Note 3 - Securities - Securities in a Continuous Loss Position (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Securities available for sale, continuous unrealized loss position, less than 12 months	$ 32,243,000	$ 72,791,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	395,000	1,582,000
Securities available for sale, continuous unrealized loss position, 12 months or more	85,330,000	205,540,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	859,000	9,775,000
Securities available for sale, continuous unrealized loss position	117,573,000	278,331,000
Securities available for sale, continuous unrealized loss position, unrealized loss	1,254,000	11,357,000
US Government Agencies Debt Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	25,650,000	31,220,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	349,000	1,136,000
Securities available for sale, continuous unrealized loss position, 12 months or more	73,913,000	136,445,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	793,000	8,206,000
Securities available for sale, continuous unrealized loss position	99,563,000	167,665,000
Securities available for sale, continuous unrealized loss position, unrealized loss	1,142,000	9,342,000
Collateralized Mortgage Backed Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	2,838,000	11,460,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	28,000	136,000
Securities available for sale, continuous unrealized loss position, 12 months or more	10,423,000	23,762,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	54,000	656,000
Securities available for sale, continuous unrealized loss position	13,261,000	35,222,000
Securities available for sale, continuous unrealized loss position, unrealized loss	82,000	792,000
Municipal General Obligation Bonds [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	3,755,000	28,923,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	18,000	299,000
Securities available for sale, continuous unrealized loss position, 12 months or more	994,000	43,961,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	12,000	866,000
Securities available for sale, continuous unrealized loss position	4,749,000	72,884,000
Securities available for sale, continuous unrealized loss position, unrealized loss	30,000	1,165,000
Municipal Revenue Bonds [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	0	1,188,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	0	11,000
Securities available for sale, continuous unrealized loss position, 12 months or more	0	1,372,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	0	47,000
Securities available for sale, continuous unrealized loss position	0	2,560,000
Securities available for sale, continuous unrealized loss position, unrealized loss	0	58,000
Other Debt and Equity Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	0	0
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	0	0
Securities available for sale, continuous unrealized loss position, 12 months or more	0	0
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	0	0
Securities available for sale, continuous unrealized loss position	0	0
Securities available for sale, continuous unrealized loss position, unrealized loss	$ 0	$ 0