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Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 USD ($) Contract | Dec. 31, 2018 USD ($) Contract | Dec. 31, 2017 USD ($) Contract
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 38 | 58 | 41
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 8,302 | $ 11,281 | $ 11,054
Financing Receivable, Troubled Debt Restructuring | 1,928 | 8,829 | 8,274
Financing Receivable Troubled Debt Restructuring Specific Reserve | 0 | 0 | 596
Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 7,525 | 10,635 | 1,878
Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 760 | 330 | 2,095
Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 17 | $ 316 | $ 7,081
Commercial Loan [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 2 | 3 | 6
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 156 | $ 8,324 | $ 9,561
Financing Receivable, Troubled Debt Restructuring | 154 | 6,104 | 6,946
Financing Receivable Troubled Debt Restructuring Specific Reserve | 0 | 0 | 566
Commercial Loan [Member] | Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 156 | 8,250 | 987
Commercial Loan [Member] | Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 | 0 | 1,806
Commercial Loan [Member] | Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 0 | $ 74 | $ 6,768
Residential Real Estate [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 20 | 37 | 20
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 1,186 | $ 1,799 | $ 968
Financing Receivable, Troubled Debt Restructuring | 1,059 | 1,638 | 851
Financing Receivable Troubled Debt Restructuring Specific Reserve | 0 | 0 | 1
Residential Real Estate [Member] | Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 965 | 1,316 | 573
Residential Real Estate [Member] | Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 204 | 241 | 261
Residential Real Estate [Member] | Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 17 | $ 242 | $ 134
Commercial Real Estate [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 5 | 3 | 5
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 6,817 | $ 1,016 | $ 448
Financing Receivable, Troubled Debt Restructuring | 594 | 975 | 412
Financing Receivable Troubled Debt Restructuring Specific Reserve | 0 | 0 | 29
Commercial Real Estate [Member] | Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 6,261 | 1,016 | 269
Commercial Real Estate [Member] | Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 556 | 0 | 0
Commercial Real Estate [Member] | Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 0 | $ 0 | $ 179
Loans To Individuals [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Modifications, Number of Contracts | Contract | 11 | 15 | 10
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 143 | $ 142 | $ 77
Financing Receivable, Troubled Debt Restructuring | 121 | 112 | 65
Financing Receivable Troubled Debt Restructuring Specific Reserve | 0 | 0 | 0
Loans To Individuals [Member] | Contractual Payment Modification [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 143 | 53 | 49
Loans To Individuals [Member] | Contractual Interest Rate Reduction [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | 0 | 89 | 28
Loans To Individuals [Member] | Extended Maturity [Member] |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Troubled Debt Restructuring, Premodification | $ 0 | $ 0 | $ 0

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