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Fair Value of Financial Instruments - Quantitative Information about Unobservable Inputs Used in Recurring and Nonrecurring Level 3 Fair Value Measurements (Detail) $ in Thousands | Sep. 30, 2021 USD ($) | Dec. 31, 2020 USD ($)
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Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair Value | $ 426,717 | $ 307,812
State and Local Governments [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair Value | 64,618 | 70,515
Level 3 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair Value | 3,767 | 1,562
Level 3 [Member] | State and Local Governments [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair Value | $ 3,767 | $ 1,562
Valuation Technique | us-gaap:ValuationTechniqueDiscountedCashFlowMember | us-gaap:ValuationTechniqueDiscountedCashFlowMember
Unobservable Inputs | us-gaap:MeasurementInputDiscountRateMember | us-gaap:MeasurementInputDiscountRateMember
Level 3 [Member] | Collateral Dependent Impaired Loans [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair Value | $ 6,925 | $ 7,703
Valuation Technique | us-gaap:MarketApproachValuationTechniqueMember | us-gaap:MarketApproachValuationTechniqueMember
Level 3 [Member] | Other Real Estate Owned-Residential [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair Value | $ 30 |
Valuation Technique | us-gaap:MarketApproachValuationTechniqueMember | us-gaap:MarketApproachValuationTechniqueMember
Unobservable Inputs | us-gaap:MeasurementInputAppraisedValueMember | us-gaap:MeasurementInputAppraisedValueMember
Level 3 [Member] | Minimum [Member] | State and Local Governments [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 0.34 | 1.19
Level 3 [Member] | Minimum [Member] | Collateral Dependent Impaired Loans [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 34.54 | 0.71
Level 3 [Member] | Minimum [Member] | Other Real Estate Owned-Residential [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 0.0 |
Level 3 [Member] | Maximum [Member] | State and Local Governments [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 1.34 | 1.19
Level 3 [Member] | Maximum [Member] | Collateral Dependent Impaired Loans [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 81.41 | 100
Level 3 [Member] | Maximum [Member] | Other Real Estate Owned-Residential [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 7.32 |
Level 3 [Member] | Weighted Average [Member] | State and Local Governments [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 0.86 | 1.19
Level 3 [Member] | Weighted Average [Member] | Collateral Dependent Impaired Loans [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 32.44 | 17.71
Level 3 [Member] | Weighted Average [Member] | Other Real Estate Owned-Residential [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Discount rate | 50.99 |

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