Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements and Derivative Instruments (Carrying amounts and fair value of the financial instruments) (Details)

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Fair Value Measurements and Derivative Instruments (Carrying amounts and fair value of the financial instruments) (Details) - USD ($)
$ in Thousands
Jun. 30, 2016
Dec. 31, 2015
Senior Notes Due 2021 | Senior Notes    
Debt Instrument [Line Items]    
Debt stated percentage 6.75%  
Senior Notes Due 2025 | Senior Notes    
Debt Instrument [Line Items]    
Debt stated percentage 6.875%  
Carrying Value [Member]    
Debt Instrument [Line Items]    
Current and long-term debt $ 1,348,254 $ 1,332,739
Fair Value [Member]    
Debt Instrument [Line Items]    
Current and long-term debt $ 1,400,504 $ 1,390,743