Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Allowance for doubtful accounts	$ 182	$ 169
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 Class A [Member]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	60,000,000	60,000,000
Common stock, shares issued (in shares)	25,796,457	25,656,760
Common stock, shares outstanding (in shares)	20,940,790	20,891,069
Treasury stock, shares (in shares)	4,855,667	4,765,691
Common Class B [Member]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	80,000,000	80,000,000
Common stock, shares issued (in shares)	4,317,656	4,308,875
Common stock, shares outstanding (in shares)	3,540,244	3,539,931
Treasury stock, shares (in shares)	777,412	768,944