Loan Portfolio and Credit Quality Loans by Portfolio Segment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 5,295,013	$ 5,269,936
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	966,838	953,085
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,763,041	1,788,403
Construction and land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	137,094	125,349
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,143,036	2,132,095
Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	116,190	114,859
Consumer and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 168,814	$ 156,145