| **Fair Value Measurements and Derivative Instruments (Tables)**                   | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
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| **Fair Value Disclosures [Abstract]**                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Fair Value Assets And Liabilities Measured On Recurring Basis                     | Assets and liabilities measured at fair value on a recurring basis as of March 31, 2015 and December 31, 2014 are as follows (amounts in thousands):March 31, 2015Level 1 (1) Level 2 (2) Level 3 (3) TotalAssets:       Deferred compensation plan assets (mutual funds)$1,899 — — 1,899Liabilities:       Derivative stock appreciation rights$— — 23,780 23,780        December 31, 2014 Level 1 (1) Level 2 (2) Level 3 (3) TotalAssets:       Deferred compensation plan assets (mutual funds)$2,068 — — 2,068        (1) Quoted prices in active markets for identical assets or liabilities(2) Observable inputs other than quoted prices in active markets for identical assets and liabilities(3) Inputs that are generally unobservable and not corroborated by market data |
| Fair Value, by Balance Sheet Grouping                                             | The carrying amounts and approximate fair values of our current and long-term debt, excluding capital leases, at March 31, 2015 and December 31, 2014 are as follows (amounts in thousands): March 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Amount Fair ValueCurrent and long-term debt$1,326,172 1,376,834 1,036,678 1,055,952                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation | The following table summarizes the changes in fair value of all financial instruments measured at fair value on a recurring basis using significant unobservable inputs (Level 3) during the three months ended March 31, 2015:Fair Value Measurement Using Level 3 Inputs Derivative Stock Appreciation RightsBalance, January 1, 2015$—Issuance21,660Fair value adjustment at end of period, included in Other Income (Expense)2,120Balance, March 31, 2015$23,780                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |

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| - Definition
Tabular disclosure of the fair value measurement of assets using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset.
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| - Definition
Tabular disclosure of the fair value of financial instruments, including financial assets and financial liabilities, and the measurements of those instruments, assets, and liabilities.
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| - Definition
Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).
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