Number of stock option plans.

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Share based compensation arrangement by share based payment award award exercisable period.

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Share based compensation arrangement by share based payment award percentage of award achieved.

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Share based compensation arrangement by share based payment award performance period.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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

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Amount of stock repurchase plan authorized.

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Number of shares that have been repurchased during the period and are being held in treasury.

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Stockholders' Equity - Additional Information (Detail)	3 Months Ended
Stockholders' Equity - Additional Information (Detail)	Jul. 31, 2018 USD ($) OptionPlan shares	Jul. 31, 2017 USD ($) shares	Apr. 30, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of common stock \| shares	0
Number of stock incentive option plans \| OptionPlan	2
Intrinsic value of stock outstanding \| $	$ 853,000	$ 4,700,000
Intrinsic value of stock exercisable \| $	853,000	$ 4,700,000
Intrinsic value of stock exercised \| $	$ 76,000
Proceeds from exercise of employee stock options (in shares) \| shares	17,399	0
Unrecognized compensation cost of outstanding stock options \| $	$ 0
Stock-based compensation expense \| $	$ 2,000,000	$ 1,900,000
Performance period	3 years
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value of vested RSUs and PSUs \| $	$ 1,700,000
Stock units, forfeited \| shares	6,180
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock units, awarded \| shares		105,500
Stock units, forfeited \| shares	112,000
Share based payment award percentage of award achieved		115.20%
RSUs and PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $	$ 1,800,000	$ 1,700,000
Stock units, awarded \| shares	140,771	180,184
Grant date fair value of vested RSUs and PSUs \| $		$ 1,700,000
Stock units, forfeited \| shares	118,180	92,902
Stock units, vested \| shares	146,523	247,491
Unrecognized compensation cost related to unvested RSUs and PSUs \| $	$ 9,300,000
Weighted average remaining contractual term	1 year 9 months 18 days
Non-Executive Employees \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock units, awarded \| shares	140,771	164,180
Executive Officer \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock units, vested \| shares		121,504
2013 Incentive Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option, exercisable period	10 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase authorization \| $			$ 50,000,000
Maximum \| 2013 Incentive Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period to award vested and calculate volatility rate	4 years
Minimum \| 2013 Incentive Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period to award vested and calculate volatility rate	3 years