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Employee Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Retirement Plan [Member]
Deferred Compensation Arrangement with Individual, Requisite Service Period	1 year
Defined Contribution Plan, Employer Voluntary Matching, Bank Contribution	50.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	100.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	6 years
Defined Benefit Plan, Contributions by Employer	$ 156,000	$ 143,000	$ 155,000
Retirement Plan [Member] | Middlefield Banking Company [Member]
Defined Contribution Plan Annual Vesting Percentage	20.00%
Directors Retirement Plan [Member] | Middlefield Banking Company [Member]
Deferred Compensation Arrangement with Individual, Requisite Service Period	5 years
Retirement Benefits Term	10 years
Post-retirement Benefits Percentage of Compensation	25.00%
Executive Deferred Compensation Plan [Member] | Middlefield Banking Company [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 65,000	$ 115,000	$ 120,000

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- Definition

Defined Contribution Plan Annual Vesting Percentage

+ References

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- Definition

The percentage of matching voluntary contributions that the bank bases its contributions to the plan on.

+ References

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- Definition

Postretirement benefits percentage of compensation.

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Retirement Benefits Term

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- Definition

Minimum period the individual is required to perform services to be fully vested under the deferred compensation arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6409961&loc=d3e20487-108367

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
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X

- Definition

Amount of contributions made by the employer to defined benefit plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(ii)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
-Section 35
-Paragraph 123
-Subparagraph B
-URI http://asc.fasb.org/extlink&oid=64937487&loc=d3e36068-114959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Amount of discretionary contributions made by an employer to a defined contribution plan.

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

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- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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