Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) $ in Thousands	Jun. 30, 2016 USD ($) loan	Dec. 31, 2015 USD ($) loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	309	377
Number of Loans 60-89 Days | loan	42	48
Number of Loans 90 Days or More | loan	101	87
Number of Loans Total Past Due | loan	452	512
Principal Balance Total Past Due	$ 26,944	$ 31,057
Current	5,647,309	5,516,664
Loans and Leases Receivable, Gross	5,674,253	5,547,721
Recorded Investment >90 Days and Accruing	$ 1	$ 0
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	3	9
Number of Loans 60-89 Days | loan	0	4
Number of Loans 90 Days or More | loan	10	8
Number of Loans Total Past Due | loan	13	21
Principal Balance Total Past Due	$ 2,888	$ 4,459
Current	872,276	838,817
Loans and Leases Receivable, Gross	875,164	843,276
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	14	19
Number of Loans 60-89 Days | loan	3	6
Number of Loans 90 Days or More | loan	9	13
Number of Loans Total Past Due | loan	26	38
Principal Balance Total Past Due	$ 12,056	$ 13,434
Current	2,715,087	2,640,000
Loans and Leases Receivable, Gross	2,727,143	2,653,434
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	0	0
Number of Loans 60-89 Days | loan	0	0
Number of Loans 90 Days or More | loan	0	1
Number of Loans Total Past Due | loan	0	1
Principal Balance Total Past Due	$ 0	$ 304
Current	367,559	373,064
Loans and Leases Receivable, Gross	367,559	373,368
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	10	11
Number of Loans 60-89 Days | loan	3	4
Number of Loans 90 Days or More | loan	17	13
Number of Loans Total Past Due | loan	30	28
Principal Balance Total Past Due	$ 280	$ 171
Current	110,755	96,075
Loans and Leases Receivable, Gross	111,035	96,246
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	20
Number of Loans 60-89 Days | loan	8	11
Number of Loans 90 Days or More | loan	23	19
Number of Loans Total Past Due | loan	50	50
Principal Balance Total Past Due	$ 7,574	$ 8,601
Current	620,774	630,005
Loans and Leases Receivable, Gross	628,348	638,606
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	20	21
Number of Loans 60-89 Days | loan	12	11
Number of Loans 90 Days or More | loan	26	20
Number of Loans Total Past Due | loan	58	52
Principal Balance Total Past Due	$ 3,861	$ 3,767
Current	944,715	924,036
Loans and Leases Receivable, Gross	948,576	927,803
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	243	297
Number of Loans 60-89 Days | loan	16	12
Number of Loans 90 Days or More | loan	16	13
Number of Loans Total Past Due | loan	275	322
Principal Balance Total Past Due	$ 285	$ 321
Current	16,143	14,667
Loans and Leases Receivable, Gross	16,428	14,988
Recorded Investment >90 Days and Accruing	1	0
Financing Receivables, 30 to 59 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	10,972	12,717
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	243	399
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	6,360	7,349
Financing Receivables, 30 to 59 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	0	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	26	93
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	2,763	3,119
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	1,371	1,526
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	209	231
Financing Receivables, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	3,321	5,674
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	0	1,021
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	1,576	1,627
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	68	9
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	1,172	2,049
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	478	903
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	27	65
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	12,651	12,666
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	2,645	3,039
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	4,120	4,458
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	304
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	186	69
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	3,639	3,433
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	2,012	1,338
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	$ 49	$ 25