Stockholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of stock option activity
Option outstanding, Number of Shares, Beginning Balance	8,374,190
Option granted, Number of Shares	1,352,150
Options exercised, Number of Shares	(326,688)
Options canceled, Number of Shares	(215,306)
Option Outstanding, Number of Shares, Ending Balance	9,184,346	8,374,190
Options vested and expected to vest at December 31, 2012, Number of Shares	8,806,544
Options exercisable at December 31, 2012, Number of Shares	6,435,730
Options outstanding, Weighted-Average Exercise per Share Price, Beginning Balance	$ 6.28
Options granted, Weighted-Average Exercise per Share Price	$ 5.38
Options exercised, Weighted-Average Exercise per Share Price	$ 3.73
Options canceled, Weighted-Average Exercise per Share Price	$ 7.04
Options outstanding, Weighted-Average Exercise per Share Price, Ending Balance	$ 6.21	$ 6.28
Options vested and expected to vest at December 31, 2012, Weighted-Average Exercise Per Share Price	$ 6.25
Options exercisable at December 31, 2012, Weighted Average Exercise per Share Price	$ 6.62
Options outstanding, Weighted-Average Remaining Contractual Term, Beginning Balance	6 years 5 months 16 days	6 years 9 months 11 days
Options outstanding, Weighted-Average Remaining Contractual Term, Ending Balance	6 years 5 months 16 days	6 years 9 months 11 days
Options vested and expected to vest at December 31, 2012, Weighted Average Remaining Contractual Term	6 years 3 months 22 days
Options exercisable at December 31, 2012, Weighted-Average Remaining Contractual Term	5 years 4 months 28 days
Options outstanding, Aggregate Intrinsic Value	$ 8,821
Options vested and expected to vest at December 31, 2012, Aggregate Intrinsic Value	8,523
Options exercisable at December 31, 2012, Aggregate Intrinsic Value	$ 6,679	$ 1,000	$ 500