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Loans and allowance for loan losses - Loan Modification Activities to Borrowers Experiencing Financial Difficulty on Financing Receivables (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 356,000 | $ 330,000 | $ 1,035,000 | $ 996,000
Percent of Total Loan Class | 0.26% | 0.24% | 0.76% | 0.73%
Guaranteed by Government-Related Entities |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 40,000 | $ 33,000 | $ 109,000 | $ 117,000
Commercial and industrial |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 100,000 | $ 117,000 | $ 275,000 | $ 270,000
Percent of Total Loan Class | 0.16% | 0.19% | 0.44% | 0.44%
Commercial | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 156,000 | $ 164,000 | $ 350,000 | $ 425,000
Percent of Total Loan Class | 0.77% | 0.73% | 1.74% | 1.90%
Residential builder and developer | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 0 | $ 2,000 | $ 0 | $ 13,000
Percent of Total Loan Class | 0.00% | 0.17% | 0.00% | 1.27%
Other commercial construction | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 52,000 | $ 2,000 | $ 272,000 | $ 139,000
Percent of Total Loan Class | 1.33% | 0.03% | 6.98% | 2.62%
Residential | Residential Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 46,000 | $ 45,000 | $ 126,000 | $ 146,000
Percent of Total Loan Class | 0.18% | 0.20% | 0.51% | 0.63%
Home equity lines and loans | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 1,000 | $ 0 | $ 1,000 | $ 2,000
Percent of Total Loan Class | 0.00% | 0.00% | 0.02% | 0.04%
Recreational finance | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 1,000 | $ 0 | $ 1,000 | $ 1,000
Percent of Total Loan Class | 0.00% | 0.00% | 0.00% | 0.01%
Automobile | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 0 | $ 0 | $ 0 | $ 0
Percent of Total Loan Class | 0.00% | 0.00% | 0.00% | 0.00%
Other | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 0 | $ 0 | $ 10,000 | $ 0
Percent of Total Loan Class | 0.00% | 0.00% | 0.43% | 0.00%
Unfunded Loan Commitment |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 53,000 | $ 8,000 | $ 89,000 | $ 43,000
Term Extension |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 231,000 | 295,000 | 811,000 | 892,000
Term Extension | Commercial and industrial |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 12,000 | 92,000 | 104,000 | 190,000
Term Extension | Commercial | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 130,000 | 163,000 | 324,000 | 420,000
Term Extension | Residential builder and developer | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 2,000 | 0 | 13,000
Term Extension | Other commercial construction | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 52,000 | 2,000 | 272,000 | 139,000
Term Extension | Residential | Residential Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 36,000 | 36,000 | 100,000 | 128,000
Term Extension | Home equity lines and loans | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 1,000
Term Extension | Recreational finance | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 1,000 | 0 | 1,000 | 1,000
Term Extension | Automobile | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Term Extension | Other | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 10,000 | 0
Other (a) |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 85,000 | 29,000 | 94,000 | 91,000
Other (a) | Commercial and industrial |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 85,000 | 23,000 | 90,000 | 78,000
Other (a) | Commercial | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 1,000 | 0 | 1,000
Other (a) | Residential builder and developer | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Other (a) | Other commercial construction | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Other (a) | Residential | Residential Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 5,000 | 4,000 | 12,000
Other (a) | Home equity lines and loans | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Other (a) | Recreational finance | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Other (a) | Automobile | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Other (a) | Other | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Combination of Modification Types |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 40,000 | 6,000 | 130,000 | 13,000
Combination of Modification Types | Commercial and industrial |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 3,000 | 2,000 | 81,000 | 2,000
Combination of Modification Types | Commercial | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 26,000 | 0 | 26,000 | 4,000
Combination of Modification Types | Residential builder and developer | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Combination of Modification Types | Other commercial construction | Commercial Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Combination of Modification Types | Residential | Residential Real Estate |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 10,000 | 4,000 | 22,000 | 6,000
Combination of Modification Types | Home equity lines and loans | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 1,000 | 0 | 1,000 | 1,000
Combination of Modification Types | Recreational finance | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Combination of Modification Types | Automobile | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | 0 | 0 | 0 | 0
Combination of Modification Types | Other | Consumer |  |  |  |
Financing Receivable, Modifications other than Troubled Debt Restructuring [Line Items] |  |  |  |
Modified in period | $ 0 | $ 0 | $ 0 | $ 0

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- Definition Amortized cost excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 42 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481962/310-10-50-42 + Details
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