Note 7 - Earnings Per Share - Net Income Per Share Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Net income	$ 6,521	$ 5,506
Common Class A [Member]
Net income	3,234	2,735
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(27)	(23)
Net income attributable to common shareholders	$ 3,207	$ 2,712
Weighted average common shares outstanding - basic (in shares)	20,737	20,710
Net income per share – basic (in dollars per share)	$ 0.15	$ 0.13
Weighted average effect of dilutive securities – stock options (in shares)	508	302
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	21,245	21,012
Net income per share – diluted (in dollars per share)	$ 0.15	$ 0.13
Common Class B [Member]
Net income	$ 3,287	$ 2,771
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(27)	(22)
Net income attributable to common shareholders	$ 3,260	$ 2,749
Weighted average common shares outstanding - basic (in shares)	3,513	3,489
Net income per share – basic (in dollars per share)	$ 0.93	$ 0.79
Weighted average effect of dilutive securities – stock options (in shares)	63	60
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	3,576	3,549
Net income per share – diluted (in dollars per share)	$ 0.91	$ 0.77