Note 1 - Organization and Summary of Significant Accounting Policies (Details Textual) - USD ($)	3 Months Ended
Jul. 31, 2019	Jul. 31, 2018	Apr. 30, 2019
Money Market Funds, at Carrying Value	$ 3,080,000		$ 5,617,000
Net Cash Provided by (Used in) Investing Activities, Total	(648,000)	$ (491,000)
Accounting Standards Update 2016-15 [Member]
Net Cash Provided by (Used in) Investing Activities, Total	$ (2,900,000)	$ (2,300,000)
EAM Trust [Member]
Non Voting Profits Interest Percent	50.00%
EAM Trust [Member] \| Minimum [Member]
Non Voting Revenues Interest Percent	41.00%
Percentage of Non Voting Profits Interests Due from Ex Subsidiary Payable to Parent under Agreement	90.00%
EAM Trust [Member] \| Maximum [Member]
Non Voting Revenues Interest Percent	55.00%

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

No definition available.

Name:	us-gaap_MoneyMarketFundsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant