Note 4 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Temporarily impaired securities, less than 12 months, fair value	$ 1,497	$ 39,454
Temporarily impaired securities, less than 12 months unrealized loss	85	762
Temporarily impaired securities, 12 months or more fair value	250,803	281,626
Temporarily impaired securities, 12 months or more unrealized loss	3,123	7,365
US Government Agencies Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	941	17,730
Temporarily impaired securities, less than 12 months unrealized loss	1	216
Temporarily impaired securities, 12 months or more fair value	235,610	259,992
Temporarily impaired securities, 12 months or more unrealized loss	2,859	6,450
US States and Political Subdivisions Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	556	16,882
Temporarily impaired securities, less than 12 months unrealized loss	84	352
Temporarily impaired securities, 12 months or more fair value	12,300	20,758
Temporarily impaired securities, 12 months or more unrealized loss	164	814
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	2,893	876
Temporarily impaired securities, 12 months or more unrealized loss	$ 100	$ 101