| **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, 2016 and December 31, 2015 are as follows (amounts in thousands):March 31, 2016Level 1 (1) Level 2 (2) Level 3 (3) TotalAssets:       Deferred compensation plan assets (mutual funds)$1,483 — — 1,483Liabilities:       Derivative stock appreciation rights$— — 28,290 28,290        December 31, 2015Level 1 (1) Level 2 (2) Level 3 (3) TotalAssets:       Deferred compensation plan assets (mutual funds)$1,728 — — 1,728Liabilities:       Derivative stock appreciation rights$— — 32,820 32,820        (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, 2016 and December 31, 2015 are as follows (amounts in thousands): March 31, 2016 December 31, 2015 Carrying Amount Fair Value Carrying Amount Fair ValueCurrent and long-term debt$1,337,989 1,393,992 1,332,739 1,390,743                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Fair Value Inputs, Liabilities, Quantitative Information                               | The following table shows our significant assumptions and inputs used in the lattice-based valuation model to value the stock appreciation right liability at March 31, 2016: March 31, 2016Expected term (in years)2.8 - 6.8Volatility40%Risk-free interest rate1.5%                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation | The following table summarizes the changes in fair value of our financial instrument measured at fair value on a recurring basis using significant unobservable inputs (Level 3) during the three months ended March 31, 2016 and 2015:Fair Value Measurement Using Level 3 Inputs Derivative Stock Appreciation RightsBalances at January 1, 2015$—Issuance21,660Fair value adjustment at end of period, included in Other Income (Expense)2,120Balances at March 31, 201523,780  Balances at January 1, 201632,820Fair value adjustment at end of period, included in Other Income (Expense)(4,530)Balances at March 31, 2016$28,290                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |

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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 quantitative information about the inputs used in the fair value measurement of liabilities. This disclosure may include, but is not limited to, the fair value of the liability, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs.
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| - Definition
Tabular disclosure of the fair value measurement of liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes 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 liability.
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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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