Loans - Risk Category of Loans at Amortized Cost, by Portfolio Segment Based on Year of Origination (Detail) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Grand Total	$ 2,658,275	$ 2,560,795
Consumer Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	41,227	40,400
2024	32,137	64,555
2023	54,878	80,069
2022	73,421	91,137
2021	85,851	75,461
Prior	157,622	107,166
Term Total	445,136	458,788
Revolving Loans Amortized Cost Basis	76,772	61,352
Revolving Loans Converted to Term	1,022	252
Grand Total	522,930	520,392
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]
2025	40,968	40,257
2024	31,813	64,316
2023	54,353	79,503
2022	72,918	89,800
2021	84,269	74,996
Prior	155,908	106,007
Term Total	440,229	454,879
Revolving Loans Amortized Cost Basis	76,729	61,097
Revolving Loans Converted to Term	882	237
Grand Total	517,840	516,213
Consumer Real Estate [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023		37
2022		551
2021	132
Prior	49	119
Term Total	181	707
Revolving Loans Amortized Cost Basis	19	19
Grand Total	200	726
Consumer Real Estate [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	259	143
2024	324	239
2023	525	529
2022	503	786
2021	1,450	465
Prior	1,665	1,040
Term Total	4,726	3,202
Revolving Loans Amortized Cost Basis	24	236
Revolving Loans Converted to Term	140	15
Grand Total	4,890	3,453
Agricultural Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	22,991	29,513
2024	26,411	28,088
2023	25,619	34,840
2022	32,566	22,983
2021	22,020	23,639
Prior	92,228	76,982
Term Total	221,835	216,045
Revolving Loans Amortized Cost Basis	88	92
Revolving Loans Converted to Term	0
Grand Total	221,923	216,137
Agricultural Real Estate [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	22,991	23,817
2024	21,521	28,088
2023	24,750	34,469
2022	31,689	22,983
2021	20,954	23,639
Prior	91,857	76,964
Term Total	213,762	209,960
Revolving Loans Amortized Cost Basis	88	92
Grand Total	213,850	210,052
Agricultural Real Estate [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022	32
Prior	283	13
Term Total	315	13
Grand Total	315	13
Agricultural Real Estate [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025		5,696
2024	4,890
2023	869	371
2022	845
2021	1,066
Prior	88	5
Term Total	7,758	6,072
Grand Total	7,758	6,072
Agricultural [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	21,487	14,915
2024	9,596	10,534
2023	7,569	14,381
2022	10,217	5,624
2021	3,923	3,233
Prior	4,863	3,911
Term Total	57,655	52,598
Revolving Loans Amortized Cost Basis	121,250	99,783
Revolving Loans Converted to Term	794
Grand Total	179,699	152,381
Agricultural [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	19,076	14,915
2024	9,563	10,500
2023	7,462	14,381
2022	9,855	5,616
2021	3,902	3,204
Prior	4,863	3,911
Term Total	54,721	52,527
Revolving Loans Amortized Cost Basis	106,985	98,283
Revolving Loans Converted to Term	794
Grand Total	162,500	150,810
Agricultural [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	2,011
2024		13
2022	305	8
2021	21
Term Total	2,337	21
Revolving Loans Amortized Cost Basis	12,545	30
Grand Total	14,882	51
Agricultural [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	400
2024	33	21
2023	107
2022	57
2021		29
Term Total	597	50
Revolving Loans Amortized Cost Basis	1,720	1,470
Grand Total	2,317	1,520
Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	165,754	128,608
2024	144,051	234,491
2023	223,844	425,696
2022	401,198	218,309
2021	209,281	111,787
Prior	208,562	189,570
Term Total	1,352,690	1,308,461
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term	0
Grand Total	1,352,690	1,308,461
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]
2025	162,678	128,608
2024	144,051	200,192
2023	174,606	413,106
2022	374,782	218,309
2021	195,265	110,435
Prior	198,130	188,239
Term Total	1,249,512	1,258,889
Grand Total	1,249,512	1,258,889
Commercial Real Estate [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	1,345
2023	15,551	12,590
2022	24,527
2021	12,619	1,352
Prior	3,716	753
Term Total	57,758	14,695
Grand Total	57,758	14,695
Commercial Real Estate [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	1,731
2024		34,299
2023	33,687
2022	1,889
2021	1,397
Prior	6,716	578
Term Total	45,420	34,877
Grand Total	45,420	34,877
Commercial & Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	32,600	31,972
2024	27,011	55,066
2023	42,741	39,694
2022	31,064	15,235
2021	12,035	13,506
Prior	8,919	1,738
Term Total	154,370	157,211
Revolving Loans Amortized Cost Basis	141,055	117,386
Revolving Loans Converted to Term	390	222
Grand Total	295,815	274,819
Gross charge-offs - fiscal year 2022	26
Gross charge-offs - fiscal year 2021		101
Gross charge-offs - Term Total	26	101
Gross charge-offs - Revolving Loans Converted to Term		5
Gross charge-offs - Grand Total	26	106
Commercial & Industrial [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	32,600	31,933
2024	26,840	54,581
2023	42,252	39,665
2022	31,040	15,047
2021	11,838	13,480
Prior	8,586	1,294
Term Total	153,156	156,000
Revolving Loans Amortized Cost Basis	128,248	113,446
Revolving Loans Converted to Term	78	222
Grand Total	281,482	269,668
Commercial & Industrial [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024		137
2023	207
2022		188
2021	171	26
Prior	333	416
Term Total	711	767
Revolving Loans Amortized Cost Basis	9,117	459
Revolving Loans Converted to Term	312
Grand Total	10,140	1,226
Commercial & Industrial [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025		39
2024	171	348
2023	282	29
2022	24
2021	26
Prior		28
Term Total	503	444
Revolving Loans Amortized Cost Basis	3,493	3,481
Grand Total	3,996	3,925
Commercial & Industrial [Member] \| Doubtful [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans Amortized Cost Basis	197
Grand Total	197
Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Grand Total	61,132	63,627
Consumer [Member] \| Payment Performance [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	19,806	13,477
2024	9,647	13,521
2023	9,020	27,304
2022	17,749	5,952
2021	3,278	2,314
Prior	1,163	582
Term Total	60,663	63,150
Revolving Loans Amortized Cost Basis	469	477
Grand Total	61,132	63,627
Gross charge-offs - fiscal year 2025	154	201
Gross charge-offs - fiscal year 2024	55	69
Gross charge-offs - fiscal year 2023	128	62
Gross charge-offs - fiscal year 2022	162	14
Gross charge-offs - fiscal year 2021	61
Gross charge-offs - Prior	1
Gross charge-offs - Term Total	561	346
Gross charge-offs - Grand Total	561	346
Consumer [Member] \| Performing [Member] \| Payment Performance [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	19,806	13,437
2024	9,647	13,521
2023	8,998	27,264
2022	17,733	5,917
2021	3,261	2,310
Prior	1,158	582
Term Total	60,603	63,031
Revolving Loans Amortized Cost Basis	469	477
Grand Total	61,072	63,508
Consumer [Member] \| Nonperforming [Member] \| Payment Performance [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025		40
2023	22	40
2022	16	35
2021	17	4
Prior	5
Term Total	60	119
Grand Total	60	119
Other Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	584
2024	0
2023	0
2022	0	15,829
2021	15,491	5,068
Prior	8,011	4,081
Term Total	24,086	24,978
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term	0
Grand Total	24,086	24,978
Other Loan [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2025	584
2022		15,829
2021	15,491	5,068
Prior	8,011	4,081
Term Total	24,086	24,978
Grand Total	$ 24,086	$ 24,978

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Financing receivable allowance for credit losses writeoffs three years before latest fiscal year.

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Financing receivable term loan.

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-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6A

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