Loans - Risk Category of Loans by Portfolio Class Based on Year of Origination (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Grand Total	$ 2,535,291	$ 2,578,472
Consumer Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	32,347	78,526
2023	67,066	88,996
2022	81,987	90,697
2021	93,107	82,843
2020	77,689	32,548
Prior	113,266	95,380
Term Total	465,462	468,990
Revolving Loans Amortized Cost Basis	58,717	52,918
Revolving Loans Converted to Term	91
Grand Total	524,270	521,908
Gross charge-offs - Prior	13
Gross charge-offs - Term Total	13
Gross charge-offs - Grand Total	13
Consumer Real Estate [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	32,347	77,298
2023	67,066	88,695
2022	81,338	90,139
2021	91,901	82,680
2020	77,460	32,302
Prior	112,018	94,294
Term Total	462,130	465,408
Revolving Loans Amortized Cost Basis	58,545	52,904
Revolving Loans Converted to Term	91
Grand Total	520,766	518,312
Consumer Real Estate [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024		1,228
2023		40
2022	38
2021	416
Prior	122	134
Term Total	576	1,402
Revolving Loans Amortized Cost Basis	19
Grand Total	595	1,402
Consumer Real Estate [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023		261
2022	611	558
2021	790	163
2020	229	246
Prior	1,126	952
Term Total	2,756	2,180
Revolving Loans Amortized Cost Basis	153	14
Grand Total	2,909	2,194
Agricultural Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	26,841	30,504
2023	28,716	38,060
2022	35,822	37,378
2021	23,600	26,060
2020	24,451	18,864
Prior	80,529	72,516
Term Total	219,959	223,382
Revolving Loans Amortized Cost Basis	92	97
Grand Total	220,051	223,479
Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	20,875	30,504
2023	28,716	37,199
2022	35,451	25,168
2021	23,600	25,874
2020	24,451	18,456
Prior	80,510	68,651
Term Total	213,603	205,852
Revolving Loans Amortized Cost Basis	92	97
Grand Total	213,695	205,949
Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023		861
2022	246	14
2020		149
Prior	14	359
Term Total	260	1,383
Grand Total	260	1,383
Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	5,966
2022	125	12,196
2021		186
2020		259
Prior	5	3,506
Term Total	6,096	16,147
Grand Total	6,096	16,147
Agricultural [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	9,097	18,339
2023	11,755	21,585
2022	15,845	10,477
2021	6,601	4,974
2020	3,611	3,856
Prior	4,172	1,880
Term Total	51,081	61,111
Revolving Loans Amortized Cost Basis	86,495	71,652
Revolving Loans Converted to Term	11
Grand Total	137,587	132,763
Agricultural [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	7,996	17,787
2023	11,712	20,330
2022	15,845	8,356
2021	6,593	4,476
2020	3,569	3,856
Prior	4,172	1,880
Term Total	49,887	56,685
Revolving Loans Amortized Cost Basis	84,934	69,824
Revolving Loans Converted to Term	11
Grand Total	134,832	126,509
Agricultural [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024		38
2023	19	621
2022		112
2021	8
Term Total	27	771
Revolving Loans Amortized Cost Basis	30	330
Grand Total	57	1,101
Agricultural [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	1,101	514
2023	24	634
2022		2,009
2021		498
2020	42
Term Total	1,167	3,655
Revolving Loans Amortized Cost Basis	1,531	1,498
Grand Total	2,698	5,153
Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	70,907	259,096
2023	246,975	447,816
2022	430,877	245,273
2021	221,122	133,524
2020	117,542	136,851
Prior	211,506	112,515
Term Total	1,298,929	1,335,075
Grand Total	1,298,929	1,335,075
Gross charge-offs - Prior	15
Gross charge-offs - Term Total	15
Gross charge-offs - Grand Total	15
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	70,907	224,232
2023	212,460	438,716
2022	418,161	245,273
2021	221,122	122,656
2020	116,176	136,225
Prior	210,309	99,378
Term Total	1,249,135	1,266,480
Grand Total	1,249,135	1,266,480
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024		34,864
2023	33,610	9,100
2022	12,716
2021		10,793
2020	1,366	626
Prior		12,342
Term Total	47,692	67,725
Grand Total	47,692	67,725
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023	905
Prior	1,197	795
Term Total	2,102	795
Grand Total	2,102	795
Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		75
Term Total		75
Grand Total		75
Commercial & Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	25,614	57,014
2023	58,149	52,186
2022	42,553	25,087
2021	16,810	20,399
2020	15,185	2,610
Prior	2,158	1,306
Term Total	160,469	158,602
Revolving Loans Amortized Cost Basis	99,875	96,156
Revolving Loans Converted to Term	144
Grand Total	260,488	254,758
Gross charge-offs - fiscal year 2021		565
Gross charge-offs - fiscal year 2020	101
Gross charge-offs - Term Total	101	565
Gross charge-offs - Revolving Loans Converted to Term	5
Gross charge-offs - Grand Total	106	565
Commercial & Industrial [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	25,573	56,224
2023	57,631	51,663
2022	42,542	24,876
2021	16,616	20,071
2020	15,185	2,142
Prior	1,689	932
Term Total	159,236	155,908
Revolving Loans Amortized Cost Basis	96,175	90,018
Revolving Loans Converted to Term	144
Grand Total	255,555	245,926
Commercial & Industrial [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024		716
2023	72	69
2022		211
2021	194	146
2020		437
Prior	337	357
Term Total	603	1,936
Revolving Loans Amortized Cost Basis	2	6,016
Grand Total	605	7,952
Commercial & Industrial [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	41	74
2023	446	454
2022	11
2020		31
Prior	132	17
Term Total	630	576
Revolving Loans Amortized Cost Basis	3,698	122
Grand Total	4,328	698
Commercial & Industrial [Member] | Doubtful [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		182
Term Total		182
Grand Total		182
Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Grand Total	68,050	80,353
Consumer [Member] | Payment Performance [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	10,831	21,537
2023	15,823	40,787
2022	30,583	10,666
2021	6,859	5,012
2020	2,883	1,825
Prior	868	482
Term Total	67,847	80,309
Revolving Loans Amortized Cost Basis	203	44
Grand Total	68,050	80,353
Gross charge-offs - fiscal year 2024	161	236
Gross charge-offs - fiscal year 2023	45	51
Gross charge-offs - fiscal year 2022	50	100
Gross charge-offs - fiscal year 2021	10	38
Gross charge-offs - Term Total	266	425
Gross charge-offs - Grand Total	266	425
Consumer [Member] | Performing [Member] | Payment Performance [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	10,805	21,511
2023	15,819	40,729
2022	30,544	10,666
2021	6,859	5,006
2020	2,879	1,825
Prior	868	480
Term Total	67,774	80,217
Revolving Loans Amortized Cost Basis	203	44
Grand Total	67,977	80,261
Consumer [Member] | Nonperforming [Member] | Payment Performance [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	26	26
2023	4	58
2022	39
2021		6
2020	4
Prior		2
Term Total	73	92
Grand Total	73	92
Other Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024		2,810
2022		16,761
2021	16,439	5,790
2020	5,299	445
Prior	4,178	4,330
Term Total	25,916	30,136
Grand Total	25,916	$ 30,136
Other Loan [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	16,439
2020	5,299
Prior	4,178
Term Total	25,916
Grand Total	$ 25,916