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Allowance for Loan Losses - Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | $ 72.1 | $ 76.2 | $ 76.8 |  |  |
Provision charged (credited) to operating expense | 8.6 | 11.0 | 10.0 |  |  |
Less loans charged-off | (19.7) | (22.8) | (19.8) |  |  |
Add back recoveries of loans previously charged-off | 12.0 | 7.7 | 9.2 |  |  |
Ending balance | 73.0 | 72.1 | 76.2 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | $ 6.8 | $ 10.8 | $ 14.0
Collectively evaluated for impairment |  |  |  | 66.2 | 61.3 | 62.2
Ending balance | 72.1 | 76.2 | 76.8 | 73.0 | 72.1 | 76.2
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 64.8 | 83.2 | 104.7
Collectively evaluated for impairment |  |  |  | 8,405.6 | 7,484.5 | 5,312.0
Total loans held for investment |  |  |  | 8,470.4 | 7,567.7 | 5,416.7
Allowance for loans losses |  |  |  | 0.8 | 1.0 |
Real Estate |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 31.7 | 28.6 | 52.3 |  |  |
Provision charged (credited) to operating expense | (0.7) | 6.0 | (21.7) |  |  |
Less loans charged-off | (3.7) | (4.3) | (5.2) |  |  |
Add back recoveries of loans previously charged-off | 3.7 | 1.4 | 3.2 |  |  |
Ending balance | 31.0 | 31.7 | 28.6 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 1.3 | 6.2 | 4.6
Collectively evaluated for impairment |  |  |  | 29.7 | 25.5 | 24.0
Ending balance | 31.7 | 28.6 | 52.3 | 31.0 | 31.7 | 28.6
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 41.8 | 58.3 | 68.6
Collectively evaluated for impairment |  |  |  | 5,791.7 | 5,118.5 | 3,445.4
Total loans held for investment |  |  |  | 5,833.5 | 5,176.8 | 3,514.0
Consumer |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 8.7 | 7.7 | 5.1 |  |  |
Provision charged (credited) to operating expense | 6.8 | 8.1 | 8.4 |  |  |
Less loans charged-off | (11.3) | (11.3) | (8.6) |  |  |
Add back recoveries of loans previously charged-off | 4.5 | 4.2 | 2.8 |  |  |
Ending balance | 8.7 | 8.7 | 7.7 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0.0 | 0.0 | 0.0
Collectively evaluated for impairment |  |  |  | 8.7 | 8.7 | 7.7
Ending balance | 8.7 | 7.7 | 5.1 | 8.7 | 8.7 | 7.7
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0.0 | 0.0 | 0.0
Collectively evaluated for impairment |  |  |  | 1,070.2 | 1,034.4 | 970.3
Total loans held for investment |  |  |  | 1,070.2 | 1,034.4 | 970.3
Commercial |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 30.5 | 38.1 | 18.8 |  |  |
Provision charged (credited) to operating expense | 1.9 | (2.9) | 21.9 |  |  |
Less loans charged-off | (4.7) | (6.8) | (5.8) |  |  |
Add back recoveries of loans previously charged-off | 3.6 | 2.1 | 3.2 |  |  |
Ending balance | 31.3 | 30.5 | 38.1 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 5.2 | 4.4 | 9.3
Collectively evaluated for impairment |  |  |  | 26.1 | 26.1 | 28.8
Ending balance | 30.5 | 38.1 | 18.8 | 31.3 | 30.5 | 38.1
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 19.9 | 23.8 | 32.4
Collectively evaluated for impairment |  |  |  | 1,290.4 | 1,191.6 | 765.5
Total loans held for investment |  |  |  | 1,310.3 | 1,215.4 | 797.9
Agriculture |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 1.2 | 1.8 | 0.6 |  |  |
Provision charged (credited) to operating expense | 0.6 | (0.2) | 1.4 |  |  |
Less loans charged-off | 0.0 | (0.4) | (0.2) |  |  |
Add back recoveries of loans previously charged-off | 0.2 | 0.0 | 0.0 |  |  |
Ending balance | 2.0 | 1.2 | 1.8 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0.3 | 0.2 | 0.1
Collectively evaluated for impairment |  |  |  | 1.7 | 1.0 | 1.7
Ending balance | 1.2 | 1.8 | 0.6 | 2.0 | 1.2 | 1.8
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 3.1 | 1.1 | 3.7
Collectively evaluated for impairment |  |  |  | 251.7 | 135.1 | 129.2
Total loans held for investment |  |  |  | 254.8 | 136.2 | 132.9
Other |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 0.0 | 0.0 | 0.0 |  |  |
Provision charged (credited) to operating expense | 0.0 | 0.0 | 0.0 |  |  |
Less loans charged-off | 0.0 | 0.0 | 0.0 |  |  |
Add back recoveries of loans previously charged-off | 0.0 | 0.0 | 0.0 |  |  |
Ending balance | 0.0 | 0.0 | 0.0 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0.0 | 0.0 | 0.0
Collectively evaluated for impairment |  |  |  | 0.0 | 0.0 | 0.0
Ending balance | $ 0.0 | $ 0.0 | $ 0.0 | 0.0 | 0.0 | 0.0
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0.0 | 0.0 | 0.0
Collectively evaluated for impairment |  |  |  | 1.6 | 4.9 | 1.6
Total loans held for investment |  |  |  | $ 1.6 | $ 4.9 | $ 1.6

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- Definition Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524 + Details
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- Definition Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows previously expected. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 15 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544 + Details
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