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Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	$ 7,017	$ 12,562
Balance at period end	6,678	9,285
Commercial Portfolio Segment [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	1,312	3,660
Balance at period end	1,237	1,415
Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	3,817	0
Balance at period end	3,566	0
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	1,888	6,606
Balance at period end	1,875	6,585
Construction Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	0	1,192
Balance at period end	0	1,181
Consumer Loan [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	0	1,104
Balance at period end	$ 0	$ 104

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- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

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- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

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