Loans - Analysis of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				$ 7,049				$ 7,095	$ 7,049	$ 7,095
Charge Offs									(841)	(580)	$ (288)
Recoveries									156	163	150
Provision (Credit)	$ 728	$ 247	$ 133	30	$ 105	$ 47	$ 132	40	1,138	324	222
Other Non-interest expense related to unfunded									205	47
Ending Balance	7,707				7,049				7,707	7,049	7,095
Ending balance: individually evaluated for impairment	197				31				197	31
Ending balance: collectively evaluated for impairment	7,510				7,018				7,510	7,018
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	1,218,999				846,374				1,218,999	846,374
Ending balance: individually evaluated for impairment	3,061				2,054				3,061	2,054
Ending balance: collectively evaluated for impairment	1,215,786				844,204				1,215,786	844,204
Ending balance: loans acquired with deteriorated credit quality	152				116				152	116
Consumer Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				247				343	247	343
Charge Offs									(98)	(63)
Recoveries										18
Provision (Credit)									162	(51)
Ending Balance	311				247				311	247	343
Ending balance: individually evaluated for impairment	30				26				30	26
Ending balance: collectively evaluated for impairment	281				221				281	221
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	164,691				80,232				164,691	80,232
Ending balance: individually evaluated for impairment	829				757				829	757
Ending balance: collectively evaluated for impairment	163,816				79,359				163,816	79,359
Ending balance: loans acquired with deteriorated credit quality	46				116				46	116
Agricultural Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				250				244	250	244
Provision (Credit)									64	6
Ending Balance	314				250				314	250	244
Ending balance: collectively evaluated for impairment	314				250				314	250
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	198,859				68,588				198,859	68,588
Ending balance: collectively evaluated for impairment	198,859				68,588				198,859	68,588
Agricultural [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				768				667	768	667
Charge Offs									(37)
Recoveries									3	8
Provision (Credit)									(43)	93
Ending Balance	691				768				691	768	667
Ending balance: individually evaluated for impairment	21								21
Ending balance: collectively evaluated for impairment	670				768				670	768
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	111,949				108,616				111,949	108,616
Ending balance: individually evaluated for impairment	691								691
Ending balance: collectively evaluated for impairment	111,258				108,616				111,258	108,616
Commercial Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				3,217				3,149	3,217	3,149
Charge Offs										(16)
Recoveries									11	10
Provision (Credit)									406	74
Ending Balance	3,634				3,217				3,634	3,217	3,149
Ending balance: collectively evaluated for impairment	3,634				3,217				3,634	3,217
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	550,082				419,131				550,082	419,131
Ending balance: individually evaluated for impairment	299				194				299	194
Ending balance: collectively evaluated for impairment	549,783				418,937				549,783	418,937
Commercial and Industrial [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				1,305				1,546	1,305	1,546
Charge Offs									(215)	(142)
Recoveries									22	13
Provision (Credit)									615	(112)
Ending Balance	1,727				1,305				1,727	1,305	1,546
Ending balance: individually evaluated for impairment	142				5				142	5
Ending balance: collectively evaluated for impairment	1,585				1,300				1,585	1,300
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	144,009				127,752				144,009	127,752
Ending balance: individually evaluated for impairment	1,209				1,103				1,209	1,103
Ending balance: collectively evaluated for impairment	142,694				126,649				142,694	126,649
Ending balance: loans acquired with deteriorated credit quality	106								106
Consumer [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				484				441	484	441
Charge Offs									(491)	(359)
Recoveries									120	114
Provision (Credit)									438	288
Ending Balance	551				484				551	484	441
Ending balance: individually evaluated for impairment	4								4
Ending balance: collectively evaluated for impairment	547				484				547	484
Ending balance: loans acquired with deteriorated credit quality	0				0				0	0
FINANCING RECEIVABLES:
Ending balance	49,409				42,055				49,409	42,055
Ending balance: individually evaluated for impairment	33								33
Ending balance: collectively evaluated for impairment	49,376				42,055				49,376	42,055
Unallocated [Member]
ALLOWANCE FOR CREDIT LOSSES:
Beginning balance				504				478	504	478
Provision (Credit)									(504)	26
Ending Balance					504					504	478
Ending balance: collectively evaluated for impairment					504					504
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				$ 274				$ 227	274	227
Other Non-interest expense related to unfunded									205	47
Ending Balance	479				274				479	274	$ 227
Ending balance: collectively evaluated for impairment	479				274				479	274
Ending balance: loans acquired with deteriorated credit quality	$ 0				$ 0				$ 0	$ 0