Loan Portfolio and Credit Quality Loans by Grade or Nonaccrual Status (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,751,497	$ 5,719,212
Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,600,757	5,565,016
Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	67,328	69,211
Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	64,224	58,414
Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	19,188	26,571
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,042,917	1,111,555
Commercial and industrial [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,009,528	1,070,438
Commercial and industrial [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	17,084	28,643
Commercial and industrial [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,199	11,455
Commercial and industrial [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,106	1,019
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,977,312	1,914,134
Commercial real estate [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,895,974	1,841,603
Commercial real estate [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	35,760	27,594
Commercial real estate [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	38,644	33,705
Commercial real estate [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,934	11,232
Construction and land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	142,549	183,434
Construction and land [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	125,069	162,563
Construction and land [Member] | Special Mention [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,796	12,974
Construction and land [Member] | Substandard [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,823	4,600
Construction and land [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	861	3,297
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,280,116	2,229,540
Residential [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,264,593	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	6,556	6,675
Residential [Member] | Substandard [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,967	9,661
Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	125,486	119,828
Home equity [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	124,191	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	1,295	1,306
Consumer and other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	183,117	160,721
Consumer and other [Member] | Pass [Member] | Performing Financial Instruments [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	181,402	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	$ 25	$ 56