Note 2 - Investment Securities (Details) - Investment Securities in a Continuous Unrealized Loss Position - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
U.S. Government Agencies
Continous unrealized loss, less than 12 months, fair value	$ 28,854	$ 66,609
Continous unrealized loss, less than 12 months, gross unrealized losses	(182)	(397)
Continous unrealized loss, greater than 12 months, fair value	142,938	185,025
Continous unrealized loss, greater than 12 months, gross unrealized losses	(3,953)	(7,127)
Continous unrealized loss, fair value	171,792	251,634
Continous unrealized loss, gross unrealized losses	(4,135)	(7,524)
US Government Agencies Debt Securities [Member]
U.S. Government Agencies
Continous unrealized loss, less than 12 months, fair value	27,858	66,609
Continous unrealized loss, less than 12 months, gross unrealized losses	(162)	(397)
Continous unrealized loss, greater than 12 months, fair value	142,938	183,646
Continous unrealized loss, greater than 12 months, gross unrealized losses	(3,953)	(7,114)
Continous unrealized loss, fair value	170,796	250,255
Continous unrealized loss, gross unrealized losses	(4,115)	(7,511)
US States and Political Subdivisions Debt Securities [Member]
U.S. Government Agencies
Continous unrealized loss, less than 12 months, fair value	996
Continous unrealized loss, less than 12 months, gross unrealized losses	(20)
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	996	1,379
Continous unrealized loss, gross unrealized losses	$ (20)	$ (13)