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Income Taxes (Details) - USD ($) | 6 Months Ended | 12 Months Ended
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Jun. 30, 2018 | Dec. 31, 2017
Income Tax Disclosure [Abstract] |  |
Provisional one-time net benefit from changes in U.S. tax laws |  | $ 194,100,000
Changes in provisional amount of initial one-time benefit recorded resulting from change in U.S. tax laws | $ 0 |

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- Definition Tax Cuts And Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit) + References No definition available. + Details
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