Note 4 - Loans - Impaired Loan Balances by Portfolio Segment (Details) $ in Thousands	12 Months Ended
Dec. 31, 2022 USD ($)
Recorded investment, with no related allowance recorded	$ 5,094
Unpaid principal balance, with no related allowance recorded	5,100
Average recorded investment, with no related allowance recorded	3,668
Interest income recognized, with no related allowance recorded	169
Recorded investment, with a related allowance recorded	0
Unpaid principal balance, with a related allowance recorded	0
Average recorded investment, with a related allowance recorded	218
Interest income recognized, with a related allowance recorded	0
Related allowance	0
Recorded investment	5,094
Unpaid principal balance	5,100
Average recorded investment	3,886
Interest income recognized	169
Commercial Portfolio Segment [Member]
Recorded investment, with no related allowance recorded	0
Unpaid principal balance, with no related allowance recorded	0
Average recorded investment, with no related allowance recorded	0
Interest income recognized, with no related allowance recorded	0
Recorded investment, with a related allowance recorded	0
Unpaid principal balance, with a related allowance recorded	0
Average recorded investment, with a related allowance recorded	139
Interest income recognized, with a related allowance recorded	0
Related allowance	0
Recorded investment	0
Unpaid principal balance	0
Average recorded investment	139
Interest income recognized	0
Commercial Real Estate Portfolio Segment [Member] \| Construction and Land Development [Member]
Recorded investment, with no related allowance recorded	0
Unpaid principal balance, with no related allowance recorded	0
Average recorded investment, with no related allowance recorded	0
Interest income recognized, with no related allowance recorded	0
Recorded investment, with a related allowance recorded	0
Unpaid principal balance, with a related allowance recorded	0
Average recorded investment, with a related allowance recorded	0
Interest income recognized, with a related allowance recorded	0
Related allowance	0
Recorded investment	0
Unpaid principal balance	0
Average recorded investment	0
Interest income recognized	0
Commercial Real Estate Portfolio Segment [Member] \| Owner Occupied Commercial Real Estate [Member]
Recorded investment, with no related allowance recorded	2,420
Unpaid principal balance, with no related allowance recorded	2,420
Average recorded investment, with no related allowance recorded	1,454
Interest income recognized, with no related allowance recorded	108
Recorded investment, with a related allowance recorded	0
Unpaid principal balance, with a related allowance recorded	0
Average recorded investment, with a related allowance recorded	0
Interest income recognized, with a related allowance recorded	0
Related allowance	0
Recorded investment	2,420
Unpaid principal balance	2,420
Average recorded investment	1,454
Interest income recognized	108
Commercial Real Estate Portfolio Segment [Member] \| Non-owner Occupied Commercial Real Estate [Member]
Recorded investment, with no related allowance recorded	1,360
Unpaid principal balance, with no related allowance recorded	1,359
Average recorded investment, with no related allowance recorded	1,186
Interest income recognized, with no related allowance recorded	40
Recorded investment, with a related allowance recorded	0
Unpaid principal balance, with a related allowance recorded	0
Average recorded investment, with a related allowance recorded	0
Interest income recognized, with a related allowance recorded	0
Related allowance	0
Recorded investment	1,360
Unpaid principal balance	1,359
Average recorded investment	1,186
Interest income recognized	40
Residential Portfolio Segment [Member] \| Residential [Member]
Recorded investment, with no related allowance recorded	1,149
Unpaid principal balance, with no related allowance recorded	1,156
Average recorded investment, with no related allowance recorded	935
Interest income recognized, with no related allowance recorded	21
Recorded investment, with a related allowance recorded	0
Unpaid principal balance, with a related allowance recorded	0
Average recorded investment, with a related allowance recorded	41
Interest income recognized, with a related allowance recorded	0
Related allowance	0
Recorded investment	1,149
Unpaid principal balance	1,156
Average recorded investment	976
Interest income recognized	21
Residential Portfolio Segment [Member] \| Home Equity Line of Credit [Member]
Recorded investment, with no related allowance recorded	165
Unpaid principal balance, with no related allowance recorded	165
Average recorded investment, with no related allowance recorded	93
Interest income recognized, with no related allowance recorded	0
Recorded investment, with a related allowance recorded	0
Unpaid principal balance, with a related allowance recorded	0
Average recorded investment, with a related allowance recorded	0
Interest income recognized, with a related allowance recorded	0
Related allowance	0
Recorded investment	165
Unpaid principal balance	165
Average recorded investment	93
Interest income recognized	0
Consumer Portfolio Segment [Member]
Recorded investment, with no related allowance recorded	0
Unpaid principal balance, with no related allowance recorded	0
Average recorded investment, with no related allowance recorded	0
Interest income recognized, with no related allowance recorded	0
Recorded investment, with a related allowance recorded	0
Unpaid principal balance, with a related allowance recorded	0
Average recorded investment, with a related allowance recorded	38
Interest income recognized, with a related allowance recorded	0
Related allowance	0
Recorded investment	0
Unpaid principal balance	0
Average recorded investment	38
Interest income recognized	$ 0

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-17

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

+ Details

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

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-14A

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRelatedAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

+ Details

Name:	us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=amnb_ConstructionAndLandDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=amnb_OwnerOccupiedCommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=amnb_NonownerOccupiedCommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=amnb_ResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: