Loans Held for Investment and Allowance for Loan Losses - Schedule of Loans Modified and Considered Troubled Debt Restructurings (Detail) $ in Thousands	1 Months Ended	12 Months Ended
Dec. 31, 2017 USD ($) SecurityLoan	Dec. 31, 2018 USD ($)
Financing Receivable, Modifications [Line Items]
Number	17	18
Pre-Modification Recorded Investment	$ 1,545	$ 1,720
Post-Modification Recorded Investment	$ 1,545	$ 1,720
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number	11	4
Pre-Modification Recorded Investment	$ 895	$ 864
Post-Modification Recorded Investment	$ 895	$ 864
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number		1
Pre-Modification Recorded Investment		$ 4
Post-Modification Recorded Investment		$ 4
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number	5	5
Pre-Modification Recorded Investment	$ 625	$ 643
Post-Modification Recorded Investment	$ 625	$ 643
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number	1	8
Pre-Modification Recorded Investment	$ 25	$ 209
Post-Modification Recorded Investment	$ 25	$ 209

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

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Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

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