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Income Taxes - Effective Income Tax Rate (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Income Tax Disclosure [Abstract] |  |  |  |
Income Taxes at Federal Statutory Rate | $ 24,508 | $ 22,418 | $ 61,849 | $ 64,748
Income Taxes at Federal Statutory Rate | 21.00% | 21.00% | 21.00% | 21.00%
Increases (Decreases) in Tax from: |  |  |  |
State Taxes on Income, Net of Federal Tax | $ 5,832 | $ 5,338 | $ 14,725 | $ 15,416
Production Tax Credits (PTCs) | (5,192) | (3,828) | (14,421) | (12,514)
Amortization of Excess Deferred Income Taxes | (741) | (955) | (2,161) | (2,033)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax | (220) | (150) | (530) | (505)
Corporate-Owned Life Insurance | (120) | 241 | (998) | 1,383
Other, Net | 660 | (551) | (371) | (352)
Income Tax Expense / Effective Tax Rate | $ 24,727 | $ 22,513 | $ 58,093 | $ 66,143
Increases (Decreases) in Tax from: |  |  |  |
State Taxes on Income, Net of Federal Tax | 5.00% | 5.00% | 5.00% | 5.00%
Production Tax Credits (PTCs) | (4.40%) | (3.60%) | (4.90%) | (4.10%)
Amortization of Excess Deferred Income Taxes | (0.60%) | (0.90%) | (0.70%) | (0.70%)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax | (0.20%) | (0.10%) | (0.20%) | (0.20%)
Corporate-Owned Life Insurance | (0.10%) | 0.20% | (0.30%) | 0.40%
Other, Net | 0.50% | (0.50%) | (0.20%) | 0.10%
Income Tax Expense / Effective Tax Rate | 21.20% | 21.10% | 19.70% | 21.50%

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