	13,721,000	1,392,000	145,000
Unrecognized compensation cost related to nonvested stock awards	$ 15,924,000
Weighted average period over which unrecognized compensation cost is expected to be recognized	2 years 1 month 6 days