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Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | $ 7,614.5 | $ 7,567.7
Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 2,821.9 | 2,822.9
Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 364.6 | 348.7
Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 230.6 | 240.2
Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 140.8 | 119.4
Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 736.0 | 708.3
Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1,486.6 | 1,487.4
Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 156.9 | 158.2
Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 5,201.4 | 5,176.8
Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 782.9 | 784.7
Other consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 173.0 | 175.1
Credit card |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 75.2 | 74.6
Total consumer loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1,031.1 | 1,034.4
Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1,244.1 | 1,215.4
Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 133.9 | 136.2
Other Assets Especially Mentioned |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 159.5 | 155.1
Other Assets Especially Mentioned | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 76.7 | 78.0
Other Assets Especially Mentioned | Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 5.5 | 3.2
Other Assets Especially Mentioned | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 4.0 | 2.3
Other Assets Especially Mentioned | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 7.9 | 2.4
Other Assets Especially Mentioned | Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 17.4 | 7.9
Other Assets Especially Mentioned | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 6.7 | 3.9
Other Assets Especially Mentioned | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 6.4 | 4.3
Other Assets Especially Mentioned | Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 107.2 | 94.1
Other Assets Especially Mentioned | Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.7 | 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 | 1.1 | 1.2
Other Assets Especially Mentioned | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 47.5 | 54.7
Other Assets Especially Mentioned | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3.7 | 5.1
Substandard |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 212.4 | 217.2
Substandard | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 92.8 | 96.4
Substandard | Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 15.6 | 16.4
Substandard | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 1.0 | 1.7
Substandard | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3.6 | 3.6
Substandard | Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 20.2 | 21.7
Substandard | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 11.4 | 12.5
Substandard | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 18.9 | 19.1
Substandard | Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 143.3 | 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 | 55.5 | 56.3
Substandard | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 10.6 | 8.3
Doubtful |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 24.6 | 28.2
Doubtful | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 8.0 | 10.3
Doubtful | Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.0 | 0.0
Doubtful | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.5 | 0.5
Doubtful | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 3.5 | 3.5
Doubtful | Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 4.0 | 4.0
Doubtful | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.9 | 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 | 12.9 | 16.2
Doubtful | Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.2 | 0.3
Doubtful | Other consumer |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 0.2 | 0.2
Doubtful | Total consumer loans |  |
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 | 10.8 | 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 | 396.5 | 400.5
Total Criticized Loans | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 177.5 | 184.7
Total Criticized Loans | Land acquisition & development |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 21.1 | 19.6
Total Criticized Loans | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 5.5 | 4.5
Total Criticized Loans | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 15.0 | 9.5
Total Criticized Loans | Total construction loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 41.6 | 33.6
Total Criticized Loans | Residential |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 19.0 | 18.3
Total Criticized Loans | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 25.3 | 23.4
Total Criticized Loans | Total real estate loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 263.4 | 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 | 1.4 | 1.3
Total Criticized Loans | Total consumer loans |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 4.5 | 4.6
Total Criticized Loans | Commercial |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | 113.8 | 122.1
Total Criticized Loans | Agricultural |  |
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items] |  |
Loans held for investment | $ 14.8 | $ 13.8

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