Net Loss Per Share - Weighted Average Number of Common Shares Outstanding (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Numerator:
Net loss for basic earnings per share	$ (4,561)us-gaap_NetIncomeLoss	$ (6,673)us-gaap_NetIncomeLoss
Diluted net loss applicable to common stockholders	$ (4,561)	$ (6,673)
Denominator:
Weighted average common shares outstanding (in shares)	99,849	97,668
Weighted average unvested common shares subject to repurchase (in shares)	(829)	(830)
Weighted average common shares outstanding—basic (in shares)	99,020	96,838
Effect of dilutive securities:
Shares used in calculating diluted net loss per share (in shares)	99,020	96,838
Net loss per share:
Net loss per basic share (In dollars per share)	$ (0.05)us-gaap_EarningsPerShareBasic	$ (0.07)us-gaap_EarningsPerShareBasic
Net loss per diluted share (in dollars per share)	$ (0.05)us-gaap_EarningsPerShareDiluted	$ (0.07)us-gaap_EarningsPerShareDiluted

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of shares of common stock subject to repurchase or cancellation determined by relating the portion of time within a reporting period that these shares have been outstanding to the total time in that period. Common stock subject to repurchase are outstanding common shares that are contingently returnable (that is, subject to recall).

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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