Pension (Narrative) (Details)	6 Months Ended
Jun. 30, 2012 Y
Pension [Abstract]
Final average pay plan, years	5
Number of years that produce highest average salary under final average pay plan	10

Number of years that produce highest average salary under final average pay plan

No definition available.

Name:	mbvt_NumberOfYearsThatProduceHighestAverageSalaryUnderFinalAveragePayPlan
Namespace Prefix:	mbvt_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration