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Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 | Dec. 31, 2019 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2018
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |
Loans and Leases Receivable, Impaired, Troubled Debt, Interest Income | $ 3.0 | $ 2.5 |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 87.4 | $ 107.9 |  | $ 83.0
Recorded Investment With No Allowance |  | 37.2 | 51.4 |  | 36.0
Recorded Investment With Allowance |  | 27.5 | 31.8 |  | 28.8
Total Recorded Investment |  | 64.7 | 83.2 |  | 64.8
Related Allowance |  | 3.6 | 10.8 |  | 6.8
Average Recorded Investment | 74.0 | 64.7 |  | $ 94.0 |
Income Recognized | 0.3 | 0.3 |  | 0.5 |
Impaired Loans, interest lost on nonaccrual loans |  |  | 3.5 |  |
Commercial |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 29.2 | 45.6 |  | 22.2
Recorded Investment With No Allowance |  | 12.9 | 20.9 |  | 8.6
Recorded Investment With Allowance |  | 10.8 | 14.1 |  | 7.7
Total Recorded Investment |  | 23.7 | 35.0 |  | 16.3
Related Allowance |  | 0.7 | 3.9 |  | 0.7
Land Acquisition & Development Construction Financing Receivable [Member] |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  |  | 10.0 |  |
Recorded Investment With No Allowance |  |  | 3.4 |  |
Recorded Investment With Allowance |  |  | 0.5 |  |
Total Recorded Investment |  |  | 3.9 |  |
Related Allowance |  |  | 0.0 |  |
Land Acquisition And Development Construction Financing Receivable [Member] |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 9.2 |  |  | 10.0
Recorded Investment With No Allowance |  | 0.4 |  |  | 0.4
Recorded Investment With Allowance |  | 2.6 |  |  | 3.5
Total Recorded Investment |  | 3.0 |  |  | 3.9
Related Allowance |  | 0.5 |  |  | 0.2
Residential |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 0.1 | 1.8 |  | 1.1
Recorded Investment With No Allowance |  | 0.0 | 1.7 |  | 0.6
Recorded Investment With Allowance |  | 0.0 | 0.0 |  | 0.4
Total Recorded Investment |  | 0.0 | 1.7 |  | 1.0
Related Allowance |  | 0.0 | 0.0 |  | 0.1
Commercial |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 1.0 | 4.7 |  | 0.7
Recorded Investment With No Allowance |  | 0.5 | 0.4 |  | 0.2
Recorded Investment With Allowance |  | 0.0 | 3.5 |  | 0.0
Total Recorded Investment |  | 0.5 | 3.9 |  | 0.2
Related Allowance |  | 0.1 | 2.2 |  | 0.0
Total construction loans |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 10.3 | 16.5 |  | 11.8
Recorded Investment With No Allowance |  | 0.9 | 5.5 |  | 1.2
Recorded Investment With Allowance |  | 2.6 | 4.0 |  | 3.9
Total Recorded Investment |  | 3.5 | 9.5 |  | 5.1
Related Allowance |  | 0.6 | 2.2 |  | 0.3
Residential |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 6.9 | 11.5 |  | 8.8
Recorded Investment With No Allowance |  | 3.9 | 8.2 |  | 5.7
Recorded Investment With Allowance |  | 1.8 | 2.0 |  | 2.0
Total Recorded Investment |  | 5.7 | 10.2 |  | 7.7
Related Allowance |  | 0.2 | 0.1 |  | 0.3
Agricultural |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 8.6 | 3.7 |  | 12.9
Recorded Investment With No Allowance |  | 5.2 | 3.6 |  | 12.5
Recorded Investment With Allowance |  | 3.0 | 0.0 |  | 0.2
Total Recorded Investment |  | 8.2 | 3.6 |  | 12.7
Related Allowance |  | 0.2 | 0.0 |  | 0.0
Total real estate loans |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 55.0 | 77.3 |  | 55.7
Recorded Investment With No Allowance |  | 22.9 | 38.2 |  | 28.0
Recorded Investment With Allowance |  | 18.2 | 20.1 |  | 13.8
Total Recorded Investment |  | 41.1 | 58.3 |  | 41.8
Related Allowance |  | 1.7 | 6.2 |  | 1.3
Average Recorded Investment | 50.0 | 41.4 |  | 63.5 |
Income Recognized | 0.1 | 0.1 |  | 0.3 |
Commercial |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 25.5 | 29.5 |  | 24.1
Recorded Investment With No Allowance |  | 12.0 | 12.4 |  | 5.5
Recorded Investment With Allowance |  | 5.3 | 11.4 |  | 14.4
Total Recorded Investment |  | 17.3 | 23.8 |  | 19.9
Related Allowance |  | 1.7 | 4.4 |  | 5.2
Average Recorded Investment | 21.9 | 18.7 |  | 28.1 |
Income Recognized | 0.2 | 0.2 |  | 0.2 |
Agricultural |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance |  | 6.9 | 1.1 |  | 3.2
Recorded Investment With No Allowance |  | 2.3 | 0.8 |  | 2.5
Recorded Investment With Allowance |  | 4.0 | 0.3 |  | 0.6
Total Recorded Investment |  | 6.3 | 1.1 |  | 3.1
Related Allowance |  | 0.2 | $ 0.2 |  | $ 0.3
Average Recorded Investment | 2.1 | 4.6 |  | 2.4 |
Income Recognized | $ 0.0 | $ 0.0 |  | $ 0.0 |

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