Note 4 - Earnings Per Share - Earnings Per Share Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator for basic and diluted earnings per share – Net income available to common shareholders	$ 21,039	$ 14,479
Denominator for basic earnings per share – weighted average shares outstanding (in shares)	39,665	39,409
Effect of dilutive securities– Employee stock options and restricted stock awards (in shares)	1,427	1,292
Denominator for basic earnings per share – adjusted weighted average shares outstanding and assumed conversions shares outstanding (in shares)	41,092	40,701
Basic earnings per common share (in dollars per share)	$ 0.53	$ 0.37
Diluted earnings per common share and common share equivalents (in dollars per share)	$ 0.51	$ 0.36