Loans Held for Investment and Allowance for Loan Losses - Schedule of Loans Modified and Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020 USD ($) SecurityLoan	Jun. 30, 2019 USD ($) SecurityLoan	Jun. 30, 2020 USD ($) SecurityLoan	Jun. 30, 2019 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	5	4	12	17
Pre-Modification Recorded Investment	$ 319	$ 375	$ 755	$ 1,548
Post-Modification Recorded Investment	$ 319	$ 375	$ 755	$ 1,548
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	4	2	9	3
Pre-Modification Recorded Investment	$ 196	$ 122	$ 484	$ 279
Post-Modification Recorded Investment	$ 196	$ 122	$ 484	$ 279
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan		2	1	10
Pre-Modification Recorded Investment		$ 253	$ 134	$ 619
Post-Modification Recorded Investment		253	$ 134	$ 619
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	1		1	4
Pre-Modification Recorded Investment	$ 123		$ 123	$ 650
Post-Modification Recorded Investment	$ 123		$ 123	$ 650
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan			1
Pre-Modification Recorded Investment			$ 14
Post-Modification Recorded Investment		$ 0	$ 14

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Number of financing receivables that have been modified by troubled debt restructurings.

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

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

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