Equity Incentive Plans and Stock-Based Compensation (Details 2) (Employee Stock Option [Member], USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Employee Stock Option [Member]
Number of Shares
Outstanding, at the beginning of the period (in shares)	11,441,646
Options granted (in shares)	362,335	1,797,462
Options exercised (in shares)	(217,241)
Options forfeited (in shares)	(518,778)
Outstanding, at the end of the period (in shares)	11,067,962
Vested or expected to vest at the end of the period (in shares)	10,524,492
Options exercisable at the end of the period (in shares)	6,207,537
Weighted Average Exercise Price
Outstanding at the beginning of the year (in dollars per shares)	$ 10.73
Options granted (in dollars per share)	$ 11.27
Options exercised (in dollars per share)	$ 6.90
Options forfeited (in dollars per share)	$ 16.37
Outstanding at the end of the period (in dollars per shares)	$ 10.55
Vested or expected to vest at the end of the period (in dollars per share)	$ 10.64
Options exercisable at the end of the period (in dollars per share)	$ 12.84
Weighted Average Remaining Contractual Term
Outstanding	5 years 11 months 12 days
Vested or expected to vest	5 years 9 months 22 days
Options exercisable	4 years 3 months 18 days
Aggregate Intrinsic Value
Outstanding	$ 45,831
Vested or expected to vest	43,741
Options exercisable	$ 21,336

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Weighted average price of options that were either forfeited or expired.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Net number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of fully vested and expected to vest options that are exercisable.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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