CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS’ EQUITY (Parenthetical) - USD ($) $ in Thousands			12 Months Ended
	Jan. 01, 2023	Jan. 01, 2022	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Retained earnings			$ (2,084,503)	$ (2,047,754)
Deferred income tax expense (benefit)			$ 36,059	$ (18,267)	$ 5,262
Dividends declared (in dollars per share)			$ 0.45	$ 0.41	$ 0.40
Accounting Standards Update [Extensible Enumeration]					Accounting Standards Update 2022-02	Accounting Standards Update 2016-13
Restricted Stock Awards | Cambridge Bancorp
Restricted stock, shares cancelled upon vesting for employee withholdings (in shares)			15,487
Restricted stock, shares cancelled upon forfeitures (in shares)			3,026
Issuance of restricted stock awards (in shares)			118,693
Restricted stock award shares, at fair value			$ 1,100
Cumulative effect accounting adjustment
Retained earnings	$ 1,100	$ 28,000
Deferred income tax expense (benefit)	$ 300	$ 7,900