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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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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 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 exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

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Stock Options and Share-Based Compensation - Summary of Options Outstanding, Exercisable, and Weighted Average Exercise Prices within Exercise Price Range (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016	Apr. 26, 2015
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding	137,250	180,350	185,375	239,575
Weighted average exercise price	$ 18.01	$ 17.29	$ 14.68	$ 13.24
Exercise Price Range Range One [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range lower limit	8.59
Exercise price range upper limit	$ 11.78
Options outstanding	17,550
Weighted average exercise price	$ 11.35
Weighted average remaining contractual life	4 years 10 days
Aggregate intrinsic value	$ 414,000
Options exercisable	17,550
Weighted average exercise price	$ 11.35
Aggregate intrinsic value	$ 414,000
Exercise Price Range Range Two [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range lower limit	$ 15.85
Exercise price range upper limit	$ 23.62
Options outstanding	119,700
Weighted average exercise price	$ 18.98
Weighted average remaining contractual life	6 years 8 months 4 days
Aggregate intrinsic value	$ 1,911,000
Options exercisable	61,550
Weighted average exercise price	$ 17.69
Aggregate intrinsic value	$ 1,062,000