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Note 14 - Employee Benefits (Details Textual) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | $ 538,000 |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $ 0 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | 8,237 | 500 |
Payments For Stock Options Exercised | $ (184,000) | $ 6,000 | $ 7,000
Restricted Stock [Member] |  |  |
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures | 0 | 0 | 0
Employee Stock Option [Member] |  |  |
Payments For Stock Options Exercised | $ 95,000 | $ 6,000 |
Restricted Stock Units (RSUs) [Member] |  |  |
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures | 5,825 | 5,090 | 3,905
Allocated Share-based Compensation Expense | $ 196,000 | $ 123,000 | $ 55,000
Retirement Plan [Member] |  |  |
Defined Contribution Plan Employer Voluntary Matching Bank Contribution | 50.00% |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay | 6.00% |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | 6 years |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | $ 258,000 | 156,000 | 156,000
Retirement Plan [Member] | Middlefield Banking Company [Member] |  |  |
Defined Contribution Plan Annual Vesting Percentage | 20.00% |  |
Retirement Plan [Member] | Liberty Bank, N.A. [Member] |  |  |
Deferred Compensation Arrangement with Individual, Requisite Service Period | 3 years |  |
Directors Retirement Plan [Member] | Middlefield Banking Company [Member] |  |  |
Deferred Compensation Arrangement with Individual, Requisite Service Period | 5 years |  |
Retirement Benefits Term | 10 years |  |
Postretirement Benefits Percentage of Compensation | 25.00% |  |
Executive Deferred Compensation Plan [Member] | Middlefield Banking Company [Member] |  |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount | $ 110,000 | $ 99,000 | $ 65,000
Stock Option and Restricted Stock Plan [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 160,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term | 10 years |  |
Shares, Outstanding | 92,759 |  |
The 2017 Plan [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 224,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term | 10 years |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 218,175 |  |
Omnibus Equity Plan [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | 0 | 0 |

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- Definition Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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