Loans Held for Investment - Schedule of Loans by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2022	Dec. 31, 2021
Loans and Leases Receivable
Loans and Leases Receivable, Deferred Income		$ (15.6)	$ (12.3)
Loans and Leases Receivable, Net of Deferred Income		18,099.2	9,331.7
Accounts Receivable, Allowance for Credit Loss	$ (144.3)	(220.1)	(122.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	73.0
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	30.0
Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(54.8)	(74.6)	(43.9)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	19.5
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	15.3
Loans and Leases Receivable, Collateral for Secured Borrowings		8,528.6	3,971.5
Residential Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(1.6)	(3.6)	(2.4)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	1.5
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.9
Loans and Leases Receivable, Collateral for Secured Borrowings		516.2	262.0
Commercial Real Estate Construction [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(7.3)	(31.2)	(6.0)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	2.7
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	1.3
Loans and Leases Receivable, Collateral for Secured Borrowings		1,042.0	498.0
Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable
Loans and Leases Receivable, Collateral for Secured Borrowings		1,944.4	1,007.8
Residential Mortgage [Member]
Loans and Leases Receivable
Loans and Leases Receivable, Collateral for Secured Borrowings		2,188.3	1,538.2
Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(2.7)	(5.9)	(1.9)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	0.5
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	1.8
Loans and Leases Receivable, Collateral for Secured Borrowings		794.9	213.9
Real Estate Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(80.5)	(138.7)	(69.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	28.9
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	28.5
Loans and Leases Receivable, Collateral for Secured Borrowings		13,456.2	6,731.4
Indirect consumer
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(16.7)	(15.3)	(14.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	4.5
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	8.8
Loans and Leases Receivable, Collateral for Secured Borrowings		829.7	737.6
Other consumer
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(4.6)	(5.2)	(4.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	2.9
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	3.0
Loans and Leases Receivable, Collateral for Secured Borrowings		152.9	129.2
Credit card consumer
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(2.6)	(2.8)	(2.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	2.5
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.3
Loans and Leases Receivable, Collateral for Secured Borrowings		75.9	64.9
Total consumer loans
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(23.9)	(23.3)	(21.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	9.9
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	12.1
Loans and Leases Receivable, Collateral for Secured Borrowings		1,058.5	931.7
Commercial Portfolio Segment [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(39.2)	(54.9)	(31.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	32.6
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	10.0
Loans and Leases Receivable, Collateral for Secured Borrowings		2,882.6	1,475.5
Agricultural Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(0.7)	(3.2)	(0.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	1.6
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.6
Loans and Leases Receivable, Collateral for Secured Borrowings		708.3	203.9
Other, including overdrafts
Loans and Leases Receivable
Loans and Leases Receivable, Collateral for Secured Borrowings		9.2	1.5
Loans held for investment
Loans and Leases Receivable
Loans and Leases Receivable, Collateral for Secured Borrowings		18,114.8	9,344.0
Non Owner Occupied Loans
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(25.5)	(27.2)	(17.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	8.8
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	4.9
Commercial Real Estate Owner Occupied
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(18.3)	(19.5)	(13.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	10.0
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	3.5
Commercial Real Estate Multifamily
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(11.0)	(27.9)	(13.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	0.7
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	6.9
Land Acquisition And Development Construction Financing Receivable [Member]
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(1.3)	(1.3)	(0.5)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	1.9
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.1
Loans and Leases Receivable, Collateral for Secured Borrowings		386.2	247.8
Construction Loans
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(10.2)	(36.1)	(8.9)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	6.1
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	0.3
Residential Real Estate 1-4 Family
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(11.4)	(20.5)	(13.4)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	1.8
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	(10.6)
Home Equity Loan
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(1.4)		(1.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	1.0
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	(0.5)
Residential Real Estate
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(12.8)	(22.1)	(14.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	2.8
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	(11.1)
Commercial and Floor Plans
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(34.2)	(49.0)	(27.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	25.5
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	5.1
Commercial Purpose Secured by 1-4 Family
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(4.7)	(5.7)	(4.4)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	5.9
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	3.8
Commercial Borrower
Loans and Leases Receivable
Accounts Receivable, Allowance for Credit Loss	(0.3)	$ (0.2)	$ (0.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance	1.2
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	$ 1.1