Loan Portfolio and Credit Quality Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 7,067,151	$ 6,893,158
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	695,029	623,037
Commercial tax-exempt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	448,488	451,671
Total commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,143,517	1,074,708
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,533,346	2,395,692
Construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	209,741	240,306
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,964,042	2,948,973
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	84,432	90,421
Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 132,073	$ 143,058