Consolidated Condensed Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jan. 31, 2020	Apr. 30, 2019
Short term investments	$ 2,739	$ 5,617
Allowance for doubtful accounts	$ 22	$ 22
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)	360,455	336,439	[1],[2],[3]

[1] Includes 207,047 shares that were acquired during the $3 million repurchase program which was authorized in September 2012 and expired in October 2018.

[2] Includes 49,789 shares that were acquired during the $2 million repurchase program which was authorized in October 2018.

[3] Includes 85,219 shares 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.