Acquisition Fair value of assets acquired and liabilities assumed (Details) - USD ($) $ in Thousands	Jul. 01, 2025	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Business Combination [Line Items]
Business Combination, Recognized Asset Acquired, Asset		$ 4,930,778		$ 0
Business Combination, Recognized Liability Assumed, Liability	$ 4,551,272	4,551,272		$ 0
Goodwill		$ 1,083,374	$ 985,072
Enterprise Bancorp, Inc
Business Combination [Line Items]
Business Combination, Recognized Asset Acquired, Property, Plant, and Equipment	35,706
Business Combination, Recognized Asset Acquired, Identifiable Intangible Asset, Excluding Goodwill	137,503
Business Combination, Recognized Asset Acquired, Other Asset, Noncurrent	164,908
Business Combination, Recognized Asset Acquired, Asset	5,054,416
Business Combination, Recognized Liabilities Assumed, Deposits	4,362,710
Business Combination, Recognized Liability Assumed, Long-Term Debt, Current	62,472
Business Combination, Recognized Liability Assumed, Subordinated Debt	59,974
Business Combination, Recognized Liability Assumed, Other Liability, Noncurrent	66,116
Goodwill	98,302
Business Combination, Recognized Asset Acquired to Liability Assumed, Excess (Less), and Goodwill	503,144
Business Combination, Recognized Asset Acquired, Cash and Cash Equivalent	123,638
Business Combination, Recognized Assets Acquired, Investments	590,267
Business Combination, Recognized Assets Acquired, Loans	3,913,112
Financing Receivable, Purchased with Credit Deterioration, Allowance for Credit Loss at Acquisition Date	$ (9,020)