Loans, Allowance for Credit Losses and Credit Quality - Financing Receivable Past Due (Details) $ in Thousands		Sep. 30, 2025 USD ($) loan	Dec. 31, 2024 USD ($) loan
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan		570	761
Total loans	[1]	$ 18,452,443	$ 14,508,378	[2]
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan		44	28
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan		84	37
Number Of Financing Receivables Total Past Due | loan		698	826
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		$ 34,194	$ 47,521
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		26,201	2,201
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		30,247	37,686
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total loans		90,642	87,408
Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total loans		$ 18,361,801	$ 14,420,970
Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan		34	125
Total loans	[1],[3]	$ 4,532,294	$ 3,246,455	[2]
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan		17	5
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan		33	8
Number Of Financing Receivables Total Past Due | loan		84	138
Commercial And Industrial [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		$ 8,630	$ 5,864
Commercial And Industrial [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		10,081	29
Commercial And Industrial [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		10,018	13,872
Commercial And Industrial [Member] | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total loans		28,729	19,765
Commercial And Industrial [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total loans		$ 4,503,565	$ 3,226,690
Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan		18	4
Total loans	[1],[3]	$ 8,241,458	$ 6,839,705	[2]
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan		2	0
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan		7	3
Number Of Financing Receivables Total Past Due | loan		27	7
Commercial Real Estate [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		$ 8,715	$ 33,860
Commercial Real Estate [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		1,489	0
Commercial Real Estate [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		6,907	20,458
Commercial Real Estate [Member] | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total loans		17,111	54,318
Commercial Real Estate [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total loans		$ 8,224,347	$ 6,785,387
Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan		3	0
Total loans	[1]	$ 1,439,876	$ 782,078	[2]
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan		3	0
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan		2	0
Number Of Financing Receivables Total Past Due | loan		8	0
Construction Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		$ 8,867	$ 0
Construction Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		10,737	0
Construction Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		7,722	0
Construction Loans [Member] | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total loans		27,326	0
Construction Loans [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total loans		$ 1,412,550	$ 782,078
Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan		21	27
Total loans	[1]	$ 2,917,101	$ 2,460,600	[2]
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan		10	9
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan		16	10
Number Of Financing Receivables Total Past Due | loan		47	46
Residential Real Estate [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		$ 5,086	$ 6,310
Residential Real Estate [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		3,031	1,401
Residential Real Estate [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		3,489	2,224
Residential Real Estate [Member] | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total loans		11,606	9,935
Residential Real Estate [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total loans		$ 2,905,495	$ 2,450,665
Home Equity Loan [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan		22	9
Total loans	[1]	$ 1,284,139	$ 1,140,168	[2]
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan		6	11
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan		19	10
Number Of Financing Receivables Total Past Due | loan		47	30
Home Equity Loan [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		$ 2,583	$ 1,046
Home Equity Loan [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		854	764
Home Equity Loan [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans		2,105	1,126
Home Equity Loan [Member] | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total loans		5,542	2,936
Home Equity Loan [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total loans		$ 1,278,597	$ 1,137,232
Consumer - Other [Member]
Financing Receivable, Past Due [Line Items]
Number Of Financing Receivables Thirty To Fifty Nine Days Past Due | loan	[4]	472	596
Total loans	[4]	$ 37,575	$ 39,372	[2]
Number of Financing Receivables Sixty to Eighty Nine Days Past Due | loan	[4]	6	3
Number Of Financing Receivables Equal To Greater Than Ninety Days | loan	[4]	7	6
Number Of Financing Receivables Total Past Due | loan	[4]	485	605
Consumer - Other [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans	[4]	$ 313	$ 441
Consumer - Other [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans	[4]	9	7
Consumer - Other [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total loans	[4]	6	6
Consumer - Other [Member] | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total loans	[4]	328	454
Consumer - Other [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total loans	[4]	$ 37,247	$ 38,918

[1] (2)Loan origination dates in the tables above reflect the original origination date, or the date of a material modification of a previously originated loan.

[2] The amount of net deferred fees/costs on originated loans included in the ending balance was $7.2 million and $6.1 million at September 30, 2025 and December 31, 2024, respectively. Net unamortized discounts on acquired loans included in the ending balance were $163.1 million and $8.1 million at September 30, 2025 and December 31, 2024, respectively.

[3] (1)Commercial and industrial and commercial real estate balances as of September 30, 2025 presented above vary from amounts previously reported in the Company’s third quarter 2025 earnings release. These reported amounts reflect a reclassification of commercial and industrial loan balances to the commercial real estate category based upon further review of loan classifications subsequent to the system conversion of Enterprise Bancorp, Inc., parent of Enterprise Bank and Trust Company (collectively “Enterprise”). Reported amounts throughout this Form 10-Q are reflective of this reclassification, where applicable.

[4] Other consumer portfolio is inclusive of deposit account overdrafts recorded as loan balances. (2)The amount of net deferred fees/costs on originated loans included in the ending balance was $7.2 million and $6.1 million at September 30, 2025 and December 31, 2024, respectively. Net unamortized discounts on acquired loans included in the ending balance were $163.1 million and $8.1 million at September 30, 2025 and December 31, 2024, respectively.