Loans, Allowance for Credit Losses and Credit Quality Troubled Debt Restructurings (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($) contract	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($) contract	Dec. 31, 2019 USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	5	5	17	9
Tdrs Recorded Investment On Accrual Status	$ 17,521		$ 17,521		$ 19,599
Tdrs Recorded Investment On Nonaccrual Status	23,810		23,810		24,766
Financing Receivable Recorded Investment Trouble Debt Restructuring	41,331		41,331		44,365
Amount Of Specific Reserves Included In Allowance For Loan Losses Associated With Trouble Debt Restructuring					855
Additional Commitments To Lend To Borrower For Trouble Debt Restructuring	158		158		$ 63
Financing Receivable, Troubled Debt Restructuring, Premodification	827	$ 448	3,580	$ 784
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 827	$ 453	$ 3,639	$ 789
Commercial And Industrial [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	2	1	5	2
Financing Receivable, Troubled Debt Restructuring, Premodification	$ 83	$ 87	$ 391	$ 184
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 83	$ 87	$ 391	$ 184
Commercial Real Estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	3	1	8	2
Financing Receivable, Troubled Debt Restructuring, Premodification	$ 744	$ 133	$ 2,518	$ 283
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 744	$ 133	$ 2,518	$ 283
Small Business [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	0	1	2	2
Financing Receivable, Troubled Debt Restructuring, Premodification		$ 19	$ 112	$ 33
Financing Receivable, Troubled Debt Restructuring, Postmodification		19	$ 88	$ 33
Residential Real Estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	0		2	1
Financing Receivable, Troubled Debt Restructuring, Premodification		163	$ 559	$ 163
Financing Receivable, Troubled Debt Restructuring, Postmodification		$ 168	$ 642	$ 168
Home Equity Line of Credit [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract		1		2
Financing Receivable, Troubled Debt Restructuring, Premodification		$ 46		$ 121
Financing Receivable, Troubled Debt Restructuring, Postmodification		$ 46		$ 121