Note 4 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Temporarily impaired securities, less than 12 months, fair value	$ 106,353	$ 270,457
Temporarily impaired securities, less than 12 months unrealized loss	835	2,769
Temporarily impaired securities, 12 months or more fair value	622	39,553
Temporarily impaired securities, 12 months or more unrealized loss	17	85
US States and Political Subdivisions Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	20,438	35,934
Temporarily impaired securities, less than 12 months unrealized loss	566	596
Temporarily impaired securities, 12 months or more fair value	622	591
Temporarily impaired securities, 12 months or more unrealized loss	17	48
US Government Agencies Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value		53,244
Temporarily impaired securities, less than 12 months unrealized loss		738
Temporarily impaired securities, 12 months or more fair value		38,962
Temporarily impaired securities, 12 months or more unrealized loss		37
Commercial Mortgage Backed Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	85,915	181,279
Temporarily impaired securities, less than 12 months unrealized loss	$ 269	$ 1,435