Note 4 - Supplementary Cash Flows Information - Supplementary Cash Flow Elements (Details) - USD ($)	9 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Apr. 30, 2020
Cash and cash equivalents	$ 16,182,000	$ 3,555,000	$ 4,954,000
Restricted cash	469,000	469,000
Total cash, cash equivalents, and restricted cash shown in the Consolidated Condensed Statement of Cash Flows	16,651,000	4,024,000
State and local income tax payments	1,139,000	1,089,000
Federal income tax payments to the Parent	$ 5,210,000	$ 3,325,000