Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2022 USD ($) Segment $ / shares	Dec. 31, 2021 USD ($)	Dec. 31, 2020
Significant Accounting Policies [Line Items]
Allowance for loan losses related to commercial, commercial real estate and farm real estate loans	$ 1,500,000
Number of days reaching which loans are considered for nonaccrual status	90 days
Loans past due charged down to the net realizable value period	90 days
Federal Home Loan Bank par value | $ / shares	$ 100
Reserve amount	$ 0
Number of operating segments | Segment	1
Other assets	$ 25,196,000	$ 22,814,000
Subordinated debentures	103,799,000	103,735,000
Revisions
Significant Accounting Policies [Line Items]
Other assets	922,000,000
Subordinated debentures	$ 922,000,000
ASU 2016-13 [Member]
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Early Adoption [true false]	true
Increase in allowance for credit losses	$ 3,300,000
ASU 2016-13 [Member] | Unfunded Loan Commitment [Member]
Significant Accounting Policies [Line Items]
Liability for unfunded loan commitments	3,400,000
Cash and Cash Equivalents [Member] | Interest Rate Swap [Member]
Significant Accounting Policies [Line Items]
Cash pledged as collateral	$ 0	$ 10,780,000
Unsecured Debt [Member]
Significant Accounting Policies [Line Items]
Retail loans past due charge off period	90 days
Secured Debt [Member]
Significant Accounting Policies [Line Items]
Residential real estate loans past due assessment of value period	180 days
Other Debt [Member]
Significant Accounting Policies [Line Items]
Loans past due charged down to the net realizable value period	90 days
Maximum [Member]
Significant Accounting Policies [Line Items]
Percentage of insurance commission revenue of total revenue	1.00%	1.00%	1.00%
Original maturities for cash and cash equivalents	90 days
Estimated useful life of intangible assets	12 years
Lease term	6 years
Maximum [Member] | Furniture and Equipment [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of asset	7 years
Maximum [Member] | Buildings and Improvements [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of asset	50 years
Maximum [Member] | WSP [Member]
Significant Accounting Policies [Line Items]
Percentage of insurance commission revenue of total revenue	1.00%	1.00%	1.00%
Maximum [Member] | CIVB Risk Management, Inc. [Member]
Significant Accounting Policies [Line Items]
Percentage of insurance commission revenue of total revenue	1.00%	1.00%	1.00%
Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	5 years
Lease term	3 years
Minimum [Member] | Furniture and Equipment [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of asset	3 years
Minimum [Member] | Buildings and Improvements [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of asset	7 years