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Note 16 - Regulatory Capital (Details) - Capital Ratios (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
To Be Well Capitalized 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
To Be Well Capitalized 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
To Be Well Capitalized 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Middlefield Banc Corp. [Member]    
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Actual 70,693us-gaap_Capital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 64,220us-gaap_Capital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
Actual 14.64%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 14.06%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
For Capital Adequacy Purposes 38,642us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 36,541us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
For Capital Adequacy Purposes 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
To Be Well Capitalized 48,302us-gaap_CapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 45,676us-gaap_CapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
To Be Well Capitalized 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
Actual 64,645us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 58,494us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
Actual 13.38%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 12.81%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
For Capital Adequacy Purposes 19,321us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 18,270us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
For Capital Adequacy Purposes 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
To Be Well Capitalized 28,981us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 27,406us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
To Be Well Capitalized 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
Actual 64,645us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 58,494us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
Actual 9.60%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 8.97%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
For Capital Adequacy Purposes 26,945us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 26,093us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
For Capital Adequacy Purposes 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
To Be Well Capitalized 33,682us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 32,617us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
To Be Well Capitalized 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember		 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBancCorpMember
Middlefield Banking Company [Member]    
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Actual 68,325us-gaap_Capital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 53,194us-gaap_Capital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
Actual 14.19%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 13.77%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
For Capital Adequacy Purposes 38,507us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 30,906us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
For Capital Adequacy Purposes 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
To Be Well Capitalized 48,134us-gaap_CapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 38,632us-gaap_CapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
To Be Well Capitalized 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
Actual 62,315us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 48,364us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
Actual 12.95%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 12.52%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
For Capital Adequacy Purposes 19,253us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 15,453us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
For Capital Adequacy Purposes 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
To Be Well Capitalized 28,880us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 23,179us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
To Be Well Capitalized 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
Actual 62,315us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 48,364us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
Actual 9.25%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 8.51%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
For Capital Adequacy Purposes 26,945us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 22,735us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
For Capital Adequacy Purposes 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
To Be Well Capitalized 33,682us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 28,419us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
To Be Well Capitalized 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember		 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
/ dei_LegalEntityAxis
= mbcn_MiddlefieldBankingCompanyMember
Emerald Bank [Member]    
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Actual   9,482us-gaap_Capital
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
Actual   13.76%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
For Capital Adequacy Purposes   5,514us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
For Capital Adequacy Purposes   8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
To Be Well Capitalized   6,893us-gaap_CapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
To Be Well Capitalized   10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
Actual   8,605us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
Actual   12.48%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
For Capital Adequacy Purposes   2,757us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
For Capital Adequacy Purposes   4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
To Be Well Capitalized   4,136us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
To Be Well Capitalized   6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
Actual   8,605us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
Actual   10.92%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
For Capital Adequacy Purposes   3,152us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
For Capital Adequacy Purposes   4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
To Be Well Capitalized   3,940us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember
To Be Well Capitalized   5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
/ dei_LegalEntityAxis
= mbcn_EmeraldBankMember