| Document And Entity Information - USD ($) $ in Millions | 12 Months Ended | ||
| Dec. 31, 2023 | Mar. 28, 2024 | Jun. 30, 2023 | |
| Document Information [Line Items] | |||
| Entity, Registrant Name | Middlefield Banc Corp. | ||
| Current Fiscal Year End Date | --12-31 | ||
| Document, Fiscal Period Focus | FY | ||
| Document, Fiscal Year Focus | 2023 | ||
| Document, Type | 10-K/A | ||
| Document, Annual Report | true | ||
| Document, Period End Date | Dec. 31, 2023 | ||
| Document, Transition Report | false | ||
| Entity, File Number | 001-36613 | ||
| Entity, Incorporation, State or Country Code | OH | ||
| 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 | 44062-0035 | ||
| City Area Code | 440 | ||
| Local Phone Number | 632-1666 | ||
| Trading Symbol | MBCN | ||
| Title of 12(b) Security | Common Stock, Without Par Value | ||
| Security Exchange Name | NASDAQ | ||
| Entity, Well-known Seasoned Issuer | No | ||
| Entity, Voluntary Filers | No | ||
| Entity, Current Reporting Status | Yes | ||
| Entity, Interactive Data, Current | Yes | ||
| Entity, Filer Category | Non-accelerated Filer | ||
| Entity, Small Business | true | ||
| Entity, Emerging Growth Company | false | ||
| ICFR Auditor Attestation Flag | false | ||
| Document, Financial Statement Error Correction Flag | false | ||
| Entity, Shell Company | false | ||
| Entity, Public Float | $ 215.2 | ||
| Entity, Common Stock Shares, Outstanding | 8,069,144 | ||
| Amendment Description | Middlefield Banc Corp (“Company”) is filing this Amendment No. 1 to its Annual Report on Form 10-K (“Form 10-K/A") for the fiscal year ended December 31, 2023, originally filed with the Securities and Exchange Commission (“SEC") on March 28, 2024 (“Original Filing”). This Form 10-K/A is being filed to correct the Report of Independent Registered Public Accounting Firm of S. R. Snodgrass, P.C. included in the Original Filing due to an inadvertent administrative error. This Amendment does not alter in any way S. R. Snodgrass, P.C.’s opinion on the Company’s financial statements. This Form 10-K/A is also being filed to reflect correct dates in Management’s Annual Report on Internal Control Over Financial Reporting and amend wording in Item 9A(b). In accordance with Rule 12b-15 under the Securities Exchange Act of 1934, as amended, certifications by the Company’s principal executive officer and principal financial officer are filed as exhibits to this Form 10-K/A under Item 15 of Part IV. Additionally, this Form 10-K/A does not include the certifications under Section 906 of the Sarbanes-Oxley Act of 2002, as no financial statements are being filed with this Form 10-K/A. Except as described above, this Form 10-K/A does not amend, modify, or otherwise update any other information in the Original Filing. We have not updated or amended the disclosures contained in the Original Filing to reflect events that have occurred since the Original Filing. Accordingly, this Form 10-K/A should be read in conjunction with our Original Filing. | ||
| Auditor Name | S. R. Snodgrass, P.C | ||
| Auditor Location | Cranberry Township, Pennsylvania | ||
| Auditor Firm ID | 74 | ||
| Amendment Flag | true | ||
| Entity, Central Index Key | 0000836147 |
