Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Accounting	The consolidated financial statements include the accounts of American National Bankshares Inc. (the "Company") and its wholly owned subsidiary, American National Bank and Trust Company (the "Bank"). The Bank offers a wide variety of retail, commercial, secondary market mortgage lending, and trust and investment services which also include non-deposit products such as mutual funds and insurance policies. The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America ("GAAP") requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of the allowance for loan losses, goodwill and intangible assets, unfunded pension liability, other-than-temporary impairment of securities, accounting for merger and acquisition activity, accounting for acquired loans with specific credit-related deterioration, the valuation of deferred tax assets and liabilities, and the valuation of other real estate owned ("OREO"). All significant inter-company transactions and accounts are eliminated in consolidation, with the exception of the AMNB Trust and the MidCarolina Trusts, as detailed in Note 8. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments (consisting of normal recurring accruals) necessary to present fairly the results of the interim periods. The results of operations for the interim periods are not necessarily indicative of the results that may occur for any other period. Certain reclassifications have been made to prior period balances to conform to the current period presentation.
Adoption of New Accounting Standards and Recent Accounting Pronouncements	Adoption of New Accounting Standards On January 1, 2018, the Company adopted Accounting Standards Update ("ASU") 2016-01, "Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities," which amended the guidance on the classification and measurement of financial instruments. Upon adoption of ASU 2016-01, the Company reclassified $650,000 from other comprehensive income to retained earnings for the difference in amortized cost and fair value. For the quarter ended March 31, 2018, the Company recognized the equity securities fair value change in net income. Previously, the fair value changes were recognized, net of tax, in other comprehensive income (loss). The adoption of ASU 2016-01 did not have a material effect on the Company's consolidated financial statements. During the first quarter of 2018, the Company adopted ASU 2014-09, "Revenue from Contracts with Customers", and all subsequent amendments to the ASU (collectively "ASC 606"), which (i) creates a single framework for recognizing revenue from contracts with customers that fall within its scope and (ii) revises when it is appropriate to recognize a gain (loss) from the transfer of nonfinancial assets, such as OREO. The majority of the Company's revenue is from interest income, including loans and securities, that are outside the scope of the the standard. The services that fall within the scope of the standard are presented within noninterest income on the consolidated statement of income and are recognized as revenue as the Company satisfies its obligations to the customer. The revenue that falls within the scope of ASC 606 is primarily related to service charges on deposit accounts, cardholder and merchant income, wealth advisory services income, other service charges and fees, sales of other real estate, insurance commissions and miscellaneous fees. ASC 606 did not result in a change to the accounting for any in-scope revenue streams; as such, no cumulative effect adjustment was recorded. Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-02, "Leases (Topic 842)." Among other things, in the amendments in ASU 2016-02, lessees will be required to recognize the following for all leases (with the exception of short-term leases) at the commencement date: (1) a lease liability, which is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis; and (2) a right-of-use asset, which is an asset that represents the lessee's right to use, or control the use of, a specified asset for the lease term. Under the new guidance, lessor accounting is largely unchanged. Certain targeted improvements were made to align, where necessary, lessor accounting with the lessee accounting model and Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early application is permitted upon issuance. Lessees (for capital and operating leases) and lessors (for sales-type, direct financing, and operating leases) must apply a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective approach would not require any transition accounting for leases that expired before the earliest comparative period presented. Lessees and lessors may not apply a full retrospective transition approach. The Company has analyzed all leases currently in place and determined the adoption of ASU 2016-02 will not have a material impact on its consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments." The amendments in this ASU, among other things, require the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Financial institutions and other organizations will now use forward-looking information to better inform their credit loss estimates. Many of the loss estimation techniques applied today will still be permitted, although the inputs to those techniques will change to reflect the full amount of expected credit losses. In addition, the ASU amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. The amendments in this ASU are effective for Securities and Exchange Commission ("SEC") filers for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company has formed a committee to address the adoption of the standard and engaged a third party vendor to assist with the data gathering and analysis. The Company is currently assessing the impact that ASU 2016-13 will have on its consolidated financial statements. In January 2017, the FASB issued ASU No. 2017-04, "Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment". The amendments in this ASU simplify how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. Instead, under the amendments in this ASU, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. Public business entities that are SEC filers should adopt the amendments in this ASU for annual or interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of ASU 2017-04 to have a material impact on its consolidated financial statements. In March 2017, the FASB issued ASU 2017-08, "Receivables-Nonrefundable Fees and Other Costs (Subtopic 310‐20), Premium Amortization on Purchased Callable Debt Securities." The amendments in this ASU shorten the amortization period for certain callable debt securities purchased at a premium. Upon adoption of the standard, premiums on these qualifying callable debt securities will be amortized to the earliest call date. Discounts on purchased debt securities will continue to be accreted to maturity. The amendments are effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. Upon transition, entities should apply the guidance on a modified retrospective basis, with a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption and provide the disclosures required for a change in accounting principle. The Company is currently assessing the impact that ASU 2017-08 will have on its consolidated financial statements. In August 2017, the FASB issued ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities.” The amendments in this ASU modify the designation and measurement guidance for hedge accounting as well as provide for increased transparency regarding the presentation of economic results on both the financial statements and related footnotes. Certain aspects of hedge effectiveness assessments will also be simplified upon implementation of this update. The amendments are effective for annual periods, including interim periods within those annual periods, beginning after December 15, 2018. Early adoption is permitted, including adoption in any interim period. The Company is currently assessing the impact that ASU 2017-12 will have on its consolidated financial statements.

Adoption of New Accounting Standards

On January 1, 2018, the Company adopted Accounting Standards Update ("ASU") 2016-01, "Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities," which amended the guidance on the classification and measurement of financial instruments. Upon adoption of ASU 2016-01, the Company reclassified $650,000 from other comprehensive income to retained earnings for the difference in amortized cost and fair value. For the quarter ended March 31, 2018, the Company recognized the equity securities fair value change in net income. Previously, the fair value changes were recognized, net of tax, in other comprehensive income (loss). The adoption of ASU 2016-01 did not have a material effect on the Company's consolidated financial statements.

During the first quarter of 2018, the Company adopted ASU 2014-09, "Revenue from Contracts with Customers", and all subsequent amendments to the ASU (collectively "ASC 606"), which (i) creates a single framework for recognizing revenue from contracts with customers that fall within its scope and (ii) revises when it is appropriate to recognize a gain (loss) from the transfer of nonfinancial assets, such as OREO. The majority of the Company's revenue is from interest income, including loans and securities, that are outside the scope of the the standard. The services that fall within the scope of the standard are presented within noninterest income on the consolidated statement of income and are recognized as revenue as the Company satisfies its obligations to the customer. The revenue that falls within the scope of ASC 606 is primarily related to service charges on deposit accounts, cardholder and merchant income, wealth advisory services income, other service charges and fees, sales of other real estate, insurance commissions and miscellaneous fees. ASC 606 did not result in a change to the accounting for any in-scope revenue streams; as such, no cumulative effect adjustment was recorded.

Recent Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-02, "Leases (Topic 842)." Among other things, in the amendments in ASU 2016-02, lessees will be required to recognize the following for all leases (with the exception of short-term leases) at the commencement date: (1) a lease liability, which is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis; and (2) a right-of-use asset, which is an asset that represents the lessee's right to use, or control the use of, a specified asset for the lease term. Under the new guidance, lessor accounting is largely unchanged. Certain targeted improvements were made to align, where necessary, lessor accounting with the lessee accounting model and Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early application is permitted upon issuance. Lessees (for capital and operating leases) and lessors (for sales-type, direct financing, and operating leases) must apply a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective approach would not require any transition accounting for leases that expired before the earliest comparative period presented. Lessees and lessors may not apply a full retrospective transition approach. The Company has analyzed all leases currently in place and determined the adoption of ASU 2016-02 will not have a material impact on its consolidated financial statements.

In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments." The amendments in this ASU, among other things, require the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Financial institutions and other organizations will now use forward-looking information to better inform their credit loss estimates. Many of the loss estimation techniques applied today will still be permitted, although the inputs to those techniques will change to reflect the full amount of expected credit losses. In addition, the ASU amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. The amendments in this ASU are effective for Securities and Exchange Commission ("SEC") filers for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company has formed a committee to address the adoption of the standard and engaged a third party vendor to assist with the data gathering and analysis. The Company is currently assessing the impact that ASU 2016-13 will have on its consolidated financial statements.

In January 2017, the FASB issued ASU No. 2017-04, "Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment". The amendments in this ASU simplify how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. Instead, under the amendments in this ASU, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. Public business entities that are SEC filers should adopt the amendments in this ASU for annual or interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of ASU 2017-04 to have a material impact on its consolidated financial statements.

In March 2017, the FASB issued ASU 2017-08, "Receivables-Nonrefundable Fees and Other Costs (Subtopic 310‐20), Premium Amortization on Purchased Callable Debt Securities." The amendments in this ASU shorten the amortization period for certain callable debt securities purchased at a premium. Upon adoption of the standard, premiums on these qualifying callable debt securities will be amortized to the earliest call date. Discounts on purchased debt securities will continue to be accreted to maturity. The amendments are effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. Upon transition, entities should apply the guidance on a modified retrospective basis, with a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption and provide the disclosures required for a change in accounting principle. The Company is currently assessing the impact that ASU 2017-08 will have on its consolidated financial statements.

In August 2017, the FASB issued ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities.” The amendments in this ASU modify the designation and measurement guidance for hedge accounting as well as provide for increased transparency regarding the presentation of economic results on both the financial statements and related footnotes. Certain aspects of hedge effectiveness assessments will also be simplified upon implementation of this update. The amendments are effective for annual periods, including interim periods within those annual periods, beginning after December 15, 2018. Early adoption is permitted, including adoption in any interim period. The Company is currently assessing the impact that ASU 2017-12 will have on its consolidated financial statements.