Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended
Jul. 31, 2018	Jul. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Option to purchase common stock	557,000	872,000
Stock-based compensation expense	$ 398,000	$ 316,000
Income tax excess benefit	$ 274,000	$ (33,000)
Stock options exercised	295,813	101,516
Total intrinsic value of options exercised	$ 1,700,000	$ 207,000
Unrecognized compensation cost related to unvested stock option	$ 4,400,000
Weighted average period for Unrecognized compensation cost	1 year 11 months 15 days

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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 options awarded to employees as compensation.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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

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

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