Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015 loan	Dec. 31, 2014 loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	97	112
Principal Balance 30-59 Days	$ 8,078	$ 20,609
Number of Loans 60-89 Days	37	47
Principal Balance 60-89 Days	3,370	4,725
Number of Loans 90 Days or More	120	110
Principal Balance 90 Days or More	16,866	14,270
Number of Loans Total Past Due	254	269
Principal Balance Total Past Due	28,314	39,604
Current	5,364,804	4,931,129
Total Financing Receivables	5,393,118	4,970,733
Recorded Investment >90 Days and Accruing	187	119
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	8	18
Principal Balance 30-59 Days	236	3,192
Number of Loans 60-89 Days	7	10
Principal Balance 60-89 Days	973	1,007
Number of Loans 90 Days or More	25	19
Principal Balance 90 Days or More	4,256	2,320
Number of Loans Total Past Due	40	47
Principal Balance Total Past Due	5,465	6,519
Current	823,915	854,320
Total Financing Receivables	829,380	860,839
Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	16	19
Principal Balance 30-59 Days	3,189	13,428
Number of Loans 60-89 Days	5	6
Principal Balance 60-89 Days	714	1,480
Number of Loans 90 Days or More	23	16
Principal Balance 90 Days or More	6,896	4,225
Number of Loans Total Past Due	44	41
Principal Balance Total Past Due	10,799	19,133
Current	2,595,645	2,328,190
Total Financing Receivables	2,606,444	2,347,323
Commercial Construction [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days		1
Principal Balance 30-59 Days		506
Number of Loans 90 Days or More	1	1
Principal Balance 90 Days or More	311	311
Number of Loans Total Past Due	1	2
Principal Balance Total Past Due	311	817
Current	291,355	265,177
Total Financing Receivables	291,666	265,994
Small Business [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	9	7
Principal Balance 30-59 Days	134	21
Number of Loans 60-89 Days	3	8
Principal Balance 60-89 Days	45	113
Number of Loans 90 Days or More	11	7
Principal Balance 90 Days or More	211	173
Number of Loans Total Past Due	23	22
Principal Balance Total Past Due	390	307
Current	87,319	84,940
Total Financing Receivables	87,709	85,247
Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	13	13
Principal Balance 30-59 Days	3,275	1,670
Number of Loans 60-89 Days	7	10
Principal Balance 60-89 Days	1,044	1,798
Number of Loans 90 Days or More	28	36
Principal Balance 90 Days or More	3,061	4,826
Number of Loans Total Past Due	48	59
Principal Balance Total Past Due	7,380	8,294
Current	673,999	521,965
Total Financing Receivables	681,379	530,259
Recorded Investment >90 Days and Accruing	103	106
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	17	20
Principal Balance 30-59 Days	1,098	1,559
Number of Loans 60-89 Days	7	7
Principal Balance 60-89 Days	535	307
Number of Loans 90 Days or More	22	23
Principal Balance 90 Days or More	2,078	2,402
Number of Loans Total Past Due	46	50
Principal Balance Total Past Due	3,711	4,268
Current	873,205	859,595
Total Financing Receivables	876,916	863,863
Recorded Investment >90 Days and Accruing	38
Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	34	34
Principal Balance 30-59 Days	146	233
Number of Loans 60-89 Days	8	6
Principal Balance 60-89 Days	59	20
Number of Loans 90 Days or More	10	8
Principal Balance 90 Days or More	53	13
Number of Loans Total Past Due	52	48
Principal Balance Total Past Due	258	266
Current	19,366	16,942
Total Financing Receivables	19,624	17,208
Recorded Investment >90 Days and Accruing	$ 46	$ 13