Repurchase Agreements (Details) $ in Thousands	9 Months Ended
Sep. 30, 2015 USD ($)
Available-for-sale Securities Pledged as Collateral	$ 170,629
Held-to-maturity Securities Pledged as Collateral	$ 97,166
Percentage Overwhich securities qualifies for pledging	100.00%
Overnight and Continuous [Member]
Available-for-sale Securities Pledged as Collateral	$ 170,228
Held-to-maturity Securities Pledged as Collateral	97,166
Greater than 90 Days [Member]
Available-for-sale Securities Pledged as Collateral	401
U.S. Treasury Obligations [Member]
Available-for-sale Securities Pledged as Collateral	24,649
U.S. Treasury Obligations [Member] \| Overnight and Continuous [Member]
Available-for-sale Securities Pledged as Collateral	24,649
U.S. Agency Obligations [Member]
Held-to-maturity Securities Pledged as Collateral	13,953
U.S. Agency Obligations [Member] \| Overnight and Continuous [Member]
Held-to-maturity Securities Pledged as Collateral	13,953
U.S. GSEs [Member]
Available-for-sale Securities Pledged as Collateral	15,451
U.S. GSEs [Member] \| Overnight and Continuous [Member]
Available-for-sale Securities Pledged as Collateral	15,451
FHLB Obligations [Member]
Available-for-sale Securities Pledged as Collateral	42,278
FHLB Obligations [Member] \| Overnight and Continuous [Member]
Available-for-sale Securities Pledged as Collateral	42,278
Agency MBSs [Member]
Available-for-sale Securities Pledged as Collateral	44,249
Held-to-maturity Securities Pledged as Collateral	18,694
Agency MBSs [Member] \| Overnight and Continuous [Member]
Available-for-sale Securities Pledged as Collateral	43,848
Held-to-maturity Securities Pledged as Collateral	18,694
Agency MBSs [Member] \| Greater than 90 Days [Member]
Available-for-sale Securities Pledged as Collateral	401
Agency CMBSs [Member]
Available-for-sale Securities Pledged as Collateral	14,008
Agency CMBSs [Member] \| Overnight and Continuous [Member]
Available-for-sale Securities Pledged as Collateral	14,008
Agency CMOs [Member]
Available-for-sale Securities Pledged as Collateral	29,994
Held-to-maturity Securities Pledged as Collateral	64,519
Agency CMOs [Member] \| Overnight and Continuous [Member]
Available-for-sale Securities Pledged as Collateral	29,994
Held-to-maturity Securities Pledged as Collateral	$ 64,519

Represents the percentage above the gross outstanding balance of repurchase agreements, which the company manages the risk by pledging the securities.

No definition available.

+ Details

Name:	mbvt_PercentageOverWhichSecuritiesQualifiesForPledging
Namespace Prefix:	mbvt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value of available-for-sale securities that serve as collateral for borrowings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5086-111524

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying amount of held-to-maturity securities that serve as collateral for borrowings.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesPledgedAsCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis=us-gaap_MaturityOvernightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis=us-gaap_MaturityOver90DaysMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_FederalHomeLoanBankCertificatesAndObligationsFHLBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=mbvt_CollateralizedMortgageObligationsIssuedByUSGovernmentSponsoredEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: