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Note 17 - Regulatory Capital (Tables) | 12 Months Ended
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Dec. 31, 2017
Notes Tables |
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] |
|  | As of December 31, 2017 |
|  |  |  |  |  | Tier 1 Risk |  |  | Common |  |  | Total Risk |
|  | Leverage |  |  | Based |  |  | Equity Tier 1 |  |  | Based |
The Middlefield Banking Company |  |  | 9.47 | % |  |  | 10.88 | % |  |  | 10.88 | % |  |  | 11.64 | %
Middlefield Banc Corp. |  |  | 10.20 | % |  |  | 11.64 | % |  |  | 10.79 | % |  |  | 12.41 | %
Adequately capitalized ratio |  |  | 4.00 | % |  |  | 6.00 | % |  |  | 4.50 | % |  |  | 8.00 | %
Adequately capitalized ratio plus fully phased-in capital conservation buffer |  |  | 4.00 | % |  |  | 8.50 | % |  |  | 7.00 | % |  |  | 10.50 | %
Well-capitalized ratio (Bank only) |  |  | 5.00 | % |  |  | 8.00 | % |  |  | 6.50 | % |  |  | 10.00 | %
|  | As of December 31, 2016 |
|  |  |  |  |  | Tier 1 Risk |  |  | Common |  |  | Total Risk |
|  | Leverage |  |  | Based |  |  | Equity Tier 1 |  |  | Based |
The Middlefield Banking Company |  |  | 9.29 | % |  |  | 13.03 | % |  |  | 13.03 | % |  |  | 14.25 | %
Middlefield Banc Corp. |  |  | 9.27 | % |  |  | 13.07 | % |  |  | 13.07 | % |  |  | 15.75 | %
Adequately capitalized ratio |  |  | 4.00 | % |  |  | 6.00 | % |  |  | 4.50 | % |  |  | 8.00 | %
Adequately capitalized ratio plus fully phased-in capital conservation buffer |  |  | 4.00 | % |  |  | 8.50 | % |  |  | 7.00 | % |  |  | 10.50 | %
Well-capitalized ratio (Bank only) |  |  | 5.00 | % |  |  | 8.00 | % |  |  | 6.50 | % |  |  | 10.00 | %

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- Definition Tabular disclosure of the capital amounts and ratios as of the balance sheet date, indicating whether the entity or entities are in compliance with regulatory capital requirements, by entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958570-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1G -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958577-112826 + Details
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