Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Beginning Balance, Shares	746
Granted, Shares	217
Exercised, Shares	(195)
Forfeited, Shares	(95)
Expired or canceled, Shares	(4)
Outstanding, Ending Balance, Shares	669
Exercisable, Ending Balance, Shares	381
Outstanding, Beginning Balance, Outstanding Weighted-Average Exercise Price	$ 43.47
Granted, Outstanding Weighted-Average Exercise Price	$ 70.47
Exercised, Outstanding Weighted-Average Exercise Price	$ 30.85
Forfeited, Outstanding Weighted-Average Exercise Price	$ 66.44
Expired or canceled, Outstanding Weighted-Average Exercise Price	$ 71.85
Outstanding, Ending Balance, Outstanding Weighted-Average Exercise Price	$ 52.46
Exercisable, Ending Balance, Outstanding Weighted-Average Exercise Price	$ 40.94
Outstanding, Ending Balance, Aggregate Intrinsic Value	$ 9,215
Exercisable, Ending Balance, Aggregate Intrinsic Value	$ 8,465
Outstanding, Ending Balance, Weighted-Average Remaining Contractual Life	4 years 2 months 12 days
Exercisable, Ending Balance, Weighted-Average Remaining Contractual Life	3 years

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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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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

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

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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 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 could have acquired the underlying shares with respect to stock options of the plan that expired.

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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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