Loan Portfolio and Credit Quality Loans by Past Due Status (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	$ 2,292	$ 13,030
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	1,331	712
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	483	65
Financing Receivable Recorded Investment Still Accruing	4,106	13,807
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	16,252	18,996
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	913	2,673
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	16,376	23,093
Financing Receivable, Recorded Investment, Nonaccrual Status	33,541	44,762
Financing Receivable, Recorded Investment, Current	5,175,844	5,053,890
Total loans	5,213,491	5,112,459
Commercial and industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	842	1,075
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	90	454
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	430	0
Financing Receivable Recorded Investment Still Accruing	1,362	1,529
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	190	1,192
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	0	0
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	1,966	2,292
Financing Receivable, Recorded Investment, Nonaccrual Status	2,156	3,484
Financing Receivable, Recorded Investment, Current	927,310	861,040
Total loans	930,828	866,053
Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	1,437	775
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	0	0
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	53	0
Financing Receivable Recorded Investment Still Accruing	1,490	775
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	12,891	13,337
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	471	0
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	3,458	10,630
Financing Receivable, Recorded Investment, Nonaccrual Status	16,820	23,967
Financing Receivable, Recorded Investment, Current	1,789,731	1,788,652
Total loans	1,808,041	1,813,394
Construction and land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	0	1,631
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	0	21
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0	65
Financing Receivable Recorded Investment Still Accruing	0	1,717
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	375	392
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	90	43
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	3,152	3,054
Financing Receivable, Recorded Investment, Nonaccrual Status	3,617	3,489
Financing Receivable, Recorded Investment, Current	126,928	148,711
Total loans	130,545	153,917
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	0	8,181
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	1,232	226
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0	0
Financing Receivable Recorded Investment Still Accruing	1,232	8,407
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	2,666	4,058
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	350	1,630
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	5,523	7,089
Financing Receivable, Recorded Investment, Nonaccrual Status	8,539	12,777
Financing Receivable, Recorded Investment, Current	2,087,756	2,011,110
Total loans	2,097,527	2,032,294
Home equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	0	542
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	0	4
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0	0
Financing Receivable Recorded Investment Still Accruing	0	546
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	101	0
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	0	1,000
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	1,222	20
Financing Receivable, Recorded Investment, Nonaccrual Status	1,323	1,020
Financing Receivable, Recorded Investment, Current	107,904	112,094
Total loans	109,227	113,660
Consumer and other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	13	826
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	9	7
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0	0
Financing Receivable Recorded Investment Still Accruing	22	833
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	29	17
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	2	0
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	1,055	8
Financing Receivable, Recorded Investment, Nonaccrual Status	1,086	25
Financing Receivable, Recorded Investment, Current	136,215	132,283
Total loans	$ 137,323	$ 133,141