Low Income Housing Tax Credits and Other Tax Credit Investments - Schedule of the Company's Investments in Low Income Housing Projects Accounted for Using the Proportional Amortization Method (Details) - USD ($) $ in Thousands		12 Months Ended
	Jul. 12, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Investment Program, Proportional Amortization Method, Elected [Line Items]
Current recorded investment included in other assets		$ 220,845	$ 221,190
Commitments to fund qualified affordable housing projects included in recorded investment noted above		89,801	149,207
Tax credits and other tax benefits recognized		20,750	11,624	$ 9,146
Amortization expense included in income tax expense		$ 16,452	$ 9,577	$ 7,503
Investment, Proportional Amortization Method, Elected, Statement of Financial Position [Extensible Enumeration]		Other assets	Other assets
Investment Program Proportional Amortization Method Elected Income Tax Credit And Other Income Tax Benefit Before Amortization Statement Of Income Or Comprehensive Income Extensible Enumeration Not Disclosed Flag		Tax credits and other tax benefits recognized	Tax credits and other tax benefits recognized	Tax credits and other tax benefits recognized
Investment Program Proportional Amortization Method Elected Income Tax Credit And Other Income Tax Benefit Before Amortization Statement Of Cash Flows Extensible Enumeration Not Disclosed Flag		Tax credits and other tax benefits recognized	Tax credits and other tax benefits recognized	Tax credits and other tax benefits recognized
Investment Program, Proportional Amortization Method, Applied, Amortization Expense, Statement of Income or Comprehensive Income [Extensible Enumeration]		Income tax expense (benefit)	Income tax expense (benefit)	Income tax expense (benefit)
Investment Program Proportional Amortization Method Applied Income Tax Credit And Other Tax Benefit Amortization Statement Of Cash Flows Extensible Enumeration Not Disclosed Flag		Amortization expense included in income tax expense	Amortization expense included in income tax expense	Amortization expense included in income tax expense
Cambridge Bancorp
Investment Program, Proportional Amortization Method, Elected [Line Items]
Acquired investment in LIHTC projects	$ 7,400