Loans - Analysis of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	$ 6,265	$ 6,112
Charge Offs	(550)	(1,030)	$ (778)
Recoveries	156	557	298
Provision (Credit)	1,121	625
Other Non-interest expense related to unfunded	9	1
Ending Balance	7,001	6,265	6,112
Ending balance: individually evaluated for impairment	135	330
Ending balance: collectively evaluated for impairment	6,866	5,935
Ending balance: loans acquired with deteriorated credit quality	1	1
FINANCING RECEIVABLES:
Ending balance	760,149	685,878
Ending balance: individually evaluated for impairment	1,852	2,136
Ending balance: collectively evaluated for impairment	758,297	683,742
Agricultural Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	211	184
Provision (Credit)	30	27
Ending Balance	241	211	184
Ending balance: collectively evaluated for impairment	241	211
FINANCING RECEIVABLES:
Ending balance	63,352	58,463
Ending balance: individually evaluated for impairment	132	63
Ending balance: collectively evaluated for impairment	63,220	58,400
Agricultural [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	582	547
Charge Offs	(21)
Recoveries	10	64
Provision (Credit)	45	(29)
Ending Balance	616	582	547
Ending balance: collectively evaluated for impairment	616	582
FINANCING RECEIVABLES:
Ending balance	84,692	82,762
Ending balance: collectively evaluated for impairment	84,692	82,762
Commercial And Industrial and Industrial Development Bonds [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	1,229	1,421
Charge Offs	(20)	(536)
Recoveries	11	91
Provision (Credit)	98	253
Ending Balance	1,318	1,229	1,421
Ending balance: individually evaluated for impairment	35	114
Ending balance: collectively evaluated for impairment	1,283	1,115
FINANCING RECEIVABLES:
Ending balance	115,093	106,689
Ending balance: individually evaluated for impairment	116	182
Ending balance: collectively evaluated for impairment	114,977	106,507
Unfunded Loan Commitment & Letters of Credit [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	208	207
Other Non-interest expense related to unfunded	9	1
Ending Balance	217	208	207
Ending balance: collectively evaluated for impairment	217	208
Receivables Acquired with Deteriorated Credit Quality [Member]
FINANCING RECEIVABLES:
Ending balance: loans acquired with deteriorated credit quality	200	507
Consumer Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	338	537
Charge Offs	(106)	(38)
Recoveries	28	41
Provision (Credit)	56	(202)
Ending Balance	316	338	537
Ending balance: individually evaluated for impairment	34	64
Ending balance: collectively evaluated for impairment	282	274
Ending balance: loans acquired with deteriorated credit quality	1	1
FINANCING RECEIVABLES:
Ending balance	86,912	87,947
Ending balance: individually evaluated for impairment	1,103	431
Ending balance: collectively evaluated for impairment	85,809	87,516
Consumer Real Estate [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
FINANCING RECEIVABLES:
Ending balance: loans acquired with deteriorated credit quality	200	507
Commercial Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	2,516	2,367
Charge Offs	(93)	(143)
Recoveries	20	204
Provision (Credit)	807	88
Ending Balance	3,250	2,516	2,367
Ending balance: individually evaluated for impairment	66	152
Ending balance: collectively evaluated for impairment	3,184	2,364
FINANCING RECEIVABLES:
Ending balance	376,887	322,230
Ending balance: individually evaluated for impairment	501	1,460
Ending balance: collectively evaluated for impairment	376,386	320,770
Consumer [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	337	323
Charge Offs	(310)	(313)
Recoveries	87	157
Provision (Credit)	280	170
Ending Balance	394	337	323
Ending balance: collectively evaluated for impairment	394	337
FINANCING RECEIVABLES:
Ending balance	33,213	27,787
Ending balance: collectively evaluated for impairment	33,213	27,787
Unallocated [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	844	526
Provision (Credit)	(195)	318
Ending Balance	649	844	$ 526
Ending balance: collectively evaluated for impairment	$ 649	$ 844

Allowance For Credit Losses [Abstract]

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Financing receivable allowance for credit losses acquired with deteriorated credit quality ending period.

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Financing Receivables [Abstract]

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Other non interest Income expense (recovery) related to unfunded.

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Amount of expense related to estimated loss and recoveries from loan and lease transactions.

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

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