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Federal and State Income Taxes Federal and State Income Taxes (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract] |  |  |  |  |
Federal statutory tax | $ 31,182 | $ 47,800 | $ 59,804 | $ 92,168 |
Tax exempt revenue | (1,653) | (3,224) | (3,465) | (6,335) |
Effect of state income taxes, net of federal benefit | 3,288 | 2,944 | 6,945 | 5,389 |
Utilization of tax credits, net of proportional amortization of low-income housing limited partnership investments | (1,334) | (889) | (2,667) | (2,976) |
Share-based compensation | (424) | 1,636 | (2,044) | (2,301) |
Adjustment to provisional amounts related to tax reform | 0 | 0 | 1,895 | 0 |
Other, net | 2,271 | (562) | 3,810 | (137) |
Total income tax expense | $ 33,330 | $ 47,705 | $ 64,278 | $ 85,808 |
Effective Income Tax Rate Reconciliation, Percent [Abstract] |  |  |  |  |
Federal statutory tax (in hundredths) | 21.00% | 35.00% | 21.00% | 35.00% | 35.00%
Tax exempt revenue (in hundredths) | (1.10%) | (2.40%) | (1.20%) | (2.40%) |
Effect of state income taxes, net of federal benefit (in hundredths) | 2.20% | 2.20% | 2.40% | 2.00% |
Utilization of tax credits, net of proportional amortization of low-income housing limited partnership investments (in hundredths) | (0.90%) | (0.70%) | (0.90%) | (1.10%) |
Share-based compensation (in hundredths) | (0.30%) | 1.20% | (0.70%) | (0.90%) |
Adjustment to provisional amounts related to tax reform (in hundredths) | 0.00% | 0.00% | 0.70% | 0.00% |
Other, net (in hundredths) | 1.50% | (0.40%) | 1.30% | 0.00% |
Total (in hundredths) | 22.40% | 34.90% | 22.60% | 32.60% |

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