Note 7 - Earnings Per Share - Net Income Per Share Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 5,752	$ 4,558	$ 12,272	$ 10,065
Common Class A [Member]
Net income per share – basic (in dollars per share)	$ 0.14	$ 0.11	$ 0.29	$ 0.24
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	21,525	20,992	21,404	21,002
Net income per share – diluted (in dollars per share)	$ 0.13	$ 0.11	$ 0.28	$ 0.24
Net income	$ 2,855	$ 2,260	$ 6,088	$ 4,994
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(22)	(19)	(48)	(43)
Net income attributable to common shareholders	$ 2,833	$ 2,241	$ 6,040	$ 4,951
Weighted average common shares outstanding - basic (in shares)	20,752	20,711	20,745	20,711
Weighted average effect of dilutive securities – stock options (in shares)	773	281	659	291
Common Class B [Member]
Net income per share – basic (in dollars per share)	$ 0.82	$ 0.65	$ 1.75	$ 1.44
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	3,591	3,565	3,584	3,557
Net income per share – diluted (in dollars per share)	$ 0.80	$ 0.64	$ 1.71	$ 1.41
Net income	$ 2,897	$ 2,298	$ 6,184	$ 5,071
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(22)	(20)	(49)	(44)
Net income attributable to common shareholders	$ 2,875	$ 2,278	$ 6,135	$ 5,027
Weighted average common shares outstanding - basic (in shares)	3,514	3,508	3,514	3,498
Weighted average effect of dilutive securities – stock options (in shares)	77	57	70	59