Loan Portfolio and Credit Quality Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 6,279,928	$ 6,114,354
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	541,756	611,370
Commercial Tax Exempt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	416,157	398,604
Commercial and Industrial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	957,913	1,009,974
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,356,345	2,302,244
Construction and land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	130,904	104,839
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,525,225	2,379,861
Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	108,549	118,817
Consumer and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 200,992	$ 198,619