Loans - Analysis of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	$ 6,265	$ 6,112	$ 6,112
Charge Offs	(84)	(92)	(1,030)
Recoveries	35	50	557
Provision (Credit)	277	114
Other Non-interest expense related to unfunded	12	(5)
Ending Balance	6,505	6,179	6,265
Ending balance: individually evaluated for impairment	426	428
Ending balance: collectively evaluated for impairment	6,079	5,751
Ending balance: loans acquired with deteriorated credit quality	1	1
FINANCING RECEIVABLES:
Ending balance	707,660	614,709	685,878
Ending balance: individually evaluated for impairment	2,211	2,243
Ending balance: collectively evaluated for impairment	705,449	612,466
Agricultural Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	211	184	184
Provision (Credit)	61	3
Ending Balance	272	187	211
Ending balance: individually evaluated for impairment	57
Ending balance: collectively evaluated for impairment	215	187
FINANCING RECEIVABLES:
Ending balance	59,479	51,396	58,463
Ending balance: individually evaluated for impairment	219
Ending balance: collectively evaluated for impairment	59,260	51,396
Agricultural [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	582	547	547
Recoveries	4	1
Provision (Credit)	(38)	(24)
Ending Balance	548	524	582
Ending balance: individually evaluated for impairment		24
Ending balance: collectively evaluated for impairment	548	500
FINANCING RECEIVABLES:
Ending balance	78,021	71,571	82,762
Ending balance: individually evaluated for impairment		24
Ending balance: collectively evaluated for impairment	78,021	71,547
Commercial And Industrial and Industrial Development Bonds [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	1,229	1,421	1,421
Charge Offs	(20)
Recoveries	3	5
Provision (Credit)	39	(7)
Ending Balance	1,251	1,419	1,229
Ending balance: individually evaluated for impairment	113	238
Ending balance: collectively evaluated for impairment	1,138	1,181
FINANCING RECEIVABLES:
Ending balance	109,386	99,895	106,689
Ending balance: individually evaluated for impairment	181	827
Ending balance: collectively evaluated for impairment	109,205	99,068
Unfunded Loan Commitment & Letters of Credit [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	208	207	207
Other Non-interest expense related to unfunded	12	(5)
Ending Balance	220	202	208
Ending balance: collectively evaluated for impairment	220	202
Receivables Acquired with Deteriorated Credit Quality [Member]
FINANCING RECEIVABLES:
Ending balance: loans acquired with deteriorated credit quality	502	520
Consumer Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	338	537	537
Recoveries	2	2
Provision (Credit)	117	(42)
Ending Balance	457	497	338
Ending balance: individually evaluated for impairment	104	35
Ending balance: collectively evaluated for impairment	353	462
Ending balance: loans acquired with deteriorated credit quality	1	1
FINANCING RECEIVABLES:
Ending balance	88,097	97,019	87,947
Ending balance: individually evaluated for impairment	874	253
Ending balance: collectively evaluated for impairment	87,223	96,766
Consumer Real Estate [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
FINANCING RECEIVABLES:
Ending balance: loans acquired with deteriorated credit quality	502	520
Commercial Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	2,516	2,367	2,367
Charge Offs	(3)
Recoveries	1	1
Provision (Credit)	164	(156)
Ending Balance	2,678	2,212	2,516
Ending balance: individually evaluated for impairment	152	131
Ending balance: collectively evaluated for impairment	2,526	2,081
FINANCING RECEIVABLES:
Ending balance	344,661	271,201	322,230
Ending balance: individually evaluated for impairment	937	1,139
Ending balance: collectively evaluated for impairment	343,724	270,062
Consumer [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	337	323	323
Charge Offs	(61)	(92)
Recoveries	25	41
Provision (Credit)	34	12
Ending Balance	335	284	337
Ending balance: collectively evaluated for impairment	335	284
FINANCING RECEIVABLES:
Ending balance	28,016	23,627	27,787
Ending balance: collectively evaluated for impairment	28,016	23,627
Unallocated [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	844	526	526
Provision (Credit)	(100)	328
Ending Balance	744	854	$ 844
Ending balance: collectively evaluated for impairment	$ 744	$ 854

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
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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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