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Loans and Allowance for Credit Losses - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2020 USD ($) Contract numberOfLoans | Dec. 31, 2019 USD ($) Contract | Dec. 31, 2018 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 | $ 33,436,000 | $ 15,989,000 |
Provision for credit losses | 53,472,000 |  |
Charge-offs | 19,250,000 | $ 12,300,000 |
Recorded Investment | $ 54,053,000 |  |
Number of loans modified | Contract | 41 | 38 | 58
Total amount of loan modified | $ 13,969,000 | $ 1,928,000 | $ 8,829,000
Total gains or losses included in earnings | 0 | 198,000 |
Loans with modification to rate and payment due to amortization | $ 800,000 | 800,000 | 300,000
Minimum days required for conversion of trouble debt to be in default | 90 days |  |
Unearned Deferred (Fees) Costs on Loans | $ 6,000,000.0 | 2,800,000 |
Unearned Premiums | (7,000,000.0) | (8,500,000) |
Loans | 6,761,183,000 | 6,189,148,000 | 5,774,139,000
Loans and Leases Receivable, Gross | $ 6,761,183,000 |  |
Forecasted Value, National Unemployment, Percent | 6.68% |  |
Weighted Average [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Forecasted Value, National Unemployment, Percent | 7.25% |  |
Maximum [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Forecasted Value, National Unemployment, Percent | 7.48% |  |
Total Deferrals Granted |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans and Leases Receivable, Number of Contracts | numberOfLoans | 6,800 |  |
Loans and Leases Receivable, Gross | $ 1,400,000,000 |  |
Total Deferrals Still in Forbearance |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans and Leases Receivable, Gross | 113,800,000 |  |
Impaired Loans [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Unfunded commitments related to nonperforming loans | $ 200,000 | 1,700,000 |
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 | $ 13,000 | 0 |
Gain (loss) on sale of impaired loans | 0 | 400,000 | $ 1,800,000
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 | 26,000 | 12,000 |
Commercial Loan [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans | 1,555,986,000 | $ 1,241,853,000 |
Loans and Leases Receivable, Gross | 1,555,986,000 |  |
Commercial Loan [Member] | Payroll Protection Program Loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans | $ 478,900,000 |  |

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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 The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of loans and leases that were sold during the reporting period. This element refers to the gain (loss) and not to the cash proceeds of the sales. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 + Details
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- Definition Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522 + Details
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