Debt (Summary of Senior Notes) (Details) (USD $)
In Thousands, unless otherwise specified |
3 Months Ended | 12 Months Ended | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Mar. 31, 2014
|
Dec. 31, 2013
|
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | $ 1,814,041 | [1] | $ 2,058,168 | [1] | ||||||
Estimated fair value | 1,891,326 | 2,070,744 | ||||||||
Unsecured Senior Notes 5.20% due February 2015 [Member]
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | 0 | [2] | 95,633 | [2] | ||||||
Interest Rate, Stated Percentage | 5.20% | 5.20% | ||||||||
Maturity Date, Description | February 2015 | February 2015 | ||||||||
Unsecured Senior Notes 5.25% due June 2015 [Member]
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | 233,926 | [2] | 233,085 | [2] | ||||||
Interest Rate, Stated Percentage | 5.25% | 5.25% | ||||||||
Maturity Date, Description | June 2015 | June 2015 | ||||||||
Unsecured Senior Notes 6.50% due May 2016 [Member]
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | 460,189 | [2] | 459,581 | [2] | ||||||
Interest Rate, Stated Percentage | 6.50% | 6.50% | ||||||||
Maturity Date, Description | May 2016 | May 2016 | ||||||||
Unsecured Senior Notes 7.625% due October 2017 [Member]
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | 122,685 | [3] | 122,663 | [3] | ||||||
Interest Rate, Stated Percentage | 7.625% | 7.625% | ||||||||
Maturity Date, Description | October 2017 | October 2017 | ||||||||
Unsecured Senior Notes 7.875% due June 2032 [Member]
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | 299,207 | [2] | 299,196 | [2] | ||||||
Interest Rate, Stated Percentage | 7.875% | 7.875% | ||||||||
Maturity Date, Description | June 2032 | June 2032 | ||||||||
Unsecured Senior Notes 6.375% due May 2033 [Member]
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | 398,585 | [2] | 398,567 | [2] | ||||||
Interest Rate, Stated Percentage | 6.375% | 6.375% | ||||||||
Maturity Date, Description | May 2033 | May 2033 | ||||||||
Unsecured Senior Notes 6.00% due February 2035 [Member]
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | 299,449 | [2] | 299,443 | [2] | ||||||
Interest Rate, Stated Percentage | 6.00% | 6.00% | ||||||||
Maturity Date, Description | February 2035 | February 2035 | ||||||||
Unsecured Senior Notes 7.375% due June 2046 [Member]
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Debt Instrument [Line Items] | ||||||||||
Senior note carrying value | $ 0 | [2] | $ 150,000 | [2] | ||||||
Interest Rate, Stated Percentage | 7.375% | 7.375% | ||||||||
Maturity Date, Description | June 2046 | June 2046 | ||||||||
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