Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) $ in Thousands	Jun. 30, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	275	301
Number of Loans 60-89 Days | loan	41	72
Number of Loans 90 Days or More | loan	122	91
Number of Loans Total Past Due | loan	438	464
Principal Balance Total Past Due	$ 51,515	$ 19,911
Current	6,218,181	5,979,694
Total loans	6,269,696	5,999,605
Recorded Investment >90 Days and Accruing	$ 8	$ 2
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	3	8
Number of Loans 60-89 Days | loan	7	32
Number of Loans 90 Days or More | loan	42	6
Number of Loans Total Past Due | loan	52	46
Principal Balance Total Past Due	$ 33,582	$ 2,833
Current	877,354	899,220
Total loans	910,936	902,053
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	8	5
Number of Loans 60-89 Days | loan	2	8
Number of Loans 90 Days or More | loan	9	8
Number of Loans Total Past Due | loan	19	21
Principal Balance Total Past Due	$ 7,390	$ 6,580
Current	3,075,630	3,004,218
Total loans	3,083,020	3,010,798
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	0
Number of Loans 60-89 Days | loan	0	0
Number of Loans 90 Days or More | loan	0	0
Number of Loans Total Past Due | loan	0	0
Principal Balance Total Past Due	$ 0	$ 0
Current	340,757	320,391
Total loans	340,757	320,391
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	10	9
Number of Loans 60-89 Days | loan	5	0
Number of Loans 90 Days or More | loan	16	19
Number of Loans Total Past Due | loan	31	28
Principal Balance Total Past Due	$ 558	$ 463
Current	131,105	122,263
Total loans	131,663	122,726
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	14	11
Number of Loans 60-89 Days | loan	8	9
Number of Loans 90 Days or More | loan	18	27
Number of Loans Total Past Due | loan	40	47
Principal Balance Total Past Due	$ 6,292	$ 6,734
Current	743,100	637,692
Total loans	749,392	644,426
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	17	19
Number of Loans 60-89 Days | loan	10	11
Number of Loans 90 Days or More | loan	15	16
Number of Loans Total Past Due | loan	42	46
Principal Balance Total Past Due	$ 3,460	$ 3,093
Current	1,039,999	985,054
Total loans	1,043,459	988,147
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	223	249
Number of Loans 60-89 Days | loan	9	12
Number of Loans 90 Days or More | loan	22	15
Number of Loans Total Past Due | loan	254	276
Principal Balance Total Past Due	$ 233	$ 208
Current	10,236	10,856
Total loans	10,469	11,064
Recorded Investment >90 Days and Accruing	8	2
Financing Receivables, 30 to 59 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	7,072	4,519
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	222	100
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	3,847	1,518
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	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	198	323
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	1,712	1,277
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	946	1,117
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	147	184
Financing Receivables, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	21,946	4,944
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	18,644	253
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	422	1,957
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	49	0
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	1,529	1,950
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	1,258	767
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	44	17
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	22,497	10,448
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	14,716	2,480
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	3,121	3,105
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	0	0
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	311	140
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	3,051	3,507
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	1,256	1,209
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	$ 42	$ 7