Loan Portfolio and Credit Quality Loans by Grade or Nonaccrual Status (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,162,470	$ 5,112,459
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,974,869	4,938,369
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	103,427	87,313
Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	42,120	42,015
Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	42,054	44,762
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	852,201	866,053
Commercial and industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	832,923	849,535
Commercial and industrial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,701	4,857
Commercial and industrial [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,528	8,177
Commercial and industrial [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,049	3,484
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,858,634	1,813,394
Commercial real estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,739,064	1,709,265
Commercial real estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	76,087	60,305
Commercial real estate [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,574	19,857
Commercial real estate [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,909	23,967
Construction and land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	174,716	153,917
Construction and land [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	153,076	128,667
Construction and land [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	17,646	21,172
Construction and land [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	540	589
Construction and land [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,454	3,489
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,035,855	2,032,294
Residential [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,011,735	2,006,707
Residential [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Residential [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,749	12,810
Residential [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,371	12,777
Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	108,963	113,660
Home equity [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	107,223	112,065
Home equity [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Home equity [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	722	575
Home equity [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,018	1,020
Consumer and other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	132,101	133,141
Consumer and other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	130,848	132,130
Consumer and other [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	993	979
Consumer and other [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7	7
Consumer and other [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 253	$ 25