Loans Receivable and Credit Quality Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 6,505,028	$ 6,114,354
Commercial and Industrial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	939,690	1,009,974
Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	520,992	611,370
Commercial Tax Exempt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	418,698	398,604
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,440,220	2,302,244
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	164,990	104,839
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,682,533	2,379,861
Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	99,958	118,817
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 177,637	$ 198,619