Note 2 - Securities - Available-for-sale Securities (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Securities available for sale, amortized cost	$ 305,396,000	$ 329,979,000
Securities available for sale, gross unrealized gains	7,543,000	5,930,000
Securities available for sale, gross unrealized losses	(515,000)	(1,254,000)
Securities available for sale, fair value	312,424,000	334,655,000
US Government Agencies Debt Securities [Member]
Securities available for sale, amortized cost	170,970,000	185,103,000
Securities available for sale, gross unrealized gains	658,000	2,449,000
Securities available for sale, gross unrealized losses	(497,000)	(1,142,000)
Securities available for sale, fair value	171,131,000	186,410,000
Collateralized Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	27,816,000	41,998,000
Securities available for sale, gross unrealized gains	1,088,000	554,000
Securities available for sale, gross unrealized losses	(1,000)	(82,000)
Securities available for sale, fair value	28,903,000	42,470,000
Municipal General Obligation Bonds [Member]
Securities available for sale, amortized cost	95,725,000	98,245,000
Securities available for sale, gross unrealized gains	5,399,000	2,864,000
Securities available for sale, gross unrealized losses	0	(30,000)
Securities available for sale, fair value	101,124,000	101,079,000
Municipal Revenue Bonds [Member]
Securities available for sale, amortized cost	10,385,000	4,133,000
Securities available for sale, gross unrealized gains	398,000	63,000
Securities available for sale, gross unrealized losses	(17,000)	0
Securities available for sale, fair value	10,766,000	4,196,000
Other Debt and Equity Securities [Member]
Securities available for sale, amortized cost	500,000	500,000
Securities available for sale, gross unrealized gains	0	0
Securities available for sale, gross unrealized losses	0	0
Securities available for sale, fair value	$ 500,000	$ 500,000