Note I - Stock-based Compensation - Stock Option Plan Comparison (Details)	9 Months Ended
Jan. 31, 2017 shares
Minimum exercise price as a percentage of fair market value at date of grant	100.00%
Shares available for grant at January 31, 2017 (in shares)	286,000
The 1997 Plan [Member]
Last expiration date for outstanding options	Aug. 10, 2026

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant