Note 1 - Summary of Significant Accounting Policies - Net Income Per Share Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator for net income per share - basic:
Net income	$ 20,518	$ 17,610	$ 18,156
Common Class A [Member]
Numerator for net income per share - basic:
Net income	10,178	8,759	9,062
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(88)	(76)
Net income attributable to common shareholders	$ 10,090	$ 8,683	$ 9,062
Basic earnings per share:
Weighted average common shares outstanding - basic (in shares)	20,713	20,741	20,764
Net income per share - basic (in dollars per share)	$ 0.49	$ 0.42	$ 0.44
Net income attributable to common shareholders	$ 10,090	$ 8,683	$ 9,062
Weighted average effect of dilutive securities – stock options: (in shares)	324	240	312
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	21,037	20,981	21,076
Net income per share - diluted (in dollars per share)	$ 0.48	$ 0.41	$ 0.43
Common Class B [Member]
Numerator for net income per share - basic:
Net income	$ 10,341	$ 8,851	$ 9,094
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(88)	(77)
Net income attributable to common shareholders	$ 10,253	$ 8,774	$ 9,094
Basic earnings per share:
Weighted average common shares outstanding - basic (in shares)	3,505	3,478	3,473
Net income per share - basic (in dollars per share)	$ 2.93	$ 2.52	$ 2.62
Net income attributable to common shareholders	$ 10,253	$ 8,774	$ 9,094
Weighted average effect of dilutive securities – stock options: (in shares)	55	44	63
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	3,560	3,522	3,536
Net income per share - diluted (in dollars per share)	$ 2.88	$ 2.49	$ 2.57