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Income tax expense (benefit) statutory rate versus actual rate (Details 7) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Computed tax at federal statutory rate |  |  |  |
Computed tax at federal statutory rate |  | $ 122,509 | $ 114,179 | $ 86,468
Federal statutory rate |  | 35.00% | 35.00% | 35.00%
Increases (reductions) resulting from: |  |  |  |
State income taxes, net of federal income tax |  | $ 10,724 | $ 9,027 | $ 8,208
State income tax rate |  | 3.10% | 2.80% | 3.30%
Federal renewable energy credit |  | $ (13,958) | $ (13,544) | $ (3,400)
Federal renewable energy credit rate |  | (4.00%) | (4.20%) | (1.40%)
Tax compliance and uncertain tax positions |  | $ (643) | $ (3,028) | $ (2,607)
Tax compliance and uncertain tax positions |  | (0.20%) | (0.90%) | (1.00%)
Domestic production deduction |  | $ (6,849) | $ (6,251) | $ (6,842)
Domestic production deduction, rate |  | (2.00%) | (1.90%) | (2.80%)
TCJA revaluation |  | $ (47,242) | $ 0 | $ 0
TCJA revaluation, rate |  | (13.50%) | 0.00% | 0.00%
TCJA revaluation related to accumulated other comprehensive loss balance | $ (39,500) | $ 7,735 | $ 0 | $ 0
TCJA revaluation related to accumulated other comprehensive loss balance, rate |  | 2.20% | 0.00% | 0.00%
Other |  | $ (7,235) | $ (7,251) | $ (11,163)
Other rate |  | (2.00%) | (2.30%) | (4.50%)
Total income tax expense |  | $ 65,041 | $ 93,132 | $ 70,664
Total income tax expense rate |  | 18.60% | 28.50% | 28.60%

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