Note 9 - Net Income Per Common Share - Net Income Per Common Share Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Basic:
Net income	$ 27,017	$ 23,322
Average common shares outstanding (in shares)	34,070	33,519
Basic net income per common share (in dollars per share)	$ 0.79	$ 0.70
Diluted:
Net income	$ 27,017	$ 23,322
Average common shares outstanding (in shares)	34,070	33,519
Adjustment for common share equivalents (in shares)	214	585
Average common shares outstanding-diluted (in shares)	34,284	34,104
Diluted net income per common share (in dollars per share)	$ 0.79	$ 0.68
Anti-dilutive shares (in shares)	7	5