Note 3 - Securities - Securities in a Continuous Loss Position (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Securities available for sale, continuous unrealized loss position, less than 12 months	$ 72,791,000	$ 60,173,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	1,582,000	733,000
Securities available for sale, continuous unrealized loss position, 12 months or more	205,540,000	192,348,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	9,775,000	6,826,000
Securities available for sale, continuous unrealized loss position	278,331,000	252,521,000
Securities available for sale, continuous unrealized loss position, unrealized loss	11,357,000	7,559,000
US Government Agencies Debt Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	31,220,000	35,677,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	1,136,000	434,000
Securities available for sale, continuous unrealized loss position, 12 months or more	136,445,000	115,374,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	8,206,000	5,918,000
Securities available for sale, continuous unrealized loss position	167,665,000	151,051,000
Securities available for sale, continuous unrealized loss position, unrealized loss	9,342,000	6,352,000
Collateralized Mortgage Backed Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	11,460,000	10,179,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	136,000	156,000
Securities available for sale, continuous unrealized loss position, 12 months or more	23,762,000	21,084,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	656,000	354,000
Securities available for sale, continuous unrealized loss position	35,222,000	31,263,000
Securities available for sale, continuous unrealized loss position, unrealized loss	792,000	510,000
Municipal General Obligation Bonds [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	28,923,000	12,807,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	299,000	114,000
Securities available for sale, continuous unrealized loss position, 12 months or more	43,961,000	54,703,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	866,000	524,000
Securities available for sale, continuous unrealized loss position	72,884,000	67,510,000
Securities available for sale, continuous unrealized loss position, unrealized loss	1,165,000	638,000
Municipal Revenue Bonds [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	1,188,000	0
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	11,000	0
Securities available for sale, continuous unrealized loss position, 12 months or more	1,372,000	1,187,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	47,000	30,000
Securities available for sale, continuous unrealized loss position	2,560,000	1,187,000
Securities available for sale, continuous unrealized loss position, unrealized loss	58,000	30,000
Other Debt and Equity Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	0	1,510,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	0	29,000
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	1,510,000
Securities available for sale, continuous unrealized loss position, unrealized loss	$ 0	$ 29,000