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International Bancshares Corporation (Parent Company Only) Financial Information Statements of Income (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Expenses: |  |  |
Interest expense (Debentures) | $ 5,392 | $ 4,600 | $ 4,099
Income before federal income taxes and equity in undistributed net income of subsidiaries | 221,642 | 197,003 | 206,842
Income tax expense | 64,206 | 63,071 | 70,116
Net income | 157,436 | 133,932 | 136,726
Parent Company |  |  |
Income: |  |  |
Dividends from subsidiaries | 64,600 | 84,432 | 51,575
Interest income on notes receivable |  | 2 | 7
Interest income on other investments | 8,100 | 8,958 | 5,738
Other | 26 | 255 | 3,442
Total income | 72,726 | 93,647 | 60,762
Expenses: |  |  |
Interest expense (Debentures) | 5,392 | 4,600 | 4,099
Other | 5,648 | 3,637 | 3,037
Total expenses | 11,040 | 8,237 | 7,136
Income before federal income taxes and equity in undistributed net income of subsidiaries | 61,686 | 85,410 | 53,626
Income tax expense | (2,076) | 311 | 386
Income before equity in undistributed net income of subsidiaries | 63,762 | 85,099 | 53,240
Equity in undistributed net income of subsidiaries | 93,674 | 48,833 | 83,486
Net income | $ 157,436 | $ 133,932 | $ 136,726

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