Allowance for Loan Losses - Impaired Financing Receivables Excluding PCI Loans - Recorded Investment and Unpaid Principal Balances (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	$ 3,470	$ 5,121
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	3,734	6,145
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment	2,263	1,418
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	2,817	1,972
Impaired financing receivables, with an allowance recorded, Related Allowance	348	188
Impaired financing receivables, Recorded Investment, Total	5,733	6,539
Impaired financing receivables, Unpaid Principal Balance, Total	6,551	8,117
Impaired financing receivables, Related Allowance, Total	348	188
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	375	1,230
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	376	1,751
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment	1,187	753
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	1,737	1,303
Impaired financing receivables, with an allowance recorded, Related Allowance	235	82
Impaired financing receivables, Recorded Investment, Total	1,562	1,983
Impaired financing receivables, Unpaid Principal Balance, Total	2,113	3,054
Impaired financing receivables, Related Allowance, Total	235	82
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	1,485	1,658
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,650	1,803
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment	230	238
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	230	238
Impaired financing receivables, with an allowance recorded, Related Allowance	4	4
Impaired financing receivables, Recorded Investment, Total	1,715	1,896
Impaired financing receivables, Unpaid Principal Balance, Total	1,880	2,041
Impaired financing receivables, Related Allowance, Total	4	4
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	355	359
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	381	386
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, Recorded Investment, Total	355	359
Impaired financing receivables, Unpaid Principal Balance, Total	381	386
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	1,105	1,259
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,177	1,590
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment	382	427
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	386	431
Impaired financing receivables, with an allowance recorded, Related Allowance	103	102
Impaired financing receivables, Recorded Investment, Total	1,487	1,686
Impaired financing receivables, Unpaid Principal Balance, Total	1,563	2,021
Impaired financing receivables, Related Allowance, Total	103	102
Farm Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	150	614
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	150	614
Impaired financing receivables, with no related allowance recorded, Related Allowance	0	0
Impaired financing receivables, with an allowance recorded, Recorded Investment	464
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	464
Impaired financing receivables, with an allowance recorded, Related Allowance	6
Impaired financing receivables, Recorded Investment, Total	614	614
Impaired financing receivables, Unpaid Principal Balance, Total	614	614
Impaired financing receivables, Related Allowance, Total	6
Consumer and Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment		1
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance		1
Impaired financing receivables, with no related allowance recorded, Related Allowance	$ 0	0
Impaired financing receivables, Recorded Investment, Total		1
Impaired financing receivables, Unpaid Principal Balance, Total		$ 1

Impaired financing receivable with and no related allowance.

No definition available.

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- Definition

Impaired financing receivable with no related allowance.

+ References

No definition available.

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- Definition

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+ References

No definition available.

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- Definition

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=84173941&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
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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- Definition

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=84173941&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.

+ References

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- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no 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=84173941&loc=d3e5212-111524

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- Definition

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

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- Definition

Unpaid principal balance of impaired financing receivables for which there is 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 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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