Consolidated Condensed Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jul. 31, 2017	Apr. 30, 2017
Short term investments	$ 6,217	$ 6,066
Allowance for doubtful accounts	$ 21	$ 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)	290,688	288,335	[1],[2]

[1] Includes 85,219 shares with a total average cost of $1,036,000 that were acquired during the former repurchase program, which was authorized in January 2011 and expired in January 2012; 18,400 shares were acquired prior to January 2011.

[2] Were acquired during the $3 million repurchase program authorized in September 2012.