Information Regarding Stock Options Outstanding Stock Options Vested and Expected to Vest and Stock Options Exercisable (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Number of Shares
Stock options outstanding	8,504	7,362	7,007	6,565
Stock options vested and expected to vest	8,140	6,900	6,705
Stock options exercisable	5,150	4,058	4,323
Weighted Average Exercise Price
Stock options outstanding	$ 3.40	$ 4.70	$ 6.42	$ 7.38
Stock options vested and expected to vest	$ 3.42	$ 4.86	$ 6.60
Stock options exercisable	$ 3.77	$ 6.70	$ 8.93
Weighted Average Remaining Contractual
Stock options outstanding	6 years 7 months 2 days	6 years 7 months 28 days	6 years 2 months 19 days
Stock options vested and expected to vest	6 years 5 months 27 days	6 years 5 months 19 days	6 years 29 days
Stock options exercisable	5 years 5 months 5 days	5 years	4 years 9 months 29 days
Aggregate intrinsic value
Stock options outstanding	$ 5,433	$ 4,065	$ 2,761
Stock options vested and expected to vest	5,310	3,835	2,610
Stock options exercisable	$ 3,582	$ 1,902	$ 922

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

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