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Financial Instruments - Fair Value, by Balance Sheet Grouping (Details) (Senior Notes, USD $)
In Thousands, unless otherwise specified |
Jun. 30, 2012
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Dec. 31, 2011
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2013 Senior Notes | Carrying Amount
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| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Carrying amount and estimated fair value of debt instruments | $ 550,000 | [1] | $ 550,000 | [1] | ||
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2013 Senior Notes | Estimated Fair Value
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| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Carrying amount and estimated fair value of debt instruments | 569,250 | [1] | 555,500 | [1] | ||
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2016 Senior Notes | Carrying Amount
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| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Carrying amount and estimated fair value of debt instruments | 1,644,765 | 1,642,418 | [1] | |||
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2016 Senior Notes | Estimated Fair Value
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| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Carrying amount and estimated fair value of debt instruments | $ 1,722,892 | [1] | $ 1,650,630 | [1] | ||
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