Employee Stock Plans (Stock Options And SARs Transactions) (Details) (Stock Options And SARs [Member], USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Jul. 31, 2011
Stock Options And SARs [Member]
Options, Outstanding, beginning of period	1,833,000
Options Granted	48,000
Options, Exercised	(115,000)
Options, Forfeited/expired	(65,000)
Options, Outstanding, end of period	1,701,000
Options Exercisable	1,201,000
Weighted-Average Exercise Price, Outstanding, April 30, 2011	$ 13.78
Weighted-Average Exercise Price, Granted	$ 22.71
Weighted-Average Exercise Price, Exercised	$ 14.72
Weighted-Average Exercise Price, Forfeited/expired	$ 17.05
Weighted-Average Exercise Price, Outstanding, July 31, 2011	$ 13.82
Weighted-Average Exercise Price, Exercisable, Outstanding, July 31, 2011	$ 14.03
Weighted-Average Remaining Contractual Life (In Years), Outstanding, July 31, 2011	3.87
Weighted-Average Remaining Contractual Life (In Years), Exercisable, July 31, 2011	3.20
Aggregate Intrinsic Value, Outstanding	$ 13,192
Aggregate Intrinsic Value, Exercisable	$ 9,045

The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance sheet date.

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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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The weighted average period between the balance sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years.

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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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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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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 total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to options outstanding under the plan as of the balance sheet date.

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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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The weighted average period between the balance sheet date and expiration for all awards outstanding under the plan, which may be expressed in a decimal value for number of years.

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

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