Note 8 - Net Income Per Share Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Common Class A [Member]
Net income	$ 2,260		$ 2,028	$ 4,994	$ 3,765
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(19)		(14)	(43)	(27)
Net income attributable to common shareholders	$ 2,241		$ 2,014	$ 4,951	$ 3,738
Weighted average common shares outstanding - basic (in shares)	20,711		20,790	20,711	20,791
Basic earnings per share (in dollars per share)	$ 0.11	$ 0.13	$ 0.10	$ 0.24	$ 0.18
Weighted average effect of dilutive securities – stock options (in shares)	281		239	291	240
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	20,992	21,012	21,029	21,002	21,031
Diluted earnings per share (in dollars per share)	$ 0.11	$ 0.13	$ 0.10	$ 0.24	$ 0.18
Common Class B [Member]
Net income	$ 2,298		$ 2,036	$ 5,071	$ 3,780
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(20)		(14)	(44)	(27)
Net income attributable to common shareholders	$ 2,278		$ 2,022	$ 5,027	$ 3,753
Weighted average common shares outstanding - basic (in shares)	3,508		3,478	3,498	3,478
Basic earnings per share (in dollars per share)	$ 0.65	$ 0.79	$ 0.58	$ 1.44	$ 1.08
Weighted average effect of dilutive securities – stock options (in shares)	57		44	59	45
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	3,565	3,549	3,522	3,557	3,523
Diluted earnings per share (in dollars per share)	$ 0.64	$ 0.77	$ 0.57	$ 1.41	$ 1.07
Net income	$ 4,558	$ 5,506	$ 4,064	$ 10,065	$ 7,544