Loans Held for Investment - Schedule of Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense	$ 32.2	$ 82.7	$ (14.6)
Less loans charged-off	(35.9)	(45.0)	(16.6)
Recoveries Collected	12.4	14.9	9.3
Accounts Receivable, Allowance for Credit Loss	227.7	220.1	122.3	$ 144.3
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal)	31.1	68.4	(14.7)
Non Owner Occupied Loans
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		(4.2)	(8.3)
Less loans charged-off		(3.5)	0.0
Recoveries Collected		0.4	0.1
Accounts Receivable, Allowance for Credit Loss		27.2	17.3	25.5
Commercial Real Estate Owner Occupied
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		(2.7)	(2.7)
Less loans charged-off		(2.5)	(2.3)
Recoveries Collected		1.9	0.0
Accounts Receivable, Allowance for Credit Loss		19.5	13.3	18.3
Commercial Real Estate Multifamily
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		8.7	2.3
Less loans charged-off		(5.7)	0.0
Recoveries Collected		0.7	0.0
Accounts Receivable, Allowance for Credit Loss		27.9	13.3	11.0
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		1.8	(8.7)
Less loans charged-off	(7.6)	(11.7)	(2.3)
Recoveries Collected		3.0	0.1
Accounts Receivable, Allowance for Credit Loss		74.6	43.9	54.8
Land Acquisition And Development Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		(0.4)	(0.1)
Less loans charged-off		(2.6)	(1.2)
Recoveries Collected		0.4	0.5
Accounts Receivable, Allowance for Credit Loss		1.3	0.5	1.3
Residential Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		1.1	0.9
Less loans charged-off		0.0	(0.1)
Recoveries Collected		0.1	0.0
Accounts Receivable, Allowance for Credit Loss		3.6	2.4	1.6
Commercial Real Estate Construction [Member]
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		31.6	(1.3)
Less loans charged-off		(6.6)	(0.1)
Recoveries Collected		0.0	0.1
Accounts Receivable, Allowance for Credit Loss		31.2	6.0	7.3
Construction Loans
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		32.3	(0.5)
Less loans charged-off		(9.2)	(1.4)
Recoveries Collected		0.5	0.6
Accounts Receivable, Allowance for Credit Loss		36.1	8.9	10.2
Residential Real Estate 1-4 Family
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		6.9	2.0
Less loans charged-off		(0.2)	0.0
Recoveries Collected		0.3	0.0
Accounts Receivable, Allowance for Credit Loss		20.5	13.4	11.4
Residential Real Estate
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		6.9	1.6
Less loans charged-off	(0.6)	(0.3)	(0.1)
Recoveries Collected		0.8	0.3
Accounts Receivable, Allowance for Credit Loss		22.1	14.6	12.8
Agricultural Real Estate Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		1.5	(0.1)
Less loans charged-off	0.0	(0.2)	(0.7)
Recoveries Collected		0.4	0.0
Accounts Receivable, Allowance for Credit Loss		5.9	1.9	2.7
Real Estate Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense	35.2	42.5	(7.7)
Less loans charged-off	(18.5)	(21.4)	(4.5)
Recoveries Collected	4.7	4.7	1.0
Accounts Receivable, Allowance for Credit Loss	160.1	138.7	69.3	80.5
Indirect consumer
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		2.7	(1.4)
Less loans charged-off	(7.3)	(4.0)	(3.5)
Recoveries Collected		2.3	2.5
Accounts Receivable, Allowance for Credit Loss		15.3	14.3	16.7
Other consumer
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		2.2	1.7
Less loans charged-off	(4.1)	(3.7)	(2.9)
Recoveries Collected		2.1	1.2
Accounts Receivable, Allowance for Credit Loss		5.2	4.6	4.6
Credit card consumer
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		2.4	0.6
Less loans charged-off	(2.6)	(2.4)	(1.8)
Recoveries Collected		0.6	0.8
Accounts Receivable, Allowance for Credit Loss		2.8	2.2	2.6
Total consumer loans
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense	(1.0)	7.3	0.9
Less loans charged-off	(14.0)	(10.1)	(8.2)
Recoveries Collected	4.7	5.0	4.5
Accounts Receivable, Allowance for Credit Loss	13.0	23.3	21.1	23.9
Commercial and Floor Plans
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		15.1	(7.3)
Less loans charged-off		(6.6)	(3.0)
Recoveries Collected		2.2	3.2
Accounts Receivable, Allowance for Credit Loss		49.0	27.1	34.2
Commercial Purpose Secured by 1-4 Family
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		1.2	(0.5)
Less loans charged-off		(0.2)	(0.3)
Recoveries Collected		0.1	0.5
Accounts Receivable, Allowance for Credit Loss		5.7	4.4	4.7
Commercial Borrower
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		1.4	0.1
Less loans charged-off		(1.3)	(0.4)
Recoveries Collected		0.0	0.1
Accounts Receivable, Allowance for Credit Loss		0.2	0.1	0.3
Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense	(3.9)	17.7	(7.7)
Less loans charged-off	(3.4)	(8.1)	(3.7)
Recoveries Collected	2.6	2.3	3.8
Accounts Receivable, Allowance for Credit Loss	50.2	54.9	31.6	39.2
Agricultural Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense	0.8	0.9	(0.2)
Less loans charged-off	0.0	(5.4)	(0.2)
Recoveries Collected	0.4	2.9	0.0
Accounts Receivable, Allowance for Credit Loss	$ 4.4	3.2	0.3	0.7
Home Equity Loan
Financing Receivable, Allowance for Credit Losses
Provision charged (credited) to operating expense		0.0	(0.4)
Less loans charged-off		(0.1)	(0.1)
Recoveries Collected		0.5	0.3
Accounts Receivable, Allowance for Credit Loss		$ 1.6	$ 1.2	$ 1.4