Summary of Stock Option Activity and Related Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share based compensation arrangement by share based payment award outstanding
Number of options, outstanding beginning	17,177,000
Number of options, granted	2,656,000
Number of options, exercised	(232,448)	(96,267)	(54,921)
Number of options, expired	(2,399,000)
Number of options, forfeited	(1,601,000)
Number of options, outstanding ending	15,601,000	17,177,000
Number of options, exercisable	10,978,000
Number of options, vested and expected to vest	14,453,000
Share based compensation arrangement by share based payment award outstanding weighted average exercise price
Weighted average exercise price, outstanding beginning	$ 4.47
Weighted average exercise price, granted	$ 2.62
Weighted average exercise price, exercised	$ 2.36
Weighted average exercise price, expired	$ 6.29
Weighted average exercise price, forfeited	$ 2.89
Weighted average exercise price, outstanding ending	$ 4.00	$ 4.47
Weighted average exercise price, exercisable	$ 4.53
Weighted average exercise price, vested and expected to vest	$ 4.11
Weighted average remaining contractual term, outstanding	5 years 3 months 18 days
Weighted average remaining contractual term, exercisable	4 years
Weighted average remaining contractual term, vested and expected to vest	5 years
Aggregate intrinsic value, outstanding	$ 4,787
Aggregate intrinsic value, exercisable	2,136
Aggregate intrinsic value, vested and expected to vest	$ 4,128

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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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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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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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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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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