Note 4 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Temporarily impaired securities, less than 12 months, fair value	$ 182,732	$ 270,457
Temporarily impaired securities, less than 12 months unrealized loss	4,485	2,769
Temporarily impaired securities, 12 months or more fair value	596	39,553
Temporarily impaired securities, 12 months or more unrealized loss	42	85
US Government Agencies Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	4,972	53,244
Temporarily impaired securities, less than 12 months unrealized loss	24	738
Temporarily impaired securities, 12 months or more fair value		38,962
Temporarily impaired securities, 12 months or more unrealized loss		37
US States and Political Subdivisions Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	14,157	35,934
Temporarily impaired securities, less than 12 months unrealized loss	500	596
Temporarily impaired securities, 12 months or more fair value	596	591
Temporarily impaired securities, 12 months or more unrealized loss	42	48
Commercial Mortgage Backed Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	163,603	181,279
Temporarily impaired securities, less than 12 months unrealized loss	3,961	1,435
Temporarily impaired securities, 12 months or more fair value
Temporarily impaired securities, 12 months or more unrealized loss