Loans, Allowance for Loan Losses and Credit Quality (Details 5) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012 loan	Dec. 31, 2011 loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	209	349
Principal Balance 30-59 Days	$ 9,523	$ 12,221
Number of Loans 60-89 Days	77	106
Principal Balance 60-89 Days	5,573	9,902
Number of Loans 90 Days or More	140	172
Principal Balance 90 Days or More	16,893	16,385
Number of Loans Total Past Due	426	627
Principal Balance Total Past Due	31,989	38,508
Current	4,024,146	3,755,882
Total Financing Receivables	4,056,135	3,794,390
Recorded Investment >90 Days and Accruing	76	41
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	11	21
Principal Balance 30-59 Days	1,266	2,143
Number of Loans 60-89 Days	10	10
Principal Balance 60-89 Days	987	2,709
Number of Loans 90 Days or More	25	20
Principal Balance 90 Days or More	1,783	1,279
Number of Loans Total Past Due	46	51
Principal Balance Total Past Due	4,036	6,131
Current	649,825	569,585
Total Financing Receivables	653,861	575,716
Recorded Investment >90 Days and Accruing
Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	12	7
Principal Balance 30-59 Days	2,375	3,684
Number of Loans 60-89 Days	7	7
Principal Balance 60-89 Days	1,319	2,522
Number of Loans 90 Days or More	27	29
Principal Balance 90 Days or More	6,580	6,737
Number of Loans Total Past Due	46	43
Principal Balance Total Past Due	10,274	12,943
Current	1,928,971	1,834,711
Total Financing Receivables	1,939,245	1,847,654
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	155
Number of Loans 60-89 Days
Principal Balance 60-89 Days
Number of Loans 90 Days or More		3
Principal Balance 90 Days or More		280
Number of Loans Total Past Due	1	3
Principal Balance Total Past Due	155	280
Current	175,576	128,624
Total Financing Receivables	175,731	128,904
Recorded Investment >90 Days and Accruing
Small Business [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	9	19
Principal Balance 30-59 Days	410	320
Number of Loans 60-89 Days	3	3
Principal Balance 60-89 Days	46	21
Number of Loans 90 Days or More	8	12
Principal Balance 90 Days or More	315	148
Number of Loans Total Past Due	20	34
Principal Balance Total Past Due	771	489
Current	78,023	78,020
Total Financing Receivables	78,794	78,509
Recorded Investment >90 Days and Accruing
Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	15	14
Principal Balance 30-59 Days	3,352	2,770
Number of Loans 60-89 Days	9	10
Principal Balance 60-89 Days	2,698	3,208
Number of Loans 90 Days or More	30	31
Principal Balance 90 Days or More	6,365	6,065
Number of Loans Total Past Due	54	55
Principal Balance Total Past Due	12,415	12,043
Current	363,245	404,527
Total Financing Receivables	375,660	416,570
Recorded Investment >90 Days and Accruing
Residential Construction [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days
Principal Balance 30-59 Days
Number of Loans 60-89 Days
Principal Balance 60-89 Days
Number of Loans 90 Days or More
Principal Balance 90 Days or More
Number of Loans Total Past Due
Principal Balance Total Past Due
Current	9,288	9,631
Total Financing Receivables	9,288	9,631
Recorded Investment >90 Days and Accruing
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	17	28
Principal Balance 30-59 Days	993	1,483
Number of Loans 60-89 Days	8	19
Principal Balance 60-89 Days	327	1,139
Number of Loans 90 Days or More	20	19
Principal Balance 90 Days or More	1,696	1,502
Number of Loans Total Past Due	45	66
Principal Balance Total Past Due	3,016	4,124
Current	791,359	691,939
Total Financing Receivables	794,375	696,063
Recorded Investment >90 Days and Accruing	35
Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days	144	260
Principal Balance 30-59 Days	972	1,821
Number of Loans 60-89 Days	40	57
Principal Balance 60-89 Days	196	303
Number of Loans 90 Days or More	30	58
Principal Balance 90 Days or More	154	374
Number of Loans Total Past Due	214	375
Principal Balance Total Past Due	1,322	2,498
Current	27,859	38,845
Total Financing Receivables	29,181	41,343
Recorded Investment >90 Days and Accruing	$ 41	$ 41