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Fair Values of Assets and Liabilities - Quantitative Inputs and Assumptions Used in Level 3 Fair Value Measurements (Detail) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Assets, Fair Value Disclosure | $ 957,719,000 | $ 779,966,000
Other Assets, Fair Value Disclosure | 4,465,000 | 3,921,000
Other investments | 32,126,000 | 29,837,000
Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Assets, Fair Value Disclosure | 953,353,000 | 752,507,000
Other Assets, Fair Value Disclosure | 1,769,000 | 1,778,000
Other investments | 30,456,000 |
Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Assets, Fair Value Disclosure | 4,366,000 | 27,459,000
Other Assets, Fair Value Disclosure | $ 2,696,000 | 2,143,000
Other Assets [Member] | Par Value [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Equity Securities, FV-NI, Measurement Input [Extensible List] | Par Value |
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Other investments | $ 1,670,000 |
Equity Securities [Member] | Par Value [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Equity Securities, FV-NI, Measurement Input [Extensible List] | Carrying Value |
Impaired Loans [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Assets, Fair Value Disclosure | $ 3,249,000 |
Equity Securities, FV-NI, Measurement Input [Extensible List] | Discounted Cash Flow |
Impaired Loans [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Assets, Fair Value Disclosure | $ 1,104,000 |
Equity Securities, FV-NI, Measurement Input [Extensible List] | Gas Reserve study |
Impaired Loans [Member] | Discount Rates [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Equity Securities, FV-NI, Measurement Input [Extensible List] | Discount Rate |
Impaired Loans [Member] | Discount Rates [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Equity Securities, FV-NI, Measurement Input [Extensible List] | Discount rate |
Impaired Loans [Member] | Gas Per Million Cubic Feet [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Equity Securities, FV-NI, Measurement Input [Extensible List] | Gas per MMBTU |
Impaired Loans [Member] | Oil Per Barrels Per Day [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Equity Securities, FV-NI, Measurement Input [Extensible List] | Oil per BBL/d |
Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Assets, Fair Value Disclosure | $ 34,431,000 | 41,758,000
Other Real Estate Owned Assets Fair Value | 4,035,000 | 3,264,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Assets, Fair Value Disclosure | 19,111,000 | 26,513,000
Other Real Estate Owned Assets Fair Value | 4,035,000 | 3,264,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Assets, Fair Value Disclosure | 15,320,000 | 15,245,000
Other Real Estate Owned Assets Fair Value | $ 0 | $ 0
Maximum [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Input, Discount Rate | 9.50% |
Maximum [Member] | Gas Per Million Cubic Feet [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Weighted Average Inputs Price | $ 3.35 |
Maximum [Member] | Oil Per Barrels Per Day [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Weighted Average Inputs Price | $ 59.55 |
Weighted Average [Member] | Impaired Loans [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Input, Discount Rate | 10.00% |
Minimum [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Input, Discount Rate | 1.90% |
Minimum [Member] | Gas Per Million Cubic Feet [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Weighted Average Inputs Price | $ 2.81 |
Minimum [Member] | Oil Per Barrels Per Day [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Weighted Average Inputs Price | $ 51.59 |

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Description of the valuation processes in place for fair value measurements categorized within Level 3 of the fair value hierarchy. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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