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Loans and Allowance for Credit Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | --- | ---
Financing Receivable, Past Due [Line Items] |  |  |
Total | $ 7,981,007 | $ 7,742,958 |
Nonaccrual | 49,618 | 27,937 | $ 22,947
Current |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 7,897,242 | 7,703,543 |
Total Past Due Loans |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 83,765 | 39,415 |
30-59 Days Past Due |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 30,157 | 5,431 |
60-89 Days Past Due |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 3,990 | 6,047 |
Commercial loans | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,950,110 | 2,708,531 |
Nonaccrual | 25,648 | 3,228 | 6,320
Commercial loans | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,275,985 | 1,351,637 |
Nonaccrual | 8,979 | 11,173 | 878
Commercial loans | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 307,012 | 341,266 |
Nonaccrual | 869 | 0 | 4,960
Commercial loans | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,316,346 | 1,303,258 |
Nonaccrual | 4,146 | 2,988 | 4,147
Commercial loans | Current | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,915,311 | 2,705,303 |
Commercial loans | Current | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,251,241 | 1,338,053 |
Commercial loans | Current | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 306,143 | 340,230 |
Commercial loans | Current | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,309,315 | 1,297,651 |
Commercial loans | Total Past Due Loans | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 34,799 | 3,228 |
Commercial loans | Total Past Due Loans | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 24,744 | 13,584 |
Commercial loans | Total Past Due Loans | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 869 | 1,036 |
Commercial loans | Total Past Due Loans | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 7,031 | 5,607 |
Commercial loans | 30-59 Days Past Due | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 9,151 | 0 |
Commercial loans | 30-59 Days Past Due | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 15,765 | 415 |
Commercial loans | 30-59 Days Past Due | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 0 | 0 |
Commercial loans | 30-59 Days Past Due | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,358 | 2,336 |
Commercial loans | 60-89 Days Past Due | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 0 | 0 |
Commercial loans | 60-89 Days Past Due | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 0 | 1,996 |
Commercial loans | 60-89 Days Past Due | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 0 | 1,036 |
Commercial loans | 60-89 Days Past Due | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 527 | 283 |
Consumer loans | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,028,954 | 1,933,509 |
Nonaccrual | 9,812 | 10,318 | 6,312
Consumer loans | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 102,600 | 104,757 |
Nonaccrual | 164 | 230 | $ 330
Consumer loans | Current | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,013,275 | 1,918,150 |
Consumer loans | Current | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 101,957 | 104,156 |
Consumer loans | Total Past Due Loans | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 15,679 | 15,359 |
Consumer loans | Total Past Due Loans | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 643 | 601 |
Consumer loans | 30-59 Days Past Due | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,763 | 2,464 |
Consumer loans | 30-59 Days Past Due | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 120 | 216 |
Consumer loans | 60-89 Days Past Due | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 3,104 | 2,577 |
Consumer loans | 60-89 Days Past Due | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | $ 359 | $ 155 |

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