Note 8 - Long-term Borrowings - Junior Subordinated Debt Outstanding Payables (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2019	Apr. 07, 2006
Principal amount			$ 20,619,000
Junior Subordinated Debt [Member]
Principal amount	$ 28,156,000	$ 28,130,000
Junior Subordinated Debt [Member] | AMNB Statutory Trust I [Member]
Principal amount	20,619,000	20,619,000
Junior Subordinated Debt [Member] | MidCarolina Trust I [Member]
Principal amount	4,503,000	4,489,000
Junior Subordinated Debt [Member] | MidCarolina Trust II [Member]
Principal amount	$ 3,034,000	$ 3,022,000
London Interbank Offered Rate (LIBOR) [Member] | Junior Subordinated Debt [Member] | AMNB Statutory Trust I [Member]
Interest rate	1.35%
London Interbank Offered Rate (LIBOR) [Member] | Junior Subordinated Debt [Member] | MidCarolina Trust I [Member]
Interest rate	3.45%
London Interbank Offered Rate (LIBOR) [Member] | Junior Subordinated Debt [Member] | MidCarolina Trust II [Member]
Interest rate	2.95%