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Allowance for Probable Loan Losses (Impaired Loans) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | $ 14,874 |  | $ 14,874 |  | $ 15,346
Period of time for determining the historical charge-off experience |  |  | 3 years |  |
Period of charge off for past due unsecured commercial loans |  |  | 90 days |  |
Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with related allowance | 1,544 |  | $ 1,544 |  | 1,894
Total impaired loans with no related allowance | 33,896 |  | 33,896 |  | 61,310
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded | 2,161 |  | 2,161 |  | 2,336
Total impaired loans with no related allowance recorded | 62,218 |  | 62,218 |  | 89,664
Related Allowance | 576 |  | 576 |  | 434
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded | 1,747 | $ 3,233 | 1,805 | $ 3,758 | 1,985
Total impaired loans with no related allowance recorded | 64,903 | 41,202 | 65,399 | 42,196 | 40,450
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 94 | 128 | 184 | 250 | 547
Commercial |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 6,742 |  | 6,742 |  | 6,910
Commercial | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with related allowance | 1,402 |  | 1,402 |  |
Total impaired loans with no related allowance | 16,531 |  | 16,531 |  | 16,646
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded | 1,992 |  | 1,992 |  |
Total impaired loans with no related allowance recorded | 43,980 |  | 43,980 |  | 44,095
Related Allowance | 460 |  | 460 |  |
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded | 1,604 | 1,152 | 1,661 | 1,158 |
Total impaired loans with no related allowance recorded | 16,594 | 20,005 | 16,738 | 20,463 | 19,354
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 1 | 1 | 1 | 1 | 3
Commercial Real Estate:Other Construction and Land Development | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with related allowance | 142 |  | 142 |  | 1,300
Total impaired loans with no related allowance | 2,024 |  | 2,024 |  | 2,310
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded | 169 |  | 169 |  | 1,577
Total impaired loans with no related allowance recorded | 2,230 |  | 2,230 |  | 2,455
Related Allowance | 116 |  | 116 |  | 300
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded | 143 | 767 | 144 | 1,033 | 1,346
Total impaired loans with no related allowance recorded | 2,148 | 2,482 | 2,216 | 2,610 | 2,336
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded |  |  |  |  | 67
Commercial Real Estate: Farmland and Commercial | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with related allowance |  |  |  |  | 145
Total impaired loans with no related allowance | 6,020 |  | 6,020 |  | 32,675
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded |  |  |  |  | 169
Total impaired loans with no related allowance recorded | 6,520 |  | 6,520 |  | 33,275
Related Allowance |  |  |  |  | 116
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded |  | 1,314 |  | 1,567 | 150
Total impaired loans with no related allowance recorded | 36,790 | 8,532 | 36,686 | 8,774 | 8,523
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded |  | 30 |  | 58 | 110
Commercial Real Estate: Multifamily | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with related allowance |  |  |  |  | 449
Total impaired loans with no related allowance | 664 |  | 664 |  | 476
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded |  |  |  |  | 590
Total impaired loans with no related allowance recorded | 696 |  | 696 |  | 505
Related Allowance |  |  |  |  | 18
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded |  |  |  |  | 489
Total impaired loans with no related allowance recorded | 664 | 521 | 568 | 530 | 401
Residential First Lien |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 5,902 |  | 5,902 |  | 6,140
Residential First Lien | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 6,387 |  | 6,387 |  | 6,852
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 6,508 |  | 6,508 |  | 6,968
Average recorded investment: |  |  |  |  |
Total impaired loans with no related allowance recorded | 6,426 | 6,774 | 6,864 | 6,874 | 6,860
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 76 | 81 | 152 | 159 | 298
Residential Junior Lien |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 799 |  | 799 |  | 712
Residential Junior Lien | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 799 |  | 799 |  | 723
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 810 |  | 810 |  | 736
Average recorded investment: |  |  |  |  |
Total impaired loans with no related allowance recorded | 803 | 977 | 811 | 982 | 1,011
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 12 | 12 | 22 | 23 | 52
Consumer |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 1,101 |  | 1,101 |  | 1,237
Consumer | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 1,141 |  | 1,141 |  | 1,281
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 1,144 |  | 1,144 |  | 1,283
Average recorded investment: |  |  |  |  |
Total impaired loans with no related allowance recorded | 1,145 | 1,156 | 1,179 | 1,212 | 1,214
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 1 |  | 2 | 1 | 1
Foreign |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 330 |  | 330 |  | 347
Foreign | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 330 |  | 330 |  | 347
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 330 |  | 330 |  | 347
Average recorded investment: |  |  |  |  |
Total impaired loans with no related allowance recorded | 333 | 755 | 337 | 751 | 751
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | $ 4 | $ 4 | $ 7 | $ 8 | $ 16

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