Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
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)	25,592,812	25,475,662
Common stock, shares outstanding (in shares)	20,848,168	20,894,286
Treasury stock, shares (in shares)	4,744,644	4,581,376
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)	4,271,413	4,251,889
Common stock, shares outstanding (in shares)	3,510,150	3,494,865
Treasury stock, shares (in shares)	761,263	757,024
Allowance for doubtful accounts	$ 173	$ 206
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