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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net income	$ 11,982	$ 12,382	$ 33,335	$ 34,521
Basic - weighted-average shares outstanding: (in shares)	26,416,041	26,083,405	26,334,738	25,952,451
Effect of dilutive securities:
Employee stock options and other (in shares)	193,837	297,908	204,340	338,307
Diluted - weighted-average shares outstanding: (in shares)	26,609,878	26,381,313	26,539,078	26,290,758
Net income per share:
Basic (in dollars per share)	$ 0.45	$ 0.47	$ 1.27	$ 1.33
Diluted (in dollars per share)	$ 0.45	$ 0.47	$ 1.26	$ 1.31