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Fair Values of Assets and Liabilities - Quantitative Inputs and Assumptions Used in Level 3 Fair Value Measurements (Detail) - USD ($) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Other Investments | $ 48,979,000 | $ 26,414,000
Assets | 991,940,000 | 869,373,000
Impaired Loans [Member] | Reserve Study [Member] |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Assets | $ 253,000 | $ 363,000
Impaired Loans [Member] | Reserve Study [Member] | Discount rates [Member] | Weighted average [Member] |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Discount Rate | 10.00% | 10.00%
Impaired Loans [Member] | Reserve Study [Member] | Gas per MCF [Member] | Minimum [Member] |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair Value Inputs Monetary | $ 3.00 | $ 3.00
Impaired Loans [Member] | Reserve Study [Member] | Gas per MCF [Member] | Maximum [Member] |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair Value Inputs Monetary | 3.00 | 3.00
Impaired Loans [Member] | Reserve Study [Member] | Oil per BBL/d [Member] | Minimum [Member] |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair Value Inputs Monetary | 80.00 | 80.00
Impaired Loans [Member] | Reserve Study [Member] | Oil per BBL/d [Member] | Maximum [Member] |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair Value Inputs Monetary | 80.00 | 80.00
Limited Partnership Investment [Member] |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Assets | 26,397,000 | 17,691,000
Level 3 [Member] |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Other Investments | 6,182,000 | 1,170,000
Assets | $ 32,579,000 | $ 18,861,000

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
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