Loan Portfolio and Credit Quality Loans by Grade or Nonaccrual Status (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,106,051	$ 5,112,459
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,917,837	4,938,369
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	106,601	87,313
Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,993	42,015
Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	41,620	44,762
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	882,463	866,053
Commercial and industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	860,727	849,535
Commercial and industrial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,548	4,857
Commercial and industrial [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,011	8,177
Commercial and industrial [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,177	3,484
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,780,901	1,813,394
Commercial real estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,663,408	1,709,265
Commercial real estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	77,407	60,305
Commercial real estate [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,665	19,857
Commercial real estate [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	19,421	23,967
Construction and land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	150,422	153,917
Construction and land [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	128,892	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	488	589
Construction and land [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,396	3,489
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,039,072	2,032,294
Residential [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,014,692	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	10,300	12,810
Residential [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,080	12,777
Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	112,504	113,660
Home equity [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	110,709	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	522	575
Home equity [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,273	1,020
Consumer and other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	140,689	133,141
Consumer and other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	139,409	132,130
Consumer and other [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	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	$ 1,273	$ 25