Allowance for Loan Losses - Changes in the Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 13,786	$ 12,867	$ 13,679	$ 13,134
Charge-offs	(36)	(133)	(431)	(784)
Recoveries	244	207	746	591
Provision	150	390	150	390
Ending Balance	14,144	13,331	14,144	13,331
Commercial and Agriculture [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1,828	1,630	1,747	1,562
Charge-offs			(27)	(248)
Recoveries	61	64	65	168
Provision	43	(63)	147	149
Ending Balance	1,932	1,631	1,932	1,631
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,009	2,161	1,962	2,043
Charge-offs			(60)	(193)
Recoveries	43	18	282	148
Provision	85	(136)	(47)	45
Ending Balance	2,137	2,043	2,137	2,043
Commercial Real Estate Non Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	5,867	5,135	5,803	5,307
Charge-offs		(76)		(121)
Recoveries	55	2	99	23
Provision	226	384	246	236
Ending Balance	6,148	5,445	6,148	5,445
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1,698	1,691	1,531	1,910
Charge-offs	(20)	(12)	(223)	(74)
Recoveries	67	88	229	181
Provision	(136)	32	72	(218)
Ending Balance	1,609	1,799	1,609	1,799
Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1,135	861	1,046	834
Charge-offs			(24)
Recoveries	1		1
Provision	47	120	160	147
Ending Balance	1,183	981	1,183	981
Farm Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	365	410	397	430
Recoveries	1	1	3	4
Provision	1	(18)	(33)	(41)
Ending Balance	367	393	367	393
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	201	300	284	290
Charge-offs	(16)	(45)	(97)	(148)
Recoveries	16	34	67	67
Provision	52	26	(1)	106
Ending Balance	253	315	253	315
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	683	679	909	758
Provision	(168)	45	(394)	(34)
Ending Balance	$ 515	$ 724	$ 515	$ 724