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Disclosure Of Compensation Related Costs, Share Based Payments (Schedule Of Issuance Of Stock Option Plans) (Details) (USD $)	9 Months Ended
	Jan. 31, 2012
Disclosure Of Compensation Related Costs, Share Based Payments [Abstract]
Number of Shares, Outstanding April 30, 2011	775,609
Number of Shares, Granted	441,000
Number of Shares, Exercised	(96,700)
Number of Shares, Forfeited	(3,500)
Number of Shares, Outstanding at January 31, 2012	1,116,409
Weighted Average Exercise Price, Outstanding April 30, 2011	$ 23.38
Weighted Average Exercise Price, Granted	$ 44.39
Weighted Average Exercise Price, Exercised	$ 19.93
Weighted Average Exercise Price, Forfeited	$ 36.19
Weighted Average Exercise Price, Outstanding at January 31, 2012	$ 31.94

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The weighted average price at which option holders acquired shares when converting their stock options into shares under the plan during the reporting period.

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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 weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated during the reporting period due to noncompliance with plan terms during the reporting period.

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

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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 stock options awarded under the plan during the reporting 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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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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