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Allowance for Probable Loan Losses (Impaired Loans) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | $ 14,596 |  | $ 14,596 |  | $ 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 | 1,757 |  | $ 1,757 |  | 1,894
Total impaired loans with no related allowance | 30,735 |  | 30,735 |  | 61,310
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded | 2,381 |  | 2,381 |  | 2,336
Total impaired loans with no related allowance recorded | 59,022 |  | 59,022 |  | 89,664
Related Allowance | 700 |  | 700 |  | 434
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded | 1,759 | $ 2,864 | 1,936 | $ 3,086 | 1,985
Total impaired loans with no related allowance recorded | 32,938 | 38,855 | 65,134 | 42,273 | 40,450
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 92 | 120 | 276 | 371 | 547
Receivables from Domestic Operations [Member] | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with related allowance | 138 |  | 138 |  |
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded | 169 |  | 169 |  |
Related Allowance | 116 |  | 116 |  |
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded | 139 |  | 142 |  |
Commercial |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 6,440 |  | 6,440 |  | 6,910
Commercial | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 15,617 |  | 15,617 |  | 16,646
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 43,068 |  | 43,068 |  | 44,095
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded |  | 2,215 |  | 2,439 |
Total impaired loans with no related allowance recorded | 15,758 | 18,547 | 16,464 | 18,931 | 19,354
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded |  | 1 | 2 | 2 | 3
Commercial Real Estate:Other Construction and Land Development | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with related allowance | 1,619 |  | 1,619 |  | 1,300
Total impaired loans with no related allowance | 1,992 |  | 1,992 |  | 2,310
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded | 2,212 |  | 2,212 |  | 1,577
Total impaired loans with no related allowance recorded | 2,199 |  | 2,199 |  | 2,455
Related Allowance | 584 |  | 584 |  | 300
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded | 1,620 | 149 | 1,794 | 151 | 1,346
Total impaired loans with no related allowance recorded | 1,994 | 2,296 | 2,203 | 3,456 | 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 | 4,157 |  | 4,157 |  | 32,675
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded |  |  |  |  | 169
Total impaired loans with no related allowance recorded | 4,660 |  | 4,660 |  | 33,275
Related Allowance |  |  |  |  | 116
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded |  | 500 |  | 496 | 150
Total impaired loans with no related allowance recorded | 5,986 | 7,936 | 36,633 | 9,456 | 8,523
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded |  | 21 |  | 79 | 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 | 586 |  | 586 |  | 476
Unpaid principal balance: |  |  |  |  |
Total impaired loans with an allowance recorded |  |  |  |  | 590
Total impaired loans with no related allowance recorded | 617 |  | 617 |  | 505
Related Allowance |  |  |  |  | 18
Average recorded investment: |  |  |  |  |
Total impaired loans with an allowance recorded |  |  |  |  | 489
Total impaired loans with no related allowance recorded | 590 | 502 | 575 | 521 | 401
Residential First Lien |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 5,976 |  | 5,976 |  | 6,140
Residential First Lien | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 6,173 |  | 6,173 |  | 6,852
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 6,257 |  | 6,257 |  | 6,968
Average recorded investment: |  |  |  |  |
Total impaired loans with no related allowance recorded | 6,362 | 6,733 | 6,929 | 6,903 | 6,860
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 76 | 81 | 228 | 241 | 298
Residential Junior Lien |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 740 |  | 740 |  | 712
Residential Junior Lien | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 740 |  | 740 |  | 723
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 748 |  | 748 |  | 736
Average recorded investment: |  |  |  |  |
Total impaired loans with no related allowance recorded | 743 | 765 | 807 | 975 | 1,011
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 11 | 11 | 33 | 35 | 52
Consumer |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 1,134 |  | 1,134 |  | 1,237
Consumer | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 1,164 |  | 1,164 |  | 1,281
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 1,167 |  | 1,167 |  | 1,283
Average recorded investment: |  |  |  |  |
Total impaired loans with no related allowance recorded | 1,187 | 1,317 | 1,192 | 1,278 | 1,214
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | 1 | 2 | 2 | 2 | 1
Foreign |  |  |  |  |
Interest Recognized |  |  |  |  |
Total trouble debt restructuring | 306 |  | 306 |  | 347
Foreign | Class of Financing Receivable |  |  |  |  |
Recorded investment: |  |  |  |  |
Total impaired loans with no related allowance | 306 |  | 306 |  | 347
Unpaid principal balance: |  |  |  |  |
Total impaired loans with no related allowance recorded | 306 |  | 306 |  | 347
Average recorded investment: |  |  |  |  |
Total impaired loans with no related allowance recorded | 318 | 759 | 331 | 753 | 751
Interest Recognized |  |  |  |  |
Total impaired loans with no related allowance recorded | $ 4 | $ 4 | $ 11 | $ 12 | $ 16

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