Loan Portfolio and Credit Quality Loans by Grade or Nonaccrual Status (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,295,013	$ 5,269,936
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,130,732	5,110,154
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	86,146	76,740
Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,002	38,860
Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,133	44,182
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	966,838	953,085
Commercial and industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	931,605	928,228
Commercial and industrial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	24,975	15,703
Commercial and industrial [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,105	7,025
Commercial and industrial [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	153	2,129
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,763,041	1,788,403
Commercial real estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,681,384	1,703,064
Commercial real estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	47,993	47,782
Commercial real estate [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	17,654	19,072
Commercial real estate [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,010	18,485
Construction and land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	137,094	125,349
Construction and land [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	114,944	100,672
Construction and land [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,178	13,255
Construction and land [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,500	0
Construction and land [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,472	11,422
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,143,036	2,132,095
Residential [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,122,733	2,112,129
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	10,234	10,253
Residential [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,069	9,713
Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	116,190	114,859
Home equity [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	114,349	113,017
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	522
Home equity [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,319	1,320
Consumer and other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	168,814	156,145
Consumer and other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	165,717	153,044
Consumer and other [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer and other [Member] | Accruing Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,987	1,988
Consumer and other [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,110	$ 1,113