Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 loan	Dec. 31, 2013 loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	93	209
Principal Balance 30-59 Days	$ 14,829	$ 15,925
Number of Loans 60-89 Days	51	60
Principal Balance 60-89 Days	6,630	3,498
Number of Loans 90 Days or More	110	161
Principal Balance 90 Days or More	14,465	21,116
Number of Loans Total Past Due	254	430
Principal Balance Total Past Due	35,924	40,539
Current	4,911,931	4,677,768
Total Financing Receivables	4,947,855	4,718,307
Recorded Investment >90 Days and Accruing	239	525
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	12	9
Principal Balance 30-59 Days	2,871	743
Number of Loans 60-89 Days	2	6
Principal Balance 60-89 Days	560	327
Number of Loans 90 Days or More	16	20
Principal Balance 90 Days or More	2,069	3,763
Number of Loans Total Past Due	30	35
Principal Balance Total Past Due	5,500	4,833
Current	837,333	779,369
Total Financing Receivables	842,833	784,202
Recorded Investment >90 Days and Accruing
Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	9	21
Principal Balance 30-59 Days	7,001	8,643
Number of Loans 60-89 Days	9	2
Principal Balance 60-89 Days	4,088	356
Number of Loans 90 Days or More	16	30
Principal Balance 90 Days or More	4,221	8,155
Number of Loans Total Past Due	34	53
Principal Balance Total Past Due	15,310	17,154
Current	2,323,331	2,232,106
Total Financing Receivables	2,338,641	2,249,260
Recorded Investment >90 Days and Accruing
Commercial Construction [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days		1
Principal Balance 30-59 Days		847
Number of Loans 60-89 Days
Principal Balance 60-89 Days
Number of Loans 90 Days or More	1	1
Principal Balance 90 Days or More	311	100
Number of Loans Total Past Due	1	2
Principal Balance Total Past Due	311	947
Current	276,282	222,912
Total Financing Receivables	276,593	223,859
Recorded Investment >90 Days and Accruing
Small Business [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	8	18
Principal Balance 30-59 Days	168	353
Number of Loans 60-89 Days	4	6
Principal Balance 60-89 Days	23	227
Number of Loans 90 Days or More	4	14
Principal Balance 90 Days or More	158	247
Number of Loans Total Past Due	16	38
Principal Balance Total Past Due	349	827
Current	81,086	76,413
Total Financing Receivables	81,435	77,240
Recorded Investment >90 Days and Accruing
Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	15	23
Principal Balance 30-59 Days	3,547	2,903
Number of Loans 60-89 Days	12	8
Principal Balance 60-89 Days	1,480	1,630
Number of Loans 90 Days or More	35	39
Principal Balance 90 Days or More	5,184	6,648
Number of Loans Total Past Due	62	70
Principal Balance Total Past Due	10,211	11,181
Current	526,611	530,262
Total Financing Receivables	536,822	541,443
Recorded Investment >90 Days and Accruing	217	462
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	12	27
Principal Balance 30-59 Days	1,068	1,922
Number of Loans 60-89 Days	7	8
Principal Balance 60-89 Days	431	852
Number of Loans 90 Days or More	28	23
Principal Balance 90 Days or More	2,491	2,055
Number of Loans Total Past Due	47	58
Principal Balance Total Past Due	3,990	4,829
Current	850,656	817,312
Total Financing Receivables	854,646	822,141
Recorded Investment >90 Days and Accruing
Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	37	110
Principal Balance 30-59 Days	174	514
Number of Loans 60-89 Days	17	30
Principal Balance 60-89 Days	48	106
Number of Loans 90 Days or More	10	34
Principal Balance 90 Days or More	31	148
Number of Loans Total Past Due	64	174
Principal Balance Total Past Due	253	768
Current	16,632	19,394
Total Financing Receivables	16,885	20,162
Recorded Investment >90 Days and Accruing	$ 22	$ 63