Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011 Year
Number of Shares
Outstanding January 1, 2011	10,028,000
Granted	4,445,000
Cancelled/Expired	(328,000)
Exercised	(2,273,221)
Outstanding, December 31, 2011	11,871,000
Exercisable, December 31, 2011	3,495,000
Vested and Expected to Vest, December 31, 2011	11,787,000
Available for future grant at December 31, 2011	2,231,000
Weighted Average Exercise Price
Outstanding January 1, 2011	$ 2.69
Granted	$ 10.53
Cancelled/Expired	$ 16.43
Exercised	$ 2.27
Outstanding, December 31, 2011	$ 5.33
Exercisable, December 31, 2011	$ 2.69
Vested and Expected to Vest, December 31, 2011	$ 5.32
Weighted Average Remaining Contractual Term
Outstanding, December 31, 2011	8.68
Exercisable, December 31, 2011	8.09
Vested and Expected to Vest, December 31, 2011	8.68
Aggregate Intrinsic Value
Outstanding, December 31, 2011	$ 40,475
Exercisable, December 31, 2011	17,972
Vested and Expected to Vest, December 31, 2011	$ 40,250

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance sheet date.

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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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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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The weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated during the reporting period due to noncompliance with plan terms during the reporting period.

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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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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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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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