Note 4 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Temporarily impaired securities, less than 12 months, fair value	$ 49,277	$ 270,457
Temporarily impaired securities, less than 12 months unrealized loss	423	2,769
Temporarily impaired securities, 12 months or more fair value	5,637	39,553
Temporarily impaired securities, 12 months or more unrealized loss	16	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	25	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	26,545	35,934
Temporarily impaired securities, less than 12 months unrealized loss	338	596
Temporarily impaired securities, 12 months or more fair value	626	591
Temporarily impaired securities, 12 months or more unrealized loss	12	48
Commercial Mortgage Backed Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	17,760	181,279
Temporarily impaired securities, less than 12 months unrealized loss	60	$ 1,435
Temporarily impaired securities, 12 months or more fair value	5,011
Temporarily impaired securities, 12 months or more unrealized loss	$ 4