Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Allowance for doubtful accounts	$ 300	$ 327
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)		0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	45,000,000	45,000,000
Common stock, shares issued (in shares)	23,595,160	23,595,160
Common stock, shares outstanding (in shares)	22,260,917	21,839,369
Treasury stock, shares (in shares)	1,334,243	1,755,791