Consolidated Balance Sheets (Parentheticals) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts	$ 2,000	$ 9,000
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	6,825,183	4,845,697
Common stock, shares outstanding (in shares)	6,825,183	4,845,697