Loan Portfolio and Credit Quality Loans by Grade or Nonaccrual Status (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,658,181	$ 5,719,212
Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,491,209	5,565,016
Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	86,925	69,211
Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	55,691	58,414
Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	24,356	26,571
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,069,971	1,111,555
Commercial and industrial [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,025,215	1,070,438
Commercial and industrial [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,547	28,643
Commercial and industrial [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,903	11,455
Commercial and industrial [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,306	1,019
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,925,519	1,914,134
Commercial real estate [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,841,174	1,841,603
Commercial real estate [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,792	27,594
Commercial real estate [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,518	33,705
Commercial real estate [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,035	11,232
Construction and land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	166,674	183,434
Construction and land [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	146,326	162,563
Construction and land [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,898	12,974
Construction and land [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,600	4,600
Construction and land [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,850	3,297
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,216,875	2,229,540
Residential [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,202,376	2,213,204
Residential [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Residential [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,668	6,675
Residential [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,831	9,661
Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	118,807	119,828
Home equity [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	117,506	118,522
Home equity [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Home equity [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Home equity [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,301	1,306
Consumer and other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	160,335	160,721
Consumer and other [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	158,612	158,686
Consumer and other [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,688	0
Consumer and other [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	1,979
Consumer and other [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 33	$ 56