Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Apr. 30, 2018	Apr. 30, 2017
Short term investments	$ 4,982	$ 6,066
Allowance for doubtful accounts	$ 14	$ 20
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)	308,380	288,335