Stock Options and SAR Transactions (Detail) (Stock Options, USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
Jan. 31, 2013
Stock Options
Options
Outstanding, April 30, 2012	1,492,000
Exercised	(171,000)
Forfeited/expired.	(151,000)
Outstanding, January 31, 2013	1,170,000
Exercisable, January 31, 2013	923,000
Weighted Average Exercise Price
Outstanding, April 30, 2012	$ 14.00
Exercised	$ 8.42
Forfeited/expired.	$ 16.93
Outstanding, January 31, 2013	$ 14.55
Exercisable, January 31, 2013	$ 14.77
Weighted - Average Remaining Contractual Life (in years)
Outstanding, January 31, 2013	2 years 8 months 12 days
Exercisable, January 31, 2013	2 years 3 months 29 days
Aggregate Intrinsic Value
Outstanding, January 31, 2013	$ 4,062
Exercisable, January 31, 2013	$ 3,041

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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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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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