Stock Options and SAR Transactions (Detail) (Stock Options And Stock Appreciation Rights, USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Jul. 31, 2012
Stock Options And Stock Appreciation Rights
Options
Outstanding, April 30, 2012	1,492,000
Exercised	(24,000)
Forfeited/expired.	(35,000)
Outstanding, July 31, 2012	1,433,000
Exercisable, July 31, 2012	1,164,000
Weighted Average Exercise Price
Outstanding, April 30, 2012	$ 14.00
Exercised	$ 7.95
Forfeited/expired.	$ 18.65
Outstanding, July 31, 2012	$ 14.02
Exercisable, July 31, 2012	$ 14.08
Weighted - Average Remaining Contractual Life (in years)
Outstanding, July 31, 2012	2 years 10 months 21 days
Exercisable, July 31, 2012	2 years 6 months
Aggregate Intrinsic Value
Outstanding, July 31, 2012	$ 2,489
Exercisable, July 31, 2012	$ 2,179

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of options outstanding.

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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 remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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