Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) $ in Thousands	Mar. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	420	447
Number of Loans 60-89 Days | loan	33	43
Number of Loans 90 Days or More | loan	109	113
Number of Loans Total Past Due | loan	562	603
Principal Balance Total Past Due	$ 29,357	$ 25,485
Current	8,887,073	8,848,154
Total loans	8,916,430	8,873,639
Recorded Investment >90 Days and Accruing	$ 25	$ 2,157
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	13	1
Number of Loans 60-89 Days | loan	0	2
Number of Loans 90 Days or More | loan	6	5
Number of Loans Total Past Due | loan	19	8
Principal Balance Total Past Due	$ 3,008	$ 1,336
Current	1,445,216	1,393,700
Total loans	1,448,224	1,395,036
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	18	7
Number of Loans 60-89 Days | loan	2	1
Number of Loans 90 Days or More | loan	7	8
Number of Loans Total Past Due | loan	27	16
Principal Balance Total Past Due	$ 8,871	$ 3,922
Current	4,052,476	3,998,437
Total loans	4,061,347	4,002,359
Recorded Investment >90 Days and Accruing	$ 0	$ 218	[1]
Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	1	1
Number of Loans 60-89 Days | loan	0	0
Number of Loans 90 Days or More | loan	0	0
Number of Loans Total Past Due | loan	1	1
Principal Balance Total Past Due	$ 331	$ 560
Current	526,807	546,733
Total loans	527,138	547,293
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Small Business [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	12	11
Number of Loans 60-89 Days | loan	8	3
Number of Loans 90 Days or More | loan	5	6
Number of Loans Total Past Due | loan	25	20
Principal Balance Total Past Due	$ 1,391	$ 967
Current	176,429	173,530
Total loans	177,820	174,497
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	19	17
Number of Loans 60-89 Days | loan	5	17
Number of Loans 90 Days or More | loan	39	38
Number of Loans Total Past Due | loan	63	72
Principal Balance Total Past Due	$ 9,866	$ 12,312
Current	1,518,550	1,578,257
Total loans	1,528,416	1,590,569
Recorded Investment >90 Days and Accruing	$ 0	$ 1,652	[1]
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	22	23
Number of Loans 60-89 Days | loan	7	8
Number of Loans 90 Days or More | loan	36	40
Number of Loans Total Past Due | loan	65	71
Principal Balance Total Past Due	$ 5,338	$ 6,067
Current	1,140,932	1,127,731
Total loans	1,146,270	1,133,798
Recorded Investment >90 Days and Accruing	$ 0	$ 265	[1]
Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	335	387	[2]
Number of Loans 60-89 Days | loan	11	12	[2]
Number of Loans 90 Days or More | loan	16	16	[2]
Number of Loans Total Past Due | loan	362	415	[2]
Principal Balance Total Past Due	$ 552	$ 321	[2]
Current	26,663	29,766	[2]
Total loans	27,215	30,087	[2]
Recorded Investment >90 Days and Accruing	25	22	[2]
Financial Asset, 30 to 59 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	14,787	7,511
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	1,930	253
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	6,989	1,690
Financial Asset, 30 to 59 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	331	560
Financial Asset, 30 to 59 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	1,030	837
Financial Asset, 30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	2,614	2,237
Financial Asset, 30 to 59 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	1,507	1,689
Financial Asset, 30 to 59 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	386	245	[2]
Financial Asset, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	2,430	4,155
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	0	323
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	383	194
Financial Asset, 60 to 89 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	185	15
Financial Asset, 60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	994	3,055
Financial Asset, 60 to 89 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	801	524
Financial Asset, 60 to 89 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	67	44	[2]
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	12,140	13,819
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	1,078	760
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	1,499	2,038
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	176	115
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	6,258	7,020
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	3,030	3,854
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	$ 99	$ 32	[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.