Note 3 - Net Income per Common Share - Computation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net income	$ 11,686	$ 10,956	$ 22,139	$ 21,058
Basic (in shares)	25,921,111	25,620,005	25,885,888	25,597,055
Effect of dilutive securities:
Employee stock options and other (in shares)	356,392	526,843	359,247	535,210
Diluted - weighted-average shares outstanding: (in shares)	26,277,503	26,146,848	26,245,135	26,132,265
Net income per share:
Basic (in dollars per share)	$ 0.45	$ 0.43	$ 0.86	$ 0.82
Diluted (in dollars per share)	$ 0.44	$ 0.42	$ 0.84	$ 0.81