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Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
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Debt Instrument [Line Items] |  |
Deferred finance costs | $ 30,733 | $ 34,781
Senior notes | 6.625% Senior Notes Due 2023 |  |
Debt Instrument [Line Items] |  |
Deferred finance costs | 4,400 |
Senior notes | 6.000% Senior Notes Due 2024 |  |
Debt Instrument [Line Items] |  |
Deferred finance costs | 8,700 |
Senior notes | 6.375% Senior Notes Due 2025 |  |
Debt Instrument [Line Items] |  |
Deferred finance costs | 12,500 |
Senior notes | 6.375% Senior Notes Due 2026 |  |
Debt Instrument [Line Items] |  |
Deferred finance costs | 5,000 |
Carrying value | Senior notes |  |
Debt Instrument [Line Items] |  |
Fair value of notes | 2,000,000 |
Fair value | Senior notes |  |
Debt Instrument [Line Items] |  |
Fair value of notes | $ 1,800,000 |

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