Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2017
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. These reclassifications did not have an impact on net income and were considered immaterial. These statements should be read in conjunction with the Notes to Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2016.
Adoption of New Accounting Standard and Recent Accounting Pronouncements	Adoption of New Accounting Standard During the first quarter of 2017, the Company adopted Accounting Standards Update ("ASU") 2016-09, "Compensation-Stock Compensation (Topic 718): Improvements to Employer Share- Based Payment Accounting." This ASU simplifies several aspects of the accounting for share-based payment award transactions, one of which is the recognition of excess tax benefits and deficiencies related to share-based payments, including tax benefits of dividends on share-based payment awards. Prior to the adoption of ASU 2016-09, such tax consequences were recognized as components of additional paid-in capital. With the adoption of this ASU, tax benefits and deficiencies are recognized within income tax expense. In accordance with the adoption provisions of ASU 2016-09, the results for the second quarter and first six months of 2016 include only the excess tax (expense) benefits attributable to the second quarter and first six months of 2016 in the amount of $2,000 and $50,000, respectively. Recent Accounting Pronouncements In January 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-01, "Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities." The amendments in ASU 2016-01, among other things: (1) requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income; (2) requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes; (3) requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset (i.e., securities or loans and receivables); and (4) eliminates the requirement for public business entities to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost. The amendments in this ASU are effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company is currently assessing the impact that ASU 2016-01 will have on its consolidated financial statements. In February 2016, the 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 is currently assessing the impact that ASU 2016-02 will have on its consolidated financial statements. During 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 is currently assessing the impact that ASU 2016-13 will have on its consolidated financial statements. During August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments", to address diversity in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The amendments are effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The amendments should be applied using a retrospective transition method to each period presented. If retrospective application is impractical for some of the issues addressed by the update, the amendments for those issues would be applied prospectively as of the earliest date practicable. Early adoption is permitted, including adoption in an interim period. The Company does not expect the adoption of ASU 2016-15 to have a material impact on its consolidated financial statements. During January 2017, the FASB issued ASU No. 2017-01, "Business Combinations (Topic 805): Clarifying the Definition of a Business". The amendments in this ASU clarify the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. Under the current implementation guidance in Topic 805, there are three elements of a business-inputs, processes, and outputs. While an integrated set of assets and activities (collectively referred to as a "set") that is a business usually has outputs, outputs are not required to be present. In addition, all the inputs and processes that a seller uses in operating a set are not required if market participants can acquire the set and continue to produce outputs. The amendments in this ASU provide a screen to determine when a set is not a business. If the screen is not met, the amendments (1) require that to be considered a business, a set must include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create output and (2) remove the evaluation of whether a market participant could replace missing elements. The ASU provides a framework to assist entities in evaluating whether both an input and a substantive process are present. The amendments in this ASU are effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods. The amendments in this ASU should be applied prospectively on or after the effective date. No disclosures are required at transition. The Company does not expect the adoption of ASU 2017-01 to have a material impact on its consolidated financial statements. During 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. During March 2017, the FASB issued ASU 2017-07, "Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost." The amendments in this ASU require an employer that offers defined benefit pension plans, other postretirement benefit plans, or other types of benefits accounted for under Topic 715 to report the service cost component of net periodic benefit cost in the same line item(s) as other compensation costs arising from services rendered during the period. The other components of net periodic benefit cost are required to be presented in the income statement separately from the service cost component. If the other components of net periodic benefit cost are not presented on a separate line or lines, the line item(s) used in the income statement must be disclosed. In addition, only the service cost component will be eligible for capitalization as part of an asset, when applicable. The amendments are effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods. Early adoption is permitted. The Company does not expect the adoption of ASU 2017-07 to have a material impact on its consolidated financial statements. During 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. During May 2017, the FASB issued ASU 2017-09, "Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting." The amendments provide guidance on determining which changes to the terms and conditions of share-based payment awards require an entity to apply modification accounting under Topic 718. The amendments are effective for all entities for annual periods, including interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted, including adoption in any interim period, for reporting periods for which financial statements have not yet been issued. The Company is currently assessing the impact that ASU 2017-09 will have on its consolidated financial statements.

Adoption of New Accounting Standard

During the first quarter of 2017, the Company adopted Accounting Standards Update ("ASU") 2016-09, "Compensation-Stock Compensation (Topic 718): Improvements to Employer Share- Based Payment Accounting." This ASU simplifies several aspects of the accounting for share-based payment award transactions, one of which is the recognition of excess tax benefits and deficiencies related to share-based payments, including tax benefits of dividends on share-based payment awards. Prior to the adoption of ASU 2016-09, such tax consequences were recognized as components of additional paid-in capital. With the adoption of this ASU, tax benefits and deficiencies are recognized within income tax expense. In accordance with the adoption provisions of ASU 2016-09, the results for the second quarter and first six months of 2016 include only the excess tax (expense) benefits attributable to the second quarter and first six months of 2016 in the amount of $2,000 and $50,000, respectively.

Recent Accounting Pronouncements

In January 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-01, "Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities." The amendments in ASU 2016-01, among other things: (1) requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income; (2) requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes; (3) requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset (i.e., securities or loans and receivables); and (4) eliminates the requirement for public business entities to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost. The amendments in this ASU are effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company is currently assessing the impact that ASU 2016-01 will have on its consolidated financial statements.

In February 2016, the 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 is currently assessing the impact that ASU 2016-02 will have on its consolidated financial statements.

During 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 is currently assessing the impact that ASU 2016-13 will have on its consolidated financial statements.

During August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments", to address diversity in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The amendments are effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The amendments should be applied using a retrospective transition method to each period presented. If retrospective application is impractical for some of the issues addressed by the update, the amendments for those issues would be applied prospectively as of the earliest date practicable. Early adoption is permitted, including adoption in an interim period. The Company does not expect the adoption of ASU 2016-15 to have a material impact on its consolidated financial statements.

During January 2017, the FASB issued ASU No. 2017-01, "Business Combinations (Topic 805): Clarifying the Definition of a Business". The amendments in this ASU clarify the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. Under the current implementation guidance in Topic 805, there are three elements of a business-inputs, processes, and outputs. While an integrated set of assets and activities (collectively referred to as a "set") that is a business usually has outputs, outputs are not required to be present. In addition, all the inputs and processes that a seller uses in operating a set are not required if market participants can acquire the set and continue to produce outputs. The amendments in this ASU provide a screen to determine when a set is not a business. If the screen is not met, the amendments (1) require that to be considered a business, a set must include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create output and (2) remove the evaluation of whether a market participant could replace missing elements. The ASU provides a framework to assist entities in evaluating whether both an input and a substantive process are present. The amendments in this ASU are effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods. The amendments in this ASU should be applied prospectively on or after the effective date. No disclosures are required at transition. The Company does not expect the adoption of ASU 2017-01 to have a material impact on its consolidated financial statements.

During 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.

During March 2017, the FASB issued ASU 2017-07, "Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost." The amendments in this ASU require an employer that offers defined benefit pension plans, other postretirement benefit plans, or other types of benefits accounted for under Topic 715 to report the service cost component of net periodic benefit cost in the same line item(s) as other compensation costs arising from services rendered during the period. The other components of net periodic benefit cost are required to be presented in the income statement separately from the service cost component. If the other components of net periodic benefit cost are not presented on a separate line or lines, the line item(s) used in the income statement must be disclosed. In addition, only the service cost component will be eligible for capitalization as part of an asset, when applicable. The amendments are effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods. Early adoption is permitted. The Company does not expect the adoption of ASU 2017-07 to have a material impact on its consolidated financial statements.

During 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.

During May 2017, the FASB issued ASU 2017-09, "Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting." The amendments provide guidance on determining which changes to the terms and conditions of share-based payment awards require an entity to apply modification accounting under Topic 718. The amendments are effective for all entities for annual periods, including interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted, including adoption in any interim period, for reporting periods for which financial statements have not yet been issued. The Company is currently assessing the impact that ASU 2017-09 will have on its consolidated financial statements.