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Loans - Recorded Investment in Nonaccrual Loans by Portfolio Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	$ 1,003	$ 1,384
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	101	132
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	708	1,091
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	38
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	7
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	$ 149	$ 161

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+ References

No definition available.

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

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