Loans and Leases, Credit Risk Rating Categories for Loans and Leases Held-for-Investment (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	$ 3,696,295	$ 3,654,689
Allowance for credit losses	75,018	74,965	$ 66,885
Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	3,637,088	3,618,482
Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	57,237	34,240
Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	1,970	1,967
Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Real Estate [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	2,703,362	2,669,281
Allowance for credit losses	46,128	46,039
Real Estate [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	2,667,752	2,649,431
Real Estate [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	34,418	18,540
Real Estate [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	1,192	1,310
Real Estate [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Commercial [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	1,344,380	1,314,928
Allowance for credit losses	22,414	26,093
Commercial [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	1,337,274	1,308,717
Commercial [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	7,106	6,211
Commercial [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Commercial [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Agricultural [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	726,041	742,009
Allowance for credit losses	11,377	7,744
Agricultural [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	698,309	729,135
Agricultural [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	27,186	12,329
Agricultural [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	546	545
Agricultural [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Residential and Home Equity [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	405,526	399,982
Allowance for credit losses	7,721	7,770	7,508
Residential and Home Equity [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	404,754	399,217
Residential and Home Equity [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	126	0
Residential and Home Equity [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	646	765
Residential and Home Equity [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Construction [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	227,415	212,362
Allowance for credit losses	4,616	4,432	3,026
Construction [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	227,415	212,362
Construction [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Construction [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Construction [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Commercial & Industrial [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	497,028	499,373
Allowance for credit losses	11,559	13,380
Commercial & Industrial [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	482,584	486,439
Commercial & Industrial [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	13,950	12,458
Commercial & Industrial [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	494	476
Commercial & Industrial [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Agricultural [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	317,955	313,737
Allowance for credit losses	10,292	8,872
Agricultural [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	315,136	310,496
Agricultural [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	2,764	3,236
Agricultural [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	55	5
Agricultural [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Commercial Leases [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	172,149	167,086
Allowance for credit losses	6,923	6,537	1,924
Commercial Leases [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	166,044	167,080
Commercial Leases [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	6,105	6
Commercial Leases [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Commercial Leases [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Consumer and Other [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	5,801	5,212
Allowance for credit losses	116	137	$ 171
Consumer and Other [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	5,572	5,036
Consumer and Other [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	0	0
Consumer and Other [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	229	176
Consumer and Other [Member] | Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Gross loans and leases	$ 0	$ 0