Schedule of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2013	Dec. 31, 2012
Stock Options
Number of Shares
Number of Shares, Outstanding Beginning Balance	4,027
Granted	1,290
Cancelled	(626)
Number of Shares, Outstanding Ending Balance	4,691	4,027
Exercisable at June 30, 2013	2,200
Weighted Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Outstanding Beginning Balance	$ 5.16
Weighted-Average Exercise Price Per Share, Granted	$ 0.95
Weighted-Average Exercise Price Per Share, Cancelled	$ 3.33
Weighted-Average Exercise Price Per Share, Outstanding Ending Balance	$ 4.24	$ 5.16
Weighted-Average Exercise Price Per Share, Exercisable at June 30, 2013	$ 5.89
Weighted Average Remaining Contractual Term (in years)
Weighted Average Remaining Contractual Term (in years), Outstanding	7 years 9 months 29 days	7 years 9 months 4 days
Weighted Average Remaining Contractual Term (in years), Exercisable at June 30, 2013	6 years 4 months 28 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value of In-the-Money Options, Outstanding at December 31, 2012	$ 208
Aggregate Intrinsic Value of In-the-Money Options, Outstanding at June 30, 2013		208
Aggregate Intrinsic Value of In-the-Money Options, Exercisable at June 30, 2013
Stock Options That Contain Performance And Market Based Conditions
Number of Shares
Number of Shares, Outstanding Beginning Balance	953
Cancelled	(81)
Number of Shares, Outstanding Ending Balance	872	953
Exercisable at June 30, 2013	476
Weighted Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Outstanding Beginning Balance	$ 3.73
Weighted-Average Exercise Price Per Share, Cancelled	$ 5.14
Weighted-Average Exercise Price Per Share, Outstanding Ending Balance	$ 3.60	$ 3.73
Weighted-Average Exercise Price Per Share, Exercisable at June 30, 2013	$ 3.73
Weighted Average Remaining Contractual Term (in years)
Weighted Average Remaining Contractual Term (in years), Outstanding	8 years 6 months 26 days	9 years 3 months 18 days
Weighted Average Remaining Contractual Term (in years), Exercisable at June 30, 2013	8 years 4 months 6 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value of In-the-Money Options, Outstanding at December 31, 2012	74
Aggregate Intrinsic Value of In-the-Money Options, Outstanding at June 30, 2013		$ 74

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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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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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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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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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