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Loans Held for Investment - Schedule of Modifications to Borrowers (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 43.0	$ 31.7	$ 63.5	$ 89.4
Financing Receivable, Modification to Total Financing Receivables, Excluding Accrued Interest, Percent	0.27%	0.18%	0.40%	0.50%
Interest Receivable	$ 106.6		$ 106.6		$ 106.6		$ 116.8
Financing Receivable, Modified in Period, Accrued Interest, Amount			0.7	$ 1.1
Accruing
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period					0.8	$ 0.5
Nonaccrual 30 or more DPD
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period					10.5	$ 9.2
Principal Forgiveness
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	0.0	$ 0.0	0.0	0.0
Extended Maturity [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	40.2	31.2	59.6	66.4
Extended Maturity and Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	2.8	0.5	3.9	23.0
Principal Forgiven
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	0.0	0.0	0.0	0.0
Agricultural
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 14.9	$ 6.5	$ 14.9	$ 12.1
Financing Receivable, Modification to Total Financing Receivables, Excluding Accrued Interest, Percent	2.39%	0.89%	2.39%	1.67%
Financing Receivable, Loan in Process	$ 2.4		$ 2.4		2.4		10.4
Financing Receivable, Modified, Weighted Average Term Increase from Modification	12 years 7 months 6 days	7 years 8 months 12 days	12 years 7 months 6 days	7 years 4 months 24 days
Agricultural | Principal Forgiveness
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Agricultural | Extended Maturity [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	12.1	6.5	12.1	12.1
Agricultural | Extended Maturity and Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	2.8	0.0	2.8	0.0
Agricultural | Principal Forgiven
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Agricultural | Weighted-Average Months of Term Extension
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period, Term Extension, Weighted-Average Months	4 years	0 years	4 years	0 years
Agricultural | Weighted-Average Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Combination Term Extension and Interest Rate Reduction Percent	0.30%	0.00%	0.30%	0.00%
Agricultural
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 3.7	$ 21.4	$ 6.0	$ 45.4
Financing Receivable, Modification to Total Financing Receivables, Excluding Accrued Interest, Percent	0.75%	3.10%	1.21%	6.58%
Financing Receivable, Loan in Process	$ 1.1		$ 1.1		1.1		5.2
Financing Receivable, Modified, Weighted Average Term Increase from Modification	7 years 2 months 12 days	3 years 10 months 24 days	7 years 3 months 18 days	4 years 1 month 6 days
Agricultural | Principal Forgiveness
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Agricultural | Extended Maturity [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	3.7	21.4	6.0	23.2
Agricultural | Extended Maturity and Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	0.0	0.0	0.0	22.2
Agricultural | Principal Forgiven
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Agricultural | Weighted-Average Months of Term Extension
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period, Term Extension, Weighted-Average Months	0 years	0 years	0 years	55 years 2 months 12 days
Agricultural | Weighted-Average Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Combination Term Extension and Interest Rate Reduction Percent	0.00%	0.00%	0.00%	1.10%
Other, including overdrafts
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Loan in Process	$ 0.0		$ 0.0		0.0		0.0
Commercial
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 2.3	$ 0.5	$ 15.3	$ 14.7
Financing Receivable, Modification to Total Financing Receivables, Excluding Accrued Interest, Percent	0.03%	0.01%	0.18%	0.16%
Financing Receivable, Loan in Process	$ 5.2		$ 5.2		5.2		7.7
Financing Receivable, Modified, Weighted Average Term Increase from Modification	7 years 8 months 12 days	5 years 10 months 24 days	13 years 2 months 12 days	6 years 9 months 18 days
Commercial | Principal Forgiveness
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Commercial | Extended Maturity [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	2.3	0.5	14.5	14.7
Commercial | Extended Maturity and Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	0.0	0.0	0.8	0.0
Commercial | Principal Forgiven
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Commercial | Weighted-Average Months of Term Extension
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period, Term Extension, Weighted-Average Months	0 years	0 years	13 years 3 months 18 days	0 years
Commercial | Weighted-Average Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Combination Term Extension and Interest Rate Reduction Percent	0.00%	0.00%	0.90%	0.00%
Total construction loans
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 1.7	$ 1.9	$ 1.9	$ 1.9
Financing Receivable, Modification to Total Financing Receivables, Excluding Accrued Interest, Percent	0.18%	0.15%	0.20%	0.15%
Financing Receivable, Loan in Process	$ 0.3		$ 0.3		0.3		3.7
Financing Receivable, Modified, Weighted Average Term Increase from Modification	12 years	4 years	7 years 4 months 24 days	4 years
Total construction loans | Principal Forgiveness
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Total construction loans | Extended Maturity [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	1.7	1.9	1.9	1.9
Total construction loans | Extended Maturity and Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	0.0	0.0	0.0	0.0
Total construction loans | Principal Forgiven
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Total construction loans | Weighted-Average Months of Term Extension
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period, Term Extension, Weighted-Average Months	0 years	0 years	0 years	0 years
Total construction loans | Weighted-Average Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Combination Term Extension and Interest Rate Reduction Percent	0.00%	0.00%	0.00%	0.00%
Residential
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period			$ 0.4	$ 0.4
Financing Receivable, Modification to Total Financing Receivables, Excluding Accrued Interest, Percent			0.02%	0.02%
Financing Receivable, Loan in Process	$ 3.2		$ 3.2		3.2		9.7
Financing Receivable, Modified, Weighted Average Term Increase from Modification			22 years 3 months 18 days	11 years
Residential | Principal Forgiveness
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period			$ 0.0	$ 0.0
Residential | Extended Maturity [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period			0.3	0.1
Residential | Extended Maturity and Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period			0.1	0.3
Residential | Principal Forgiven
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period			$ 0.0	$ 0.0
Residential | Weighted-Average Months of Term Extension
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period, Term Extension, Weighted-Average Months			84 years 9 months 18 days	31 years 2 months 12 days
Residential | Weighted-Average Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Combination Term Extension and Interest Rate Reduction Percent			2.20%	3.40%
Total real estate
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 18.9	$ 8.9	$ 32.5	$ 29.1
Financing Receivable, Modification to Total Financing Receivables, Excluding Accrued Interest, Percent	0.15%	0.07%	0.27%	0.22%
Financing Receivable, Loan in Process	$ 11.1		$ 11.1		11.1		31.5
Total real estate | Principal Forgiveness
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	0.0	$ 0.0	0.0	$ 0.0
Total real estate | Extended Maturity [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	16.1	8.9	28.8	28.8
Total real estate | Extended Maturity and Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	2.8	0.0	3.7	0.3
Total real estate | Principal Forgiven
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	0.0	0.0	0.0	0.0
Commercial
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 20.4	$ 1.4	$ 25.0	$ 14.9
Financing Receivable, Modification to Total Financing Receivables, Excluding Accrued Interest, Percent	0.83%	0.05%	1.02%	0.51%
Financing Receivable, Loan in Process	$ 7.5		$ 7.5		7.5		14.8
Financing Receivable, Modified, Weighted Average Term Increase from Modification	4 years 10 months 24 days	5 years 3 months 18 days	6 years 4 months 24 days	7 years 8 months 12 days
Commercial | Principal Forgiveness
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Commercial | Extended Maturity [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	20.4	0.9	24.8	14.4
Commercial | Extended Maturity and Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	0.0	0.5	0.2	0.5
Commercial | Principal Forgiven
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Commercial | Weighted-Average Months of Term Extension
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified Period, Term Extension, Weighted-Average Months	0 years	59 years	20 years 8 months 12 days	9 years 2 months 12 days
Commercial | Weighted-Average Interest Rate Reduction
Financing Receivable, Modifications to Borrowers [Line Items]
Combination Term Extension and Interest Rate Reduction Percent	0.00%	0.80%	0.80%	1.00%
Indirect consumer
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Loan in Process	$ 8.2		$ 8.2		8.2		11.7
Credit Card Receivable [Member]
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Loan in Process	0.0		0.0		0.0		2.2
Total consumer loans
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Loan in Process	9.4		9.4		9.4		15.0
Consumer Loan
Financing Receivable, Modifications to Borrowers [Line Items]
Financing Receivable, Loan in Process	$ 1.2		$ 1.2		$ 1.2		$ 1.1

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Amount of accrued interest on financing receivable modified during period for debtor experiencing financial difficulty.

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