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, 2018 USD ($) SecurityLoan	Jun. 30, 2017 USD ($) SecurityLoan	Jun. 30, 2018 USD ($) SecurityLoan	Jun. 30, 2017 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	6	4	12	9
Pre-Modification Recorded Investment	$ 480	$ 276	$ 921	$ 566
Post-Modification Recorded Investment	$ 480	$ 276	$ 921	$ 566
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	1	2	1	6
Pre-Modification Recorded Investment	$ 279	$ 90	$ 279	$ 324
Post-Modification Recorded Investment	$ 279	$ 90	$ 279	$ 324
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan			1
Pre-Modification Recorded Investment			$ 4
Post-Modification Recorded Investment			$ 4
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	2	1	4	2
Pre-Modification Recorded Investment	$ 162	$ 161	$ 525	$ 217
Post-Modification Recorded Investment	$ 162	$ 161	$ 525	$ 217
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	3	1	6	1
Pre-Modification Recorded Investment	$ 39	$ 25	$ 113	$ 25
Post-Modification Recorded Investment	$ 39	$ 25	$ 113	$ 25

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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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