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Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | $ 97.6 |  | $ 97.6 |  | $ 107.9
Recorded Investment With No Allowance | 41.5 |  | 41.5 |  | 51.4
Recorded Investment With Allowance | 40.2 |  | 40.2 |  | 31.8
Total Recorded Investment | 81.7 |  | 81.7 |  | 83.2
Related Allowance | 10.5 |  | 10.5 |  | 10.8
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income |  |  |  |  |
Average Recorded Investment | 79.0 | $ 97.5 | 82.5 | $ 101.0 |
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract] |  |  |  |  |
Income Recognized | 0.2 | 0.2 | 0.2 | 0.4 |
Commercial |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 38.2 |  | 38.2 |  | 45.6
Recorded Investment With No Allowance | 13.0 |  | 13.0 |  | 20.9
Recorded Investment With Allowance | 15.6 |  | 15.6 |  | 14.1
Total Recorded Investment | 28.6 |  | 28.6 |  | 35.0
Related Allowance | 3.3 |  | 3.3 |  | 3.9
Land acquisition & development |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 5.8 |  | 5.8 |  | 10.0
Recorded Investment With No Allowance | 1.7 |  | 1.7 |  | 3.4
Recorded Investment With Allowance | 3.3 |  | 3.3 |  | 0.5
Total Recorded Investment | 5.0 |  | 5.0 |  | 3.9
Related Allowance | 0.2 |  | 0.2 |  | 0.0
Residential |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 0.6 |  | 0.6 |  | 1.8
Recorded Investment With No Allowance | 0.5 |  | 0.5 |  | 1.7
Recorded Investment With Allowance | 0.3 |  | 0.3 |  | 0.0
Total Recorded Investment | 0.8 |  | 0.8 |  | 1.7
Related Allowance | 0.0 |  | 0.0 |  | 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 | 3.4 |  | 3.4 |  | 3.5
Total Recorded Investment | 3.6 |  | 3.6 |  | 3.9
Related Allowance | 2.1 |  | 2.1 |  | 2.2
Total construction loans |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 10.8 |  | 10.8 |  | 16.5
Recorded Investment With No Allowance | 2.4 |  | 2.4 |  | 5.5
Recorded Investment With Allowance | 7.0 |  | 7.0 |  | 4.0
Total Recorded Investment | 9.4 |  | 9.4 |  | 9.5
Related Allowance | 2.3 |  | 2.3 |  | 2.2
Residential |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 9.2 |  | 9.2 |  | 11.5
Recorded Investment With No Allowance | 6.1 |  | 6.1 |  | 8.2
Recorded Investment With Allowance | 1.8 |  | 1.8 |  | 2.0
Total Recorded Investment | 7.9 |  | 7.9 |  | 10.2
Related Allowance | 0.3 |  | 0.3 |  | 0.1
Agricultural |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 13.2 |  | 13.2 |  | 3.7
Recorded Investment With No Allowance | 13.0 |  | 13.0 |  | 3.6
Recorded Investment With Allowance | 0.0 |  | 0.0 |  | 0.0
Total Recorded Investment | 13.0 |  | 13.0 |  | 3.6
Related Allowance | 0.0 |  | 0.0 |  | 0.0
Total real estate loans |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 71.4 |  | 71.4 |  | 77.3
Recorded Investment With No Allowance | 34.5 |  | 34.5 |  | 38.2
Recorded Investment With Allowance | 24.4 |  | 24.4 |  | 20.1
Total Recorded Investment | 58.9 |  | 58.9 |  | 58.3
Related Allowance | 5.9 |  | 5.9 |  | 6.2
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income |  |  |  |  |
Average Recorded Investment | 56.4 | 62.9 | 58.6 | 65.5 |
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract] |  |  |  |  |
Income Recognized | 0.1 | 0.1 | 0.1 | 0.3 |
Commercial |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 24.4 |  | 24.4 |  | 29.5
Recorded Investment With No Allowance | 5.7 |  | 5.7 |  | 12.4
Recorded Investment With Allowance | 15.4 |  | 15.4 |  | 11.4
Total Recorded Investment | 21.1 |  | 21.1 |  | 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 | 32.5 | 22.5 | 32.2 |
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract] |  |  |  |  |
Income Recognized | 0.1 | 0.1 | 0.1 | 0.1 |
Agricultural |  |  |  |  |
Impaired Financing Receivable, Unpaid Principal Balance |  |  |  |  |
Unpaid Total Principal Balance | 1.8 |  | 1.8 |  | 1.1
Recorded Investment With No Allowance | 1.3 |  | 1.3 |  | 0.8
Recorded Investment With Allowance | 0.4 |  | 0.4 |  | 0.3
Total Recorded Investment | 1.7 |  | 1.7 |  | 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 | 2.1 | 1.4 | 3.3 |
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract] |  |  |  |  |
Income Recognized | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 |

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