Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) $ in Thousands	Jun. 30, 2015 USD ($) loan	Dec. 31, 2014 USD ($) loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	79	112
Number of Loans 60-89 Days | loan	38	47
Number of Loans 90 Days or More | loan	90	110
Number of Loans Total Past Due | loan	207	269
Principal Balance Total Past Due	$ 26,531	$ 39,604
Current	5,408,251	4,931,129
Total Financing Receivables	5,434,782	4,970,733
Recorded Investment >90 Days and Accruing	$ 104	$ 119
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	11	18
Number of Loans 60-89 Days | loan	5	10
Number of Loans 90 Days or More | loan	11	19
Number of Loans Total Past Due | loan	27	47
Principal Balance Total Past Due	$ 5,902	$ 6,519
Current	867,203	854,320
Total Financing Receivables	873,105	860,839
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	12	19
Number of Loans 60-89 Days | loan	7	6
Number of Loans 90 Days or More | loan	19	16
Number of Loans Total Past Due | loan	38	41
Principal Balance Total Past Due	$ 11,286	$ 19,133
Current	2,618,776	2,328,190
Total Financing Receivables	2,630,062	2,347,323
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	1
Number of Loans 60-89 Days | loan	0	0
Number of Loans 90 Days or More | loan	1	1
Number of Loans Total Past Due | loan	1	2
Principal Balance Total Past Due	$ 309	$ 817
Current	278,383	265,177
Total Financing Receivables	278,692	265,994
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	7	7
Number of Loans 60-89 Days | loan	2	8
Number of Loans 90 Days or More | loan	9	7
Number of Loans Total Past Due | loan	18	22
Principal Balance Total Past Due	$ 230	$ 307
Current	91,137	84,940
Total Financing Receivables	91,367	85,247
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	8	13
Number of Loans 60-89 Days | loan	5	10
Number of Loans 90 Days or More | loan	25	36
Number of Loans Total Past Due | loan	38	59
Principal Balance Total Past Due	$ 5,665	$ 8,294
Current	647,705	521,965
Total Financing Receivables	653,370	530,259
Recorded Investment >90 Days and Accruing	$ 104	$ 106
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	16	20
Number of Loans 60-89 Days | loan	11	7
Number of Loans 90 Days or More | loan	18	23
Number of Loans Total Past Due | loan	45	50
Principal Balance Total Past Due	$ 2,962	$ 4,268
Current	887,931	859,595
Total Financing Receivables	890,893	863,863
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	25	34
Number of Loans 60-89 Days | loan	8	6
Number of Loans 90 Days or More | loan	7	8
Number of Loans Total Past Due | loan	40	48
Principal Balance Total Past Due	$ 177	$ 266
Current	17,116	16,942
Total Financing Receivables	17,293	17,208
Recorded Investment >90 Days and Accruing	0	13
Financing Receivables, 30 to 59 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	6,591	20,609
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	1,528	3,192
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	3,052	13,428
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	506
Financing Receivables, 30 to 59 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	143	21
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	1,030	1,670
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	688	1,559
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	150	233
Financing Receivables, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	6,774	4,725
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	1,423	1,007
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	3,792	1,480
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	2	113
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	855	1,798
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	692	307
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	10	20
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	13,166	14,270
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	2,951	2,320
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	4,442	4,225
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	309	311
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	85	173
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	3,780	4,826
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	1,582	2,402
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	$ 17	$ 13