Note 2 - Investment Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
US Government Agencies Debt Securities [Member]
Continuous unrealized loss, less than 12 months, fair value	$ 37,615	$ 139,765
Continuous unrealized loss, less than 12 months, gross unrealized losses	(202)	(1,270)
Continuous unrealized loss, greater than 12 months, fair value	126,577	139,720
Continuous unrealized loss, greater than 12 months, gross unrealized losses	(2,431)	(5,522)
Continuous unrealized loss, fair value	164,192	279,485
Continuous unrealized loss, gross unrealized losses	(2,633)	(6,792)
US States and Political Subdivisions Debt Securities [Member]
Continuous unrealized loss, less than 12 months, fair value	701	1,035
Continuous unrealized loss, less than 12 months, gross unrealized losses	(12)	$ (20)
Continuous unrealized loss, greater than 12 months, fair value	249
Continuous unrealized loss, greater than 12 months, gross unrealized losses	(7)
Continuous unrealized loss, fair value	950	$ 1,035
Continuous unrealized loss, gross unrealized losses	(19)	(20)
Continuous unrealized loss, less than 12 months, fair value	38,316	140,800
Continuous unrealized loss, less than 12 months, gross unrealized losses	(214)	(1,290)
Continuous unrealized loss, greater than 12 months, fair value	126,826	139,720
Continuous unrealized loss, greater than 12 months, gross unrealized losses	(2,438)	(5,522)
Continuous unrealized loss, fair value	165,142	280,520
Continuous unrealized loss, gross unrealized losses	$ (2,652)	$ (6,812)