Summary of Significant Accounting Policies (Details) $ in Thousands			3 Months Ended		12 Months Ended
	May 01, 2018 USD ($) payment	Dec. 15, 2017 USD ($) branch shares	Jun. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) office loan bankingLocation reportingUnit plan location trust	Dec. 31, 2019 USD ($)	Jan. 01, 2020 USD ($)
Business Acquisition [Line Items]
Number of banking locations | bankingLocation					41
Number of wealth offices | office					7
Number of insurance and risk management locations | location					2
Number of trusts acquired | trust					2
Cash reserve deposit required and made					$ 0	$ 24,600
Delinquency period after which the accrual of Interest Is generally discontinued					90 days
Delinquency period after which a lease Is charged off					120 days
Available for sale securities, accrued interest					$ 2,000
Held-to-maturity securities, accrued interest					37
Financing receivable, accrued interest					12,100
Interest deferrals, COVID-19					64
ACL on OBS credit exposure					2,900		$ 360
Provision for credit losses on OBS credit exposure					$ 1,700
Troubled debt restructuring, number of contracts, COVID-19 | loan					66
Troubled debt restructuring, percent of total loans, COVID-19					2.10%
Federal home loan bank stock					$ 12,666	23,744
Federal reserve bank stock					12,500
Capitalized software implementation costs					6,900	2,900
Capitalized contract costs, amortization					$ 618	$ 280
Number of non-qualified defined benefit supplemental executive retirement plans | plan					2
Number of reporting units | reportingUnit					3
Consumer
Business Acquisition [Line Items]
Troubled debt restructuring, amount, COVID-19					$ 7,300
Commercial and industrial
Business Acquisition [Line Items]
Troubled debt restructuring, number of contracts, COVID-19 | loan					37
Troubled debt restructuring, amount, COVID-19					$ 67,700
Domenick
Business Acquisition [Line Items]
Value of consideration	$ 1,456
Cash paid at closing	$ 750		$ 175	$ 225
Number of contingent cash payments | payment	1
Maximum contingent cash payment amount per period	$ 250
RBPI
Business Acquisition [Line Items]
Value of consideration		$ 138,740
Number of shares issued | shares		3,101,316
Number of securities called by warrants (in shares) | shares		140,224
Warrants to purchase BMTC common stock value		$ 1,900
Cash-out of certain options		112
Cash in lieu of fractional shares		7
Loans assumed		570,400
Investment securities available for sale		121,587
Deposits		$ 593,172
Number of branches acquired | branch		12