Loan Portfolio and Credit Quality Loans Restructured (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($) loan	Sep. 30, 2019 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan		4
Restructuring Current Quarter, Pre-modification recorded investment		$ 3,675
Restructuring Current Quarter, Post-modification recorded investment		$ 3,689
TDRs that defaulted that were restructured in prior twelve months, Number of Loans | loan		0
TDRs that defaulted that were restructured in prior twelve months, Post-modification recorded investment		$ 0
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	1	1
Restructuring Current Quarter, Pre-modification recorded investment		$ 179
Restructuring Current Quarter, Post-modification recorded investment	$ 179	$ 179
TDRs that defaulted that were restructured in prior twelve months, Number of Loans | loan		0
TDRs that defaulted that were restructured in prior twelve months, Post-modification recorded investment		$ 0
Commercial tax-exempt
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan		0
Restructuring Current Quarter, Pre-modification recorded investment		$ 0
Restructuring Current Quarter, Post-modification recorded investment		$ 0
TDRs that defaulted that were restructured in prior twelve months, Number of Loans | loan		0
TDRs that defaulted that were restructured in prior twelve months, Post-modification recorded investment		$ 0
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Pre-modification recorded investment		$ 0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
TDRs that defaulted that were restructured in prior twelve months, Number of Loans | loan		0
TDRs that defaulted that were restructured in prior twelve months, Post-modification recorded investment		$ 0
Construction and land
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Pre-modification recorded investment		$ 0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
TDRs that defaulted that were restructured in prior twelve months, Number of Loans | loan		0
TDRs that defaulted that were restructured in prior twelve months, Post-modification recorded investment		$ 0
Residential
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	2	2
Restructuring Current Quarter, Pre-modification recorded investment		$ 3,222
Restructuring Current Quarter, Post-modification recorded investment	$ 3,227	$ 3,227
TDRs that defaulted that were restructured in prior twelve months, Number of Loans | loan		0
TDRs that defaulted that were restructured in prior twelve months, Post-modification recorded investment		$ 0
Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	1	1
Restructuring Current Quarter, Pre-modification recorded investment		$ 274
Restructuring Current Quarter, Post-modification recorded investment	$ 283	$ 283
TDRs that defaulted that were restructured in prior twelve months, Number of Loans | loan		0
TDRs that defaulted that were restructured in prior twelve months, Post-modification recorded investment		$ 0
Consumer and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Pre-modification recorded investment		$ 0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
TDRs that defaulted that were restructured in prior twelve months, Number of Loans | loan		0
TDRs that defaulted that were restructured in prior twelve months, Post-modification recorded investment		$ 0
Extension of term | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	1	1
Restructuring Current Quarter, Post-modification recorded investment	$ 179	$ 179
Extension of term | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Extension of term | Construction and land
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Extension of term | Residential
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Extension of term | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Extension of term | Consumer and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Temporary rate reduction | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Temporary rate reduction | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Temporary rate reduction | Construction and land
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Temporary rate reduction | Residential
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	2	2
Restructuring Current Quarter, Post-modification recorded investment	$ 3,227	$ 3,227
Temporary rate reduction | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	1	1
Restructuring Current Quarter, Post-modification recorded investment	$ 283	$ 283
Temporary rate reduction | Consumer and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Payment deferral | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Payment deferral | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Payment deferral | Construction and land
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Payment deferral | Residential
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Payment deferral | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Payment deferral | Consumer and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Combination Of Concessions | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Combination Of Concessions | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Combination Of Concessions | Construction and land
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Combination Of Concessions | Residential
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Combination Of Concessions | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0
Combination Of Concessions | Consumer and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructuring Current Quarter, Number of Loans | loan	0	0
Restructuring Current Quarter, Post-modification recorded investment	$ 0	$ 0