Note 3 - Net Income Per Common Share - Computation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 12,086	$ 10,691	$ 24,286	$ 21,353
Basic - weighted-average shares outstanding: (in shares)	26,541,978	26,368,001	26,554,262	26,295,074
Employee stock options and other (in shares)	107,174	193,147	155,955	231,555
Diluted - weighted-average shares outstanding: (in shares)	26,649,152	26,561,148	26,710,217	26,526,629
Basic (in dollars per share)	$ 0.46	$ 0.41	$ 0.91	$ 0.81
Diluted (in dollars per share)	$ 0.45	$ 0.40	$ 0.91	$ 0.80