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Income Taxes (Income Tax Expense Differences from the Amount Computed by Applying the U.S. Federal Income Tax Rate) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Income Taxes |  |  |
U.S. Federal income tax rate (as a percent) | 21.00% | 21.00% | 21.00%
Reasons for the difference of income tax expense |  |  |
Computed expected tax expense | $ 110,065 | $ 80,893 | $ 68,011
Change in taxes resulting from: |  |  |
Tax-exempt interest income | (3,663) | (2,433) | (2,970)
State tax, net of federal income taxes and tax credit and refunds | 4,808 | 4,094 | 3,966
Other investment income | (2,761) | (1,391) | (1,753)
Net investment expense, low-income housing investment | 1,974 | 1,906 | 203
Other | 1,321 | (662) | 948
Total income taxes | $ 111,744 | $ 82,407 | $ 68,405

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