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Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | $ 8,480.3 | $ 7,567.7
Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3,213.1 | 2,822.9
Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 314.5 | 348.7
Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 250.6 | 240.2
Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 219.6 | 119.4
Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 784.7 | 708.3
Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1,581.2 | 1,487.4
Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 217.8 | 158.2
Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 5,796.8 | 5,176.8
Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 800.8 | 784.7
Other consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 198.1 | 175.1
Credit card |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 79.4 | 74.6
Total consumer loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1,078.3 | 1,034.4
Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1,337.2 | 1,215.4
Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 264.8 | 136.2
Other Assets Especially Mentioned |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 198.9 | 155.1
Other Assets Especially Mentioned | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 108.1 | 78.0
Other Assets Especially Mentioned | Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 5.4 | 3.2
Other Assets Especially Mentioned | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 4.1 | 2.3
Other Assets Especially Mentioned | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1.5 | 2.4
Other Assets Especially Mentioned | Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 11.0 | 7.9
Other Assets Especially Mentioned | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 5.5 | 3.9
Other Assets Especially Mentioned | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 8.4 | 4.3
Other Assets Especially Mentioned | Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 133.0 | 94.1
Other Assets Especially Mentioned | Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.8 | 0.8
Other Assets Especially Mentioned | Other consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.4 | 0.4
Other Assets Especially Mentioned | Total consumer loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1.2 | 1.2
Other Assets Especially Mentioned | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 50.6 | 54.7
Other Assets Especially Mentioned | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 14.1 | 5.1
Substandard |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 201.1 | 217.2
Substandard | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 81.4 | 96.4
Substandard | Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 7.0 | 16.4
Substandard | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.3 | 1.7
Substandard | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3.7 | 3.6
Substandard | Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 11.0 | 21.7
Substandard | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 11.0 | 12.5
Substandard | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 24.6 | 19.1
Substandard | Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 128.0 | 149.7
Substandard | Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 2.2 | 2.2
Substandard | Other consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.8 | 0.7
Substandard | Total consumer loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3.0 | 2.9
Substandard | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 48.6 | 56.3
Substandard | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 21.5 | 8.3
Doubtful |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 24.9 | 28.2
Doubtful | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 4.8 | 10.3
Doubtful | Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3.3 | 0.0
Doubtful | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.4 | 0.5
Doubtful | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3.4 | 3.5
Doubtful | Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 7.1 | 4.0
Doubtful | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1.1 | 1.9
Doubtful | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.0 | 0.0
Doubtful | Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 13.0 | 16.2
Doubtful | Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.1 | 0.3
Doubtful | Other consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.1 | 0.2
Doubtful | Total consumer loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.2 | 0.5
Doubtful | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 11.2 | 11.1
Doubtful | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.5 | 0.4
Total Criticized Loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 424.9 | 400.5
Total Criticized Loans | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 194.3 | 184.7
Total Criticized Loans | Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 15.7 | 19.6
Total Criticized Loans | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 4.8 | 4.5
Total Criticized Loans | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 8.6 | 9.5
Total Criticized Loans | Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 29.1 | 33.6
Total Criticized Loans | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 17.6 | 18.3
Total Criticized Loans | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 33.0 | 23.4
Total Criticized Loans | Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 274.0 | 260.0
Total Criticized Loans | Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3.1 | 3.3
Total Criticized Loans | Other consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1.3 | 1.3
Total Criticized Loans | Total consumer loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 4.4 | 4.6
Total Criticized Loans | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 110.4 | 122.1
Total Criticized Loans | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | $ 36.1 | $ 13.8

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