Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014 loan	Dec. 31, 2013 loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	175	209
Principal Balance 30-59 Days	$ 11,751	$ 15,925
Number of Loans 60-89 Days	49	60
Principal Balance 60-89 Days	7,424	3,498
Number of Loans 90 Days or More	137	161
Principal Balance 90 Days or More	21,796	21,116
Number of Loans Total Past Due	361	430
Principal Balance Total Past Due	40,971	40,539
Current	4,766,298	4,677,768
Total Financing Receivables	4,807,269	4,718,307
Recorded Investment >90 Days and Accruing	392	525
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	18	9
Principal Balance 30-59 Days	1,491	743
Number of Loans 60-89 Days	9	6
Principal Balance 60-89 Days	1,460	327
Number of Loans 90 Days or More	19	20
Principal Balance 90 Days or More	3,021	3,763
Number of Loans Total Past Due	46	35
Principal Balance Total Past Due	5,972	4,833
Current	816,537	779,369
Total Financing Receivables	822,509	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	18	21
Principal Balance 30-59 Days	5,144	8,643
Number of Loans 60-89 Days	8	2
Principal Balance 60-89 Days	3,917	356
Number of Loans 90 Days or More	19	30
Principal Balance 90 Days or More	9,230	8,155
Number of Loans Total Past Due	45	53
Principal Balance Total Past Due	18,291	17,154
Current	2,264,648	2,232,106
Total Financing Receivables	2,282,939	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	100	100
Number of Loans Total Past Due	1	2
Principal Balance Total Past Due	100	947
Current	239,436	222,912
Total Financing Receivables	239,536	223,859
Recorded Investment >90 Days and Accruing
Small Business [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	11	18
Principal Balance 30-59 Days	276	353
Number of Loans 60-89 Days		6
Principal Balance 60-89 Days		227
Number of Loans 90 Days or More	16	14
Principal Balance 90 Days or More	354	247
Number of Loans Total Past Due	27	38
Principal Balance Total Past Due	630	827
Current	77,517	76,413
Total Financing Receivables	78,147	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	20	23
Principal Balance 30-59 Days	2,760	2,903
Number of Loans 60-89 Days	9	8
Principal Balance 60-89 Days	1,737	1,630
Number of Loans 90 Days or More	39	39
Principal Balance 90 Days or More	6,293	6,648
Number of Loans Total Past Due	68	70
Principal Balance Total Past Due	10,790	11,181
Current	527,836	530,262
Total Financing Receivables	538,626	541,443
Recorded Investment >90 Days and Accruing	368	462
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	19	27
Principal Balance 30-59 Days	1,604	1,922
Number of Loans 60-89 Days	6	8
Principal Balance 60-89 Days	278	852
Number of Loans 90 Days or More	27	23
Principal Balance 90 Days or More	2,749	2,055
Number of Loans Total Past Due	52	58
Principal Balance Total Past Due	4,631	4,829
Current	822,654	817,312
Total Financing Receivables	827,285	822,141
Recorded Investment >90 Days and Accruing
Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	89	110
Principal Balance 30-59 Days	476	514
Number of Loans 60-89 Days	17	30
Principal Balance 60-89 Days	32	106
Number of Loans 90 Days or More	16	34
Principal Balance 90 Days or More	49	148
Number of Loans Total Past Due	122	174
Principal Balance Total Past Due	557	768
Current	17,670	19,394
Total Financing Receivables	18,227	20,162
Recorded Investment >90 Days and Accruing	$ 24	$ 63