Note 6 - Summary of Earnings and Weighted Average Number of Common Shares Used in Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Employee Stock Option [Member]
Diluted:
Dilutive effect of options (in shares)	150,395	82,764	154,113	63,944
Restricted Stock [Member]
Diluted:
Dilutive effect of options (in shares)		2,814	1,577	3,657
Weighted average common shares outstanding (in shares)	13,801,245	13,805,430	13,778,705	13,838,891
Net income	$ 12,567	$ 12,829	$ 38,167	$ 38,569
Dividends to preferred stockholders	(2,152)	(2,167)	(6,487)	(6,502)
Net income available to common stockholders	$ 10,415	$ 10,662	$ 31,680	$ 32,067
Earnings per common share, basic (in dollars per share)	$ 0.75	$ 0.77	$ 2.30	$ 2.32
Weighted average common shares outstanding (in shares)	13,801,245	13,805,430	13,778,705	13,838,891
Dilutive effect of contingent issuable stock (in shares)	471,020	345,504	430,856	323,539
Assumed average common shares outstanding (in shares)	14,422,660	14,236,512	14,365,251	14,230,031
Net income available to common stockholders	$ 10,415	$ 10,662	$ 31,680	$ 32,067
Earnings per common share, diluted (in dollars per share)	$ 0.72	$ 0.75	$ 2.21	$ 2.25