Loan Portfolio and Credit Quality Loan Participation Amounts (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	$ 91,018	$ 127,783
Total loans serviced for others	119,389	33,168
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	14,358	8,024
Commercial tax-exempt
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	18,711	19,105
Commercial real estate
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	34,816	60,688
Construction and land
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	23,133	39,966
Residential
Financing Receivable, Impaired [Line Items]
Total loans serviced for others	$ 119,389	$ 33,168