Disclosure of Compensation Related Costs, Share Based Payments (Stock Option Activity) (Details) (USD $)	6 Months Ended
Oct. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Exercise Price, Outstanding at April 30, 2012	$ 32.59
Weighted Average Exercise Price, Granted
Weighted Average Exercise Price, Exercised	$ 24.13
Weighted Average Exercise Price, Forfeited	$ 14.08
Weighted Average Exercise Price, Outstanding at October 31, 2012	$ 34.02
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding	66,198
Number of Shares, Granted	46,998
Number of Shares, Exercised
Number of Shares, Forfeited
Number of Shares, Outstanding	113,196
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding	1,053,509
Number of Shares, Granted
Number of Shares, Exercised	(151,098)
Number of Shares, Forfeited	(500)
Number of Shares, Outstanding	901,911

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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.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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

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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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