Loans - Analysis of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				$ 7,707				$ 7,049	$ 7,707	$ 7,049
Charge Offs									(720)	(841)	$ (580)
Recoveries									183	156	163
Provision (Credit)	$ 1,995	$ 1,987	$ 1,569	1,430	$ 728	$ 247	$ 133	30	6,981	1,138	324
Other Non-interest expense related to unfunded									162	205
Ending Balance	14,313				7,707				14,313	7,707	7,049
Ending balance: individually evaluated for impairment	1,657				197				1,657	197
Ending balance: collectively evaluated for impairment	12,656				7,510				12,656	7,510
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	1,302,990				1,218,999				1,302,990	1,218,999
Ending balance: individually evaluated for impairment	14,532				3,061				14,532	3,061
Ending balance: collectively evaluated for impairment	1,288,310				1,215,786				1,288,310	1,215,786
Ending balance: loans acquired with deteriorated credit quality	148				152				148	152
Consumer Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				311				247	311	247
Charge Offs									(35)	(98)
Recoveries									9
Provision (Credit)									348	162
Ending Balance	633				311				633	311	247
Ending balance: individually evaluated for impairment	31				30				31	30
Ending balance: collectively evaluated for impairment	602				281				602	281
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	175,316				164,691				175,316	164,691
Ending balance: individually evaluated for impairment	1,001				829				1,001	829
Ending balance: collectively evaluated for impairment	174,273				163,816				174,273	163,816
Ending balance: loans acquired with deteriorated credit quality	42				46				42	46
Agricultural Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				314				250	314	250
Provision (Credit)									644	64
Ending Balance	958				314				958	314	250
Ending balance: individually evaluated for impairment	600								600
Ending balance: collectively evaluated for impairment	358				314				358	314
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	188,826				198,859				188,826	198,859
Ending balance: individually evaluated for impairment	6,756								6,756
Ending balance: collectively evaluated for impairment	182,070				198,859				182,070	198,859
Agricultural [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				691				768	691	768
Charge Offs										(37)
Recoveries										3
Provision (Credit)									10	(43)
Ending Balance	701				691				701	691	768
Ending balance: individually evaluated for impairment	116				21				116	21
Ending balance: collectively evaluated for impairment	585				670				585	670
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	94,490				111,949				94,490	111,949
Ending balance: individually evaluated for impairment	467				691				467	691
Ending balance: collectively evaluated for impairment	94,023				111,258				94,023	111,258
Commercial Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				3,634				3,217	3,634	3,217
Charge Offs									(8)
Recoveries									10	11
Provision (Credit)									3,779	406
Ending Balance	7,415				3,634				7,415	3,634	3,217
Ending balance: individually evaluated for impairment	20								20
Ending balance: collectively evaluated for impairment	7,395				3,634				7,395	3,634
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	587,654				550,082				587,654	550,082
Ending balance: individually evaluated for impairment	2,950				299				2,950	299
Ending balance: collectively evaluated for impairment	584,704				549,783				584,704	549,783
Commercial and Industrial [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				1,727				1,305	1,727	1,305
Charge Offs									(297)	(215)
Recoveries									24	22
Provision (Credit)									1,892	615
Ending Balance	3,346				1,727				3,346	1,727	1,305
Ending balance: individually evaluated for impairment	890				142				890	142
Ending balance: collectively evaluated for impairment	2,456				1,585				2,456	1,585
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	204,043				144,009				204,043	144,009
Ending balance: individually evaluated for impairment	3,335				1,209				3,335	1,209
Ending balance: collectively evaluated for impairment	200,602				142,694				200,602	142,694
Ending balance: loans acquired with deteriorated credit quality	106				106				106	106
Consumer [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				551				484	551	484
Charge Offs									(380)	(491)
Recoveries									140	120
Provision (Credit)									295	438
Ending Balance	606				551				606	551	484
Ending balance: individually evaluated for impairment					4					4
Ending balance: collectively evaluated for impairment	606				547				606	547
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	52,661				49,409				52,661	49,409
Ending balance: individually evaluated for impairment	23				33				23	33
Ending balance: collectively evaluated for impairment	52,638				49,376				52,638	49,376
Unallocated [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance								504		504
Provision (Credit)									13	(504)
Ending Balance	13								13		504
Ending balance: collectively evaluated for impairment	13								13
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
Unfunded Loan Commitment & Letters of Credit [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				$ 479				$ 274	479	274
Other Non-interest expense related to unfunded									162	205
Ending Balance	641				479				641	479	$ 274
Ending balance: collectively evaluated for impairment	641				479				641	479
Ending balance: loans acquired with deteriorated credit quality	$ 0				$ 0				$ 0	$ 0