Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) $ in Thousands	Sep. 30, 2015 USD ($) loan	Dec. 31, 2014 USD ($) loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	367	396
Number of Loans 60-89 Days | loan	42	57
Number of Loans 90 Days or More | loan	87	117
Number of Loans Total Past Due | loan	496	570
Principal Balance Total Past Due	$ 23,477	$ 39,758
Current	5,474,644	4,930,975
Total Financing Receivables	5,498,121	4,970,733
Recorded Investment >90 Days and Accruing	$ 0	$ 119
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	6	18
Number of Loans 60-89 Days | loan	3	10
Number of Loans 90 Days or More | loan	10	19
Number of Loans Total Past Due | loan	19	47
Principal Balance Total Past Due	$ 4,637	$ 6,519
Current	857,875	854,320
Total Financing Receivables	862,512	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	6	19
Number of Loans 60-89 Days | loan	4	6
Number of Loans 90 Days or More | loan	16	16
Number of Loans Total Past Due | loan	26	41
Principal Balance Total Past Due	$ 6,737	$ 19,133
Current	2,652,605	2,328,190
Total Financing Receivables	2,659,342	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	$ 306	$ 817
Current	307,908	265,177
Total Financing Receivables	308,214	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	8	7
Number of Loans 60-89 Days | loan	4	8
Number of Loans 90 Days or More | loan	10	7
Number of Loans Total Past Due | loan	22	22
Principal Balance Total Past Due	$ 176	$ 307
Current	92,102	84,940
Total Financing Receivables	92,278	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	12	13
Number of Loans 60-89 Days | loan	9	10
Number of Loans 90 Days or More | loan	23	36
Number of Loans Total Past Due | loan	44	59
Principal Balance Total Past Due	$ 7,476	$ 8,294
Current	644,461	521,965
Total Financing Receivables	651,937	530,259
Recorded Investment >90 Days and Accruing	$ 0	$ 106
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	27	20
Number of Loans 60-89 Days | loan	13	7
Number of Loans 90 Days or More | loan	14	23
Number of Loans Total Past Due | loan	54	50
Principal Balance Total Past Due	$ 3,834	$ 4,268
Current	904,060	859,595
Total Financing Receivables	907,894	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	308	318
Number of Loans 60-89 Days | loan	9	16
Number of Loans 90 Days or More | loan	13	15
Number of Loans Total Past Due | loan	330	349
Principal Balance Total Past Due	$ 311	$ 420
Current	15,633	16,788
Total Financing Receivables	15,944	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	5,284	20,758
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	383	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	1,222	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	27	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	1,620	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	1,770	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	262	382
Financing Receivables, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	4,255	4,728
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	920	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	746	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	44	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	1,760	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	769	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	16	23
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	13,938	14,272
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	3,334	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	4,769	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	306	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	105	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	4,096	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	1,295	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	$ 33	$ 15