Note 4 - Stock-based Compensation (Details Textual)	9 Months Ended
Jan. 27, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	25,100
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price \| $ / shares	$ 15.89
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	1,300
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price \| $ / shares	$ 17.59
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	357,695
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price \| $ / shares	$ 11.15
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2,811,314

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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Number of options outstanding, including both vested and non-vested options.

+ References

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-Publisher FASB
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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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-Publisher FASB
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Weighted average price at which option holders acquired shares when converting their stock options into shares.

+ References

No definition available.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

+ References

No definition available.

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

+ References

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-Publisher FASB
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