Disclosure Of Compensation Related Costs, Share Based Payments (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Jul. 31, 2011	Jul. 31, 2010
Each award of stock options issued, reduction in shares available amount	1
Each award of restricted stock or restricted unit issued, reduction in shares available amount	2
Restricted shares granted	15,000
Date vested	May 1, 2014
Stock granted	441,000
Share based compensation, cost to grantee	$ 0
Aggregate intrinsic value of options outstanding	15,449
Weighted average remaining contractual life of options outstanding (years)	7.6
Options vested	371,109
Weighted average exercise price of options vested	$ 22.18
Weighted average remaining contractual life of vested options (years)	4.6
Aggregate intrinsic value of options vested	8,468
Aggregate intrinsic value of options exercised	1,512
Total fair value of shares vested	6,461
Total compensation costs	477	810
Maximum [Member]
Stock options, expiration date	2021
Minimum [Member]
Stock options, expiration date	2012
Stock Options [Member]
Date vested	June 23, 2014
2009 Stock Incentive Plan [Member]
Shares available for grant	4,454,604
2000 Stock Option Plan [Member]
Unrecognized compensation costs	7,283
Restricted Stock [Member]
Restricted shares granted	9,198
Date vested	June 23, 2014
Share based compensation, cost to grantee	0
Unrecognized compensation costs	$ 989

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The total fair value of equity-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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Net number of share options (or share units) granted during the 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 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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As of the balance sheet date, the total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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The weighted-average period between the balance sheet date and expiration date for fully vested and expected to vest options outstanding, which may be expressed in a decimal value for number of years.

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