Allowance for Loan Losses - Impaired Loans Excluding PCI Loans - Recorded Investment and Unpaid Principal Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	$ 6,494	$ 5,738
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	8,273	6,823
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment	720	1,747
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	739	1,705
Impaired financing receivables, with an allowance recorded, Related Allowance	117	386
Impaired financing receivables, Recorded Investment, Total	7,214	7,485
Impaired financing receivables, Unpaid Principal Balance, Total	9,012	8,528
Impaired financing receivables, Related Allowance, Total	117	386
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	2,386	851
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	3,457	1,034
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment		22
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance		23
Impaired financing receivables, with an allowance recorded, Related Allowance		23
Impaired financing receivables, Recorded Investment, Total	2,386	873
Impaired financing receivables, Unpaid Principal Balance, Total	3,457	1,057
Impaired financing receivables, Related Allowance, Total		23
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	1,697	1,224
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,842	1,343
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment	242	917
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	242	999
Impaired financing receivables, with an allowance recorded, Related Allowance	4	103
Impaired financing receivables, Recorded Investment, Total	1,939	2,141
Impaired financing receivables, Unpaid Principal Balance, Total	2,084	2,342
Impaired financing receivables, Related Allowance, Total	4	103
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	369	1,742
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	396	1,826
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, Recorded Investment, Total	369	1,742
Impaired financing receivables, Unpaid Principal Balance, Total	396	1,826
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	1,376	965
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,912	1,591
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment	478	808
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	497	683
Impaired financing receivables, with an allowance recorded, Related Allowance	113	260
Impaired financing receivables, Recorded Investment, Total	1,854	1,773
Impaired financing receivables, Unpaid Principal Balance, Total	2,409	2,274
Impaired financing receivables, Related Allowance, Total	113	260
Farm Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	665	953
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	665	1,026
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, Recorded Investment, Total	665	953
Impaired financing receivables, Unpaid Principal Balance, Total	665	1,026
Consumer and Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	1	3
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1	3
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, Recorded Investment, Total	1	3
Impaired financing receivables, Unpaid Principal Balance, Total	$ 1	$ 3

Impaired financing receivable with and no related allowance.

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Impaired financing receivable with no related allowance.

+ References

No definition available.

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953550-111524

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

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Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

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- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

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Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

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Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

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Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

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