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Loans Held for Investment and Allowance for Credit Losses on Loans - Collateral-dependent Gross Loans Held for Investment by Collateral Type and Related Specific Allocation (Detail) - USD ($) $ in Thousands | Sep. 30, 2025 | Jun. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2024 | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | --- | --- | --- | --- | ---
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | $ 8,278,247 |  | $ 8,025,110 | $ 8,180,361 |  |
Specific Allocation | 99,511 | $ 96,988 | 99,497 | 101,882 | $ 99,626 | $ 96,800
Real Estate Asset [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 9,301 |  | 30,222 |  |  |
Business Assets [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 9,893 |  | 10,197 |  |  |
Other Assets [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 636 |  | 520 |  |  |
Specific Allocation [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 4,504 |  | 7,988 |  |  |
Collateral Pledged [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 19,830 |  | 40,939 |  |  |
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 937,976 |  | 931,709 |  |  |
Specific Allocation | 7,531 | 7,248 | 6,869 | 7,408 | 7,370 | 7,483
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 1,703,037 |  | 1,578,483 |  |  |
Specific Allocation | 35,479 | 35,217 | 33,097 | 33,746 | 33,867 | 33,080
Real Estate [Member] | Construction and Development Less than 60 Months [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 661,882 |  | 756,662 |  |  |
Specific Allocation | 4,830 | 4,907 | 8,671 | 8,355 | 6,780 | 3,950
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 249,539 |  | 250,373 |  |  |
Specific Allocation | 2,527 | 2,265 | 2,336 | 3,341 | 3,519 | 3,414
Real Estate [Member] | Residential Real Estate First Lien [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 1,486,440 |  | 1,431,265 |  |  |
Specific Allocation | 4,769 | 4,645 | 4,568 | 5,646 | 5,572 | 4,914
Real Estate [Member] | Residential Real Estate All Other [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 305,294 |  | 275,461 |  |  |
Specific Allocation | 2,007 | 1,821 | 1,741 | 1,737 | 1,729 | 1,646
Real Estate [Member] | Real Estate Asset [Member] | Commercial Real Estate Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 4,445 |  |  |  |  |
Real Estate [Member] | Real Estate Asset [Member] | Commercial Real Estate Non-Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 2,473 |  | 7,890 |  |  |
Real Estate [Member] | Real Estate Asset [Member] | Construction and Development Less than 60 Months [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 859 |  | 20,142 |  |  |
Real Estate [Member] | Real Estate Asset [Member] | Construction Residential Real Estate Less than 60 Months [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 829 |  | 206 |  |  |
Real Estate [Member] | Real Estate Asset [Member] | Residential Real Estate First Lien [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 410 |  | 300 |  |  |
Real Estate [Member] | Real Estate Asset [Member] | Residential Real Estate All Other [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 207 |  | 100 |  |  |
Real Estate [Member] | Real Estate Asset [Member] | Agriculture [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 78 |  | 1,584 |  |  |
Real Estate [Member] | Business Assets [Member] | Commercial Real Estate Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 551 |  |  |  |  |
Real Estate [Member] | Business Assets [Member] | Agriculture [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 164 |  | 110 |  |  |
Real Estate [Member] | Other Assets [Member] | Agriculture [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 12 |  | 13 |  |  |
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 585 |  |  |  |  |
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Non-Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 644 |  | 879 |  |  |
Real Estate [Member] | Specific Allocation [Member] | Construction and Development Less than 60 Months [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 251 |  | 3,755 |  |  |
Real Estate [Member] | Specific Allocation [Member] | Construction Residential Real Estate Less than 60 Months [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 229 |  | 75 |  |  |
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate First Lien [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 160 |  | 93 |  |  |
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate All Other [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 147 |  | 34 |  |  |
Real Estate [Member] | Specific Allocation [Member] | Agriculture [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 124 |  | 688 |  |  |
Real Estate [Member] | Collateral Pledged [Member] | Commercial Real Estate Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 4,996 |  |  |  |  |
Real Estate [Member] | Collateral Pledged [Member] | Commercial Real Estate Non-Owner Occupied [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 2,473 |  | 7,890 |  |  |
Real Estate [Member] | Collateral Pledged [Member] | Construction and Development Less than 60 Months [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 859 |  | 20,142 |  |  |
Real Estate [Member] | Collateral Pledged [Member] | Construction Residential Real Estate Less than 60 Months [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 829 |  | 206 |  |  |
Real Estate [Member] | Collateral Pledged [Member] | Residential Real Estate First Lien [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 410 |  | 300 |  |  |
Real Estate [Member] | Collateral Pledged [Member] | Residential Real Estate All Other [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 207 |  | 100 |  |  |
Real Estate [Member] | Collateral Pledged [Member] | Agriculture [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 254 |  | 1,707 |  |  |
Commercial Non-real Estate [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 1,458,122 |  | 1,363,462 |  |  |
Specific Allocation | 24,889 | 24,047 | 24,150 | 22,260 | 21,475 | 22,745
Commercial Non-real Estate [Member] | Business Assets [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 8,089 |  | 10,087 |  |  |
Commercial Non-real Estate [Member] | Other Assets [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 0 |  | 108 |  |  |
Commercial Non-real Estate [Member] | Specific Allocation [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 1,978 |  | 2,222 |  |  |
Commercial Non-real Estate [Member] | Collateral Pledged [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 8,089 |  | 10,195 |  |  |
Consumer Non-real Estate [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 493,900 |  | 478,647 |  |  |
Specific Allocation | 5,097 | 4,837 | 4,833 | 4,380 | 4,383 | 4,401
Consumer Non-real Estate [Member] | Other Assets [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 624 |  | 399 |  |  |
Consumer Non-real Estate [Member] | Specific Allocation [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 276 |  | 242 |  |  |
Consumer Non-real Estate [Member] | Collateral Pledged [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 624 |  | 399 |  |  |
Oil and Gas [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 536,527 |  | 509,858 |  |  |
Specific Allocation | 7,256 | $ 6,870 | $ 7,536 | $ 9,092 | $ 9,014 | $ 9,030
Oil and Gas [Member] | Business Assets [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | 1,089 |  |  |  |  |
Oil and Gas [Member] | Specific Allocation [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Specific Allocation | 110 |  |  |  |  |
Oil and Gas [Member] | Collateral Pledged [Member] |  |  |  |  |  |
Financing Receivable Allowance For Credit Losses [Line Items] |  |  |  |  |  |
Collateral Dependent Loans | $ 1,089 |  |  |  |  |

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