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Loans Held for Investment - Schedule of Contractual Aging of Loans by Portfolio (Details) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Accrued interest reversal | $ 0.0 | $ 0.0 |
Credit card |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.2 |  | $ 1.6
Nonaccrual Loans | 0.0 |  | 0.0
Total Loans | 64.1 |  | 70.2
Commercial real estate |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 10.4 |  | 12.8
Nonaccrual Loans | 8.8 |  | 9.6
Total Loans | 3,883.2 |  | 3,743.2
Indirect consumer |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 5.3 |  | 8.9
Nonaccrual Loans | 1.5 |  | 1.9
Total Loans | 756.8 |  | 805.1
Direct and advance lines |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.0 |  | 1.2
Nonaccrual Loans | 0.2 |  | 0.4
Total Loans | 132.9 |  | 150.6
Land acquisition & development |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.9 |  | 3.7
Nonaccrual Loans | 0.5 |  | 0.7
Total Loans | 260.2 |  | 265.0
Residential construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 1.9
Nonaccrual Loans | 0.0 |  | 1.1
Total Loans | 268.4 |  | 250.9
Commercial construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.9 |  | 12.2
Nonaccrual Loans | 0.0 |  | 0.1
Total Loans | 610.2 |  | 523.5
Total construction loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 2.8 |  | 17.8
Nonaccrual Loans | 0.5 |  | 1.9
Total Loans | 1,138.8 |  | 1,039.4
Residential |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 4.3 |  | 6.8
Nonaccrual Loans | 4.3 |  | 4.6
Total Loans | 1,554.9 |  | 1,396.3
Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.4 |  | 2.0
Nonaccrual Loans | 5.6 |  | 6.2
Total Loans | 229.9 |  | 220.6
Total real estate loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 18.9 |  | 39.4
Nonaccrual Loans | 19.2 |  | 22.3
Total Loans | 6,806.8 |  | 6,399.5
Total consumer loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 7.5 |  | 11.7
Nonaccrual Loans | 1.7 |  | 2.3
Total Loans | 953.8 |  | 1,025.9
Commercial |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 5.2 |  | 9.2
Nonaccrual Loans | 7.1 |  | 11.8
Total Loans | 1,668.7 |  | 2,153.9
Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.8 |  | 2.4
Nonaccrual Loans | 1.9 |  | 3.1
Total Loans | 212.4 |  | 247.6
Other, including overdrafts |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0
Nonaccrual Loans | 0.0 |  | 0.0
Total Loans | 1.3 |  | 1.6
Loans And Leases Held For Investment [Member] |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 32.4 |  | 62.7
Nonaccrual Loans | 29.9 |  | 39.5
Total Loans | 9,643.0 |  | 9,828.5
30 to 59 Days Past Due | Credit card |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.6 |  | 0.6
30 to 59 Days Past Due | Commercial real estate |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 6.1 |  | 7.6
30 to 59 Days Past Due | Indirect consumer |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 4.0 |  | 6.4
30 to 59 Days Past Due | Direct and advance lines |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.7 |  | 0.8
30 to 59 Days Past Due | Land acquisition & development |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.7 |  | 2.5
30 to 59 Days Past Due | Residential construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 1.5
30 to 59 Days Past Due | Commercial construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.9 |  | 12.2
30 to 59 Days Past Due | Total construction loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 2.6 |  | 16.2
30 to 59 Days Past Due | Residential |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 4.7
30 to 59 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 2.0
30 to 59 Days Past Due | Total real estate loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 8.9 |  | 30.5
30 to 59 Days Past Due | Total consumer loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 5.3 |  | 7.8
30 to 59 Days Past Due | Commercial |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 3.7 |  | 6.2
30 to 59 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.3 |  | 0.4
30 to 59 Days Past Due | Other, including overdrafts |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0
30 to 59 Days Past Due | Loans And Leases Held For Investment [Member] |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 18.2 |  | 44.9
60 to 89 Days Past Due | Credit card |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.4
60 to 89 Days Past Due | Commercial real estate |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 4.0 |  | 1.2
60 to 89 Days Past Due | Indirect consumer |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.1 |  | 2.0
60 to 89 Days Past Due | Direct and advance lines |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.2
60 to 89 Days Past Due | Land acquisition & development |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 1.1
60 to 89 Days Past Due | Residential construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.4
60 to 89 Days Past Due | Commercial construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0
60 to 89 Days Past Due | Total construction loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 1.5
60 to 89 Days Past Due | Residential |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 2.7 |  | 1.6
60 to 89 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.0
60 to 89 Days Past Due | Total real estate loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 6.9 |  | 4.3
60 to 89 Days Past Due | Total consumer loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.5 |  | 2.6
60 to 89 Days Past Due | Commercial |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.6 |  | 1.8
60 to 89 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.6
60 to 89 Days Past Due | Other, including overdrafts |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0
60 to 89 Days Past Due | Loans And Leases Held For Investment [Member] |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 9.0 |  | 9.3
Equal to or Greater than 90 Days Past Due | Credit card |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.4 |  | 0.6
Equal to or Greater than 90 Days Past Due | Commercial real estate |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.3 |  | 4.0
Equal to or Greater than 90 Days Past Due | Indirect consumer |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.5
Equal to or Greater than 90 Days Past Due | Direct and advance lines |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.1 |  | 0.2
Equal to or Greater than 90 Days Past Due | Land acquisition & development |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.1
Equal to or Greater than 90 Days Past Due | Residential construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0
Equal to or Greater than 90 Days Past Due | Commercial construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0
Equal to or Greater than 90 Days Past Due | Total construction loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.1
Equal to or Greater than 90 Days Past Due | Residential |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.4 |  | 0.5
Equal to or Greater than 90 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.2 |  | 0.0
Equal to or Greater than 90 Days Past Due | Total real estate loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 3.1 |  | 4.6
Equal to or Greater than 90 Days Past Due | Total consumer loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.7 |  | 1.3
Equal to or Greater than 90 Days Past Due | Commercial |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.9 |  | 1.2
Equal to or Greater than 90 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.5 |  | 1.4
Equal to or Greater than 90 Days Past Due | Other, including overdrafts |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0
Equal to or Greater than 90 Days Past Due | Loans And Leases Held For Investment [Member] |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 5.2 |  | 8.5
Financial Asset, Not Past Due | Credit card |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 62.9 |  | 68.6
Financial Asset, Not Past Due | Commercial real estate |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 3,864.0 |  | 3,720.8
Financial Asset, Not Past Due | Indirect consumer |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 750.0 |  | 794.3
Financial Asset, Not Past Due | Direct and advance lines |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 131.7 |  | 149.0
Financial Asset, Not Past Due | Land acquisition & development |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 258.8 |  | 260.6
Financial Asset, Not Past Due | Residential construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 268.4 |  | 247.9
Financial Asset, Not Past Due | Commercial construction |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 608.3 |  | 511.2
Financial Asset, Not Past Due | Total construction loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1,135.5 |  | 1,019.7
Financial Asset, Not Past Due | Residential |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1,546.3 |  | 1,384.9
Financial Asset, Not Past Due | Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 222.9 |  | 212.4
Financial Asset, Not Past Due | Total real estate loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 6,768.7 |  | 6,337.8
Financial Asset, Not Past Due | Total consumer loans |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 944.6 |  | 1,011.9
Financial Asset, Not Past Due | Commercial |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1,656.4 |  | 2,132.9
Financial Asset, Not Past Due | Agricultural |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 209.7 |  | 242.1
Financial Asset, Not Past Due | Other, including overdrafts |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | 1.3 |  | 1.6
Financial Asset, Not Past Due | Loans And Leases Held For Investment [Member] |  |  |
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items] |  |  |
Financing Receivable, Loan in Process | $ 9,580.7 |  | $ 9,726.3

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- Definition Amount of writeoff of accrued interest on financing receivable recognized by reversing interest income. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3D -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267969-210447 + Details
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