Share-Based Compensation - Activity Related to Stock Options (Detail) (USD $)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Number of shares, Outstanding options, Beginning balance	1,236,075	1,097,620
Number of shares, Outstanding options, Granted	75,722	217,230
Number of shares, Outstanding options, Exercised	(91,348)	(34,278)
Number of shares, Outstanding options, Forfeited or expired	(14,270)	(3,258)
Number of shares, Outstanding options, Ending balance	1,206,179	1,277,314
Number of shares, Exercisable options	777,945	796,208
Weighted average exercise price, Outstanding options, Beginning balance	$ 51.48	$ 50.14
Weighted average exercise price, Outstanding options, Granted	$ 52.36	$ 51.78
Weighted average exercise price, Outstanding options, Exercised	$ 34.81	$ 28.98
Weighted average exercise price, Outstanding options, Forfeited or expired	$ 57.19	$ 51.19
Weighted average exercise price, Outstanding options, Ending balance	$ 52.73	$ 50.98
Weighted average exercise price, Exercisable options	$ 52.21	$ 42.59
Weighted average remaining contract life, Outstanding options, Ending period	5 years 1 month 6 days	5 years 2 months 12 days
Weighted average remaining contract life, Outstanding exercisable, Ending period	3 years 4 months 24 days
Weighted average remaining contract life, Exercisable options		3 years 2 months 12 days

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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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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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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 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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Weighted average remaining contractual term of exercisable stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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

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