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Long-Term Debt (Long-Term Debt) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Schedule of Capitalization, Long-term Debt [Line Items]    
Long-term debt $ 2,320us-gaap_OtherLongTermDebt $ 2,403us-gaap_OtherLongTermDebt
FHLB Notes, Payable Through March 2029, Rates Ranging From 1.50% to 2.50% [Member]    
Schedule of Capitalization, Long-term Debt [Line Items]    
Interest rate range, minimum 1.50%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
/ us-gaap_LongtermDebtTypeAxis
= mbvt_FederalHomeLoanBankNotesPayableThroughMarchTwoThousandTwentyNineMember		  
Interest rate range, maximum 2.50%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
/ us-gaap_LongtermDebtTypeAxis
= mbvt_FederalHomeLoanBankNotesPayableThroughMarchTwoThousandTwentyNineMember		  
FHLB Notes $ 2,320us-gaap_FederalHomeLoanBankAdvancesLongTerm
/ us-gaap_LongtermDebtTypeAxis
= mbvt_FederalHomeLoanBankNotesPayableThroughMarchTwoThousandTwentyNineMember		 $ 2,403us-gaap_FederalHomeLoanBankAdvancesLongTerm
/ us-gaap_LongtermDebtTypeAxis
= mbvt_FederalHomeLoanBankNotesPayableThroughMarchTwoThousandTwentyNineMember