Loan Portfolio and Credit Quality Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 5,658,181	$ 5,719,212
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,069,971	1,111,555
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,925,519	1,914,134
Construction and land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	166,674	183,434
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,216,875	2,229,540
Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	118,807	119,828
Consumer and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 160,335	$ 160,721