Loan Portfolio and Credit Quality Loans by Grade or Nonaccrual Status (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,213,491	$ 5,112,459
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,033,738	4,938,369
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	103,025	87,313
Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	43,187	42,015
Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,541	44,762
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	930,828	866,053
Commercial and industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	903,352	849,535
Commercial and industrial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,918	4,857
Commercial and industrial [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,402	8,177
Commercial and industrial [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,156	3,484
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,808,041	1,813,394
Commercial real estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,700,863	1,709,265
Commercial real estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	71,361	60,305
Commercial real estate [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	18,997	19,857
Commercial real estate [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,820	23,967
Construction and land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	130,545	153,917
Construction and land [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	109,282	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	0	589
Construction and land [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,617	3,489
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,097,527	2,032,294
Residential [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,078,710	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	10,278	12,810
Residential [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,539	12,777
Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	109,227	113,660
Home equity [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	107,382	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	1,323	1,020
Consumer and other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	137,323	133,141
Consumer and other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	134,149	132,130
Consumer and other [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	100	979
Consumer and other [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,988	7
Consumer and other [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,086	$ 25