Loan Portfolio and Credit Quality Nonaccrual Loans by Class of Financing Receivable (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 16,176	$ 17,315
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	697	572
Commercial Tax Exempt [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	0	0
Commercial and Industrial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	697	572
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	3,004	4,583
Construction and land [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	232	179
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	11,173	10,908
Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	1,070	1,072
Consumer and other [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 0	$ 1