Stock-based Compensation - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value of options granted		$ 2.95
Options vested and expected to vest	6,424,796		6,663,152
Options vested and expected to vest, weighted average exercise price	$ 5.19		$ 5.08
Options vested and expected to vest, weighted average contractual life	6 years 10 months 24 days		7 years 1 month 6 days
Options outstanding, aggregate intrinsic value	$ 57,700,000
Options exercisable, aggregate intrinsic value	40,500,000
Aggregate intrinsic value of options exercised	3,200,000	18,000
Total fair value of shares vested	1,100,000	202,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 9,300,000
Unrecognized compensation expense expected to be recognized	3 years 2 months 27 days

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Aggregate unrecognized cost of option awards made to employees under a stock option plan or plans, that have yet to vest.

+ References

No definition available.

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- Definition

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.

+ References

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- Definition

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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- Definition

Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of options outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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- Definition

As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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- Definition

Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

+ References

No definition available.

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