Securities, Other Than Temporary Impairment (Details)	Mar. 31, 2013 Security
Securities [Abstract]
Number of securities temporarily impaired	58
Number of securities temporarily impaired in investment grade	57
Number of securities temporarily impaired in speculative grade	1

Total number of securities impaired in speculative grade during the period.

No definition available.

Name:	mbrg_NumberOfSecuritiesTemporarilyImpairedInSpeculativeGrade
Namespace Prefix:	mbrg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant