Loans Held for Investment - Schedule of Loans by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2024	Dec. 31, 2023
Loans and Leases Receivable
Loans and Leases Receivable, Deferred Income		$ (11.1)	$ (12.5)
Accounts Receivable, Allowance for Credit Loss	$ (220.1)	(204.1)	(227.7)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	122.3
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	59.5
Loans and Leases Receivable, Collateral for Secured Borrowings		17,844.9	18,279.6
Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(74.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	43.9
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	37.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		9,263.2	8,869.2
Residential Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(3.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	2.4
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.0
Commercial Real Estate Construction [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(31.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	6.0
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.2
Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		1,244.6	1,826.5
Residential Mortgage [Member]
Loans and Leases Receivable
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		2,191.6	2,244.3
Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(5.9)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	1.9
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	2.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		701.1	716.8
Real Estate Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(138.7)	(139.4)	(160.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	69.3
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	43.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		13,400.5	13,656.8
Indirect consumer
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(15.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	14.3
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		725.0	740.9
Other consumer
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(5.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	4.6
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		134.0	141.6
Credit card consumer
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(2.8)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	2.2
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		77.6	76.5
Total consumer loans
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(23.3)	(16.8)	(13.0)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	21.1
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		936.6	959.0
Commercial Portfolio Segment [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(54.9)	(38.9)	(50.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	31.6
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	11.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		2,829.4	2,906.8
Agricultural Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(3.2)	(9.0)	(4.4)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	0.3
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	4.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		687.9	769.4
Other, including overdrafts
Loans and Leases Receivable
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		1.6	0.1
Loans held for investment
Loans and Leases Receivable
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		17,856.0	18,292.1
Non Owner Occupied Loans
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(27.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	17.3
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	17.2
Commercial Real Estate Owner Occupied
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(19.5)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	13.3
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	9.5
Commercial Real Estate Multifamily
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(27.9)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	13.3
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	10.9
Land Acquisition And Development Construction Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(1.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	0.5
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	3.4
Construction Loans
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(36.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	8.9
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	3.6
Residential Real Estate 1-4 Family
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(20.5)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	13.4
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.1
Home Equity Loan
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(1.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	1.2
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.0
Residential Real Estate
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(22.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	14.6
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.1
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process		$ 2,191.6	$ 2,244.3
Commercial and Floor Plans
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(49.0)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	27.1
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	11.2
Commercial Purpose Secured by 1-4 Family
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(5.7)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	4.4
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.2
Commercial Borrower
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(0.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	0.1
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	$ 0.0