Option Transactions (Detail) (USD $)	3 Months Ended
Aug. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares Under Option, Outstanding at May 31, 2012	1,508,533
Shares Under Option, Exercised	(22,076)
Shares Under Option, Canceled	(24,000)
Shares Under Option, Outstanding at November 30, 2012	1,462,457
Shares Under Option, Exercisable at November 30, 2012	840,137
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted-Average Option Price, Outstanding at May 31, 2012	$ 40.68
Weighted-Average Option Price, Exercised	$ 41.92
Weighted-Average Option Price, Canceled	$ 66.00
Weighted-Average Option Price, Outstanding at November 30, 2012	$ 40.24
Weighted-Average Option Price, Exercisable at November 30, 2012	$ 45.39

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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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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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 could have acquired the underlying shares with respect to stock options that were terminated.

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

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