Equity Incentive Plans and Stock-Based Compensation (Details 2) (Stock Option Plans, USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Stock Options with Market Condition	Dec. 31, 2013 Stock Options with Market Condition
Number of Shares
Outstanding, at the beginning of the period (in shares)	11,377,146		1,315,000	1,315,000
Options granted (in shares)	1,797,462	1,619,437
Options exercised (in shares)	(206,843)
Options forfeited (in shares)	(269,083)
Outstanding, at the end of the period (in shares)	12,698,682		1,315,000	1,315,000
Vested or expected to vest at the end of the period (in shares)	11,752,766
Options exercisable at the end of the period (in shares)	6,303,547
Weighted Average Exercise Price
Outstanding at the beginning of the year (in dollars per shares)	$ 11.32
Options granted (in dollars per share)	$ 8.78
Options exercised (in dollars per share)	$ 6.73
Options forfeited (in dollars per share)	$ 15.20
Outstanding at the end of the period (in dollars per shares)	$ 10.95
Vested or expected to vest at the end of the period (in dollars per share)	$ 11.25
Options exercisable at the end of the period (in dollars per share)	$ 14.94
Weighted Average Remaining Contractual Term
Outstanding	6 years 1 month 16 days
Vested or expected to vest	5 years 10 months 28 days
Options exercisable	3 years 8 months 26 days
Aggregate Intrinsic Value
Outstanding	$ 36,153
Vested or expected to vest	32,643
Options exercisable	$ 10,850
Closing stock price (in dollars per share)	$ 10.75
Total number of in-the-money outstanding (in shares)	8,833,026
Total number of in-the-money exercisable (in shares)	2,656,578