Non-Performing Loans and Leases (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased credit-impaired loans	$ 90	$ 90

Loans And Leases Receivable Purchased Credit Impaired Became Non Performing Subsequent To Acquisition

No definition available.

Name:	bmtc_LoansAndLeasesReceivablePurchasedCreditImpairedBecameNonPerformingSubsequentToAcquisition
Namespace Prefix:	bmtc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration