Activity Under Equity Incentive Plans Related to Stock Options (Detail) - 2008 Equity Incentive Plan shares in Thousands	12 Months Ended
Dec. 31, 2017 $ / shares shares
Activity under the Company's equity incentive plans related to stock options
Number of Options Outstanding, Beginning Balance \| shares	15,787
Granted, Number of Options Outstanding \| shares	3,304
Forfeited, Number of Options Outstanding \| shares	(1,087)
Expired, Number of Options Outstanding \| shares	(322)
Exercised, Number of Options Outstanding \| shares	(544)
Number of Options Outstanding, Ending Balance \| shares	17,138
Weighted Average Exercise Price per Share
Weighted Average Exercise Price per Share, Beginning Balance \| $ / shares	$ 4.39
Granted, Weighted Average Exercise Price per Share \| $ / shares	4.14
Forfeited, Weighted Average Exercise Price per Share \| $ / shares	5.18
Expired, Weighted Average Exercise Price per Share \| $ / shares	7.80
Exercised, Weighted Average Exercise Price per Share \| $ / shares	3.11
Weighted Average Exercise Price per Share, Ending Balance \| $ / shares	$ 4.27

Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(4)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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

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

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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