No definition available.

Name:	amnb_LoanAbstract
Namespace Prefix:	amnb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

+ Details

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

- References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossAdditionalInformationAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

+ Details

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

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

+ Details

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

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5074-111524

+ Details

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

- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

+ Details

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

- Details

Name:	us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis=us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- 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_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
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:

- Details

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

Allowance for Loan Losses and Reserve for Unfunded Lending Commitments - Allowance by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan Losses
Balance, beginning of year	$ 12,601	$ 12,427	$ 12,600
Charge-offs	(326)	(1,200)	(964)
Recoveries	276	424	391
Provision	250	950	400
Balance, end of year	12,801	12,601	12,427
Allowance for Loan Losses
Individually evaluated for impairment				$ 23	$ 35
Collectively evaluated for impairment				12,429	12,159
Total	12,601	12,427	12,600	12,801	12,601
Loans
Individually evaluated for impairment				4,844	4,707
Collectively evaluated for impairment				1,131,308	966,940
Loans, net of unearned income				1,164,821	1,005,525
Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses
Balance, beginning of year	407
Balance, end of year	349	407
Allowance for Loan Losses
Total	407	407		349	407
Loans
Loans, net of unearned income				28,669	33,878
Commercial
Allowance for Loan Losses
Balance, beginning of year	2,065	1,818
Charge-offs	(40)	(175)
Recoveries	40	32
Provision	30	390
Balance, end of year	2,095	2,065	1,818
Allowance for Loan Losses
Individually evaluated for impairment				0	0
Collectively evaluated for impairment				2,087	2,065
Total	2,065	1,818	1,818	2,095	2,065
Loans
Individually evaluated for impairment				43	95
Collectively evaluated for impairment				208,258	176,798
Loans, net of unearned income				208,717	177,481
Commercial \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses
Balance, beginning of year	0
Balance, end of year	8	0
Allowance for Loan Losses
Total	0	0		8	0
Loans
Loans, net of unearned income				416	588
Commercial real estate
Allowance for Loan Losses
Balance, beginning of year	6,930	6,814
Charge-offs	(10)	(482)
Recoveries	32	124
Provision	403	474
Balance, end of year	7,355	6,930	6,814
Allowance for Loan Losses
Individually evaluated for impairment				0	9
Collectively evaluated for impairment				7,248	6,750
Total	6,930	6,814	6,814	7,355	6,930
Loans
Individually evaluated for impairment				2,186	2,245
Collectively evaluated for impairment				610,462	487,177
Loans, net of unearned income				625,218	503,154
Commercial real estate \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses
Balance, beginning of year	171
Balance, end of year	107	171
Allowance for Loan Losses
Total	171	171		107	171
Loans
Loans, net of unearned income				12,570	13,732
Residential real estate
Allowance for Loan Losses
Balance, beginning of year	3,546	3,715
Charge-offs	(87)	(323)
Recoveries	68	139
Provision	(224)	15
Balance, end of year	3,303	3,546	3,715
Allowance for Loan Losses
Individually evaluated for impairment				23	26
Collectively evaluated for impairment				3,046	3,284
Total	3,546	3,715	3,715	3,303	3,546
Loans
Individually evaluated for impairment				2,588	2,346
Collectively evaluated for impairment				307,600	297,281
Loans, net of unearned income				325,855	318,883
Residential real estate \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses
Balance, beginning of year	236
Balance, end of year	234	236
Allowance for Loan Losses
Total	236	236		234	236
Loans
Loans, net of unearned income				15,667	19,256
Consumer
Allowance for Loan Losses
Balance, beginning of year	60	80
Charge-offs	(189)	(220)
Recoveries	136	129
Provision	41	71
Balance, end of year	48	60	80
Allowance for Loan Losses
Individually evaluated for impairment				0	0
Collectively evaluated for impairment				48	60
Total	60	80	80	48	60
Loans
Individually evaluated for impairment				27	21
Collectively evaluated for impairment				4,988	5,684
Loans, net of unearned income				5,031	6,007
Consumer \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses
Balance, beginning of year	0
Balance, end of year	0	0
Allowance for Loan Losses
Total	0	0		0	0
Loans
Loans, net of unearned income				16	302
Unallocated
Allowance for Loan Losses
Balance, beginning of year	0	0
Charge-offs	0	0
Recoveries	0	0
Provision	0	0
Balance, end of year	0	0	0
Allowance for Loan Losses
Individually evaluated for impairment				0	0
Collectively evaluated for impairment				0	0
Total	0	0	$ 0	0	0
Loans
Individually evaluated for impairment				0	0
Collectively evaluated for impairment				0	0
Loans, net of unearned income				0	0
Unallocated \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses
Balance, beginning of year	0
Balance, end of year	0	0
Allowance for Loan Losses
Total	$ 0	$ 0		0	0
Loans
Loans, net of unearned income				$ 0	$ 0