Loan Portfolio and Credit Quality Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 6,767,123	$ 6,505,028
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	583,193	520,992
Commercial Tax Exempt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	438,882	418,698
Commercial and Industrial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,022,075	939,690
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,504,521	2,440,220
Construction and land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	172,024	164,990
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,808,206	2,682,533
Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	91,801	99,958
Consumer and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 168,496	$ 177,637