Note 2 - Investment Securities (Details) - Investment Securities in a Continuous Unrealized Loss Position - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
U.S. Government Agencies
Continous unrealized loss, less than 12 months, fair value	$ 80,073	$ 66,609
Continous unrealized loss, less than 12 months, gross unrealized losses	(572)	(397)
Continous unrealized loss, greater than 12 months, fair value	151,542	185,025
Continous unrealized loss, greater than 12 months, gross unrealized losses	(5,766)	(7,127)
Continous unrealized loss, fair value	231,615	251,634
Continous unrealized loss, gross unrealized losses	(6,338)	(7,524)
US Government Agencies Debt Securities [Member]
U.S. Government Agencies
Continous unrealized loss, less than 12 months, fair value	77,965	66,609
Continous unrealized loss, less than 12 months, gross unrealized losses	(537)	(397)
Continous unrealized loss, greater than 12 months, fair value	151,542	183,646
Continous unrealized loss, greater than 12 months, gross unrealized losses	(5,766)	(7,114)
Continous unrealized loss, fair value	229,507	250,255
Continous unrealized loss, gross unrealized losses	(6,303)	(7,511)
US States and Political Subdivisions Debt Securities [Member]
U.S. Government Agencies
Continous unrealized loss, less than 12 months, fair value	2,108
Continous unrealized loss, less than 12 months, gross unrealized losses	(35)
Continous unrealized loss, greater than 12 months, fair value		1,379
Continous unrealized loss, greater than 12 months, gross unrealized losses		(13)
Continous unrealized loss, fair value	2,108	1,379
Continous unrealized loss, gross unrealized losses	$ (35)	$ (13)