Significant Accounting Policies (Policies)	3 Months Ended
Significant Accounting Policies (Policies)	Mar. 31, 2026
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]	Basis of Presentation The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“US GAAP”) for interim information and with the instructions to the Quarterly Report on Form 10-Q, as applicable to a smaller reporting company. Accordingly, they do not include all the information and notes required by US GAAP for complete financial statements. The financial statements are unaudited; but in the opinion of management include all adjustments (consisting only of normal recurring adjustments) necessary for a fair presentation thereof. The balances as of December 31, 2025 have been derived from the audited consolidated financial statements. These interim period financial statements should be read in conjunction with the audited consolidated financial statements and accompanying notes thereto contained in the Form 10-K for the year ended December 31, 2025, filed by the Company with the SEC on March 13, 2026. The results of operations for the three months ended March 31, 2026 are not necessarily indicative of the results that may be expected for the year ending December 31, 2026, or any other period. The Company’s significant accounting policies followed in preparation of the unaudited consolidated financial statements, are disclosed in Note 1 of the Notes to Consolidated Financial Statements in the 2025 Form 10-K. There have been no significant changes to the application of significant accounting policies since December 31, 2025.
Consolidation, Policy [Policy Text Block]	Principles of Consolidation – The consolidated financial statements include accounts of the Company and its wholly-owned subsidiaries, the Bank and MainStreet Community Capital, LLC. All significant intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates, Policy [Policy Text Block]	Use of estimates – The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting period. Actual results could differ from the estimates.
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Adopted Accounting Developments There were no accounting standard updates adopted in the three months ended March 31, 2026. Impact of Recently Issued Accounting Pronouncements In November 2024, the Financial Accounting Standards Board (FASB) issued ASU 2024-03, “Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses.” ASU 2024-03 requires public companies to disclose, in the notes to the financial statements, specific information about certain costs and expenses at each interim and annual reporting period. This includes disclosing amounts related to employee compensation, depreciation, and intangible asset amortization. In addition, public companies will need to provide qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated quantitatively. The FASB subsequently issued ASU 2025-01, “Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Clarifying the Effective Date”, which amends the effective date of ASU 2024-03 to clarify that all public business entities are required to adopt the guidance in ASU 2024-03 in annual reporting periods beginning after December 15, 2026, and interim periods within annual reporting periods beginning after December 15, 2027. Early adoption of ASU 2024-03 is permitted. Implementation of ASU 2024-03 may be applied prospectively or retrospectively. The Company does not expect the adoption of ASU 2024-03 to have a material impact on its consolidated financial statements. In November 2025, the Financial Accounting Standards Board (FASB) issued ASU 2025-08, “Financial Instruments—Credit Losses (Topic 326): Purchased Loans.” The amendments in this ASU expand the population of acquired financial assets accounted for using the gross-up approach. Acquired loans (excluding credit cards) are deemed purchased seasoned loans and accounted for using the gross-up approach upon acquisition if criteria established by the new guidance are met. This change aims to enhance comparability, consistency, and better reflect the economics of acquiring financial assets. This ASU is effective for annual reporting periods beginning after December 15, 2026, and for interim reporting periods within those annual reporting periods. Early adoption is permitted in an interim or annual reporting period in which financial statements have not yet been issued or made available for issuance. If an entity adopts this ASU in an interim reporting period, it should apply it as of the beginning of that interim reporting period or the beginning of the annual reporting period that includes that interim reporting period. The Company does not expect the adoption of ASU 2025-08 to have a material impact on its consolidated financial statements.

Disclosure of accounting policy for the use of estimates in the preparation of financial statements in conformity with generally accepted accounting principles.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

MainStreet Bancshares, Inc. 10-Q