Premises and Equipment - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2024 USD ($) property	Dec. 31, 2023 USD ($) property	Dec. 31, 2022 USD ($) property
Property, Plant and Equipment [Line Items]
Depreciation | $	$ 12,500	$ 10,500	$ 10,700
Number of properties transferred to held for sale	4	0	0
Aggregate book value of premises held for sale | $	$ 17,100
Properties transferred to held for sale, write-down, amount | $	$ 3,000
Number of properties sold	3	0	5
Proceeds from sale of bank premises and equipment | $	$ 15,116	$ 0	$ 17,313
Gain (loss) on disposition of property plant equipment | $	$ 400		$ 1,400
Land and Building
Property, Plant and Equipment [Line Items]
Number of properties transferred to held for sale	1
Number of properties sold	1
Cambridge Bancorp
Property, Plant and Equipment [Line Items]
Number of properties transferred to held for sale	2
Number of properties sold	2
Century Bancorp, Inc.
Property, Plant and Equipment [Line Items]
Number of properties sold			4