Summary of Stock Options Outstanding (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011 Year	Dec. 31, 2010
Options Exercisable
Number of options	5,055,872
Weighted average exercise price per share	$ 4.84
Aggregate intrinsic value	$ 37,468
Weighted average remaining contractual term	4.07
Options vested and expected to vest
Number of options	7,066,555
Weighted average exercise price per share	$ 5.21
Aggregate intrinsic value	49,717
Weighted average remaining contractual term	5.38
Options Outstanding
Number of options	7,381,329	7,177,191
Weighted average exercise price per share	$ 5.22	$ 4.42
Aggregate intrinsic value	$ 51,878
Weighted average remaining contractual term	5.52

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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 weighted average period between the balance sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years.

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to options outstanding under the plan as of the balance sheet date.

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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 total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of fully vested and expected to vest options outstanding.

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