Loan Portfolio and Credit Quality Loan Participation Amounts (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Loan participations serviced for others	$ 127,783	$ 115,912
Loans serviced for others	33,168	41,440
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Loan participations serviced for others	8,024	8,484
Commercial tax-exempt
Loans and Leases Receivable Disclosure [Line Items]
Loan participations serviced for others	19,105	19,805
Commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Loan participations serviced for others	60,688	49,783
Construction and land
Loans and Leases Receivable Disclosure [Line Items]
Loan participations serviced for others	39,966	37,840
Residential
Loans and Leases Receivable Disclosure [Line Items]
Loans serviced for others	$ 33,168	$ 41,440