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Derivatives Derivatives not designated as hedging instruments narrative (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Derivative [Line Items]    
Notional Amount $ 11,498,000invest_DerivativeNotionalAmount $ 8,470,000invest_DerivativeNotionalAmount
Not Designated as Hedging Instrument [Member] | Open best efforts interest rate lock commitments [Member]    
Derivative [Line Items]    
Notional Amount   103,500,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= mbrg_OpenBestEffortsInterestRateLockCommitmentsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Not Designated as Hedging Instrument [Member] | Open forward sales commitments to investors [Member]    
Derivative [Line Items]    
Notional Amount   $ 114,400,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= mbrg_OpenForwardSalesCommitmentsToInvestorsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember