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Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | $ 92.5 |  | $ 92.5 |  | $ 107.9
Recorded Investment With No Allowance | 38.7 |  | 38.7 |  | 51.4
Recorded Investment With Allowance | 33.7 |  | 33.7 |  | 31.8
Total Recorded Investment | 72.4 |  | 72.4 |  | 83.2
Related Allowance | 8.2 |  | 8.2 |  | 10.8
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income |  |  |  |  |
Average Recorded Investment | 77.1 | $ 93.8 | 77.7 | $ 97.5 |
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract] |  |  |  |  |
Income Recognized | 0.0 | 0.1 | 0.2 | 0.5 |
Commercial |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 29.1 |  | 29.1 |  | 45.6
Recorded Investment With No Allowance | 12.5 |  | 12.5 |  | 20.9
Recorded Investment With Allowance | 8.7 |  | 8.7 |  | 14.1
Total Recorded Investment | 21.2 |  | 21.2 |  | 35.0
Related Allowance | 1.7 |  | 1.7 |  | 3.9
Land acquisition & development |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 10.4 |  | 10.4 |  | 10.0
Recorded Investment With No Allowance | 0.7 |  | 0.7 |  | 3.4
Recorded Investment With Allowance | 3.5 |  | 3.5 |  | 0.5
Total Recorded Investment | 4.2 |  | 4.2 |  | 3.9
Related Allowance | 0.2 |  | 0.2 |  | 0.0
Residential |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 0.7 |  | 0.7 |  | 1.8
Recorded Investment With No Allowance | 0.2 |  | 0.2 |  | 1.7
Recorded Investment With Allowance | 0.4 |  | 0.4 |  | 0.0
Total Recorded Investment | 0.6 |  | 0.6 |  | 1.7
Related Allowance | 0.1 |  | 0.1 |  | 0.0
Commercial |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 4.4 |  | 4.4 |  | 4.7
Recorded Investment With No Allowance | 0.2 |  | 0.2 |  | 0.4
Recorded Investment With Allowance | 3.3 |  | 3.3 |  | 3.5
Total Recorded Investment | 3.5 |  | 3.5 |  | 3.9
Related Allowance | 1.2 |  | 1.2 |  | 2.2
Total construction loans |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 15.5 |  | 15.5 |  | 16.5
Recorded Investment With No Allowance | 1.1 |  | 1.1 |  | 5.5
Recorded Investment With Allowance | 7.2 |  | 7.2 |  | 4.0
Total Recorded Investment | 8.3 |  | 8.3 |  | 9.5
Related Allowance | 1.5 |  | 1.5 |  | 2.2
Residential |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 8.8 |  | 8.8 |  | 11.5
Recorded Investment With No Allowance | 5.6 |  | 5.6 |  | 8.2
Recorded Investment With Allowance | 2.1 |  | 2.1 |  | 2.0
Total Recorded Investment | 7.7 |  | 7.7 |  | 10.2
Related Allowance | 0.4 |  | 0.4 |  | 0.1
Agricultural |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 12.8 |  | 12.8 |  | 3.7
Recorded Investment With No Allowance | 12.6 |  | 12.6 |  | 3.6
Recorded Investment With Allowance | 0.0 |  | 0.0 |  | 0.0
Total Recorded Investment | 12.6 |  | 12.6 |  | 3.6
Related Allowance | 0.0 |  | 0.0 |  | 0.0
Total real estate loans |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 66.2 |  | 66.2 |  | 77.3
Recorded Investment With No Allowance | 31.8 |  | 31.8 |  | 38.2
Recorded Investment With Allowance | 18.0 |  | 18.0 |  | 20.1
Total Recorded Investment | 49.8 |  | 49.8 |  | 58.3
Related Allowance | 3.6 |  | 3.6 |  | 6.2
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income |  |  |  |  |
Average Recorded Investment | 54.5 | 59.9 | 54.1 | 63.0 |
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract] |  |  |  |  |
Income Recognized | 0.0 | 0.1 | 0.1 | 0.4 |
Commercial |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 24.1 |  | 24.1 |  | 29.5
Recorded Investment With No Allowance | 5.2 |  | 5.2 |  | 12.4
Recorded Investment With Allowance | 15.2 |  | 15.2 |  | 11.4
Total Recorded Investment | 20.4 |  | 20.4 |  | 23.8
Related Allowance | 4.4 |  | 4.4 |  | 4.4
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income |  |  |  |  |
Average Recorded Investment | 20.7 | 31.6 | 22.0 | 31.9 |
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract] |  |  |  |  |
Income Recognized | 0.0 | 0.0 | 0.1 | 0.1 |
Agricultural |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 2.2 |  | 2.2 |  | 1.1
Recorded Investment With No Allowance | 1.7 |  | 1.7 |  | 0.8
Recorded Investment With Allowance | 0.5 |  | 0.5 |  | 0.3
Total Recorded Investment | 2.2 |  | 2.2 |  | 1.1
Related Allowance | 0.2 |  | 0.2 |  | $ 0.2
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income |  |  |  |  |
Average Recorded Investment | 1.9 | 2.3 | 1.6 | 2.6 |
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract] |  |  |  |  |
Income Recognized | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 |

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