Consolidated Balance Sheets (Parentheticals) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts	$ 83,000	$ 66,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, shares outstanding (in shares)	14,290,749	15,411,556