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, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator for net income per share - basic:
Net income	$ 30,047
Common Stock [Member]
Numerator for net income per share - basic:
Net income	25,423	$ 11,388	$ 10,178
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(82)	(88)	(88)
Net income attributable to common shareholders	$ 25,341	$ 11,300	$ 10,090
Basic earnings per share:
Weighted average common shares outstanding - basic (in shares)	23,562	20,770	20,713
Net income per share - basic (in dollars per share)	$ 1.08	$ 0.54	$ 0.49
Diluted earnings per share:
Net income attributable to common shareholders	$ 25,341	$ 11,300	$ 10,090
Weighted average common shares outstanding - basic (in shares)	23,562	20,770	20,713
Weighted average effect of dilutive securities – stock options: (in shares)	886	857	324
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	24,448	21,627	21,037
Net income per share - diluted (in dollars per share)	$ 1.04	$ 0.52	$ 0.48
Common Class B [Member]
Numerator for net income per share - basic:
Net income	$ 4,624	$ 11,555	$ 10,341
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(18)	(87)	(88)
Net income attributable to common shareholders	$ 4,606	$ 11,468	$ 10,253
Basic earnings per share:
Weighted average common shares outstanding - basic (in shares)	3,527	3,514	3,505
Net income per share - basic (in dollars per share)	$ 1.31	$ 3.26	$ 2.93
Diluted earnings per share:
Net income attributable to common shareholders	$ 4,606	$ 11,468	$ 10,253
Weighted average common shares outstanding - basic (in shares)	3,527	3,514	3,505
Weighted average effect of dilutive securities – stock options: (in shares)	101	89	55
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	3,628	3,603	3,560
Net income per share - diluted (in dollars per share)	$ 1.27	$ 3.18	$ 2.88