Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts	$ 169	$ 173
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)	25,656,760	25,592,812
Common stock, shares outstanding (in shares)	20,891,069	20,848,168
Treasury stock, shares (in shares)	4,765,691	4,744,644
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)	4,308,875	4,271,413
Common stock, shares outstanding (in shares)	3,539,931	3,510,150
Treasury stock, shares (in shares)	768,944	761,263