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Debt (Details 3) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Carrying Amount [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt | $ 1,904,001 | $ 2,077,752
Carrying Amount [Member] | Unsecured Senior Notes [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt | 1,187,515 | 1,185,842
Carrying Amount [Member] | Other fixed-rate debt [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt | 155,544 | 282,716
Carrying Amount [Member] | Variable-rate debt [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt | 560,942 | 609,194
Estimated Fair Value [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt | 1,935,606 | 2,114,636
Estimated Fair Value [Member] | Unsecured Senior Notes [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt | 1,220,282 | 1,211,658
Estimated Fair Value [Member] | Other fixed-rate debt [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt | 156,887 | 291,991
Estimated Fair Value [Member] | Variable-rate debt [Member] |  |
Debt Instrument [Line Items] |  |
Long-term debt | $ 558,437 | $ 610,987

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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