Loans and Allowance for Credit Losses - Schedule of Allowance for Credit Losses on Off-Balance Sheet Credit Exposures (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	$ 43,487	$ 44,449	$ 43,520	$ 44,544	$ 45,103	$ 45,847
SEC Schedule, 12-09, Allowance, Credit Loss [Member] | Off Balance Sheet Credit Loss Liability [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	1,446		1,625
Commercial Real Estate [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	14,492	13,582	13,476	16,652	16,611	16,731
Commercial Real Estate [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member] | Off Balance Sheet Credit Loss Liability [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	322		285
Commercial and Industrial [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	16,407	17,651	17,954	15,194	15,620	14,951
Commercial and Industrial [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member] | Off Balance Sheet Credit Loss Liability [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	1,071		1,053
Agricultural Real Estate [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	2,254	1,688	1,718	583	586	819
Agricultural Real Estate [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member] | Off Balance Sheet Credit Loss Liability [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	6		2
Residential Real Estate [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	8,066	8,319	7,784	8,855	8,751	8,608
Residential Real Estate [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member] | Off Balance Sheet Credit Loss Liability [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	36		35
Agricultural [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	522	1,612	995	1,289	1,547	2,457
Agricultural [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member] | Off Balance Sheet Credit Loss Liability [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses			3
Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	1,746	$ 1,597	1,593	$ 1,971	$ 1,988	$ 2,281
Consumer [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member] | Off Balance Sheet Credit Loss Liability [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, allowance for credit losses	$ 11		$ 247