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

The pro forma non interest expense and income taxes for the period as if the business combination or combinations had been completed at the beginning of a period.

No definition available.

Name:	amnb_BusinessAcquisitionProFormaNonInterestExpenseandIncomeTaxes
Namespace Prefix:	amnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The pro forma non interest income for the period as if the business combination or combinations had been completed at the beginning of a period.

No definition available.

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

The pro forma provision for loan loss for the period as if the business combination or combinations had been completed at the beginning of a period.

No definition available.

Name:	amnb_BusinessAcquisitionProFormaProvisionForLoanLoss
Namespace Prefix:	amnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

Name:	us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.