Note 12 - Derivative Financial Instruments and Hedging Activities (Details Textual) $ in Thousands	Oct. 16, 2023 USD ($)
Proceeds From Termination of Derivative Agreement	$ 2,000
Cash Collateral for Termination of Derivative Agreement	$ 850

Cash outflow for termination of derivative agreement.

No definition available.

Name:	amnb_CashCollateralForTerminationOfDerivativeAgreement
Namespace Prefix:	amnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration