Loan Portfolio and Credit Quality - Loan Participation Amounts (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	$ 371,570	$ 352,618
Total loans serviced for others	146,080	168,110
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	110,284	110,589
Commercial tax-exempt
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	22,845	17,604
Commercial real estate
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	136,019	130,551
Construction and land
Financing Receivable, Impaired [Line Items]
Total loan participations serviced for others	102,422	93,874
Residential
Financing Receivable, Impaired [Line Items]
Total loans serviced for others	$ 146,080	$ 168,110