Stock Options Transactions (Detail) (Stock Options, USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
Oct. 31, 2013
Stock Options
Options
Outstanding, April 30, 2013	1,100,000
Exercised	(315,000)
Forfeited/expired	(26,000)
Outstanding, October 31, 2013	759,000
Exercisable, October 31, 2013	685,000
Weighted Average Exercise Price
Outstanding, April 30, 2013	$ 14.72
Exercised	$ 12.53
Forfeited/expired	$ 12.51
Outstanding, October 31, 2013	$ 15.70
Exercisable, October 31, 2013	$ 15.60
Weighted - Average Remaining Contractual Life (in years)
Outstanding, October 31, 2013	2 years 3 months 11 days
Exercisable, October 31, 2013	2 years 1 month 10 days
Aggregate Intrinsic Value
Outstanding, October 31, 2013	$ 6,145
Exercisable, October 31, 2013	$ 5,616

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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 by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-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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