Schedule of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Stock Options
Number of Shares
Number of Shares, Outstanding Beginning Balance	4,027
Granted	1,275
Cancelled	(485)
Number of Shares, Outstanding Ending Balance	4,817	4,027
Exercisable at December 31, 2012	1,994
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	$ 3.42
Weighted-Average Exercise Price Per Share, Outstanding Ending Balance	$ 4.22	$ 5.16
Weighted-Average Exercise Price Per Share, Exercisable at march 31, 2013	$ 6.26
Weighted Average Remaining Contractual Term (in years)
Weighted Average Remaining Contractual Term (in years), Outstanding	8 years 1 month 2 days	7 years 9 months 4 days
Weighted Average Remaining Contractual Term (in years), Exercisable at March 31, 2013	6 years 4 months 21 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 March 31, 2013	56	208
Aggregate Intrinsic Value of In-the-Money Options, Exercisable at March 31, 2013	23
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 December 31, 2012	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 march 31, 2013	$ 3.73
Weighted Average Remaining Contractual Term (in years)
Weighted Average Remaining Contractual Term (in years), Outstanding	8 years 9 months 26 days	9 years 3 months 18 days
Weighted Average Remaining Contractual Term (in years), Exercisable at March 31, 2013	8 years 7 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 March 31, 2013	$ 36	$ 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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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including 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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