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Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Taxes [Abstract] |  |  |
Federal statutory tax rate | 21.00% | 35.00% | 35.00%
Federal tax credits | (16.70%) | (14.00%) | (18.20%)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent | 0.00% | 6.10% | 0.00%
State and local taxes, net of federal tax benefit | 6.50% | 5.00% | 4.80%
Flow through depreciation and cost basis differences | 1.50% | 1.50% | 0.20%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amortization, Percent | (4.10%) | 0.00% | 0.00%
Other | (0.80%) | (2.10%) | (1.20%)
Effective tax rate | 7.40% | 31.50% | 20.60%

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