Loan Portfolio and Credit Quality Loan Participation Amounts (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	$ 92,841	$ 127,783
Total loans serviced for others	30,394	33,168
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	9,269	8,024
Commercial tax-exempt
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	18,824	19,105
Commercial real estate
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	44,613	60,688
Construction and land
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	20,135	39,966
Residential
Financing Receivable, Impaired [Line Items]
Total loans serviced for others	$ 30,394	$ 33,168