Stock-Based Compensation Expense - Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Annual Activity of Stock Option Plans [Line Items]
Outstanding, Shares	4,473
Granted	34
Exercised	(745)
Forfeited or expired	(87)
Outstanding, Shares	3,675
Exercisable, Shares	1,265
Outstanding, Weighted-Average Exercise Price	$ 24.48
Granted, Weighted-Average Exercise Price	$ 37.24
Exercised, Weighted-Average Exercise Price	$ 20.89
Forfeited or expired, Weighted-Average Exercise Price	$ 22.77
Outstanding, Weighted-Average Exercise Price	$ 25.37
Exercisable, Weighted-Average Exercise Price	$ 21.12
Outstanding, Weighted-Average Remaining Contractual Term (in years)	7 years 3 months 18 days
Exercisable, Weighted-Average Remaining Contractual Term (in years)	5 years 7 months 6 days
Outstanding, Aggregate Intrinsic Value	$ 34,143
Exercisable, Aggregate Intrinsic Value	$ 17,123

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Share based compensation arrangement by share based payment award options exercisable aggregate intrinsic value.

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- Definition

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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- Definition

For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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Net number of share options (or share units) granted during the period.

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- Definition

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

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- Definition

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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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees can acquire the shares reserved for issuance on stock options awarded.

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Number of share options (or share units) exercised during the current period.

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