Note 3 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Temporarily impaired securities, less than 12 months, fair value	$ 270,457	$ 39,454
Temporarily impaired securities, less than 12 months unrealized loss	2,769	762
Temporarily impaired securities, 12 months or more fair value	39,553	281,626
Temporarily impaired securities, 12 months or more unrealized loss	85	7,365
US Government Agencies Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	53,244	17,730
Temporarily impaired securities, less than 12 months unrealized loss	738	216
Temporarily impaired securities, 12 months or more fair value	38,962	259,992
Temporarily impaired securities, 12 months or more unrealized loss	37	6,450
US States and Political Subdivisions Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	35,934	16,882
Temporarily impaired securities, less than 12 months unrealized loss	596	352
Temporarily impaired securities, 12 months or more fair value	591	20,758
Temporarily impaired securities, 12 months or more unrealized loss	48	814
Collateralized Mortgage Backed Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	181,279
Temporarily impaired securities, less than 12 months unrealized loss	1,435
Temporarily impaired securities, 12 months or more fair value
Temporarily impaired securities, 12 months or more unrealized loss
Corporate Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value		4,842
Temporarily impaired securities, less than 12 months unrealized loss		194
Temporarily impaired securities, 12 months or more fair value		876
Temporarily impaired securities, 12 months or more unrealized loss		$ 101