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Condensed Consolidating Financial Information (Narrative) (Details) - Senior notes - USD ($) | Dec. 21, 2016 | Oct. 31, 2016 | Oct. 14, 2016 | Apr. 21, 2015 | Aug. 18, 2014
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7.75% Senior Notes due 2020 |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |
Debt instrument, amount |  |  |  |  | $ 600,000,000.0
Amount validly tendered |  | $ 600,000,000.0 |  |  |
6.625% Senior Notes due 2023 |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |
Debt instrument, amount |  |  |  | $ 350,000,000.0 |
6.000% Senior Notes due 2024 |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |
Debt instrument, amount |  |  | $ 650,000,000.0 |  |
6.375% Senior Notes due 2025 |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |
Debt instrument, amount | $ 600,000,000.0 |  |  |  |

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