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Note 13 - Employee Benefits (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term   9 years 350 days  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in Shares)   9,000  
Retirement Plan [Member]
     
Deferred Compensation Arrangement with Individual, Requisite Service Period one    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 6 years    
Defined Benefit Plan, Contributions by Employer (in Dollars) $ 125,000 $ 104,000 $ 106,000
Directors Retirement Plan [Member] | Middlefield Banking Company [Member]
     
Deferred Compensation Arrangement with Individual, Requisite Service Period five    
Retirement Benefits Term 10 years    
Executive Deferred Compensation Plan [Member] | Middlefield Banking Company [Member]
     
Defined Contribution Plan, Employer Discretionary Contribution Amount (in Dollars) $ 139,000 $ 91,000 $ 92,000
Stock Option and Restricted Stock Plan [Member] | Maximum [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term 10 years    
Stock Option and Restricted Stock Plan [Member] | Minimum [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 1 year    
Stock Option and Restricted Stock Plan [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in Shares) 160,000    
Omnibus Equity Plan [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in Shares) 1,722 2,400 110