Allowance for Loan Losses - Schedule of Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017 USD ($) Contract	Jun. 30, 2018 USD ($) Contract	Jun. 30, 2017 USD ($) Contract
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts \| Contract	1	3	1
Pre- Modification Outstanding Recorded Investment	$ 13	$ 591	$ 13
Post-Modification Outstanding Recorded Investment	$ 13	$ 591	$ 13
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts \| Contract		3
Pre- Modification Outstanding Recorded Investment		$ 591
Post-Modification Outstanding Recorded Investment		$ 591
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts \| Contract	1		1
Pre- Modification Outstanding Recorded Investment	$ 13		$ 13
Post-Modification Outstanding Recorded Investment	$ 13		$ 13

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

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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