Mergers and Acquisitions - Schedule of Estimated Fair Values of the Assets Acquired and the Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jul. 12, 2024	Dec. 31, 2023
Assets
Goodwill	$ 914,957		$ 557,635
Cambridge Bancorp
Assets
Cash and due from banks		$ 20,008
Short-term investments		4,877
Investment securities		883,021
Loans		3,650,600
Allowance for loan losses		(55,830)
FHLB stock		27,255
Premises and equipment		23,417
Bank owned life insurance		35,676
Goodwill		357,322
Intangible assets		141,200
Deferred income taxes, net		107,989
Other assets		134,608
Total assets acquired		5,330,143
Liabilities
Deposits		3,873,717
FHLB advances		782,000
Escrow deposits of borrowers		3,633
Other liabilities		90,200
Total liabilities assumed		4,749,550
Purchase price		580,593
Fair value of time deposits		$ 418,700