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, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator for net income per share - basic:
Net income	$ 32,406	$ 30,047	$ 22,943
Common Stock [Member]
Numerator for net income per share - basic:
Net income	32,406	25,423	11,388
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(109)	(82)	(88)
Net income attributable to common shareholders	$ 32,297	$ 25,341	$ 11,300
Basic earnings per share:
Weighted average common shares outstanding - basic (in shares)	24,809	23,562	20,770
Net income per share - basic (in dollars per share)	$ 1.30	$ 1.08	$ 0.54
Diluted earnings per share:
Net income attributable to common shareholders	$ 32,297	$ 25,341	$ 11,300
Weighted average common shares outstanding - basic (in shares)	24,809	23,562	20,770
Weighted average effect of dilutive securities – stock options: (in shares)	844	886	857
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	25,653	24,448	21,627
Net income per share - diluted (in dollars per share)	$ 1.26	$ 1.04	$ 0.52
Common Class B [Member]
Numerator for net income per share - basic:
Net income		$ 4,624	$ 11,555
Allocation of distributed and undistributed income to unvested restricted stock shareholders		(18)	(87)
Net income attributable to common shareholders		$ 4,606	$ 11,468
Basic earnings per share:
Weighted average common shares outstanding - basic (in shares)		3,527	3,514
Net income per share - basic (in dollars per share)		$ 1.31	$ 3.26
Diluted earnings per share:
Net income attributable to common shareholders		$ 4,606	$ 11,468
Weighted average common shares outstanding - basic (in shares)		3,527	3,514
Weighted average effect of dilutive securities – stock options: (in shares)		101	89
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)		3,628	3,603
Net income per share - diluted (in dollars per share)		$ 1.27	$ 3.18