Consolidated Condensed Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jan. 31, 2022	Apr. 30, 2021
Short term investments	$ 29,081	$ 18,209
Allowance for doubtful accounts	$ 39	$ 36
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	30,000,000	30,000,000
Common stock, shares issued (in shares)	10,000,000	10,000,000
Treasury stock, shares (in shares)	470,837	436,830