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International Bancshares Corporation (Parent Company Only) Financial Information Statements of Income (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Expenses: |  |  |
Interest expense (Debentures) | $ 6,989 | $ 5,392 | $ 4,600
Income before federal income taxes and equity in undistributed net income of subsidiaries | 272,583 | 221,642 | 197,003
Income tax expense | 56,652 | 64,206 | 63,071
Net income | 215,931 | 157,436 | 133,932
Parent Company | Reportable Legal Entities |  |  |
Income: |  |  |
Dividends from subsidiaries | 105,000 | 64,600 | 84,432
Interest income on notes receivable |  |  | 2
Interest income on other investments | 8,208 | 8,100 | 8,958
Other | 1,988 | 26 | 255
Total income | 115,196 | 72,726 | 93,647
Expenses: |  |  |
Interest expense (Debentures) | 6,989 | 5,392 | 4,600
Other | 2,930 | 5,648 | 3,637
Total expenses | 9,919 | 11,040 | 8,237
Income before federal income taxes and equity in undistributed net income of subsidiaries | 105,277 | 61,686 | 85,410
Income tax expense | 481 | (2,076) | 311
Income before equity in undistributed net income of subsidiaries | 104,796 | 63,762 | 85,099
Equity in undistributed net income of subsidiaries | 111,135 | 93,674 | 48,833
Net income | $ 215,931 | $ 157,436 | $ 133,932

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