Premises and Equipment - Schedule of Premises and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total cost	$ 174,420	$ 156,002
Accumulated depreciation	(108,564)	(107,334)
Premises and equipment used in operations, net	65,856	48,668
Premises and equipment held for sale	15,128	730
Net premises and equipment (1)	80,984	49,398
Century Bancorp, Inc.
Property, Plant and Equipment [Line Items]
Net premises and equipment (1)	64,500
Land
Property, Plant and Equipment [Line Items]
Total cost	12,814	7,410
Buildings
Property, Plant and Equipment [Line Items]
Total cost	$ 71,415	58,112
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	30 years
Equipment
Property, Plant and Equipment [Line Items]
Total cost	$ 48,035	55,919
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total cost	$ 42,156	$ 34,561
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	25 years