Loans Held for Investment - Schedule of Allowance for Credit Losses for Loans Held for Investment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 247.2	$ 136.6	$ 122.3	$ 144.3
Provision charged to operating expense	(1.7)	0.0	59.6	(5.1)
Loans Charged-Off	(3.7)	(4.8)	(23.6)	(9.7)
Ending balance	220.4	135.5	220.4	135.5
Financing Receivable, Allowance for Credit Loss, Recovery	3.4	3.7	6.6	5.7
Commercial Real Estate Non Owner Occupied Loans [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	45.2	23.0	17.3	25.5
Provision charged to operating expense	(8.8)	(0.2)	(2.1)	(2.7)
Loans Charged-Off	0.0	0.0	(2.9)	0.0
Ending balance	29.5	22.9	29.5	22.9
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	0.1	0.0	0.1
Agricultural Financing Receivable [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	(1.0)	0.6	0.3	0.7
Provision charged to operating expense	6.3	0.0	5.8	(0.1)
Loans Charged-Off	(0.1)	(0.2)	(5.4)	(0.2)
Ending balance	6.5	0.4	6.5	0.4
Financing Receivable, Allowance for Credit Loss, Recovery	0.2	0.0	1.3	0.0
Commercial and Floor Plans [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	52.9	31.0	27.1	34.2
Provision charged to operating expense	1.9	(3.4)	20.3	(5.2)
Loans Charged-Off	(1.1)	(0.3)	(5.3)	(2.1)
Ending balance	54.1	29.0	54.1	29.0
Financing Receivable, Allowance for Credit Loss, Recovery	0.4	1.7	0.8	2.1
Commercial Real Estate Owner Occupied [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	25.2	17.4	13.3	18.3
Provision charged to operating expense	1.4	1.4	6.0	0.6
Loans Charged-Off	0.0	(2.2)	(2.2)	(2.3)
Ending balance	26.6	16.6	26.6	16.6
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	0.0	0.0	0.0
Commercial Real Estate Multi-family [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	54.6	11.8	13.3	11.0
Provision charged to operating expense	(2.9)	(0.2)	8.5	0.6
Loans Charged-Off	0.0	0.0	0.0	0.0
Ending balance	33.4	11.6	33.4	11.6
Financing Receivable, Allowance for Credit Loss, Recovery	0.7	0.0	0.7	0.0
Commercial real estate
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	125.0	52.2	43.9	54.8
Provision charged to operating expense	(10.3)	1.0	12.4	(1.5)
Loans Charged-Off	0.0	(2.2)	(5.1)	(2.3)
Ending balance	89.5	51.1	89.5	51.1
Financing Receivable, Allowance for Credit Loss, Recovery	0.7	0.1	0.7	0.1
Land Acquisition And Development Construction Financing Receivable [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0.5	1.2	0.5	1.3
Provision charged to operating expense	0.2	(0.4)	(0.6)	(0.6)
Loans Charged-Off	0.0	(0.1)	(2.7)	(0.1)
Ending balance	0.8	1.0	0.8	1.0
Financing Receivable, Allowance for Credit Loss, Recovery	0.1	0.3	0.2	0.4
Residential construction
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3.3	1.4	2.4	1.6
Provision charged to operating expense	0.1	0.2	1.0	0.0
Loans Charged-Off	0.0	(0.1)	0.0	(0.1)
Ending balance	3.4	1.5	3.4	1.5
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	0.0	0.0	0.0
Commercial construction
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	10.2	7.2	6.0	7.3
Provision charged to operating expense	4.7	0.9	8.7	0.7
Loans Charged-Off	0.0	(0.1)	0.0	(0.1)
Ending balance	14.9	8.0	14.9	8.0
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	0.0	0.0	0.1
Construction Loans [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	14.0	9.8	8.9	10.2
Provision charged to operating expense	5.0	0.7	9.1	0.1
Loans Charged-Off	0.0	(0.3)	(2.7)	(0.3)
Ending balance	19.1	10.5	19.1	10.5
Financing Receivable, Allowance for Credit Loss, Recovery	0.1	0.3	0.2	0.5
Residential Real Estate 1-4 Family [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	18.7	11.5	13.4	11.4
Provision charged to operating expense	(0.7)	1.9	4.5	2.0
Loans Charged-Off	0.0	0.0	(0.1)	0.0
Ending balance	18.2	13.4	18.2	13.4
Financing Receivable, Allowance for Credit Loss, Recovery	0.2	0.0	0.3	0.0
Home Equity Line of Credit [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1.4	1.4	1.2	1.4
Provision charged to operating expense	(0.1)	(0.1)	0.0	(0.1)
Loans Charged-Off	0.0	0.0	0.0	(0.1)
Ending balance	1.5	1.4	1.5	1.4
Financing Receivable, Allowance for Credit Loss, Recovery	0.2	0.1	0.3	0.2
Residential Real Estate [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	20.1	12.9	14.6	12.8
Provision charged to operating expense	(0.8)	1.8	4.5	1.9
Loans Charged-Off	0.0	0.0	(0.1)	(0.1)
Ending balance	19.7	14.8	19.7	14.8
Financing Receivable, Allowance for Credit Loss, Recovery	0.4	0.1	0.6	0.2
Agricultural Real Estate Financing Receivable [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	10.5	2.8	1.9	2.7
Provision charged to operating expense	(5.1)	0.2	1.3	0.3
Loans Charged-Off	(0.1)	0.0	(0.2)	0.0
Ending balance	5.4	3.0	5.4	3.0
Financing Receivable, Allowance for Credit Loss, Recovery	0.1	0.0	0.1	0.0
Real Estate Financing Receivable [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	169.6	77.7	69.3	80.5
Provision charged to operating expense	(11.2)	3.7	27.3	0.8
Loans Charged-Off	(0.1)	(2.5)	(8.1)	(2.7)
Ending balance	133.7	79.4	133.7	79.4
Financing Receivable, Allowance for Credit Loss, Recovery	1.3	0.5	1.6	0.8
Consumer Indirect Financing Receivable [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	13.5	16.0	14.3	16.7
Provision charged to operating expense	(0.4)	(0.2)	(0.7)	(0.2)
Loans Charged-Off	(0.8)	(0.8)	(1.7)	(2.1)
Ending balance	13.1	15.8	13.1	15.8
Financing Receivable, Allowance for Credit Loss, Recovery	0.8	0.8	1.2	1.4
Direct consumer
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	4.6	4.8	4.6	4.6
Provision charged to operating expense	0.5	0.0	0.4	0.7
Loans Charged-Off	(0.6)	(0.4)	(1.4)	(1.2)
Ending balance	5.0	4.6	5.0	4.6
Financing Receivable, Allowance for Credit Loss, Recovery	0.5	0.2	1.4	0.5
Credit Card Receivable [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2.3	1.5	2.2	2.6
Provision charged to operating expense	0.7	0.3	1.3	(0.4)
Loans Charged-Off	(0.9)	(0.4)	(1.5)	(1.0)
Ending balance	2.2	1.6	2.2	1.6
Financing Receivable, Allowance for Credit Loss, Recovery	0.1	0.2	0.2	0.4
Consumer
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	20.4	22.3	21.1	23.9
Provision charged to operating expense	0.8	0.1	1.0	0.1
Loans Charged-Off	(2.3)	(1.6)	(4.6)	(4.3)
Ending balance	20.3	22.0	20.3	22.0
Financing Receivable, Allowance for Credit Loss, Recovery	1.4	1.2	2.8	2.3
Commercial Purpose secured by 1-4 Family [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	5.0	4.7	4.4	4.7
Provision charged to operating expense	0.4	(0.4)	0.8	(0.6)
Loans Charged-Off	0.0	(0.1)	0.0	(0.1)
Ending balance	5.5	4.4	5.5	4.4
Financing Receivable, Allowance for Credit Loss, Recovery	0.1	0.2	0.1	0.4
Commercial Borrower [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0.3	0.3	0.1	0.3
Provision charged to operating expense	0.1	0.0	0.4	0.2
Loans Charged-Off	(0.1)	(0.1)	(0.2)	(0.3)
Ending balance	0.3	0.3	0.3	0.3
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	0.1	0.0	0.1
Commercial Portfolio Segment [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	58.2	36.0	31.6	39.2
Provision charged to operating expense	2.4	(3.8)	21.5	(5.6)
Loans Charged-Off	(1.2)	(0.5)	(5.5)	(2.5)
Ending balance	59.9	33.7	59.9	33.7
Financing Receivable, Allowance for Credit Loss, Recovery	$ 0.5	$ 2.0	$ 0.9	$ 2.6