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Income Taxes - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018 | Oct. 04, 2016
Operating Loss Carryforwards [Line Items] |  |  |
Income tax expense due to TCJA | $ 243.8 |  |
Subject to limitation |  |  | $ 1,900.0
Expected to expire |  | $ 1,600.0 |
Domestic Tax Authority |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Federal net operating loss carryovers |  | 1,100.0 |
Operating loss carryforwards, subject to expiration |  | 800.0 |
Operating loss carryforwards, not subject to expiration |  | 300.0 |
Tax credits, not subject to expiration |  | $ 32.0 |

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