Loan Portfolio and Credit Quality - Loan Participation Amounts (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	$ 229,737	$ 230,014
Total loans serviced for others	130,114	204,696
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	15,122	14,533
Commercial tax-exempt
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	17,829	18,101
Commercial real estate
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	124,312	121,929
Construction and land
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	72,474	75,451
Residential
Financing Receivable, Impaired [Line Items]
Total loans serviced for others	$ 130,114	$ 204,696