Note 14 - Employee Benefits (Details Textual) - USD ($)		12 Months Ended
May 10, 2017	Dec. 31, 2024	Dec. 31, 2023
Share-Based Payment Arrangement, Expense		$ 714,000	$ 391,000
Share-Based Payment Arrangement, Expense, Tax Benefit		150,000	82,000
Deferred Compensation Share-Based Arrangements, Liability, Current and Noncurrent		$ 462,000	$ 758,000
Share-Based Payment Arrangement, Nonemployee [Member]
Shares Issued, Shares, Share-Based Payment Arrangement, before Forfeiture (in shares)		6,768	7,475
Shares Issued, Value, Share-Based Payment Arrangement, before Forfeiture		$ 187,000	$ 203,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term (Year)		2 years 4 months 24 days
Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture (in shares)		70,538	36,173
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)		19,745	10,713
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 22.98	$ 27.57
Share-Based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount		$ 1,800,000
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)		2 years 1 month 6 days
Restricted Stock [Member] \| Vested in Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)		311,000	195,000
Restricted Stock [Member] \| Vested in Cash [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value		$ 213,000	$ 114,000
Retirement Plan [Member]
Defined Contribution Plan Employer Voluntary Matching Bank Contribution		66.00%	66.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay		6.00%	6.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)		6 years
Defined Benefit Plan, Plan Assets, Contributions by Employer		$ 520,000	$ 641,000
Retirement Plan [Member] \| Middlefield Banking Company [Member]
Defined Contribution Plan Annual Vesting Percentage		20.00%
Executive Deferred Compensation Plan [Member] \| Middlefield Banking Company [Member]
Deferred Compensation Arrangement with Individual, Recorded Liability		$ 3,500,000	3,800,000
Defined Contribution Plan, Employer Discretionary Contribution Amount		$ 91,000	$ 437,000
The 2017 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)	448,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term (Year)	10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)		352,063

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Number of shares authorized for issuance under share-based payment arrangement.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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