Loans - Analysis of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	$ 7,001	$ 6,265	$ 6,265
Charge Offs	(44)	(84)	(550)
Recoveries	37	35	156
Provision (Credit)	73	277	1,121
Other Non-interest expense related to unfunded	2	12
Ending Balance	7,069	6,505	7,001
Ending balance: individually evaluated for impairment	117	426
Ending balance: collectively evaluated for impairment	6,952	6,079
Ending balance: loans acquired with deteriorated credit quality		1
FINANCING RECEIVABLES:
Ending balance	771,206	707,660	758,094
Ending balance: individually evaluated for impairment	1,793	2,211
Ending balance: collectively evaluated for impairment	769,413	705,449
Agricultural Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	241	211	211
Provision (Credit)	3	61
Ending Balance	244	272	241
Ending balance: individually evaluated for impairment		57
Ending balance: collectively evaluated for impairment	244	215
FINANCING RECEIVABLES:
Ending balance	62,803	59,479	62,336
Ending balance: individually evaluated for impairment	101	219
Ending balance: collectively evaluated for impairment	62,702	59,260
Agricultural [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	616	582	582
Recoveries	1	4
Provision (Credit)	17	(38)
Ending Balance	634	548	616
Ending balance: collectively evaluated for impairment	634	548
FINANCING RECEIVABLES:
Ending balance	87,078	78,021	84,692
Ending balance: collectively evaluated for impairment	87,078	78,021
Commercial And Industrial and Industrial Development Bonds [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	1,318	1,229	1,229
Charge Offs		(20)
Recoveries	3	3
Provision (Credit)	(22)	39
Ending Balance	1,299	1,251	1,318
Ending balance: individually evaluated for impairment	33	113
Ending balance: collectively evaluated for impairment	1,266	1,138
FINANCING RECEIVABLES:
Ending balance	121,183	109,386	115,093
Ending balance: individually evaluated for impairment	115	181
Ending balance: collectively evaluated for impairment	121,068	109,205
Unfunded Loan Commitment & Letters of Credit [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	217	208	208
Other Non-interest expense related to unfunded	2	12
Ending Balance	219	220	217
Ending balance: collectively evaluated for impairment	219	220
Receivables Acquired with Deteriorated Credit Quality [Member]
FINANCING RECEIVABLES:
Ending balance: loans acquired with deteriorated credit quality	198	502
Consumer Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	316	338	338
Recoveries	10	2
Provision (Credit)	(49)	117
Ending Balance	277	457	316
Ending balance: individually evaluated for impairment	23	104
Ending balance: collectively evaluated for impairment	254	353
Ending balance: loans acquired with deteriorated credit quality		1
FINANCING RECEIVABLES:
Ending balance	84,081	88,097	85,873
Ending balance: individually evaluated for impairment	1,081	874
Ending balance: collectively evaluated for impairment	83,000	87,223
Consumer Real Estate [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
FINANCING RECEIVABLES:
Ending balance: loans acquired with deteriorated credit quality	198	502
Commercial Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	3,250	2,516	2,516
Charge Offs		(3)
Recoveries	2	1
Provision (Credit)	(244)	164
Ending Balance	3,008	2,678	3,250
Ending balance: individually evaluated for impairment	61	152
Ending balance: collectively evaluated for impairment	2,947	2,526
FINANCING RECEIVABLES:
Ending balance	382,183	344,661	376,887
Ending balance: individually evaluated for impairment	496	937
Ending balance: collectively evaluated for impairment	381,687	343,724
Consumer [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	394	337	337
Charge Offs	(44)	(61)
Recoveries	21	25
Provision (Credit)	26	34
Ending Balance	397	335	394
Ending balance: collectively evaluated for impairment	397	335
FINANCING RECEIVABLES:
Ending balance	33,878	28,016	33,213
Ending balance: collectively evaluated for impairment	33,878	28,016
Unallocated [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	649	844	844
Provision (Credit)	342	(100)
Ending Balance	991	744	$ 649
Ending balance: collectively evaluated for impairment	$ 991	$ 744

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 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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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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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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