Loan Portfolio and Credit Quality Loan Participation Amounts (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Loan Participation Amounts by Loan Type [Line Items]
Loan Participation Serviced for Others Amount	$ 109,206	$ 115,912
Loan Serviced for Others Amount	38,217	41,440
Commercial and industrial [Member]
Loan Participation Amounts by Loan Type [Line Items]
Loan Participation Serviced for Others Amount	8,313	8,484
Commercial Tax Exempt [Member]
Loan Participation Amounts by Loan Type [Line Items]
Loan Participation Serviced for Others Amount	19,464	19,805
Commercial real estate [Member]
Loan Participation Amounts by Loan Type [Line Items]
Loan Participation Serviced for Others Amount	49,200	49,783
Construction and land [Member]
Loan Participation Amounts by Loan Type [Line Items]
Loan Participation Serviced for Others Amount	32,229	37,840
Residential [Member]
Loan Participation Amounts by Loan Type [Line Items]
Loan Serviced for Others Amount	$ 38,217	$ 41,440