Loan Portfolio and Credit Quality - Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	$ 7,332,954	$ 6,976,704
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	565,748	694,034
Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	370,034	0
Commercial tax-exempt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	419,264	447,927
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	2,676,708	2,551,274
Construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	240,211	225,983
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	2,859,627	2,839,155
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	84,588	83,657
Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Receivable	$ 116,774	$ 134,674