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Loans - Schedule of Recorded Investment in Past Due Loans by Class (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Loans held for investment | $ 7,567,720 | $ 5,416,750 |
Mortgage loans held for sale | 46,635 | 61,794 |
Total loans | 7,614,355 | 5,478,544 |
Interest income on non-accrual loans if accrued | 3,500 | 3,400 | $ 3,200
Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 3,700 | 8,700 |
Current Loans | 2,792,400 | 1,799,500 |
Non-accrual Loans | 26,800 | 26,200 |
Loans held for investment | 2,822,900 | 1,834,400 |
Land acquisition & development |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 7,900 | 1,300 |
Current Loans | 337,800 | 202,200 |
Non-accrual Loans | 3,000 | 5,000 |
Loans held for investment | 348,700 | 208,500 |
Residential |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 2,100 | 1,200 |
Current Loans | 236,400 | 146,200 |
Non-accrual Loans | 1,700 | 500 |
Loans held for investment | 240,200 | 147,900 |
Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Current Loans | 115,600 | 124,800 |
Non-accrual Loans | 3,800 | 800 |
Loans held for investment | 119,400 | 125,600 |
Total construction loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 10,000 | 2,500 |
Current Loans | 689,800 | 473,200 |
Non-accrual Loans | 8,500 | 6,300 |
Loans held for investment | 708,300 | 482,000 |
Residential |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 15,100 | 6,000 |
Current Loans | 1,464,100 | 1,015,000 |
Non-accrual Loans | 8,200 | 6,400 |
Loans held for investment | 1,487,400 | 1,027,400 |
Agricultural |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 500 | 600 |
Current Loans | 154,300 | 165,300 |
Non-accrual Loans | 3,400 | 4,300 |
Loans held for investment | 158,200 | 170,200 |
Total real estate loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 29,300 | 17,800 |
Current Loans | 5,100,600 | 3,453,000 |
Non-accrual Loans | 46,900 | 43,200 |
Loans held for investment | 5,176,800 | 3,514,000 |
Indirect consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 10,300 | 11,400 |
Current Loans | 772,600 | 740,200 |
Non-accrual Loans | 1,800 | 800 |
Loans held for investment | 784,700 | 752,400 |
Other consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 2,200 | 1,700 |
Current Loans | 172,600 | 146,100 |
Non-accrual Loans | 300 | 300 |
Loans held for investment | 175,100 | 148,100 |
Credit card consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 2,200 | 1,400 |
Current Loans | 72,400 | 68,400 |
Non-accrual Loans | 0 | 0 |
Loans held for investment | 74,600 | 69,800 |
Total consumer loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 14,700 | 14,500 |
Current Loans | 1,017,600 | 954,700 |
Non-accrual Loans | 2,100 | 1,100 |
Loans held for investment | 1,034,400 | 970,300 |
Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 6,300 | 4,600 |
Current Loans | 1,189,500 | 767,900 |
Non-accrual Loans | 19,600 | 25,400 |
Loans held for investment | 1,215,400 | 797,900 |
Agricultural |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 1,900 | 1,900 |
Current Loans | 133,500 | 128,000 |
Non-accrual Loans | 800 | 3,000 |
Loans held for investment | 136,200 | 132,900 |
Other, including overdrafts |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 300 |
Current Loans | 4,900 | 1,300 |
Non-accrual Loans | 0 | 0 |
Loans held for investment | 4,900 | 1,600 |
Loans held for investment |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 52,200 | 39,100 |
Current Loans | 7,446,100 | 5,304,900 |
Non-accrual Loans | 69,400 | 72,700 |
Loans held for investment | 7,567,700 | 5,416,700 |
Mortgage loans originated for sale |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Current Loans | 46,600 | 61,800 |
Non-accrual Loans | 0 | 0 |
Mortgage loans held for sale | 46,600 |  |
Total loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 52,200 | 39,100 |
Current Loans | 7,492,700 | 5,366,700 |
Non-accrual Loans | 69,400 | 72,700 |
Total loans | 7,614,300 | 5,478,500 |
Financing Receivables, 30 to 59 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 2,900 | 7,300 |
Financing Receivables, 30 to 59 Days Past Due | Land acquisition & development |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 7,300 | 600 |
Financing Receivables, 30 to 59 Days Past Due | Residential |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 2,100 | 900 |
Financing Receivables, 30 to 59 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, 30 to 59 Days Past Due | Total construction loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 9,400 | 1,500 |
Financing Receivables, 30 to 59 Days Past Due | Residential |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 13,300 | 4,000 |
Financing Receivables, 30 to 59 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 300 | 300 |
Financing Receivables, 30 to 59 Days Past Due | Total real estate loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 25,900 | 13,100 |
Financing Receivables, 30 to 59 Days Past Due | Indirect consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 7,800 | 8,400 |
Financing Receivables, 30 to 59 Days Past Due | Other consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 1,600 | 1,300 |
Financing Receivables, 30 to 59 Days Past Due | Credit card consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 900 | 500 |
Financing Receivables, 30 to 59 Days Past Due | Total consumer loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 10,300 | 10,200 |
Financing Receivables, 30 to 59 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 3,900 | 3,200 |
Financing Receivables, 30 to 59 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 1,800 | 1,500 |
Financing Receivables, 30 to 59 Days Past Due | Other, including overdrafts |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, 30 to 59 Days Past Due | Loans held for investment |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 41,900 | 28,000 |
Financing Receivables, 30 to 59 Days Past Due | Mortgage loans originated for sale |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, 30 to 59 Days Past Due | Total loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 41,900 | 28,000 |
Financing Receivables, 60 to 89 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 500 | 1,100 |
Financing Receivables, 60 to 89 Days Past Due | Land acquisition & development |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 300 | 400 |
Financing Receivables, 60 to 89 Days Past Due | Residential |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 300 |
Financing Receivables, 60 to 89 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, 60 to 89 Days Past Due | Total construction loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 300 | 700 |
Financing Receivables, 60 to 89 Days Past Due | Residential |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 1,400 | 1,300 |
Financing Receivables, 60 to 89 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 300 |
Financing Receivables, 60 to 89 Days Past Due | Total real estate loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 2,200 | 3,400 |
Financing Receivables, 60 to 89 Days Past Due | Indirect consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 2,100 | 2,300 |
Financing Receivables, 60 to 89 Days Past Due | Other consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 500 | 200 |
Financing Receivables, 60 to 89 Days Past Due | Credit card consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 600 | 300 |
Financing Receivables, 60 to 89 Days Past Due | Total consumer loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 3,200 | 2,800 |
Financing Receivables, 60 to 89 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 1,700 | 700 |
Financing Receivables, 60 to 89 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 100 | 400 |
Financing Receivables, 60 to 89 Days Past Due | Other, including overdrafts |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, 60 to 89 Days Past Due | Loans held for investment |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 7,200 | 7,300 |
Financing Receivables, 60 to 89 Days Past Due | Mortgage loans originated for sale |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, 60 to 89 Days Past Due | Total loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 7,200 | 7,300 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 300 | 300 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Land acquisition & development |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 300 | 300 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Residential |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Total construction loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 300 | 300 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Residential |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 400 | 700 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 200 | 0 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Total real estate loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 1,200 | 1,300 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Indirect consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 400 | 700 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Other consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 100 | 200 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Credit card consumer |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 700 | 600 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Total consumer loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 1,200 | 1,500 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Commercial |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 700 | 700 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Agricultural |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Other, including overdrafts |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 300 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Loans held for investment |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 3,100 | 3,800 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Mortgage loans originated for sale |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | 0 | 0 |
Financing Receivables, Equal to Greater than 90 Days Past Due | Total loans |  |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |  |
Total Loans 30 or More Days Past Due | $ 3,100 | $ 3,800 |

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- Definition Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524 + Details
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- Definition Recorded Investment in financing receivables that are past due at the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524 + Details
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- Definition Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522 + Details
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- Definition Amount, after allowance for bad debt, of mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522 + Details
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