Income Taxes - Components of Provisional Tax Expense Related to Tax Law Changes (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Deferred taxes related to items recognized in continuing operations	$ (1,895)	$ 14,411
Deferred taxes on net actuarial loss on defined benefit post-retirement benefit plans	0	275
Deferred taxes on net unrealized losses on available for sale investment securities	0	507
Provisional Tax Expense Related to Tax Law Changes	$ (1,895)	$ 15,193

The amount of income tax expenses related to deferred taxes on net actuarial loss on defined benefit post-retirement benefit plans for the Tax Cuts and Jobs Act of 2017.

No definition available.

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