| **Fair Value Of Financial Instruments (Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt) (Details) - USD ($) $ in Thousands** | Jun. 30, 2017 | Dec. 31, 2016 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Carrying Amount [Member]                                                                                                                              |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                                     |          |          |
| Long-term debt                                                                                                                                        | $ 1,987,909   | $ 1,910,633   |
| Estimated Fair Value [Member]                                                                                                                         |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                                     |          |          |
| Long-term debt                                                                                                                                        | $ 2,049,090   | $ 2,018,933   |

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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**Name:**us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
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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**Name:**us-gaap_LongTermDebtFairValue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
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