|**Fair Value Measurements and Derivative Instruments (Tables)**                                      | 9 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 ofSeptember 30, 2016andDecember 31, 2015are as follows (amounts in thousands):September 30, 2016Level 1(1)Level 2(2)Level 3(3)TotalAssets:Deferred compensation plan assets (mutual funds)$1,462——1,462Liabilities:Derivative stock appreciation rights$——16,98016,980December 31, 2015Level 1(1)Level 2(2)Level 3(3)TotalAssets:Deferred compensation plan assets (mutual funds)$1,728——1,728Liabilities:Derivative stock appreciation rights$——32,82032,820(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
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|September 30, 2016                                                                                   | Level 1(1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Assets:                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Deferred compensation plan assets (mutual funds)                                                     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Liabilities:                                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Derivative stock appreciation rights                                                                 | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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|December 31, 2015                                                                                    | Level 1(1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Assets:                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Deferred compensation plan assets (mutual funds)                                                     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Liabilities:                                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Derivative stock appreciation rights                                                                 | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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|(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, atSeptember 30, 2016andDecember 31, 2015are as follows (amounts in thousands):September 30, 2016December 31, 2015Carrying AmountFair ValueCarrying AmountFair ValueCurrent and long-term debt$1,333,5351,392,6261,348,1061,390,743                                                                                                                                                                                                                                                                                                                                                                                                                                          
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|                                                                                                     | September 30, 2016                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|                                                                                                     | Carrying Amount                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Current and long-term debt                                                                           | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|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 atSeptember 30, 2016:September 30, 2016Contractual term (in years)2.3 - 6.3Volatility40%Risk-free interest rate1.3%                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
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|                                                                                                     | September 30, 2016                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Contractual term (in years)                                                                          | 2.3 - 6.3                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Volatility                                                                                           | 40                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Risk-free interest rate                                                                              | 1.3                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|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 thenine months ended September 30, 2016and2015(amounts in thousands):Fair Value Measurement Using Level 3 InputsDerivative Stock Appreciation RightsBalance at January 1, 2015$—Issuance21,660Fair value adjustment at end of period, included in Other Income (Expense)5,040Balance at September 30, 201526,700Balance at January 1, 201632,820Fair value adjustment at end of period, included in Other Income (Expense)(15,840)Balance at September 30, 2016$16,980                                                                                                                            
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|Fair Value Measurement Using Level 3 Inputs                                                         
|                                                                                                     | Derivative Stock Appreciation Rights                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Balance at January 1, 2015                                                                           | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Issuance                                                                                             | 21,660                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Fair value adjustment at end of period, included in Other Income (Expense)                           | 5,040                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Balance at September 30, 2015                                                                        | 26,700                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
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|Balance at January 1, 2016                                                                           | 32,820                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Fair value adjustment at end of period, included in Other Income (Expense)                           | (15,840                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Balance at September 30, 2016                                                                        | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

X- DefinitionTabular 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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