Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Allowance for doubtful accounts	$ 107	$ 120
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	110,000,000	60,000,000
Common stock, shares issued (in shares)	30,850,131	30,775,154
Common stock, shares outstanding (in shares)	25,439,013	25,390,968
Treasury stock, shares (in shares)	5,411,118	5,384,186