Loans - Loans Individually Evaluated for Impairment by Portfolio Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	$ 5,835	$ 1,228	$ 2,461	$ 5,835	$ 2,461	$ 1,228
With a specific allowance recorded, Recorded Investment	4,918	10,711	9,388	4,918	9,388	10,711
Related Allowance	2,436	2,184	2,400	2,436	2,400	2,184
Recorded Investment	10,753	11,939	11,849	10,753	11,849	11,939
Average Recorded Investment	10,662	11,676	11,639	11,059	12,360	12,247
Consumer Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	624	604	714	624	714	604
With no related allowance recorded, Unpaid Principal Balance	624	604	714	624	714	604
With no related allowance recorded, Average Recorded Investment	352		453	372	485	456
With no related allowance recorded, Interest Income Recognized	1		1	3	4	5
With no related allowance recorded, Interest Income Recognized Cash Basis	5		3	10	10	15
With a specific allowance recorded, Average Recorded Investment						59
Recorded Investment	624	604	714	624	714	604
Unpaid Principal Balance	624	604	714	624	714	604
Average Recorded Investment	352		453	372	485	515
Interest Income Recognized	1		1	3	4	5
Interest Income Recognized Cash Basis	5		3	10	10	15
Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	2,588	423	1,207	2,588	1,207	423
With no related allowance recorded, Unpaid Principal Balance	2,693	423	1,207	2,693	1,207	423
With no related allowance recorded, Average Recorded Investment	2,467		1,047	1,953	1,191	1,000
With no related allowance recorded, Interest Income Recognized	6		19	19	53
With no related allowance recorded, Interest Income Recognized Cash Basis	1			6
With a specific allowance recorded, Recorded Investment		6,302	4,844		4,844	6,302
With a specific allowance recorded, Unpaid Principal Balance		6,406	4,844		4,844	6,406
Related Allowance		691	636		636	691
With a specific allowance recorded, Average Recorded Investment			5,104	1,850	5,273	5,414
With a specific allowance recorded, Interest Income Recognized			4		15	54
Recorded Investment	2,588	6,725	6,051	2,588	6,051	6,725
Unpaid Principal Balance	2,693	6,829	6,051	2,693	6,051	6,829
Average Recorded Investment	2,467		6,151	3,803	6,464	6,414
Interest Income Recognized	6		23	19	68	87
Interest Income Recognized Cash Basis	1			6
With no related allowance recorded, Adjusted Interest Income Recognized						33
Agricultural [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	1,334		130	1,334	130
With no related allowance recorded, Unpaid Principal Balance	1,334		130	1,334	130
With no related allowance recorded, Average Recorded Investment	1,309		130	591	161	143
With no related allowance recorded, Interest Income Recognized			4		8	18
With no related allowance recorded, Interest Income Recognized Cash Basis				2		3
With a specific allowance recorded, Recorded Investment		20	117		117	20
With a specific allowance recorded, Unpaid Principal Balance		20	117		117	20
Related Allowance		1	54		54	1
With a specific allowance recorded, Average Recorded Investment			117		123	94
With a specific allowance recorded, Interest Income Recognized					4
Recorded Investment	1,334	20	247	1,334	247	20
Unpaid Principal Balance	1,334	20	247	1,334	247	20
Average Recorded Investment	1,309		247	591	284	237
Interest Income Recognized			4		12	18
Interest Income Recognized Cash Basis				2		3
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	1,251	180	180	1,251	180	180
With no related allowance recorded, Unpaid Principal Balance	1,251	180	180	1,251	180	180
With no related allowance recorded, Average Recorded Investment	1,505		2,519	1,162	1,768	1,445
With no related allowance recorded, Interest Income Recognized	9		4	20	38	70
With no related allowance recorded, Interest Income Recognized Cash Basis	14		1	33	7	9
With a specific allowance recorded, Recorded Investment	2,936	3,381	3,427	2,936	3,427	3,381
With a specific allowance recorded, Unpaid Principal Balance	2,936	3,381	3,427	2,936	3,427	3,381
Related Allowance	500	664	710	500	710	664
With a specific allowance recorded, Average Recorded Investment	2,960		1,395	3,270	1,800	2,199
With a specific allowance recorded, Interest Income Recognized	39		31	113	58	70
With a specific allowance recorded, Interest Income Recognized Cash Basis					3	3
Recorded Investment	4,187	3,561	3,607	4,187	3,607	3,561
Unpaid Principal Balance	4,187	3,561	3,607	4,187	3,607	3,561
Average Recorded Investment	4,465		3,914	4,432	3,568	3,644
Interest Income Recognized	48		35	133	96	140
Interest Income Recognized Cash Basis	14		1	33	10	12
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	21	21	215	21	215	21
With no related allowance recorded, Unpaid Principal Balance	21	21	215	21	215	21
With no related allowance recorded, Average Recorded Investment	63		525	175	1,206	920
With no related allowance recorded, Interest Income Recognized				2	24	24
With no related allowance recorded, Interest Income Recognized Cash Basis			1	10	4	158
With a specific allowance recorded, Recorded Investment	1,982	982	1,000	1,982	1,000	982
With a specific allowance recorded, Unpaid Principal Balance	1,982	982	1,000	1,982	1,000	982
Related Allowance	1,936	825	1,000	1,936	1,000	825
With a specific allowance recorded, Average Recorded Investment	1,989		333	1,665	334	498
With a specific allowance recorded, Interest Income Recognized	72		2	138	2	17
Recorded Investment	2,003	1,003	1,215	2,003	1,215	1,003
Unpaid Principal Balance	2,003	1,003	1,215	2,003	1,215	1,003
Average Recorded Investment	2,052		858	1,840	1,540	1,418
Interest Income Recognized	72		2	140	26	41
Interest Income Recognized Cash Basis			1	10	4	158
Consumer [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance recorded, Recorded Investment	17		15	17	15
With no related allowance recorded, Unpaid Principal Balance	17		15	17	15
With no related allowance recorded, Average Recorded Investment	17		16	18	19	17
With no related allowance recorded, Interest Income Recognized				1	1
With a specific allowance recorded, Recorded Investment		26				26
With a specific allowance recorded, Unpaid Principal Balance		26				26
Related Allowance		3				3
With a specific allowance recorded, Average Recorded Investment				3		2
With a specific allowance recorded, Interest Income Recognized						1
Recorded Investment	17	26	15	17	15	26
Unpaid Principal Balance	17	$ 26	15	17	15	26
Average Recorded Investment	$ 17		$ 16	21	19	19
Interest Income Recognized				$ 1	$ 1	$ 1

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
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- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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Amount of allowance for credit losses related to recorded investment.

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Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

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