Loans And The Allowance For Credit Losses (Narrative) (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,200,170,000	$ 1,182,334,000
Net deferred loan origination cost	702,000mbvt_NetDeferredLoanOriginationCost	734,000mbvt_NetDeferredLoanOriginationCost
Overdrawn deposit balances classified as loan balances	219,000	235,000
Allowance for loan losses	11,989,000	11,833,000
Past due loans	1,293,000	933,000
91 Days more past due and Accruing	0
Nonaccruing TDR's	58,000	63,000
Commitments to lend additional funds to borrowers	0
Exposure threshold for loans subject to formal review	1,000,000
Real Estate Loans – Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	461,459,000	469,529,000
Allowance for loan losses	3,024,000	3,038,000
Real Estate Loans – Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	419,500,000	412,447,000
Allowance for loan losses	5,149,000	5,209,000
Commercial, Financial And Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	195,782,000	177,597,000
Allowance for loan losses	2,859,000	2,583,000
Past due loans	497,000	49,000
Residential And Commerical Loans Serviced For Others [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	13,660,000	13,530,000
Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Past due loans	228,000	414,000
Non-Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Past due loans	1,070,000	519,000
Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
91 Days more past due and Accruing		0
Restructured [Member]
Financing Receivable, Recorded Investment [Line Items]
Past due loans	0	0
Number of loans	0
Additional Analysis [Member]
Financing Receivable, Recorded Investment [Line Items]
Allowance for loan losses	$ 702,000	$ 1,230,000

Net deferred loan origination cost.

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- Definition

Nonaccruing troubled debt restructuring.

+ References

No definition available.

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- Definition

Threshold for loans subject to formal review.

+ References

No definition available.

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- Definition

Amount of deposits held by the entity that have been reclassified as loan balances receivable, for example, but not limited to, overdrafts receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 405

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479006&loc=d3e64164-112818

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953676-111524

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- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5111-111524

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- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph d

-Article 9

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-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

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-Paragraph 2

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1

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- Definition

Reflects the unfunded portion of contractual agreements to lend funds to borrowers for loans whose terms have been modified by troubled debt restructuring.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 1

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

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