Loan Portfolio and Credit Quality Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 6,413,201	$ 6,114,354
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	618,256	611,370
Commercial Tax Exempt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	431,350	398,604
Commercial and Industrial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,049,606	1,009,974
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,363,159	2,302,244
Construction and land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	118,291	104,839
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,600,788	2,379,861
Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	107,227	118,817
Consumer and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 174,130	$ 198,619