Note 2 - Securities - Available-for-sale Securities (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Securities available for sale, amortized cost	$ 436,481,000	$ 380,403,000
Securities available for sale, gross unrealized gains	6,107,000	7,843,000
Securities available for sale, gross unrealized losses	(8,331,000)	(899,000)
Securities available for sale, fair value	434,257,000	387,347,000
US Government Agencies Debt Securities [Member]
Securities available for sale, amortized cost	274,038,000	242,522,000
Securities available for sale, gross unrealized gains	362,000	516,000
Securities available for sale, gross unrealized losses	(7,572,000)	(897,000)
Securities available for sale, fair value	266,828,000	242,141,000
Collateralized Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	35,211,000	23,869,000
Securities available for sale, gross unrealized gains	925,000	1,021,000
Securities available for sale, gross unrealized losses	(328,000)	0
Securities available for sale, fair value	35,808,000	24,890,000
Municipal General Obligation Bonds [Member]
Securities available for sale, amortized cost	111,294,000	101,991,000
Securities available for sale, gross unrealized gains	4,517,000	5,833,000
Securities available for sale, gross unrealized losses	(274,000)	0
Securities available for sale, fair value	115,537,000	107,824,000
Municipal Revenue Bonds [Member]
Securities available for sale, amortized cost	15,438,000	11,521,000
Securities available for sale, gross unrealized gains	303,000	473,000
Securities available for sale, gross unrealized losses	(157,000)	(2,000)
Securities available for sale, fair value	15,584,000	11,992,000
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