Mergers and Acquisitions - Schedule of Merger-Related Expenses (Details) - Cambridge Bancorp - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Business Acquisition [Line Items]
Acquisition-related and professional fee costs	$ 36,664	$ 5,495
Salaries and employee benefits
Business Acquisition [Line Items]
Acquisition-related and professional fee costs	14,719	5
Office occupancy and equipment
Business Acquisition [Line Items]
Acquisition-related and professional fee costs	4,583	2
Data processing
Business Acquisition [Line Items]
Acquisition-related and professional fee costs	4,919	1,357
Professional services
Business Acquisition [Line Items]
Acquisition-related and professional fee costs	7,320	4,080
Marketing
Business Acquisition [Line Items]
Acquisition-related and professional fee costs	70	0
Other noninterest expense
Business Acquisition [Line Items]
Acquisition-related and professional fee costs	$ 5,053	$ 51