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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, 2023	Dec. 31, 2022
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, Fair Value Disclosure	$ 1,161,482,000	$ 869,373,000
Other Assets, Fair Value Disclosure	59,805,000	68,429,000
Other investments	50,871,000	26,414,000
Fair Value, Inputs, Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, Fair Value Disclosure	1,128,163,000	850,512,000
Other Assets, Fair Value Disclosure	32,668,000	50,738,000
Other investments	44,689,000	25,244,000
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, Fair Value Disclosure	33,319,000	18,861,000
Other Assets, Fair Value Disclosure	$ 27,137,000	$ 17,691,000
Other Assets [Member] | Par Value [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurements, Valuation Processes, Description	Par Value	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	$ 6,182,000	$ 1,170,000
Equity Securities [Member] | Par Value [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurements, Valuation Processes, Description	Carrying Value	Carrying Value
Impaired Loans [Member] | Reserve [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, Fair Value Disclosure		$ 363,000
Fair Value Measurements, Valuation Processes, Description		Gas Reserve study
Impaired Loans [Member] | Discount Rates [Member] | Reserve [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurements, Valuation Processes, Description		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)
Fair Value Measurements, Valuation Processes, Description		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)
Fair Value Measurements, Valuation Processes, Description		Oil per BBL/d
Fair Value, Nonrecurring [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, Fair Value Disclosure	$ 35,532,000	$ 35,329,000
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, Fair Value Disclosure	25,824,000	23,693,000
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, Fair Value Disclosure	$ 9,708,000	11,636,000
Minimum [Member] | Impaired Loans [Member] | Reserve [Member] | Gas Per Million Cubic Feet [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Weighted Average Inputs Price		3.00
Minimum [Member] | Impaired Loans [Member] | Reserve [Member] | Oil Per Barrels Per Day [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Weighted Average Inputs Price		$ 80.00
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%
Maximum [Member] | Impaired Loans [Member] | Reserve [Member] | Gas Per Million Cubic Feet [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Weighted Average Inputs Price		$ 3.00
Maximum [Member] | Impaired Loans [Member] | Reserve [Member] | Oil Per Barrels Per Day [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Weighted Average Inputs Price		$ 80.00

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+ References

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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

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

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