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Significant Accounting Policies Income Taxes (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Significant Accounting Policies [Abstract] |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent | 21.00% | 35.00% |
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Deferred TaxLiability, Provisional Income Tax (Expense) Benefit | $ 0 | $ 32,789 | $ 0
PortionOfTaxBenefitRecordedPositionsMoreLikelyThanNotToBeSustained | 50.00% |  |

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