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Loans and Allowance for Credit Losses - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2019 USD ($) Contract | Dec. 31, 2018 USD ($) Contract | Dec. 31, 2017 USD ($) Contract
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Non Accrual Status Of Loans After Number Of Days Past Due | 90 days |  |
Loans Receivable Held-for-sale, Amount | $ 15,989,000 | $ 11,881,000 |
Provision for credit losses | 14,533,000 | 12,531,000 | $ 5,087,000
Charge-offs | $ 12,300,000 | $ 15,100,000 |
Number of loans modified | Contract | 38 | 58 | 41
Total amount of loan modified | $ 1,928,000 | $ 8,829,000 | $ 8,274,000
Total gains or losses included in earnings | 198,000 | 8,102,000 |
Loans with modification to rate and payment due to amortization | $ 800,000 | 300,000 | 300,000
Minimum days required for conversion of trouble debt to be in default | 90 days |  |
Impaired Loans [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Unfunded commitments related to nonperforming loans | $ 1,700,000 | 1,600,000 |
Loans To Individuals [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Non Accrual Status Of Loans After Number Of Days Past Due | 150 days |  |
Nonaccrual Commercial Loans [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans Receivable Held-for-sale, Amount | $ 0 | 0 |
Gain (loss) on sale of impaired loans | 400,000 | $ 1,800,000 | $ 21,000
SEC Schedule, 12-09, Reserve, Off-balance Sheet Activity [Member] | Impaired Loans [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Off balance sheet reserve to nonperforming loans | $ 12,000 |  |

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- Definition Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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- Definition Amount of writeoff of financing receivable, charged against allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=118955255&loc=SL82922352-210448 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(7)(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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