Note 4 - Allowance for Loan Losses and Impaired Loans - Troubled Debt Restructuring (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Number of contracts		0	1	1	5
Premodification		$ 0	$ 12	$ 73	$ 537
Postmodification		0	12	71	540
Premodification, subsequently defaulted	[1]	0	0	0	0
Postmodification, subsequently defaulted	[1]	$ 0	$ 0	$ 0	$ 0
Construction and Development Loan [Member]
Number of contracts		0	1	0	3
Premodification		$ 0	$ 12	$ 0	$ 471
Postmodification		0	12	0	470
Premodification, subsequently defaulted	[1]	0	0	0	0
Postmodification, subsequently defaulted	[1]	$ 0	$ 0	$ 0	$ 0
Farmland Loan [Member]
Number of contracts		0	0	0	0
Premodification		$ 0	$ 0	$ 0	$ 0
Postmodification		0	0	0	0
Premodification, subsequently defaulted	[1]	0	0	0	0
Postmodification, subsequently defaulted	[1]	$ 0	$ 0	$ 0	$ 0
Residential Loan [Member]
Number of contracts		0	0	0	1
Premodification		$ 0	$ 0	$ 0	$ 46
Postmodification		0	0	0	50
Premodification, subsequently defaulted	[1]	0	0	0	0
Postmodification, subsequently defaulted	[1]	$ 0	$ 0	$ 0	$ 0
Commercial Mortgage Loan [Member]
Number of contracts		0	0	1	0
Premodification		$ 0	$ 0	$ 73	$ 0
Postmodification		0	0	71	0
Premodification, subsequently defaulted	[1]	0	0	0	0
Postmodification, subsequently defaulted	[1]	$ 0	$ 0	$ 0	$ 0
Commercial and Agricultural Loan [Member]
Number of contracts		0	0	0	1
Premodification		$ 0	$ 0	$ 0	$ 20
Postmodification		0	0	0	20
Premodification, subsequently defaulted	[1]	0	0	0	0
Postmodification, subsequently defaulted	[1]	$ 0	$ 0	$ 0	$ 0
Consumer and Other Loan [Member]
Number of contracts		0	0	0	0
Premodification		$ 0	$ 0	$ 0	$ 0
Postmodification		0	0	0	0
Premodification, subsequently defaulted	[1]	0	0	0	0
Postmodification, subsequently defaulted	[1]	$ 0	$ 0	$ 0	$ 0

[1] Loans past due 30 days or more are considered to be in default.