Loan Portfolio and Credit Quality Loan Participation Amounts (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	$ 229,964	$ 230,014
Total loans serviced for others	145,299	204,696
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	14,706	14,533
Commercial tax-exempt
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	17,959	18,101
Commercial real estate
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	117,782	121,929
Construction and land
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	79,517	75,451
Residential
Financing Receivable, Impaired [Line Items]
Total loans serviced for others	$ 145,299	$ 204,696