Summary of Changes in Outstanding Options (Detail) - USD ($)	12 Months Ended
Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of Shares Outstanding at May 1, 2016	3,489,857
Number of Shares Granted	360,000
Number of Shares Exercised	(754,811)	(306,848)	(490,912)
Number of Shares Forfeited	(15,900)
Number of Shares Outstanding at April 30, 2017	3,079,146	3,489,857
Number of Shares Exercisable at April 30, 2017	1,365,586
Weighted Average Exercise Price Outstanding at May 1, 2016	$ 8.58
Weighted Average Exercise Price Granted	10.08
Weighted Average Exercise Price Exercised	7.57
Weighted Average Exercise Price Forfeited	9.09
Weighted Average Exercise Price Outstanding at April 30, 2017	9.00	$ 8.58
Weighted Average Exercise Price Exercisable at April 30, 2017	$ 8.82
Weighted Average Remaining Contractual Term Outstanding at April 30, 2017	3 years 2 months 12 days
Weighted Average Remaining Contractual Term Exercisable at April 30, 2017	2 years 2 months 12 days
Aggregate Intrinsic Value Outstanding at April 30, 2017	$ 6,073,168
Aggregate Intrinsic Value Exercisable at April 30, 2017	$ 2,941,982

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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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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.

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

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

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

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