Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) $ in Thousands		Mar. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		282	319
Number of Loans 60-89 Days | loan		36	48
Number of Loans 90 Days or More | loan		106	92
Number of Loans Total Past Due | loan		424	459
Principal Balance Total Past Due		$ 50,021	$ 48,746
Current		6,312,035	6,306,807
Total loans	[1]	6,362,056	6,355,553
Recorded Investment >90 Days and Accruing		$ 9	$ 8
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		4	2
Number of Loans 60-89 Days | loan		2	2
Number of Loans 90 Days or More | loan		14	14
Number of Loans Total Past Due | loan		20	18
Principal Balance Total Past Due		$ 31,150	$ 32,572
Current		872,064	855,956
Total loans	[1]	903,214	888,528
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		9	7
Number of Loans 60-89 Days | loan		4	0
Number of Loans 90 Days or More | loan		6	9
Number of Loans Total Past Due | loan		19	16
Principal Balance Total Past Due		$ 5,793	$ 4,853
Current		3,096,478	3,111,708
Total loans	[1]	3,102,271	3,116,561
Recorded Investment >90 Days and Accruing		$ 0	$ 0
Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		2	0
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		2	0
Principal Balance Total Past Due		$ 855	$ 0
Current		400,079	401,797
Total loans	[1]	400,934	401,797
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		11	17
Number of Loans 60-89 Days | loan		8	11
Number of Loans 90 Days or More | loan		23	10
Number of Loans Total Past Due | loan		42	38
Principal Balance Total Past Due		$ 523	$ 540
Current		133,143	131,830
Total loans	[1]	133,666	132,370
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		13	6
Number of Loans 60-89 Days | loan		7	13
Number of Loans 90 Days or More | loan		19	22
Number of Loans Total Past Due | loan		39	41
Principal Balance Total Past Due		$ 5,986	$ 6,726
Current		755,345	747,603
Total loans	[1]	761,331	754,329
Recorded Investment >90 Days and Accruing		$ 0	$ 0
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		22	22
Number of Loans 60-89 Days | loan		8	6
Number of Loans 90 Days or More | loan		26	20
Number of Loans Total Past Due | loan		56	48
Principal Balance Total Past Due		$ 5,588	$ 3,786
Current		1,045,864	1,048,302
Total loans	[1]	1,051,452	1,052,088
Recorded Investment >90 Days and Accruing		$ 0	$ 0
Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		221	265	[2]
Number of Loans 60-89 Days | loan		7	16	[2]
Number of Loans 90 Days or More | loan		18	17	[2]
Number of Loans Total Past Due | loan		246	298	[2]
Principal Balance Total Past Due		$ 126	$ 269	[2]
Current		9,062	9,611	[2]
Total loans	[1]	9,188	9,880	[2]
Recorded Investment >90 Days and Accruing		9	8
Financing Receivables, 30 to 59 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		8,704	5,971
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		411	195
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		3,127	3,060
Financing Receivables, 30 to 59 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		855	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		107	339
Financing Receivables, 30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		1,834	870
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		2,266	1,310
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		104	197	[2]
Financing Receivables, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		3,407	3,377
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		101	370
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		1,253	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		69	144
Financing Receivables, 60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		1,100	2,385
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		882	451
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		2	27	[2]
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		37,910	39,398
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		30,638	32,007
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		1,413	1,793
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		347	57
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		3,052	3,471
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		2,440	2,025
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		$ 20	$ 45	[2]

[1] The amount of net deferred costs on originated loans included in the ending balance was $6.4 million and $6.1 million at March 31, 2018 and December 31, 2017, respectively. Net unamortized discounts on acquired loans not deemed to be purchased credit impaired ("PCI") included in the ending balance was $9.1 million and $9.4 million at March 31, 2018 and December 31, 2017, respectively.

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