Consolidated Condensed Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Jul. 31, 2020	Apr. 30, 2020
Short term investments	$ 7,146	$ 2,115
Allowance for doubtful accounts	$ 37	$ 38
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)	383,279	383,279