Note 5 - Employees' Profit Sharing and Savings Plan (Details Textual) - USD ($)	3 Months Ended
Jul. 31, 2017	Jul. 31, 2016
Deferred Compensation Arrangement with Individual, Contributions by Employer	$ 107,000	$ 108,000

Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

No definition available.

Name:	us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration