Loans - Analysis of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	$ 7,049	$ 7,095	$ 7,095
Charge Offs	(207)	(145)	(580)
Recoveries	38	37	163
Provision (Credit)	30	40	324
Other Non-interest expense related to unfunded	72	38
Ending Balance	6,982	7,065	7,049
Ending balance: individually evaluated for impairment	59	104	31
Ending balance: collectively evaluated for impairment	6,923	6,961	7,018
Ending balance: loans acquired with deteriorated credit quality	0	0	0
FINANCING RECEIVABLES:
Ending balance	1,101,963	834,737	846,374
Ending balance: individually evaluated for impairment	2,169	1,606	2,054
Ending balance: collectively evaluated for impairment	1,097,405	833,010	844,204
Ending balance: loans acquired with deteriorated credit quality	2,389	121	116
Consumer Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	247	343	343
Charge Offs		(34)
Provision (Credit)	21	(55)
Ending Balance	268	254	247
Ending balance: individually evaluated for impairment	59	20	26
Ending balance: collectively evaluated for impairment	209	234	221
Ending balance: loans acquired with deteriorated credit quality	0	0	0
FINANCING RECEIVABLES:
Ending balance	160,489	84,052	80,232
Ending balance: individually evaluated for impairment	902	569	757
Ending balance: collectively evaluated for impairment	159,241	83,362	79,359
Ending balance: loans acquired with deteriorated credit quality	346	121	116
Agricultural Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	250	244	244
Provision (Credit)	20	19
Ending Balance	270	263	250
Ending balance: collectively evaluated for impairment	270	263	250
Ending balance: loans acquired with deteriorated credit quality	0	0	0
FINANCING RECEIVABLES:
Ending balance	192,887	67,569	68,588
Ending balance: collectively evaluated for impairment	192,887	67,569	68,588
Agricultural [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	768	667	667
Recoveries	1	3
Provision (Credit)	(63)	36
Ending Balance	706	706	768
Ending balance: collectively evaluated for impairment	706	706	768
Ending balance: loans acquired with deteriorated credit quality	0	0	0
FINANCING RECEIVABLES:
Ending balance	115,043	99,954	108,616
Ending balance: collectively evaluated for impairment	115,043	99,954	108,616
Commercial Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	3,217	3,149	3,149
Charge Offs		(14)
Recoveries	2	2
Provision (Credit)	(16)	537
Ending Balance	3,203	3,674	3,217
Ending balance: individually evaluated for impairment		42
Ending balance: collectively evaluated for impairment	3,203	3,632	3,217
Ending balance: loans acquired with deteriorated credit quality	0	0	0
FINANCING RECEIVABLES:
Ending balance	440,488	414,666	419,131
Ending balance: individually evaluated for impairment	192	618	194
Ending balance: collectively evaluated for impairment	440,296	414,048	418,937
Commercial and Industrial [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	1,305	1,546	1,546
Recoveries	3	2
Provision (Credit)	182	(105)
Ending Balance	1,490	1,443	1,305
Ending balance: individually evaluated for impairment		42	5
Ending balance: collectively evaluated for impairment	1,490	1,401	1,300
Ending balance: loans acquired with deteriorated credit quality	0	0	0
FINANCING RECEIVABLES:
Ending balance	145,360	129,865	127,752
Ending balance: individually evaluated for impairment	1,075	419	1,103
Ending balance: collectively evaluated for impairment	142,242	129,446	126,649
Ending balance: loans acquired with deteriorated credit quality	2,043
Consumer [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	484	441	441
Charge Offs	(207)	(97)
Recoveries	32	30
Provision (Credit)	187	57
Ending Balance	496	431	484
Ending balance: collectively evaluated for impairment	496	431	484
Ending balance: loans acquired with deteriorated credit quality	0	0	0
FINANCING RECEIVABLES:
Ending balance	47,696	38,631	42,055
Ending balance: collectively evaluated for impairment	47,696	38,631	42,055
Unallocated [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	504	478	478
Provision (Credit)	(301)	(449)
Ending Balance	203	29	504
Ending balance: collectively evaluated for impairment	203	29	504
Ending balance: loans acquired with deteriorated credit quality	0	0	0
Unfunded Loan Commitment & Letters of Credit [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance	274	227	227
Other Non-interest expense related to unfunded	72	38
Ending Balance	346	265	274
Ending balance: collectively evaluated for impairment	346	265	274
Ending balance: loans acquired with deteriorated credit quality	$ 0	$ 0	$ 0

Allowance For Credit Losses [Abstract]

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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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