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Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Debt Instrument [Line Items] |  |
Deferred finance costs | $ 34,781 | $ 27,174
Senior notes | 6.625% Senior Notes Due 2023 |  |
Debt Instrument [Line Items] |  |
Deferred finance costs | 5,200 |
Senior notes | 6.000% Senior Notes Due 2024 |  |
Debt Instrument [Line Items] |  |
Deferred finance costs | 9,900 |
Senior notes | 6.375% Senior Notes Due 2025 |  |
Debt Instrument [Line Items] |  |
Deferred finance costs | 14,000 |
Senior notes | 6.375% Senior Notes Due 2026 |  |
Debt Instrument [Line Items] |  |
Deferred finance costs | 5,500 |
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 | $ 2,100,000 |

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- Definition Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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