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Loans and Allowance for Credit Losses - Recorded Investment and Unpaid Principal Balance for Impaired Loans with Associated Allowance (Detail) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2020 USD ($) Contract | Jun. 30, 2019 USD ($) Contract | Jun. 30, 2020 USD ($) Contract | Jun. 30, 2019 USD ($) Contract | Dec. 31, 2019 USD ($)
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Number of Contracts | Contract | 5 | 10 | 16 | 20 |
Total Pre-Modification Outstanding Recorded Investment | $ 200 | $ 6,233 | $ 471 | $ 7,164 |
Post- Modification Outstanding Recorded Investment | 197 | 5,964 | 451 | 6,869 |
Troubled Debt Restructuring [Policy Text Block] | 0 | 969 | 0 | 1,006 |
Extended Maturity [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Total Pre-Modification Outstanding Recorded Investment | 0 | 0 | 0 | 17 |
Contractual Interest Rate Reduction [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Total Pre-Modification Outstanding Recorded Investment | 53 | 68 | 71 | 117 |
Contractual Payment Modification [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Total Pre-Modification Outstanding Recorded Investment | $ 147 | $ 6,165 | $ 400 | $ 7,030 |
Loans to individuals [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Number of Contracts | Contract | 3 | 3 | 10 | 5 |
Total Pre-Modification Outstanding Recorded Investment | $ 54 | $ 14 | $ 195 | $ 62 |
Post- Modification Outstanding Recorded Investment | 55 | 14 | 186 | 56 |
Troubled Debt Restructuring [Policy Text Block] | 0 | 0 | 0 | 0 |
Loans to individuals [Member] | Extended Maturity [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Total Pre-Modification Outstanding Recorded Investment | 0 | 0 | 0 | 0 |
Loans to individuals [Member] | Contractual Interest Rate Reduction [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Total Pre-Modification Outstanding Recorded Investment | 53 | 0 | 71 | 0 |
Loans to individuals [Member] | Contractual Payment Modification [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Total Pre-Modification Outstanding Recorded Investment | 1 | 14 | 124 | 62 |
Acquired Loans [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 4,015 | 4,197 | 3,518 | 3,806 |
Impaired Financing Receivable, Interest Income, Accrual Method | 15 | 21 | 17 | 23 |
Related allowance | 347 |  | 347 |  | $ 0
Recorded investment | 3,955 |  | 3,955 |  | 2,519
Unpaid principal balance | 4,385 |  | 4,385 |  | 2,993
Acquired Loans [Member] | Commercial Loan [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 0 | 0 | 0 | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Related allowance | 0 |  | 0 |  | 0
Recorded investment | 0 |  | 0 |  | 0
Unpaid principal balance | 0 |  | 0 |  | 0
Acquired Loans [Member] | Commercial Financial Agricultural And Other With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 74 | 1,630 | 74 | 1,035 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Recorded investment | 74 |  | 74 |  | 73
Unpaid principal balance | 74 |  | 74 |  | 73
Acquired Loans [Member] | Real Estate Construction With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 0 | 0 | 0 | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Recorded investment | 0 |  | 0 |  | 0
Unpaid principal balance | 0 |  | 0 |  | 0
Acquired Loans [Member] | Residential Real Estate With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 1,753 | 1,969 | 1,922 | 1,975 |
Impaired Financing Receivable, Interest Income, Accrual Method | 15 | 4 | 17 | 5 |
Recorded investment | 1,499 |  | 1,499 |  | 2,136
Unpaid principal balance | 1,875 |  | 1,875 |  | 2,585
Acquired Loans [Member] | Commercial Real Estate With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 246 | 423 | 238 | 620 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 17 | 0 | 18 |
Recorded investment | 245 |  | 245 |  | 298
Unpaid principal balance | 260 |  | 260 |  | 320
Acquired Loans [Member] | Loans To Individuals With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 11 | 14 | 11 | 14 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Recorded investment | 11 |  | 11 |  | 12
Unpaid principal balance | 14 |  | 14 |  | 15
Acquired Loans [Member] | With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 2,084 | 4,036 | 2,245 | 3,644 |
Impaired Financing Receivable, Interest Income, Accrual Method | 15 | 21 | 17 | 23 |
Recorded investment | 1,829 |  | 1,829 |  | 2,519
Unpaid principal balance | 2,223 |  | 2,223 |  | 2,993
Acquired Loans [Member] | Real Estate Construction With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 103 | 0 | 51 | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Related allowance | 171 |  | 171 |  | 0
Recorded investment | 308 |  | 308 |  | 0
Unpaid principal balance | 308 |  | 308 |  | 0
Acquired Loans [Member] | Residential Real Estate With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 0 | 0 | 0 | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Related allowance | 0 |  | 0 |  | 0
Recorded investment | 0 |  | 0 |  | 0
Unpaid principal balance | 0 |  | 0 |  | 0
Acquired Loans [Member] | Commercial Real Estate With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 1,828 | 161 | 1,222 | 162 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Related allowance | 176 |  | 176 |  | 0
Recorded investment | 1,818 |  | 1,818 |  | 0
Unpaid principal balance | 1,854 |  | 1,854 |  | 0
Acquired Loans [Member] | Loans To Individuals With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 0 | 0 | 0 | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Related allowance | 0 |  | 0 |  | 0
Recorded investment | 0 |  | 0 |  | 0
Unpaid principal balance | 0 |  | 0 |  | 0
Acquired Loans [Member] | With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 1,931 | 161 | 1,273 | 162 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Related allowance | 347 |  | 347 |  | 0
Recorded investment | 2,126 |  | 2,126 |  | 0
Unpaid principal balance | 2,162 |  | 2,162 |  | 0
Originated Loans [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 53,897 | 27,815 | 45,580 | 26,294 |
Impaired Financing Receivable, Interest Income, Accrual Method | 144 | 214 | 271 | 345 |
Related allowance | 6,548 |  | 6,548 |  | 2,432
Recorded investment | 52,068 |  | 52,068 |  | 29,698
Unpaid principal balance | 62,808 |  | 62,808 |  | 39,122
Originated Loans [Member] | Commercial Loan [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 2,028 | 3,957 | 1,881 | 3,784 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 16 | 1 | 30 |
Related allowance | 958 |  | 958 |  | 1,580
Recorded investment | 2,019 |  | 2,019 |  | 8,290
Unpaid principal balance | 7,071 |  | 7,071 |  | 10,032
Originated Loans [Member] | Commercial Financial Agricultural And Other With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 6,758 | 2,268 | 6,894 | 2,216 |
Impaired Financing Receivable, Interest Income, Accrual Method | 12 | 5 | 34 | 7 |
Recorded investment | 7,620 |  | 7,620 |  | 1,848
Unpaid principal balance | 10,557 |  | 10,557 |  | 6,997
Originated Loans [Member] | Real Estate Construction With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 0 | 0 | 0 | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Recorded investment | 0 |  | 0 |  | 0
Unpaid principal balance | 0 |  | 0 |  | 0
Originated Loans [Member] | Residential Real Estate With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 9,836 | 10,242 | 10,182 | 10,577 |
Impaired Financing Receivable, Interest Income, Accrual Method | 80 | 115 | 159 | 186 |
Recorded investment | 9,778 |  | 9,778 |  | 10,372
Unpaid principal balance | 11,770 |  | 11,770 |  | 12,437
Originated Loans [Member] | Commercial Real Estate With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 17,411 | 3,034 | 14,367 | 3,256 |
Impaired Financing Receivable, Interest Income, Accrual Method | 48 | 65 | 67 | 101 |
Recorded investment | 14,786 |  | 14,786 |  | 3,015
Unpaid principal balance | 15,053 |  | 15,053 |  | 3,210
Originated Loans [Member] | Loans To Individuals With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 468 | 357 | 457 | 340 |
Impaired Financing Receivable, Interest Income, Accrual Method | 4 | 5 | 6 | 7 |
Recorded investment | 475 |  | 475 |  | 406
Unpaid principal balance | 845 |  | 845 |  | 640
Originated Loans [Member] | With No Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 34,473 | 15,901 | 31,900 | 16,389 |
Impaired Financing Receivable, Interest Income, Accrual Method | 144 | 190 | 266 | 301 |
Recorded investment | 32,659 |  | 32,659 |  | 15,641
Unpaid principal balance | 38,225 |  | 38,225 |  | 23,284
Originated Loans [Member] | Real Estate Construction With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 0 | 0 | 0 | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Related allowance | 0 |  | 0 |  | 0
Recorded investment | 0 |  | 0 |  | 0
Unpaid principal balance | 0 |  | 0 |  | 0
Originated Loans [Member] | Residential Real Estate With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 254 | 653 | 290 | 571 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 7 | 0 | 12 |
Related allowance | 0 |  | 0 |  | 1
Recorded investment | 254 |  | 254 |  | 474
Unpaid principal balance | 358 |  | 358 |  | 498
Originated Loans [Member] | Commercial Real Estate With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 17,142 | 7,304 | 11,509 | 5,550 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 1 | 4 | 2 |
Related allowance | 5,590 |  | 5,590 |  | 851
Recorded investment | 17,136 |  | 17,136 |  | 5,293
Unpaid principal balance | 17,154 |  | 17,154 |  | 5,308
Originated Loans [Member] | Loans To Individuals With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 0 | 0 | 0 | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | 0 | 0 | 0 |
Related allowance | 0 |  | 0 |  | 0
Recorded investment | 0 |  | 0 |  | 0
Unpaid principal balance | 0 |  | 0 |  | 0
Originated Loans [Member] | With Related Allowance [Member] |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |
Impaired Financing Receivable, Average Recorded Investment | 19,424 | 11,914 | 13,680 | 9,905 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 | $ 24 | 5 | $ 44 |
Related allowance | 6,548 |  | 6,548 |  | 2,432
Recorded investment | 19,409 |  | 19,409 |  | 14,057
Unpaid principal balance | $ 24,583 |  | $ 24,583 |  | $ 15,838

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