Business Combinations - Schedule of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 01, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Fair value of liabilities assumed:
Goodwill		$ 351,613	$ 241,222	$ 241,222
Holdco Merger
Fair value of consideration transferred:
Value of consideration transferred, equity interest	$ 1,147
Cash paid for fractional shares	49
Total purchase consideration	1,210,647
Fair value of assets acquired:
Cash and due from banks	105,440
Short-term investments	978,667
Investment securities available-for-sale	1,102,464
Loans held for sale	3,471
Loans held for investment	9,081,447
Premises and equipment	73,368
Bank owned life insurance	246,979
Accrued interest receivable	49,717
Other assets	314,345
Total assets acquired	12,144,313
Fair value of liabilities assumed:
Deposits	10,287,573
Borrowings	559,402
Accrued expenses and other liabilities	197,082
Total liabilities assumed	11,044,057
Net assets acquired	1,100,256
Goodwill	110,391
Holdco Merger | Core deposits
Fair value of assets acquired:
Intangible asset	174,415
Holdco Merger | Customer relationships intangible asset
Fair value of assets acquired:
Intangible asset	14,000
Holdco Merger | Brookline Bancorp, Inc.
Fair value of consideration transferred:
Value of consideration transferred, equity interest	1,209,451
Holdco Merger | Berkshire Hills Bancorp, Inc
Fair value of consideration transferred:
Value of consideration transferred, equity interest	$ 1,147