Loan Portfolio and Credit Quality Loans by Past Due Status (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	$ 10,531	$ 13,030
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	46	712
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	593	65
Financing Receivable Recorded Investment Still Accruing	11,170	13,807
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	16,261	18,996
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	2,143	2,673
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	23,650	23,093
Financing Receivable, Recorded Investment, Nonaccrual Status	42,054	44,762
Financing Receivable, Recorded Investment, Current	5,109,246	5,053,890
Total loans	5,162,470	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	433	1,075
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	0	454
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0	0
Financing Receivable Recorded Investment Still Accruing	433	1,529
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	1,082	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	1,967	2,292
Financing Receivable, Recorded Investment, Nonaccrual Status	3,049	3,484
Financing Receivable, Recorded Investment, Current	848,719	861,040
Total loans	852,201	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	2,998	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	526	0
Financing Receivable Recorded Investment Still Accruing	3,524	775
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	11,613	13,337
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	362	0
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	9,934	10,630
Financing Receivable, Recorded Investment, Nonaccrual Status	21,909	23,967
Financing Receivable, Recorded Investment, Current	1,833,201	1,788,652
Total loans	1,858,634	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	20	1,631
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	13	21
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	67	65
Financing Receivable Recorded Investment Still Accruing	100	1,717
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	351	392
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	17	43
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	3,086	3,054
Financing Receivable, Recorded Investment, Nonaccrual Status	3,454	3,489
Financing Receivable, Recorded Investment, Current	171,162	148,711
Total loans	174,716	153,917
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 to 59 Days Past Due Still Accruing	6,769	8,181
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	0	226
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0	0
Financing Receivable Recorded Investment Still Accruing	6,769	8,407
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	3,201	4,058
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	1,764	1,630
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	7,406	7,089
Financing Receivable, Recorded Investment, Nonaccrual Status	12,371	12,777
Financing Receivable, Recorded Investment, Current	2,016,715	2,011,110
Total loans	2,035,855	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	287	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	287	546
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	0	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	1,018	20
Financing Receivable, Recorded Investment, Nonaccrual Status	1,018	1,020
Financing Receivable, Recorded Investment, Current	107,658	112,094
Total loans	108,963	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	24	826
Financing Receivable Recorded Investment 60 to 89 Days Past Due Still Accruing	33	7
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0	0
Financing Receivable Recorded Investment Still Accruing	57	833
Financing Receivable Recorded Investment Nonaccrual Current Payment Status	14	17
Financing Receivable Recorded Investment Nonaccrual 30 to 89 Days Past Due	0	0
Financing Receivable Recorded Investment Nonaccrual Over 89 Days Past Due	239	8
Financing Receivable, Recorded Investment, Nonaccrual Status	253	25
Financing Receivable, Recorded Investment, Current	131,791	132,283
Total loans	$ 132,101	$ 133,141