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Allowance for Loan Losses - Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | $ 76,214 | $ 76,800 | $ 74,200 |  |  |
Provision charged (credited) to operating expense | 11,053 | 9,991 | 6,822 |  |  |
Less loans charged-off | (22,900) | (19,800) | (11,700) |  |  |
Add back recoveries of loans previously charged-off | 7,700 | 9,200 | 7,500 |  |  |
Ending balance | 72,147 | 76,214 | 76,800 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | $ 10,800 | $ 14,000 | $ 11,600
Collectively evaluated for impairment |  |  |  | 61,300 | 62,200 | 65,200
Ending balance | 76,214 | 76,800 | 74,200 | 72,147 | 76,214 | 76,800
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 83,200 | 104,700 | 92,000
Collectively evaluated for impairment |  |  |  | 7,484,500 | 5,312,000 | 5,101,400
Total loans held for investment |  |  |  | 7,567,700 | 5,416,700 | 5,193,400
Allowance for loans losses |  |  |  | 1,000 | 400 |
Real Estate |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 28,600 | 52,300 | 53,900 |  |  |
Provision charged (credited) to operating expense | 6,000 | (21,700) | (600) |  |  |
Less loans charged-off | (4,400) | (5,200) | (4,100) |  |  |
Add back recoveries of loans previously charged-off | 1,400 | 3,200 | 3,100 |  |  |
Ending balance | 31,600 | 28,600 | 52,300 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 6,200 | 4,600 | 4,800
Collectively evaluated for impairment |  |  |  | 25,400 | 24,000 | 47,500
Ending balance | 28,600 | 52,300 | 53,900 | 31,600 | 28,600 | 52,300
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 58,300 | 68,600 | 66,500
Collectively evaluated for impairment |  |  |  | 5,118,500 | 3,445,400 | 3,346,600
Total loans held for investment |  |  |  | 5,176,800 | 3,514,000 | 3,413,100
Consumer |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 7,700 | 5,100 | 5,000 |  |  |
Provision charged (credited) to operating expense | 8,100 | 8,400 | 3,200 |  |  |
Less loans charged-off | (11,300) | (8,600) | (5,700) |  |  |
Add back recoveries of loans previously charged-off | 4,200 | 2,800 | 2,600 |  |  |
Ending balance | 8,700 | 7,700 | 5,100 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0 | 0 | 0
Collectively evaluated for impairment |  |  |  | 8,700 | 7,700 | 5,100
Ending balance | 7,700 | 5,100 | 5,000 | 8,700 | 7,700 | 5,100
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0 | 0 | 0
Collectively evaluated for impairment |  |  |  | 1,034,400 | 970,300 | 844,400
Total loans held for investment |  |  |  | 1,034,400 | 970,300 | 844,400
Commercial |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 38,100 | 18,800 | 14,300 |  |  |
Provision charged (credited) to operating expense | (2,800) | 21,900 | 4,400 |  |  |
Less loans charged-off | (6,800) | (5,800) | (1,700) |  |  |
Add back recoveries of loans previously charged-off | 2,100 | 3,200 | 1,800 |  |  |
Ending balance | 30,600 | 38,100 | 18,800 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 4,400 | 9,300 | 6,500
Collectively evaluated for impairment |  |  |  | 26,200 | 28,800 | 12,300
Ending balance | 38,100 | 18,800 | 14,300 | 30,600 | 38,100 | 18,800
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 23,800 | 32,400 | 24,500
Collectively evaluated for impairment |  |  |  | 1,191,600 | 765,500 | 767,900
Total loans held for investment |  |  |  | 1,215,400 | 797,900 | 792,400
Agriculture |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 1,800 | 600 | 1,000 |  |  |
Provision charged (credited) to operating expense | (200) | 1,400 | (200) |  |  |
Less loans charged-off | (400) | (200) | (200) |  |  |
Add back recoveries of loans previously charged-off | 0 | 0 | 0 |  |  |
Ending balance | 1,200 | 1,800 | 600 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 200 | 100 | 300
Collectively evaluated for impairment |  |  |  | 1,000 | 1,700 | 300
Ending balance | 1,800 | 600 | 1,000 | 1,200 | 1,800 | 600
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 1,100 | 3,700 | 1,000
Collectively evaluated for impairment |  |  |  | 135,100 | 129,200 | 141,200
Total loans held for investment |  |  |  | 136,200 | 132,900 | 142,200
Other |  |  |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |  |  |
Beginning balance | 0 | 0 | 0 |  |  |
Provision charged (credited) to operating expense | 0 | 0 | 0 |  |  |
Less loans charged-off | 0 | 0 | 0 |  |  |
Add back recoveries of loans previously charged-off | 0 | 0 | 0 |  |  |
Ending balance | 0 | 0 | 0 |  |  |
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0 | 0 | 0
Collectively evaluated for impairment |  |  |  | 0 | 0 | 0
Ending balance | $ 0 | $ 0 | $ 0 | 0 | 0 | 0
Total loans: |  |  |  |  |  |
Individually evaluated for impairment |  |  |  | 0 | 0 | 0
Collectively evaluated for impairment |  |  |  | 4,900 | 1,600 | 1,300
Total loans held for investment |  |  |  | $ 4,900 | $ 1,600 | $ 1,300

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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://www.xbrl.org/2003/role/presentationRef -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 Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + 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://www.xbrl.org/2003/role/presentationRef -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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -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 + Details
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- Definition Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for 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 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB Topic 6.L.1) -URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(1)(ii) -URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544 + Details
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