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Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) Contract | Dec. 31, 2019 USD ($) Contract | Dec. 31, 2018 USD ($) Contract
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 41 | 38 | 58
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 14,874 | $ 8,302 | $ 11,281
Financing Receivable, Troubled Debt Restructuring | 13,969 | 1,928 | 8,829
Financing Receivable Troubled Debt Restructuring Specific Reserve | 636 | 0 | 0
Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 14,098 | 7,525 | 10,635
Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 776 | 760 | 330
Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 0 | $ 17 | $ 316
Commercial Loan [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 4 | 2 | 3
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 2,805 | $ 156 | $ 8,324
Financing Receivable, Troubled Debt Restructuring | 2,196 | 154 | 6,104
Financing Receivable Troubled Debt Restructuring Specific Reserve | $ 636 | 0 | 0
Commercial Loan [Member] | Time and demand loans |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 4 |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 2,805 |  |
Financing Receivable, Troubled Debt Restructuring | 2,196 |  |
Financing Receivable Troubled Debt Restructuring Specific Reserve | 636 |  |
Commercial Loan [Member] | Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 2,176 | 156 | 8,250
Commercial Loan [Member] | Contractual Payment Modification [Member] | Time and demand loans |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 2,176 |  |
Commercial Loan [Member] | Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 629 | 0 | 0
Commercial Loan [Member] | Contractual Interest Rate Reduction [Member] | Time and demand loans |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 629 |  |
Commercial Loan [Member] | Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 | $ 0 | $ 74
Commercial Loan [Member] | Extended Maturity [Member] | Time and demand loans |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 0 |  |
Residential Real Estate [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 18 | 20 | 37
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 950 | $ 1,186 | $ 1,799
Financing Receivable, Troubled Debt Restructuring | 791 | 1,059 | 1,638
Financing Receivable Troubled Debt Restructuring Specific Reserve | $ 0 | 0 | 0
Residential Real Estate [Member] | Senior Lien |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 9 |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 546 |  |
Financing Receivable, Troubled Debt Restructuring | 411 |  |
Financing Receivable Troubled Debt Restructuring Specific Reserve | $ 0 |  |
Residential Real Estate [Member] | Junior Lien |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 9 |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 404 |  |
Financing Receivable, Troubled Debt Restructuring | 380 |  |
Financing Receivable Troubled Debt Restructuring Specific Reserve | 0 |  |
Residential Real Estate [Member] | Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 917 | 965 | 1,316
Residential Real Estate [Member] | Contractual Payment Modification [Member] | Senior Lien |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 513 |  |
Residential Real Estate [Member] | Contractual Payment Modification [Member] | Junior Lien |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 404 |  |
Residential Real Estate [Member] | Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 33 | 204 | 241
Residential Real Estate [Member] | Contractual Interest Rate Reduction [Member] | Senior Lien |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 33 |  |
Residential Real Estate [Member] | Contractual Interest Rate Reduction [Member] | Junior Lien |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 |  |
Residential Real Estate [Member] | Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 | $ 17 | $ 242
Residential Real Estate [Member] | Extended Maturity [Member] | Senior Lien |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 |  |
Residential Real Estate [Member] | Extended Maturity [Member] | Junior Lien |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 0 |  |
Commercial Real Estate [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 5 | 5 | 3
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 10,857 | $ 6,817 | $ 1,016
Financing Receivable, Troubled Debt Restructuring | 10,758 | 594 | 975
Financing Receivable Troubled Debt Restructuring Specific Reserve | $ 0 | 0 | 0
Commercial Real Estate [Member] | Nonowner Occupied Commercial Real Estate |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 4 |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 10,289 |  |
Financing Receivable, Troubled Debt Restructuring | 10,263 |  |
Financing Receivable Troubled Debt Restructuring Specific Reserve | $ 0 |  |
Commercial Real Estate [Member] | Owner Occupied Commercial Real Estate |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 1 |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 568 |  |
Financing Receivable, Troubled Debt Restructuring | 495 |  |
Financing Receivable Troubled Debt Restructuring Specific Reserve | 0 |  |
Commercial Real Estate [Member] | Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 10,857 | 6,261 | 1,016
Commercial Real Estate [Member] | Contractual Payment Modification [Member] | Nonowner Occupied Commercial Real Estate |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 10,289 |  |
Commercial Real Estate [Member] | Contractual Payment Modification [Member] | Owner Occupied Commercial Real Estate |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 568 |  |
Commercial Real Estate [Member] | Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 | 556 | 0
Commercial Real Estate [Member] | Contractual Interest Rate Reduction [Member] | Nonowner Occupied Commercial Real Estate |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 |  |
Commercial Real Estate [Member] | Contractual Interest Rate Reduction [Member] | Owner Occupied Commercial Real Estate |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 |  |
Commercial Real Estate [Member] | Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 | $ 0 | $ 0
Commercial Real Estate [Member] | Extended Maturity [Member] | Nonowner Occupied Commercial Real Estate |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 |  |
Commercial Real Estate [Member] | Extended Maturity [Member] | Owner Occupied Commercial Real Estate |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 0 |  |
Loans To Individuals [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 14 | 11 | 15
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 262 | $ 143 | $ 142
Financing Receivable, Troubled Debt Restructuring | 224 | 121 | 112
Financing Receivable Troubled Debt Restructuring Specific Reserve | $ 0 | 0 | 0
Loans To Individuals [Member] | Automobiles |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 14 |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 262 |  |
Financing Receivable, Troubled Debt Restructuring | 224 |  |
Financing Receivable Troubled Debt Restructuring Specific Reserve | 0 |  |
Loans To Individuals [Member] | Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 148 | 143 | 53
Loans To Individuals [Member] | Contractual Payment Modification [Member] | Automobiles |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 148 |  |
Loans To Individuals [Member] | Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 114 | 0 | 89
Loans To Individuals [Member] | Contractual Interest Rate Reduction [Member] | Automobiles |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 114 |  |
Loans To Individuals [Member] | Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 | $ 0 | $ 0
Loans To Individuals [Member] | Extended Maturity [Member] | Automobiles |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 0 |  |

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- Definition Number of financing receivables that have been modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524 + Details
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