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Capital Requirements (Capital Amounts and Ratios) (Details) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2016 | Jul. 31, 2013
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Capital Requirements |  |  |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) |  |  | 2.50% | 0.625% |
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent) |  |  |  |  | 6.00%
Minimum |  |  |  |  |
Capital Requirements |  |  |  |  |
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent) |  |  | 4.50% |  |
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent) |  |  |  |  | 4.00%
Parent Company |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Amount | $ 1,711,682 | $ 1,584,665 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 17.55% | 17.11% |  |  |
Total Capital (to Risk Weighted Assets), Actual Amount | $ 1,925,905 | $ 1,807,107 |  |  |
Tier 1 Capital (to Risk Weighted Assets), Actual Amount | 1,859,536 | 1,734,595 |  |  |
Tier 1 Capital (to Average Assets), Actual Amount | $ 1,859,536 | $ 1,734,595 |  |  |
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 19.74% | 19.51% |  |  |
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 19.06% | 18.73% |  |  |
Tier 1 capital (to Average Assets), Actual Ratio (as a percent) | 15.87% | 14.62% |  |  |
Parent Company | Minimum |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 621,850 | $ 532,579 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 6.375% | 5.75% |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 963,258 | $ 856,757 |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | 768,168 | 671,512 |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount | $ 468,593 | $ 474,675 |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 9.875% | 9.25% |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 7.875% | 7.25% |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent) | 4.00% | 4.00% |  |  |
International Bank of Commerce, Laredo |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Amount | $ 1,201,462 | $ 1,119,173 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 17.24% | 17.10% |  |  |
Total Capital (to Risk Weighted Assets), Actual Amount | $ 1,248,107 | $ 1,173,068 |  |  |
Tier 1 Capital (to Risk Weighted Assets), Actual Amount | 1,201,462 | 1,119,173 |  |  |
Tier 1 Capital (to Average Assets), Actual Amount | $ 1,201,462 | $ 1,119,173 |  |  |
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 17.91% | 17.93% |  |  |
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 17.24% | 17.10% |  |  |
Tier 1 capital (to Average Assets), Actual Ratio (as a percent) | 14.45% | 13.44% |  |  |
International Bank of Commerce, Laredo | Minimum |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 444,207 | $ 376,245 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 452,917 | $ 425,320 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 6.375% | 5.75% |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 6.50% | 6.50% |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 688,086 | $ 605,263 |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 696,796 | 654,339 |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | 548,727 | 474,395 |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 557,437 | 523,471 |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount | 332,507 | 333,166 |  |  |
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 415,634 | $ 416,458 |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 9.875% | 9.25% |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 10.00% | 10.00% |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 7.875% | 7.25% |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 8.00% | 8.00% |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent) | 4.00% | 4.00% |  |  |
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 5.00% | 5.00% |  |  |
International Bank Of Commerce Oklahoma |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Amount | $ 188,997 | $ 169,279 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 13.95% | 13.41% |  |  |
Total Capital (to Risk Weighted Assets), Actual Amount | $ 198,293 | $ 178,057 |  |  |
Tier 1 Capital (to Risk Weighted Assets), Actual Amount | 188,997 | 169,279 |  |  |
Tier 1 Capital (to Average Assets), Actual Amount | $ 188,997 | $ 169,279 |  |  |
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 14.64% | 14.11% |  |  |
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 13.95% | 13.41% |  |  |
Tier 1 capital (to Average Assets), Actual Ratio (as a percent) | 12.53% | 11.31% |  |  |
International Bank Of Commerce Oklahoma | Minimum |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 86,344 | $ 72,586 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 88,037 | $ 82,054 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 6.375% | 5.75% |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 6.50% | 6.50% |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 133,749 | $ 116,769 |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 135,442 | 126,237 |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | 106,660 | 91,521 |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 108,354 | 100,989 |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount | 60,344 | 59,854 |  |  |
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 75,430 | $ 74,818 |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 9.875% | 9.25% |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 10.00% | 10.00% |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 7.875% | 7.25% |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 8.00% | 8.00% |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent) | 4.00% | 4.00% |  |  |
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 5.00% | 5.00% |  |  |
International Bank of Commerce, Brownsville |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Amount | $ 177,456 | $ 165,034 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 24.73% | 25.94% |  |  |
Total Capital (to Risk Weighted Assets), Actual Amount | $ 183,554 | $ 170,613 |  |  |
Tier 1 Capital (to Risk Weighted Assets), Actual Amount | 177,456 | 165,034 |  |  |
Tier 1 Capital (to Average Assets), Actual Amount | $ 177,456 | $ 165,034 |  |  |
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 25.58% | 26.82% |  |  |
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 24.73% | 25.94% |  |  |
Tier 1 capital (to Average Assets), Actual Ratio (as a percent) | 17.25% | 17.17% |  |  |
International Bank of Commerce, Brownsville | Minimum |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 45,741 | $ 36,583 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 46,638 | $ 41,355 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 6.375% | 5.75% |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 6.50% | 6.50% |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 70,854 | $ 58,851 |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 71,750 | 63,623 |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | 56,503 | 46,127 |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 57,400 | 50,899 |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount | 41,144 | 38,440 |  |  |
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 51,430 | $ 48,050 |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 9.875% | 9.25% |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 10.00% | 10.00% |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 7.875% | 7.25% |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 8.00% | 8.00% |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent) | 4.00% | 4.00% |  |  |
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 5.00% | 5.00% |  |  |
International Bank of Commerce, Zapata |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Amount | $ 70,984 | $ 66,406 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 30.77% | 30.58% |  |  |
Total Capital (to Risk Weighted Assets), Actual Amount | $ 73,726 | $ 68,718 |  |  |
Tier 1 Capital (to Risk Weighted Assets), Actual Amount | 70,984 | 66,406 |  |  |
Tier 1 Capital (to Average Assets), Actual Amount | $ 70,984 | $ 66,406 |  |  |
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 31.96% | 31.64% |  |  |
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 30.77% | 30.58% |  |  |
Tier 1 capital (to Average Assets), Actual Ratio (as a percent) | 16.22% | 14.20% |  |  |
International Bank of Commerce, Zapata | Minimum |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 14,707 | $ 12,487 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 14,996 | $ 14,116 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 6.375% | 5.75% |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 6.50% | 6.50% |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 22,782 | $ 20,088 |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 23,070 | 21,717 |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | 18,168 | 15,745 |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 18,456 | 17,374 |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount | 17,507 | 18,701 |  |  |
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 21,884 | $ 23,376 |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 9.875% | 9.25% |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 10.00% | 10.00% |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 7.875% | 7.25% |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 8.00% | 8.00% |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent) | 4.00% | 4.00% |  |  |
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 5.00% | 5.00% |  |  |
Commerce Bank |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Amount | $ 89,305 | $ 79,330 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 32.95% | 33.22% |  |  |
Total Capital (to Risk Weighted Assets), Actual Amount | $ 90,894 |  |  |  |
Tier 1 Capital (to Risk Weighted Assets), Actual Amount | 89,305 | $ 81,278 |  |  |
Tier 1 Capital (to Average Assets), Actual Amount | $ 89,305 | $ 79,330 |  |  |
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 33.54% | 34.03% |  |  |
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent) | 32.95% | 33.22% |  |  |
Tier 1 capital (to Average Assets), Actual Ratio (as a percent) | 15.53% | 14.56% |  |  |
Commerce Bank | Minimum |  |  |  |  |
Capital Requirements |  |  |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 17,276 | $ 13,733 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 17,615 | $ 15,524 |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 6.375% | 5.75% |  |  |
Common Equity Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 6.50% | 6.50% |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | $ 26,761 | $ 22,092 |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 27,100 | 23,884 |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount | 21,341 | 17,316 |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | 21,680 | 19,107 |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount | 23,000 | 21,789 |  |  |
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount | $ 28,750 | $ 27,236 |  |  |
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 9.875% | 9.25% |  |  |
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 10.00% | 10.00% |  |  |
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent) | 7.875% | 7.25% |  |  |
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 8.00% | 8.00% |  |  |
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent) | 4.00% | 4.00% |  |  |
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent) | 5.00% | 5.00% |  |  |

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