Note 3 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Temporarily impaired securities, less than 12 months, fair value	$ 39,454	$ 87,068
Temporarily impaired securities, less than 12 months unrealized loss	762	1,065
Temporarily impaired securities, 12 months or more fair value	281,626	229,675
Temporarily impaired securities, 12 months or more unrealized loss	7,365	4,750
US Government Agencies Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	17,730	68,380
Temporarily impaired securities, less than 12 months unrealized loss	216	871
Temporarily impaired securities, 12 months or more fair value	259,992	225,738
Temporarily impaired securities, 12 months or more unrealized loss	6,450	4,623
US States and Political Subdivisions Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	16,882	18,688
Temporarily impaired securities, less than 12 months unrealized loss	352	194
Temporarily impaired securities, 12 months or more fair value	20,758	2,989
Temporarily impaired securities, 12 months or more unrealized loss	814	98
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	948
Temporarily impaired securities, 12 months or more unrealized loss	$ 101	$ 29