Stock Option Activity and Related Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2013
Options Outstanding
Outstanding at December 31, 2012	6,730,520
Granted
Exercised	(218,484)
Forfeited	(28,227)
Outstanding at March 31, 2013	6,483,809
Weighted average exercise price
Outstanding at December 31, 2012	$ 5.10
Granted
Exercised	$ 1.83
Forfeited	$ 5.44
Outstanding at March 31, 2013	$ 5.21
Options Exercisable
Outstanding at December 31, 2012	3,352,116
Outstanding at March 31, 2013	3,543,365
Exercisable Weighted Average Exercise Price per Share
Outstanding at December 31, 2012	$ 2.20
Outstanding at March 31, 2013	$ 2.70

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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-Name Accounting Standards Codification

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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.

+ References

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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 option holders acquired shares when converting their stock options into shares.

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