Loans, Allowance for Credit Losses and Credit Quality Financing Receivable Past Due (Details) $ in Thousands	Mar. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	420	447
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 25	$ 2,157
Financing Receivable, Past Due	29,357	25,485
Financing Receivable, Not Past Due	8,887,073	8,848,154
Loans and Leases Receivable, Gross	$ 8,916,430	$ 8,873,639
Number Of Financing Receivables Total Past Due | loan	562	603
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	33	43
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	109	113
Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	13	1
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 0	$ 0
Financing Receivable, Past Due	3,008	1,336
Financing Receivable, Not Past Due	1,445,216	1,393,700
Loans and Leases Receivable, Gross	$ 1,448,224	$ 1,395,036
Number Of Financing Receivables Total Past Due | loan	19	8
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	0	2
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	6	5
Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	18	7
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 0	$ 218	[1]
Financing Receivable, Past Due	8,871	3,922
Financing Receivable, Not Past Due	4,052,476	3,998,437
Loans and Leases Receivable, Gross	$ 4,061,347	$ 4,002,359
Number Of Financing Receivables Total Past Due | loan	27	16
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	2	1
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	7	8
Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	1	1
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 0	$ 0
Financing Receivable, Past Due	331	560
Financing Receivable, Not Past Due	526,807	546,733
Loans and Leases Receivable, Gross	$ 527,138	$ 547,293
Number Of Financing Receivables Total Past Due | loan	1	1
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	0	0
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	0	0
Small Business [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	12	11
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 0	$ 0
Financing Receivable, Past Due	1,391	967
Financing Receivable, Not Past Due	176,429	173,530
Loans and Leases Receivable, Gross	$ 177,820	$ 174,497
Number Of Financing Receivables Total Past Due | loan	25	20
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	8	3
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	5	6
Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	19	17
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 0	$ 1,652	[1]
Financing Receivable, Past Due	9,866	12,312
Financing Receivable, Not Past Due	1,518,550	1,578,257
Loans and Leases Receivable, Gross	$ 1,528,416	$ 1,590,569
Number Of Financing Receivables Total Past Due | loan	63	72
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	5	17
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	39	38
Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	22	23
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 0	$ 265	[1]
Financing Receivable, Past Due	5,338	6,067
Financing Receivable, Not Past Due	1,140,932	1,127,731
Loans and Leases Receivable, Gross	$ 1,146,270	$ 1,133,798
Number Of Financing Receivables Total Past Due | loan	65	71
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	7	8
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	36	40
Consumer - Other [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	335	387	[2]
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 25	$ 22	[2]
Financing Receivable, Past Due	552	321	[2]
Financing Receivable, Not Past Due	26,663	29,766	[2]
Loans and Leases Receivable, Gross	$ 27,215	$ 30,087	[2]
Number Of Financing Receivables Total Past Due | loan	362	415	[2]
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	11	12	[2]
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	16	16	[2]
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 2,430	$ 4,155
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	323
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	383	194
Financial Asset, 60 to 89 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Small Business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	185	15
Financial Asset, 60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	994	3,055
Financial Asset, 60 to 89 Days Past Due [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	801	524
Financial Asset, 60 to 89 Days Past Due [Member] | Consumer - Other [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	67	44	[2]
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	12,140	13,819
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,078	760
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,499	2,038
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Small Business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	176	115
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	6,258	7,020
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	3,030	3,854
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer - Other [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	99	32	[2]
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	14,787	7,511
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,930	253
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	6,989	1,690
Financial Asset, 30 to 59 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	331	560
Financial Asset, 30 to 59 Days Past Due [Member] | Small Business [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,030	837
Financial Asset, 30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	2,614	2,237
Financial Asset, 30 to 59 Days Past Due [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,507	1,689
Financial Asset, 30 to 59 Days Past Due [Member] | Consumer - Other [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 386	$ 245	[2]

[1] (2) Represents purchased credit impaired loans that were accruing interest due to expectations of future cash collections.

[2] (1) Other consumer portfolio is inclusive of deposit account overdrafts recorded as loan balances.