Note 3 - Computation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net income	$ 46,514	$ 41,635	$ 35,277
Basic (in shares)	26,005,858	25,692,699	25,198,556
Effect of dilutive securities:
Employee stock options and other (in shares)	314,426	407,621	661,185
Diluted - weighted-average shares outstanding: (in shares)	26,320,284	26,100,320	25,859,741
Net income per share attributable to common shareholders:
Basic (in dollars per share)	$ 1.79	$ 1.62	$ 1.40
Diluted (in dollars per share)	$ 1.77	$ 1.60	$ 1.36