| Document and Entity Information | Dec. 01, 2022 |
| Cover [Abstract] | |
| Entity Registrant Name | MIDDLEFIELD BANC CORP |
| Amendment Flag | true |
| Entity Central Index Key | 0000836147 |
| Document Type | 8-K/A |
| Document Period End Date | Dec. 01, 2022 |
| Entity Incorporation State Country Code | OH |
| Entity File Number | 001-36613 |
| Entity Tax Identification Number | 34-1585111 |
| Entity Address, Address Line One | 15985 East High Street |
| Entity Address, City or Town | Middlefield |
| Entity Address, State or Province | OH |
| Entity Address, Postal Zip Code | 44062 |
| City Area Code | (440) |
| Local Phone Number | 632-1666 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, no par value |
| Trading Symbol | MBCN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Description | On December 1, 2022, Middlefield Banc Corp. (the “Company”) filed a Current Report on Form 8-K (the “Original Report”) to report that the Company completed its merger with Liberty Bancshares, Inc. (“Liberty”), pursuant to the Agreement and Plan of Merger, dated as of May 26, 2022, by and among the Company, MBCN Merger Subsidiary, LLC, a wholly owned subsidiary of the Company (“Merger Sub”) and Liberty (the “Merger Agreement”). Pursuant to the terms of the Merger Agreement, at the effective time of the Merger (the “Effective Time”) Liberty merged with and into Merger Sub (the “Merger”), with Merger Sub as the surviving entity in the Merger. This Current Report on Form 8-K/A (the “Amendment”) amends the Original Report to include the financial statements of Liberty and the pro forma financial information required by Item 9.01 of Form 8-K. Except as expressly set forth herein, this Amendment does not amend, modify, or update the disclosures contained in the Original Report. |
