Loans and Allowance for Credit Losses - Troubled Debt Restructuring is 90 Days or More Past Due (Detail) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts \| Contract	2	1	3	2
Financing Receivable, Modifications, Subsequent Default, Recorded Investment \| $	$ 57	$ 2	$ 329	$ 11
Commercial, financial, agricultural and other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts \| Contract			1	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment \| $			$ 272	$ 0
Residential real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts \| Contract	1	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment \| $	$ 49	$ 0
Residential real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts \| Contract			1	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment \| $			$ 49	$ 9
Loans to individuals [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts \| Contract	1	1	1	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment \| $	$ 8	$ 2	$ 8	$ 2

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

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