Summary of Changes in Outstanding Options (Detail) (USD $)	12 Months Ended
Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares Outstanding at May 1, 2013	3,751,180
Number of Shares Granted	644,500
Number of Shares Exercised	(890,341)	(386,356)	(986,875)
Number of Shares Forfeited / cancelled	(611,267)
Number of Shares Outstanding at April 30, 2014	2,894,072	3,751,180
Number of Shares Exercisable at April 30, 2014	1,071,812
Weighted Average Exercise Price Outstanding at May 1, 2013	$ 7.12
Weighted Average Exercise Price Granted	$ 9.35
Weighted Average Exercise Price Exercised	$ 6.15
Weighted Average Exercise Price Forfeited/cancelled	$ 8.69
Weighted Average Exercise Price Outstanding at April 30, 2014	$ 7.59	$ 7.12
Weighted Average Exercise Price Exercisable at April 30, 2014	$ 6.63
Weighted Average Remaining Contractual Term Outstanding at April 30, 2014	3 years 6 months
Weighted Average Remaining Contractual Term Exercisable at April 30, 2014	2 years 6 months
Aggregate Intrinsic Value Outstanding at April 30, 2014	$ 5,992,532
Aggregate Intrinsic Value Exercisable at April 30, 2014	$ 3,221,689

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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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Weighted average price of options that were either forfeited or expired.

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- Definition

Gross number of share options (or share units) granted during the period.

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No definition available.

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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 per share amount at which grantees can acquire shares of common stock by exercise of options.

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

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