Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) $ in Thousands	Mar. 31, 2016 USD ($) loan	Dec. 31, 2015 USD ($) loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	324	377
Number of Loans 60-89 Days | loan	54	48
Number of Loans 90 Days or More | loan	89	87
Number of Loans Total Past Due | loan	467	512
Principal Balance Total Past Due	$ 29,912	$ 31,057
Current	5,559,319	5,516,664
Total Financing Receivables	5,589,231	5,547,721
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	5	9
Number of Loans 60-89 Days | loan	6	4
Number of Loans 90 Days or More | loan	9	8
Number of Loans Total Past Due | loan	20	21
Principal Balance Total Past Due	$ 3,459	$ 4,459
Current	831,877	838,817
Total Financing Receivables	835,336	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	21	19
Number of Loans 60-89 Days | loan	3	6
Number of Loans 90 Days or More | loan	13	13
Number of Loans Total Past Due | loan	37	38
Principal Balance Total Past Due	$ 14,390	$ 13,434
Current	2,697,467	2,640,000
Total Financing Receivables	2,711,857	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	357,867	373,064
Total Financing Receivables	357,867	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	12	11
Number of Loans 60-89 Days | loan	14	4
Number of Loans 90 Days or More | loan	9	13
Number of Loans Total Past Due | loan	35	28
Principal Balance Total Past Due	$ 320	$ 171
Current	103,003	96,075
Total Financing Receivables	103,323	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	14	20
Number of Loans 60-89 Days | loan	10	11
Number of Loans 90 Days or More | loan	22	19
Number of Loans Total Past Due | loan	46	50
Principal Balance Total Past Due	$ 7,219	$ 8,601
Current	624,669	630,005
Total Financing Receivables	631,888	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	22	21
Number of Loans 60-89 Days | loan	11	11
Number of Loans 90 Days or More | loan	23	20
Number of Loans Total Past Due | loan	56	52
Principal Balance Total Past Due	$ 4,167	$ 3,767
Current	931,144	924,036
Total Financing Receivables	935,311	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	250	297
Number of Loans 60-89 Days | loan	10	12
Number of Loans 90 Days or More | loan	13	13
Number of Loans Total Past Due | loan	273	322
Principal Balance Total Past Due	$ 357	$ 321
Current	13,292	14,667
Total Financing Receivables	13,649	14,988
Recorded Investment >90 Days and Accruing	0	0
Financing Receivables, 30 to 59 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	13,818	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	1	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	9,409	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	197	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	2,270	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	1,634	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	307	231
Financing Receivables, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	3,591	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	689	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	299	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	39	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	2,031	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	519	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	14	65
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	12,503	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	2,769	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	4,682	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	84	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	2,918	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	2,014	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	$ 36	$ 25